Baseline 94 1.8 5.2 7 1.55 Slower Rate of Withdrawal 12 13.9 3.2 17 0.78 Intermediate Withdrawal Rate and Longer Drain Time 40 4.3 11.9 16.3 0.75 Source: Reference 4. a The effects of changing the withdrawal rate and drain time were measured at a printed circuit board manufacturing facility.

The following is a list of drag out reduction practices that facilities can implement on electroplating or surface finishing lines:

  Lower process solution viscosity and/ or surface tension by decreasing chemical concentration, increasing bath temperature, or using wetting agents;

  Reduce drag out volume by modifying rack/ barrel design and perform rack maintenance to avoid solution trapping;

  Position parts on racks in a manner that avoids trapping solution;

  Reduce speed of rack/ barrel withdrawal from process solution an/ or increase dwell time over process tank;

  Rotate barrels over the process tank to improve drainage;

  Use spray/ fog rinsing over the process tank ( limited applicability);

  Use drip boards and return process solution to the process tank;

D 12 Appendix D  Pollution Prevention and Water Conservation Practices   Use drag out tanks, where applicable, and return solution to the process tank; and   Work with customers to ensure that part design maximizes drainage.

D. 1.2 Improved Rinse Tank Design and Rinsing Configurations Rinse tank design and rinsing configuration greatly influence water usage. The key objectives for optimal rinse tank design are to quickly remove drag out from the part and completely disperse the drag out throughout the rinse tank. Achieving these objectives reduces the time necessary for rinsing and minimizes the concentration of contaminants on the part when it leaves the rinse tank. Examples of good design include locating water inlet and discharge points of the tank at opposite positions in the tank to avoid short circuiting, and using air agitation for better mixing ( 5).

Various rinsing configurations are used by MP& M facilities. Having single rinse tanks following each process tank is the most inefficient use of rinse water. Multiple rinse tanks connected in series ( i. e., countercurrent cascade rinsing) reduces the water needs of a given rinsing operation by one or more orders of magnitude. Spray rinsing can also reduce water use requirements, but the achievable percent reduction is usually less than for countercurrent cascade rinsing. Other configurations that reduce water use include cascade, reactive, and dual purpose rinses.

D. 1.3 Rinse Water Use Control Devices Regardless of the type of rinsing configuration used, facilities can reduce their water use by coordinating water use and water use requirements. Matching water use to water use requirements can optimize the quantity of rinse water used for a given work load and tank arrangement ( 5). Not controlling water use negates the benefits of using multiple rinse tanks or other water conservation practices and increases water usage.

Facilities may wish to implement at least one effective method of water use control on all electroplating or surface finishing lines. Effective water use controls include, but are not limited to:

  Use of softened or deionized water for rinsing.

  Flow restrictors ( flow restrictors as a stand alone method of rinse water control are only effective with plating lines that have constant production rates, such as automatic plating machines. For other operations, there must also be a mechanism or procedure for stopping water flow during idle periods.).

  Conductivity controls.

D 13 Appendix D  Pollution Prevention and Water Conservation Practices   Timer rinse controls.

  Production activated controls ( e. g., spray systems activated when a rack or barrel enters/ exits a rinse station).

D. 1.4 Metal Recovery and Rinse Water Reuse Technologies MP& M facilities use various technologies to recover metals drag out and rinses and reuse the rinse water. The technologies most commonly used are evaporation, ion exchange, electrolytic recovery ( also referred to as electrowinning), reverse osmosis, and electrodialysis. Table D 7 presents examples of metal recovery technologies and the drag out/ rinses to which they are primarily applied.

Table D 7 Examples of Metal Recovery Methods Chemistry or Process with Which Rinse is Associated Recovery Technology Brass electroplating Electrolytic recovery, evaporation Cadmium ( cyanide) electroplating Electrodialysis, electrolytic recovery, evaporation, ion exchange, reverse osmosis Cadmium ( noncyanide) electroplating Electrodialysis, electrolytic recovery, evaporation, ion exchange, reverse osmosis Chromate conversion coating of aluminum Evaporation Chromium ( hard) anodizing Evaporation, mist eliminator Chromium electroplating  decorative ( Cr+ 6) Evaporation Chromium electroplating  decorative ( Cr+ 3) Evaporation Copper ( cyanide and sulfate) electroplating Electrolytic recovery, evaporation, ion exchange, reverse osmosis Gold electroplating Electrolytic recovery, ion exchange Lead tin electroplating Evaporation, ion exchange Nickel electroplating Electrodialysis, electrolytic recovery, evaporation, ion exchange, reverse osmosis Nickel electroless plating Evaporation, ion exchange Nickel sealant Reverse osmosis Silver electroplating Electrolytic recovery, evaporation, ion exchange Zinc ( cyanide) electroplating Electrolytic recovery, evaporation, reverse osmosis Zinc ( noncyanide) electroplating Electrolytic recovery, evaporation, ion exchange, reverse osmosis Zincate Evaporation Source: Reference 5.

D 14 Appendix D  Pollution Prevention and Water Conservation Practices D 15 Hand Valve Fresh Water Work Flow 5 sec. withdraw rate 5 sec. dwell time Plating Tank Rinse Tank Figure D 1( a).

Hand Valve Fresh Water Work Flow 15sec. withdraw rate 15sec. dwell time Plating Tank Rinse Tank Flow Restrictor Figure D 1( b). Rinse Tank with Flow Reduction D. 1.5Summary of Water Conservation Methods Figures D 1( a) through ( f) present six examples of rinsing configurations with increasingly good levels of water use practices. nse systems is described below. These configurations can be operated to provide adequate rinsing and are common at MP& M facilities. ver, the quantity of water needed for the same rinse quality may vary by as much as two orders of magnitude from the lowest level to the best level of water use.

Single Rinse Tank Single Each of these ri Howe Appendix D  Pollution Prevention and Water Conservation Practices D 16 Fresh Water Work Flow 15 sec. withdraw rate 15 sec. dwell time Plating Tank Rinse Tank Hand Valve Fresh Water Rinse Tank Flow Restrictor Figure D 1( c). e Tanks with Flow Reduction Work Flow15 sec. withdraw rate 15 sec. dwell time Plating Tank Rinse Tank Fresh Water Rinse Tank Conductivity Controller Drag Out Tank Recovered Rinse Figure D 1( e). ltiple Rinse Tanks with Flow Reduction and Drag Out Recovery Work Flow 15 sec. withdraw rate 15 sec. dwell time Plating Tank Rinse Tank Hand Valve Fresh Water Rinse Tank Flow Restrictor Figure D 1( d). ntercurrent Rinsing with Flow Reduction Multiple Rins Mu Cou Appendix D  Pollution Prevention and Water Conservation Practices Work Flow15 s e c . w ithdraw ra te 15 s e c . dw ell tim e Pla tin g Tank R e cycle Rin s e Tank D rag  O ut Tank R e c o v e red R ins e Cation Colmn Anion column To tre a tm e n t E lectro w inning Un it M e ta l d epleted elec troly te reus e d fo r re g eneratio n R egen erants Scrap metal to recycle Figure D 1( f). Multiple Rinse Tanks with Water Recycle, Drag Out Recovery, and Metal Recovery Figure D 1( a) is an example of inefficient water use. This configuration uses a single rinse tank with either continuous water flow or manual use control. To coordinate rinse water needs and use, the operator manually turns on the water valve to give the correct flow rate and then turns it off when the flow is no longer needed. The flow rate setting will usually vary by operator and the water valve may be left open during idle production periods. The single rinse tank configuration uses rinse water at a very high rate, even if water use is coordinated with the introduction of drag out. In the example shown, with a 1 gallon per hour ( gph) drag out rate, the rinse water requirement is 30 gallons per minute ( gpm), based on rinsing of Watts nickel plating solution and a rinsing criterion of 50 milligrams per liter ( mg/ L) nickel. If water use and drag out introduction are not coordinated, an even higher rinse water use rate would be needed to meet a given rinse criterion.

Figure D 1( b) shows a rinsing configuration where simple rinse water reduction methods have been implemented. The water use is still inefficient because a single rinse tank is used versus multiple rinse tanks. However, with this configuration, the drag out rate is reduced by controlling the withdrawal rate of the part ( increasing the withdrawal rate from 5 to 15 seconds) and by holding the part over the process tank ( increasing dwell time from 5 to 15 D 17 Appendix D  Pollution Prevention and Water Conservation Practices seconds) to permit the drag out to drip into the tank. The rinse water flow rate is controlled at a constant flow by a flow restrictor. The flow restrictor is usually sized to provide adequate rinsing at all times, and is more acceptable for constant production rates, such as those often found with automated plating machines. However, this configuration is inefficient when the work is intermittent because the rinse water flow rate must be set high enough to provide adequate rinsing during peak production periods. In addition, a large quantity of rinse water is wasted during low or idle production periods, unless the water flow is manually stopped.

Figure D 1( c) shows a rinsing configuration using multiple rinse tanks, which provides a moderately efficient use of water. This configuration is referred to as parallel rinsing, where each of the two rinse tanks are fed with fresh water and they each discharge to treatment. This arrangement can reduce water use to less than 50 percent of that used in Figure D 1( a).

Figure D 1( d) shows a more efficient rinsing configuration. This configuration is similar to that shown in Figure D 1( c), except that wastewater from the second rinse tank flows back into the first rinse tank to provide more efficient rinsing with less water use. Wastewater from the first rinse tank is then discharged to treatment. In this configuration, known as countercurrent cascade rinsing, the rinse water flows in a direction opposite to the part flow. This arrangement can reduce water use by more than 90 percent over the rinse configuration in Figure D 1( a).

Figure D 1( e) shows a very efficient rinsing configuration. There are three key elements to this rinse system: drag out reduction/ recovery, countercurrent cascade rinsing, and water use control. This configuration reduces/ recovers drag out by controlling the withdrawal rate and dwell time and by installing a drag out recovery tank. This tank can reduce the drag out entering the countercurrent cascade rinses by up to 90 percent, depending on the surface evaporation rate of the process tank. A conductivity controller controls the feed to the countercurrent cascade rinses. This type of device coordinates water use with drag out introduction and reduces the influence of human error found with manually controlled rinses. An alternative device is a timer rinse control, which is as effective as a conductivity controller when there is no variability in drag out volume between rinsing events.

Figure D 1( f) shows a rinse system that uses an ion exchange/ electrolytic recovery unit as a chemical recovery and water recycling technology. This rinsing configuration can reduce water use by more than 99 percent compared to the rinse configuration in Figure D 1( a), since wastewater is discharged only from the regeneration cycle of the ion exchange unit.

Table D 1 presents examples of additional practices and technologies that could be components of a well designed rinse system.

D. 1.6 Influences on Flow Rates Available data show that rinse water use rates are related to production when measured in terms of the surface area of parts processed. Other factors that influence rinse water D 18 Appendix D  Pollution Prevention and Water Conservation Practices use rates include the drag out rate ( gallons per 1,000 square feet of workload), the rinse water purity criteria ( mg/ L metal), the concentration of TDS in the bath ( mg/ L TDS), rinse tank design and configuration ( e. g., single overflow rinse versus countercurrent cascade rinse), and the type of rinse water flow control ( e. g., manual versus conductivity controlled). Section D. 1.5 discusses drag out rinse tank design and configuration and rinse water flow control. The other factors are discussed below.

