Influence of pH, Oxygen, and Humic Substances on Ability of Sunlight To Damage Fecal Coliforms in Waste Stabilization Pond Water

Detection and genetic analysis of Escherichia coli from Tonle Sap Lake and its tributaries in Cambodia: Spatial distribution, seasonal variation, pathogenicity, and antimicrobial resistance

As an indicator of fecal contamination, Escherichia coli was monitored in Tonle Sap Lake, Cambodia, and its tributaries during low- and high-water seasons, focusing on the impacts on floating villagers inhabiting boathouses. E. coli concentrations in the floating villages (3.6 × 10³ and 5.7 × 10³ CFU/100 mL during the low- and high-water seasons, respectively) were significantly higher than those in other lake sites (4.0 × 10¹ and 7.0 × 10⁰ CFU/100 mL during the low- and high-water seasons, respectively) and rivers (3.3 × 10² and 8.9 × 10² CFU/100 mL during the low- and high-water seasons, respectively), most likely because fecal materials from the boathouses were discharged without treatment. At most of the lake sampling sites remote from the boathouses, the E. coli concentration was lower during the high-water season than that during the low-water season, due to dilution by lake water. E. coli colonies detected during monitoring were isolated for pathotyping, antimicrobial susceptibility testing, beta-lactamase gene detection, and multilocus sequencing typing (MLST). Of the 659 E. coli isolates, 101 (15.3%) were diarrheagenic E. coli (DEC). The prevalence of DEC (52.2%) in the floating villages during the low-water season was higher than that during the high-water season (4.2%) and that in other sites during both seasons (10.6-21.3%). The DEC isolates from the floating villages during the low-water season showed high antimicrobial resistance, including ampicillin (83.4%) and ciprofloxacin (83.4%), and frequently possessed a beta-lactamase gene (bla_TEM) (83.4%). MLST analysis indicated that the predominant sequence type (ST) of DEC isolates from the floating villages possibly originated from humans, whereas more diverse STs were detected in isolates from other sites. We revealed the wide presence of diarrheagenic and antimicrobial-resistant E. coli in Tonle Sap Lake and identified a considerable infection risk in floating villages, especially during the low-water season.

Effect of pH on endogenous sunlight inactivation rates of laboratory strain and wastewater sourced E. coli and enterococci

Understanding the influence of environmental factors like pH on solar disinfection in sunlight-dependent wastewater treatment systems can aid in improving their design. Previous research found pH to influence the solar disinfection rates of bacteria in water containing exogenous photosensitizers that facilitate photo-oxidative inactivation. However, limited research has been conducted on the role of external pH on endogenous solar inactivation processes that occur independent of exogenous photosensitizers. As such, we studied the inactivation rates of laboratory-cultured and wastewater-sourced E. coli and enterococci in sensitizer-free matrices with pH ranging from 4 to 10 under full-spectrum and UVB-filtered simulated sunlight. Elevated solar inactivation rates were observed at pH 4 for all bacterial populations evaluated, and at pH 10 for laboratory-cultured and wastewater-sourced E. coli. Dark inactivation was observed at the pH extremes for some bacteria, but did not contribute significantly to the increased inactivation rates observed under simulated sunlight at these pH, except for laboratory-cultured E. coli at pH 10. UVB light was found to play an important role in sunlight inactivation, albeit the contribution of UVB light to solar inactivation observed for Enterococcus spp. diminished at pH 4 and 5, suggesting that indirect endogenous inactivation pathways facilitated by longer wavelength light were enhanced under acidic conditions. Our findings demonstrate that external pH affects the kinetics of endogenous sunlight inactivation processes, and the results have potential to be integrated into models for predicting inactivation kinetics in sunlight-mediated treatment systems that operate over a range of pH conditions.

Implication of microplastic toxicity on functioning of microalgae in aquatic system

Microplastics (MPs) released from both primary and secondary sources affect the functioning of aquatic system. These MPs and components leached, can interact with aquatic organisms of all trophic levels, including the primary producers, such as microalgae. Considering the ecological value of microalgae and the toxicological effects of MPs towards them, this review provides: (1) a detailed understanding of the interactions between MPs and microalgae in the complex natural environment; (2) a discussion about the toxic effects of single type and mixtures of plastic particles on the microalgae cells, and (3) a discussion about the impacts of MPs on various features of microalgae -based bioremediation technology. For this purpose, toxic effects of MPs on various microalgal species were compiled and plastic components of MPs were ranked on the basis of their toxic effects. Based on available data, ranking for various plastic components was found to be: Polystyrene (PS) (rank 1) > Polyvinyl Chloride (PVC) > Polypropylene (PP) > Polyethylene (PE) (rank 4). Furthermore, the review suggested the need to understand joint toxicity of MPs along with co-contaminants on microalgae as the presence of other pollutants along with MPs might affect microalgae differently. In-depth investigations are required to check the impact of MPs on microalgae-based wastewater treatment technology and controlling factors.

Fecal indicator bacteria diversity and decay in an estuarine mangrove ecosystem of the Xuan Thuy National Park, Vietnam

Mangroves are complex and dynamic ecosystems that are highly dependent on diverse microbial activities. In this study, laboratory experiments and field studies for fecal indicator bacteria (FIB) decay rates are carried out for the first time in the Xuan Thuy Mangrove Forest Reserve of Vietnam. Results show that there are significant differences in bacterial diversity in the water of mangrove areas that have been deforested compared to those which have been planted. The highest mean total coliform (TC) and Escherichia coli (EC) values were found in the natural mangroves (3,807±2,922 and 964±1133 CFU 100 ml^-1, respectively). The results indicated that the source of contamination and seasonal changes affect the abundance of fecal bacteria. These results were exceeding by far the safety guidelines for individual, non-commercial water supplies in most of the samples. In the planted mangrove sampling sites, the highest mean Fecal streptococci (FS) values of 1,520±1,652 CFU 100 ml^-1 were found. Microbial die-off rates were calculated over 5 days, and observed to be systematically higher for TC than for EC.

Study from microcosms and mesocosms reveals Escherichia coli removal in high rate algae ponds during domestic wastewater treatment is primarily caused by dark decay

While high rate algal ponds (HRAPs) can provide efficient pathogen removal from wastewater, the mechanisms involved remain unclear. To address this knowledge gap, the mechanisms potentially causing Escherichia coli (E. coli) removal during microalgae-based wastewater treatment were successively assessed using laboratory microcosms designed to isolate known mechanisms, and bench scale assays performed in real HRAP broth. During laboratory assays, E. coli decay was only significantly increased by alkaline pH (above temperature-dependent thresholds) due to pH induced toxicity, and direct sunlight exposure via UV-B damage and/or endogenous photo-oxidation. Bench assays confirmed alkaline pH toxicity caused significant decay but sunlight-mediated decay was not significant, likely due to light attenuation in the HRAP broth. Bench assays also evidenced the existence of uncharacterized ‘dark’ decay mechanism(s) not observed in laboratory microcosms. To numerically evaluate the contribution of each mechanism and the uncertainty associated, E. coli decay was modelled assuming dark decay, alkaline pH induced toxicity, and direct sunlight-mediated decay were independent mechanisms. The simulations confirmed E. coli decay was mainly caused by dark decay during bench assays (48.2–89.5% estimated contribution to overall decay at the 95% confidence level), followed by alkaline-pH induced toxicity (8.3–46.5%), and sunlight-mediated decay (0.0–21.9%).

