Dr. Sandeep Singh Shekhawat - Academia.edu (original) (raw)

Papers by Dr. Sandeep Singh Shekhawat

Water Science and Technology, Jul 11, 2022

Though chlorine is a cost-effective disinfectant for water and wastewaters, the bacteria survivin... more Though chlorine is a cost-effective disinfectant for water and wastewaters, the bacteria surviving after chlorination pose serious public health and environmental problems. This review critically assesses the mechanism of chlorine disinfection as described by various researchers; factors affecting chlorination efficacy; and the re-growth potential of microbial contaminations in treated wastewater post chlorination to arrive at meaningful doses for ensuring health safety. Literature analysis shows procedural inconsistencies in the assessment of chlorine tolerant bacteria, making it extremely difficult to compare the tolerance characteristics of different reported tolerant bacteria. A comparison of logarithmic reduction after chlorination and the concentration-time values for prominent pathogens led to the generation of a standard protocol for the assessment of chlorine tolerance. The factors that need to be critically monitored include applied chlorine doses, contact time, determination of chlorine demands of the medium, and the consideration of bacterial counts immediately after chlorination and in post chlorinated samples (regrowth). The protocol devised here appropriately assesses the chlorine-tolerant bacteria and urges the scientific community to report the regrowth characteristics as well. This would increase the confidence in data interpretation that can provide a better understanding of chlorine tolerance in bacteria and aid in formulating strategies for effective chlorination.

Journal of environmental chemical engineering, Jun 1, 2021

Abstract Chlorine tolerance is a major concern during disinfection of treated wastewater. Here, t... more Abstract Chlorine tolerance is a major concern during disinfection of treated wastewater. Here, the UV disinfection efficacy was assessed for controlling two previously reported chlorine tolerant bacteria, Stenotrophomonas maltophilia and Klebsiella sp. along with a standard E.coli strain using a collimated beam apparatus. UV exposure was applied in two sets - short exposure (0–60 s) and long exposure (0–60 min). Bacterial counts immediately after, and 24 h post irradiation (regrowth) were analysed using media plating. Morphological characteristics and intracellular Mn/Fe ratio were examined by SEM and ICP-OES respectively, to understand the possible reasons for sensitivity/ resistance to irradiation. E.coli and Klebsiella sp. were effectively reduced (> 4 log) but S. maltophilia showed low Effective Reduction (ER

Elsevier eBooks, 2020

Abstract Indiscriminate use of antibiotics in humans and animals and release of inadequately trea... more Abstract Indiscriminate use of antibiotics in humans and animals and release of inadequately treated hospital, animal farming, and aquaculture wastewater into the domestic sewage have led to an increased concentration of antibiotics in the wastewater. In the presence of positive selection pressure due to subinhibitory concentration favoring antibiotic-resistant strains, wastewater treatment plants serve as a hotspot for rapid dissemination of antibiotic resistance genes in susceptible strains. The technologies used water treatment plants, especially the tertiary treatment, which may play a pivotal role in checking the release of antibiotics and antibiotic-resistant genes into the environment. Conventional treatments involving chlorination as well as advanced oxidation processes like ozonation, Fenton process, photo-Fenton process, and their combination with UV/H2O2 are being studied for degradation of various antibiotics during water treatment. Similarly, a large number of culture-based and metagenomics analyses have been carried out on the removal of antibiotic resistance genes in various pilot scale and field scale wastewater treatment systems. This chapter discusses the role of different tertiary treatments in handling antibiotics and antibiotic resistance genes in wastewater. The different types of tertiary treatment technologies are compared in terms of their efficiencies in dealing with these emerging pollutants so as to devise a treatment strategy that poses minimum threat to the ecosystem.

Bioresource Technology, Nov 1, 2021

This paper explores the effect of hybrid chlorine and UV disinfection treatment against their ind... more This paper explores the effect of hybrid chlorine and UV disinfection treatment against their individual usage on microbial community, functional genes, antibiotic resistant genes (ARGs) and disinfection by-products (DBPs) formation. The disinfectant doses of 2.5 mg L-1 chlorine and 41 mJ cm-2 UV were selected based on the coliform counts to be attained in treated sewage. The highest bacterial diversity was observed in control (secondary treated) sample followed by UV, chlorine and hybrid disinfection. The highest elimination of bacterial species (296) was achieved in hybrid treatment, which was far better than the standalone treatments. The disinfection with all the disinfectants used resulted in increased abundance of ARGs. Motility genes were found to be enriched in hybrid disinfected samples. DBP concentrations were within the stipulated norms for all the disinfectant treatments used. Hybrid disinfection was observed to be more effective in alleviating the risks associated with the reuse of treated sewage.

