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Waste Management The Standard Technology: Standard Plumbing + Septic Tank + Leach Field
The septic tank allows standard plumbing (flush toilets, dish and clothes washing machines,
sinks, showers) to be used without an urban waste-disposal system. The positive
qualities of the flush toilet listed by Peter Harper should be noted: A septic tank has two or more closed watertight chambers. It features anaerobic (no oxygen) bacteria that digest the bulk of stuff thrown into it into sludge which sinks, crust which floats, and liquid which passes out of the septic tank. The liquid output from a septic tank is still loaded with infectious bacteria and is dangerous to have near the surface. The standard treatment of the liquid is to let it drain into the earth from a system of leach pipes. The leach pipes have small holes drilled in them. The pipes are buried a foot or more deep in order to avoid having the water near the surface. An Alternative: Composting Toilets and Gray Water Composting toilets convert feces and urine to compost over a period of a year or more. For maximum safety, the compost is aged a few more years before being used for gardening. The output water from the remaining standard plumbing fixtures, sinks, bath, shower, and washers, is termed gray water. (Black water is the term used for the output from a flush toilet.) The composting toilet takes care of the most common, most infectious wastes separately from other wastes, and without the use of water. Two major varieties of composting toilet are in use. One type is exemplified by the Sun-Mar Excell composting toilet. It can handle the waste from three or four people on a regular basis. The first composting is done aerobically (oxygen-using bacteria) in a horizontally mounted drum. A heating element and fan evaporate water and blow all gasses out a vent. In operation it requires a peak of 250 watts and an average of 150 watts AC (this may adjust upwards for four people). The operation also requires some labor: every three or four days the drum is turned about seven times by hand in order to keep the composting aerobic and about yearly the compost tray needs to be removed and emptied. The other class of composting toilets does not use electricity but requires much larger storage volumes. The Clivus Multrum is an example of this type. A large volume, typically in a basement, is required to hold decomposing feces. This is sloped so that decomposition and gravity serve to move the older, more nearly composted feces to the end of the chamber. Compost is removed from the end of the chamber with a shovel. Composting toilets are reasonably competitive with flush toilets in many ways. The technology has advanced enough so that it is hygienic in appearance and odor as well as in fact. It is reliable. It requires just a little more effort to operate and maintain than a flush toilet. It also has an advantage that the flush toilet does not, that much of the nutrients from the human excreta are retained for use of plants. The flaw with composting toilets is that they do not interface that well with gray-water disposal. Gray water can be collected in barrels and automatically pumped out to water a garden. An advanced gray-water system comprises tank and pump, filter, and irrigation pipe. The output from such a system can be used to water plants other than root crops provided the irrigation pipes are placed under a couple of inches of mulch. It is not healthy to allow the gray water into the air or onto parts of plants which will be eaten (e.g., don't water potatoes with gray water). A publication advocating the use of gray water for home irrigation is "Your Complete Guide to Managing Greywater in the Landscape." It is published by Oasis, a company which makes soaps and other products for use with septic and gray-water systems. Their products are more easily handled by biosystems than standard products. The book also spells out problem areas in using gray water, and would seem to be a reliable source when citing such problems. Among the problems that it lists are: * laundering diapers. This makes the water output from the laundry black water instead of gray water. * grease from a kitchen sink. Less of a problem in a vegetarian household. The grease can clog gray-water distribution. Where regulated, the kitchen sink output is usually classed as black water. * hair from bath or shower. This can clog the system. * many household discharges will have sodium. This will build up in an irrigated area and eventually prevent plant growth. In addition, the composting toilets require an overflow pipe for excess liquids from the evaporating trays. (Ninety percent of feces is water. A large part of what happens in composting is evaporation of this water. Trays to hold water until it evaporates are part of both composting toilets mentioned above.) In difficult situations, the advice in the book is to divert the questionable water to the municipal sewer system or to a septic system. It becomes clear that the book is suggesting a gray-water irrigation system in addition to a standard septic system. Gray-water system catalogs include valves designed for switching flows. Thus it seems that composting toilets plus gray water are nearly but not quite a complete system. In addition, mechanical filtering of the input to gray-water systems is clearly necessary, but it is also trouble-prone. Another Alternative: Septic Tank and Effluent Use: "The septic tank sidesteps the bugaboo of higher-tech gray-water distribution systems by 'filtering' the water without a mesh that can clog." (From the Oasis book.) The effluent from a septic tank can be used directly to irrigate trees and other deep-rooted crops. In such a use, one must design the leach pipes so that roots can be removed or the system will eventually clog up. The permaculture approach is a constructed wetlands as shown in the following diagram. The septic tank effluent is first passed through filters of mussel shells, gravel, and sand. The top centimeter of these filter materials needs to be removed once a year and either roasted or washed. This water is then passed to bulrushes, water lilies, and water hyacinths. It is then suitable for aquaculture with filter feeders first, then fish. The water is apparently potable at this point. (Mollinson, pp. 172-180; Morrow, pp. 43-44) |
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Of these constructed wetlands the Oasis book says, "Caution: Proven for cleaning up
large flows of partially treated municipal wastewater but still emerging as a system for
untreated household gray water, though systems appear to be successful with
prefiltration." The initial part apparently refers to Ocean Arks' "Living Machine" work.
A variation is to use gray water to flush toilets. The problem here is that most gray water cannot stand without being filtered or aerated, or anaerobic bacteria will turn it foul within a day or two. This variation is being pursued by the Earthship designers on an experimental permit and is being pursued experimentally elsewhere, such as at the "Florida house." This approach can also be combined with a low-flush toilet or a composting toilet. The drawback is the cost of the septic tank, although I believe this is less than the cost of a leach field. This alternative would appear to be the best in the long run since it presents a fully closed cycle and leads naturally into a multispecies aquaculture. To establish it in the short run, some experience beyond the theory and designs in Mollinson and in Marrow appears to be needed, especially if we locate in a county with waste-disposal regulations. References: Harper, Peter. Fertile Waste: Dealing Ecologically with Your Domestic Sewage. Machynlleth, Powys, U.K.: Centre for Alternative Technology, 1996. Ludwig, Art. Create an Oasis with Greywater: Your Complete Guide to Managing Greywater in the Landscape. Santa Barbara, California: Oasis Design, 1994. Mollinson, Bill. Permaculture: A Designer's Manual. Tyalgum, Australia: Tagari Publications, 1988. Morrow, Rosemary. Earth User's Guide to Permaculture. Kenhurst, NSW, Australia: Kangaroo Press, 1993.
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