Effectiveness, Constrains and Scientific Perspectives of Land Application of Sewage Sludge in the Southern Jiangsu Province

Most of sewage sludge from secondary sewage treatment plant in the southern Jiangsu Province contain 35 to 70% of organic matter, 3 to 5% of nitrogen, 1.1 to 1.8% of phosphorus, and other nutrients. Depending on wastewater sources, the sewage sludges also contain 1,300mg/kg of Zn, 300mg/kg of more of Cu, and some other heavy metal including Cd, Cr, Pb, As, and Hg. In the light of the regulations of land application of sludge in China (GB4284-84), these sewage sludge can be applied on land as an economic disposal method. The results from incubation experiments showed that the mineralization rate of organic carbon and nitrogen in sludge is faster than many farmyard manure. Thiry to 60% of organic nitrogen in sludge can be mineralized in the incubation period of 3 months. Sewage sludge significantly improved soil physical, chemical, and biological properties and increased the biomass of the tested plants. However, heavy metals and pathogen in sewage sludge and its poor physical structure constrain, to a great extend, the wide application of sewage sludge on farmland. The removal of heavy metal in sludge by bioleaching method, immpbilizing heavy metal and killing pathgon by mixed with alkali materials such as fly coal ash, and stabilizing sludge by composting are feasible approaches for safe utilization of sludge. Besides, developing sludge into an organic-inorganic granular compound fertilizer for cropland may be an applicable way. It was concluded that, to develop more economic and safer land disposal technique of sewage sludge in the southern Jiangsu province, composting sludge forllowed by developing the composted sludge into alternative substrates for ornamental plants in best approach for sludge disposal at the present.