What is sewage?
The unprocessed and untreated waste material generated from commercial and household activities such as washing dishes and clothes, taking a shower and flushing the toilet. 
What is involved in the sewage treatment process?

Primary treatment - is where liquids and solids are separated from the raw sewage using fine screens.
Secondary treatment – is where the screened sewage from the primary treatment is further treated using a biological nutrient removal process. The activated sludge consisting of bacterial strains adapted to the environmental conditions in the secondary treatment system consume most of the nutrients and pollutants contained in the raw sewage. The treated wastewater is separated from the mixture of water and activated sludge in the clarifier. The treated wastewater is further disinfected using chlorine gas or sodium hypochlorite to ensure that the treated wastewater is free of pathogens before re-use for irrigation.

The excess activated sludge generated during the secondary treatment process is further processed to produce a dewatered activated sludge. The sludge is rich in organic carbon, trace elements and essential plant nutrients such as nitrogen, phosphorus and sulphur. The council is currently investigating options to process the sludge to a standard that meets the requirements of the “Australian Biosolids Guidelines” before making it available to the community as a soil improver.

Tertiary treatment – The tertiary treatment consist of raw sewage screening, secondary treatment and membrane filtration. The tertiary filtration provides an advanced level of treatment of the incoming sewage and physical disinfection using membranes. This type of treatment was adopted by Whitsunday Regional Council for the Cannonvale Sewage Treatment Plant to protect the environment.

What happens after the sewage is treated?

Once the wastewater has been treated and tested to meet the standard required for recycled water reuse. Recycled water may be used for agriculture and industries that don’t require potable water. The excess treated and disinfected wastewater is returned to our waterways.

What is involved in disinfection?
The biologically treated wastewater after separation from the activated sludge is disinfected chemically or physically to inactivate or remove the potentially disease causing organisms from the treated wastewater. The disinfection methods used at council’s sewage treatment plants are either chemical (chlorine gas or sodium hypochlorite) or physical (membrane filtration).

What is activated sludge?
Activated sludge is the mixed populations of microorganisms responsible for sewage treatment. Bacteria live, grow and multiply by using sewage components as a food source. During these processes the activated sludge contained in the treatment system increases continuously requiring regular wasting to ensure optimum environmental conditions for the remaining microorganisms responsible for sewage treatment.

What are biosolids?
Biosolids refers to the stabilized organic material produced during the sewage treatment process. Biosolids may contain macronutrients, such as nitrogen, phosphorus, potassium and sulphur as well as micronutrients, such as copper, zinc, calcium, magnesium, iron, boron, molybdenum and manganese. Biosolids must meet the Australian Biosolids Guidelines for safe recycling. Biosolids for reuse and areas of usage and application rates depend on the stability grade and class of biosolids produced. Biosolids contain nutrients, key to stimulating plant growth and improving the productivity of soils. Strict state and federal guidelines specify how biosolids can be used. More information about biosolids is available at
What is recycled water?
Recycled water is sewage wastewater treated to a standard that meets the requirements of the “Water Quality Guidelines for Recycled Water Schemes”. 
What is a bioreactor?
A bioreactor is a tank containing activated sludge suspended in wastewater. The environment that makes the sewage treatment process possible is essential and is maintained using 24 hours continuous SCADA monitoring and telemetry. Any deviation from the optimal environmental conditions in the bioreactor will trigger an alarm and remedial action from the on-call plant operator.
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