A novel carbon emission evaluation model for anaerobic-anoxic-oxic urban sewage treatment.

The proposal of the dual carbon goal and the blue economy in China has sparked a keen interest in carbon emissions reduction from sewage treatment. Carbon accounting in urban sewage plants serves as the foundation for carbon emission reduction in sewage treatment. This paper re-evaluated carbon accounting in the operational processes for urban sewage treatment plants to develop a novel carbon emission evaluation model for anaerobic-anoxic-oxic treatment plants. The results show that the carbon emissions generated by non-carbon dioxide gases far exceed the carbon emissions from carbon dioxide alone. Moreover, the recycling of sewage leads to carbon emissions reduction that offsets the carbon emissions generated during the operation of the sewage plant. Also, the carbon emissions generated by sewage treatment plants are lower than those generated by untreated sewage. The findings and insights provided in this paper provide valuable references for carbon accounting and the implementation of low-carbon practices in urban sewage treatment plants.

Removal of pharmaceutical active compounds in wastewater by constructed wetlands: Performance and mechanisms.

The occurrence of pharmaceutical active compounds (PhACs) in aquatic environments is a cause for concern due to potential adverse effects on human and ecosystem health. Constructed wetlands (CWs) are cost-efficient and sustainable wastewater treatment systems for the removal of these PhACs. The removal processes and mechanisms comprise a complex interplay of photodegradation, biodegradation, phytoremediation, and sorption. This review synthesized the current knowledge on CWs for the removal of 20 widely detected PhACs in wastewater. In addition, the major removal mechanisms and influencing factors are discussed, enabling comprehensive and critical understanding for optimizing the removal of PhACs in CWs. Consequently, potential strategies for intensifying CWs system performance for PhACs removal are discussed. Overall, the results of this review showed that CWs performance in the elimination of some pharmaceuticals was on a par with conventional wastewater treatment plants (WWTPs) and, for others, it was above par. Furthermore, the findings indicated that system design, operational, and environmental factors played important but highly variable roles in the removal of pharmaceuticals. Nonetheless, although CWs were proven to be a more cost-efficient and sustainable technology for pharmaceuticals removal than other engineered treatment systems, there were still several research gaps to be addressed, mainly including the fate of a broad range of emerging contaminants in CWs, identification of specific functional microorganisms, transformation pathways of specific pharmaceuticals, assessment of transformation products and the ecotoxicity evaluation of CWs effluents.

First flush stormwater pollution in urban catchments: A review of its characterization and quantification towards optimization of control measures.

Identification, quantification, and control of First-Flush (FF) are considered extremely crucial in urban stormwater management. This paper reviews the methods for FF phenomenon identification, characteristics of pollutants flushes, technologies for FF pollution control, and the relationships among these factors. It further discusses FF quantification methods and optimization of control measures, aiming to reveal directions for future studies on FF management. Results showed that statistical analyses and Runoff Pollutographs Applying Curve (RPAC) fitting modelling of wash-off processes are the most applicable FF identification methods currently available. Furthermore, deep insights into the pollutant mass flushing of roof runoff may be a critical approach to characterizing FF stormwater. Finally, a novel strategy for FF control is established comprising multi-stage objectives, coupling LID/BMPs optimization schemes and Information Feedback (IF) mechanisms, aiming towards its application for the management of urban stormwater at the watershed scale.

Calcium ions-effect on performance, growth and extracellular nature of microalgal-bacterial symbiosis system treating wastewater.

Microalgal-bacterial symbiosis (MABS) system treating wastewater has attracted great concern because of its advantages of carbon dioxide reduction and biomass energy production. However, due to the low density and negative surface charge of microalgae cells, the sedimentation and harvesting performance of microalgae biomass has been one limitation for the application of MABS system on wastewater treatment. This study investigated the performance enhancement of microalgae harvesting and wastewater treatment contributed by calcium ions (i.e., Ca2+) in the MABS system. Results showed that a low Ca2+ loading (i.e., 0.1 mM) promoted both COD and nutrients removal, with growth rates of 11.95, 6.53 and 1.21% for COD, TN and TP compared to control, and chlorophyll a was increased by 64.15%. Differently, a high Ca2+ loading (i.e., 10 mM) caused removal reductions by improving the aggregation of microalgae, with reduction rates of 34.82, 3.50 and 10.30% for COD, NH4+-N and TP. Mechanism analysis indicated that redundant Ca2+ adsorbed on MABS aggregates and dissolved in wastewater decreased the dispersibility of microalgae cells by electrical neutralization and compressed double electric layer. Moreover, the presence of Ca2+ could improve extracellular secretions and promoted flocculation performance, with particle size increasing by 336.22%. The findings of this study may provide some solutions for the enhanced microalgae biomass harvest and nutrients removal from wastewater.

