延安市污水处理厂提标改造工程设计方案与实施效果

延安市污水处理厂一期工程处理规模为5×10⁴ m³·d⁻¹，原采用以“厌氧池+氧化沟+二沉池”为核心的污水处理工艺。提标改造前，污水处理系统存在设计水质偏低而污泥负荷偏高等问题，导致冬季低温或进水水质波动较大时，出水水质难以稳定达标。对此，通过加高氧化沟池体的方式，将生化池总水力停留时间延长至19.82 h；结合MBR工艺，利用膜组件的高效固液分离能力实现泥水分离，将生化池平均污泥浓度提高至7 050 mg·L⁻¹，并在内沟好氧池中增设搅拌机及碳源投加装置，使冬季低温或进水总氮较高时，生化系统整体以AAOAO的方式运行，从而进一步控制出水总氮含量。提标改造工程实施后，一期生化处理系统反硝化污泥负荷和BOD₅污泥负荷(以每天单位MLSS的TN/BOD₅测定值计)分别降低至0.030和0.033 kg·(kg·d)⁻¹，5 ℃条件下污水处理系统的理论TN和BOD₅去除能力分别提升至44.32和286.19 mg·L⁻¹，达到了污染物去除需求。提标改造后污水处理系统运行良好，出水可稳定达到《陕西省黄河流域污水综合排放标准》(DB 61/224-2018)中的A标准，可为该地区同类型污水处理厂提标改造提供参考。

Design scheme and implementation effect of upgrading project for Yan'an sewage treatment plant

The scale of the first-phase project of the Yan’an Sewage Treatment Plant is 5×104 m3·d−1, and the core treatment process is “anaerobic tank+oxidation ditch+secondary sedimentation tank”. Before the upgrade, there were some issues of the sewage treatment system such as low design inlet water quality and high sludge load, which led to violation of effluent discharge standards under low water temperature in winter or great fluctuation in inlet water quality. In this regard, the total hydraulic residence time of biochemical pool was extended to 19.82 h by rising the height of the aeration unit. The membrane module and associated equipment were added after the original biochemical tank to achieve the high-efficiency separation of sludge and water. The average sludge concentration of the biochemical tank was increased to 7 050 mg ·L−1. In addition, a mixer and a carbon source feeding device were equipped to the inner ditch aerobic unit to make the biochemical pool operate in AAOAO mode when the temperature is low in winter or the total nitrogen of the inlet water is high, further controlling the total nitrogen content in the effluent. After the implementation of the project, the denitrifying sludge load and BOD5 sludge load (measured as TN/BOD5 of MLSS per day) of the first stage biochemical treatment system were reduced to 0.03 kg·(kg·d)−1 and 0.03 kg·(kg·d)−1 respectively. The theoretical TN and BOD5 removal capacity of the system were increased to 44.32 mg·L−1 and 286.19 mg·L−1 respectively at 5 ℃, meeting the pollutant removal requirements. After the upgrade, the sewage treatment operates stably meeting the Class A level in the “Integrated Wastewater Discharge Standard for the Yellow River Basin of Shaanxi Province” (DB 61/224-2018).