| Popis: |
The biological depuration of liquid sewage produces a sludge-type residue of organic compounds and minerals essential for soil fertility maintenance. The conditions for the proper utilization of these sludges differ according to their origin, the treatment process employed, and the soils and crops in question. The Ministry for the Environment has therefore prepared a booklet of reccomandations for local technical offices. This paper illustrates this booklet. The decantation operations carried out in the course of liquid waste depuration permits the extraction of what are called fresh sludges. The basic characteristics of these fresh sludges greatly limit their direct and immediate use in agriculture. They must be treated in such a way as to supply the user with an easy to handle, odorless, risk-free, and stable product. The final physical, chemical, and biological properties of the sludge depend upon these treatments. Sludges are rich in nitrogen and phosphate and should be promoted for use in agriculture in liquid form. They can be spread on pasture land and extensive crops with positive results as long as agronomic criteria such as proper dosage and spreading periods are respected. Maize is a well indicated crop in this regard. In certain particular cases it may be interesting to use sludge in market-gardening, horticulture, forestry, viticulture, and soil reconstitution projects. Liquid sludges would then be used as a fertilizer, and sludges in dry form as an organic complement or support for the crop. In practical terms, the promotion of sludge for use as a fertilizer will make it necessary to equip the depuration station with a well organized distribution network to supply users with material and technical assistance. In economic terms, the use of sludge in agriculture and allied areas is the least expensive way to provide for their disposal and should therefore be encouraged. |