D. 1.6.1 Rinse Water Purity Criteria Rinse water purity criteria are the levels of tolerable contamination in the rinse water. These levels vary for different processes and types of products. For example, rinse water used after cleaning typically does not have to be as pure as rinse water used following plating, since rinse water that remains on the plated part ( essentially the drag out from the rinse tank) will leave spots after it evaporates if the concentration of dissolved solids in the rinse water is too high. Although preliminary and intermediate processing steps such as cleaning and etching usually do not require as pure a rinse water as final rinsing, the rinse water needs to be pure enough to stop chemical reactions ( e. g., etching) and prevent the contamination of subsequent process solutions. Among plating processes, differences also exist in rinse water quality requirements. Parts plated for engineering or functional purposes ( e. g., corrosion resistance) can often be rinsed in water that is significantly less pure than decoratively plated parts rinses.

High purity water is needed for various rinsing operations. In some cases ( e. g., electronics parts rinsing), tap water is not pure enough to serve as rinse water. Before use as rinse water for this type of operation, the source water is purified by reverse osmosis and/ or ion exchange to remove dissolved solids and other constituents. Source water is sometimes treated even for common rinsing operations, especially when the water supply is high in dissolved solids.

The metal finishing industry has had rinse water quality requirements for decades. They are typically expressed in mg/ L of TDS or in conductivity or resistivity units ( resistivity is the inverse of conductivity). Table D 8 summarizes some generalized rinse criteria found in the literature ( 4).

D 19 Appendix D  Pollution Prevention and Water Conservation Practices Table D 8 Generalized Rinse Criteria Type of Rinse Normal Range for Adequate Rinsing ( mg/ L TDS)

Alkaline Treatment/ Acid Treatment Rinse 400 to 1,000 Functional or Engineering Plating Rinse 100 to 700 Decorative or Bright Plating Rinse 5 to 40 Source: Reference 4.

D. 1.6.2 Bath Concentration The concentration of a bath ( which can be expressed in g/ L TDS) will affect the quantity of water needed for good rinsing. Baths that are more concentrated ( i. e., higher TDS) will require more rinse water to meet the same rinse water purity criteria as a less concentrated bath. The bath concentration depends on the type of bath. For example, a typical acid zinc electroplating bath will have a TDS concentration of 166 g/ L and a typical copper cyanide electroplating bath will have a TDS concentration of 250 g/ L ( 6,7). For equal volumes of drag out from these two baths, the copper cyanide rinse flow must be 1.5 times greater to achieve the same rinse quality criteria ( i. e., 250/ 166 = 1.5). This calculation does not account for the differences in viscosity that will also affect the volume of drag out. For example, for flat surfaces, the drag out rate for a 396 g/ L chromic acid bath is 3.8 times greater than that of a 247 g/ L bath ( 6,7). In some cases, the TDS concentration of the bath inadvertently increases due to a buildup of bath contaminants ( e. g., iron may accumulate in a chromic acid bath due to the attack of the base metal). The TDS added by the contaminants may affect the drag out rate in the same manner as its intended bath constituents ( e. g., chromic acid). Therefore, operating a bath at the lowest concentration necessary to perform the job properly and maintaining bath contaminants at low levels is a significant pollution prevention measure.

D. 1.7 Technical Literature Table D 9 presents, for several types of rinses, calculated flow rates for a single stage overflow rinsing configuration and a two stage countercurrent cascade rinsing configuration. Both rinsing configurations are assumed to have flow control ( i. e., water use is coordinated with drag out introduction using a conductivity control or other device). This table presents the TDS concentration in the associated bath ( from literature), the target TDS in the rinse ( based on the rinsing criteria), the part type, the assumed drag out rate, and two production normalized flow ( PNF) values.

The first value, PNF 100% Control, is a calculated value based on the assumption that a facility perfectly coordinates work flow and rinse water use ( e. g., using a conductivity controller). In actual operations, perfect coordination is nearly impossible to achieve because the quantity of rinse D 20 Appendix D  Pollution Prevention and Water Conservation Practices D 21 Table D 9 Rinse Water Required for Various Plating Processes Based on Literature Values Process Rinse Configuration TDS Concentrationa Target TDS Concentration in Rinsea Part Type Drag out Ratea PNF 100% Control ( gal/ ft2) PNF 100% Excess ( gal/ ft2)

Acid Zinc Single overflow 166 g/ L Functional: 100 700 mg/ L ( used 400 mg/ L) Flat 1.3 gal/ 1,000 ft2 0.54 1.1 Contoured 3.5 gal/ 1,000 ft2 1.5 2.9 2 stage countercurrent cascade 166 g/ L Functional: 100 700 mg/ L ( used 400 mg/ L) Flat 1.3 gal/ 1,000 ft2 0.024 0.048 Contoured 3.5 gal/ 1,000 ft2 0.072 0.14 Silver Cyanide Single overflow 370 g/ L Bright: 5 40 mg/ L ( used 20 mg/ L) Flat 1.2 gal/ 1,000 ft2 22 44 Contoured 3.2 gal/ 1,000 ft2 58 120 2 stage countercurrent cascade 370 g/ L Bright: 5 40 mg/ L ( used 20 mg/ L) Flat 1.2 gal/ 1,000 ft2 0.16 0.32 Contoured 3.2 gal/ 1,000 ft2 0.43 0.87 Copper Cyanide Single overflow 250 g/ L Functional: 100 700 mg/ L ( used 400 mg/ L) Flat 0.91 gal/ 1,000 ft2 0.57 1.1 Contoured 3.2 gal/ 1,000 ft2 2 4 2 stage countercurrent cascade 250 g/ L Functional: 100 700 mg/ L ( used 400 mg/ L) Flat 0.91 gal/ 1,000 ft2 0.023 0.046 Contoured 3.2 gal/ 1,000 ft2 0.081 0.16 Acid Descale Single Overflow 248 g/ L Clean: 400 1000 mg/ L ( used 700 mg/ L) Flat 1 gal/ 1,000 ft2 ( estimated) 3.5 7.1 Contoured 3 gal/ 1,000 ft2 ( estimated) 11 21 2 stage countercurrent cascade 248 g/ L Clean: 400 1000 mg/ L ( used 700 mg/ L) Flat 1 gal/ 1,000 ft2 ( estimated) 0.019 0.038 Contoured 3 gal/ 1,000 ft2 ( estimated) 0.056 0.11 Alkaline Clean ( Proprietary Chemistry) Single overflow 90 g/ L Clean: 400 1000 mg/ L ( used 700 mg/ L) Flat 1 gal/ 1,000 ft2 ( estimated) 0.13 0.26 Contoured 3 gal/ 1,000 ft2 ( estimated) 0.39 0.77 2 stage countercurrent cascade 90 g/ L Clean: 400 1000 mg/ L ( used 700 mg/ L) Flat 1 gal/ 1,000 ft2 ( estimated) 0.011 0.022 Contoured 3 gal/ 1,000 ft2 ( estimated) 0.033 0.066 Sources: References 4, 6, and 7.

a TDS concentrations are from References 6 and 7, based on bath formulations. Target TDS concentrations are based on criteria presented in Section 3.2.1 ( Reference 4). Drag out rates are from References 4 and 5 unless data were not available, in which case rates were assumed based on technical knowledge of the operations. Appendix D  Pollution Prevention and Water Conservation Practices Table D 9 ( Continued)

1. Acid zinc formulation:

ZnSO4 ( 7H2 O) 240 g/ L NH4 Cl 15 g/ L Al2 ( SO4 ) 3 ( 18H2 O) 30 g/ L Licorice 1 g/ L 2. Equation used to calculate rinse flow and flow per square foot for single overflow rinse: Solving for Q: Where:

D = Drag out per ft2 ( gal) Ce = Target concentration of rinse ( oz/ gal) Co = Concentration of process bath ( oz/ gal) Cr = Target concentration of final rinse ( oz/ gal) M = Interval between drag out events ( minutes) Q = Flow ( gal/ min)

Note: Any interval M can be chosen. Q, when divided by the work rate, ft2 / M, yields the gal/ ft2 in the table and the gal/ ft2 number remains the same for any M.

3. Equation used to calculate 100 percent controlled flow and gallons per square foot for countercurrent cascade rinse:

xWhere n = number of rinse stages For 50 percent controlled flow, Q was multiplied by a factor of 2.

With 100 percent controlled flow, the introduction of drag out and rinse water into the rinse tank are perfectly coordinated and, therefore, the rinse water required to meet the target concentration of the final rinse is equal to Q. With 100 percent excess flow, the introduction of drag out and rinse water are not perfectly coordinated and an excess of 100 percent of Q ( or 2Q) is used to meet the target concentration of the final rinse.

4. Silver cyanide formulation ( middle of high speed bath range):

AgCN 97.5 g/ L KCN 152.5 g/ L K2 CO3 52.5 g/ L KNO3 50 g/ L KOH 17 g/ L 5. High efficiency copper cyanide formulation:

CuCN 75 g/ L KCN 133 g/ L KOH 42 g/ L 6. Acid descale formulation:

20% H2 NO3 ( by volume) 1.5% HF ( by volume)

All bath formulations and equations are from References 4, 6, and 7.

D 22 Appendix D  Pollution Prevention and Water Conservation Practices water needed to meet a given rinse criterion usually cannot be added exactly at the time that drag out enters and is dispersed in the rinse tank. For example, when a barrel of parts is rinsed, it is usually placed in a rinse tank for 1 to 3 minutes. The rinse water volume needed to meet the rinse criterion may be 50 gallons or more. The flow rate of water into the rinse tank is typically less than 10 gpm ( flow rates into rinse tanks vary depending on the pipe size and water pressure and may be reduced by a flow restrictor). Therefore, it may take 5 minutes to add the 50 gallons of rinse water. Because of this, actual water use rates will be higher than those presented in the column, PNF 100% Control. A reasonable assumption is that good water flow control will result in a PNF twice that of the calculated values that assume 100 percent control. These flows are shown as PNF 100% Excess.

Machining Operations Many machining operations use metal working fluids to cool and lubricate parts and machining tools during cutting, drilling, milling, and other machining operations. These fluids become contaminated and begin to lose their working characteristics. If neglected, the fluids become unusable and require treatment and disposal. Through proper care, the life span of the fluids can be extended indefinitely. For most machining operations, prolonging metal working fluid life reduces the cost of treatment and disposal, as well as the cost of fresh coolant.

Many MP& M facilities use some type of pollution prevention and water conservation practices for machining wastewaters. Some facilities have implemented numerous pollution prevention and water conservation methods and technologies that result in very low machining wastewater discharge rates and in some cases eliminate the discharge of machining fluids. Pollution prevention and water conservation practices are applicable to all machining operations; however, process related factors and site specific conditions may restrict the utility of certain methods.

D. 2.1 Wastewater Generation from Machining Operations Various types of metal working fluids, also termed cutting fluids and coolants, are used in machining operations to improve the life and function of machine tools. During machining, these fluids are circulated over working surfaces, reducing friction, cooling the tool and part, and removing metal chips from the work face. The type of fluid used depends on the type of machining being performed and the preference of the site. The fluids are broadly divided into four groups: straight oil ( neat oils), synthetic oils, semisynthetic, and soluble oil. The most commonly used fluids are soluble oils, synthetics, and semisynthetics.

