城镇污水处理厂次氯酸钠消毒效果的影响因素研究

Influence Factors of Sodium Hypochlorite Disinfection Performance in Municipal Wastewater Treatment Plant

次氯酸钠消毒是目前我国城镇污水处理厂应用最广泛的一种消毒方式,但行业内对次氯酸钠的运行参数如投加量等及其消毒效果尚未达成共识。为此,以执行《城镇污水处理厂污染物排放标准》(GB 18918—2002)一级A标准的某城镇污水处理厂二沉池出水为研究对象,开展了以次氯酸钠为消毒药剂的加氯消毒试验。结果表明,二沉池出水的粪大肠菌群对数去除率与消毒工艺中的有效氯投加量、接触时间以及水温均呈正相关,消毒后出水的氧化还原电位(ORP)可间接表征消毒效果,CT值(接触时间T×接触时间结束时消毒剂残留浓度C)可指导消毒药剂的投加量。在保持接触时间为12 min的前提下,当有效氯投加量为3. 67 mg/L时,粪大肠菌群对数去除率可达到2. 5-lg以上,确保消毒后出水的粪大肠菌群数达到一级A排放标准,此时,ORP为578m V,总氯CT值为7. 6 mg·min/L,游离氯CT值为3. 3 mg·min/L。

Sodium hypochlorite disinfection is the most widely used disinfection method in municipal wastewater treatment plants in China. However,no consensus has been reached on the operation parameters of sodium hypochlorite( such as dosage) and its disinfection performance. In view of the above problems,the sodium hypochlorite disinfection experiment was carried out to treat the effluent from the secondary settling tank of a municipal wastewater treatment plant in accordance with first level A criteria specified in Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant( GB 18918-2002). Logarithmic removal efficiency of fecal coliform in the effluent from the secondary settling tank was positively correlated with available chlorine dosage,contact time and temperature in the process of disinfection. ORP of the effluent after disinfection could indirectly characterize the disinfection performance,and CT values( contact time T × disinfectant residual concentration C at the end of contact time) could guide the dosage of disinfectant. Under the premise of contact time of 12 min,when available chlorine dosage was 3. 67 mg/L,the logarithmic removal rate of fecal coliform could reach more than2. 5-lg,which ensured the fecal coliform count in the effluent after disinfection to reach first level A discharge standard. At this time,ORP was 578 m V,CT value of total chlorine was 7. 6 mg·min/L,and CT value of free chlorine was 3. 3 mg·min/L.