Efficiency of natural systems for removal of bacteria and pathogenic parasites from wastewater

Origin, fluxes, and reservoirs of Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa in aquatic ecosystems of a French floodplain

The release and spread of opportunistic pathogens - some of which are resistant to antibiotics - in the environment is a major public health challenge worldwide. In this study, we found evidence of the origin of such microorganisms and characterized their dispersal and survival in floodplain ecosystems to understand their fate in the environment. We determined the concentrations of Escherichia coli, extended-spectrum β-lactamases (ESBL)-producing E. coli, Klebsiella pneumoniae, ESBL-producing K. pneumoniae, and Pseudomonas aeruginosa in a floodplain of Eastern France using a culture-based method. Furthermore, we assessed the population structure of E. coli isolates by quadruplex PCR, their plasmid replicon content by PCR-based replicon typing, and the nature of their bla_ESBL genes by PCR and sequencing. The main aquatic ecosystems of the floodplain (river, tributaries, riverine wetlands, and groundwater) were sampled monthly over a one-year cycle. The majority of E. coli isolates retrieved in the studied floodplain were likely of human origin. Moreover, contamination of floodplain aquatic ecosystems by opportunistic pathogens mainly resulted from hydrological fluxes during high-flow periods, suggesting that dispersal and dilution predominated. During low-flow periods, E. coli may be able to survive for several months in isolated ecosystems in which it may find favourable conditions to thrive. The most nutrient-rich and isolated wetlands are consequently potential pathogen reservoirs. The production of ESBL was not a disadvantage for E. coli in low-anthropized floodplain ecosystems.

Insights into the microbial community of treated wastewater, its year-round variability and impact on the receiver, using cultivation, microscopy and amplicon-based methods

Apart from chemical constituents, wastewater treatment plant (WWTP) effluents also release microorganisms that can be important to the receiving water bodies either from a sanitary point of view, or taking to the account the biogeochemical potential of the recipients. However, little is known about the treated wastewater microbial community, its composition, seasonal changes, functions and fate in the waters of the receiver. Thus, this study presents a synergistic approach coupling new and traditional methods: analytical chemistry, classical microbiology (cultivation- and microscopy-based methods), as well as Next Generation Sequencing and a quantitative real-time polymerase chain reaction (qPCR). The results show that in terms of bacterial community composition, treated wastewater differed from the environmental samples, irrespectively if they were related or unrelated to the WWTP effluent discharge. The canonical correspondence analysis (CCA) taking into account chemical parameters and taxonomical biodiversity indirectly confirmed the seasonal deterioration of the treated wastewater quality as a result of temperature-driven change of activated sludge community structure and biomass washout (observed also by DAPI staining). Despite seasonal fluctuations of total suspended solids and inter-related parameters (such as COD, BOD, TN, TP), the treated wastewater quality remained within current discharge limits. It was due to treatment processes intensively adjusted by WWTP operators, particularly those necessary to maintain an appropriate rate of autotrophic processes of nitrification and to support biological phosphorus removal. This can explain the observed microbiome composition similarity among WWTP effluents at high taxonomic levels. Obtained data also suggest that besides wastewater treatment efficiency, WWTP effluents are still sources of both human-related microorganisms as well as bacteria equipped in genes involved in N-cycling. Their potential of participation in nutrients cycling in the receivers is widely unknown and require critical attention and better understanding.

Effect of Wastewater Treatment on Bacterial Community, Antibiotic-Resistant Bacteria and Endoparasites

Wastewater and wastewater treatment plants serve as urban reservoirs of pathogenic microorganisms. Wastewaters frequently contain bacteria, antibiotic-resistant bacteria, and developmental stages of parasites with significant zoonotic potential. Five wastewater treatment plants in the central part of Slovakia were investigated to determine the effect of treatment on bacterial community, antibiotic-resistant bacteria, and the occurrence of helminth eggs. Although all monitored chemical factors (chemical oxygen demand, biochemical oxygen demand, N-NH4, total nitrogen, and total phosphorus) in the effluent were in line with the legislative standards for discharge into public waterways, the results of minimal inhibitory concentrations show that reclaimed water harbors E. coli resistant to several commonly used antibiotics (ampicillin, piperacillin, and tazobactam, combine ampicillin and sulbactam, cefotaxime, tetracycline). The presence of endoparasite developmental stages in wastewater and sludge (Ascaris spp., Hymenolepis nana, eggs from the Ancylostomatidae family, Giardia duodenalis) indicates potential health risks for humans and workers at these sites. Treatment such as composting before applying sludge to land is necessary to reduce human pathogens.

COVID-19 and waste management in Indian scenario: challenges and possible solutions

The outbreak of COVID-19 pandemic has created havoc all across the globe causing exponential casualties and tremendous health and economic loss. With increasing COVID-19 cases, the amount of biomedical waste has increased manifolds making more people vulnerable to the pandemic. The developing and underdeveloped countries are already facing the challenges of waste management, and the waste generated during the pandemic scenario has added to the already existing challenges. The improper waste management practices need to be corrected; otherwise, the world will be facing a new disaster that could be termed as 'waste disaster'. The increase in COVID-19-associated waste (CAW) quantity and their availability in the environment will result in their easy approach to other organisms, which will possibly increase the potential risk of food chain contamination. Some of the countries have already started to make backup plans and are struggling to overcome the 'waste disaster'. In light of the limited knowledge available on the mutational properties and possible hosts of this newly emerged COVID-19, there is a great demand to have an efficient strategy to prevent the environment from further contamination in India. The necessity of the prevailing time is to create a more efficient, automatic, mechanized, and well-modified waste management system for handling the present situation and delaying the projected waste disaster in the near future in the era of COVID-19. The article aims to address the issues that originated from waste discharges, their potential sources along with possible sustainable solutions.

