制革废水处理系统各级出水的生态毒性评价

Ecological toxicity evaluation of effluents from different process for tannery wastewater treatment

采用生态毒理学常用的大型溞(Daphnia magna)和活性污泥(activated sludge)作为试验系统,对制革废水处理系统各个环节出水进行毒性试验,以评价其处理效果。按照OECD标准试验方法,选取本实验室繁殖的大型溞(溞龄小于24 h),和采自以处理生活污水为主的污水处理厂活性污泥,分别使用重铬酸钾和3,5-二氯酚作为参比物验证大型溞和活性污泥的毒性敏感性。以大型溞活动抑制和活性污泥呼吸抑制作为毒性终点,利用48 h静态试验和3 h曝气试验分别评价水样对于大型溞活动和活性污泥呼吸作用的急性毒性效应。统计各试验组大型溞的活动情况和活性污泥的呼吸速率,分别将其与空白对照组进行比较,计算大型溞的活动抑制率和活性污泥的呼吸抑制率,采用Bliss法统计制革废水处理系统各个环节出水对大型溞和活性污泥的半数抑制浓度(EC50)。结果表明:制革废水依次经过厌氧脱硫反应器、脱色厌氧反应器、微曝气反应器和厌氧氨氧化反应器的生物处理系统处理,其出水对大型溞和活性污泥的急性毒性已大为降低。进水、厌氧脱硫反应器出水、脱色厌氧反应器出水、微曝气反应器出水和厌氧氨氧化反应器出水对大型溞活动抑制试验的48 h-EC50分别为41.3%、32.2%、48.0%、91.2%和无抑制作用;活性污泥呼吸抑制试验3 h-EC50则分别为178.2%、101.5%、689.7%、184.6%和无抑制作用。总体上毒性呈现逐渐降低的趋势,而且大型溞比活性污泥更为灵敏。大型溞和活性污泥的生态毒性结果与化学分析的结果相互补充。

Ecological toxicity of effluents from different process of the biochemical tannery wastewater treatment was evaluated using Daphnia magna and activated sludge, the common test systems in ecotoxicity. According to the standard OECD testing guidelines, the test daphnia were bred in our laboratory with age 〈 24 h and the activated sludge was collected from the sewage treatment plant which predominantly treats domestic sewage were selected as biomarkers, potassium bichromate and 3, 5-dichlorophenol were used as reference substances to verify the sensitivities of Daphnia magna and activated sludge, respectively. With the toxicity endpoints of acute immobilization for Daphnia magna and respiration inhibition for activated sludge, 48 h static test and 3 h aeration test were performed to evaluate the water samples for their abilities to generate acute toxic effects on the mobility of Daphnia magna and on the respiration of activated sludge, respectively. Motility of daphnia and respiration rates of sludge in each test group were measured, which were compared with those in blank control groups and the inhibition rates were calculated accordingly. The bliss method was adopted to determine the median inhibition concentrations （EC50） of effluents from different process of the biochemical tannery wastewater treatment. The results showed that the toxicity of tannery wastewater was significantly reduced after the different treatment process of UASB （for sulfate reduction）, ABR （for decolorization）, microaerophilic reactor and ABR （for Anammox） in sequence. 48 h-EC50 values to Daphnia magna and 3 h-EC50 values to activated sludge were 41.3%, 32.2%, 48.0%, 91.2% and 178.2%, 101.5%, 689.7%, 184.6% for raw wastewater, UASB （for sulfate reduction） effluent, ABR （for decolorization） effluent and microaerophilic reactor effluent, respectively, and ABR （for Anammox） effluent had no toxicity to Daphnia magna and activated sludge. The study also indicates that Daphnia magna is more sensitive than activated sludge in the tests. Ecological toxicity testing can be an effective complement to chemical analysis, and provide the scientific basis for early warning and evaluation of operational efficiency for tannery wastewater treatment.