Waegenaar Fien, Pluym Thomas, Vermeulen Elise, De Gusseme Bart, Boon Nico
Center for Microbial Ecology and Technology (CMET), Department of Biotechnology, Ghent University, Ghent, Belgium.
Center for Advanced Process Technology for Urban Resource Recovery (CAPTURE), Ghent, Belgium.
Appl Environ Microbiol. 2025 Jun 18;91(6):e0068625. doi: 10.1128/aem.00686-25. Epub 2025 May 13.
Ensuring high-quality drinking water remains challenging, as complaints about odors, discoloration, or contamination persist. In Belgium and beyond, traditional flushing is a common curative strategy that involves discharging large water volumes through hydrants while the network remains in use. In some cases, free chlorine (0.5 mg/L) is added, and consumers are advised not to drink the water. However, flushing can alter water biostability, potentially increasing susceptibility to microbial invasion. This study used a pilot-scale drinking water distribution system with three identical 100 m polyvinyl chloride(PVC) loops (DN 80 mm) to assess the impact of flushing with and without chlorination as practiced in chlorinated networks. Loop 1 was flushed with tap water and sodium hypochlorite (NaOCl), followed by two non-chlorinated flushes, loop 2 was unflushed, and loop 3 underwent three flushes. Biostability was assessed using online flow cytometry, and susceptibility to bacterial invasion (, , and ) was evaluated in the days following flushing. The water had a 7-day residence time. Results showed that chlorinated flushing promoted microbial regrowth (3.8 × 10 vs 2.0 × 10 and 1.6 × 10 cells/mL for loops 1, 2, and 3, respectively), primarily of resident spp. Biofilm cell densities (~4 × 10 cells/cm) remained stable across conditions. Bacterial indicators declined over time, with and surviving longer (>100 hours) than (13 hours). Decay rates were highest in chlorinated loops, likely due to increased microbial competition. For example, the decay constant of at 20°C was -0.082 h, -0.042 h, and -0.027 h for loops 1, 2, and 3, respectively.
Traditional flushing is used as a curative strategy to solve unwanted quality issues during distribution, yet its impact on microbial biostability remains poorly understood. This study provides critical insights into how traditional flushing, both with and without chlorination, influences microbial regrowth and susceptibility to invasion. Findings reveal that chlorinated flushing promotes the regrowth of resident drinking water bacteria while accelerating the decay of introduced unwanted bacterial indicators, emphasizing the complex trade-off between microbial control and system stability. Understanding these dynamics is essential for optimizing flushing procedures, minimizing unintended consequences, and improving distribution system resilience.
确保高质量饮用水仍然具有挑战性，因为关于气味、变色或污染的投诉持续存在。在比利时及其他地区，传统冲洗是一种常见的补救策略，即在供水管网仍在使用时通过消防栓排放大量的水。在某些情况下，会添加游离氯（0.5毫克/升），并建议消费者不要饮用该水。然而，冲洗会改变水的生物稳定性，可能增加对微生物入侵的易感性。本研究使用了一个中试规模的饮用水分配系统，该系统有三个相同的100米聚氯乙烯（PVC）回路（公称直径80毫米），以评估在加氯管网中进行加氯和不加氯冲洗的影响。回路1先用自来水和次氯酸钠（NaOCl）冲洗，然后进行两次非加氯冲洗，回路2未冲洗，回路3进行三次冲洗。使用在线流式细胞术评估生物稳定性，并在冲洗后的几天内评估对细菌入侵（大肠杆菌、粪肠球菌和铜绿假单胞菌）的易感性。水的停留时间为7天。结果表明，加氯冲洗促进了微生物的再生长（回路1、2和3中分别为3.8×10⁵、2.0×10⁵和1.6×10⁵个细胞/毫升），主要是常驻的嗜麦芽窄食单胞菌。生物膜细胞密度（约4×10⁴个细胞/平方厘米）在各种条件下保持稳定。细菌指标随时间下降，大肠杆菌和粪肠球菌的存活时间长于铜绿假单胞菌（分别为>100小时和13小时）。加氯回路中的衰减率最高，可能是由于微生物竞争加剧。例如，在20°C时，回路1、2和3中铜绿假单胞菌的衰减常数分别为-0.082小时⁻¹、-0.042小时⁻¹和-0.027小时⁻¹。
传统冲洗被用作一种补救策略来解决配水过程中出现的不良水质问题，但其对微生物生物稳定性的影响仍知之甚少。本研究提供了关于传统冲洗（加氯和不加氯）如何影响微生物再生长和入侵易感性的关键见解。研究结果表明，加氯冲洗促进了常驻饮用水细菌的再生长，同时加速了引入的有害细菌指标的衰减，强调了微生物控制与系统稳定性之间复杂的权衡。了解这些动态对于优化冲洗程序、最小化意外后果以及提高分配系统的恢复力至关重要。
