Investigating Disinfection Efficiency and Regrowth Control of Microorganisms in Urban Sewage Effluent Using Ultraviolet Radiation, Ozone, Gamma-Ray, and Dielectric Barrier Discharge Plasma

The current study aimed to compare ultraviolet (UV), ozone, gamma radiation, and dielectric barrier discharge (DBD) plasma at a pilot scale in terms of disinfection efficiency and regrowth control of microorganisms in urban sewage effluent. For UV and ozone disinfection systems, secondary effluent was injected continuously into 1 L reactors, and various flow rates were applied to evaluate their disinfection efficiency (10, 20, and 30 mL s(-1) for the former and 10, 15, and 20 mL s(-1) for the latter). Gamma dosages ranging from 0.5 to 6 kGy and DBD exposure times between 5 and 25 min were selected. Disinfection efficiency was assessed based on the total coliform (TC) population, and to investigate microbial regrowth, the samples were incubated for 3 days at 22 degrees C and 100 rpm in the dark. Both ozone (10 mL s(-1)) and DBD (> 20 min) decreased TC population by only 1 log immediately after treatment, which was followed by microbial regrowth up to around pretreated levels after 3 days of storage. On the contrary, although UV (all flow rates) and gamma radiation (all dosages) completely eliminated the culturable TC after application, regrowth occurred in the UV method (all flow rates), and gamma radiation was applied in dosages lower than 4 kGy. Therefore, regrowth seems to be a crucial factor in wastewater disinfection. Overall, gamma radiation has proved to be the most effective in destroying organic compounds, inactivating pathogenic microorganisms, and controlling regrowth, thus meeting authorized limits for unrestricted irrigation, while consuming acceptable amounts of energy.

Automated summary

This study aimed to compare different methods of disinfection and regrowth control in urban sewage effluent. The results showed that UV and gamma radiation were effective in disinfection, but regrowth needs to be taken into consideration.