好氧生化污水处理厂化学品暴露预测模型构建

污水处理厂是化学品进入环境的重要中转站,污水处理厂中的暴露预测是化学品环境风险评估的重要内容.以污水处理厂中最简单的传统活性污泥法为基础工艺,基于我国新化学物质登记要求的基础数据(分子量、吸附/解吸附系数、蒸气压、水溶解度、快速或固有生物降解性)、我国的环境条件(温度=283K、风速=2 m·s~(-1))和污水处理厂典型场景参数(日处理量=3.5万m~3·d~(-1)、进水BOD_5=0.15 g·L~(-1)、进水SS=0.2 kg·m~(-3)、出水SS=0.02 kg·m~(-3)、曝气池BOD_5去除率=90%、污泥密度(dw)=1.6 kg·L~(-3)、污泥有机碳含量为0.18~0.19),根据化学品的线性吸附、一级动力学降解、Whitman双阻力挥发机制以及逸度理论,建立了包含空气、水、悬浮颗粒和沉积污泥9箱质量守恒方程的污水处理厂化学品暴露预测模型CSTP(O),同时确定了快速或固有生物降解性结果外推获得STP降解速率的标准.模型验证结果表明,C-STP(O)模型对已有研究中26种化学品预测准确率为81%,对5种酚类化学品,模型预测与实测去除率绝对差值为2.5%~6.3%,C-STP(O)能准确预测具有快速或固有生物降解性的有机化学品在污水处理厂中挥发、吸附、降解、二级出水的分布比例.所建模型可为研究化学品在STP中的归趋及化学品暴露评估提供技术工具.

Development of Chemical Exposure Prediction Model for Aerobic Sewage Treatment Plant for Biochemical Wastewaters

Sewage treatment plant (STP) is a key transfer station for chemicals distributed into different environment compartment, and hence models of exposure prediction play a crucial role in the environmental risk assessment and pollution prevention of chemicals. A mass balance model namely Chinese Sewage treatment plant (C-STP(O)) was developed to predict the fate and exposure of chemicals in a conventional sewage treatment plant. The model was expressed as 9 mixed boxes by compartment of air, water, suspended solids, and settled solids. It was based on the minimum input data required on the notification in new chemicals, such as molecular weight, absorption coefficient, vapor pressure, water solubility, ready or inherent biodegradability. The environment conditions (Temperature=283 K, wind speed=2 m ·s^-1) and the classic STP scenario parameters of China, especially the scenario parameters of water quality and sludge properties were adopted in C-STP(O) model to reflect Chinese characteristics, these parameters were sewage flow of 35000 m³ ·d^-1, influent BOD₅ of 0.15 g ·L^-1, influent SS of 0.2 kg ·m^-3, effluent SS of 0.02 kg ·m^-3, BOD₅ removal in aerator of 90%, sludge density of 1.6 kg ·L^-3 and organic carbon content of 0.18-0.19. It adopted the fugacity express for mechanism of linear absorption, first-order degradation, Whitman two resistances. An overall interphase transfer constant which was the sum of surface volatilization and stripping was used to assess the volatilization in aerator. The most important and uncertain input value was the biodegradation rate constant, and determination of which required a tier test strategy from ready or inherent biodegradability data to simulate test in STP. An extrapolated criterion of US EPA to derive biodegradation rate constant using the results of ready and inherent biodegradability was compared with that of EU and was recommended. C-STP(O) was valid to predict the relative emission of volatilization, absorption, degradation and effluent, on ground of both successful simulation of the removal of 26 chemicals from references with an accuracy rate of 81% and consistency of prediction and test with absolute difference of 2.5%-6.3% for 5 phenols. In cases of prediction of three chemicals with different properties, 1,1,2-trichloroethane, Naphthalene and DEHP, the predicted fate well satisfied the monitor data. The model is therefore believed to be a simple, robust and useful tool in fate study and exposure assessment of chemicals.