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Abstract
The existing traditional drinking water disinfection technology relies mainly on chlorine disinfection alone, which has high disinfection efficiency and can effectively inactivate most of the microorganisms in the water. However, it produces a series of harmful disinfection by-products (DBPs). Therefore, it is very necessary to study an efficient and environmentally friendly disinfection technology for drinking water. For this purpose, a novel continuous-flow ultrasound (US)/chlorination water treatment system was designed and developed. Escherichia coli (E. coli), Bacillus subtilis (B. subtilis), and Staphylococcus aureus (S. aureus) were selected as indicators of water treatment effects to (1) investigate the disinfection effects of different bacteria by US treatment alone at different single or dual frequencies; (2) explore the disinfection effects of US pretreatment with 8 mg/L NaClO on different bacteria to assess the promoting effects of US pretreatment; and (3) identify the optimum system process to satisfy the national standard for drinking water quality. Results showed that the dual-frequency US had better inactivation effects compared with single-frequency US, although it could not achieve an ideal disinfection level (complete disinfection). Further, 17 + 33 kHz dual-frequency US pretreatment had obvious enhancement of the disinfection efficiency, where 3.85 (E. coli), 3.65 (S. aureus), and 3.52 (B. subtilis) log reduction were achieved when 8 mg/L NaClO disinfection lasted 10 min, and finally all three bacteria achieved 4 log reduction after 30 min. Moreover, the treated water satisfied the Chinese national standard for drinking water quality, in which the residual chlorine concentration was below 4 mg/L. The utilization efficiency of disinfectant was improved approximately 40% by 17 + 33 kHz US pretreatment.
Highlights
Water is considered as the indispensable and the most important substance for human survival and development
A maximum of 1.65 (70 kHz), 1.44 (17 kHz), and 1.24 (17 kHz) log reductions were achieved after 60 min US treatment for E. coli, S. aureus, and B. subtilis, respectively
The log reduction began to grow rapidly after 15 min of US treatment, growth remained steady after 20 min (p < 0.05)
Summary
Water is considered as the indispensable and the most important substance for human survival and development. Human health is closely correlated with water quality. If water was contaminated by microorganisms, various deadly diseases could be spread among humans, causing human disaster. The statistics of the World Health Organization (WHO) suggested that at least five thousand people around the world die of diarrhea diseases caused by water pollution each day [1]. The disinfection of drinking water plays a critical role in the prevention and the control of waterborne diseases. The vast majority of water treatment plants still use traditional water treatment technology of coagulation, sedimentation, filtration, and chlorine disinfection. With the increasing pollution of water bodies, the appearance of some chlorine-tolerant microorganisms leads to the need for higher chlorine content or longer disinfection time during water treatment.
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