Indexes for the assessment of bacterial pollution in bathing waters from point sources: The northern Adriatic Sea CADEAU service

This paper presents a novel set of water quality indexes to identify the area potentially affected by point sources of bacterial pollution in coastal bathing waters. The indexes, developed in the framework of the CADEAU service, are evaluated on the results of a modelling system based on the integration of a high-resolution ocean model, remote sensing observations and in situ monitoring data for the northern Adriatic Sea. In particular, the system is a downscaling of the Mediterranean Copernicus Marine Environment Monitoring Service and exploits data produced within the Bathing Waters Directive, the Water Framework Directive and the Urban Waste Water Treatment Directive to create added value products. The aim of the proposed indexes is to support the identification of areas of influence for bathing waters by identifying the potential threat from point sources of bacterial pollution, both in standard conditions and peculiar events such as a total bypass of wastewater treatment plants. The results for the Chioggia Municipality case study show the potential of the indexes to significantly improve the geographical identification and quantitative evaluation of the impacts of bacterial pollution sources on bathing waters, facilitating the design of mitigation measures. The proposed methodology represents a new management approach to support local authorities in defining the area of influence within the water bathing profile through the proper characterization of the point sources of bacterial pollution.

Laboratory-scale waste stabilisation pond development

The present study describes the development of a laboratory-scale waste stabilisation pond (WSP) system, undertaken in order to investigate the effects of hydraulic, physicochemical, microbial and physical parameters on wastewater treatment. Previous studies have focused predominantly on hydraulic characteristics. This system was engineered at a scale much smaller than had previously been seen in the literature. The scale of the model used here allows for improved optimisation at a shorter time scale that would be seen for larger pilot-scale systems. Additionally, with the addition of viruses, a smaller scale model allows for more control over viral concentration used. Once constructed, the system was dosed with wastewater from a wastewater treatment plant and both the influent and effluent were monitored using common testing methods as well as direct viral analysis. Successful wastewater treatment was seen in terms of reduction of indicator bacteria and virus, as determined by culture-based methods. This treatment and the associated stabilisation of physicochemical parameters such as dissolved oxygen and pH, indicates the successful development of a microbial community within the laboratory-scale WSP.

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.

Very low prevalence of Opisthorchis viverrini s.l. cercariae in Bithynia siamensis siamensis snails from the canal network system in the Bangkok Metropolitan Region, Thailand

The liver fluke Opisthorchis viverrini s.l. is associated with a long-term public health problem in Thailand. However, O. viverrini s.l. infection in Bithynia snails in the canal network system (CNS) in the Bangkok Metropolitan Region (BMR) has never been assessed. This study aimed to investigate the occurrence of B. siamensis siamensis and the prevalence of O. viverrini s.l. infection in this snail in the CNS in BMR along with morphological examination and molecular analyses on O. viverrini s.l. cercariae. The snails were randomly sampled from the CNS in all BMR areas from January 2018 to July 2019. Snail specimens were identified and examined for digenean infection by shedding and dissection. The cercariae were identified using morphology and molecular methods, including PCR with a species-specific primer and a Bayesian phylogenetic analysis of ITS2 sequences. Bithynia siamensis siamensis was found in almost all sampling localities, with different quantities and detected frequencies. From a total of 7473 B. s. siamensis specimens, O. viverrini s.l. infections were detected in the Northern Bangkok, Muang Nakhon Pathom, Krathum Baen, and Lam Luk Ka areas with an overall prevalence of 0.05% (4/7473) and prevalence of 0.22% (1/455), 0.21% (1/469), 0.40% (1/253), and 0.16% (1/614) in individual localities with positive snails, respectively. This study is the first investigation of digenean infection in the canal network system-type habitat in Thailand and revealed extremely low O. viverrini s.l. prevalence.

Screening Level Risk Assessment (SLRA) of human health risks from faecal pathogens associated with a Natural Swimming Pond (NSP)

Natural swimming ponds (NSPs) are artificially created bodies of water intended for human recreation, characterised by the substitution of chemical disinfection with natural biological processes for water purification. NSPs are growing in popularity, however little is known regarding the public health risks. A screening level risk assessment was undertaken as an initial step in assessing the first Canadian public NSP located in Edmonton, Alberta. Risk of enteric pathogens originating from pool bathers was assessed under normal conditions and following accidental faecal release events. The performance of the natural treatment train for health protection was quantified with and without the addition of UV disinfection of naturally-treated water, and compared to the US EPA benchmark to provide a reference point to consider acceptability. Estimated levels of pathogen contamination of the pond were dependant upon the discrete number of shedders present, which in turn depended upon the prevalence of infection in the population. Overall performance of the natural disinfection system was dependant upon the filtration rate of the natural treatment system or turnover time. Addition of UV disinfection reduced the uncertainty around the removal efficacy, and mitigated the impact of larger shedding events, however the impact of UV disinfection on the natural treatment biome is unknown. Further information is needed on the performance of natural barriers for pathogen removal, and therefore challenge studies are recommended. Given the identified risks, the pool is posted that there is risk from accidental faecal releases, as in any natural water body with swimmers. Screening level risk assessment was a valuable first step in understanding the processes driving the system and in identifying important data gaps.

