MABR membrane aeration biofilm reactor process was adopted for the reconstruction of a sewage treatment station in North China. MABR membrane components were added to the original CAST process and a new secondary sedimentation tank was built to reconstruct the original biochemical system. In the meanwhile, an advanced treatment system with new high-density tanks and V-shaped filters were built to ensure the quality of the final effluent. In the establishment of the MABR membrane aeration biofilm reactor process, only new aeration membrane components were added and no new equipment and civil works were needed in the original biochemical tank. No new blowers were needed due to the high aeration efficiency and low energy consumption of the biofilm system. The one-off investment is about 850 yuan·m−3 and the reconstruction period was about 15 days, indicating its advantages of short reconstruction period and low operational cost. For the new membrane aeration biofilm reactor process, the mean value of ammonia nitrogen in the inflow was 39 mg·L−1 and its mean value in the effluent was 3 mg·L−1, i.e. the average removal rate was 92%. The mean value of total nitrogen (TN) in the inflow was 63 mg·L−1 and the mean value in the effluent was 11 mg·L−1, making an average removal rate of 83%. The mean value of total phosphorus (TP) in the inflow was 7.5 mg·L−1 and the mean value in the effluent was 0.9 mg·L−1, thus the average removal rate was 88%. The TP concentration in the effluent could be kept below 0.4 mg·L−1 by chemical phosphorus removal by the follow-up advanced treatment section. The mean value of COD in the inflow was 367 mg·L−1 and the mean value of effluent was 35 mg·L−1, i.e. the average removal rate was 90%. After the reconstruction of the treatment process, the effluent quality of the sewage treatment station stably reached the Class 1A level of tHe Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant (GB 18918-2002).

Based on the existing researches related to thermal desorption technology and dioxins, this paper provides a comprehensive review on the technological process, influencing factors of dioxins formation, and the mechanisms and measures of dioxins inhibition during the direct thermal desorption remediation of organic contaminated soil. Firstly, dioxins may be produced during different technological processes: dioxins present in contaminated soil are desorbed by heating; the organic pollutants in soil undergo molecular deconstruction and recombination, thus causing the generation of dioxins during the heating process of rotary kiln; dioxins are generated by heterogeneous catalytic reactions (including precursor and de-novo synthesis reactions) at each cooling stage in the exhaust gas purification process. Secondly, thermal desorption process parameters can also affect dioxins formation, such as heating temperature, heating time, flowing rate of carrier gas, reaction atmosphere and so on. Thirdly, the presence of metal compounds, water, carbon and chlorine source in contaminated soil can catalyze the formation of dioxins. Additionally, the characteristics of site pollution also have a certain impact on dioxins production. The addition of alkaline, sulfur, ammonium/nitrogen or sulfur-nitrogen containing compounds can inhibit the formation of dioxins during thermal desorption. At the end of the paper, the challenges of dioxin inhibition during thermal desorption are summarized, including the unclear chemical transformation mechanisms of various pollutants, the development of high-efficiency and practical inhibitors, etc. In addition, some future research directions are prospected.