Pinel I S M, Hankinson P M, Moed D H, Wyseure L J, Vrouwenvelder J S, van Loosdrecht M C M
Delft University of Technology, Faculty of Applied Sciences, Department of Biotechnology, Van der Maasweg 9, 2629 HZ Delft, the Netherlands.
Evides Industriewater, Schaardijk 150, 3063 NH Rotterdam, the Netherlands.
Water Res. 2021 Jun 1;197:117047. doi: 10.1016/j.watres.2021.117047. Epub 2021 Mar 15.
Efficient control of pathogenic bacteria, specifically Legionella pneumophila, is one of the main concerns when operating industrial cooling towers. Common practices to limit proliferation involves use of disinfectants, leading to formation of disinfection by-product and increase in water corrosiveness. A disinfectant-free Legionella control method would make the industry more environmentally friendly. A pilot-scale cooling tower (1 m/h) operated with demineralized water was used to investigate the potential of high-pH conditioning as a disinfectant-free alternative for control of L. pneumophila and other pathogens. One control experiment was performed under standard full-scale operation involving sodium hypochlorite dosage. Thereafter 3 alkaline pHs of the cooling water were tested: 9.0, 9.4 and 9.6. The tests lasted between 25 and 35 days. The cooling water from the basins were analysed for total cell count by flow cytometry, L. pneumophila concentration by plate count and occasional qPCR analyses targeting the mip-gene, bacterial and eukaryotic community analyses with 16S and 18S rRNA gene amplicon sequencing, relative abundance of eukaryotic to prokaryotic DNA by qPCR of the 16S and 18S rRNA gene. The L. pneumophila analyses showed considerable growth at pH 9.0 and pH 9.4 but was maintained below detection limit (< 100 CFU/L) at pH 9.6 without disinfection. Interestingly, the results correlated with the overall abundance of protozoa in the water samples but not directly with the relative abundance of specific reported protozoan hosts of Legionella. The pathogenicity based on 16S rRNA gene amplicon sequencing of the cooling water DNA decreased with increasing pH with a strong decline between pH 9.0 and pH 9.4, from 7.1% to 1.6% of relative abundance of pathogenic genera respectively. A strong shift in microbiome was observed between each tested pH and reproducibility of the experiment at pH 9.6 was confirmed with a duplicate test lasting 80 days. High-pH conditioning ≥ 9.6 is therefore considered as an efficient disinfectant-free cooling tower operation for control of pathogenicity, including L. pneumophila.
有效控制病原菌，特别是嗜肺军团菌，是工业冷却塔运行时的主要关注点之一。限制其繁殖的常见做法包括使用消毒剂，这会导致消毒副产物的形成并增加水的腐蚀性。一种无消毒剂的军团菌控制方法将使该行业更加环保。使用一个以软化水运行的中试规模冷却塔（1立方米/小时）来研究高pH调节作为一种无消毒剂替代方法控制嗜肺军团菌和其他病原体的潜力。在涉及次氯酸钠投加量的标准全规模运行条件下进行了一项对照实验。此后，测试了冷却水中的3个碱性pH值：9.0、9.4和9.6。测试持续了25至35天。通过流式细胞术分析冷却塔水池中的冷却水总细胞数，通过平板计数法分析嗜肺军团菌浓度，并偶尔采用靶向mip基因的qPCR分析、利用16S和18S rRNA基因扩增子测序进行细菌和真核生物群落分析、通过16S和18S rRNA基因的qPCR分析真核生物与原核生物DNA的相对丰度。嗜肺军团菌分析表明，在pH 9.0和pH 9.4时其有显著生长，但在pH 9.6且无消毒的情况下，其数量维持在检测限以下（<100 CFU/L）。有趣的是，结果与水样中原生动物的总体丰度相关，但与已报道的嗜肺军团菌特定原生动物宿主的相对丰度并无直接关联。基于冷却水中DNA的16S rRNA基因扩增子测序的致病性随pH升高而降低，在pH 9.0和pH 9.4之间有显著下降，致病性属的相对丰度分别从7.1%降至1.6%。在每个测试的pH值之间观察到微生物群落有显著变化，并且通过一项持续80天的重复测试证实了在pH 9.6时实验的可重复性。因此，pH≥9.6的高pH调节被认为是一种有效的无消毒剂冷却塔运行方式，可用于控制包括嗜肺军团菌在内的致病性。
