Disinfection Efficiency of Peracetic Acid, UV and Ozone After Enhanced
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ARTICLE IN PRESS Water Research 37 (2003) 4573–4586 Disinfection efficiency of peracetic acid, UVand ozone after enhanced primary treatment of municipal wastewater Ronald Gehra,*, Monika Wagnera, Priya Veerasubramaniana, Pierre Paymentb a Department of Civil Engineering, McGill University, Montreal, Canada H3A 2K6 b INRS-Institut Armand-Frappier, UniversiteduQu! ebec,! Laval, Canada H7V 1B7 Received 6 August 2002; received in revised form 3 April 2003; accepted 17 June 2003 Abstract The City of Montreal Wastewater Treatment Plant uses enhanced physicochemical processes (ferric and/or alum coagulation) for suspended solids and phosphorus removal. The objective of this study was to assess the ability of peracetic acid (PAA), UV, or ozone to inactivate the indicator organisms fecal coliforms, Enterococci, MS-2 coliphage, or Clostridium perfringens in the effluent from this plant. PAA doses to reach the target fecal coliform level of 9000 CFU/100 mL exceeded 6 mg/L; similar results were obtained for enterococci, and no inactivation of Clostridium perfringens was observed. However a 1-log reduction of MS-2 occurred at PAA doses of 1.5 mg/L and higher. It was expected that this effluent would have a high ozone demand, and would require relatively high UVfluences, because of relatively high effluent COD, iron and suspended solids concentrations, and low UVtransmittance. This was confirmed herein. For UV,the inactivation curve for fecal coliforms showed the typical two-stage shape, with the target of 1000 CFU/100 mL (to account for photoreactivation) occurring in the asymptote zone at fluences >20 mJ/cm2. In contrast, inactivation curves for MS-2 and Clostridium perfringens were linear. Clostridium perfringens was the most resistant organism. For ozone, inactivation was already observed before any residuals could be measured. The transferred ozone doses to reach target fecal coliform levels (B2-log reduction) were 30–50 mg/L. MS-2 was less resistant, but Clostridium perfringens was more resistant than fecal coliforms. The different behaviour of the four indicator organisms studied, depending on the disinfectant, suggests that a single indicator organism might not be appropriate. The required dose of any of the disinfectants is unlikely to be economically viable, and upstream changes to the plant will be needed. r 2003 Elsevier Ltd. All rights reserved. Keywords: Enhanced primary treatment; Disinfection; Peracetic acid; UV; Ozone 1. Introduction as a polyelectrolyte to precipitate phosphorus and improve solids settling, and sedimentation prior to The City of Montreal Wastewater Treatment Plant discharge into the St. Lawrence River. At present there (CMWTP) uses physicochemical processes to treat up to is no disinfection. Since the use of chlorine for waste- 7.6  106 m3/d of combined domestic and industrial water disinfection has been banned in the Province of wastewater. These processes include screening, grit Quebec, the City of Montreal is exploring alternative removal, addition of ferric chloride and/or alum as well disinfectants in order to produce water which could be suitable for contact aquatic sports, and as a raw potable *Corresponding author. Tel.: +1-514-398-6861; fax: +1- water source to communities downstream. The dis- 514-398-7361. charge permit for this wastewater treatment plant would E-mail address: [email protected] (R. Gehr). allow for an effluent containing 9000 CFU (colony 0043-1354/$ - see front matter r 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0043-1354(03)00394-4 ARTICLE IN PRESS 4574 R. Gehr et al. / Water Research 37 (2003) 4573–4586 forming units) of fecal coliforms (FC) per 100 mL, and disinfection in a synergistic fashion (although Lubello 1000 CFU/100 mL to allow for photoreactivation if et al. [10], dispute this), and in the long term because it ultraviolet radiation (UV) is used [1]. However concerns persists longer than PAA. have been raised regarding the adequacy of indicator The disinfecting mechanism of PAA is still subject to organisms such as FC to predict the performance of some speculation. Lefevre et al. [11] and Liberti et al. [9] various disinfection processes against pathogens. Ac- suggested that the disinfectant property is due to the cordingly, the objectives of this study were (a) to assess release of ‘‘active’’ oxygen, which in turn disrupts the doses required for three disinfection processes— sulfhydryl (–SH) and sulfur (S–S) bonds within enzymes peracetic acid (PAA), UVor ozone—to reach the contained in the cell membrane. Thus transport across target FC standard, and (b) to compare the responses the cell membrane is affected, which impedes cellular of three other indicators—Enterococci (EC), Clostridium activity. perfringens (CP) and MS-2 coliphage—to these A second suggested disinfectant mechanism is the disinfectants. The data will be used to determine the release