Potential of constructed wetland treatment systems for agricultural wastewater reuse under the EU framework

One of the solutions for the problems regarding increasing water scarcity and pollution of water resources can be wastewater reuse. Constructed wetlands (CWs) are a sustainable and cost-effective technology for wastewater treatment. If they are able to produce effluent of a needed quality, they can be a valuable addition for wastewater reuse schemes. This review studied 39 treatment systems based on CWs, and it assessed their characteristics and performance on pollutant removal. Moreover, their potential to reach the new European Union standards for agricultural wastewater reuse was evaluated. The results showed that the combination of CWs with additional technologies (e.g. UV treatment, anaerobic reactors) can further increase their performance and provide better removal efficiencies in comparison with conventional horizontal and vertical subsurface flow CWs. Particularly, hybrid systems showed a better removal of organic matter and bacterial indicators than single-stage CWs. For most of the systems considered, the concentrations of biochemical oxygen demand and total suspended solids in treated effluent were below the limits for agricultural reuse. However, that was often not the case with Escherichia coli and therefore it is recommended to add a disinfection unit to the systems in order to achieve the levels required in the case of agricultural reuse.

Fecal indicator bacteria, direct pathogen detection, and microbial community analysis provide different microbiological water quality assessment of a tropical urban marine estuary

Urban marine estuaries are often impacted by microbiological contamination that impairs use and affects human health acutely, while limited is known about microbiological water quality in urban marine estuaries in the absence of reported sewage spills. This study used a tropical urban marine estuary, the Ala Wai Canal in Honolulu, Hawaii, as the model system to compare fecal indicator bacteria (FIB) concentrations, bacterial pathogen profiles, and microbial community structures. The FIB Escherichia coli exhibited higher geometric mean 132 CFU/100mL (n=28) than those of enterococci (18 CFU/100mL) and Clostridium perfringens (21 CFU/100mL). Amongst the four pathogens targeted by cultivation methods (Salmonella, Campylobacter, Listeria monocytogenes and Vibrio parahaemolyticus), only was V. parahaemolyticus detected and was detected at high frequency. Microbial community analysis through 16S rRNA gene amplicon sequencing also indicated the high prevalence of Vibrio in the water. The pathogen detection patterns and microbial community structure showed no significant correlation with FIB concentration profiles. Together, the results highlight the limitation of using traditional FIB in assessing water microbiological quality in the tropical urban marine estuary environment, indicating the need for more comprehensive microbial risk assessment approaches such as direct detection of pathogens.

Novel wastewater surveillance strategy for early detection of coronavirus disease 2019 hotspots

The novel coronavirus disease 2019, a pandemic of global concern, caused by the novel severe acute respiratory syndrome coronavirus 2 has severely revealed the need for public monitoring and efficient screening techniques. Despite the various advancements made in the medical and research field, containment of this virus has proven to be difficult on several levels. As such, it is a necessary requirement to identify possible hotspots in the early stages of any disease. Based on previous studies carried out on coronaviruses, there is a high likelihood that severe acute respiratory syndrome coronavirus 2 may also survive in wastewater. Hence, we propose the use of nanofiber filters as a wastewater pretreatment routine and upgradation of existing wastewater evaluation and treatment systems to serve as a beneficial surveillance tool.

Seeking the reuse of effluents and sludge from conventional wastewater treatment plants: Analysis of the presence of intestinal protozoa and nematode eggs

Some of the microorganisms present in urban wastewater, which include intestinal protozoa and nematodes, can be pathogenic. Their (oo)cyst and egg transmissible stages are very resistant to environmental stresses and disinfectants and they are therefore difficult to remove. Thus, they can constitute a health risk if water or sludge obtained in the purification of wastewater is reused for agricultural purposes. In this context, the presence of intestinal protozoa and nematodes were studied in influents, effluents and sludge from five wastewater treatment plants (WWTPs) in the north of Spain by optical microscopy and PCR techniques. The removal efficiency of different wastewater treatments was also compared. The presence of protozoa has increased among the population discharging waste to WWTPs in recent years. Cryptosporidium spp., Giardia duodenalis, Entamoeba spp. and nematodes were detected in all of the WWTPs. Indeed, this is the first report of Entamoeba histolytica and Entamoeba moshkovskii in Spanish WWTPs. The water treatments studied showed different removal efficiencies for each species of intestinal protozoa, with the aerated lagoons providing the best results. (Oo)cysts were also detected in sludge even after aerobic digestion and dehydration. To avoid risks, (oo)cyst viability should be analysed whenever the sludge is to be used as a fertilizer. This study reinforces the necessity of establishing legal limits on the presence of protozoa in WWTP effluents and sludges, especially if reuse is planned. Further studies are necessary for a better understanding of the presence and behaviour of intestinal parasites.

Review of Dry and Wet Decentralized Sanitation Technologies for Rural Areas: Applicability, Challenges and Opportunities

This paper reviews decentralized sanitation technologies comparing dry and wet solutions currently available, discussing their operational requirements, applicability, effluent output quality, efficiencies, environmental impacts, costs, challenges, as well as their advantages and implementation difficulties. Sanitation technologies vary from conventional centralized systems, typically used on urban areas, to decentralized systems, more common in sparse dwellings and small communities of rural areas. Compared with centralized sanitation, decentralized sanitation is being progressively considered as more sustainable solution. Most do not require energy or expensive or sophisticated operation, being easy to adapt to different geographic contexts. A general lack of consistent regulatory control over most dry rudimentary systems and primary treatment systems may compromise water quality and human health. In the future, a mix of new policies and accurate accounting of the location, performance, and degree of failure of such systems should be performed. However, forcing users and communities to face the capital, operational, or repairing costs may be challenging. Since many of the discussed technologies may be important sources of contamination with nutrients, pathogens and toxic chemicals, new opportunities are still open, which include the conversion of dry rudimentary systems into dry controlled systems.

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.

