Study On Technology Of Nitrogen Protecting And Security Risk In Windrow Composting For Municipal Sewage Sludge

The high temperature composting is an important way to transform solid organic wastes to organic fertilizer, which is of great importance in developing organic fertilizer, maintaining and increasing soil fertility, stimulating sustainable agriculture. At present nitrogen lose severely from compost during composting, thus it is nessesary to develop key technology to reduce nitrogen loss and to improve nutrient content status in organic fertilizers.The urban sewage sludge was taken as main experimental organic raw matererial for composting in this research. The experiment was carried out windrow composting and practical production system to study the effect of different additives, amendments and dry sludge dose on composting course and nitrogen maintaining. Main results were showed as follows,1. In situation of windrow composting, addition of 20 % wheat straw to sludge composting system could raise temperature of compost pile up to 67℃which was 16℃higher than no wheat straw addition, and lasted for 7 days with temperature above 50℃which was 6 days longer than check treatment, meanwhile reduced ammonia volatilization by 5 times compared to check treatment at early stage. Addition of 30% or 40% dry maturity sludge back to sludge composting system could inhibite NH4+-N accumulation and N losses, it has been found that 12.26% and 9.86% of total nitrogen lost from above treatments while 22.27% from check treatment.2. In situation of practical production system, addition of same volume of dry return product to the wet sewage sludge could improve composting, temperature in the core pile maintained for 20 days above 50℃and the maximum temperature was up to 72℃. The aim of reduction, recycling, and resource utilization of sludge by high temperature composting system with this mode could be achieved. Continuous monitoring data showed that heavy metal and nutrient content of the compost maintained stability. The various of heavy metals were below the national standard value (GB 18918-2002) when applied on soil with pH≥6.5. Organic matter content in the compost product was higher than 30%, and content of N+P₂O₅+K₂O was higher than 4%, water content was below than 20%, which meet the organic manure standard (NY 525—2002).3. In situation of windrow composting, total nitrogen content in compost changed in trend of decrease with composting process, while total phosphorus, potassium and heavy metals content accumulated.