Alfredo Katherine
Department of Civil and Environmental Engineering, University of South Florida, Tampa, FL.
Water Res. 2021 Jun 1;197:117044. doi: 10.1016/j.watres.2021.117044. Epub 2021 Mar 14.
To control microbial proliferation and nitrification within distribution systems, utilities practicing secondary disinfection chloramination often discontinue their ammonia feed and provide a short, free chlorine disinfection period (FClP), commonly referred to as a "chlorine burn". However, the success and practicality of this approach is often criticized because of the return to nitrification; yet, previous studies conducted in full-scale distribution systems do not contain the sampling frequency to determine how quickly nitrification can return. In this research, a total of 15 hydrants distributed across hydraulically modeled water ages were sampled for 21 sampling events over a period spanning two annual FClPs (2018 and 2019) to investigate the water quality, planktonic community, and, using a new sampling technique, established biofilm community impacts within a single, distribution system pressure zone. Hydrants measured elevated nitrite only 10 weeks after the end of the FClP and live cell counts in the bulk and scour samples statistically significantly increased within two weeks after the FClP ended and chloramine disinfection resumed, indicating limited impacts from a FClP. Furthermore, the FClP significantly increased iron concentrations during the period of free chlorine disinfection creating a consumer water quality concern. Microbial fingerprint analysis using flow cytometry revealed that beta diversity did not significantly change for sampling locations that experienced even periodic low total chlorine concentrations. Only locations that maintained high chlorine residuals throughout both chloramine and free chlorine disinfection periods demonstrated significant changes in bulk water microbial community. Even for these locations, microbial communities of the scoured biofilms remained similar over the course of the study.
为了控制配水系统中的微生物增殖和硝化作用，采用二次消毒氯胺化的公用事业公司通常会停止氨的投加，并提供一个短暂的自由氯消毒期（FClP），通常称为“氯冲击”。然而，这种方法的成功率和实用性常常受到批评，因为会出现硝化作用的恢复；然而，之前在全尺寸配水系统中进行的研究没有包含足够的采样频率来确定硝化作用恢复的速度有多快。在本研究中，在跨越两个年度FClP（2018年和2019年）的时间段内，对分布在水力模型水龄范围内的总共15个消防栓进行了21次采样事件，以研究单个配水系统压力区内的水质、浮游生物群落，并使用一种新的采样技术来确定生物膜群落的影响。消防栓在FClP结束后仅10周就检测到亚硝酸盐升高，并且在FClP结束和氯胺消毒恢复后的两周内，大量水样和冲刷水样中的活细胞计数在统计学上显著增加，这表明FClP的影响有限。此外，FClP在自由氯消毒期间显著提高了铁的浓度，这引发了对用户水质的担忧。使用流式细胞仪进行的微生物指纹分析表明，对于经历了周期性低总氯浓度的采样地点，β多样性没有显著变化。只有在氯胺消毒和自由氯消毒期间都保持高氯残留量的地点，大量水样中的微生物群落才出现显著变化。即使对于这些地点，在研究过程中，冲刷生物膜的微生物群落仍然相似。