A review on microbial contaminants in stormwater runoff and outfalls: Potential health risks and mitigation strategies

Demands on global water supplies are increasing in response to the need to provide more food, water, and energy for a rapidly growing population. These water stressors are exacerbated by climate change, as well as the growth and urbanisation of industry and commerce. Consequently, urban water authorities around the globe are exploring alternative water sources to meet ever-increasing demands. These alternative sources are primarily treated sewage, stormwater, and groundwater. Stormwater including roof-harvested rainwater has been considered as an alternative water source for both potable and non-potable uses. One of the most significant issues concerning alternative water reuse is the public health risk associated with chemical and microbial contaminants. Several studies to date have quantified fecal indicators and pathogens in stormwater. Microbial source tracking (MST) approaches have also been used to determine the sources of fecal contamination in stormwater and receiving waters. This review paper summarizes occurrence and concentrations of fecal indicators, pathogens, and MST marker genes in urban stormwater. A section of the review highlights the removal of fecal indicators and pathogens through water sensitive urban design (WSUD) or Best Management Practices (BMPs). We also discuss approaches for assessing and mitigating health risks associated with stormwater, including a summary of existing quantitative microbial risk assessment (QMRA) models for potable and non-potable reuse of stormwater. Finally, the most critical research gaps are identified for formulating risk management strategies.

Performance of a small-scale wastewater treatment plant for removal of pathogenic protozoa (oo)cysts and indicator microorganisms

The protozoa Giardia and Cryptosporidium are associated with numerous outbreaks of waterborne diseases worldwide. This study aimed to evaluate the concentration of Giardia spp. cysts, Cryptosporidium spp. oocysts, total coliforms, Escherichia coli and Clostridium perfringens in raw wastewater and their removals at UASB reactor, activated sludge system (operated conventionally and extended aeration) and slow sand filtration. Giardia spp. cysts were present in 100% and Cryptosporidium spp. oocysts in 31.4% of the analysed wastewater samples. The UASB reactor followed by activated sludge system obtained approximately 2.0 log of removal for total coliforms and E. coli, whereas for C. perfringens and Giardia spp. cysts, it obtained 1 log. There was a high percentage of (oo)cysts still viable after secondary treatment, therefore, the risk of contamination of water courses and, consequently, for public health is considerable. However, after tertiary filtration, no (oo)cysts were found in any of the filtered effluent samples, being a good option for future reuse. Seasonal variations did not affect the concentrations and removals of microorganisms observed. Lack of correlations of concentrations of indicator microorganisms and (oo)cysts raise caveats and doubts regarding the true microbiological quality when using only indicator microorganisms.

Constructed wetland for wastewater reuse: Role and efficiency in removing enteric pathogens

Water stress has become a perennial concern in most of the developing countries due to rapid urbanization and population growth. As the growing population requires more fresh water and better ways for wastewater disposal, the demand for wastewater reclamation has increased drastically in recent years. Wastewater, either raw or treated, is being widely used for agricultural irrigation in developing countries, which cause a serious threat to human health mainly because of its pathogenic content. One of the alternative methods to treat wastewater and make it reusable for agricultural irrigation is to implement constructed wetland (CW); a sustainable and cost-effective technology that is applicable for the elimination of both pollutants and pathogens from wastewater. Despite its wide application, the role of macrophytes that form an integral part of CW and specific mechanisms involved in pathogen removal by them is still barely understood due to complexities involved and influencing factors. This has, therefore, attracted various scientific studies to reveal further functional mechanisms involved in vegetated CW to increase its proficiencies. This review paper illustrates the comparative studies of different CW and their pathogen removal efficiencies with major emphasis on macrophytes involved and factors influencing related mechanism. Further, the paper also covers detailed information on the enteric pathogens present in wastewater and the associated health risks involved in its reuse. The ultimate objective is to further clarify the role of CW in enteric pathogen removal and its efficiency for wastewater purification in perspective with safe reuse in agriculture.

Presence of bacteria and bacteriophages in full-scale trickling filters and an aerated constructed wetland

Aerated Constructed Wetlands are a state-of-the-art design that provides a different physical and chemical environment (compared to traditional passive wetland designs) for the wastewater treatment processes and, thus, may have different pathogen removal characteristics. In order to establish the fate of bacterial and viral indicators, a field study was carried out at a Sewage Treatment Works (STW) in the UK (serving 20,000 pe). The STW consists of primary and secondary sedimentation tanks and trickling filters (TF) as the biological stage. A large (1,160 m²) pilot aerated Vertical Flow Constructed Wetland (AVFCW) was constructed at the STW as tertiary stage receiving ¼ of the total flow rate, i.e., 1250 m³/day. Effluent quality of the AVFCW complied with national and international standards for environmental discharge and reuse. For the first time, two sets of bacterial (Faecal coliforms, E.coli and intestinal enterococci) and viral indicators (Somatic coliphages, F-RNA specific bacteriophages and human-specific B. fragilis GB124 phages) were simultaneously investigated in an AVFCW and TF. High elimination rates were detected (up to 3.7 and 2.2 log reduction for bacteria indicators and phages, respectively) and strong correlations between the two sets were found. The superior efficiency of the aerated Constructed Wetlands in microbiological contamination removal compared to passive wetland systems was established for the first time, which may have implications for process selection for wastewater reuse. This field study therefore provides new evidence on the fate of bacteriophages and a first indication of their potential use for performance evaluation in TF and aerated Constructed Wetlands. It also demonstrates that the combination of TF with aerated constructed wetlands could be a novel and effective treatment scheme for new STW or for the upgrade of existing STW.

