Analysis Of Sludge Property Characteristics Of Typical Sewage Treatment Plants In Jiangsu Province

In recent years,as the number of urban sewage treatment plants in China increases year by year,wastewater treatment ratio increases rapidly.Large amount of sludge has been produced.The problem of sludge treatment and disposal is becoming more and more serious.At present,the theory of sludge treatment and disposal is relatively rich.However,the harmless and resource-based disposal of sludge is still a serious problem faced by sewage plants and local governments.The selection of sludge disposal method should consider sludge properties,local social resources,economic level and environmental benefits.Therefore,in-depth analysis of sludge properties is of great significance for the resourceful disposal of sludge in a suitable way.This study conducts a comprehensive research on 24 typical wastewater treatment plants in Jiangsu Province.The current status of sludge treatment and disposal in each wastewater plant was analyzed in depth.Excess sludge from these WWTPs was sampled and tested.Pearson correlation analysis,Student’s t test,Nemero index,Hakanson potential ecological index,and principal component analysis were used for data processing and analysis.The sludge properties characteristics of typical sewage treatment plants in Jiangsu Province were studied from the perspectives of the change of sludge properties during the past 15 years,the influence of sludge treatment methods,the influence of water intake,and the characteristics of sludge in different regions.It is found that the number of sewage treatment plants and sewage treatment capacity in Jiangsu province are increasing year by year.The development of sewage treatment in Jiangsu province is still uneven.However,the level of sewage treatment in northern part of Jiangsu has improved significantly in the past 10 years.Most sludge in Jiangsu Province is disposed of by incineration,while composting and landfill disposal decreased significantly.Sludge samples were tested for p H,water content,organic matter,nutrient content,calorific value,heavy metal,and mineral oil.This study draws the following conclusions.（1）78.26%of the surveyed sludge p H is in a reasonable range for subsequent disposal.The whole sludge is weakly alkaline.（2）The range of sludge moisture content is 37.5%-83.14%with a large difference.The average moisture content of sludge samples is 69.29%.Although 91.30%of sludge moisture content is lower than 80%,sludge moisture content is still at a high level for land application.70%of sludge samples can’t meet the requirements of land improvement on moisture content.Different dewatering methods have a significant effect on sludge moisture content.The average moisture content of sludge can be reduced to 49.59%after plate-frame dewatering,which is obviously lower than that of centrifugal and belt dewatering.（3）The investigated sludge is rich in nutrients,showing the characteristics of high nitrogen,high phosphorus,low potassium and low organic matter.The average content of nitrogen is 26.86g/kg.The average content of phosphorus（calculated by P₂O₅）is 18.31 g/kg.The average contents of potassium（calculated by K₂O）is 2.65 g/kg.Total nutrient（calculated by N+P₂O₅+K₂O）is 47.82g/kg,which basically met the requirements of land application for total nutrient in relevant standards.Moreover,nitrogen and potassium showed a certain correlation with local economic development.Compared to 10 years ago,organic matter and calorific value in sludge did not change significantly,while nitrogen and potassium contents decreased by 23.51 g/kg and 1.73 g/kg respectively.The change is mainly due to the improvement of nitrogen removal rate in sewage treatment plant,the annual decrease of chemical fertilizer application rate and,seasonal fluctuation of nutrient content.（4）Heavy metal pollution in sewage sludge is still exists.Compared to 2006,the total heavy metal content of sludge decreased by 58%.Although the total content of heavy metals has decreased significantly,the content of As and Hg has a rising trend due to the development of electroplating,medical and other industries.The regional characteristics of heavy metal content in sludge were similar to that in 2011,with most heavy metal content in southern and middle Jiangsu being higher than that in northern Jiangsu.In addition,the study found that the proportion of industrial wastewater in the influent,the industry involved and whether the industrial wastewater has been treated strictly in the plant are important factors affecting the heavy metal content in sludge.（5）In terms of organic pollutants,mineral oil components were detected in all sludge samples.Mineral oil pollution is relatively serious with the average value of 2699.75 mg/kg.Through the traceability analysis,it is found that the industrial wastewater from mechanical processing,electrical manufacturing,metal,and chemical industries is the main source of sludge mineral oil.Based on the survey of the typical sewage plant and analysis of sludge properties,this paper summarizes the problems existing in the sludge disposal and puts forward the measures.It is necessary to（1）enhance sewage plant sludge treatment technology and equipment level;（2）treat industrial wastewater at source;（3）clarify sludge disposal technology route and direction;（4）improve coordination and cooperation of sludge administrative agents.From the perspective of sludge,this paper reveals the development status and existing problems of water treatment in China.The results of the study can provide data support and reference for sludge disposal and resource utilization.