Hospital sewage treatment facilities witness the fighting against the COVID-19 pandemic.

Real-time evaluation of the fighting activities during a sudden unknown disaster like the COVID-19 pandemic is a critical challenge for control. This study demonstrates that the temporal variations of effluents from hospital sewage treatment facilities can be used as an effective indicator for such evaluation. Taking a typical infection-suffering city in China as an example, we found that there was an obvious decrease in effluent ammonia and COD concentrations in line with the start of city lockdown, and its temporal variations well indicated the major events happened during the pandemic control. Notably, the lagging period between the change point of effluent residual chlorine and the change points of COD and ammonia concentration coincided with a period in which there was a deficiency in local medical resources. In addition, the diurnal behavior of effluents from designated hospitals has varied significantly at different stages of the pandemic development. The effluent ammonia peaks shifted from daytime to nighttime after the outbreak of the COVID-19 pandemic, suggesting a high workload of the designated hospitals in fighting the rapidly emerging pandemic. This work well demonstrates the necessary for data integration at the wastewater-medical service nexus and highlights an unusual role of the effluents from hospital sewage treatment facilities in revealing the status of fighting the pandemic, which helps to control the pandemic.

Characterization and biogeochemical implications of dissolved organic matter in aquatic environments.

Dissolved organic matter (DOM) is viewed as one of the most chemically active organic substances on earth. It plays vital roles in the fate, bioavailability and toxicity of aquatic exogenous chemical species (e.g., heavy metals, organic pollutants, and nanomaterials). The characteristics of DOM such low concentrations, salt interference and complexity in aquatic environments and limitations of pretreatment for sample preparation and application of characterization techniques severely limit understanding of its nature and environmental roles. This review provides a characterization continuum of aquatic DOM, and demonstrate its biogeochemical implications, enabling in-depth insight into its nature and environmental roles. A synthesis of the effective DOM pretreatment strategies, comprising extraction and fractionation methods, and characterization techniques is presented. Additionally, the biogeochemical dynamics of aquatic DOM and its environmental implications are discussed. The findings indicate the collection of representative DOM samples from water as the first and critical step for characterizing its properties, dynamics, and environmental implications. However, various pretreatment procedures may alter DOM composition and structure, producing highly variable recoveries and even influencing its subsequent characterization. Therefore, complimentary use of various characterization techniques is highly recommended to obtain as much information on DOM as possible, as each characterization technique exhibits various advantages and limitations. Moreover, DOM could markedly change the physical and chemical properties of exogenous chemical species, influencing their transformation and mobility, and finally altering their potential bioavailability and toxicity. Several research gaps to be addressed include the impact of pretreatment on the composition and structure of aquatic DOM, molecular-level structural elucidation for DOM, and assessment of the effects of DOM dynamics on the fate, bioavailability and toxicity of exogenous chemical species.

Environmental risk assessment by using disability adjusted life year via constructing of a generalized linear model for morbidity estimation of waterborne pathogens.

The Environmental burden of disease (EBD) quantitatively evaluates the health impacts of pathogens by using the disability-adjusted life year (DALY) method. The life loss due to morbidity is a general expression for the EBD outcome and, thus, morbidity analysis is indispensable. Considering the deficiency of previous morbidity analysis methods, the objective of this study was to construct a linear morbidity model by using a generalized linear model (GLM) as a template and introducing exposure dose, pathogen toxicity and human immunity as impact variables. Human experimental data were collected for model fitting, and the results indicated a good fit of the majority of the pathogen data. Consequently, two practical cases of water reuse in Xi'an Siyuan University (Case 1) and Lake Cui, Kunming (Case 2) were selected for model validation. Results for case 1 indicated the major EBD to be attributed to rotaviruses (5.57 × 10-7 DALYs, 95% confidence interval (CI): 4.46 × 10-7-1.72 × 10-4 DALYs) and sprinkling irrigation (5.12 × 10-7 DALYs, 95% CI: 1.95 × 10-7-1.47 × 101 DALYs). Conversely, that for case 2 is mainly attributed to noroviruses (1.42 × 10-7 DALYs, 95% CI: 7.51 × 10-11-2.67 × 10-4 DALYs) and road flushing (1.62 × 10-7 DALYs, 95% CI: 1.16 × 10-7-2.67 × 10-4 DALYs). However, comparison with the suggested threshold of 10-6 DALYs indicated the EBDs for both cases are acceptable and, thus, water reuse is confirmed to be safe. The methodology for morbidity modelling proposed in this research can effectively compensate for missing data in DALY calculation and, thereby, help to optimize the process for EBD evaluation.