Water soluble coolants are prepared by mixing a concentrated coolant with water in a 1: 15 to 1: 30 ratio to produce a fluid with a 90 to 98 percent water content. Most water soluble coolants are suitable for light and medium duty operations. Synthetic coolants are designed for high cooling capacity, lubricity, and corrosion prevention. Common chemical agents in synthetics include: amines and nitrites for rust prevention; nitrates for nitrite stabilization; phosphates and borates for water softening; soaps and wetting agents for D 23 D. 2 Appendix D  Pollution Prevention and Water Conservation Practices lubrication; phosphorus, chlorine, and sulfur compounds for chemical lubrication; glycols to act as blending agents; and biocides to control bacteria growth. Semisynthetics contain small dispersions of oil in an almost otherwise organic water dilutable system. Straight oils are good lubricants, but are less effective for cooling, and therefore are limited mostly to use in low speed operations ( 8).

Metal working fluids are periodically discarded because of reduced performance or development of a rancid odor. The fluids that contain a large percentage of oil typically are contract hauled as solid waste for disposal or recovery. Fluids with lower oil content typically are sent to a site s wastewater treatment system for treatment and subsequent discharge.

Metal working fluids degrade mainly because of contamination with tramp oil and dirt and by bacterial growth, which can be accelerated by tramp oil contamination. Tramp oil contamination is caused mostly by oil from the part s surface during machining and by leaks of lubricating and hydraulic oils from the machine. Airborne dust or poor housekeeping practices can cause dirt to accumulate. Bacteria are initially contributed from the surfaces of the machine and parts and from the air. More than 2,000 known species of bacteria have been reported to affect and eventually destroy the stability of machining fluids ( 9). Bacteria feed on the fluids  chemicals, causing the fluids to lose lubricity and corrosion inhibition. Under anaerobic conditions, sometimes caused by floating tramp oil in coolant sumps, bacteria generate a hydrogen sulfide odor.

In addition to spent fluid, machining operations may generate wastewater from rinsing. Machined parts may be rinsed to remove fluid, chips and other foreign materials. However, parts typically are not rinsed following machining. More frequently, the fluid is permitted to remain on the part to inhibit corrosion, is wiped off using shop towels, or is cleaned in an alkaline cleaning or degreasing operation.

The quantity of wastewater generated by a machining operation depends primarily on the volume of work performed. Production volume can be roughly measured by the quantity of metal stock removed by turning, milling, boring, broaching, cutting and other machining operations. For most machining operations, the removed metal consists of small fragments called chips or fines. Most chips carry a thin film of fluid on their surfaces, which, when it drains, is another source of wastewater.

D. 2.2 Pollution Prevention and Water Conservation Practices for Machining Operations The Agency has identified two categories of pollution prevention and water conservation practices and technologies that can be used to reduce metal working fluid discharge: those used to prevent metal working fluid contamination and those used to extend the life of machining fluids, including recovering and recycling metal working fluids. Within each of these categories are several specific practices and technologies. Table D 10 presents several examples of these practices, which are discussed below. There may be other practices and D 24 Appendix D  Pollution Prevention and Water Conservation Practices technologies not identified here that can reduce metal working fluid discharge. Therefore, the list provided below is not exhaustive.

Table D 10 Potential Pollution Prevention and Water Conservation Methods Applicable to Machining Operations Pollution Prevention/ Water Conservation Method Examples Applicability Prevention of Metal Working Fluid Contamination Reduce contamination from tramp oil Use coolant in hydraulic and other oil systems. Applicable to most machines. In most cases, requires use of special fluid.

Replace hydraulics with electrical systems. Limited applicability. Practical only during major equipment overhaul.

Machine maintenance. Applicable to all machines. Should be performed at regularly scheduled intervals.

Reduce contamination from make up water Use deionized water for initial make up of working fluid and to account for evaporative losses. Applicable to all machining operations using a water soluble fluid. Especially important in areas where the water supply is high in TDS.

Reduce contamination from sumps Sterilize sumps during clean out using steam. Applicable to all machining operations. Especially important with large concrete sumps.

Use metal inserts or coat walls of concrete sumps. Applicable to in ground concrete sumps.

Extension of Metal Working Fluid Life Raw material substitution Use high quality fluids with needed   additive package.  Most machining operations can benefit from the use of high quality fluids that can extend fluid life, while reducing bacterial growth, improving lubricity, reducing friction, and providing corrosion protection.

Equipment modification Replace sump s air agitation with mechanical agitation. Applicable to central sumps with air agitation.

Install tramp oil removal device. Limited mainly to external sumps.

Fluid Monitoring Measure pH, coolant concentration, tramp oil concentration, and bacterial count weekly or more frequently. Applicable to all machining operations. Larger operations can use data for statistical process control.

D 25 Appendix D  Pollution Prevention and Water Conservation Practices Table D 10 ( Continued)

Pollution Prevention/ Water Conservation Method Examples Applicability Extension of Metal Working Fluid Life ( continued)

Metal working fluid recycling Use methods and technologies for removing fluid contaminants ( e. g., filtration, centrifuge, pasteurization). Simple filtration methods can be used by all machining operations. More sophisticated equipment is limited to larger operations.

Recycle chip drainage. Applicable to all machining operations. Requires clean handling and storage methods to prevent contamination.

Source: MP& M Site Visits, MP& M Surveys, Technical Literature.

D. 2.2.1 Prevention of Metal Working Fluid Contamination Facilities can implement various methods to reduce the amount of fluid contamination. Several of these methods are discussed below.

Reduction of Contamination From Tramp Oil. Tramp oil is a primary contaminant in machining fluids and for many facilities the major cause of metal working fluid degradation. EPA has identified the following methods to reduce contamination of metal working fluid with tramp oil.

  Use of Coolant in Hydraulic and Other Oil Systems . Some metal working coolants are formulated to be used as hydraulic fluid and/ or lubricant in concentrated form and as a coolant in its dilute form ( i. e., diluted with water). When used as a hydraulic fluid or lubricant, leaks of the fluid will assimilate into the coolant without causing contamination.

  Replacement of Hydraulics with Electrical Systems . Hydraulic systems on some machines can be replaced by newer electrical systems that do not contain hydraulic fluid. This replacement could be economically performed during major equipment overhauls.

  Machine Maintenance . Machine design and age may affect the quantity of hydraulic oil that leaks to the metal working fluid during machining operations. There are numerous hydraulic systems used with machines, depending on the type of machine. These systems will leak variable quantities of oil depending on design, sealing mechanisms, operating pressures, and other factors. Older machines, especially those that are not properly maintained, can leak excessively from hydraulic seals. Facilities D 26 Appendix D  Pollution Prevention and Water Conservation Practices should implement scheduled maintenance of machines to check and repair sealing mechanisms.

Reduction of Contamination from Make Up Water. Make up water contributes to the dissolved solids content of the metal working fluid, reducing fluid life. This problem occurs more rapidly when water with high TDS is used for evaporative make up. Certain dissolved solids or minerals cause more problems for metal working fluids than others. For example, chloride salts and sulfates corrode at levels of greater than 100 parts per million. Sulfates also promote the growth of sulfate reducing bacteria that cause fluids to become rancid. When minerals become concentrated in the fluid, they can cause increased corrosion, gumming, and machine wear ( 6). Consequently, using hard water can reduce the fluid life. Deionized ( DI) water can be used in place of hard water ( DI units can be either purchased or rented).

Reduction of Contamination from Sumps. EPA has identified the following examples of methods to reduce contamination from metal working fluid sumps:

  Steam Cleaning of Sumps . Machine coolant sumps harbor bacteria that degrade the fluids. If coolant sumps are not sterilized during cleanouts, residual bacteria may degrade the fresh coolant added to cleaned sumps. Steam cleaning the sumps during cleanout can eliminate bacteria.

  Sump Modification . Many coolant sumps are designed as in ground concrete tanks, whose porous concrete surfaces absorb oil and promote bacterial growth. Improving the design of the sumps can extend fluid life. Potential design changes include inserting metal tanks and coating sump walls with fiberglass or other nonporous material.

Reduce Miscellaneous Contamination. Good housekeeping practices can extend metal working fluid life by reducing contamination. Facilities can implement housekeeping procedures to keep floor sweepings, solvents, paint chips, soil, rags, paper, and other debris out of the coolant sumps.

D. 2.2.2 Extension of Metal Working Fluid Life Facilities can implement several methods to extend the life of metal working fluids. These include raw material substitution, equipment modification, and fluid monitoring, as discussed below.

Raw Material Substitution. As discussed above, four general types of metal working fluids are used in machining operations. Within a given group of fluids, such as soluble oil, various formulations are used. Within each group, the major difference from one fluid to another is the   additive package.  Additives are included in most metal working fluid formulations to improve fluid performance ( e. g., improve lubricity, reduce friction, or increase corrosion protection) and increase life span ( e. g., reduce bacterial growth). Costs of different D 27 Appendix D  Pollution Prevention and Water Conservation Practices metal working fluids can vary by 100 percent or more. Fluids with additive packages that do not meet the lubrication and cooling requirements of the specific machining operation may degrade faster than other metal working fluids. These fluids will need to be replaced more often and increase overall operating costs. These fluids may also affect tool life, further increasing operating costs. Therefore, using the proper grade metal working fluids can increase the life span of the fluid, reducing the generation of waste machining fluids and decreasing the overall operating costs.

Equipment Modification. EPA has identified the following examples of equipment modifications that can extend the life of machining fluids.

  Replacement of Air Agitation With Mechanical Agitation . Some facilities use air agitation in central coolant sumps to constantly mix the fluid and prevent phase separation and pooling of tramp oil. However, air agitation increases the activity of aerobic bacteria by adding oxygen, which causes the bacteria to consume fluid additives. An alternative method of mixing is mechanical agitation ( i. e., pumping). Mechanical agitation mixes without increasing the oxygen concentration of the coolant.

  Removal of Tramp Oil . Machining fluid life can be extended by continuous, in sump removal of tramp oil. Facilities can install continuous oil skimming devices directly in the machine sump to remove tramp oil. Absorbent blankets, fabrics, or pillows can also remove tramp oil.

Fluid Monitoring. During use, the metal working fluid undergoes various physical, chemical, and biological changes. If the properties of the fluid are monitored on a regular basis, the fluid can be adjusted before it is degraded. Parameters measured to monitor the fluid include: pH, coolant concentration ( using a refractometer or titration kit), TDS, tramp oil ( visual) and biological activity ( using dip slides available from coolant suppliers and laboratories ( 6) or other methods). Facilities can use these data to guide periodic fluid adjustments and/ or develop statistical process control ( SPC) procedures. Facilities may wish to monitor fluid concentration at least weekly, if not daily, to identify contamination. The correct pH operating range of most coolants is 8.5 to 9.5. If the pH drops below the operating range, coolants may cause rusting and be prone to increased biological activity. Dilute concentrations can shorten tool life, increase biological activity, and cause rust. Rich concentrations can lead to foaming and tramp oil contributes to biological growth.

D. 2.2.3 Metal Working Fluid Recycling Most metal working fluids can be recycled on site by removing contaminants accumulated during use and storage. Recycling methods include settling, straining, skimming, simple filtration, membrane filtration, coalescing, centrifugation, cyclone separation, magnetic separation, and pasteurization. Some of these methods can be used in combination to recover D 28 Appendix D  Pollution Prevention and Water Conservation Practices nearly 100 percent of the metal working fluid. Facilities can purchase recycling equipment or hire commercial services that perform on site processing ( 10,11,12). A self contained recycling unit can be purchased that is specifically designed for smaller machine shops and is a complete sump maintenance and fluid recycling system in one unit ( 8). In most cases, facilities can facilitate metal working fluid recycling by consolidating the types of machining fluids they use to one or two types of fluid.