Safe surface concept in vertical flow constructed wetland design to mitigate infection hazard

Decentralized wastewater management based on vertical flow constructed wetlands (VFCWs) can be an effective solution for minimizing sanitation problems also in urban landscapes, especially when considering rapidly expanding cities in developing countries. Yet, the mass implementation of VFCWs in urbanized areas first needs improvement of a few design drawbacks - among them, the control of infection hazard is of primary importance. Therefore, in this study, the possibility of mitigation of the VFCW-derived infection hazard was assessed, through analysis of bacteriostatic properties of top filtration layer materials, according to clinical experiences based on "safe" antimicrobial surfaces. The experiment was carried out on a daily operating VFCW. Coliform bacteria survival rates were measured for known VFCW construction materials such as Pinus bark, gravel, slag, charcoal and LECA. The calculated die-off rates expressed as 12-h first-order inactivation coefficients ranged between 6.91 h^-1 (slag/summer) and 0.58 h^-1 (Pinus bark/autumn). The obtained die-off curves showed charcoal, Pinus bark and LECA to have little bacteriostatic properties - even occasionally providing conditions promoting the growth of the coliform population. Meanwhile, slag and gravel were strictly inhibiting bacteria growth, reducing the population up to 99% within the first 3 h of contact time. The research showed that it is possible to significantly mitigate the infection hazard of VFCW by means of proper top-layer substrate material, similar or equal to slag or gravel.

Biotechnological approach of greywater treatment and reuse for landscape irrigation in small communities

A level of water quality intended for human consumption does not seem necessary for domestic uses such as irrigation of green spaces. Alternative water supplies like the use of greywater (GW) can thus be considered. However, GW contains pathogenic microorganisms and organic compounds which can cause environmental and health risks. As the risks related to recycling are unknown, GW treatment is necessary before reusing. To describe the risks related to GW reuses, the scientific approach performed in this study was to characterize domestic GW in order to select an appropriate treatment. The biotechnology chosen is a Horizontal sub-surface flow constructed wetland reactor. In order to minimize health risks, an optimization step based on UV disinfection was performed. The treatment performances were then determined. The treated GW produced in this study reached the threshold values expected by the Moroccan regulation for irrigation of green spaces with treated wastewater. Indeed, the COD and the TSS obtained in treated GW without disinfection are respectively 16.6 mg O₂ L⁻¹ and 0.40 mg L⁻¹. The horizontal sub-surface flow constructed wetland (HSSF CW) reactor has been used to treat 1.2 m³/d of GW for 100 days. Three lawn plots have been irrigated respectively with raw GW, treated GW and tap water as a reference. Contrary to the lawn plot irrigated with raw GW, the risk analysis performed in this study has shown no significant difference between the law plots irrigated with treated GW combined with UV disinfection and the one irrigated with tap water. Overall, UV disinfection treated GW produced from the HSSF CW reactor developed in this experiment is thought to be an effective and feasible alternative for agricultural reuse.

Cryptosporidium and Giardia in Wastewater and Surface Water Environments

and spp. are significant contributors to the global waterborne disease burden. Waterways used as sources of drinking water and for recreational activity can become contaminated through the introduction of fecal materials derived from humans and animals. Multiple studies have reported the occurence or concentrations of these pathogens in the environment. However, this information has not been comprehensively reviewed. Quantitative microbial risk assessment (QMRA) for and can be beneficial, but it often relies on the concentrations in environmental sources reported from the literature. A thorough literature review was conducted to develop an inventory of reported and concentrations in wastewater and surface water available in the literature. This information can be used to develop QMRA inputs. and (oo)cyst concentrations in untreated wastewater were up to 60,000 oocysts L and 100,000 cysts L, respectively. The maximum reported concentrations for and in surface water were 8400 oocysts L and 1000 cysts L, respectively. A summary of the factors for interpretation of concentration information including common quantification methods, survival and persistence, biofilm interactions, genotyping, and treatment removal is provided in this review. This information can help in identifying assumptions implicit in various QMRA parameters, thus providing the context and rationale to guide model formulation and application. Additionally, it can provide valuable information for water quality practitioners striving to meet the recreational water quality or treatment criteria. The goal is for the information provided in the current review to aid in developing source water protection and monitoring strategies that will minimize public health risks.

Soil-transmitted helminth infections associated with wastewater and sludge reuse: a review of current evidence

OBJECTIVE

To review current evidence on infections related to the concentration of soil-transmitted helminth (STH) eggs in wastewater, sludge and vegetables irrigated with wastewater or grown on sludge-amended soils.

METHOD

Search of Web of Science, Science Direct, PubMed and Google Scholar databases for publications reporting on STH egg concentration in wastewater, sludge and vegetables and for epidemiological studies on wastewater/sludge reuse and STH infections.

RESULTS

STH egg concentrations were variable but high in wastewater and sludge especially in developing countries. They ranged from 6 to 16 000 eggs/L in wastewater and from 0 to 23 000 eggs/g in sludge and far exceed limits set in the WHO guideline for wastewater/sludge reuse. Numbers of STH eggs on vegetables ranged from 0 to 100 eggs/g. The concentration of STH eggs in wastewater, sludge and vegetables therefore relates to risks of infection through different exposure routes.

CONCLUSION

Epidemiological evidence reveals an increased prevalence of STH infections associated with direct exposure to wastewater or sludge (farmers) and consumption of vegetables grown on soil treated with it. This calls for increased efforts to reduce the adverse health impact of wastewater and sludge reuse in line with the WHO multi-barrier approach.