Performance evaluation and siting index of the stabilization ponds based on environmental parameters: a case study in Iran

Stabilization ponds are open pools that remove total suspended solids, organic matters, microbial and pathogenic agents using physical, chemical, and biological processes. If the stabilization ponds are not well designed, they can produce odors, breed many insects, increase suspended solids concentration in the effluent and pollute groundwater. Consideration of environmental factors is critical for operation and maintenance. In this study, first, information on wastewater treatment plants and meteorological parameters were collected, and simultaneously, specialists were selected to score the effect of environmental factors on stabilization pond efficiency. A geographic information system was used to sit for suitable locations for stabilization ponds. The results showed that 23.6 % of Iran's treatment plants are stabilization ponds, which based on climate, evaporation, sunny hours, ice days, wind speed, and temperature parameters, 33.33 %, 37.3 %, 14 %, 50 %, 64 and 26 % of the stabilization ponds have obtained good points, respectively. The results also showed that 50 % of the stabilization ponds obtained an acceptable score considering all environmental parameters' simultaneous effect. A preliminary study based on considering all the environmental parameters showed that the central and southern regions are the best areas for establishing waste stabilization ponds; in contrast, northern and northeastern regions can have high operation and maintenance costs with lower efficiency. This study has shown that setup and design of the new waste stabilization ponds in Iran need to take into account by considering environmental factors because these factors have the main effect on algae growth which are one of main biological treatment.

Extremophilic Microalgae Galdieria Gen. for Urban Wastewater Treatment: Current State, the Case of “POWER” System, and Future Prospects

Over the past decades, wastewater research has increasingly focused on the use of microalgae as a tool to remove contaminants, entrapping nutrients, and whose biomass could provide both material and energy resources. This review covers the advances in the emerging research on the use in wastewater sector of thermoacidophilic, low-lipid microalgae of the genus Galdieria, which exhibit high content of protein, reserve carbohydrates, and other potentially extractable high-value compounds. The natural tolerance of Galdieria for high toxic environments and hot climates recently made it a key player in a single-step process for municipal wastewater treatment, biomass cultivation and production of energetic compounds using hydrothermal liquefaction. In this system developed in New Mexico, Galdieria proved to be a highly performing organism, able to restore the composition of the effluent to the standards required by the current legislation for the discharge of treated wastewater. Future research efforts should focus on the implementation, in the context of wastewater treatment, of more energetically efficient cultivation systems, potentially capable of generating water with increasingly higher purity levels.

Comparison of faecal indicator and viral pathogen light and dark disinfection mechanisms in wastewater treatment pond mesocosms

This study compared light and dark disinfection of faecal bacteria/viral indicator organisms (E. coli and MS2 (fRNA) bacteriophage) and human viruses (Echovirus and Norovirus) in Wastewater Treatment Pond (WTP) mesocosms. Stirred pond mesocosms were operated in either outdoor sunlight-exposed or laboratory dark conditions in two experiments during the austral summer. To investigate wavelength-dependence of sunlight disinfection, three optical filters were used: (1) polyethylene film (light control: transmitting all solar UV and visible wavelengths), (2) acrylic (removing most UVB <315 nm), and (3) polycarbonate (removing both UVB and UVA <400 nm). To assess different dark disinfection processes WTP effluent was treated before spiking with target microbes, by (a) 0.22 μm filtration to remove all but colloidal particles, (b) 0.22 μm filtration followed by heat treatment to destroy enzymes, and (c) addition of Cytochalasin B to supress protozoan grazing. Microbiological stocks containing E. coli, MS2 phage, Echovirus, and Norovirus were spiked into each mesocosm 10 min before the experiments commenced. The light control exposed to all sunlight wavelengths achieved >5-log E. coli and MS2 phage removal (from ~1.0 × 10⁶ to <1 PFU/mL) within 3 h compared with up to 6 h in UV-filtered mesocosms. This result confirms that UVB contributes to inactivation of E. coli and viruses by direct sunlight inactivation. However, the very high attenuation with depth of UVB in WTP water (99% removal in the top 8 cm) suggests that UVB disinfection may be less important than other removal processes averaged over time and full-scale pond depth. Dark removal was appreciably slower than sunlight-mediated inactivation. The dark control typically achieved higher removal of E. coli and viruses than the 0.22 μm filtered (dark) mesocosms. This result suggests that adsorption of E. coli and viruses to WTP particles (e.g., algae and bacteria bio-flocs) is an important mechanism of dark disinfection, while bacteria and virus characteristics (e.g. surface charge) and environmental conditions can influence dark disinfection processes.

Sediment and fecal indicator bacteria loading in a mixed land use watershed: Contributions from suspended sediment and bedload transport

Overland transport of fecal bacteria in water and their resuspension from bed sediments are important transport mechanisms that help explain the transport of enteric pathogens in watersheds. In this study, multiyear monitoring along with regression relationships between sediment and fecal indicator bacteria (FIB) were used to investigate annual loading in the South Fork Broad River watershed, located in northeastern Georgia, USA. Suspended transport was the dominant transport mechanism contributing to in-stream total annual loads for sediment (81.4-98.1%) and FIB (>98%). Annual bedload transport of FIB was small and Escherichia coli (up to 1.8%) contributed more to annual bedload FIB than enterococci (≤0.03%). Bedload contributions of FIB increased with the duration of critical discharge exceedance, indicating a prolonged risk of exposure to enteric pathogens during extended periods of high flows, which is important during major storm events. The risk of exposure to enteric pathogens through pathways such as recreational use and drinking water treatment could be much greater because fecal bacteria are released from sediment during higher flows and dominantly transported in suspension when bedload are not actively moving. Therefore, the combined contribution of fecal bacteria from overland and bedload-associated transport should be considered in risk assessments. Discharge, bedload, and FIB data collected over 2 yr in this study can supplement future hydrologic modeling and microbial risk assessment modeling efforts.

Removal of Pathogens in Onsite Wastewater Treatment Systems: A Review of Design Considerations and Influencing Factors

Conventional onsite wastewater treatment systems (OWTSs) could potentially contribute to the transmission of infectious diseases caused by waterborne pathogenic microorganisms and become an important human health concern, especially in the areas where OWTSs are used as the major wastewater treatment units. Although previous studies suggested the OWTSs could reduce chemical pollutants as well as effectively reducing microbial contaminants from onsite wastewater, the microbiological quality of effluents and the factors potentially affecting the removal are still understudied. Therefore, the design and optimization of pathogen removal performance necessitate a better mechanistic understanding of the hydrological, geochemical, and biological processes controlling the water quality in OWTSs. To fill the knowledge gaps, the sources of pathogens and common pathogenic indicators, along with their major removal mechanisms in OWTSs were discussed. This review evaluated the effectiveness of pathogen removal in state-of-art OWTSs and investigated the contributing factors for efficient pathogen removal (e.g., system configurations, filter materials, environmental and operational conditions), with the aim to guide the future design for optimized treatment performance.

