Treatment of clinical laboratory sewage using a decentralized treatment unit and risk reduction for its reuse in irrigation using hybrid disinfection.

The disinfection efficacy of standalone chlorine, UV and their combined approach (hybrid) was investigated for the coliform removal in BioKube 1 and 2 treated effluents collected from different environmental settings of clinical and domestic wastes. Chlorine and UV disinfection were applied to BioKube treated wastewater with doses from 0 to 4 mg L-1 and 0-166 mJ cm-2 respectively. Combined disinfection strategies were designed to reduce the dose of chlorine and UV and to exploit the synergistic effect of them. The culturable coliforms were enumerated in treated wastewater sample (control), immediately after (reduction), and 24 h post disinfections (regrowth) using culture media plating and colilert-18 media. Both the BioKube systems (1 and 2) were effective in achieving the strict norms of physicochemical parameters, but not following the coliform counts of treated effluent for reuse in irrigation. A hybrid strategy of chlorine followed by UV was found to be the most effective among various standalone and combination approaches for the removal of coliforms (>4 log ER or <1000 CFU/100 mL) from both the treated effluents. However, coliform present in treated effluent of BioKube 1 were resisting (regrowth) against all kind of applied disinfectants except chlorine followed by UV dose at or more than 0.5 mg L-1 + 41 mJ cm-2. Limited reports are available on hybrid disinfection approaches with decentralized packaged sewage treatment units and this study would help to adopt as an effective tertiary treatment strategy for reuse of treated sewage for irrigation while ensuring public health safety.

Antibiotic resistance genes and bacterial diversity: A comparative molecular study of treated sewage from different origins and their impact on irrigated soils.

Present study aims to investigate how is soil affected following irrigation with treated effluents of different origins by analysing the bacterial diversity, metabolic diversity and antibiotic resistance genes (ARGs). Comparative analysis with previously reported ARGs in effluents was performed to understand the mobility of ARGs from treated wastewater to the irrigated soil with respect to the control soil regimen. Acinetobacter, Burkholderia and Pseudomonas were observed as the most abundant genera in all the samples. The metabolic gene abundance of all the samples suggests a prominent contribution to natural mineral recycling. Most abundant ARGs observed encode resistance for clindamycin, kanamycin A, macrolides, paromomycin, spectinomycin and tetracycline. Treated effluent reuse did not appear to enhance the ARG levels in soils in most cases except for institutional treatment site (M), where the ARGs for aminoglycosides, ß-lactams and sulfonamides were found to be abundantly present in both treated effluent and the irrigated soil. This study finds the importance of wastewater treatment from different origins and the impact of treated wastewater reuse in irrigation. This study also emphasises on the better understanding of ARGs mobility from water to soil.

A systematic review on chlorine tolerance among bacteria and standardization of their assessment protocol in wastewater.

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.

Metagenomic Survey Reveals More Diverse and Abundant Antibiotic Resistance Genes in Municipal Wastewater Than Hospital Wastewater.

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 synergize and wex-cide-128, reflecting the patterns of antibiotic/disinfectant use. Of note, in the wastewater system with more chemicals, there was a strong correlation between the numbers of ARGs and BMRGs potentially harbored by common hosts. Our study highlights significant influxes of ARGs from non-hospital sources in Jaipur City, and thus more attention should be paid on the emergence of ARGs in general communities.

Impact of combined chlorine and UV technology on the bacterial diversity, antibiotic resistance genes and disinfection by-products in treated sewage.

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.

Investigation of chlorine tolerance profile of dominant gram negative bacteria recovered from secondary treated wastewater in Jaipur, India.

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 = 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 re-growth 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 (R2 > 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.