【Daily Question】Utilities - Water Supply and Drainage - 20200503

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Which of the following statements about the intermediate treatment process is incorrect? A. When a membrane treatment process is used, there should be pre-treatment procedures to ensure reliable water quality for the membranes, as well as technical measures that facilitate the cleaning and replacement of these membranes. B. Disinfection facilities must be installed for treated water. C. In building wastewater treatment systems, biological rotators should be preferred wherever possible. D. When the raw water is high-quality mixed wastewater, a primary sedimentation tank is not necessary once a regulation tank is in place. Answer: C. Option A complies with the provisions of Article 6.1.5 of the “Code for Design of Building Wastewater Reuse Systems”. The use of membrane treatment for reclaimed water has entered the practical stage in some cities and regions. Experience shows that when membrane treatment is used, reliable water quality of the feedwater, along with simple and effective techniques for cleaning and regenerating the membranes, are key factors to ensure the proper operation of membrane filtration. Therefore, standards require that membrane treatment processes include pretreatment steps to ensure reliable feedwater quality, as well as technical measures that facilitate the cleaning and replacement of membranes. Option B complies with the requirements of Article 6.2.18 of the mandatory provisions in the Code for Design of Reclaimed Water in Buildings. Disinfection is an important step in ensuring the sanitary standards of reclaimed water; it directly affects the safety of using this water. Therefore, regulations require that reclaimed water must be disinfected. Option D complies with the provisions of Article 6.2.6 of the Code for Design of Reclaimed Water in Buildings. Based on the experience with typical medium and small-scale sewage treatment plants, the absence of a primary sedimentation tank after installing a regulating tank does not affect the treatment efficiency. Moreover, since high-quality mixed wastewater contains little solid suspension, a primary sedimentation tank can be omitted in such cases. Option C does not conform to the explanatory provisions of Article 6.1.3 of the Code for Design of Reclaimed Water in Buildings. Biological rotating discs, with part of their surface exposed to the air, emit unpleasant odors that have a significant impact on the surrounding environment. Therefore, guidelines recommend using biological rotators as little as possible in building biological treatment processes.