Predicting the concentration of total coliforms in treated rural domestic wastewater by multi-soil-layering (MSL) technology using artificial neural networks

Many indicators are involved in monitoring water quality. For instance, the fecal indicator bacteria are extremely important to detect the water quality. For this purpose, to better predict the total coliforms at the outlet of a Multi-Soil-Layering (MSL) system designed to treat domestic wastewater in rural areas, a neural network model has been developed and compared with linear regression model. The data was collected from the raw and treated wastewater of a three MSL systems during a one-year period in rural village, in Al-Haouz Province, Morocco. Fifteen physicochemical and bacteriological variables have undergone feature selection to select the best ones for predicting the total coliforms concentration in the effluent of MSL system. Furthermore, 80% of the available dataset were used to train and optimize the neural model using repeated cross validation technique. The remaining part (20%) was used to test the developed model. The neural network indicated excellent results compared to the linear regression. The optimal model was a neural network with one hidden layer and 11 neurons, where the R² was about 97%. The importance analysis of each predictor was established, and it was found that pH and total suspended solids had the greatest influence on the total coliforms removal.

Antibiotic Resistance Profile of Bacteria Isolated from Wastewater Systems in Eastern Ethiopia

World Health Organizations launched a global action plan on antimicrobial resistance since 2015. Along with other objectives, the plan was aimed to strengthen knowledge of the spread of antimicrobial resistance through surveillance and research. Given their high bacterial densities and that they receive antibiotics, metals, and other selective agents, wastewater systems are a logical hotspot for antibiotic resistance surveillance. The current study reports on the result of antibiotic resistance surveillance conducted in selected wastewater systems of Eastern Ethiopia from Feb. 2018 to Oct. 2019. We monitored three wastewater systems in Eastern Ethiopia, such as the activated sludge system of Dire Dawa University, waste stabilization pond of Haramaya University, and a septic tank of Hiwot Fana Specialized University Hospital for 18 months period. We collected 66 wastewater samples from 11 sampling locations and isolated 722 bacteria using selective culture media and biochemical tests. We tested their antibiotic susceptibility using the standard Kirby-Bauer disk diffusion method on the surface of the Mueller-Hinton agar and interpreted the result according to EUCAST guidelines. The result shows the highest percentage of resistance for ampicillin among isolates of hospital wastewater effluent which is 36 (94.7%), 33 (91.7%), and 32 (88.9%) for E. coli, E. faecalis, and E. faecium, respectively. A lower rate of resistance was seen for gentamicin among isolates of activated sludge wastewater treatment system which is 10 (16.4%), 8 (13.3%), 11 (18.9%), and 12 (20.3%) for E. coli, E. faecalis, E. faecium, and P. aeruginosa, respectively. Hospital wastewater exhibited higher resistance than the other two wastewater systems. The Multiple Antibiotic Resistance Index (MARI) has significantly increased in the wastewater's course treatment process, showing the proliferation of resistance in the wastewater treatment system.

Escherichia coli removal during domestic wastewater treatment in outdoor high rate algae ponds: long-term performance and mechanistic implications

Escherichia coli (E. coli) first-order decay rates ranging from 3.34 to 11.9 d^-1 (25-75% data range, N = 128) were recorded in two outdoor pilot-scale (0.88 m³) high rate algal ponds (HRAPs) continuously fed primary domestic wastewater over two years (influent E. coli cell count of 4.74·10⁶ ± 3.37·10⁶ MPN·100 mL^-1, N = 142). The resulting removal performance was relatively constant throughout the year (log10-removal averaging 1.77 ± 0.54, N = 128), apart from a significant performance drop during a cold rainy period. E. coli removal performance was not strongly correlated to any of the meteorological or operational parameters recorded (e.g. sunlight intensity, pH, temperature). Hourly monitoring of E. coli cell count evidenced that E. coli removal, pH, dissolved oxygen (DO) and pond temperature peaked in the late afternoon of sunny summer days. Such improved daytime removal was, however, not evidenced in spring, even under sunny conditions causing milder increases in pH, DO and temperature. Overall, the data confirm the potential of HRAPs to support efficient E. coli removal during secondary domestic wastewater treatment and suggests E. coli decay was mainly caused by dark mechanisms episodically enhanced by indirect sunlight-mediated mechanisms and/or high pH toxicity.

Near-infrared NIR irradiation and sodium hypochlorite: An efficacious association to counteract the Enterococcus faecalis biofilm in endodontic infections

New strategies are necessary for the prevention of endodontic infections caused by Enterococcus faecalis, a common resistant pathogen and biofilm producer. Aim of the present study was to compare the effects of Near-Infrared (NIR) Light-Emitting Diode (LED) irradiation and different concentrations of sodium hypochlorite (NaOCl) alone or combined to each other on the E. faecalis biofilm, on artificial and human dentin surfaces. E. faecalis ATCC 29212 preformed biofilms, on polystyrene wells and on dentin discs, were treated with 880 nm NIR irradiation and NaOCl at 4%, 2.5%, 1% and 0.5% alone and combined to each other (NIR irradiation plus NaOCl 1% or 0.5%) at 5 and 10 min. Treated biofilms were compared to the controls for (i) biofilm biomass evaluation, (ii) CFU count for the quantification of cultivable cells and (iii) cells viability. All the detected experimental conditions displayed a significant reduction of biofilm biomass (p < 0.001) and CFUs/mL (p < 0.01) in respect to the controls on both tested surfaces. The effects on the E. faecalis biomass, colony count and cell viability were not time-dependent except for NaOCl 2.5% and 1% in the biofilm biomass reductions on human dentin discs. NIR-LED irradiation alone showed a reduction of E. faecalis aggregates without interfering with cell viability whereas NaOCl alone expressed a killing effect in a concentration dependent way. The combination of NIR-LED irradiation with NaOCl 1% and 0.5% displayed a double effect of cluster disaggregation and cell killing. In particular, NIR-LED irradiation combined with NaOCl 0.5% displayed an anti-biofilm activity major than those expressed by NaOCl 0.5% alone (p = 0.001) with a reduction of biomass 93% vs 71% and 97% vs 25% after 10 min, on polystyrene wells and human dentin discs, respectively. The innovative use of NIR-LED irradiation combined at short times with low concentration of NaOCl (1% and 0.5%) is capable to reach a significant effect on E. faecalis biofilm, especially on human dentin discs.

Complex Interactions Between Weather, and Microbial and Physicochemical Water Quality Impact the Likelihood of Detecting Foodborne Pathogens in Agricultural Water

Agricultural water is an important source of foodborne pathogens on produce farms. Managing water-associated risks does not lend itself to one-size-fits-all approaches due to the heterogeneous nature of freshwater environments. To improve our ability to develop location-specific risk management practices, a study was conducted in two produce-growing regions to (i) characterize the relationship between Escherichia coli levels and pathogen presence in agricultural water, and (ii) identify environmental factors associated with pathogen detection. Three AZ and six NY waterways were sampled longitudinally using 10-L grab samples (GS) and 24-h Moore swabs (MS). Regression showed that the likelihood of Salmonella detection (Odds Ratio [OR] = 2.18), and eaeA-stx codetection (OR = 6.49) was significantly greater for MS compared to GS, while the likelihood of detecting L. monocytogenes was not. Regression also showed that eaeA-stx codetection in AZ (OR = 50.2) and NY (OR = 18.4), and Salmonella detection in AZ (OR = 4.4) were significantly associated with E. coli levels, while Salmonella detection in NY was not. Random forest analysis indicated that interactions between environmental factors (e.g., rainfall, temperature, turbidity) (i) were associated with likelihood of pathogen detection and (ii) mediated the relationship between E. coli levels and likelihood of pathogen detection. Our findings suggest that (i) environmental heterogeneity, including interactions between factors, affects microbial water quality, and (ii) E. coli levels alone may not be a suitable indicator of food safety risks. Instead, targeted methods that utilize environmental and microbial data (e.g., models that use turbidity and E. coli levels to predict when there is a high or low risk of surface water being contaminated by pathogens) are needed to assess and mitigate the food safety risks associated with preharvest water use. By identifying environmental factors associated with an increased likelihood of detecting pathogens in agricultural water, this study provides information that (i) can be used to assess when pathogen contamination of agricultural water is likely to occur, and (ii) facilitate development of targeted interventions for individual water sources, providing an alternative to existing one-size-fits-all approaches.

