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Trichloramine removal with activated carbon is governed by two reductive reactions: a theoretical approach with diffusion-reaction models Taku Matsushita, Yoshihiko Matsui, Shohei Ikekame, Miki Sakuma, and Nobutaka Shirasaki Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.6b05461 • Publication Date (Web): 29 Mar 2017 Downloaded from http://pubs.acs.org on March 29, 2017
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Environmental Science & Technology
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Trichloramine removal with activated carbon is governed by two reductive
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reactions: a theoretical approach with diffusion-reaction models
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Taku Matsushita*†, Yoshihiko Matsui†, Shohei Ikekame†, Miki Sakuma††, and Nobutaka Shirasaki†
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*Corresponding author: Graduate School of Engineering, Hokkaido University, N13W8, Sapporo 060-8628, Japan;
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phone/fax +81–11–706–7279;
[email protected] 7
†Graduate School of Engineering, Hokkaido University, N13W8, Sapporo 060-8628, Japan
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††National Institute of Technology, Kisarazu College, 2-11-1 Kiyomidai Higashi, Kisarazu 292-0041, Japan
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ABSTRACT
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Mechanisms underlying trichloramine removal with activated carbon treatment were proven by
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batch experiments and theoretical analysis with diffusion-reaction models. The observed values of
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trichloramine and free chlorine were explained only by the model in which (1) both trichloramine
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and free chlorine were involved as reactants, (2) the removals of reactants were affected both by the
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intraparticle diffusion and by the reaction with activated carbon, and (3) trichloramine
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decomposition was governed by two distinct reductive reactions. One reductive reaction was
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expressed as a first-order reaction: the reductive reaction of trichloramine with the basal plane of
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PAC, which consists of graphene sheets. The other reaction was expressed as a second-order
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reaction: the reductive reaction of trichloramine with active functional groups located on the edge
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of the basal plane. Free chlorine competitively reacted with both the basal plane and the active 1
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functional groups. The fact that the model prediction succeeded even in experiments with different
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activated carbon doses, with different initial trichloramine concentrations, and with different sizes
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of activated carbon particles, clearly proved that the mechanisms described in the model were
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reasonable for explaining trichloramine removal with activated carbon treatment.
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INTRODUCTION
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Chlorinous odor is one of the major causes of consumer complaints about drinking water treatment
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plants that rely on chlorine-based methods such as chlorination and chloramination for disinfection.
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Trichloramine, unintentionally produced by reactions of free chlorine with primarily ammonium
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nitrogen and secondarily organic nitrogen compounds such as urea 1, is widely considered to be a
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major source of the chlorinous odor, even though part of the chlorinous odor is reportedly derived
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from aldehydes and organic nitrogen compounds that result from reactions of free chlorine with
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organic compounds
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mollifying the dissatisfaction of consumers with the chlorinous taste and odor of treated drinking
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water. Actually, trichloramine formation is controlled and suppressed by removing its major
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precursor, ammonium nitrogen, before contact with a chlorine-based disinfectant by first treating
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the water via slow sand filtration
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treatment, however, depends strongly on water temperature; the activity decreases with decreasing
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water temperature and becomes too small at the low water temperatures characteristic of winter to
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denitrify ammonium nitrogen efficiently. To overcome the trichloramine formation problem at low
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. Accordingly, controlling trichloramine formation could be a key to
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or activated carbon 6. Biological activity associated with such
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Environmental Science & Technology
water temperatures, treatment technologies that do not rely on biological activity are needed. Phattarapattamawong et al.
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applied an advanced oxidation process (O3/H2O2) to river water
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and reported that the process can reduce the odor strength after chlorination by ≥50% but fails to
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decrease trichloramine formation after chlorination. Soltermann et al.
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low-pressure mercury lamps to decompose chloramines and reported that trichloramine decomposes
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more rapidly than monochloramine and dichloramine. However, the fact that a large ultraviolet
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fluence (approximately 500 mJ cm–2) was required to decompose trichloramine down to 10% of its
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initial concentration may be an energetic and economic drawback of the system. Our research group
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recently applied superfine powdered activated carbon (SPAC) to remove trichloramine 9. The SPAC
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was produced from commercially available powdered activated carbon (PAC) by pulverizing the
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PAC into very fine particles (median diameter [D50]