Additional metal working fluid can be recycled by chip drainage. Chip drainage can account for up to 50 percent of annual fluid use ( 11). During machining, the metal chips ( scraps) become coated with fluid. Part of the fluid drains from the chips and part remains on the chips. In many cases, the chips and associated fluid drop to the floor and are manually collected in storage containers. Some machines send the chips and fluid to a storage container using automated equipment ( e. g., belt or pneumatic conveyor). Fluid that drains from chips can be recycled rather than discharged, which may require design changes of chip handling and storage equipment.

D. 2.2.4 Design of the Machine Fluid System Fluids used in machining are stored either in sumps dedicated to individual machines ( either internal or external to the machine), or in central sumps that serve multiple machines. Large machining operations typically use central sumps, whereas small machine shops tend to have individual sumps for each machine. Central systems usually contain three to five times greater volume of fluid per machine from individual sumps. The reservoir volumes of most machines with internal sumps are typically 10 to 50 gallons. External sumps serving a single machine typically have a volume of 1,000 to 2,500 gallons. Central sumps may have volumes that exceed 50,000 gallons.

The amount of make up fluid in a central system amounts to a smaller percentage of total fluid than in a single machine operation. Consequently, the potential for bacterial degeneration is greater in central systems as the bacteria have a longer time in which to degrade the fluid ( 9). Further, central sumps are often unlined concrete basins, whose porous walls harbor bacteria and prevent complete disinfecting during cleanouts. This reduces the time needed for the bacteria to become reestablished ( 11). Additionally, the larger pumps used in central systems keep the tramp oils suspended in the fluid so they do not readily   float out,  adding to further bacterial attack. Central systems may require more maintenance than dedicated sumps to prevent bacterial growth.

D. 2.2.5 Machining Operations Performed The ratio of scrap metal ( e. g., chips) generated to fluid used varies among machining operations. For example, metal cutting may generate large pieces of scrap metal using a small volume of fluid, whereas a milling operation usually produces a much smaller mass of chips for the same volume of fluid.

D 29 Appendix D  Pollution Prevention and Water Conservation Practices D. 2.2.6 Base Material Being Machined The type of base material being machined affects the quantity of metal working fluid used. The hardness of base materials varies, which in turn affects the speed at which the base metal can be removed. Harder metals require more fluid than softer metals for the same operation.

D. 2.2.7 Climatic Conditions The temperature of the shop can affect the life span of metal working fluid in that warmer temperatures may foster the growth of certain bacteria.

D. 2.2.8 Design and Age of Machines The design and age of machines may affect the quantity of hydraulic oil that is leaked to the metal working fluid during machining operations. Numerous hydraulic systems are used with machines. These systems will leak variable amounts of oil depending on design, sealing mechanisms, operating pressures, and other factors. Older machines, especially those that are not properly maintained, can have hydraulic seals that excessively leak.

D. 2.2.9 Uniform Coolant Use Minimizing the number of different machine coolants used at a facility reduces the chance of formulation errors. When employees are familiar with fluid properties and coolant formulation chemistry, it is less likely that coolant batches will be prepared incorrectly, which many times requires the entire batch to be discharged to the on site wastewater treatment facility. Facilities may also save money by purchasing larger volumes of coolant ( i. e., economies of scale).

Painting Operations Paint is applied to a base material for protective and decorative reasons in various forms, including dry powder, solvent diluted formulations, and water borne formulations. There are various methods of application, the most common being immersion and spraying. Water is used in painting operations in paint booth water wash systems ( water curtains), in water borne formulations, in electrophoretic painting solutions and rinses, and in clean up operations. This discussion is directed at water use in spray painting booths; however, this subsection also provides some information on rinsing following electrophoretic painting and water clean up.

D. 3.1 Wastewater Generation from Painting Operations In spray painting, an organic coating is applied to a product. During manufacturing operations, spray painting is usually performed in a booth to control the introduction of contaminants and the release of solvent and paint to the work place and D 30 D. 3 Appendix D  Pollution Prevention and Water Conservation Practices environment, and to reduce the likelihood of explosions and fires. Paint booths are categorized into two types ( dry filter or water wash) and by the method of collecting the overspray ( i. e., the paint that misses the product during application). The type of booth design selected depends mainly on production requirements, including part size and configuration, production rate and transfer efficiency, the material being sprayed, and finish quality requirements.

Dry filter booths use filters to screen out the paint solids, by pulling prefiltered air through the booth, past the spraying operation, and through the filter. The air entrains the overspray and is pulled through the filter, which collects the paint. Solvent evaporates from the paint, leaving the paint solids on the filter. Filters are periodically replaced when they become laden with paint solids and the air flow through them is restricted. Dry filter booths are most often used when paint usage does not exceed 20 gallons/ 8 hour shift/ 10 feet of chamber width ( 13). At higher usage rates, the frequency of filter changes greatly increases operating costs ( i. e., filter, filter disposal, cost, and labor).

The only water used with dry filter units is to clean painting equipment ( e. g., guns and lines) when water borne paints are used. The operation of dry filter units is essentially dry when solvent based paints are used.

Water wash booths use a   water curtain  to capture paint overspray. Air containing entrained paint overspray is pulled through a circulating water stream, which   scrubs  the overspray from the air. There are two primary types of water wash booths, side draft and downward draft. The basic difference between the two types is the way the air moves through the system to draw the paint overspray in for capture ( 14,15). Small operations typically use side draft units and large and/ or continuous operations use downward draft units.

Water wash booths use a water stream that recirculates from a sump or tank with a typical capacity of 200 to 5,000 gallons or more. Downward draft systems normally contain much larger volumes of water than side draft systems. Water is periodically added to the system as make up for evaporative losses. The sump water is periodically discharged, usually during general system cleaning or maintenance. The discharge rate depends on various factors, including booth design, paint type, overspray rate, and the water treatment methods used. Water is also used to clean the painting equipment and the paint booth. Booth cleanup may involve using paint stripper to remove dried paint from the walls of the booth and the piping system.

A common practice in water wash booth operation is to immediately detacify suspended paint solids to reduce maintenance problems and to subsequently separate and remove the solids from the water. The organic resins that make up the bulk of the paint coating are insoluble in water and tend to stay tacky if not treated with some other material added to the water ( 14,15). If left untreated, the tacky solids can plug recirculation pipes and pumps and adhere to wetted surfaces of the booth. Dissolved solids are either immediately precipitated and flocculated, removed by water treatment, or discarded when the sump is discharged.

D 31 Appendix D  Pollution Prevention and Water Conservation Practices Solids can be detacified and removed in various ways, depending on the type of paint used and the booth design. Detacification chemicals include sodium hydroxide ( caustic), metal salts, clay, and polymers. Depending on the type of paint and the detacification chemical, the paint solids may either disperse or agglomerate. Agglomerated solids may either sink or float. In solids dispersal, the suspended solids increase in concentration as overspray enters the water. Subsequently, another chemical is added to the water that causes the dispersed solids to agglomerate into a dense floc, which is then removed.

There are various ways to remove paint solids from the booth water wash system. These removal technologies vary in sophistication, automation, efficiency ( removal and separation), and capital and operating costs. The most common methods include passive settling, skimming, screening, filtration ( bag, roll bed, press), and centrifugal methods ( hydrocyclone, centrifuge).

Besides spray painting, another common method of painting is electrophoretic painting ( also known as electrocoating or electrodeposition), which is the process of coating a work piece by making it either anodic or cathodic in a bath that is generally an aqueous emulsion of the coating material. The electrophoretic painting bath contains stabilized resin, pigment, surfactants, and sometimes organic solvents in water. Electrophoretic painting is used primarily for primer coats ( e. g., bodies for motor vehicles or mobile industrial equipment) because it gives a fairly thick, highly uniform, corrosion resistant coating in relatively little time. During this process, precleaned parts carrying an electrical charge are immersed into the coating tank ( paint) and then through a rinsing system. Rinsing removes excess paint ( drag out) from the parts. The typical rinsing procedure is a three stage countercurrent cascade rinse, and may include both dip and spray rinsing. Typically, the final rinse is performed with deionized water.

Ultrafiltration is commonly used to separate and recover paint solids and recycle rinse water, by counter flowing the rinse water into the painting bath and running the bath through the ultrafilter. The ultrafilter removes excess water from the bath, recycles the paint solids to the bath, and recycles the water ( permeate) to the rinse system. Occasional blowdown of rinse water is needed to purge the system of contaminants. Processing the rinse water through a reverse osmosis unit can reduce the volume of wastewater discharged ( 16).

D. 3.2 Pollution Prevention and Water Conservation Practices for Painting Operations EPA has identified three categories of pollution prevention and water conservation practices that, if implemented, can reduce or eliminate wastewater discharges from painting operations: practices to reduce the quantity of paint entering the water system; recycling technologies for paint booth water; and conversion of water wash booths to dry filter booths. These are discussed in this subsection and summarized in Table D 11. It is possible, however, that facilities can reduce or eliminate wastewater discharges using different practices than those described here.

D 32 Appendix D  Pollution Prevention and Water Conservation Practices Table D 11 Potential Pollution Prevention and Water Conservation Methods Applicable to Painting Operations Pollution Prevention/ Water Conservation Method Examples Applicability Reduce the Quantity of Paint Entering the Water System Improve spray painting operating practices Provide operator training to improve racking and positioning of parts to reduce overspray, assure proper selection of nozzle for efficient spray pattern, improve work scheduling and reduce clean outs, improve housekeeping. Applicable to all spray painting operations.

Improve paint transfer efficiency Replace inefficient conventional compressed air spray equipment with high velocity/ low pressure equipment. Applicable to most existing spray painting operations using conventional equipment. Will require some retraining of operators.

Install gun cleaning station Use gun cleaning station to clean guns and lines. Can prevent spraying of cleaning fluid/ paint into booth. Applicable to most solvent based painting operations.

Recycle Paint Booth Water Recycle paint booth water through solids removal Use booth water maintenance system that removes paint solids. Applicable technologies include weirs, filters, and centrifuges. Applicable to most water wash booths. Usually requires treatment of booth water with chemicals to produce solids that can be separated from water.

Use Dry Filter Booths Use dry filter booths instead of water wash booths Convert existing water wash booth to a dry filter booth. Applicable to booths with low to moderate paint usage. In cases of high paint usage, dry filters clog too quickly.

Source: MP& M Site Visits, MP& M Surveys, Technical Literature.

D 33 Appendix D  Pollution Prevention and Water Conservation Practices D. 3.2.1 Reducing the Quantity of Paint Entering the Water System Facilities can implement various methods to reduce the quantity of paint entering the water system. Three of these methods are discussed below.

Improving Spray Painting Operating Practices. Facilities can implement various practices that reduce the quantity of paint and other material entering the water system of a paint booth and thereby reduce the need to discharge wastewater. Generally, implementing these practices requires only operator training. These practices include: racking and positioning parts to minimize overspray; selecting the proper nozzle for an efficient spray pattern; scheduling work to reduce color changes and associated clean outs of guns, lines, and pots; and housekeeping to prevent painting wastes and foreign materials from entering the booth s water system.

Improving Transfer Efficiency. The transfer efficiency ( i. e., spray efficiency) is the amount of coating that is applied to the part divided by the amount of coating that is sprayed from the gun. It is reported as a percentage. The transfer efficiency depends on several factors, including the spraying equipment, part size and configuration, paint type, and operating methods. Improving the transfer efficiency can reduce booth water processing requirements.

