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While chlorination has long dominated water disinfection, new approaches and technologies have emerged in the wake of disinfection byproduct (DBP) regulations. Could peracetic acid (PAA) be the option that dethrones the king? By Kati Bell and Varsha Wylie C hlorination became the standard for disinfecting treated wastewater in the 20th century and has been key to successfully protecting public health. However, awareness of environmental impacts associated with wastewater chlorination raised concerns regarding how to effectively balance destruction of pathogenic microorganisms against effects of disinfection byproducts (DBPs) that have both environmental and public health consequences. This issue prompted governments in North America 1 to reduce levels of chlorine and its byproducts in disinfected wastewater. 2 These regulatory actions prompted significant research into alternative disinfection, advancing implementation of technologies such as UV and ozone. Today, more than a quarter of all municipal wastewater treatment facilities are utilizing UV disinfection; and while there is interest in ozone disinfection for wastewater, challenges of early technologies stunted development of this market. New Regulatory Challenges 2015 was a year of significant challenges for chlorine disinfection. The U.S. EPA updated its ambient water quality criteria (AWQC) for human health. This update provided relief for concentrations of trihalomethanes (THMs); however, criteria for cyanide were lowered by nearly an order of magnitude — from 140 microns per liter (ug/L) to 4 ug/L for "Consumption of Water and Organisms." 3 Cyanide commonly occurs in municipal wastewaters, and a growing number of wastewater treatment plants (WWTPs) across the U.S. are detecting cyanide in chlorinated effluents at levels exceeding influent concentrations. This is particularly important as regulatory requirements for nutrient removal are being implemented across the country; related changes in effluent characteristics may increase cyanide formation potential, which has been the subject of several studies. 4 Additionally, it is anticipated that the EPA will eventually revisit other disinfection products such as nitrosamines and dioxins because it did not update human health criteria for these chemicals due to outstanding technical issues at the time of criteria update. In Canada, Environment Canada began work on a national strategy to manage wastewater effluents under the direction of the Canadian Council of Ministers of the Environment (CCME) in 2006. In 2007, CCME released a "Draft Canada-wide Strategy for the Management of Municipal Wastewater Effluent." At the same time, Environment Canada published a "Proposed Regulatory Framework for Wastewater" to explain how the Canada-wide Strategy would be implemented. A draft regulation based on the CCME strategy was released for comment in 2010, and on July 28, 2012, the Wastewater Systems Effluent Regulations were published in the Canada Gazette. The regulations, which went into effect in January 2015, are made under the Fisheries Act, which prohibits unauthorized deterioration, disruption, and destruction of fish habitat. The new regulations are the first federal regulations that specifically address municipal WWTP effluents not previously regulated by the provincial authorities and impose strict limits for final effluent quality related to un-ionized ammonia, acute lethality testing, and total residual chlorine (TRC). Thus, many Canadian facilities that have historically used chlorination are faced with these new requirements. Further, recent research has uncovered additional findings related to reactions of chlorine with constituents commonly found in treated wastewater, such as pharmaceuticals and personal care products (PPCPs) and other high-volume production chemicals. Many of these compounds are transformed during chlorine disinfection and can result in compounds that are more toxic than the parent chemical — and these DBPs are not eliminated by dechlorination. For example, chlorination of triclosan, an antimicrobial widely used in soaps, leads to substitution of the aromatic ring and cleavage reactions resulting in chloroform and related THMs, which are regulated DBPs. And, in surface waters downstream of WWTPs, where wastewater is disinfected with chlorine, the chlorinated triclosan derivatives undergo photochemical transformation to form di-, tri-, and tetrachlorinated dioxins that accumulate in downstream sediments. 5 The DBP formation potential from disinfection is only part of the challenge of chlorine. From 1965 through 2007, 788 railcars were involved in accidents with 11 instances of catastrophic loss (i.e., a loss of all, or nearly all) of the chlorine lading. 6 While these losses resulted in only four fatalities, it is clear that additional federal regulations and programs under the U.S. Department of Homeland Security and the U.S. Department of Transportation will be implemented to address the security of chemical production, transportation, and use of chlorine. Chlorine-associated DBPs and additional potential hazards from handling chlorine gas have prompted utilities to switch to UV disinfection. While UV disinfection eliminates formation of toxic DBPs, it also eliminates the beneficial chemical oxidation step that transforms endocrine-disrupting compounds (EDCs). 7 The EDCs most often implicated in the feminization of fish — 17β-estradiol, 17-ethinylestradiol, estrone, and nonylphenol 8 — are transformed during chlorine disinfection. 9 This unexpected consequence raises new challenges. Thus, some researchers call for more effective methods of removing DBP precursors and applying disinfectants other than chlorine. However, to avoid DBP formation, while still disinfecting and removing EDCs, a disinfectant with oxidizing capacity will be required. Ozone can meet these needs from a process standpoint, but 16 wateronline.com n Water Innovations The Age Of Peracetic Acid — A Solution To Increasingly Challenging Regulations