Graduate Institute of Environmental Engineering, National Taiwan University, 71 Chou-Shan Rd., Taipei, Taiwan.
Chemosphere. 2011 Nov;85(7):1146-53. doi: 10.1016/j.chemosphere.2011.08.037. Epub 2011 Oct 4.
It is quite rare to find biodegradation in rapid sand filtration for drinking water treatment. This might be due to frequent backwashes and low substrate levels. High chlorine concentrations may inhibit biofilm development, especially for plants with pre-chlorination. However, in tropical or subtropical regions, bioactivity on the sand surface may be quite significant due to high biofilm development--a result of year-round high temperature. The objective of this study is to explore the correlation between biodegradation and chlorine concentration in rapid sand filters, especially for the water treatment plants that practise pre-chlorination. In this study, haloacetic acid (HAA) biodegradation was found in conventional rapid sand filters practising pre-chlorination. Laboratory column studies and field investigations were conducted to explore the association between the biodegradation of HAAs and chlorine concentrations. The results showed that chlorine residual was an important factor that alters bioactivity development. A model based on filter influent and effluent chlorine was developed for determining threshold chlorine for biodegradation. From the model, a temperature independent chlorine concentration threshold (Cl(threshold)) for biodegradation was estimated at 0.46-0.5mgL(-1). The results imply that conventional filters with adequate control could be conducive to bioactivity, resulting in lower HAA concentrations. Optimizing biodegradable disinfection by-product removal in conventional rapid sand filter could be achieved with minor variation and a lower-than-Cl(threshold) influent chlorine concentration. Bacteria isolation was also carried out, successfully identifying several HAA degraders. These degraders are very commonly seen in drinking water systems and can be speculated as the main contributor of HAA loss.
在饮用水处理的快滤池中，生物降解的情况相当少见。这可能是由于频繁的反冲洗和低基质水平所致。高浓度的氯可能会抑制生物膜的发展，特别是对于那些进行预氯化的工厂。然而，在热带或亚热带地区，由于全年高温导致生物膜的大量繁殖，砂表面可能会具有相当高的生物活性。本研究的目的是探索快滤池（尤其是那些进行预氯化的水厂）中生物降解与氯浓度之间的相关性。在本研究中，发现了传统的预氯化快滤池中有卤乙酸（HAA）的生物降解。进行了实验室柱研究和现场调查，以探索 HAAs 生物降解与氯浓度之间的关系。结果表明，余氯是改变生物活性发展的重要因素。建立了一个基于滤池进水和出水氯的模型，用于确定生物降解的阈值氯。根据该模型，估计出生物降解的温度独立氯浓度阈值（Cl(threshold)）为 0.46-0.5mgL(-1)。结果表明，具有适当控制的传统滤池有利于生物活性，从而降低 HAA 浓度。通过少量变化和低于 Cl(threshold)的进水氯浓度，可以实现常规快速砂滤池对可生物降解的消毒副产物的去除优化。还进行了细菌分离，成功鉴定出几种 HAA 降解菌。这些降解菌在饮用水系统中非常常见，可以推测它们是 HAA 损失的主要贡献者。
