UC Riverside

Disinfection is the final step in wastewater treatment processes that plays a vital role in protecting water resources from pathogenic microorganisms. Currently chlorine is the most widely used disinfectant. However, the generation of the disinfection byproducts (DBPs) is a big concern. Ultraviolet (UV) disinfection systems have also been adopted for wastewater treatment due to advantages over chlorination including reducing DBP formation, no odor, and shorter contact time. Alternatively, ozone is used as a more effective disinfectant than chlorine in destroying bacteria and viruses, but there is also concern on DBP formation such as bromate. In recent years, there is a growing interest in the application of other strong but short-lived chemical oxidants as disinfectants such as hydroxyl radical (HO*). These highly oxidative radical species have been employed for water reuse applications to destruct chemically recalcitrant micro-pollutants.

This research was conducted to develop an alternative disinfection technology that has less DBP formation concerns and is economically feasible. Specifically, the disinfection efficacy of sulfate radical (SO4*-) was investigated. SO4*- is a very strong oxidant and generated from persulfate (S2O82-) by using ferrous iron (Fe2+) as an activator. This study is focused on the efficacy of SO4*- in promoting E.coli die-off rate as a function of exposure time. Hydroxylamine, a common reducing agent was introduced in the persulfate/iron system to prevent the rapid oxidation of Fe2+ to Fe3+ and accelerate the generation of SO4*-. It is found that SO4*- gave a high bacteria log removal in three hours. The disinfection kinetics of SO4*- has a very short induction time, which is an advantage over other radical species such as HO*. The introduction of hydroxylamine enhanced the efficacy of persulfate disinfection by one natural log removal. In addition, higher dosage of persulfate and ferrous ion led to an enhanced SO4*- generation and an increasing bacteria viability loss.

This system can be implemented as alternative disinfection mechanism for both wastewater and drinking water applications in the future. The final byproduct of this system, which is mostly sulfate, is not toxic to the environment and human beings. The main drawback of this technology was formation of sludge from the oxidized Fe2+. However, the application of hydroxylamine will ease the problem for large scale wastewater treatment applications.