During the past 15 to 20 years, spraying equipment has improved, primarily in response to more stringent air pollution regulations and rising paint costs. One of the key improvements has been replacement of conventional compressed air spray equipment by more efficient equipment. In terms of transfer efficiency, the common types of spray equipment are ranked as follows ( shown in order of increasing efficiency with relative transfer efficiencies shown in parenthesis): conventional compressed air ( 25 percent), airless ( 35 percent), air assisted airless ( 45 percent), electrostatic, ( 65 percent), and high volume/ low pressure ( HVLP) ( 80 percent) ( 17). The HVLP equipment has been widely implemented due to the high transfer efficiency, as well as the low cost of converting from conventional compressed air equipment. The cost is primarily for the spray guns, since the compressors and other equipment are the same as for conventional compressed air painting equipment.

Installing Gun Cleaning Station. After use, spray painting equipment must be cleaned to prevent a buildup of paint solids. Spray guns are often cleaned by spraying solvent through the lines and guns and into the booth. However, this practice increases the amount of paint entering the booth s water system and increases emissions of volatile organic compounds ( VOCs). An alternative practice is to install gun cleaning stations. A commercial gun cleaning unit is designed to sit on top of a 55 gallon drum. The gun is connected to the solvent tank and the drum. Solvent is drawn through the gun and exits into the drum, where it can be recovered by distillation ( 18).

D. 3.2.2 Booth Water Recycle Various methods and equipment can reduce or eliminate the discharge of the water used in water wash booths. These methods and equipment prevent the continuous D 34 Appendix D  Pollution Prevention and Water Conservation Practices discharge of booth waters by conditioning ( i. e., adding detacifiers and paint dispersing polymers) and removing paint solids. The least efficient paint booth water wash system, in terms of water use, is one where the paint solids are not conditioned and accumulate until booth water must be replaced. Cleaning such systems typically involves draining or pumping the water from the booth reservoir and contract hauling the entire waste product. Due to high operating costs and downtime, this procedure is usually used only by low production operations. Moderate and high production operations need daily, if not continuous, booth water maintenance to conserve water. The most basic form of booth water maintenance is removing paint solids by manual skimming and/ or raking. These solids can be removed without water conditioning since some portion of solvent based paints usually floats and/ or sinks. With the use of detacifiers and paint dispersing polymer treatments, facilities can implement more advanced methods of solids removal. Some common methods are discussed below.

Wet Vacuum Filtration. Wet vacuum filtration units consist of an industrial wet vacuum head on a steel drum containing a filter bag. The unit vacuums paint sludge from the booth. The solids are filtered by the bag and the water is returned to the booth. Large vacuum units are also commercially available that can be moved from booth to booth by forklift or permanently installed near a large booth.

Tank Side Weir. A weir attached to the side of a side draft booth tank allows floating material to overflow from the booth and be pumped to a filtering tank for dewatering ( 14,15).

Consolidator. A consolidator is a separate tank into which booth water is pumped. The water is then conditioned by adding chemicals. Detacified paint floats to the surface of the tank, where it is skimmed by a continuously moving blade. The clean water is recycled to the booth ( 14,15).

Filtration. Various types of filtration units are used to remove paint solids from booth water. The booth water is pumped to the unit where the solids are separated, and the water is returned to the booth. The simplest filtration unit consists of a gravity filter bed with paper or cloth media. Vacuum filters are also used, some of which require precoating with diatomaceous earth ( 14,15).

Centrifuge Methods. Two common types of centrifugal separators are the hydrocyclone and the centrifuge. The hydrocyclone is used to concentrate solids. The paint booth water enters a cone shaped unit under pressure and spins around the inside surface. The spinning increases the gravity, which causes most of the solid particles to be pulled outward to the walls of the cone. Treated water exits the top of the unit and the solids exit the bottom. Some systems have secondary filtration devices to further process the solids. The centrifuge works in a similar manner, except that the booth water enters a spinning drum, which imparts the centrifugal force needed to separate the water and solids. Efficient centrifugation requires close control of the booth water chemistry to assure a uniform feed. Also, auxiliary equipment such as booth water agitation equipment may be needed.

D 35 Appendix D  Pollution Prevention and Water Conservation Practices D. 3.2.3 Conversion of Water Wash Booths to Dry Filter Booths Water wash booths can be converted to or replaced by dry filter booths. The dry filter booths have the potential to eliminate the wastewater discharge, but they create a solid wastestream. The choice between using a water wash booth or a dry filter booth is primarily based on the amount of overspray. It is usually cost effective to use a dry filter booth when paint usage does not exceed 20 gallons/ 8 hour shift/ 10 feet of chamber width ( 13).

A 1989 U. S. Navy study concluded that conversion from wet to dry booths can be cost effective for a range of operations. This study included a survey of military and industrial facilities that have successfully converted and an economic analysis based on typical Navy painting operational parameters ( 1).

D. 3.3 Solvent, Paint Solids, and Other Components of Paint The chemical make up of the paint can impact wastewater generation. The recirculated water in a water wash booth contains the various constituents of the paint( s) being applied. With most solvent formulations, the solvents ( e. g., xylene, toluene, methylene chloride) are not water soluble, but can be water miscible. Some exceptions, such as acetone and methyl ethyl ketone ( MEK), are water soluble. However, in most cases, the solvents are volatile and evaporate over time and exit the booth through the air exhaust system. The organic resins that make up the bulk of the paint coating are insoluble in water and tend to stay tacky if not treated with some additional material introduced to the water ( 14,15). If left untreated, the tacky solids can plug recirculation pipes and pumps and adhere to wetted surfaces of the booth. Other paint additives, such as wetting agents, pigments, and heavy metals ( e. g., zinc and chromium salts) may be soluble in water. These constituents can be made partly insoluble and removed by adjusting the chemistry of the water.

Water based paints present two problems with regard to water use. First, these paints disperse in water rather than agglomerate like solvent based paints, making the maintenance of paint booth waters more difficult ( 14,15). Second, water is used to clean spraying equipment when water based paints are applied, which may generate wastewater. A typical equipment cleaning procedure is to flush with water, then solvent, then water ( 2).

D. 3.4 Paint Booth Maintenance Requirements Water wash paint booths are periodically shut down for maintenance, which usually involves removing the water in the booth. Various conditions can exist that may necessitate discharging the water, including odor, bacterial growth, foaming, TDS buildup, and the presence of corrosion and scale constituents.

Booth maintenance typically involves incidental repairs and cleaning the booth surfaces and piping system. Often facilities do maintenance according to a schedule, but periodic repairs may also necessitate an unplanned shut down and clean out. A common clean out D 36 Appendix D  Pollution Prevention and Water Conservation Practices procedure is to remove the accumulated paint solids from the water, transfer the water to a holding tank, and return the water after the maintenance is completed. Alternate methods are draining the booth water to a sewer or wastewater treatment system or having it hauled to a disposal site. Systems with accumulated paint solids on the wetted surfaces of the booth and in the piping system can be cleaned by circulating an alkaline cleaner or other chemical for dissolving paint. Since the amount of water discharged from water wash paint booths is a function of the system s maintenance requirements, newer systems that require less maintenance will discharge less water. Therefore, one pollution prevention option for water wash paint booths is to install new systems or upgrade existing systems to limit maintenance requirements.

Cleaning Operations Cleaning operations include aqueous degreasing, acid treatment, alkaline treatment, and electrolytic cleaning. Depending on the chemicals, equipment, and procedures used, these processes are commonly referred to as immersion, spray, or electrolytic alkaline cleaning; immersion, spray, or electrolytic acid cleaning or pickling; ultrasonic cleaning; and emulsion cleaning and parts washing.

Many MP& M facilities implement pollution prevention and water conservation methods and technologies that result in low cleaning wastewater discharge rates, and in some cases, eliminate the discharge of cleaning solutions. Pollution prevention and water conservation practices are applicable to all cleaning operations; however, process related factors and site specific conditions may restrict the utility of certain methods. This subsection identifies pollution prevention and water conservation practices and technologies applicable to cleaning operations.

D. 4.1 Wastewater Generation From Cleaning Operations MP& M facilities commonly perform cleaning as a stand alone operation or in combination with other proposed MP& M operations such as anodizing, electroplating, conversion coating, and painting. Cleaning removes surface contaminants that affect the appearance of parts or the ability to further process the parts. Various types of acidic and alkaline solutions are used for cleaning.

Alkaline cleaners are usually impacted by organic pollutants such as oil and grease. The effectiveness of most alkaline cleaners is reduced when the oil concentration of the bath is in the range of 1 to 5 g/ L or more. Oil and grease enters the alkaline cleaning bath on the parts being processed. The rate of oil buildup depends on the production rate ( measured in square feet per day) and the quantity and characteristics of the contamination on the parts. Acid treatment solutions and, to a lesser extent, alkaline treatment solutions accumulate dissolved metals from corrosion of the base metals being processed. The dissolved metal reduces the strength of the cleaning bath. As dissolved metal increases, additional acid or alkaline solution is added; however, at certain metal concentrations, the bath is no longer usable. The tolerable concentration of dissolved metals depends mostly on the type of acid or alkaline solution and the D 37 D. 4 Appendix D  Pollution Prevention and Water Conservation Practices function of the bath. The buildup rate of dissolved metal depends primarily on the production rate, type and concentration of acid or alkaline solution, type of base metal, duration of cleaning cycle, and bath temperature.

D. 4.2 Pollution Prevention and Water Conservation Practices for Cleaning Operations EPA identified three categories of pollution prevention and water conservation practices that, if implemented, can reduce or eliminate wastewater discharges from cleaning operations: housekeeping and maintenance, oil and suspended solids removal, and dissolved solids removal. These are discussed in this subsection and summarized in Table D 12. It is possible, however, that facilities can reduce or eliminate wastewater discharges using different practices than those described here.

Table D 12 Potential Pollution Prevention and Water Conservation Methods Applicable to Cleaning Operations Pollution Prevention/ Water Conservation Method Examples Applicability Housekeeping and maintenance Check the accuracy of temperature controls; remove sludge build up from tanks, heat coils and temperature regulators; retrieve parts, racks, etc. dropped into the tanks; and check the integrity of tanks and tank liners. Applicable to all cleaning operations.

Oil and suspended solids removal Technologies used to remove oil and suspended solids from cleaning solutions, thereby extending the useful life span of the solutions ( e. g., skimmers, coalescers, cartridge and membrane filters). Suspended solids removal equipment ( e. g., cartridge filters) are applicable to nearly all baths. The other types of equipment are applicable to most or all alkaline cleaning baths.

Dissolved solids removal Various technologies and processes that remove dissolved metals from baths, including acid sorption, diffusion dialysis, and membrane electrolysis. Applicable to acid and alkaline solutions that become contaminated with dissolved metal, usually due to etching of the basis metal.

Source: MP& M Site Visits, MP& M Surveys, Technical Literature.

D 38 Appendix D  Pollution Prevention and Water Conservation Practices D. 4.2.1 Housekeeping and Maintenance Facilities can implement various housekeeping and maintenance practices to reduce the quantity of cleaning solution discharge. Several of these practices are discussed below.

