Electrochemical disinfection of Escherichia coli in the presence and absence of primary sludge particulates

Electrochemical (EC) residual disinfection of Escherichia coli (E. coli) in the presence and absence of primary sludge particulates (PSPs) was studied. The kinetics followed a first-order rate law. When PSPs were absent, the EC residual disinfection rate coefficient (k) increased linearly with EC pretreatment energy (E-C, 0-0.63 kWh/m(3)). However, with 143 mg PSPs/L, Is first increased linearly with E-C (0-0.28 kWh/m(3)) and then decreased linearly with E-C (0.28-0.42 kWh/m(3)). H2O2 was detected during EC pretreatment in PSPs-free samples and the H2O2. concentration (C-H) increased with E-C (0-0.83 kWh/m(3)) linearly. Chloride was detected in PSPs aqueous samples (143 mg PSPs/L) and its concentration (C-C) changed during EC pretreatment: initially, a decrease of C-C was observed when E-C increased from 0 to 0.28 kWh/m(3), followed by an increase of C-C when E-C increased 0.28-0.42 kWh/m(3). In both cases, k correlated to the initial post-EC chloride concentration (C-CI) in an inverse linear relationship. This two-stage change of C-C and k was caused by a combination of two reactions: anodic oxidation of chloride and the reaction of chloramines with excess chlorine. This paper explains the mechanisms underlying EC residual disinfection in the presence and absence of PSPs, and proposes a feasible strategy for EC disinfection when PSPs are present, an approach that could be useful in the treatment of combined sewage overflow (CSO). (C) 2013 Elsevier Ltd. All rights reserved.