Infectious helminth ova in wastewater and sludge: A review on public health issues and current quantification practices

Raw and partially treated wastewater has been widely used to maintain the global water demand. Presence of viable helminth ova and larvae in the wastewater raised significant public health concern especially when used for agriculture and aquaculture. Depending on the prevalence of helminth infections in communities, up to 1.0 × 10³ ova/larvae can be presented per litre of wastewater and 4 gm (dry weight) of sludge. Multi-barrier approaches including pathogen reduction, risk assessment, and exposure reduction have been suggested by health regulators to minimise the potential health risk. However, with a lack of a sensitive and specific method for the quantitative detection of viable helminth ova from wastewater, an accurate health risk assessment is difficult to achieve. As a result, helminth infections are difficult to control from the communities despite two decades of global effort (mass drug administration). Molecular methods can be more sensitive and specific than currently adapted culture-based and vital stain methods. The molecular methods, however, required more and thorough investigation for its ability with accurate quantification of viable helminth ova/larvae from wastewater and sludge samples. Understanding different cell stages and corresponding gene copy numbers is pivotal for accurate quantification of helminth ova/larvae in wastewater samples. Identifying specific genetic markers including protein, lipid, and metabolites using multiomics approach could be utilized for cheap, rapid, sensitive, specific and point of care detection tools for helminth ova and larva in the wastewater.

A mechanistic review on vermifiltration of wastewater: Design, operation and performance

With global population explosion, the available water resources are slowly being polluted due to the excessive human interference. To encounter this, it is the need of this hour to find out sustainable pollution remediating technologies to meet the stringent discharge standards for domestic as well as industrial wastewaters. In addition, those techniques should have the capabilities for effective implementation even in developing countries. Based on the available literatures, one such technique, named vermifilter, has been identified which takes care of almost all the sustainable and economical criteria for its effective implementation even in developing countries. The aim of this meta-analysis is to provide a comprehensive review on assessment mechanisms involved, factors affecting the process and performance of vermifiltration under different scenarios. The present review envisages the current state of the knowledge regarding physical, chemical and biological aspects related to the treatment mechanisms and effective functioning of earthworms. This review has also proposed several suggestive plans on its application at any proposed site.

Bacteriophages as indicators of faecal pollution and enteric virus removal

Bacteriophages are an attractive alternative to faecal indicator bacteria (FIB), particularly as surrogates of enteric virus fate and transport, due to their closer morphological and biological properties. Based on a review of published data, we summarize densities of coliphages (F+ and somatic), Bacteroides spp. and enterococci bacteriophages (phages) in individual human waste, raw wastewater, ambient fresh and marine waters and removal through wastewater treatment processes utilizing traditional treatments. We also provide comparisons with FIB and enteric viruses whenever possible. Lastly, we examine fate and transport characteristics in the aquatic environment and provide an overview of the environmental factors affecting their survival. In summary, concentrations of bacteriophages in various sources were consistently lower than FIB, but more reflective of infectious enteric virus levels. Overall, our investigation indicates that bacteriophages may be adequate viral surrogates, especially in built systems, such as wastewater treatment plants.

SIGNIFICANCE AND IMPACT OF THE STUDY

Bacteriophage are alternative fecal indicators that may be better surrogates for viral pathogens than fecal indicator bacteria (FIB). This report offers a summary of the existing literature concerning the utility of bacteriophage as indicators of viral presence (fecal sources and surface waters) and persistence (in built infrastructure and aquatic environments). Our findings indicate that bacteriophage levels in all matrices examined are consistently lower than FIB, but similar to viral pathogens. Furthermore, in built infrastructure (e.g. wastewater treatment systems) bacteriophage closely mimic viral pathogen persistence suggesting they may be adequate sentinels of enteric virus removal.

Detection and quantification of soil-transmitted helminths in environmental samples: A review of current state-of-the-art and future perspectives

It is estimated that over a billion people are infected with soil-transmitted helminths (STHs) globally with majority occurring in tropical and subtropical regions of the world. The roundworm (Ascaris lumbricoides), whipworm (Trichuris trichiura), and hookworms (Ancylostoma duodenale and Necator americanus) are the main species infecting people. These infections are mostly gained through exposure to faecally contaminated water, soil or contaminated food and with an increase in the risk of infections due to wastewater and sludge reuse in agriculture. Different methods have been developed for the detection and quantification of STHs eggs in environmental samples. However, there is a lack of a universally accepted technique which creates a challenge for comparative assessments of helminths egg concentrations both in different samples matrices as well as between locations. This review presents a comparison of reported methodologies for the detection of STHs eggs, an assessment of the relative performance of available detection methods and a discussion of new emerging techniques that could be applied for detection and quantification. It is based on a literature search using PubMed and Science Direct considering all geographical locations. Original research articles were selected based on their methodology and results sections. Methods reported in these articles were grouped into conventional, molecular and emerging techniques, the main steps in each method were then compared and discussed. The inclusion of a dissociation step aimed at detaching helminth eggs from particulate matter was found to improve the recovery of eggs. Additionally the selection and application of flotation solutions that take into account the relative densities of the eggs of different species of STHs also results in higher egg recovery. Generally the use of conventional methods was shown to be laborious and time consuming and prone to human error. The alternate use of nucleic acid-based techniques has improved the sensitivity of detection and made species specific identification possible. However, these nucleic acid based methods are expensive and less suitable in regions with limited resources and skill. The loop mediated isothermal amplification method shows promise for application in these settings due to its simplicity and use of basic equipment. In addition, the development of imaging soft-ware for the detection and quantification of STHs shows promise to further reduce human error associated with the analysis of environmental samples. It may be concluded that there is a need to comparatively assess the performance of different methods to determine their applicability in different settings as well as for use with different sample matrices (wastewater, sludge, compost, soil, vegetables etc.).