Solution Testing. The chemical make up of cleaning solutions changes over time due to evaporative losses, water additions, cleaning chemical drag out, chemical reactions, and drag in of impurities. Because of these factors, cleaning baths lose strength, performance declines, and solutions require disposal. Many facilities operate cleaning baths on a three step schedule: formulate, use, and discard. This procedure can be expensive and inefficient from a production standpoint, and generates large volumes of wastewater. For this reason, facilities should frequently test the strength of the cleaning solution and appropriate chemical additions needed to continue using the solution. By implementing testing and recordkeeping, facilities can reduce the disposal frequency of cleaning baths.

Most alkaline cleaning solutions are proprietary formulations, and the vendors of these solutions provide test methods for determining the condition of a bath. Also, commercial test kits are available that include generic test methods. For example, the strength of an alkaline cleaning solution can be tested using acid base titration, which measures alkalinity. Also, there is a dual test method that indirectly measures the level of contamination in the cleaner. This process consists of titrating a measured sample of cleaner ( e. g., 5 milliliters ( ml) and then adding a color indicator ( phenolphthalein or methyl orange) with an acid of precise concentration ( e. g., 1N solution of sulfuric acid). Phenolphthalein is used as the indicator to measure free alkalinity and methyl orange is used to measure total alkalinity. By performing both tests, the ratio of total alkalinity to free alkalinity can be calculated. A ratio close to 1 indicates that the cleaner is relatively free of contamination, while a higher ratio indicates that contamination exists. Facilities sometime use this ratio to determine if they should discharge a cleaning solution. For example, a common guideline used is that the solution is discarded when the ratio exceeds 2.0. The total alkalinity/ free alkalinity test method does not work for all cleaners. Because of additives used, some alkaline cleaners do not have any free alkalinity. In such cases, the facility may want to perform more detailed tests to accurately determine the contaminant concentration ( e. g., oil and grease measurement).

Similar test methods exist for acid cleaners. The most common parameters in acid cleaner test programs are acid concentration and dissolved metal concentration. The concentration of sulfuric acid or hydrochloric acid in pickling solutions is usually measured by titrating a sample of the solution with sodium carbonate and using a methyl orange indicator. Iron and other dissolved metals can also be measured by titration or by using laboratory analytical equipment such as an atomic adsorption spectrophotometer.

Recordkeeping. Maintaining accurate records of bath additive rates and bath lives can help facilities identify trends in solution use and focus on extending the lives of those that are D 39 Appendix D  Pollution Prevention and Water Conservation Practices frequently discarded. Important records to keep are occurrences of chemical additions and solution dumps, production throughput, and chemical concentration data.

Miscellaneous Housekeeping and Maintenance. To obtain consistently good cleaning results and reduce their solution discharge, facilities should implement a regular schedule of housekeeping and maintenance. Tasks should include: checking the accuracy of temperature controls; removing sludge buildup from tanks, heating coils, and temperature regulators; retrieving parts, racks, and other foreign materials dropped into the tanks; and checking the integrity of tanks and tank liners.

D. 4.2.2 Oil and Suspended Solids Removal Cleaning baths accumulate oil and suspended solids during use. These contaminants eventually reach a concentration that interferes with the effectiveness of the cleaning process, despite the fact that most bath constituents remain usable. Also, contaminated cleaning baths may carry over contaminants to subsequent process solutions. As a result, cleaning baths are often discarded when they reach a certain concentration of contaminants. There are several technologies used to remove oil and suspended solids from cleaning solutions, thereby extending the useful life of the solutions. These technologies are primarily applicable to alkaline cleaning baths and are discussed below.

Free/ Floating Oil Separation Devices. Separation devices for oil/ water mixtures use the difference in specific gravity between oils and water to remove free or floating oil from wastewater. Common separation devices for cleaning solutions include skimming devices ( disks, belts, and rotating drum oil skimmers) and coalescers. These devices are not suited for emulsified oil removal, which typically is addressed through chemical treatment or membrane filtration.

Skimming is a simple method of separating floating oil from cleaning solutions. Skimming devices are typically mounted onto the side of a tank and operate on a continuous basis. The disk skimmer is a vertically rotating disk ( typically 12 to 24 inches in diameter) that is partially submerged into the liquid of a tank ( typically 4 to 12 inches below the surface). The disk continuously revolves between spring loaded wiper blades that are located above the surface. The adhesive characteristics of the floating oil cause it to adhere to the disk. As the disk surface passes through the wiper blades, the oil is removed and diverted to a run off spout for collection. Maximum skimming rates typically range from 2 to 10 gallons per hour of oil. Belt and drum skimmers operate similarly, with either a continuous belt or drum rotating partially submerged in a tank. As the surface of the belt or drum emerges from the liquid, the oil that adheres to its surface is scraped ( drum) or squeezed off ( belt) and diverted to a collection vessel.

Coalescers separate liquids with specific gravity differences of 0.09 and greater. Coalescers are typically tanks containing a coalescing media that accelerates phase separation ( 3). A suction skimmer removes cleaning solution and oil from the process tank and pumps it to the coalescer. The media in the coalescers is a material such as polypropylene, ceramic, or glass D 40 Appendix D  Pollution Prevention and Water Conservation Practices that attracts oil in preference to water ( i. e., oleophilic). The oil/ cleaner mixture passes through the unit and the oil adheres to the coalescing media. The oil forms droplets that conglomerate and rise to the surface of the tank, where a skimming device or weir removes them. According to Stoke s Law, the rise/ fall velocity of a dispersed phase droplet is exponentially increased with the droplet size. Therefore, the coalescing media separates the phases more rapidly than a common gravity settling device.

Media Filtration Methods. Filtration removes suspended solids from cleaning solutions. Common types of filters include cartridge filters, precoat diatomaceous earth filters, and sand or multimedia filters. Cartridge filters are available with either in tank or external configurations; the in tank filters typically are used for small tanks and the external filters for larger tanks. Most cartridges are disposable; however, washable and reusable filters are available, which further reduce waste generation. Precoat, sand, and multimedia filters are used mostly for large tank applications. The type of filter media used is based on the chemical composition of the bath. All filtration systems are sized based on solids loading and the required flow rate. Typical flow rates for cleaning solution applications are two to three bath turnovers per hour.

Membrane Filtration. Microfiltration and ultrafiltration are membrane based technologies used primarily to remove emulsified oil and other colloids from cleaning solutions. The solution entering a microfiltration or ultrafiltration unit typically is prefiltered using media filters to remove large particulates. Various devices then trap or skim floating oils and allow heavier solids to settle. The solution is pumped into the membrane compartment, where the membrane traps remaining oil and grease while water, solvent and other cleaning bath constituents pass through. The fluid flows parallel to the membrane with enough velocity to remove the reject from the membrane surface. Ceramic membranes are available in various pore sizes ranging from several hundred angstroms to over 0.2 microns. The appropriate pore size is determined by the specific cleaner to be filtered. The capacity of a unit is based on the total area and flux rate of the membrane. Commercially available units range in capacity from less than 260 to more than 1,300 gallons per day.

D. 4.2.3 Dissolved Metals Removal Metals become dissolved in acid and alkaline cleaning solutions as a result of corrosion of the base metal. The dissolved metal forms salts or other compounds that reduce the strength of the cleaning bath. Technologies used to remove dissolved metals include acid sorption, diffusion dialysis, and membrane electrolysis, discussed below.

Acid Sorption. Acid sorption is an acid purification technology that is applicable to various acid treatment solutions, as well as other acidic baths ( e. g., anodizing baths). The acid sorption unit resembles an ion exchange column. The column contains a bed of alkaline anion exchange resin that separates the acid from the metal ions.

D 41 Appendix D  Pollution Prevention and Water Conservation Practices First, spent acid is pumped upward through the resin; the acid is absorbed by the resin while the metal ions pass through it. The resulting metal rich, mildly acidic solution is collected at the top of the bed. Water is then pumped downward through the bed and desorbs the acid from the resin. The purified acid solution is collected at the bottom of the bed. This technology can recover approximately 80 percent of the free acid remaining in a spent acid treatment solution. Purification can be performed in a batch mode, but is most effective in a continuous flow mode ( usually expressed in terms of the mass of metal removed from the acid solution per unit of time). Equipment capacity ranges from 100 grams/ hour to several thousand grams/ hour. Units are sized to remove metal near or above the rate at which the metal is being introduced. Typically, a facility determines a target level of metal concentration and sizes the unit to maintain that level.

Diffusion Dialysis. Diffusion dialysis is a membrane process that separates metal contaminants from the acid solution using an acid concentration gradient between solution compartments. Anion exchange membranes makeup the compartments. The membranes are usually assembled in a membrane stack, like that used with electrodialysis. The contaminated acid passes through one set of compartments and deionized water through the adjacent compartments. Acid is diffused across the membrane into the deionized water whereas metals are blocked due to their charge and the selectivity of the membrane. Unlike electrodialysis, this process uses no electrical potential. The acid diffuses because of the difference in acid concentration on either side of the membrane ( i. e., material in high concentration moves to an area of low concentration).

Membrane Electrolysis. Membrane electrolysis is a bath maintenance technology that lowers or maintains the concentration of metallic impurities in cleaning solutions. This technology is also applicable to other metal bearing solutions ( e. g., electroplating, anodizing, and stripping solutions). This technology uses an ion exchange membrane( s) and an electrical potential applied across the membrane( s). The membrane is ion permeable and selective, permitting ions of a given electrical charge to pass through. Cation membranes allow only cations ( e. g., copper, nickel, aluminum) to pass from one electrolyte to another, while anion membranes allow only anions ( e. g., sulfates, chromates, chlorides, cyanide) to pass through. Bath maintenance units can be configured with cation or anion membranes, or both.

A typical application of membrane electrolysis is maintenance of an acid cleaning solution. The cleaning solution is placed in an anode compartment that is separated from a second electrolyte by a cation membrane. The solution in the cathode compartment ( i. e., catholyte) is typically a dilute acidic or alkaline solution. When an electrical potential is applied, the dissolved metals in the cleaning solution migrate through the cation membrane into the catholyte. The catholyte is periodically discarded when it becomes saturated with metals.

D 42 Appendix D  Pollution Prevention and Water Conservation Practices D. 4.3 Condition of the Surfaces Being Cleaned The condition of the parts being cleaned varies widely, both in terms of the types and quantities of contaminants present and the quantity of oil. For example, some parts may have been wiped clean and have only a light deposit of metal working fluids, while other parts may be heavily coated. Since metal working fluids ( oils) present on the parts are removed during the cleaning process ( aqueous degreasing), the rate of oil that is entering into the cleaning solution per square foot of part cleaned will vary. The type of oil entering the cleaning solution will also affect the cleaning fluid s life span.

D. 4.4 Cleaning Requirements Some processes, such as electroplating, require a high degree of cleanliness while others, such as phosphate conversion coating, may have less stringent requirements. The cleaning requirements will therefore vary within a facility, as well as from facility to facility, as will the type of cleaning process selected.

Some cleaning processes are more amenable to pollution prevention practices than others, based on the purpose of the cleaning process. For example, many electroplating processes require etching of the part s surface to enhance adhesion of the electroplated metal deposit. Surface etching introduces dissolved metal into the cleaning solution and will reduce its life span.

D. 4.5 Type of Cleaning Process and Equipment The life span of cleaning solutions depends on the type of cleaning process ( i. e., process chemistry and cleaning equipment). Numerous factors affect the selection of a cleaning process, including: type and characteristics of contaminants to be removed; type and condition of base metal; size and configuration of parts; degree of cleanliness required; processing capabilities at the site; subsequent operations to be performed; and financial considerations.

