Peracids have gained interest in the water treatment over the last few decades. Peracetic acid (CH 3 CO 3 H) has already become an accepted alternative disinfectant in wastewater disinfection whereas performic acid (CHO 3 H) has been studied much less, although it is also already commercially available. Peracids have also been tested for drinking water disinfection, oxidation of aqueous (micro)pollutants, sludge treatment and ballast water treatment, to name just a few examples. The purpose of this review paper is to represent comprehensive up-to-date information about the water treatment applications, aqueous reaction mechanisms, and disinfection byproduct formation of peracids, namely performic, peracetic and perpropionic acids. and PFA have several of the qualities of an ideal disinfectant: toxicity to microorganisms, but not to higher forms of life; effectivity at ambient temperatures; stability and long shelf-life; low corrosivity; deodorizing ability; widespread availability and reasonable cost [12].PAA and PFA are colorless liquids with characteristic pungent odors. Both are thermodynamically unstable and can decompose spontaneously or explode when highly concentrated, heated, under mechanical stress or exposed to catalytic effects of impurities [1,13,14]. The recommended storage temperatures are below 30 and 20°C for PAA and PFA, respectively [6,14]. Longer carbon chain length increases stability, and thus PAA is more stable than PFA [1]. However, the O-O bond dissociation energy of PFA and PAA has been calculated to be similar: 48 kcal/mol [15]. Percarboxylic acids have typically pK a values 3-4 units higher than the parent carboxylic acids [1]. Nonetheless, PFA and PAA are corrosive [16].
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3Exposure to PAA and PFA causes irritation and possibly permanent damage to the skin (cutaneous emphysema), eyes and the respiratory system. In the skin contact, 0.2% is proposed as the no-observed-effect concentration (NOEC) for short and medium length exposure [17].When inhaled, airborne concentrations less than 0.16-0.17 ppm (0.50-0.52 mg/m 3 ) are considered to cause no irritation [17,18]. However, higher concentrations are harmful and a case study suggested that PAA could cause occupational asthma [19].The largest users of PAA on a global scale (estimated in 2013) are shown in Fig. 1. Similar numbers are not available for PFA, but it is probably used at significantly lower quantities.The largest user, the food industry, applies PAA as a disinfectant in fresh produce washing water, clean-in-place (CIP) processes, on food processing equipment, and in pasteurizers, to name just a few examples [21,22]. PFA is also a suitable disinfectant in low-temperature refrigerated food processing and storage rooms [23]. In healthcare, PAA is used for instance in Recently, methods to determine the residual PAA from wastewater were compared: the spectrophotometric method using DPD and catalase was recommended for 0.1-0.5 mg/L PAA concentrations and the cerimetric/iodometric titration...
