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 (EC, 0-0.63 kWh/m(3)). However, with 143 mg PSPs/L, k first increased linearly with EC (0-0.28 kWh/m(3)) and then decreased linearly with EC (0.28-0.42 kWh/m(3)). H2O2 was detected during EC pretreatment in PSPs-free samples and the H2O2 concentration (CH) increased with EC (0-0.83 kWh/m(3)) linearly. Chloride was detected in PSPs aqueous samples (143 mg PSPs/L) and its concentration (CC) changed during EC pretreatment: initially, a decrease of CC was observed when EC increased from 0 to 0.28 kWh/m(3), followed by an increase of CC when EC increased 0.28-0.42 kWh/m(3). In both cases, k correlated to the initial post-EC chloride concentration (CCI) in an inverse linear relationship. This two-stage change of CC 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).