Source-Associated Gastroenteritis Risk from Swimming Exposure to Aging Fecal Pathogens.

Human contact with fecally contaminated waters often raises public health concern. The infection potential closely relates to the fecal source type and the aging persistence of waterborne pathogens. In this study, the health risk of contracting gastroenteritis from exposure to aging fecal contamination was predicted using source-associated markers. Microbial decay characteristics in typical summer seawater were incorporated into a pathogen dose estimation model for a constant fecal input. Results show that the median illness probability commensurate with the health benchmark of 36/1000 corresponded to the marker concentrations of ∼7.8, ∼6.6, ∼3.7, and ∼3.5 log10 gene copies/100 mL for seagulls, cattle, raw sewage, and treated effluent, respectively. The error in risk estimates due to neglecting microbial decay was linearly correlated to the decay differences between markers and pathogens. Specifically, the health risk associated with nonhuman sources, which was primarily contributed by bacterial and parasitic pathogens, can be substantially overestimated, while that for virus-dominated human sources was insignificantly affected by the differential decay. Additionally, seagulls dominated the Enterococcus concentration in waters with a mixture of the above-mentioned sources, although they posed limited health risk. This study provides an approach to understanding the influence of fecal aging on health risk estimation.

A new model framework for sponge city implementation: Emerging challenges and future developments.

Sponge City concept is emerging as a new kind of integrated urban water systems, which aims to address urban water problems. However, its implementation has encountered a variety of challenges. The lack of an integrated comprehensive model to assist Sponge City planning, implementation and life cycle assessment is one of the most challenging factors. This review briefly analyses the opportunity of existing urban water management models and discusses the limitation of recent studies in the application of current integrated models for Sponge City implementation. Furthermore, it proposes a new Sponge City model framework by integrating four main sub-models including MIKE-URBAN, LCA, W045-BEST, and MCA in which environmental, social, and economic aspects of Sponge City infrastructure options are simulated. The new structure of Sponge City model that includes the sub-model layer, input layer, module layer, output layer, and programing language layer is also illustrated. Therefore, the proposed model could be applied to optimize different Sponge City practices by not only assessing the drainage capacity of stormwater infrastructure but also pays attention to multi-criteria analysis of urban water system (including the possibility of assessing Sponge City ecosystem services for urban areas and watershed areas) as well. Balancing between simplification and innovation of integrated models, increasing the efficiency of spatial data sharing systems, defining the acceptability of model complexity level and improving the corporation of multiple stakeholders emphasizing on possible future directions of a proper Sponge City design and construction model.

Bioaerosol in a typical municipal wastewater treatment plant: concentration, size distribution, and health risk assessment.

An investigation on bioaerosol in a wastewater treatment plant (WWTP) located in Xi'an, China, was conducted to understand the characteristics of bioaerosol released from wastewater and sludge treatment facilities because the bioaerosols may pose a threat to human health. Using the Andersen impactor sampler collection and colony-counting method, bioaerosol concentrations and size distributions were detected. The risk quotient method was used to evaluate the health risks associated with inhalation of bioaerosol for WWTP staff, based on the average daily dose rates of exposure. The health risk in relation to Legionella pneumophila was quantitatively calculated using quantitative microbial risk assessment (QMRA), based on the assumption of the percentage. The maximum concentration of airborne bacteria (3,767 ± 280 colony forming units (CFU)/m3) and fungi (8,775 ± 406 CFU/m3) occurred from the aerated grit chamber and sludge thickening house, respectively, which all exceeded 500 CFU/m3 as the acceptable guideline proposed by the American Conference of Governmental Industrial Hygienists. The particle size of airborne bacteria was mainly distributed in the first three stages (>3.3 µm), while that of airborne fungi was from the second to the fourth stage (2.1-7.0 µm). The hazard index exposure to bioaerosol for adult males and females by inhalation were higher than 1. The proportion of L. pneumophila should be strictly controlled below 10-8, based on the QMRA approach.

