Nitrogen fertilizer value of sewage sludge co-composts.

We evaluated the nitrogen fertilizer value of a sewage sludge and of four composts obtained from this same sludge. The sewage sludge was extracted from the wastewater treatment plant of Beni-Mellal city (Morocco). The extracted sewage sludge was composted alone, mixed with domestic solid waste, with olive cakes and with sawdust. The experiment was carried out in pots of vegetation under natural conditions. The humidity was maintained close to 80% of the field capacity. Ray-grass from Italy was used as a plant test. The research lasted 140 days, during which 4 cuts of the plant were investigated. The results obtained showed that all the amendments tested allowed an increase in the output in dry biomass and nitrogen plant uptake. This increase was more significant with non-composted and composted sewage sludge alone than with the other co-composts. The apparent coefficient of nitrogen utilization (CAU) recorded oscillated between 50 and 38%, testifying a great aptitude of the amendments tested to provide nitrogen to plants. The values of the apparent rates of nitrogen mineralization obtained were 38, 29, 28, 27 and 25%, respectively, for non-composted sludge; sewage sludge compost; sewage sludge-olive cakes compost; sewage sludge-domestic solid waste compost and sewage sludge-wood sawdust compost.