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Consumption of poor quality water causes serious human health hazards. Therefore, it is very crucial to investigate factors influencing the quality of groundwater and its suitability for drinking purpose. In the present study, groundwater quality of the Dhenkanal district of Odisha, India was characterized and the spatial distribution of different water quality parameters were analyzed using the multivariate statistics, entropy theory, and geostatistics techniques. In the present study 112 number of groundwater tube well samples were collected from the study area. The entropy theory revealed that SO 4 2- , Mg +2 were the most influencing parameters. A similar observation was also observed based on the correlation coefficient analysis. Groundwater quality index (GWQI) and entropy-weighted water quality index (EWQI) classifications indicated that 78.57 and 43.75% of the collected groundwater samples were categorized under excellent water quality, whereas, the rest of the samples were varying from good to medium drinking water quality. In addition, the result of EWQI classification offers more realistic assessment than that of GWQIs owing to its high precision, simplicity and without application of artificial weight. The correlation coefficient between Ca - were the most influencing parameters. A similar observation was also observed based on the correlation coefficient analysis. Groundwater quality index (GWQI) and entropy-weighted water quality index (EWQI) classifications indicated that 78.57 and 43.75% of the collected groundwater samples were categorized under excellent water quality, whereas, the rest of the samples were varying from good to medium drinking water quality. In addition, the result of EWQI classification offers more realistic assessment than that of GWQIs owing to its high precision, simplicity and without application of artificial weight. The correlation coefficient between Ca +2 and HCO 3 - , Mg +2 and PO 4 in the groundwater samples. The GWQI revealed a weak spatial dependence of groundwater quality.- were significantly high which might be due the presence of CaHCO 3 and MgPO 4 in the groundwater samples. The GWQI revealed a weak spatial dependence of groundwater quality., (© 2021. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

In the present study, we report the first operation of a pilot scale ion exchange membrane bioreactor (IEMB). It treated 1–2 m3/d of water contaminated with nitrate. IEMB was made up of anion exchange membrane spiral module integrated with a fixed bed bioreactor (FBBR), a novel configuration for an IEMB system. Nitrate elimination was accomplished through Donnan dialysis using chloride as counter ion followed by heterotrophic denitrification in an anoxic FBBR employing glycerol as electron donor and carbon source. The performance of IEMB revealed an excellent nitrate removal at the selected operating conditions, successfully eliminating a nitrate loading rate of 5.0 kg NO 3 −/m3/d and producing 30 ± 5 mg/L nitrate in the effluent at steady state. Anion exchange membrane being non-selective also transferred a significant concentration of sulphate from the feed-side to the bio-side leading to sulphate accumulation in FBBR. As a result, denitrification performance was affected due to the activation of sulphate reducing bacteria leading to the upset of FBBR. Batch experimental study aiming to screen the effect of nitrate to sulphate ratio on denitrification, demonstrated the possible occurrence of sulphate reduction at [nitrate]/[sulphate] < 0.2, exhibiting a highly negative oxidation reduction potential (ORP) value (−450 mV). This signifies that a minimum [nitrate]/[sulphate] > 0.2 is required as to suppress sulphate reduction phenomenon during denitrification. IEMB calibration for denitrification using glycerol as a carbon source revealed that 100 % stoichiometric donor/acceptor (C/N) ratio was suitable for producing sufficient nitrate biodegradation and acceptable ORP value (~−220 mV). Present work established promising application prospects of IEMB comprising nitrate selective membrane module for the treatment of high nitrate wastewater with a treatment capacity of 1.5 m3/d at optimized operating conditions. • Established IEMB treated high nitrate contaminated water with a capacity of 1.5 m3/d. • Exit nitrate from the IEMB satisfied legal limits of different countries. • ORP reflects the availability of electron donor for efficient denitrification. • Activity of coexisting bacterial communities depends on nitrate to sulphate ratios. • Improper [nitrate]/[sulphate] ratio impairs denitrification and initiate sulphate reduction. [ABSTRACT FROM AUTHOR]