The competitive effect of Electro-chlorination over chlorination for controlling disinfection by-product formation in phenol and aniline enriched groundwater

: 7 Disinfection is an essential step to keep humans healthy from microorganisms present in 8 drinking water. However, the formation of disinfection by-products (DBPs) is associated with 9 adverse health effects, and the presence of organic pollutants in groundwater results in even 10 more detrimental effects. Therefore, a better treatment technique is required to disinfect and 11 remove organic pollutants simultaneously to control the formation of DBPs. Electro- 12 chlorination (EC) was carried out using graphite electrode at the current density of 0.54–1.09 13 mA/cm 2 and sodium chloride for in-situ hypochlorite generation to treat groundwater 14 contaminated with phenol and aniline. The comparative study between chlorination and EC 15 showed a significant level of oxidation of phenol and aniline, resulting in their reduction up to 16 98.48% and 99.47%, respectively, in the EC process. Due to the higher mineralization rate of 17 aniline, both chlorination and EC method are found to be effective. However, only the EC 18 method is found to be appropriate and effective for treating phenol-contaminated water as the 19 chlorination method resulted in the formation of complicated phenolic by-products. Gas- 20 Chromatography/Mass-Spectrometry (GCMS) was used to assess the by-product formation of 21 chlorination and EC in contaminated groundwater through the full-scan.


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The existence of anthropogenic organic contaminants in groundwater has been the subject of 26 profound studies in recent years worldwide. Anthropogenic organic pollutants in surface water, 27 sewage and groundwater, and potable water have been identified as contaminants (Postigo and 28 Barceló 2015; Lapworth et al., 2015). Pesticides and pharmaceuticals with metabolite, steroid, 29 industrial additive, hormone, water treatment by-products, personal care products, fire 30 retardants, and food additives are the most prominent of these pollutants (Stuart et al., 2012). 31 Several of them may have a detrimental effect on human health and the environment, 32 emphasizing that they need to consider their environmental role more effectively. In addition, 33 coke-based factories are deemed responsible for generating large amounts of wastewater 34 containing extremely hazardous, mutagenic as well as carcinogenic contaminants, including including THMs, HAAs, haloacetonitriles (HANs), and emerging iodinated THMs (i-THMs) 55 in the treated water, which was found to be cytotoxic and genotoxic in nature.

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To overcome these problems, a treatment technique is needed that will treat the organic loading 57 as well as disinfect the water at the same time. The human health risk was estimated due to exposure to aniline and phenol-contaminated Ys(t) is the phenol and aniline concentration in the shower room at time t (mins).

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According to USEPA, the threshold limit is considered as 1 for HQ (Mohanta et al., 2020).

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A comparison study was done to identify the suitable and effective method for chlorinating 132 aniline and phenol-contaminated groundwater. The chlorine demand of the raw water sample In this study, EC has been executed to avoid the formation of chlorinated by-products, and its

Results and discussions
178 UIT E V=

3.1.Effect of chlorination and electro-chlorination in aniline and phenol concentration
In the raw groundwater sample, the aniline and phenol concentrations were found to be 0.34 180 and 0.271mg/L, respectively, which is 58.4 and 292 times higher than the desired limit in 2.50E-06, respectively, therefore contributing negligible weightage to the total hazard quotient.

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In the case of chlorination, there was an insignificant reduction in HQ, while a considerable 224 reduction was observed compared to the electro-chlorinated water sample. Many phenolic 225 compounds with complicated structures were present in the raw water. Simple chlorination 226 resulted in the formation of even more complex by-products of phenolic compounds. However, in the EC process, these compounds were dissociated into simpler forms, resulting in a drastic 228 reduction of phenol content. THQ due to aniline contaminated groundwater was found to be 229 3.08, 2.73, and 3.33 for men, women, and children, respectively. High HQ value even for lower 230 aniline concentration was due to its lower Reference dose (RfD) value, i.e., 0.0068 mg/Kg-day, 231 representing a higher probabilistic non-cancer risk to the exposed population. However, a 232 remarkable reduction in HQ was observed in the case of both the chlorination and EC process 233 (

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The organic compounds in the raw and treated groundwater were studied and calculated using 244 the mass spectral library database of the National Institute of Standards and Technology (NIST) 245 (Fig 3). The results showed that organic pollutants found in groundwater were evidently 246 degraded, and only Decanedioic acid was found in abundance in EC treated water, which is 247 neither toxic nor hazardous in nature. Phenol was found in all the samples; however, its relative 248 abundance was found to be negligible in the case of EC treatment. Many new by-products such 249 as 2-Hydroxybiphenyl, 2,3,4,6-tetrachlorophenyl ester, 6-Fluoro-2-trifluoromethylbenzoic 250 acid, 2-Phenylamino-5,6(4H)dihydro-1,3-thiazine, 5-chloro-4,6-diphenyl-, 2-

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Hydroxybiphenyl, 2-Oxo-4-phenyl-6-(4-chlorophenyl)-1,2-dihydropyrimidine, etc were 252 formed in chlorination process (Table 2). In the EC process, phenol present in the water sample 253 was converted into a carboxylic acid, carbon dioxide and water, as shown in fig 2, and was 254 found at the low relative abundance in the form of 1,4-Benzenedicarboxylic acid. Some of 255 these compounds are corrosive, toxic and may cause environmental as well as health hazards.

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Aniline was present in the form of 2-Chloroaniline-5-sulfonic acid in raw water; however, it 257 was not identified in the chromatograms of both the treated groundwater due to its higher 258 mineralization rate into the end product and intermediate products (Singh et al., 2021).  GC-MS analysis chromatograms (a) Raw groundwater (b) Ex-situ chlorinated water (c) In-situ electrochlorinated water