Comprehensive Evaluation of Environmental Impact of Sewage Sludge Using Chemical Analysis and Bioassay

Sewage sludge containing heavy metals and organic pollutants are often toxic and persistent even after being released into the environment. Samples of sewage sludge were collected from seven wastewater treatment plants in Shanghai for chemical analysis in combination with microtox assay of the major pollutants in the samples. Results show that Samples S5 and S7 were high in heavy metal content( Cd,Hg and Cu),and higher than the average of the country and the criteria set in the StandardCJ / T 309- 2009for Agricultural Use of Sewage Sludge From Wastewater Treatment Plants,however,in terms of contents and compositions of PCBs,OCPs and PCDD / Fs,all the samples were found to be at the safe level; and in terms of mean PAHs concentration,were lower than Class A Criteria of the Standard for sludge to be used in agriculture in China and the standard for sludge in land-filling in US and EU,as well,except for Sample S7. Which reached up to 34. 61 mg · kg- 1,being five to six times higher than the standards in China and EU. Chemical analysis of the leachates from the seven sludge samples shows that all the samples were lower in PAHs concentration than the standards for identification of hazardous waste,but higher in DOC content than the European standard. Microtox assay indicates that in integrated toxicity,Sample S3 was the highest followed by S1,S6 and S7,and then by S2,S4 and S5,suggesting that sludge derived from domestic sewage is much higher in integrated toxicity. The findings may be cited as basic data for subsequent treatment and disposal of sewage sludge.