Effects of different substrates in the mitigation of algae-induced high pH wastewaters in a pilot-scale free water surface wetland system

Waste stabilization ponds (WSPs), as part of municipal wastewater treatment strategies, can exhibit variability in performance due to climatic conditions. Under elevated temperature and strong solar radiation, algal blooms and subsequent high pH effluents have often been observed. In this study, four substrates (gravel, peat, organic mulch, and topsoil) were evaluated for their ability to attenuate high pH effluents from a WSP. Synthetic wastewater with pH > 9.5, and low organic and nutrient loadings, was used to mimic algal-induced high pH effluents in 72 L rectangular bench-scale superficial constructed wetland configuration reactors. Peat exhibited the highest attenuation ability, where the effluent pH decreased substantially from 10.3 to 7.7, primarily due to its high organic contents. Peat also removed 53.7% of the influent total phosphorus, which could effectively limit algal growth. No statistically significant differences were discovered among gravel, topsoil, and organic mulch in terms of pH attenuation. Topsoil and organic mulch both have a relatively high alkalinity, making them ideal to maintain consistent pH levels. However, naturally high chemical oxygen demand levels in organic mulch raised concerns in the leaching of these compounds into the treated wastewater, making it less appealing for systems with low organic loading.

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.

Pathogens and fecal indicators in waste stabilization pond systems with direct reuse for irrigation: Fate and transport in water, soil and crops

Wastewater use for irrigation is expanding globally, and information about the fate and transport of pathogens in wastewater systems is needed to complete microbial risk assessments and develop policies to protect public health. The lack of maintenance for wastewater treatment facilities in low-income areas and developing countries results in sludge accumulation and compromised performance over time, creating uncertainty about the contamination of soil and crops. The fate and transport of pathogens and fecal indicators was evaluated in waste stabilization ponds with direct reuse for irrigation, using two systems in Bolivia as case studies. Results were compared with models from the literature that have been recommended for design. The removal of Escherichia coli in both systems was adequately predicted by a previously-published dispersed flow model, despite more than 10years of sludge accumulation. However, a design equation for helminth egg removal overestimated the observed removal, suggesting that this equation may not be appropriate for systems with accumulated sludge. To assess the contamination of soil and crops, ratios were calculated of the pathogen and fecal indicator concentrations in soil or on crops to their respective concentrations in irrigation water (termed soil-water and crop-water ratios). Ratios were similar within each group of microorganisms but differed between microorganism groups, and were generally below 0.1mLg(-1) for coliphage, between 1 and 100mLg(-1) for Giardia and Cryptosporidium, and between 100 and 1000mLg(-1) for helminth eggs. This information can be used for microbial risk assessments to develop safe water reuse policies in support of the United Nations' 2030 Sustainable Development Agenda.

Removal of Cryptosporidium by wastewater treatment processes: a review

Cryptosporidium is a protozoan parasite that infects humans and various animal species. The environmental stability and the low infectious dose of Cryptosporidium facilitate its transmission by water and food. Discharge of untreated wastewater may result in waterborne or foodborne Cryptosporidium outbreaks, therefore a suitable treatment may prevent its dissemination. Most studies on the prevalence of Cryptosporidium oocysts in wastewater have reported a concentration range between 10 and 200 oocysts/L and a prevalence of 6 to 100%. Activated sludge has been found to be ineffective for the removal of Cryptosporidium oocysts. Stabilization ponds and constructed wetlands are efficient for the reduction of Cryptosporidium from wastewater, especially when the retention time is longer than 20 days at suitable sunlight and temperature. High rate filtration and chlorine disinfection are inefficient for the reduction of Cryptosporidium from effluents, whereas ultrafiltration and UV irradiation were found to be very efficient for the reduction of Cryptosporidium oocysts. Adequate tertiary treatment may result in high quality effluent with low risk of Cryptosporidium for unrestricted irrigation and other non-potable applications.

Enteric and indicator virus removal by surface flow wetlands

We investigated the occurrence and attenuation of several human enteric viruses (i.e., norovirus, adenovirus, Aichi virus 1, polyomaviruses, and enterovirus) as well as a plant virus, pepper mild mottle virus (PMMoV), at two surface flow wetlands in Arizona. The retention time in one of the wetlands was seven days, whereas in the other wetland it could not be defined. Water samples were collected at the inlet and outlet from the wetlands over nine months, and concentration of viral genomes was determined by quantitative polymerase chain reaction (qPCR). Of the human enteric viruses tested, adenovirus and Aichi virus 1 were found in the greatest prevalence in treated wastewater (i.e., inlet of the wetlands). Reduction efficiencies of enteric viruses by the wetlands ranged from 1 to 3 log10. Polyomaviruses were generally removed to below detection limit, indicating at least 2 to 4 log10 removal. PMMoV was detected in a greater concentration in the inlet of both wetlands for all the viruses tested (10(4) to 10(7) genome copies/L), but exhibited little or no removal (1 log10 or less). To determine the factors associated with virus genome attenuation (as determined by qPCR), the persistence of PMMoV and poliovirus type 1 (an enterovirus) was studied in autoclaved and natural wetland water, and deionized water incubated under three different temperatures for 21 days. A combination of elevated water temperature and biological activities reduced poliovirus by 1 to 4 log10, while PMMoV was not significantly reduced during this time period. Overall, PMMoV showed much greater persistence than human viruses in the wetland treatment.