Investigation and assessment of micropollutants and associated biological effects in wastewater treatment processes.

Currently, the wastewater treatment plants (WWTPs) attempt to achieve the shifting from general pollution parameters control to reduction of organic micropollutants discharge. However, they have not been able to satisfy the increasing ecological safety needs. In this study, the removal of micropollutants was investigated, and the ecological safety was assessed for a local WWTP. Although the total concentration of 31 micropollutants detected was reduced by 83% using the traditional biological treatment processes, the results did not reflect chemicals that had poor removal efficiencies and low concentrations. Of the five categories of micropollutants, herbicides, insecticides, and bactericides were difficult to remove, pharmaceuticals and UV filters were effectively eliminated. The specific photosynthesis inhibition effect and non-specific bioluminescence inhibition effect from wastewater were detected and evaluated using hazardous concentration where 5% of aquatic organisms are affected. The photosynthesis inhibition effect from wastewater in the WWTP was negligible, even the untreated raw wastewater. However, the bioluminescence inhibition effect from wastewater which was defined as the priority biological effect, posed potential ecological risk. To decrease non-specific biological effects, especially of macromolecular dissolved organic matter, overall pollutant reduction strategy is necessary. Meanwhile, the ozonation process was used to further decrease the bioluminescence inhibition effects from the secondary effluent; ≥ 0.34 g O3/g DOC of ozone dose was recommended for micropollutants elimination control and ecological safety.

Characterization and evolution of antibiotic resistance of Salmonella in municipal wastewater treatment plants.

The objective of this study was to investigate the evolution of antibiotic resistance phenotypes, antibiotic resistance genes (ARGs) and Class 1 integron of Salmonella in municipal wastewater treatment plants (WWTPs). A total of 221 Salmonella strains were isolated from different stages of three WWTPs. After the susceptibility testing, high frequency of resistance was observed for tetracycline (TET, 47.5% of isolates) and sulfamethoxazole (SMZ, 38.5%), followed by ampicillin (AMP, 25.3%), streptomycin (STP, 17.6%), chloramphenicol (CHL, 15.4%), and gentamicin (GEN, 11.3%). Low prevalence of resistance was detected for norfloxacin (0.45%), ciprofloxacin (0.9%), and cefotaxime (0.9%). The tetA and sul3 genes were most frequently detected among the Salmonella isolates. Statistically significant correlations among AMP, CHL, GEN, and STP resistances were observed. High detection frequencies of Class 1 integron were observed in double antibiotic-resistant and multiple-antibiotic-resistant (MAR) Salmonella, which were 94.3% and 85.7%, respectively. The proliferation of MAR Salmonella and transfer of ARGs occurred in WWTPs. Class 1 integron plays a crucial role in the evolution of MAR Salmonella during WWTPs.

Speciation, Distribution and Risk Assessment of Metals in Sediments from a Water Body Replenished by Effluent from a Wastewater Treatment Plant.

To assess the status and risk of metal pollution in landscape water body replenished by wastewater treatment plant effluent, the distribution of metals in sediments from three regions [regulation pond (RP), wetland lake (WL), and main lake (ML)] of Harbor Lake, Tianjin, China, was characterized. Higher levels of all metals (except Cr and Pb) were observed in RP sediments. As, Cr, Cu, Ni, Pb, and Zn were mainly bound to organic matter and sulfide (F3) and residual fractions (F4), while the exchangeable and carbonate fraction (F1) and Fe/Mn oxide fraction (F2) were the dominant forms for Cd. Additionally, finding showed that the overall risk of sediments in aquatic systems was affected by both metal toxicity and metal fractionation. Thus, according to a modified risk assessment code (RAC), the potential adverse effect of metals in sediments was medium (although As, Cd, Ni, and Zn had high mobility risks based on the RAC), decreasing in the order RP > WL > ML.

Thermodynamic prediction and experimental investigation of short-term dynamic membrane formation in dynamic membrane bioreactors: Effects of sludge properties.