Effective control of waterborne pathogens by aquatic plants

The role of aquatic plants in treating wastewater contaminated with inorganic and organic pollutants is well established. Recent studies have shown that aquatic plants possess potential to remove pathogens from wastewater. High removal (90%) of pathogenic microbes such as Enterococci, Escherichia coli, Klebsiella pneumonia, Pseudomonas aeruginosa, Clostridium perfringens, Staphylococcus aureus, and Salmonella have been achieved using aquatic plant species viz. Typha latifolia, Cyperus papyrus, Cyperus alternifolius, Phragmites mauritianus, Pistia stratiotes, Lemna paucicostata, Spirodela polyrhiza, Eichhornia crassipes. Pathogen removal by aquatic plants mainly occurs because of toxicity exerted by exudates produced by them or attachment of pathogens to plant roots followed by filtration. Constructed wetlands have proved very efficient in treating pathogen-contaminated water. More studies are required to find out the exact mechanism of pathogen removal by these plants so that their role in phytoremediation technologies can be emphasized.

Persistence and Decay of Fecal Microbiota in Aquatic Habitats

Fecal microorganisms can enter water bodies in diverse ways, including runoff, sewage discharge, and direct fecal deposition. Once in water, the microorganisms experience conditions that are very different from intestinal habitats. The transition from host to aquatic environment may lead to rapid inactivation, some degree of persistence, or growth. Microorganisms may remain planktonic, be deposited in sediment, wash up on beaches, or attach to aquatic vegetation. Each of these habitats offers a panoply of different stressors or advantages, including UV light exposure, temperature fluctuations, salinity, nutrient availability, and biotic interactions with the indigenous microbiota (e.g., predation and/or competition). The host sources of fecal microorganisms are likewise numerous, including wildlife, pets, livestock, and humans. Most of these microorganisms are unlikely to affect human health, but certain taxa can cause waterborne disease. Others signal increased probability of pathogen presence, e.g., the fecal indicator bacteria Escherichia coli and enterococci and bacteriophages, or act as fecal source identifiers (microbial source tracking markers). The effects of environmental factors on decay are frequently inconsistent across microbial species, fecal sources, and measurement strategies (e.g., culture versus molecular). Therefore, broad generalizations about the fate of fecal microorganisms in aquatic environments are problematic, compromising efforts to predict microbial decay and health risk from contamination events. This review summarizes the recent literature on decay of fecal microorganisms in aquatic environments, recognizes defensible generalizations, and identifies knowledge gaps that may provide particularly fruitful avenues for obtaining a better understanding of the fates of these organisms in aquatic environments.

Differences in Microbial Communities and Pathogen Survival Between a Covered and Uncovered Anaerobic Lagoon

Anaerobic lagoons are a critical component of confined swine feeding operations. These structures can be modified, using a synthetic cover, to enhance their ability to capture the emission of ammonia and other malodorous compounds. Very little has been done to assess the potential of these covers to alter lagoon biological properties. Alterations in the physicochemical makeup can impact the biological properties, most notably, the pathogenic populations. To this aim, we performed a seasonal study of two commercial swine operations, one with a conventional open lagoon, the other which employed a permeable, synthetic cover. Results indicated that lagoon fecal coliforms, and Escherichia coli were significantly influenced by sampling location (lagoon vs house) and lagoon type (open vs. covered), while Enterococcus sp. were influenced by sampling location only. Comparisons against environmental variables revealed that fecal coliforms (r2 = 0.40), E. coli (r2 = 0.58), and Enterococcus sp. (r2 = 0.25) significantly responded to changes in pH. Deep 16S sequencing of lagoon and house bacterial and archaeal communities demonstrated grouping by both sampling location and lagoon type, with several environmental variables correlating to microbial community differences. Overall, these results demonstrate that permeable synthetic covers play a role in changing the lagoon microclimate, impacting lagoon physicochemical and biological properties.

Photoinactivation of uncultured, indigenous enterococci

Enterococci are used to monitor recreational water quality worldwide, so understanding their fate and transport in the environment is essential to the protection of human health. As such, researchers have documented enterococci inactivation under various exposure conditions and in diverse water matrices. However, the majority of studies have been performed using lab-cultured bacteria, which are distinct from indigenous, uncultured bacteria found in the environment. Here we investigate the photoinactivation of indigenous, uncultured enterococci from a range of sources, including wastewater treatment plants (WWTPs), marine beaches, urban streams, and a wastewater-influenced pond. We concentrated indigenous enterococci from their sources using filtration and centrifugation, placed them in a clear buffer solution, and then exposed them to simulated sunlight to measure their photoinactivation rates. First order decay rate constants (k) of indigenous, uncultured enterococci spanned an order of magnitude, from 0.3 to 2.3 m2 kJUVB-1. k values of indigenous enterococci from WWTPs tended to be larger than those from surface waters. The k value of lab-cultured Enterococcus faecalis was larger than those of indigenous, uncultured enterococci from most sources. Negative associations between the fraction of pigmented enterococci and sunlight susceptibility were observed. This work suggests that caution should be taken when extending results on bacterial photoinactivation obtained using lab-cultured bacteria to environmental bacteria, and that enterococci pigmentation may be a useful metric for estimating photoinactivation rate constants.

Persistence of bacterial pathogens, antibiotic resistance genes, and enterococci in tidal creek tributaries

Intertidal creeks form the primary hydrologic link between estuaries and land-based activities on barrier islands. Fecal indicators Enterococcus spp. (Entero1), pathogens Shigella spp. (ipaH), Salmonella spp. (invA), E. coli of EHEC/EPEC groups (eaeA), E. coli of EAEC, EIEC, and UPEC groups (set1B), E. coli of STEC group (stx1); and tetracycline resistance genes (tet(B), tet(C), tet(D), tet(E), tet(K), tet(Q), tet(W), and tet(X); TRG) were detected in the headwater of Oakdale Creek (Sapelo Island, GA) receiving runoffs from Hog Hammock village. Excavation of drainage ditches around the village caused a high increase in the incidence of the above determinants. Water samples were collected from the headwater, transferred to diffusion chambers, submersed in the headwater, saltmarsh, and mouth of the creek; and the determinants were monitored for 3 winter months. With some exceptions, their persistence decreased in order headwater > saltmarsh > mouth. Genes associated with Enterococcus spp. were the most persistent at all the sites, following in the headwater with determinants for Salmonella spp. and E. coli of EAEC, EIEC, and UPEC groups. In the mouth, the most persistent gene was eaeA indicating EHEC, EPEC, and STEC. Tet(B) and tet(C) persisted the longest in headwater and saltmarsh. No TRG persisted after 11 days in the mouth. Most determinants revealed correlations with temperature and pH, and inverse correlations with dissolved oxygen. Decay rates of the above determinants varied in the range of -0.02 to -0.81/day, and were up to 40 folds higher in the saltmarsh and mouth than in the headwater. Our data demonstrated that water parameters could to some extent predict a general trend in the fate of virulence and antibiotic resistance determinants in tidal creek tributaries but strongly suggested that their persistence in these tributaries cannot be predicted from that of enterococci, or extrapolated from one biological contaminant to another.

