Electrochemical disinfection of saline wastewater effluent

Abstract

A laboratory-scale electrochemical (EC) disinfector was used for the disinfection of various wastewater effluents, including saline primary effluent, saline secondary effluent, and freshwater secondary effluent. Such EC disinfection was highly effective for saline effluent with a salinity content of around 8%‰. A killing efficiency of 99.9% on total coliform bacteria was achieved for saline secondary effluent with a contact time of less than 10 s and a power consumption rate no more than 0.006 kWh/m 3. For primarily treated saline effluent, the same degree of disinfection was obtained with a contact time of less than 20 s and a power consumption of lower than 0.08 kWh/m 3. The efficiency of EC disinfection was regulated by both the contact time (t) and current density (I d) applied, and a kinetic function in terms of survival ratio (N/N o) was developed for the saline secondary effluent, i.e., log(N/N o)=-0.01(I dt) 1.87. While EC disinfection is highly applicable for saline effluent, it did not exhibit a similar degree of effectiveness for freshwater sewage effluent, even with a longer contact time and higher power input. Based on the results of the EC disinfection and comparative direct chlorination experiments, it is argued that the main disinfecting action of the EC process may not be electrochlorination. The EC process could produce other short-lived, more powerful germicidal substances that exert the strong killing function within a short contact time.