In dynamic membrane bioreactors (DMBRs), a dynamic membrane (DM) forms on a support material to act as the separation membrane for solids and liquids. In this study, batch filtration tests were carried out in a DMBR using nylon mesh (25 µm) as support material to filtrate sludge suspensions of variable properties from three different sources to evaluate the effects on the short-term DM formation process (within 240 min). Furthermore, the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory was applied to analyze the sludge adhesion and cohesion behaviors on the mesh surface to predict quantitative parameters of the short-term DM formation process (including initial formation and maturation stage). The filtration results showed that the order of the initial DM formation time (permeate turbidity <1 NTU as an indicator) was as follows: sludge with poor settleability and dewaterability < normal sludge < sludge with poor flocculability. Moreover, normal sludge (regarding settleability, dewaterability, flocculability, and extracellular polymeric substance) showed a more acceptable DM formation performance (short DM formation time, low permeate turbidity, and high permeate flux) than sludge with poor settleability, dewaterability and flocculability. The influence of sludge properties on the initial DM formation time corroborates the prediction of sludge adhesion behaviors by XDLVO theory. Additionally, the XDLVO calculation results showed that acid-based interaction, energy barrier, and secondary energy minimum were important determinants of the sludge adhesion and cohesion behaviors. Therefore, short-term DM formation process may be enhanced to achieve stable long-term DMBR operation through positive modification of the sludge properties.

Dynamic membrane bioreactor performance enhancement by powdered activated carbon addition: Evaluation of sludge morphological, aggregative and microbial properties.

The effects of powdered activated carbon (PAC) addition on sludge morphological, aggregative and microbial properties in a dynamic membrane bioreactor (DMBR) were investigated to explore the enhancement mechanism of pollutants removal and filtration performance. Sludge properties were analyzed through various analytical measurements. The results showed that the improved sludge aggregation ability and the evolution of microbial communities affected sludge morphology in PAC-DMBR, as evidenced by the formation of large, regularly shaped and strengthened sludge flocs. The modifications of sludge characteristics promoted the formation process and filtration flux of the dynamic membrane (DM) layer. Additionally, PAC addition did not exert very significant influence on the propagation of eukaryotes (protists and metazoans) and microbial metabolic activity. High-throughput pyrosequencing results indicated that adding PAC improved the bacterial diversity in activated sludge, as PAC addition brought about additional microenvironment in the form of biological PAC (BPAC), which promoted the enrichment of Acinetobacter (13.9%), Comamonas (2.9%), Flavobacterium (0.31%) and Pseudomonas (0.62%), all contributing to sludge flocs formation and several (such as Acinetobacter) capable of biodegrading relatively complex organics. Therefore, PAC addition could favorably modify sludge properties from various aspects and thus enhance the DMBR performance.

Tracking the reactivity of ozonation towards effluent organic matters from WWTP using two-dimensional correlation spectra.

The characteristics of effluent organic matter (EfOM) from a wastewater treatment plant (WWTP) during ozonation were investigated using excitation and emission matrix (EEM) spectra, Fourier transform infrared spectroscopy (FT-IR) and high-performance size exclusion chromatography (HPSEC) at different ozone dosages. The selectivity of ozonation towards different constituents and functional groups was analysed using two-dimensional correlation spectra (2D-COS) probed by FT-IR, synchronous fluorescence spectra and HPSEC. The results indicated that ozonation can destroy aromatic structures of EfOM and change its molecular weight distribution (MWD). According to 2D-COS analysis, microbial humic-like substances were preferentially removed, and then the protein-like fractions. Terrestrial humic-like components exhibited inactivity towards ozonation compared with the above two fractions. Protein-like substances with small molecular weight were preferentially reacted during ozonation based on 2D-COS probed by HPSEC. In addition, the selectivity of ozone towards different functional groups of EfOM exhibited the following sequence: phenolic and alcoholic CO groups > aromatic structures containing CC double bonds > aliphatic CH. X-ray photoelectron spectroscopy (XPS) further elucidated the preferential reaction of aromatic structures in EfOM during ozonation.

Application of a hybrid gravity-driven membrane filtration and dissolved ozone flotation (MDOF) process for wastewater reclamation and membrane fouling mitigation.

This study proposed a novel membrane filtration and dissolved ozone flotation integrated (MDOF) process and tested it at pilot scale. Membrane filtration in the MDOF process was operated in gravity-driven mode, and required no backwashing, flushing, or chemical cleaning. Because ozone was added in the MDOF process, ozonation, coagulation, and membrane filtration could occur in a single reactor. Moreover, in situ ozonation occurred in the MDOF process, which differs from the conventional pre-ozonation membrane filtration process. Significant enhancement of turbidity removal was further achieved through the addition of membrane filtration. Membrane fouling was mitigated in the MDOF process compared to the MDAF process. In situ ozonation in the MDOF process decreased the fluorescence intensity and transformed the high MW dissolved organics into small MW compounds. For the fouling layer, the extracellular polymeric substance (EPS) contents and cake layer morphology were analyzed. The results indicated that the contents of EPS decreased. Furthermore, a thinner and more loosely structured cake layer formed in the MDOF process. Because coagulation and ozonation occurred simultaneously in a single reactor, the generation of hydroxyl radicals was enhanced through the catalytic effect of Al-based coagulants on ozone decomposition, which further alleviated membrane fouling in the MDOF process.