Sunlight-mediated inactivation of health-relevant microorganisms in water: a review of mechanisms and modeling approaches

Health-relevant microorganisms present in natural surface waters and engineered treatment systems that are exposed to sunlight can be inactivated by a complex set of interacting mechanisms. The net impact of sunlight depends on the solar spectral irradiance, the susceptibility of the specific microorganism to each mechanism, and the water quality; inactivation rates can vary by orders of magnitude depending on the organism and environmental conditions. Natural organic matter (NOM) has a large influence, as it can attenuate radiation and thus decrease inactivation by endogenous mechanisms. Simultaneously NOM sensitizes the formation of reactive intermediates that can damage microorganisms via exogenous mechanisms. To accurately predict inactivation and design engineered systems that enhance solar inactivation, it is necessary to model these processes, although some details are not yet sufficiently well understood. In this critical review, we summarize the photo-physics, -chemistry, and -biology that underpin sunlight-mediated inactivation, as well as the targets of damage and cellular responses to sunlight exposure. Viruses that are not susceptible to exogenous inactivation are only inactivated if UVB wavelengths (280-320 nm) are present, such as in very clear, open waters or in containers that are transparent to UVB. Bacteria are susceptible to slightly longer wavelengths. Some viruses and bacteria (especially Gram-positive) are susceptible to exogenous inactivation, which can be initiated by visible as well as UV wavelengths. We review approaches to model sunlight-mediated inactivation and illustrate how the environmental conditions can dramatically shift the inactivation rate of organisms. The implications of this mechanistic understanding of solar inactivation are discussed for a range of applications, including recreational water quality, natural treatment systems, solar disinfection of drinking water (SODIS), and enhanced inactivation via the use of sensitizers and photocatalysts. Finally, priorities for future research are identified that will further our understanding of the key role that sunlight disinfection plays in natural systems and the potential to enhance this process in engineered systems.

Vertical profiling and modelling of Escherichia coli decay in a shallow maturation pond operating in a tropical climate

Maturation ponds are excellent natural treatment systems for disinfecting domestic wastewater from pathogenic bacteria because of their great sunlight exposure through depth and high pH and dissolved oxygen values - all considered important factors. Escherichia coli (E. coli) removal is higher at closer to the surface of the pond and proceeds to decrease due to the limited amount of sunlight at deeper depths. To quantify the decay coefficients (K _b) of E. coli in a shallow maturation pond, quartz vessels were used to create isolated batch experiments and submerged at different depths inside the pond during different periods of the day (morning and afternoon). K _b values ranged from 0.48 to 0.28 h^-1, considering different depths and both periods. A dark control vessel was also used to quantify dark decay rates (K _d) at the same depth and periods as the quartz vessels, and ranged from 0.14 to 0.04 h^-1. Environmental variables did not appear to influence overall disinfection. Two models for estimating final E. coli concentrations were proposed, considering the kinetic coefficients obtained in the batch experiments and the dispersed flow regime for continuous flow ponds, which resulted in very good fittings with monitoring data and demonstrated the vertical profiling of E. coli concentration.

Transcriptional Response of Staphylococcus aureus to Sunlight in Oxic and Anoxic Conditions

The transcriptional response of Staphylococcus aureus strain Newman to sunlight exposure was investigated under both oxic and anoxic conditions using RNA sequencing to gain insight into potential mechanisms of inactivation. S. aureus is a pathogenic bacterium detected at recreational beaches which can cause gastrointestinal illness and skin infections, and is of increasing public health concern. To investigate the S. aureus photostress response in oligotrophic seawater, S. aureus cultures were suspended in seawater and exposed to full spectrum simulated sunlight. Experiments were performed under oxic or anoxic conditions to gain insight into the effects of oxygen-mediated and non-oxygen-mediated inactivation mechanisms. Transcript abundance was measured after 6 h of sunlight exposure using RNA sequencing and was compared to transcript abundance in paired dark control experiments. Culturable S. aureus decayed following biphasic inactivation kinetics with initial decay rate constants of 0.1 and 0.03 m² kJ⁻¹ in oxic and anoxic conditions, respectively. RNA sequencing revealed that 71 genes had different transcript abundance in the oxic sunlit experiments compared to dark controls, and 18 genes had different transcript abundance in the anoxic sunlit experiments compared to dark controls. The majority of genes showed reduced transcript abundance in the sunlit experiments under both conditions. Three genes (ebpS, NWMN_0867, and NWMN_1608) were found to have the same transcriptional response to sunlight between both oxic and anoxic conditions. In the oxic condition, transcripts associated with porphyrin metabolism, nitrate metabolism, and membrane transport functions were increased in abundance during sunlight exposure. Results suggest that S. aureus responds differently to oxygen-dependent and oxygen-independent photostress, and that endogenous photosensitizers play an important role during oxygen-dependent indirect photoinactivation.

Detection of contaminants in water supply: A review on state-of-the-art monitoring technologies and their applications

Water monitoring technologies are widely used for contaminants detection in wide variety of water ecology applications such as water treatment plant and water distribution system. A tremendous amount of research has been conducted over the past decades to develop robust and efficient techniques of contaminants detection with minimum operating cost and energy. Recent developments in spectroscopic techniques and biosensor approach have improved the detection sensitivities, quantitatively and qualitatively. The availability of in-situ measurements and multiple detection analyses has expanded the water monitoring applications in various advanced techniques including successful establishment in hand-held sensing devices which improves portability in real-time basis for the detection of contaminant, such as microorganisms, pesticides, heavy metal ions, inorganic and organic components. This paper intends to review the developments in water quality monitoring technologies for the detection of biological and chemical contaminants in accordance with instrumental limitations. Particularly, this review focuses on the most recently developed techniques for water contaminant detection applications. Several recommendations and prospective views on the developments in water quality assessments will also be included.

Performance evaluation of a natural treatment system for small communities, composed of a UASB reactor, maturation ponds (baffled and unbaffled) and a granular rock filter in series

Post-treatment of anaerobic reactor effluent with maturation ponds is a good option for small to medium-sized communities in tropical climates. The treatment line investigated, operating in Brazil, with an equivalent capacity to treat domestic sewage from 250 inhabitants, comprised a upflow anaerobic sludge blanket reactor followed by two shallow maturation ponds (unbaffled and baffled) and a granular rock filter (decreasing grain size) in series, requiring an area of only 1.5 m² inhabitant^-1. With an overall hydraulic retention time of only 6.7 days, the performance was excellent for a natural treatment system. Based on over two years of continuous monitoring, median removal efficiencies were: biochemical oxygen demand = 93%, chemical oxygen demand = 79%, total suspended solids = 87%, ammonia = 43% and Escherichia coli = 6.1 log units. The final effluent complied with European discharge standards and WHO guidelines for some forms of irrigation, and appeared to be a suitable alternative for treating domestic sewage for small communities in warm areas, especially in developing countries.