The factors that most affect the selection of process chemistry and equipment are the type of contaminants present on the parts, type of base metal, and the subsequent finishing operation, which in turn dictate the cleaning requirements. Contaminants present on parts can include both organic and inorganic contaminants. Examples of organic contaminants are machining fluids, miscellaneous oils, waxes, and buffing compounds, which are typically removed by solvents, detergents, and alkaline solutions. Examples of inorganic contaminants are scale, smut, and grinding residue, which are typically removed by acidic solutions. Various methods are used to apply the cleaning solution. For example, solutions can be applied by spraying or immersing, and can be applied electrolytically ( including both anodic and cathodic cleaning). Application method is primarily based on the concentration and condition of the contaminant and the configuration of the parts.

D 43 Appendix D  Pollution Prevention and Water Conservation Practices The base material of the parts is also a consideration in selecting a cleaning process. Some base materials are chemically or physically altered by certain cleaning steps because of oxidation, etching, activation, and hydrogen embrittlement. Such changes may be either desirable or damaging. The base material is also important in considering the operating conditions of the cleaning process ( e. g., concentration, temperature, current). Further, the base material contaminates the cleaning solution ( e. g., etching during acid treatment) and therefore affects the life span of the solution.

References 1. Ayer, Jacqueline and McElligott, Anthony.   Navy Paint Booth Conversion Feasibility Study ( CR 89.004).  Naval Civil Engineering Laboratory, January 1989.

2. Joseph, Ron.   Low VOC Waterborne Coatings,  Metal Finishing Organic Finishing Guidebook and Directory Issue for   94 . Metal Finishing . Hackensack, NJ, May 1994.

3. Batutis, Edward, F.   Keep Your Cleaners Clean,  Products Finishing . October 1989.

4. Kushner, Joseph B. Water and Waste Control for the Plating Shop . Gardner Publications, Inc., 1976.

5. Cushnie, George C. Pollution Prevention and Control Technology for Plating Operations . National Center for Manufacturing Sciences, 1994.

6. Lownheim, Frederick A. Electroplating Fundamentals of Surface Finishing . McGraw Hill Book Co., New York, NY, 1978.

7. Murphy, Michael, Ed. Metal Finishing Guidebook and Directory Issue for 1994 . Metal Finishing . Hackensack, NJ, 1994.

8. University of Northern Iowa. Cutting Fluid Management in Small Machine Shop Operations . Iowa Waste Reduction Center, Cedar Falls, Iowa, undated.

9. Master Chemical Corporation. A Guide to Coolant Management .

10. Higgins, Thomas. Hazardous Waste Minimization Handbook . Lewis Publishers, Chelsa, MI, 1989.

11. Ebasco Environmental. Hazardous Waste Minimization Study, Air Force Plant No. 6 . Final Report, Norcross, GA, 1992.

D 44 D. 5 Appendix D  Pollution Prevention and Water Conservation Practices 12. Freeman, H. M. Standard Handbook of Hazardous Waste Treatment and Disposal . McGraw Hill, New York, NY, 1989.

13. Thomas, Barry,   Spray Booths,  Metal Finishing Organic Finishing Guidebook and Directory Issue for   94 . Metal Finishing . Hackensack, NJ, May 1994.

14. Monken, Alan.   Wastewater Treatment Systems for Finishing Operations,  Metal Finishing Organic Finishing Guidebook and Directory Issue for   94 . Metal Finishing . Hackensack, NJ, May 1994.

15. Monken, Alan.   Water Pollution Control for Paint Booths,  Metal Finishing Organic Finishing Guidebook and Directory Issue for   94 . Metal Finishing . Hackensack, NJ, May 1994.

16. Brewer, George.   Electrodeposition of Organic Coatings,  Metal Finishing Organic Finishing Guidebook and Directory Issue for   94 . Metal Finishing . Hackensack, NJ, May 1994.

17. Marg, Ken.   HVLP Spray Puts You into Compliance.  Metal Finishing . March 1989.

18. Lighthall Industries, LighthallTM SC 70 Gun Cleaner, Lighthall Industries, Santa Cruz, CA.

D 45 Appendix E  Modified Delta Lognormal Distribution Appendix E MODIFIED DELTA LOGNORMAL DISTRIBUTION Appendix E  Modified Delta Lognormal Distribution Appendix E MODIFIED DELTA LOGNORMAL DISTRIBUTION This appendix describes the use of the modified delta lognormal distribution to model treated effluent data and the estimation of the episode long term averages and variability factors used to calculate the limitations and standards. 1 This appendix describes the statistical methodology that was used to obtain the results presented in Section 10.0.

The modified delta lognormal distribution is a generalization of the familiar two parameter lognormal distribution. This generalized model can be used to model data sets that are a mixture of lognormally distributed values and values that are censored and/ or assigned a constant value such as zero or a sample specific detection limit. When only measured ( i. e., noncensored) values are present in the data, such as all the data sets used to determine the limitations, the modified delta lognormal distribution is equivalent to the familiar two parameter lognormal distribution. Researchers have concluded that the lognormal distribution is often useful for environmental data. 2,3 Furthermore, EPA has found that the lognormal consistently provides a reasonably good fit to observed effluent data distributions. 4 In this appendix, EPA has described the full model, that is, the modified delta lognormal distribution, because it was used to calculate some of the loadings used in other analyses supporting this rule. This model has been used to develop effluent limitations for currently regulated industries including the Iron and Steel industry and the Centralized Waste Treatment industry.

Basic Overview of the Modified Delta Lognormal Distribution EPA selected the modified delta lognormal distribution to model pollutant effluent concentrations from the MP& M industry in developing the long term averages and variability factors. A typical effluent data set from a sampling episode or self monitoring episode ( see Section 3.0 for a discussion of the data associated with these episodes) consists of a mixture of measured ( detected) and nondetected values. The modified delta lognormal distribution is appropriate for such data sets because it models the data as a mixture of measurements that follow a lognormal distribution and nondetect measurements that occur with a certain probability. The model also allows for the possibility that nondetect measurements occur at multiple sample specific detection limits. Because the data appeared 1In the remainder of this appendix, references to   limitations  includes   standards.

2e. g., see Richard O. Gilbert, Statistical Methods for Environmental Pollution Monitoring, Van Nostrand Reinhold, New York, 1987.

3W. J. Owen and T. A. DeRouen,   Estimation of the Mean for Lognormal Data Containing Zeroes and Left Censored Values, with Applications to the Measurement of Worker Exposure to Air Contaminants,  Biometrics 36: 707 719, 1980.

4See H. D. Kahn and M. B. Rubin,   Use of Statistical Methods in Industrial Water Pollution Control Regulations in the United States,  Environmental Monitoring and Assessment, 12: 129 148, 1989.

E 1 E. 1 Appendix E  Modified Delta Lognormal Distribution to fit the modified delta lognormal model reasonably well, EPA has determined that this model is appropriate for these data.

The modified delta lognormal distribution is a modification of the   delta distribution' originally developed by Aitchison and Brown. 5 While this distribution was originally developed to model economic data, other researchers have shown the application to environmental data. 6 The resulting mixed distributional model, which combines a continuous density portion with a discrete valued spike at zero, is also known as the delta lognormal distribution. The delta in the name refers to the proportion of the overall distribution contained in the discrete distributional spike at zero; that is, the proportion of zero amounts. The remaining nonzero, noncensored ( NC) amounts are grouped together and fit to a lognormal distribution.

EPA modified this delta lognormal distribution to incorporate multiple detection limits. In the modification of the delta portion, the single spike located at zero is replaced by a discrete distribution made up of multiple spikes. Each spike in this modification is associated with a distinct sample specific detection limit associated with nondetected ( ND) measurements in the database. 7 A lognormal density is used to represent the set of measured values. This modification of the delta lognormal distribution is illustrated in Figure 1.

5Aitchison, J. and Brown, J. A. C. ( 1963) The Lognormal Distribution. Cambridge University Press, pages 87 99.

6Owen, W. J. and T. A. DeRouen. 1980.   Estimation of the Mean for Lognormal Data Containing Zeroes and Left Censored Values, with Applications to the Measurement of Worker Exposure to Air Contaminants.  Biometrics, 36: 707 719.

7Previously, EPA had modified the delta lognormal model to account for nondetected measurements by placing the distributional   spike  at a single positive value, usually equal to the nominal quantitation limit, rather than at zero. For further details, see Kahn and Rubin, 1989. This adaptation was used in developing limitations and standards for the organic chemicals, plastics, and synthetic fibers ( OCPSF) and pesticides manufacturing rulemakings. EPA has used the current modification in several, more recent, rulemakings.

E 2 Appendix E  Modified Delta Lognormal Distribution Figure 1 The following two subsections describe the delta and lognormal portions of the modified delta lognormal distribution in further detail.

Continuous and Discrete Portions of the Modified Delta Lognormal Distribution The discrete portion of the modified delta lognormal distribution models the nondetected values corresponding to the k reported sample specific detection limits. In the model, * represents the proportion of nondetected values in the dataset and is the sum of smaller fractions, * i , each representing the proportion of nondetected values associated with each distinct detection limit value. By letting Di equal the value of the ith smallest distinct detection limit in the data set and the random variable XD represents a randomly chosen nondetected measurement, the cumulative distribution function of the discrete portion of the modified delta lognormal model can be mathematically expressed as:

1 Pr ( XD £ c) = d   d i 0 < c ( E 1) i: Di £ c The mean and variance of this discrete distribution can be calculated using the following formulas:

1 k E ( XD ) =   di Di ( E 2) d i = 1 k 2 Var ( XD ) = 1   di( Di  E ( XD )) ( E 3) d i = 1 E 3 E. 2 Appendix E  Modified Delta Lognormal Distribution The continuous, lognormal portion of the modified delta lognormal distribution was used to model the detected measurements from the MP& M industry database. The cumulative probability distribution of the continuous portion of the modified delta lognormal distribution can be mathematically expressed as:

Pr[ XC £ c] = F Ø   ln( c)  m ø   ( E 4) º s ß where the random variable XC represents a randomly chosen detected measurement, M is the standard normal distribution, and : and F are parameters of the distribution.

The expected value, E( XC ), and the variance, Var( XC ), of the lognormal distribution can be calculated as:

  2   E ( XC ) = exp   m + s 2     ( E 5)   Var ( XC ) =[ E ( XC )] 2 ( exp( s 2 )  1) ( E 6)

Combining the Continuous and Discrete Portions The continuous portion of the modified delta lognormal distribution is combined with the discrete portion to model data sets that contain a mixture of nondetected and detected measurements. It is possible to fit a wide variety of observed effluent data sets to the modified delta lognormal distribution. Multiple detection limits for nondetect measurements are incorporated, as are measured (" detected") values. The same basic framework can be used even if there are no nondetected values in the data set ( in this case, it is the same as the lognormal distribution). Thus, the modified delta lognormal distribution offers a large degree of flexibility in modeling effluent data.

The modified delta lognormal random variable U can be expressed as a combination of three other independent variables, that is,

U = Iu XD +( 1  Iu ) XC ( E 7)

where XD represents a random nondetect from the discrete portion of the distribution, XC represents a random detected measurement from the continuous lognormal portion, and Iu is an indicator variable signaling whether any particular random measurement, u, is nondetected or noncensored ( that is, Iu = 1 if u is nondetected; Iu = 0 if u is noncensored). Using a weighted sum, the cumulative distribution function from the discrete portion of the distribution ( equation 1) can be combined with the function from the E 4 E. 3         Appendix E  Modified Delta Lognormal Distribution continuous portion ( equation 4) to obtain the overall cumulative probability distribution of the modified delta lognormal distribution as follows,

Pr ( U £ c) =   d i +( 1 d ) F  Ø ln( c)  m ø   ( E 8) i: Di £ c º s ß where Di is the value of the ith sample specific detection limit.

