Evaluation of Sewage Sludge as a Source of Irrigation and Manure

Characterization ofthe sewage effluents and sludges of the Calcutta city has been made to assess their manurial values. Sewage effluents are neutral 10 slightly alkaline in reaction and contain basic ions at higher quantity, particularly in winter. Bicarbonate and chloride ions are at toxic level. The effluents are rich in NH₄-N, NO₃-N and available P. Sludges are alkaline in reaction having higher salt contents in winter. Base saturation is above 80 per cent. The sludges are also rich inorganic carbon, NH₄—N, NO₃—N, available P and K.

Continuous application of sewage effluents makes the soil alkaline and increases the salt contents. Although sewage effluents and sludges are rich in nutrients, the toxicity due to micronutrients and other heavy metals which they generally possess has to be seriously taken into consideration before their application in soils.