Removal of organic micropollutants in waste stabilisation ponds: A review

As climate change and water scarcity continue to be of concern, reuse of treated wastewater is an important water management strategy in many parts of the world, particularly in developing countries and remote communities. Many countries, especially in remote regional areas, use waste stabilisation ponds (WSPs) to treat domestic wastewater for a variety of end uses, including using the treated wastewater for irrigation of public spaces (e.g. parks and ovals) or for crop irrigation. Thus, it is vital that the resulting effluent meets the required quality for beneficial reuse. In this paper, both the performance of WSPs in the removal of organic micropollutants, and the mechanisms of removal, are reviewed. The performance of WSPs in the removal of organic micropollutants was found to be highly variable and influenced by many factors, such as the type and configuration of the ponds, the operational parameters of the treatment plant, the wastewater quality, environmental factors (e.g. sunlight, temperature, redox conditions and pH) and the characteristics of the pollutant. The removal of organic micropollutants from WSPs has been attributed to biodegradation, photodegradation and sorption processes, the majority of which occur in the initial treatment stages (e.g. in the anaerobic or facultative ponds). Out of the many hundreds of organic micropollutants identified in wastewater, only a limited number (40) have been studied in WSPs, with the majority of these pollutants being pharmaceuticals, personal care products and endocrine disrupting compounds. Thus, future research on the fate of organic micropollutants in WSPs should encompass a broader range of micropollutants and include emerging organic pollutants, such as illicit drugs and perfluorinated compounds. Further research is also needed on the formation and toxicity of transformation products from organic micropollutants in WSPs, since the transformation products of some organic micropollutants can be more toxic than the parent compound. Combining other wastewater treatment processes with WSPs for removal of recalcitrant organic micropollutants should also be considered.

Light irradiation helps magnetotactic bacteria eliminate intracellular reactive oxygen species

Magnetotactic bacteria (MTB) demonstrate photoresponse. However, little is known about the biological significance of this behaviour. Magnetosomes exhibit peroxidase-like activity and can scavenge reactive oxygen species (ROS). Magnetosomes extracted from the Magnetospirillum magneticum strain AMB-1 show enhanced peroxidase-like activity under illumination. The present study investigated the effects of light irradiation on nonmagnetic (without magnetosomes) and magnetic (with magnetosomes) AMB-1 cells. Results showed that light irradiation did not affect the growth of nonmagnetic and magnetic cells but significantly increased magnetosome synthesis and reduced intracellular ROS level in magnetic cells. Quantitative reverse transcription polymerase chain reaction (qRT-PCR) was performed to analyse the expression level of magnetosome formation-associated genes (mamA, mms6, mms13 and mmsF) and stress-related genes (recA, oxyR, SOD, amb0664 and amb2684). Results showed that light irradiation upregulated the expression of mms6, mms13 and mmsF. Furthermore, light irradiation upregulated the expression of stress-related genes in nonmagnetic cells but downregulated them in magnetic cells. Additionally, magnetic cells exhibited stronger phototactic behaviour than nonmagnetic ones. These results suggested that light irradiation could heighten the ability of MTB to eliminate intracellular ROS and help them adapt to lighted environments. This phenomenon may be related to the enhanced peroxidase-like activity of magnetosomes under light irradiation.

Staphylococcus aureus Strain Newman Photoinactivation and Cellular Response to Sunlight Exposure

Sunlight influences microbial water quality of surface waters. Previous studies have investigated photoinactivation mechanisms and cellular photostress responses of fecal indicator bacteria (FIB), including Escherichia coli and enterococci, but further work is needed to characterize photostress responses of bacterial pathogens. Here we investigate the photoinactivation of Staphylococcus aureus (strain Newman), a pigmented, waterborne pathogen of emerging concern. We measured photodecay using standard culture-based assays and cellular membrane integrity and investigated photostress response by measuring the relative number of mRNA transcripts of select oxidative stress, DNA repair, and metabolism genes. Photoinactivation experiments were performed in both oxic and anoxic systems to further investigate the role of oxygen-mediated and non-oxygen-mediated photoinactivation mechanisms. S. aureus lost culturability much faster in oxic systems than in anoxic systems, indicating an important role for oxygen in photodecay mechanisms. S. aureus cell membranes were damaged by sunlight exposure in anoxic systems but not in oxic systems, as measured by cell membrane permeability to propidium iodide. After sunlight exposure, S. aureus increased expression of a gene coding for methionine sulfoxide reductase after 12 h of sunlight exposure in the oxic system and after 6 h of sunlight exposure in the anoxic system, suggesting that methionine sulfoxide reductase is an important enzyme for defense against both oxygen-dependent and oxygen-independent photostresses. This research highlights the importance of oxygen in bacterial photoinactivation in environmentally relevant systems and the complexity of the bacterial photostress response with respect to cell structure and transcriptional regulation.IMPORTANCEStaphylococcus aureus is a pathogenic bacterium that causes gastrointestinal, respiratory, and skin infections. In severe cases, S. aureus infection can lead to life-threatening diseases, including pneumonia and sepsis. Cases of community-acquired S. aureus infection have been increasing in recent years, pointing to the importance of considering S. aureus transmission pathways outside the hospital environment. Associations have been observed between recreational water contact and staphylococcal skin infections, suggesting that recreational waters may be an important environmental transmission pathway for S. aureus However, prediction of human health risk in recreational waters is hindered by incomplete knowledge of pathogen sources, fate, and transport in this environment. This study is an in-depth investigation of the inactivation of a representative strain of S. aureus by sunlight exposure, one of the most important factors controlling the fate of microbial contaminants in clear waters, which will improve our ability to predict water quality changes and human health risk in recreational waters.

Solar radiation (PAR, UV-A, UV-B) penetration in a shallow maturation pond operating in a tropical climate

Solar radiation is considered the primary route for disinfection of pathogenic bacteria in maturation ponds. There is scarce information on depth profiling and attenuation of photosynthetically active radiation (PAR), UV-A and UV-B in shallow maturation ponds operating in tropical climates. Measurements of solar irradiance of the three wavelength ranges, together with turbidity, have been acquired from different depths for over 1 year in a shallow maturation pond (44 cm of depth) operating in Brazil. UV-A and UV-B were still detected at 10 cm from the surface, but from 15 cm both were undetectable. PAR was still detected at 30 cm of depth. Irradiation attenuation showed to be related to turbidity. Attenuation coefficients were calculated and simple models without turbidity (traditional structure) or including log₁₀ of turbidity are proposed for predicting PAR irradiance attenuation as a function of depth.

Exogenous indirect photoinactivation of bacterial pathogens and indicators in water with natural and synthetic photosensitizers in simulated sunlight with reduced UVB

AIMS

To investigate the UVB-independent and exogenous indirect photoinactivation of eight human health-relevant bacterial species in the presence of photosensitizers.

METHODS AND RESULTS

Eight bacterial species were exposed to simulated sunlight with greatly reduced UVB light intensity in the presence of three synthetic photosensitizers and two natural photosensitizers. Inactivation curves were fit with shoulder log-linear or first-order kinetic models, from which the presence of a shoulder and magnitude of inactivation rate constants were compared. Eighty-four percent reduction in the UVB light intensity roughly matched a 72-95% reduction in the overall bacterial photoinactivation rate constants in sensitizer-free water. With the UVB light mostly reduced, the exogenous indirect mechanism contribution was evident for most bacteria and photosensitizers tested, although most prominently with the Gram-positive bacteria.

CONCLUSIONS

Results confirm the importance of UVB light in bacterial photoinactivation and, with the reduction of the UVB light intensity, that the Gram-positive bacteria are more vulnerable to the exogenous indirect mechanism than Gram-negative bacteria.

