Study On The Agricultural Utilization Of Sewage Sludge

A composting process was investigated to realize the agriculture utilization of municipal sewage sludge in agriculture. The effective way to solve the problems of the sludge such as high heavy metal and phytotoxic substance content, excess of liable organic matter, pathogenic microorganism, etc. was focused in the study.In the first chapter, a comprehensive summary was given to sewage sludge's property, classification, potential threaten to environment, general treatment and disposal ways, related regulations and limits for its land application, sludge compost process and its typical procedures and operating parameters. In the presentation of compost process, a further comparison was made between different reactors, and a series of evaluation standards for the maturity of compost product was reviewed.In the second chapter, a feasibility research was carried out on the prospective land application of the sludge from Fuzhou Xiangban sewage treatment plant. A detailed investigation was made about the characteristics of the sludge such as: Total N, P, K; heavy metal contents and the chemical forms distribution of heavy metals. The result showed that the sewage sludge had a relatively high nutrient content and low heavy metal contamination, meeting China requirements for sludge application to land.In the third chapter, alkaline coal ash residues produced by a coal-fired power plant were co-composted with sewage sludge to evaluate its effect on heavy metal availability in anaerobic composting process. In order to accelerate the process, yeast powder was added to the composting mixture. Dehydrated Sewage sludge mixed with fuel ash as bulking agent at 1:1,3:1 and 4:1 (w/w) respectively, was composted for 17 days in laboratory batch reactor. Chemicaldistributions of Cu were determined by Tessie's sequential extractions of co-composted materials sampled on days 0, 3, 6, 11 and 16. The changes of soluble and plant-available Cu levels were investigated. The results showed that co-composting reduced the levels of soluble and plant-available Cu, suggesting that the extractability and exchangeablility of Cu was equally reduced. The optimal mixture rate was 3:l(sludge: ash) in terms of the stabilization effects.In the forth chapter, a laboratory composting reactor was designed. Using the mode of alternate anaerobic&aerobic composting system, Sewage sludge mixed with sawdust and coal fly ash respectively as bulking agent has been composted for 55 days. During this process, the changes in temperature, pH, volatile organic matters contents, nutrient content and Germination index were monitored. It was observed that temperature rose rapidly in both composting processes, reaching 50 *C in just 2-3 days, following a high temperature phase of two weeks . In terms of the changes in pH value, both composting were observed a rise and then a fall. However, the pH value in coal fly ash compost didn't vary as sharply as sawdust compost, owing to the buffering effect of the alkaline of coal fly ash. On account of the nutrient content, Total N, P, and K contents increased during the composting process, with the highest nutrient concentration occurring after 55 days. But biooxidation of the organic matter affected the available forms of nitrogen, resulting in the different elution of NlV-N and NCV-N. Although EC values increased during composting as the pile became richer in salt, the EC of the final compost product(3.4 ms/cm) didn't exceed the limit (4.0 ms/cm). Phytotoxicity, as assessed by cress germination, disappeared gradually in the process, with a GI as high as 97%, indicating the maturity of the compost.A field experiment was conducted to study the effect of sludge compost onthe growth and blossoming of Gerbera. By contrast with a conventional fertilizer, investigation of growth and blossoming parameters showed that the compost had a similar positive effect on Gerbera, and the contents of N and P in the leaves gathered in both group were very close. K content was slightly lower in compost group, as the content of K in the sewage sludge was relatively low.In the last chapter, an analysis was made on the current situation of sewage treatment in Fuzhou. A suggestion was put forward to set up a sewage treatment and disposal center. The mode of production process was designed, and the needed main equipments were listed.