The expected value of the random variable U can be derived as a weighted sum of the expected values of the discrete and continuous portions of the distribution ( equations 2 and 5, respectively) as follows E ( U ) = d E ( XD ) +( 1  d ) E ( XC ) ( E 9)

In a similar manner, the expected value of the random variable squared can be written as a weighted sum of the expected values of the squares of the discrete and continuous portions of the distribution as follows 22 E ( U 2 ) = d E ( XD ) +( 1 d ) E ( XC ) ( E 10)

Although written in terms of U, the following relationship holds for all random variables, U, XD , and XC .

E ( U 2 ) = Var ( U ) +[ E ( U )] 2 ( E 11)

So using equation 11 to solve for Var( U), and applying the relationships in equations 9 and 10, the variance of U can be obtained as 2 22 Var( U ) = d     Var( XD ) +[ E( XD )]

    + ( 1 d )     Var( XC ) +[ E( XC )]

     [ E( U)] ( E 12)

Episode specific Estimates Under the Modified Delta Lognormal Distribution In order to use the modified delta lognormal model to calculate the limitations, the parameters of the distribution are estimated from the data. These estimates are then used to calculate the limitations.

The parameters d$ i and d$ are estimated from the data using the following formulas:

E 5 E. 4 Appendix E  Modified Delta Lognormal Distribution nd d$ i = 1   I( dj = Di ) nj= 1 ( E 13)

d$ = nd n where nd is the number of nondetected measurements, dj , j = 1 to nd , are the detection limits for the nondetected measurements, n is the number of measurements ( both detected and nondetected) and I( ) is an indicator function equal to one if the expression within the parentheses is true and zero otherwise. The " hat" over the parameters indicates that they are estimated from the data. When all of the data are noncensored, d$ is equal to zero and the modified delta lognormal distribution is equivalent to the lognormal distribution.

The expected value and the variance of the delta portion of the modified delta lognormal distribution can be calculated from the data as:

k E$

( XD ) = 1 $   d$ i Di ( E 14) d i= 1 k 2 V$ ar( XD ) = 1 $   d$ i ( Di  E$ ( XD )) ( E 15) d i = 1 The parameters of the continuous portion of the modified delta lognormal distribution,

m$ and s$ 2 , are estimated by nc ln( xi ) m$ =   i= 1 nc nc ( ln( xi ) m$ ) 2 ( E 16)

s$ 2 =   i= 1 nc  1 where xi is the ith detected measurement value and nc is the number of detected measurements. Note that n = nd + nc .

The expected value and the variance of the lognormal portion of the modified delta lognormal distribution can be calculated from the data as:

E$ ( XC ) = exp     m$ + s$ 2     ( E 17)   2   E 6 1 2 3 4 5 6 7 8 9 10 Appendix E  Modified Delta Lognormal Distribution V$ ar( XC ) =[ E$

( XC )] 2 ( exp( s$ 2 )  1) ( E 18)

Finally, the expected value and variance of the modified delta lognormal distribution can be estimated using the following formulas:

E$ ( U ) = d$ E$ ( XD ) +( 1 d$) E$ ( XC ) ( E 19)

V$ ar( U ) = d$

      V$ ar( XD ) +[ E$

( XD )] 2       +( 1 d$)

      V$ ar( XC ) +[ E$ ( XC )] 2       [ E$ ( U )] 2 ( E 20)

Equations 17 through 20 are particularly important in the estimation of episode long term averages and variability factors as described in the following sections. These sections are preceded by a section that identifies the episode data set requirements.

Example:

Consider a facility that has 10 samples with the following concentrations:

The ND components of the variance equation are: Sample number Measurement Type Concentration ( mg/ L)

ND 10 ND 15 ND 15 ND 20 NC 25 NC 25 NC 30 NC 35 NC 35 NC 40 D1 = 10, d$ 1 = 1/ 10 D2 = 15, d$ 2 = 1/ 5 D3 = 20, d$ 3 = 1/ 10.

E 7 $ Appendix E  Modified Delta Lognormal Distribution Since d$ = 2/ 5, the expected value and the variance of the discrete portion of the modified delta

lognormal distribution are 1   111   E$ ( XD )= 2/ 5     10 · 10 + 5 · 15 + 10 · 20     = 15,

1   111 V$ ar( XD )= 2/ 5     10 · ( 10  15) 2 + 5 · ( 15  15) 2 + 10 · ( 20  15) 2       = 12.5.

The mean and variance of the log NC values are calculated as follows: n c   ln( xi )( 2 · ln( 25)+ ln( 30)+ 2 · ln( 35)+ ln( 40))$ = i= 1 == 3.44 n 6 c n c 2   ( ln( xi ) m )( 2 · ( ln( 25) 3.44) 2 )+( ln( 30) 3.44) 2 +( 2 · ( ln( 35) 3.44) 2 ) +( ln( 40) 3.44) 2 i = 1s$ == = 0.0376 nc  15 Then, the expected value and the variance of the lognormal portion of the modified delta lognormal distribution are E$

( XC )= exp       3.44 + 0.0376       = 31.779 2 V$ ar( XC )=[ 31.779] 2 ( exp( 0.0376)  1)= 38.695.

The expected value and variance of the modified delta lognormal distribution are E$ ( U) = 2 5 · 15 +

      1 2 5       · 31.779 = 25.067 V$ ar( U )= 2 · ( 12.5 + 152 ) +

      1 2   · ( 38.695+ 31.7792 )  25.0672 = 95.781. 55    E 8 2 Appendix E  Modified Delta Lognormal Distribution E. 4.1 Episode Data Set Requirements Estimates of the necessary parameters for the lognormal portion of the distribution can be calculated with as few as two distinct detected values in a data set. ( In order to calculate the variance of the modified delta lognormal distribution, two distinct detected values are the minimum number that can be used and still obtain an estimate of the variance for the distribution.)

If an episode data set for a pollutant contained three or more observations with two or more distinct detected concentration values, then EPA used the modified delta lognormal distribution to calculate long term averages and variability factors. If the episode data set for a pollutant did not meet these requirements, EPA used an arithmetic average to calculate the episode long term average and excluded the dataset from the variability factor calculations ( because the variability could not be calculated).

In statistical terms, each measurement was assumed to be independently and identically distributed from the other measurements of that pollutant in the episode data set.

The next two sections apply the modified delta lognormal distribution to the data for estimating episode long term averages and variability factors for the MP& M industry.

E. 4.2 Estimation of Episode Long Term Averages If an episode dataset for a pollutant meets the requirements described in the last section, then EPA calculated the long term average using equation 19. Otherwise, EPA calculated the long term average as the arithmetic average of the daily values where the sample specific detection limit was used for each nondetected measurement.

E. 4.3 Estimation of Episode Daily Variability Factors For each episode, EPA estimated the daily variability factors by fitting a modified delta lognormal distribution to the daily measurements for each pollutant. The episode daily variability factor is a function of the expected value, and the 99th percentile of the modified delta lognormal distribution fit to the daily concentration values of the pollutant in the wastewater from the episode. The expected value, was estimated using equation 19 ( the expected value is the same as the episode long term average).

The 99th percentile of the modified delta lognormal distribution fit to each data set was estimated by using an iterative approach. First, the pollutant specific detection limits were ordered from smallest to largest. Next, the cumulative distribution function, p, for each detection limit was computed. The general form, for a given value c, was:

E 9 º ß º ß Appendix E  Modified Delta Lognormal Distribution p =   d$ i +( 1 d$) F   Ø   ln( c s ) $  m$

  ø   ( E 21) i: Di £ c where M is the standard normal cumulative distribution function. Next, the interval containing the 99th percentile was identified. Finally, the 99th percentile of the modified delta lognormal distribution was calculated. The following steps were completed to compute the estimated 99th percentile of each data subset:

Step 1 Using equation 21, k values of p at c= Dm , m= 1,..., k were computed and labeled pm .

Step 2   The smallest value of m ( m= 1,..., k), such that pm $ 0.99, was determined and labeled as pj . If no such m existed, steps 3 and 4 were skipped and step 5 was computed instead.

Step 3 Computed p* = pj  d$ j .

Step 4 If p* < 0.99, then P$ 99 = Dj else if p* > 0.99, then   Ø j  1 ø      0.99    d$ i     P$ 99 = exp     m$ + s$ F 1    i = 1        ( E 22)    1 d$         º    ß     where M 1 is the inverse normal distribution function.

Step 5 If no such m exists such that pm > 0.99 ( m= 1,..., k), then   P$ 99 = exp   m$ + s$ F  1 Ø   0.99  d$  ø     ( E 23)      1 d$      The episode daily variability factor, VF1, was then calculated as:

P$ 99 VF1 = E$( U ) ( E 24)

Example:   Since no such m exists such that pm > 0.99 ( m= 1,..., k),   E 10 Appendix E  Modified Delta Lognormal Distribution P$ 99 = exp       3.44 + 0.194 · F  1 Ø  0.99  0.4 ø      = 47.126. º 1 0.4 ß  The episode daily variability factor, VF1, was then calculated as:

47.126 VF1 == 1.880. 25.067 To identify situations producing unexpected results, EPA reviewed all of the variability factors. EPA used several criteria to determine if the episode daily variability factors should be included in calculating the option variability factors. One criteria that EPA used was that the daily variability factors should be greater than 1.0. A variability factor less than 1.0 would result in a unexpected result where the estimated 99th percentile would be less than the long term average. This would be an indication that the estimate of s$ ( the log standard deviation) was unstable. A second criteria was that not all of the sample specific detection limits could exceed the values of the noncensored values. All the episode variability factors used for the limitations and standards met these criteria.

References 1.   Aitchison, J. and J. A. C. Brown. 1963. The Lognormal Distribution. Cambridge University Press, New York.

2.   Barakat, R. 1976.   Sums of Independent Lognormally Distributed Random Variables.  Journal of the Optical Society of America, 66: 211 216.

3.   Cohen, A. Clifford. 1976. Progressively Censored Sampling in the Three Parameter Log Normal Distribution. Technometrics, 18: 99 103.

4.   Crow, E. L. and K. Shimizu. 1988. Lognormal Distributions: Theory and Applications. Marcel Dekker, Inc., New York.

5.   Kahn, H. D., and M. B. Rubin. 1989. " Use of Statistical Methods in Industrial Water Pollution Control Regulations in the United States." Environmental Monitoring and Assessment. Vol. 12: 129 148.

6.   Owen, W. J. and T. A. DeRouen. 1980. Estimation of the Mean for Lognormal Data Containing Zeroes and Left Censored Values, with Applications to the Measurement of Worker Exposure to Air Contaminants. Biometrics, 36: 707 719.

E 11 E. 5 Appendix E  Modified Delta Lognormal Distribution 7. U. S. Environmental Protection Agency. 2000. Development Document for Effluent Limitations Guidelines and Standards for the Centralized Waste Treatment Point Source Category . Volume I, Volume II. EPA 440/ 1 87/ 009.

8.   U. S. Environmental Protection Agency. 2002. Development Document for Effluent Limitations Guidelines and Standards for the Iron and Steel Manufacturing Point Source Category . EPA 821 R 02 004.

E 12