6 .119 VI.11.6: Agricultural Area Design: It was decided to raise crops in lunar soil (instead of styrofoam or Earthsoil) in the cylindrical section of the hull. A 30-centimeter thick layer supports the root structures of most vegetables and many fruits. To protect the hull from corrosion and to contain the irrigation water, a layer of polyethylene 4 mils thick lines the soil-covered deck. Irrigation is provided by spaghetti-like small polyethylene tubes running through the soil near each row of plants. This is one of the "water trickle" methods used in the high productivity desert greenhouse in Abu Dhabi (6.18). All necessary nutrients, which must all be water soluble, are distributed through this tubing system and recovered in the recycling processes. This minimizes waste of water and helps prevent the leaching,or washing out, of potassium and calcium froM plant leaves. This is often the case in heavy rains. VI.11.7: Waste Recycling: A crucial and, even today, frustrating problem of human settlements is waste recycling. The most advanced sewage treatment systems on Earth use combinations of biological, chemical, mechanical, magnetic, and even electrical processes to transform the by-products of life into nontoxic, usable or disposable forms. The problem for the prototype colony is quite severe. The colonists could not justify jettisoning sludge waste into space. Everything must be separated and reused or shipped to a safe disposal A detailed waste recycling procedure has not been devised for the prototype. The basic ingredients to be considered have been identified. Solid wastes from people, animals, and plants must be purified and reused. Nitrogen fixing methods produce nitrites, which must not be allowed to accumulate in large amounts. From metabolic by-products and some food processing come hydrogen, carbon monoxide, hydrogen sulfide, ammonia, aldehydes, ketones, and hydrocarbons, which must be processed out of the cycles. Salt must be recovered and soap must be removed from the water system (6.4). A potential aid in waste recycling would be marine aquaculture or single-celled algae and shellfish . Recent work has shown the potential of secondary waste effluent, mixed with seawater, as a growth medium (6.9).
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