MakeShift Challenge: Potable Water: “Schmutzdecke” Honorable Mention

by William Lidwell
August 08, 2005

This is a straightforward sand filter with a more feasible way of making activated charcoal in a two-day time period. Forgione makes reference to an “organic layer” that will form on the top of the sand after a week or so. In water treatment circles, this is called “schmutzdecke,” and will further aid in filtration. Congratulations Vinnie!

I think it’s a reasonable assumption that since there is an unlimited supply of coconuts, a beach is not too far away. Have some of the locals collect some beach sand. This should work pretty well as the fine sand in the top of the filter. Coarser sand should be found closer to the village. Hopefully the locals are familiar with the geological aspects of the area. Also, we are going to need some gravel, or broken-up rocks, or similar material. These will make up the first barrel filter.

I also think that it’s not too far of a stretch that the locals know how to make charcoal. If not, skip to the “making charcoal” section. They should take advantage of the unlimited supply of coconuts, and start husking and breaking and de-meating the nuts to collect as many shells as possible. The charcoal made from coconut shells is the best for filtration. Get the locals making as much charcoal as they can. This is for the second barrel filter. We’ll have to try to activate the charcoal — that will come later.

We are also going to need the husks from the coconut. Coconut husks are great for rope, woven mats, roofs, etc in rural areas, so it might not be unreasonable to assume that the locals already have some woven into mats, which would be great. If not, then we are just going to pack the husk layers by hand for the second barrel.

OK, now that the materials from the environment have been collected, we can build the filter.

The first barrel filter

Place the barrel on an elevated surface (table, rock, etc) high enough so the drainage from the barrel will flow into the second barrel. Make a hole with tools provided about 6 inches from the bottom of the barrel, large enough to fit a section of 3-inch-diameter bamboo. This will provide a sludge collection area at the bottom. Take a 3-inch-diameter section of bamboo long enough to fit the entire length of the bottom of the barrel and out, approximately 3 feet. If there are separating cell walls in the bamboo, they will need to be knocked out to allow water flow–except for the end that will be in the barrel (of course). Drill holes on one side of the tube, and orient the tube so the holes face up. This will allow water flow out of the tube. Cut a piece of inner tube from one of the tires on the bike, and wrap it around the bamboo tube. This will seal any gap you may have between the barrel and the bamboo tube.

Make layers of gravel and medium and fine sand in the barrel, approximately 8 inches per layer. This will leave about 12 inches of space at the top. Place a flat rock on the top of the fine sand. This is to prevent the top layer from being too disturbed when pouring in the water to be filtered.

By now, you should be getting reports that the charcoal has been made — now we have to try to activate it. Commercial activation of charcoal uses superheated steam under controlled conditions. You can also chemically activate charcoal by treating it with sulfuric acid, then heating it and slowly cooling it. That’s where the car battery comes in.

CAREFULLY open (or have one of the locals do it) the vent caps on the battery. The locals should have a plastic container to collect the acid from the batter. CAREFULLY pour the acid into the container. Now, you should have anywhere from 1.8 liters to over 4 liters of acid, depending on the size of the battery. Let’s just say we only need 1 liter of acid, since any more would cost you too much of your drinking water. Battery acid is about 36% sulfuric acid and 64% water. We should use 2 liters of bottled water to get the acid down to 9%. When mixing acid with water, add the acid to the water, NOT WATER TO ACID. HOT ACID WILL SPATTER! Pour 2 liters of water into another plastic container that the locals have provided, and SLOWLY add acid to the water, stirring all the while.

You have 3 liters of acid — that should treat enough charcoal for our use. Soak the charcoal in the acid, and then reheat in the charcoal pile. With luck, this will activate enough of the charcoal to get the arsenic and benzene out of the filtered water.

Now, while the locals are activating charcoal, prep the second barrel. Make a hole in the side of the barrel a few inches from the bottom, large enough to fit a 1 or 2-inch-diameter piece of bamboo. To make a spout with a tight seal, we are going to wedge the 1 or 2-inch-diameter bamboo inside 3-inch collars. The collars will fit on either side of the barrel, with pieces of inner tube as a grommet/gasket. A cut length of inner tube will be tied firm enough to make a seal around the bamboo using coir rope or other latching material.

After the charcoal has been activated, make 8-inch layers of gravel, coconut husk, activated charcoal, and coconut husk in the second barrel. If the sand filter barrel did its job, the only thing we have to worry about is the arsenic and the benzene.

Use and Maintenance

By looking at the source water, it either needs to be decanted or screen filtered before it is poured into the sand filter barrel. Hopefully, someone is willing to sacrifice some cloth or maybe a mosquito net, which should get most of the nasty big bits of junk out of the water. Using buckets, glasses, etc, pour the filtered or decanted water onto the flat rock. Eventually, the water will work its way down through the levels of sand and rock, and out of the spout at the bottom. This water should be boiled, just in cased, before consumption.

It is possible that the top layer of the barrel will develop an organic layer in about two weeks or so. This will aid in the filtration process. Every so often, this layer will need to be removed and replaced with fresh sand. Both barrels will need to be reworked when there is a noticeable difference in water quality. That means the locals will have to procure another car battery, and save some filtered water for the dilution.

Making Charcoal

Traditional methods would put the material to be converted into carbon into a big pile, covered with earth, and a fire burned under it. You can also use a 55-gallon drum with holes poked in the bottom, and a cover on top, with just enough of a gap for venting gasses. A fire is lit underneath. It is quite possible that the locals have a 55-gallon drum. Or, at least one may be procured from the industrial plant that caused the pollution in the area in the first place.

The activation of the charcoal, after soaking in acid, should be placed in the pile or barrel, and heated again for about four hours.


> More analysis of winning MakeShift entries from MAKE 02.