of hydroxyl radicals [10]. By varying the level of disinfection required at this wastewater treat- proportion of PAA to H2O2, Lubello et al. [10] also ment plant to attain a level of risk (using a model determined that it was the PAA, and not the H2O2, proposed by Haas et al. [2]) that is acceptable to public which was responsible for the biocidal action. health and to the population, and is economically Gehr et al. [8] presented results of batch screening feasible. The risks examined will be those associated tests where PAA was assessed as a disinfectant for with recreational activities during which direct and physicochemical as well as biological effluents. For a indirect contact occurs with river water impacted by this target FC level of 1000 CFU/100 mL, and contact times effluent. of 30–120 min, PAA doses for the physicochemical effluents ranged between 2 mg/L and greater than 6 mg/L, whereas for biological effluents lower doses of 2. Background 0.6–4 mg/L were required. Another recent study [10] assessed the possibility of using PAA in conjunction 2.1. Peracetic acid (PAA) with UVas a type of advanced oxidation process. A UV fluence of 120 mJ/cm2 applied simultaneously with a Of the three disinfectants being studied, PAA is PAA dose of 8 mg/L (30 min contact time) was able to the newest alternative for applications in North Amer- achieve over 4-log reduction of total coliforms, or less ica, though it has been used in Europe for waste- than 2 CFU total coliforms/100 mL, which is Italy’s water disinfection for many years. Interest in the use standard for unrestricted wastewater reuse in agricul- of PAA as a disinfectant for wastewaters began in ture. Such levels of inactivation were not possible with the late 1980s with publications by Baldry and cow- PAA or UVused separately. orkers [3,4]. Grantham [5] presented results from PAA reacts with organic matter in the sewage. If many internal studies of the National River Authority there is little organic matter, the disinfection reaction (NRA) of England and Wales. He pointed out that will be fast, and the additional disinfection after since PAA is an equilibrium mixture, the PAA dose 30 min contact will be insignificant. However, at stated in terms of the initial concentration of the high concentration levels of organic matter, dis- mixture will actually underestimate the dose of infection could also occur after this time, provided PAA delivered. The EPA [6] and Atasi et al. [7] have that the initial PAA dose was high enough to satisfy suggested that PAA could be particularly suited to the PAA demand of the sewage, and to establish a disinfection of combined sewer overflows (CSOs), and residual [8]. Gehr et al. [8] reported that PAA might be more As with all disinfectants, PAA has varying effective- appropriate as a disinfectant for biologically treated ness depending on the organism. Baldry et al. [4] found effluents, rather than those from physicochemical that E. coli and MS-2 coliphages had similar (low) effluents. resistance, but poliovirus, echovirus and coxsackievirus Commercially available PAA (also known as ethane- were considerably more resistant. Studies by Lazarova peroxoic acid or peroxyacetic acid) is available in a et al. [12] showed that different bacteriophages had quaternary equilibrium mixture containing acetic acid, vastly different sensitivities to PAA: using the same hydrogen peroxide, peracetic acid and water, as shown wastewater effluent and 120 min contact time, 10 mg/L in the equation below: PAA was able to reduce f  174 bacteriophage by 7.5 logs, whereas 5 mg/L PAA was needed to reduce MS-2 CH CO H þ H O 2CH CO H þ H O: ð1Þ 3 2 2 2 3 3 2 coliphage by only 3.5 logs. Liberti et al. [9] determined The biocidal form is considered to be the undissociated that although PAA was effective against total coliforms, acid (i.e. CH3CO3H) which is predominant at pHo4:7 it was ineffective towards Giardia and Cryptosporidium [9]. However the H2O2 may also contribute directly to parasites. ARTICLE IN PRESS R. Gehr et al. / Water Research 37 (2003) 4573–4586 4575 2.2. Ultraviolet radiation (UV) used for wastewater disinfection due to operation and maintenance problems of first generation systems, as UVradiation is now the most common alternative to well as the high ozone demand of many effluents [22,23]. chlorination for wastewater disinfection in North Grantham [5] notes that water and wastewater utilities America [13]. UVlamps emit significant radiation in in England and Wales do not use ozone due to the high the range 240–260 nm, exactly that range over which costs involved. We have not been able to find examples nucleic acids (such as DNA and RNA) absorb energy. of current usage of ozone for large scale wastewater When exposed to UVlight, adjacent thymine bases on disinfection in North America, but several smaller plants the nucleic acid strands dimerize. Thus accurate exist in the US, Canada, Japan, Korea and Europe transcription of this DNA strand cannot occur, and [24,25].