SIGNIFICANCE AND IMPACT OF THE STUDY

UVB is the most important range of the sunlight spectrum for bacterial photoinactivation. In aquatic environments where photosensitizers are present and there is high UVB light attenuation, UVA and visible wavelengths can contribute to exogenous indirect photoinactivation.

A practical model for sunlight disinfection of a subtropical maturation pond

Maturation ponds are a type of waste stabilisation pond (WSP) designed to reduce carbon, nutrients and pathogens in the final stages of a WSP wastewater treatment system. In this study, a one-dimensional plug-flow pond model is proposed to predict temperature and E. coli concentration distributions and overall pond disinfection performance. The model accounts for the effects of vertical mixing and ultraviolet light-dependent die-off rate kinetics. Measurements of radiation, wind-speed, humidity and air temperature are recorded for model inputs and good agreement with measured vertical temperature distributions and outlet E. coli concentrations is found in an operational, subtropical maturation pond. Measurements and the model both show a diurnal pattern of stratification during daylight hours and natural convective mixing at night on days corresponding to low wind speeds, strong heat input from solar radiation and clear night skies. In the evenings, the thermal stratification is shown to collapse due to surface energy loss via longwave radiation which triggers top-down natural convective mixing. The disinfection model is found to be sensitive to the choice of die-off kinetics. The diurnal mixing pattern is found to play a vital role in the disinfection process by ensuring that pathogens are regularly transported to the near-surface layer where ultraviolet light penetration is effective. The model proposed in this paper offers clear advantages to pond designers by including geographical specific, time-varying boundary conditions and accounting for the important physical aspects of vertical mixing and sunlight inactivation processes, yet is computationally straightforward.

Seasonal influence of environmental variables and artificial aeration on Escherichia coli in small urban lakes

This study investigated patterns of Escherichia coli in urban lakes in Lubbock, Texas. Specific objectives were to (1) document seasonal patterns in abundance of E. coli over a 3-year period, (2) identify environmental factors, including effects of migratory geese and artificial aeration devices that may influence E. coli abundance, and (3) determine if E. coli abundance over time was similar for individual lakes. Water samples were collected monthly for 36 months from six lakes, three of which contained artificial aeration devices (fountains). Regression models were constructed to determine which environmental variables most influence E. coli abundance in summer and winter seasons. Escherichia coli is present in the lakes of Lubbock, Texas year-round and typically exceeds established bacterial thresholds for recreational waters. Models most frequently contained pH and dissolved oxygen as predictor variables and explained from 17.4% to 92.4% of total variation in E. coli. Lakes with fountains had a higher oxygen concentration during summer and contained consistently less E. coli. We conclude that solar irradiation in synergy with pH and dissolved oxygen is the primary control mechanism for E. coli in study lakes, and that fountains help control abundance of fecal bacteria within these systems.

Modeling fate and transport of fecally-derived microorganisms at the watershed scale: State of the science and future opportunities

Natural waters serve as habitat for a wide range of microorganisms, a proportion of which may be derived from fecal material. A number of watershed models have been developed to understand and predict the fate and transport of fecal microorganisms within complex watersheds, as well as to determine whether microbial water quality standards can be satisfied under site-specific meteorological and/or management conditions. The aim of this review is to highlight and critically evaluate developments in the modeling of microbial water quality of surface waters over the last 10 years and to discuss the future of model development and application at the watershed scale, with a particular focus on fecal indicator organisms (FIOs). In doing so, an agenda of research opportunities is identified to help deliver improvements in the modeling of microbial water quality draining through complex landscape systems. This comprehensive review therefore provides a timely steer to help strengthen future modeling capability of FIOs in surface water environments and provides a useful resource to complement the development of risk management strategies to reduce microbial impairment of freshwater sources.

How long can culturable bacteria and total DNA persist in environmental waters? The role of sunlight and solid particles

In this work, sunlight inactivation of two indicator bacteria in freshwater, with and without solid particles, was studied and the persistence of culturable cells and total DNA was compared. Environmental water was used to prepare two matrices, with and without solid particles, which were spiked with Escherichia coli and Enterococcus faecalis. These matrices were used to prepare microcosm bags that were placed in two containers: one exposed to sunlight and the other in the dark. During one month, samples were removed from each container and detection was done by membrane filter technique and real-time PCR. Kinetic parameters were calculated to assess sunlight effect. Indicator bacteria without solid particles exposed to sunlight suffered an immediate decay (<4h) compared with the ones which were shielded from them. In addition, the survival of both bacteria with solid particles varied depending on the situation analyzed (T99 from 3 up to 60days), being always culturable E. coli more persistent than E. faecalis. On the other side, E. faecalis DNA persisted much longer than culturable cells (T99>40h in the dark with particles). In this case active cells were more prone to sunlight than total DNA and the protective effect of solid particles was also observed. Results highlight that the effects caused by the parameters which describe the behavior of culturable microorganisms and total DNA in water are different and must be included in simulation models but without forgetting that these parameters will also depend on bacterial properties, sensitizers, composition, type, and uses of the aquatic environment under assessment.

Modelling microbial health risk of wastewater reuse: A systems perspective

There is a widespread need for the use of quantitative microbial risk assessment (QMRA) to determine reclaimed water quality for specific uses, however neither faecal indicator levels nor pathogen concentrations alone are adequate for assessing exposure health risk. The aim of this study was to build a conceptual model representing factors contributing to the microbiological health risks of reusing water treated in maturation ponds. This paper describes the development of an unparameterised model that provides a visual representation of theoretical constructs and variables of interest. Information was collected from the peer-reviewed literature and through consultation with experts from regulatory authorities and academic disciplines. In this paper we explore how, considering microbial risk as a modular system, following the QMRA framework enables incorporation of the many factors influencing human exposure and dose response, to better characterise likely human health impacts. By using and expanding upon the QMRA framework we deliver new insights into this important field of environmental exposures. We present a conceptual model of health risk of microbial exposure which can be used for maturation ponds and, more importantly, as a generic tool to assess health risk in diverse wastewater reuse scenarios.

Inactivation of Escherichia coli in a baffled pond with attached growth: treating anaerobic effluent under the Sahelian climate

This study aimed to investigate and understand the zero-level detection of Escherichia coli (E. coli) at the outlet of an improved waste stabilization pond. Wastewaters were collected from the International Institute for Water and Environmental Engineering (2iE) campus and were subjected to biological treatment. The system included two-stage Anaerobic Reactors followed by a Baffled Pond (AR-BP) with recycled plastic media as a medium for attached growth and a control pond (CP). Three vertical baffles were installed, giving four compartments in the baffled pond (BP). The research was conducted on the pilot scale from March to July 2014, by monitoring E. coli, pH, temperature, dissolved oxygen (DO) and chlorophyll-a in each compartment and at different depths. The results show that E. coli concentrations were lower in top layers of all compartments with an undetectable level in the last compartment up to 0.60 m deep. E. coli mean removal efficiencies and decay rates were achieved by significant difference in BP (4.5 log-units, 9.1 day(-1)) and CP (1.1 log-units, 1.1 day(-1)). Higher values of pH (≥9), temperature (≥32°C), DO (≥ 8 mg/L) and chlorophyll-a (≥ 1000 µg/L) were observed at the surface of BP, whereas lower values were shown at the bottom. Sedimentation combined with the synergetic effects of the physicochemical parameters and environmental factors would be responsible for the inactivation of E. coli in BP. It was concluded that the AR-BP could be applied as an alternative low-cost wastewater treatment technology for developing countries and recommended for reuse of their effluent for restricted peri-urban irrigation.

