Individual and combined use of ultraviolet (UV) light with hydrogen peroxide, peracetic acid, and ferrate(VI) for wastewater disinfection

Abstract

This work explores the use of chlorine-free chemicals hydrogen peroxide (HP), peracetic acid (PAA), and ferrate(VI) as well as physical disinfection method, ultraviolet light (UV), alone and combination for wastewater disinfection. To evaluate treatments the culturability of indicator-organism Escherichia coli was compared to that of spore-forming Bacillus subtilis and C. perfringens. Remaining culturable and viable E. coli were studied using a method combining propidium monoazide (PMA) and quantitative polymerase chain reaction (qPCR). Changes to culturability were monitored for up to 48 hours after treatment to evaluate regrowth, reactivation and resuscitation levels. In Chapter 4 culturable and viable E. coli were studied following disinfection with sodium hypochlorite (NaClO), HP, PAA, ferrate(VI), and ultraviolet light (UV). All methods reduced culturable E. coli to below 2 log CFU/mL but 3-6 log CCE/mL of E. coli remained viable following chemical treatments. The largest reduction of viable cells was achieved with Ferrate(VI) followed by PAA, NaClO, and HP. In Chapters 5 and 6 the use of UV and ferrate(VI) both alone and in combination was studied. The combination of 40 mJ/cm2 UV and 9 mg/L ferrate(VI) provided an additional 80% reduction in coliform bacteria compared to the use of UV alone. The use of ferrate(VI) increased turbidity by up to 95.6%. UV fluence of 40 mJ/cm2 reduced C. perfringens 95.5% but neither ferrate(VI) nor combining UV and ferrate(VI) offered further reductions. A concentration of 9mg/L of ferrate(VI) reduced viable E. coli by 0.9 log CCE/mL and by 2 logs CCE/mL when combined with 40 mJ/cm2. No regrowth following ferrate(VI) was observed, however regrowth and reactivation were observed after 40 mJ/cm2 UV as well as following combined treatment. In Chapter 7 the use of UV and PAA were studied. Combining 40 mJ/cm2 UV and 2.3 mg/L PAA allowed for an additional 1.7 log reduction in culturable E. coli but no additional reduction in B. subtilis was observed when compared to the use of UV alone. The combined treatment offered an additional 0.8 log reduction in viable E. coli. Regrowth was observed after a lag period between 6 and 24 hours without additional nutrient supplementation.