Study On Reclaimed Water Disinfection By Electrochemical Method

In recent years, due to the global shortage of recycled water, reuse of wastewater is gaining increasing attention, and the disinfection of reclaimed water is important for the safe use of reclaimed water. As an "environmentally friendly technology", electrochemical technology is gaining increasing attention because of its high efficiency, low cost and simple configuration in water disinfection process. In this theisis, the characteristics and optimization of electrochemical disinfection method for reclaimed water are studied. By studying E. coli in water disinfection, we optimized device parameters, and grasp the impact of operating conditions. On this basis, we study the disinfection of E. coli, Staphylococcus aureus, Bacillus subtilis by electrochemical, then we investigated the disinfection of total heterotrophic bacteria and antibiotic-resistant bacteria in reclaimed water, and detecting the reactivation of microorganism. By this studying, we get the following conclusions.The titanium anode coated with ruthenium/iridium had a significant higher inactivation ratio than those coated with plumbum or iridium/tantalum under the same disinfection conditions. The device with a plate distance of 50 mm exhibited the highest inactivation ratio among the four devices. Further study indicated that the inactivation ratio by electrochemical disinfection was negatively correlated with pH, while positively correlated with water temperature and NaCl concentration.The inactivation ratio of Escherichia coli without antibiotic resistance, resistant Escherichia coli, Staphylococcus aureus and Bacillus subtilis by electrochemical disinfection is descending under the same conditions. The log inactivation ratio for Bacillus subtilis can reach 3-log with 0.05% NaCl, 20 V voltage and 30 s residence time. After disinfection, the resistance level of survived tetracycline-resistant E. coli to tetracycline, penicillin and chloramphenicol dropped firstly and then increased as the disinfection time extended.The disinfection tests on the secondary effluent from wastewater treatment plant showed that, when the voltage was 25 V, residence time was 100 s, logarithmic inactivation rate of total heterotrophic bacteria in water could reach 4-log, generating residual chlorine 2.5mg·L-1, the elimination of chlorine after disinfection will significantly reduce bacterial inactivation rate. The ability to inactivate penicillin-resistant bacteria was significantly better than the total heterotrophic bacteria by electrochemical, ampicillin-resistant and rifampicin-resistant inactivation and total heterotrophic bacteria were similar, but chloramphenicol-resistant and tetracycline-resistant was significantly lower than the total heterotrophic bacteria. After disinfection, the percentage of antibiotic resistance from total heterotrophic bacteria generally did not exceed 15%.When the residence time was 50 s and 100 s, after the electrochemical disinfection, the concentration of total heterotrophic bacteria will reach the concentration before the disinfection through reactivation and re-growth after 3d. The proportion of antibiotic-resistant bacteria from total heterotrophic bacteria was no significant difference compared to the proportion before disinfection.