College of Environmental Science and Engineering, Tongji University, Shanghai 200092,China.
State Environmental Protection Key Laboratory of Environmental Risk Assessment and Control on Chemical Process, School of Resources and Environmental Engineering, East China University of Science and Technology, Shanghai 200237, China.
Sci Total Environ. 2018 Sep 1;635:716-724. doi: 10.1016/j.scitotenv.2018.04.162. Epub 2018 Apr 24.
Elimination of polycyclic aromatic hydrocarbons (PAHs) from coke wastewater is crucial to minimize the PAHs contamination levels to the environment. Knowledge about the characteristics of PAHs removal in biological treatment processes, especially hybrid systems, for real coke wastewater treatment has been very scarce. In this study, a lab-scale hybrid anaerobic-anoxic-oxic (A/A/O) process was used to treat highly toxic coke wastewater and operated more than 600 d at total hydraulic retention time (HRT) of 50 h, 40 h, 30 h, 20 h and internal mixed liquor recirculation ratio (R) of 3, 6, 9. Removal performance and behaviors of priority PAHs in the hybrid A/A/O system were investigated. The results showed that the appropriate total HRT and R from oxic reactor to anoxic reactor for organics and nitrogen removal was 40 h and 3, respectively. The concentrations of total PAHs were very high (254-488 μg/L) in the raw coke wastewater, and effectively reduced to 4.1-4.5 μg/L in the final effluent by the present system under the optimized operational conditions. Among the three treatment units, anoxic reactor made the largest contribution to the total PAHs removal. Large amounts of PAHs (415-1310 μg/g) were adsorbed to the activated sludge in the anoxic and oxic reactor, leading to a much higher load of PAHs (2535 μg/d) in the excess sludge than that in the treated coke wastewater (93 μg/d) at SRT 60 d. Therefore, the excess sludge was identified as the major emission source of PAHs in coke wastewater during the hybrid A/A/O process, and might pose an environmental risk if the excess sludge was not properly treated and disposed.
从焦废水（coke wastewater）中消除多环芳烃（polycyclic aromatic hydrocarbons，PAHs）对于将 PAHs 污染水平降至最低至关重要。然而，关于生物处理工艺（尤其是混合系统）中 PAHs 去除的特性，特别是针对实际焦废水处理的知识非常匮乏。在这项研究中，采用实验室规模的混合厌氧-缺氧-好氧（anaerobic-anoxic-oxic，A/A/O）工艺处理高毒性焦废水，在总水力停留时间（hydraulic retention time，HRT）为 50、40、30 和 20 小时，内循环比（mixed liquor recirculation ratio，R）为 3、6 和 9 的条件下，运行时间超过 600 天。考察了混合 A/A/O 系统中优先 PAHs 的去除性能和行为。结果表明，对于有机物和氮的去除，好氧反应器至缺氧反应器的适当总 HRT 和 R 分别为 40 小时和 3。在优化的运行条件下，原焦废水中总 PAHs 的浓度非常高（254-488μg/L），但经本系统处理后，最终出水中总 PAHs 的浓度降至 4.1-4.5μg/L。在三个处理单元中，缺氧反应器对总 PAHs 的去除贡献最大。大量的 PAHs（415-1310μg/g）被吸附到缺氧和好氧反应器中的活性污泥中，导致在 SRT 为 60 天时，剩余污泥中的 PAHs 负荷（2535μg/d）远高于处理后的焦废水中的 PAHs 负荷（93μg/d）。因此，如果剩余污泥得不到妥善处理和处置，混合 A/A/O 工艺中剩余污泥被认为是焦废水中 PAHs 的主要排放源，可能会对环境造成风险。
