Characteristics Of Sewage Sludge And Its Agricultural Utilization In Chongqing

Sewage sludge which mainly comes from the primary settling tank and discharge of surplus sludge is the deposit produced in each operating unit in municipal wastewater treatment plant. Sewage sludge abounds many microelements and organic matters such as nitrogen, phosphor and potassium while it contains pathogen, parasite, heavy metals as well as toxic and hazardous organic pollutants which has caused a tremendous stress on ecologic environment. Research on secure and proper disposal and diposition of sludge has been carried on enthusiasticly by scholars at home and abroad. However, studies and reports on characteristics of sludge from different operating process and workshop section are still gaps to be filled.Characteristics of Sewage sludge and content differentia of heavy metals in different operating processes and workship sections were studied on the basis of analysis of sludge from ten wastewater treatment plants with six different operating processes in Chongqing municipality. This research which could provide basic and scientific datum for proper disposal and diposition of sludge is of great theoretic and pratical significance.By analysis of dewatered sludge from wastewater treatment plants in Chongqing, it was found pH of sewage sludge ranging from 5.95~7.73 was basically neutral or slightly alkaline and the average water content of dewatered primary sludge was 77.2%. Organic content of the sludge whose total nitrogen, total phosphorus and total potassium are respectively 47.15g/kg,19.72g/kg and 13.87g/kg equals that of pig manure. The content of available nitrogen in the sludge was low only accounting for 4~8% of total nitrogen while average content of available phosphorus accounted for 10% of total phosphorus. Content of available potassium was high with a average value of 4.70g/kg accounting for 30~50% of total potassium. With regard to nutrient, content of nitrogen, phosphorus and potassium in sludge of wastewater treatmrnt plants in Chongqing was considerably high. Content of total nitrogen, phosphorus and potassium was respectively five times, 4.2 times and 1.46 times higher than that in pig manure. It followed that the sludge was of high agricultural value that could be developed to organic fertilizers or used in farmland directly and properly.