The Chemical Analysis And Toxicity Test Based On The Ocean Dumping Of Sewage Sludge

An appropriate and safe treatment and disposal of sewage sludge in China is of great significant to environmental protection and reduce the health risk of human for its huge production and complex chemical constitution. There was little research and essential data about ocean dumping of sewage sludge among different disposal methods in China. However, the ocean dumping of sewage sludge may trigger the releasing of contaminants contained in sewage and thus exert negative effects on marine organisms.Hence, an comprehensive investigate in the sewage sludge from 7 typical wastewater treatment plants in Shanghai throughout chemical analysis both on sewage sludge and its leachate combined with in vivo and in vitro bioassay to evaluate the safety of ocean dumping of sewage sludge were carried out.1, The total amounts of chemical compounds in sewage sludge were analyzed by instrument and compared with guidelines and other researches.(1) The heavy metals detected in sewage sludge were higher than the average level of China. The concentrations of Cu from S2, S5, S7(1984 ~ 2395 mg/kg) in sewage sludge was exceed the national agricultural utilization standard.(2) The total amounts of toxicity equivalency quantity of PCDD/Fs was 4.8~22 ng/kg which was lower than the national agricultural utilization standard(100ng/kg) and the safe concentration in sediments(20ng/kg) and the conger of PCDD/Fs were characterized by high chlorinated compound with lower toxicity(57%~87%).(3) The total amounts of PAHs detected in sewage sludge were ranged from 1.2-34.6 mg/kg and most of the samples do not exceed the criterion of agricultural utilization set by China and EU except for S7. The low molecular weight conger were dominated in PAHs(41%~71%) with low temperature sources.(4) The amounts of PCBs in most sewage sludge samples were below the detected limitation and only p,p-DDE in parts of samples were detected(0.003~0.026mg/kg)among all OCPs congers. These two compounds were under a relative low contaminant burden.2, The amounts of contaminants that release from different sewage sludge leachateprotocol were analyzed.(1) The sea water leachate procedure with longer shake time and salinity was conductive to the release of Cu, Zn, As than horizontal vibration extraction and TCLP procedure. The TCLP procedure with lower p H was incline to release more Hg than others. The heavy metals contained in sewage sludge leachates was not exceed the guideline of China and EU about hazardous waste. But we should pay attention to the huge amounts of Cu and Zn in leachates when consider its strong ability of releasing and toxicity to organism. S2 and S7 with the highest Cu(1468~1728 mg/L and 390~2338 mg/L) in leachate were found in relationship with its contaminant load in sewage sludge.(2) Only four kinds of PAHs congers with low molecular weight were detected in parts of sewage sludge leachate(PHE, NAP, PYR and FLT) and the ΣPAHs was ranged from ND to 1.9 μg/L which was closed to the level of PAHs in the water from Yangtze Estuary. Thus, the PAHs may be with a lower environmental risk in comparison to heavy metals.(3) The DOC contained in sewage sludge leachates(90~1570 mg/L) was extremely higher than EU guideline(100 mg/L) which may be the principle contaminants in the sewage sludge leachates.3, The results of toxic effects of sewage sludge and its sea water leachate on marine organisms from different position of food chain were listed as followed.(1) The acute toxicity from sea water leachate can be observed when the mortality in 96 h,growth inhibition in 72 h and luminescent inhibition in 15 min were selected as the end points of toxicology experiments for microalgae, Photobacterium phosphoreum,Artemia saline and Sparus macrocephlus. The results were presented as a full dose-response curve with the increasing of the concentrations of sea water leachate in the test system. By the way, the low concentrations of leachates in tests have stimulative effect on the growth of microalgae and Artemia saline and bioluminescence of Photobacterium phosphoreum. The EC50 obtained in experiments was 4.9%~57% and8.2%~30% for microalgae and Photobacterium phosphoreum. The LD50 obtained in experiments was 27% ~ 74% and 0.2% ~ 3.8% for Artemia saline and Sparus macrocephlus and growth inhibition of Artemia saline can be observed under a sub-lethal dose of the concentration of sea water leachate at 25%. According to the toxicity grading criteria from USEPA based on effluent, the diversity of sensitivity to the toxicity of sea water leachate among the test organisms were ranked as Sparus macrocephlus(extremely high)>>microalgae and Photobacterium phosphoreum(moderate~high)> Artemia saline(low~moderate) which was dependingon the selection of end points and interspecific difference.(4) The principal component analysis based on the toxicology data indicated that the leachate from S1 and S3 have the greatest toxic effect on marine organism and the toxicity of leachate decrease a little with the increasing of industrial effluents in the corresponding wastewater treatment plants can be found.(5)The average mortality of Ruditapes philippinarum and Cyclina sinensis in sewage sludge was 94% and 49% in 10 d. Bioaccumulation of Cu, Cd, Pb and As can be found at the end of 14 d bio-accumulation experiment in Cyclina sinensis.The residual level of Cu was the highest in organism which was approach to the guideline for marine organism quality at level III. The BCF values were ranked as Cu(135)>As(58)>Pb(7.6) and Cu tend to express a strong ability of bioaccumulation in Cyclina sinensis.4,The results from in-vitro bioassay indicated that the baseline toxicity,genotoxicity and the Ah receptor activity can be observed in the organic extract of sewage sludge and the corresponding toxicity equivalency quantity aquired were 133~3400 mg3,5-DCP/kg, ND~25 mg 4-NQO/kg and 73~6839 ng TCDD/kg respectively.The level of estrogenic effect was less than 0.02 ng E2/g among all samples. The baseline and genotoxicity were uncorrelated to the organic pollutant detected in sewage sludge. At the same time, Most of the Ah receptor agonists in sewage sludge were derived from those unknown chemicals and the greatest contribution of dioxin like effect among the detected dioxin like compounds in sewage sludge was Bk F.In this study, the sewage sludge can not be dumping into ocean for the following reasons at least. Firstly, the great amounts of Cu and DOCs in both sewage sludge and leachates may tend to release into water and lead an unpredictable environmental risk.Secondly, For the relatively high level of toxic effects to marine organism, and the bioaccumulation of heavy metals in sewage sludge and its leachate may increase the ecological and human health risk. Thirdly, a certain amounts of baseline toxicity,gentoxicity and the Ah receptor agonists were detected in sewage sludge and most of them were derived from those unknown chemicals that may be the potential pollutants in sewage sludge.