Composting of Sewage Sludge and Different Plant Residues

Abstract

Ten-week composting experiment was conducted at Faculty of Agriculture Farm, Suez Canal University, Ismailia Governorate, during Summer 1999. Sewage sludge has been stabilized by composting in mixtures with the following plant residues at rates 10 and 20 : 1 w/w; 1) wood carpentry refuse, 2) peanut shells 3) rice straw, 4) wheat straw, 5) corn straw, 6) sugar cane refuse, 7) grass clippings, 8) peanut shoots, 9) chickpea residues and 10) lupine residues. The objective of the experiment is to produce a compost environmentally safe material that is free from pathogens, and can be used beneficially on agricultural newly reclaimed soil as a organic fertilizer by composting of sewage sludge with plant wastes.The data indicated that, organic C content of sludge-plant residue treatments was gradually significant decreased with the time till the end of the experiment (10 th week). Increasing the rate of sewage sludge application resulted in a marked decrease in total N content of the mixture. It can be arrange the different plant residues according to low C/N ratio as well `as high organic C decomposition rate in the following order: chickpea residues  peanut shoots  wheat straw  lupine residues  corn straw  grass clippings  sugar can refuse  wood carpentry refuse  peanut shells  rice straw at 10:1 sewage sludge : plant waste. While, wood carpentry refuse  corn straw = grass clippings  peanut shoots  chickpea residues = sugar can refuse  wheat straw  lupine residues  rice straw  peanut shells at 20:1 sewage sludge : plant waste.Salinity levels of the different treatments of the final compost product were still low and practice for agricultural use, K content not significantly increased, N content decreased and P content significantly increased by increasing the rate of sewage sludge upto 20:1 plant residues. Total Cd, Pb, Cu, Zn and Ni concentrations in the final compost are very lower than maximum permissible concentrations for agricultural use.Raw sewage sludge has pathogenic bacteria and parasites in the range of the infective dose to human. However, composting conditions of sewage sludge-plant residues were greatly effective in reduction of total bacteria and coliforms, pathogenic bacteria i.e. Salmonella sp., Shigella sp. and Vibrio sp and pathogenic parasites i.e. Ascaris lumbericoides, Trichuris trichiura, Entrobius vermiculus and Hyenolepis spp.