Cloro residual

Chemosphere 85 (2011) 1146–1153

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Chemosphere
journal homepage: www.elsevier.com/locate/chemosphere

Chlorine residuals and haloacetic acid reduction in rapid sand filtration
Yi-Hsueh Chuang a, Gen-Shuch Wang b, Hsin-hsin Tung a,⇑
a b

Graduate Institute of Environmental Engineering, National Taiwan University, 71, Chou-Shan Rd., Taipei10673, Taiwan Institute of Environmental Health, National Taiwan University, R753, 7F., No. 17, Xuzhou Rd., Taipei 100, Taiwan

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a b s t r a c t
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 yearround 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 practisepre-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 bioactivitydevelopment. 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 (Clthreshold) for biodegradation was estimated at 0.46–0.5 mg LÀ1. The results imply that conventional filters with adequate control could be conducive to bioactivity, resulting in lower HAAconcentrations. Optimizing biodegradable disinfection by-product removal in conventional rapid sand filter could be achieved with minor variation and a lower-than-Clthreshold 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 HAAloss. Ó 2011 Elsevier Ltd. All rights reserved.

Article history: Received 10 May 2011 Received in revised form 15 August 2011 Accepted 18 August 2011 Available online 4 October 2011 Keywords: Rapid sand filtration Biodegradation Chlorine residual Haloacetic acid Backwash

1. Introduction It is common to use pre-oxidation for algae and microbial control in areas with higher average temperature(subtropical or tropical weather) for surface water treatment. In places where water resources are limited to river and reservoirs, the major problems are usually the high organic contents and algae. In such cases, pre-chlorination practise is an essential step to prevent algal growth in the treatment train. Most water treatment plants (WTPs) in Taiwan practise conventional treatment processeswhich include pre-chlorination, coagulation, sedimentation, rapid sand filtration and post-chlorination. Chlorine gas and sodium hypochlorite are the most common disinfectants used for both pre- and post-chlorination. Therefore, chlorinated disinfection by-products (C-DBPs) such as trihalomethanes (THMs), haloacetic acids (HAAs), haloketones and haloacetaldehydes are commonly found in pre-chlorinatedwater.

⇑ Corresponding author. Tel.: +886 2 3366 4404; fax: +886 2 2392 8830.
E-mail address: htung@ntu.edu.tw (H.-h. Tung). 0045-6535/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.chemosphere.2011.08.037

A significant amount of C-DBPs is formed during pre-chlorination process and cannot be removed effectively by conventional treatment processes. These DBPs...