A comparative evaluation of performic acid, peracetic acid, and sodium hypochlorite for bacterial disinfection of secondary effluent

Abstract

Chlorine-based disinfectants are often used to achieve the required microbiological effluent limits and to ensure appropriate public health protection against waterborne pathogens; however, they can produce potentially harmful disinfection by-products and negatively affect the ecosystem of effluent receiving bodies. Peracetic Acid (PAA) and Performic Acid (PFA) are emerging as promising disinfectants in water treatment due to their effectiveness against a wide spectrum of microbes and minimal environmental impact, addressing some of the limitations associated with traditional chlorine-based disinfectants. In present work, we present and analyze the secondary effluent wastewater bench test results for demand, decay, and microbial inactivation kinetics of PAA, PFA, and sodium hypochlorite (SH) from six North American water resource recovery facilities (WRRFs) using an advanced fitting method based on uncertainty ellipses. To evaluate the effectiveness and suitability of alternative disinfectants, the inactivation performance of the PAA and PFA against E. coli, fecal coliform and enterococci were investigated and compared to the inactivation performance of SH. When comparing the integral-CT or ICT (i.e., integral of disinfectant concentration over time) based exposure performance of PFA against SH and PAA, it exhibits the superior inactivation performance in the limited ICT values for all the fecal indicator bacteria. For instance, to achieve a 2-log₁₀ reduction of E. coli inactivation, ICT required for PFA ranges from approximately 1 to 3.6 mg min/L, for PAA from 8.2 to 21 mg min/L and for SH from 0.6 to 22 mg min/L across six WRRFs. Additionally, the residual concentration of the disinfectant dosage was examined to understand the uncertainties in demand/decay model development. Developing a confidence region provides guidance for conducting future experiments to improve the accuracy and reliability of subsequent tests. Later, the results of demand/decay and inactivation kinetics are utilized in process modeling, considering four dosing control schemes. Our findings indicate that the advanced dosing scheme, which accounts for wastewater variability and the hydraulic characteristics of the contact chamber, reduces disinfectant usage by up to 36% compared to the conventional flow pacing strategy while ensuring compliance with regulatory standards. Additionally, the advanced control scheme demonstrated steady and reliable performance in achieving target microbial limits throughout its operation.