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Undoubtedly, recycling or re-using water can offer very significant economies. One of the greatest obstacles is the fact that much of the wastewater is disposed of through septic tanks or other small systems of disposal, even into the sea. Ideally, all wastewater should be collected as sewage, treated and recycled for some use or another. The obstacle to this is that sewage treatment plants should be sited close to the sea, a perennial river or a large lake, to receive water which has been treated but is unsuitable for re-use. The implication is that sewage plants should be placed close to the sea and sewage piped to them or, if they are sited inland, pipes to the sea will need to be installed for the wastewater. The latter may be more economical if water is recycled for any purpose.
Recycling of Water in Raw Sewage
The notion of recycling sewage is often fraught with psychological difficulties. Let it be said from the start that it is perfectly feasible to turn raw sewage into potable water. In many countries, treated sewage is poured into watercourses, which are used as a source of potable water downstream. Sewage treatment consists of mechanical filtration to remove solid matter, which is converted to sludge. It then passes to a digestion chamber where aerobic acting bacteria convert most of the organic matter to water and carbon dioxide. An anaerobic chamber removes the remaining organic matter by converting it to methane. This process may take two, three or more days. The final stage is usually filtration through a sand bed. The resultant water is clear but may still contain dangerous microorganisms. If it is necessary to recycle to potable water, these microorganisms may be eliminated by chlorination or ultraviolet radiation.
There are two ways in which agriculture may use treated sewage. The sludge which is formed by the collection of solid matter, when fermented, makes an excellent compost with high nitrogen contents. It als...
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