Advancing peracetic acid as a wastewater disinfection alternative
New disinfectants come to market because of their potential to reduce health or ecological impacts compared to traditional methods, or they may require lower energy and offer cost savings. Disinfection is a crucial but often costly process in water treatment. Peracetic acid (PAA) is gaining momentum in the U.S. as a cost-effective alternative to chlorine that can simultaneously address concerns around public and environmental health. The U.S. EPA has approved four uses for PAA products in wastewater, however state regulatory agencies face challenges with permitting due to vague regulatory requirements.
To explore the potential of PAA, The Water Research Foundation (WRF) completed the study, “Applications of Peracetic Acid for Municipal Wastewater Processes.” The objective of the study was to advance PAA as a wastewater disinfectant by evaluating its efficacy and effluent toxicity impacts. The research involved demonstration studies at seven utilities, including five in Texas and two in California.
The studies in Texas sought to determine PAA dose and contact times to achieve compliance with discharge permit criteria at different wastewater facilities. The tests in California similarly provided dose and contact times for target organisms different than those in Texas. PAA should eliminate the trihalomethane production issue associated with chlorine in wastewater applications. The study was intended to assist participants in making an informed decision on the feasibility of applying PAA at their facilities, and to give a broader understanding for how PAA can be effective using the same implementation methods at other facilities.
Historically, PAA has been used as a disinfectant in the food, beverage, medical and pharmaceutical industries. PAA has the properties of hydrogen peroxide and greater lipid solubility, making it useful for medical device sterilization, surface disinfection at hospitals, food processing plants and even direct application to food surfaces to reduce incidences of foodborne illnesses like salmonella and E. coli.
While EPA has approved a few uses for PAA, there is no framework to permit wastewater facilities for PAA disinfection use. Commercial use of PAA in wastewater is a new possibility in the U.S. that shows promise as an effective alternative treatment. It is preferable because it can mitigate public health concerns, health and safety issues, and cost issues associated with chlorine disinfection. The primary use of PAA is for disinfection of wastewater following secondary clarification, but it also could be employed after tertiary filtration or for control of algae or other biogrowth. PAA also may be able to provide bacterial inactivation over a wide scale of wastewater characteristics and at a competitive cost.
As part of the study, disinfection data was generated at bench-scale, pilot-scale and at full-scale filtration process for wastewater treatment in Texas and California to gain a better understanding of dose requirements. The target organism for demonstration testing was E. coli or enterococcus in accordance with the limits of each facility.
The bench scale trials provided an initial range of minimum and maximum PAA dose and contact times to meet compliance requirements. The study aimed to understand what doses would meet compliance measures and disinfection criteria, and whether there were observable water quality and aquatic toxicity impacts.
The Texas and Northern California facilities met their targeted permit limits for E. coli and enterococci. For disinfection pilot reactor contact times of 17 or 30 minutes, the Texas and Northern California facilities met their targeted permit limits for E. coli or enterococci at PAA doses at or below 4 mg/L. Three Texas participants had maximum E. coli concentration study targets of 63 MPN (most probable number)/100 mL and two of 126 MPN/100 mL. The results showed the four utilities conducting pilot studies could meet targeted levels using PAA depending on the doses (ranging from 1 to 2.5 mg/L) and contact times (ranging from 17 to 30 minutes) employed.
The one full-scale trial that added PAA ahead of filtration met its target at 2 mg/L of PAA, but only at the highest flow rate employed (20 million gal per day) and a post-filter contact time of 20 minutes. Initial bench-scale PAA dose and contact time evaluations to full-scale installations need to consider full-scale hydraulic performance, such as varying flow conditions, and how it might impact doses and contact times. The participating facilities demonstrated the viability of PAAs as a disinfectant and showed no toxic effects for either target species for all wastewaters tested.
PAA dose and contact time requirements need to be assessed on an individual facility basis due to different capabilities and efficiencies, as well as differences in permitted effluent limits.
As more facilities implement PAA, there will be more data to build an informational and operational database of compliance, giving agencies the information they need to adapt to this technology.
The ability to meet targets demonstrates promise for implementation. An additional benefit is potential cost savings. PAA has the potential to eliminate the need for dechlorination and can be a viable alternative for facilities that may require a more cost-effective measure.