Co-Variation between Distribution of Microbial Communities and Biological Metabolization of Organics in Urban Sewer Systems.

Distribution characteristics and biodiversity of microbial communities were studied in a 1200 m pilot sewer system. Results showed that the dominant microorganisms, fermentation bacteria (FB), hydrogen-producing acetogen (HPA), sulfate-reducing bacteria (SRB) and methanogenic archaea (MA) changed significantly along the sewer systems, from start to the end. The distribution of the functional microorganisms could induce substrate transformation and lead to the accumulation of micromolecular organics (i.e., acetic acid, propionic acid and amino acid). However, substrate transformation induced by these microbes was affected by environmental factors such as oxidation-reduction potential, pH and dissolved oxygen. Changes in environmental conditions along the sewer resulted in the variation of dominant bioreactions. FB were enriched at the beginning of the sewer, while SRB and MA were found toward the end. Furthermore, based on Spearman rank correlation analysis of microbial communities, environmental factors and substrates, covariation between microbial community distribution and organics metabolization along the sewer was identified. This study could provide a theoretical foundation for understanding wastewater quality variation during transportation from sewers to treatment plants, therefore, promoting optimization of design and operation of wastewater treatment.

Construction of a Dose-Illness Relationship via Modeling Morbidity and Application to Risk Assessment of Wastewater Reuse.

A disease burden (DB) evaluation for environmental pathogens is generally performed using disability-adjusted life years with the aim of providing a quantitative assessment of the health hazard caused by pathogens. A critical step in the preparation for this evaluation is the estimation of morbidity between exposure and disease occurrence. In this study, the method of a traditional dose-response analysis was first reviewed, and then a combination of the theoretical basis of a "single-hit" and an "infection-illness" model was performed by incorporating two critical factors: the "infective coefficient" and "infection duration." This allowed a dose-morbidity model to be built for direct use in DB calculations. In addition, human experimental data for typical intestinal pathogens were obtained for model validation, and the results indicated that the model was well fitted and could be further used for morbidity estimation. On this basis, a real case of a water reuse project was selected for model application, and the morbidity as well as the DB caused by intestinal pathogens during water reuse was evaluated. The results show that the DB attributed to Enteroviruses was significant, while that for enteric bacteria was negligible. Therefore, water treatment technology should be further improved to reduce the exposure risk of Enteroviruses. Since road flushing was identified as the major exposure route, human contact with reclaimed water through this pathway should be limited. The methodology proposed for model construction not only makes up for missing data of morbidity during risk evaluation, but is also necessary to quantify the maximum possible DB.

Mechanisms of ultraviolet disinfection and chlorination of Escherichia coli: Culturability, membrane permeability, metabolism, and genetic damage.

Traditional culture methods may underestimate the tolerance of microorganisms to disinfectants because of the existence of viable but nonculturable or sublethally injured cells after disinfection. The selection of a strict method is crucial for the evaluation of disinfection performance. The actions of 2 typical disinfectants - ultraviolet (UV) and chlorine - on the fecal indicator Escherichia coli were investigated by the detection of culturability, membrane permeability, metabolic activity, deoxyribonucleic acid (DNA), and messenger ribonucleic acid (mRNA). During UV disinfection, the irreversible damages in the cell membrane and cellular adenosine triphosphate (ATP) were negligible at low UV doses (<80mJ/cm2). However, membrane permeability was damaged at low doses of chlorine (<5mg/L), leading to leakage of cellular ATP. Our study showed that a slight lesion in DNA was detected even at high doses of UV (400mJ/cm2) and chlorine (>5mg/L) treatments. The decay of mRNA was more rapid than that of DNA. The degradation level of mRNA depended on the choice of target genes. After exposure to 50mJ/cm2 UV dose or 5mg/L chlorine for 30min, the DNA damage repair function (RecA mRNA) was inhibited. The mRNA involved in the DNA damage repair function can be a potential indicator of bacterial viability.