Stable-isotope probing and metagenomics reveal predation by protozoa drives E. coli removal in slow sand filters

Stable-isotope probing and metagenomics were applied to study samples taken from laboratory-scale slow sand filters 0.5, 1, 2, 3 and 4 h after challenging with (13)C-labelled Escherichia coli to determine the mechanisms and organisms responsible for coliform removal. Before spiking, the filters had been continuously operated for 7 weeks using water from the River Kelvin, Glasgow as their influent source. Direct counts and quantitative PCR assays revealed a clear predator-prey response between protozoa and E. coli. The importance of top-down trophic-interactions was confirmed by metagenomic analysis, identifying several protozoan and viral species connected to E. coli attrition, with protozoan grazing responsible for the majority of the removal. In addition to top-down mechanisms, indirect mechanisms, such as algal reactive oxygen species-induced lysis, and mutualistic interactions between algae and fungi, were also associated with coliform removal. The findings significantly further our understanding of the processes and trophic interactions underpinning E. coli removal. This study provides an example for similar studies, and the opportunity to better understand, manage and enhance E. coli removal by allowing the creation of more complex trophic interaction models.

Temporal stability of the microbial community in sewage-polluted seawater exposed to natural sunlight cycles and marine microbiota

Billions of gallons of untreated wastewater enter the coastal ocean each year. Once sewage microorganisms are in the marine environment, they are exposed to environmental stressors, such as sunlight and predation. Previous research has investigated the fate of individual sewage microorganisms in seawater but not the entire sewage microbial community. The present study used next-generation sequencing (NGS) to examine how the microbial community in sewage-impacted seawater changes over 48 h when exposed to natural sunlight cycles and marine microbiota. We compared the results from microcosms composed of unfiltered seawater (containing naturally occurring marine microbiota) and filtered seawater (containing no marine microbiota) to investigate the effect of marine microbiota. We also compared the results from microcosms that were exposed to natural sunlight cycles with those from microcosms kept in the dark to investigate the effect of sunlight. The microbial community composition and the relative abundance of operational taxonomic units (OTUs) changed over 48 h in all microcosms. Exposure to sunlight had a significant effect on both community composition and OTU abundance. The effect of marine microbiota, however, was minimal. The proportion of sewage-derived microorganisms present in the microcosms decreased rapidly within 48 h, and the decrease was the most pronounced in the presence of both sunlight and marine microbiota, where the proportion decreased from 85% to 3% of the total microbial community. The results from this study demonstrate the strong effect that sunlight has on microbial community composition, as measured by NGS, and the importance of considering temporal effects in future applications of NGS to identify microbial pollution sources.

Conceptual model and experimental framework to determine the contributions of direct and indirect photoreactions to the solar disinfection of MS2, phiX174, and adenovirus

Sunlight inactivates waterborne viruses via direct (absorption of sunlight by the virus) and indirect processes (adsorption of sunlight by external chromophores, which subsequently generate reactive species). While the mechanisms underlying these processes are understood, their relative importance remains unclear. This study establishes an experimental framework to determine the kinetic parameters associated with a virus' susceptibility to solar disinfection and proposes a model to estimate disinfection rates and to apportion the contributions of different inactivation processes. Quantum yields of direct inactivation were determined for three viruses (MS2, phiX174, and adenovirus), and second-order rate constants associated with indirect inactivation by four reactive species ((1)O2, OH(•), CO3(•-), and triplet states) were established. PhiX174 exhibited the greatest quantum yield (1.4 × 10(-2)), indicating that it is more susceptible to direct inactivation than MS2 (2.9 × 10(-3)) or adenovirus (2.5 × 10(-4)). Second-order rate constants ranged from 1.7 × 10(7) to 7.0 × 10(9) M(-1) s(-1) and followed the sequence MS2 > adenovirus > phiX174. A predictive model based on these parameters accurately estimated solar disinfection of MS2 and phiX174 in a natural water sample and approximated that of adenovirus within a factor of 6. Inactivation mostly occurred by direct processes, though indirect inactivation by (1)O2 also contributed to the disinfection of MS2 and adenovirus.

Energy positive domestic wastewater treatment: the roles of anaerobic and phototrophic technologies

The negative energy balance of wastewater treatment could be reversed if anaerobic technologies were implemented for organic carbon oxidation and phototrophic technologies were utilized for nutrient recovery. To characterize the potential for energy positive wastewater treatment by anaerobic and phototrophic biotechnologies we performed a comprehensive literature review and analysis, focusing on energy production (as kJ per capita per day and as kJ m(-3) of wastewater treated), energy consumption, and treatment efficacy. Anaerobic technologies included in this review were the anaerobic baffled reactor (ABR), anaerobic membrane bioreactor (AnMBR), anaerobic fluidized bed reactor (AFB), upflow anaerobic sludge blanket (UASB), anaerobic sequencing batch reactor (ASBR), microbial electrolysis cell (MEC), and microbial fuel cell (MFC). Phototrophic technologies included were the high rate algal pond (HRAP), photobioreactor (PBR), stirred tank reactor, waste stabilization pond (WSP), and algal turf scrubber (ATS). Average energy recovery efficiencies for anaerobic technologies ranged from 1.6% (MFC) to 47.5% (ABR). When including typical percent chemical oxygen demand (COD) removals by each technology, this range would equate to roughly 40-1200 kJ per capita per day or 110-3300 kJ m(-3) of treated wastewater. The average bioenergy feedstock production by phototrophic technologies ranged from 1200-4700 kJ per capita per day or 3400-13 000 kJ m(-3) (exceeding anaerobic technologies and, at times, the energetic content of the influent organic carbon), with usable energy production dependent upon downstream conversion to fuels. Energy consumption analysis showed that energy positive anaerobic wastewater treatment by emerging technologies would require significant reductions of parasitic losses from mechanical mixing and gas sparging. Technology targets and critical barriers for energy-producing technologies are identified, and the role of integrated anaerobic and phototrophic bioprocesses in energy positive wastewater management is discussed.

Sunlight mediated inactivation mechanisms of Enterococcus faecalis and Escherichia coli in clear water versus waste stabilization pond water

Escherichia coli and enterococci have been previously reported to differ in the mechanisms and conditions that affect their sunlight-mediated inactivation in waste stabilization ponds. This study was undertaken to further characterize these mechanisms, using simulated sunlight and single strains of laboratory-grown E. coli and Enterococcus faecalis, with a focus on characterizing the contribution of exogenous reactive oxygen species to the inactivation process. We found that direct damage by UVB light (280-320 nm) was not a significant inactivation mechanism for either organism. E. coli inactivation was strongly dependent on dissolved oxygen concentrations and the presence of UVB wavelengths but E. coli were not susceptible to inactivation by exogenous sensitizers present in waste stabilization pond water. In contrast, E. faecalis inactivation in pond water occurred primarily through exogenous mechanisms, with strong evidence that singlet oxygen is an important transient reactive species. The exogenous mechanism could utilize wavelengths into the visible spectrum and sensitizers were mainly colloidal, distributed between 0.2 and ∼1 μm in size. Singlet oxygen is likely an important endogenous species in both E. faecalis and E. coli inactivation due to sunlight. Although the two organisms had similar inactivation rates in buffered, clear water, the inactivation rate of E. faecalis was 7 times greater than that of E. coli in air-saturated pond water at circumneutral pH due to its susceptibility to exogenous sensitizers and longer wavelengths.