Water Quality Research Journal of Canada, Jul 30, 2021

Antibiotic resistance surveillance is an objective of global action plan on antimicrobial resista... more Antibiotic resistance surveillance is an objective of global action plan on antimicrobial resistance endorsed by the World Health Organization. The current study reports the identification of frequently occurring Gram-negative bacterial community (GNBC) previously isolated from municipal treated wastewater and their antibiotic resistance profiles. Further, the genes responsible for extended-spectrum beta lactamases (ESBL) activity were identified in ESBL-positive organisms. The isolates were characterized using biochemical assays and identification was confirmed by VITEK ® 2 automated system. Antibiotic susceptibility testing against seven different classes of antibiotics was also performed on the same system using AST-N280 cards. The most dominant isolates identified were Acinetobacter baumannii, Morganella morganii, Kluyvera intermedia, Stenotrophomonas maltophilia, Escherichia coli, Aeromonas hydrophila/caviae, Klebsiella pneumoniae, Enterobacter cloacae and Citrobacter freundii. The isolates were observed to be significantly resistant against the antibiotics amoxicillin-clavulanic acid, cefuroxime, cefuroxime axetil and colistin. Two of the isolates, E. cloacae sp. dissolvens and S. maltophilia, were found to be positive for ESBL activity encoded by blaCTX-M gene. The possible intrusion of hospital wastewater in domestic sewage is also discussed. This study may help assess the risk of wastewater reuse by detecting dominant bacteria as a step towards the development of new microbiological standards.

Journal of Environmental Management

Bioresource Technology

Water Science and Technology

Journal of Environmental Chemical Engineering, 2021

Water Quality Research Journal, 2021

Frontiers in Microbiology, 2021

Alongside antibiotic resistance, co-selection of antibiotics, biocides, and metal resistance is a... more Alongside antibiotic resistance, co-selection of antibiotics, biocides, and metal resistance is a growing concern. While hospital wastewater is considered a hotspot for antibiotic-resistant bacteria (ARB) and genes (ARGs), the scenario in India, one of the biggest consumers of antibiotics, remains poorly described. In this study, we used metagenomic sequencing to characterize ARGs and biocide/metal resistance genes (BMRGs) in four wastewater treatment plants (WWTPs) in Jaipur City of India. We observed a significantly lower richness and abundance of ARGs in the influent of a WWTP exclusively receiving hospital wastewater when compared to other three WWTPs involving municipal wastewater treatment. Several tetracycline and macrolide-lincosamide-streptogramin resistance genes were enriched in influents of these three municipal wastewater-related treatment plants, whereas hospital wastewater had a higher abundance of genes conferring resistance to disinfectant-related compounds such as ...

Journal of Environmental Management, 2020

Management of bacterial survival post chlorine disinfection is vital for safe wastewater reuse fo... more Management of bacterial survival post chlorine disinfection is vital for safe wastewater reuse for irrigation, as the presence of microorganisms in large numbers may lead to subsequent contamination of the surface and ground water reservoirs. Even after satisfying the current norms of coliform counts after disinfection (less than 1000 MPN per 100 mL), chlorine tolerant bacteria surviving in inadequately treated wastewater may pose a public health threat as many of these bacteria are able to re-grow upon storage. The current study is aimed to assess the magnitude of the problem posed by chlorine tolerant bacteria during chlorine disinfection and attempts to derive a strategy for safe disinfection. The chlorine tolerance was examined in the dominant gram negative bacteria (GNB) recovered from secondary treated sewage from a treatment plant located at Jaipur, India. Bacterial survival and re-growth (after 24 h) studies on test species (n ¼ 11) with reference to E.coli ATCC 25922 reveal that, while the lethal doses of isolates ranged from 0.5 to 1.25 mgL 1 ,the chlorine doses for complete inhibition of regrowth were much higher (0.75-1.75 mgL 1).The isolates showing highest lethal dose and re-growth inhibition dose, identified as Citrobacter freundii, Klebsiella sp. and Stenotrophomonas maltophilia also exhibited very low log effective reduction (0.72-1.90) values and were selected as chlorine tolerant bacteria. Results of inactivation kinetics experiments on chlorine tolerant bacteria reveal a strong correlation (R 2 > 0.89-0.99) between log reduction values and contact time. In re-growth kinetics experiments, maximum re-growth was observed after 6 h exposure following which, only marginal increase was registered up to 24 h. The study indicates that the existing approach of bacterial elimination post chlorine treatment may be grossly inadequate to assess the performance of the disinfection process adopted for drinking water treatment. It further brings out a novel approach to arrive at meaningful chlorine doses that take bacterial re-growth into account for achieving safe disinfection. particularly important as the microorganisms present in treated wastewater might act as a source of contamination for the surface and ground water (Kuriqi, 2014; Kuriqi et al., 2016). Hence, wastewater disinfection is a crucial step to meet a wholesome water quality (Eslamian et al., 2015). Disinfection can be carried out using chlorine, ozone, ultra violet irradiation, etc. However, chlorination is most widely practised disinfection method because it is cost effective and has potential oxidising capacity to inactivate the bacterial population, viruses and pathogens in water (

New Journal of Chemistry, 2019

A simpler methodology has reported for the fabrication of non-toxic functionalized soluble carbon... more A simpler methodology has reported for the fabrication of non-toxic functionalized soluble carbon nano-rods for the sensing of Fe(iii) and Cr(vi) in aqueous media.

Acta Scientific Agriculture, 2020

46. Jeong H., et al. "Irrigation water quality standards for indirect wastewater reuse in agricul... more 46. Jeong H., et al. "Irrigation water quality standards for indirect wastewater reuse in agriculture: a contribution toward sustainable wastewater reuse in South Korea". Water 8.4 (2016):169. 47. Rai PK and Tripathi BD. "Microbial contamination in vegetables due to irrigation with partially treated municipal wastewater in a tropical city".