STUDY ON UTILIZATION OF MUNICIPAL SEWAGE SLUDGE IN FARMLAND AND FOREST LAND

The composition of municipal sewage sludge and its effect on plant growth,soil fertility and agroenvironments were studied by filed.greenhouse and incubation experiments.The results showed that sewage sludge contained quite a lot of organic matter and plant nutrients such as nitrogen and phosphrous.Bioavailabilities of N and P of sludge origin were higher than those from ordinary farmyard manures.Sewage sludge significantly improved soil physical,chemical and biological properties by increasing soil waterstable aggreates,soil organic matter,humus,nitrogen and phosphrous contents,also enhancing soil respiration and the number of total microorganisms and lowering soil bulk density at the same time.Consequently,higher yield could be obtained owing to application of sludge.However,sewage sludge also contained pollutants such as heavy metals and pathogen.It was found that sludgeborne metals were easily accumulated in soil and plant,especially in vegetable soil and foliar vegetables.Besides,sludge had a pronounced effect in lowering soil pH which might affect the mobilization of heavy metals in soil.Generally speaking,it was feasible for municipal sewage sludge to apply on soil as fertilizer or soil amendent if the pollutant contents in the sludge and pollutant concentration in soil amended with sewage sludge were under the upper limited value.But sewage sludge should be avoided to apply directly on vegetable soil.It was suggested that developing organoinorganic compound fertilizer with sludge was a practical method to dispose sewage sludge on the farmland.