Sanitation in constructed wetlands: A review on the removal of human pathogens and fecal indicators

Removal of human pathogens from wastewater is a critical factor with linkage to human health. Constructed Wetlands (CWs) are environmental friendly ecosystems that are applicable not only for chemical pollution control, but also for the reduction of pathogens from wastewater. Yet the knowledge on the fate and removal of such indicator bacteria in CWs is still not sufficient due to the complexity of removal mechanisms and influencing factors. This review serves to provide a better understanding of this state-of-the-art technology, which is necessary for further investigations and design development. The fecal indicator bacteria in CWs mainly come from three sources, namely, influent wastewaters, regrowth within the CWs, and animal activities. The properties of microbial contamination vary depending on the different sources. The removal of pathogens is a complex process that is influenced by operational parameters such as hydraulic regime and retention time, vegetation, seasonal fluctuation, and water composition. The most frequent and well-validated removal mechanisms include natural die-off due to starvation or predation, sedimentation and filtration, and adsorption. The concentration of the main fecal indicator bacteria in the effluent was found to be exponentially related to the loading rate. Generally, horizontal subsurface flow CWs have better reduction capacity than free water surface flow CWs, and hybrid wetland systems were found to be the most efficient due to a longer retention time. Further improvement of fecal indicator bacteria removal in CWs is needed, however, levels in CW effluents are still higher than most of the regulation standards for reuse.

COD, nutrient removal and disinfection efficiency of a combined subsurface and surface flow constructed wetland: A case study

A constructed wetland system composed of a subsurface flow wetland, a surface flow wetland and a facultative pond was studied from July 2008 until May 2012. It was created to treat the domestic sewage produced by a hamlet of 150 inhabitants. Monthly physicochemical and microbiological analyses were carried out in order to evaluate the removal efficiency of each stage of the process and of the total treatment system. Pair-wise Student's t-tests showed that the mean removal of each considered parameter was significantly different (α = 0.05) between the various treatment phases. Two-way ANOVA and Tukey's HSD tests were used to find significant differences between wetland types and seasons in the removal efficiency of the considered water quality parameters. Significant differences in percent removal efficiency between the treatment phases were observed for total phosphorus, total nitrogen, ammonia nitrogen and organic load (expressed as Chemical Oxygen Demand). In general, the wastewater treatment was carried by the sub-superficial flow phase mainly, both in growing season and in quiescence season. Escherichia coli removal ranged from 98% in quiescence season to >99% in growing season (approximately 2-3 orders of magnitude). The inactivation of fecal bacteria was not influenced by the season, but only by the treatment phase.

Can constructed wetlands treat wastewater for reuse in agriculture? Review of guidelines and examples in South Europe

South Europe is one of the areas negatively affected by climate change. Issues with water shortage are already visible, and are likely to increase. Since agriculture is the biggest freshwater consumer, it is important to find new water sources that could mitigate the climate change impact. In order to overcome problems and protect the environment, a better approach towards wastewater management is needed. That includes an increase in the volume of wastewater that is treated and a paradigm shift towards a more sustainable system where wastewater is actually considered as a resource. This study evaluates the potential of constructed wetlands (CWs) to treat domestic wastewater and produce effluent that will be suitable for reuse in agriculture. In South Europe, four countries (Greece, Italy, Portugal and Spain) have national standards that regulate wastewater reuse in agriculture. Wastewater treatment plants (WWTPs) that are based on CWs in these four countries were analysed and their effluents compared with the quality needed for reuse. In general, it was found that CWs have trouble reaching the strictest standards, especially regarding microbiological parameters. However, their effluents are found to be suitable for reuse in areas that do not require water of the highest quality.

Performance of three pilot-scale hybrid constructed wetlands for total coliforms and Escherichia coli removal from primary effluent - a 2-year study in a subtropical climate

Three pilot-scale two-stage hybrid constructed wetlands were evaluated in order to compare their efficiency for total coliforms (TCol) and Escherichia coli removal and to analyze their performances in two 1-year periods of experimentation. System I consisted of a horizontal flow (HF) constructed wetland (CW) followed by a stabilization pond. System II was also configured with a HF CW as a first stage which was then followed by a vertical flow (VF) CW as a second stage. System III was configured with a VF CW followed by a HF CW. In the first year of evaluation, the HF-VF system was the most effective for TCol removal (p < 0.05) and achieved a reduction of 2.2 log units. With regard to E. coli removal, the HF-VF and VF-HF systems were the most effective (p < 0.05) with average reductions of 3.2 and 3.8 log units, respectively. In the second year, the most effective were those with a VF component for both TCol and E. coli which underwent average reductions of 2.34-2.44 and 3.44-3.74 log units, respectively. The reduction achieved in E. coli densities, in both years, satisfy the World Health Organization guidelines that require a 3-4 log unit pathogen reduction in wastewater treatment systems.

The effect of seasonal temperature on pathogen removal efficacy of vermifilter for wastewater treatment

The present study explored the effects of seasonal temperature on the treatment efficiency and pathogen removal efficacy from synthetic domestic wastewater, earthworm population characteristics and microbial population in the filter media of a lab-scale vermifilter (VF). The experimental phase lasted for one year and daily mean room temperature showed a difference of 2-16 °C between winter (Dec-Feb), spring (Mar-May), summer (Jun-Aug) and autumn (Sep-Nov) periods. The results showed that variation in ambient temperature had a significant effect on chemical oxygen demand (COD) and biochemical oxygen demand (BOD) reduction, indicator organisms and pathogen removal, earthworm population, bacterial and actinomycetes number, but had no effect on total suspended solids (TSS) removal and fungi number. The study showed that higher BOD and COD removal was accomplished during the spring and autumn period when the mean temperature was 25-27 °C. This temperature range is optimum for the earthworm species Eisenia fetida for its activity, growth and reproduction and any variation in temperature from the optimum range led to decrease in treatment efficiency and earthworm population. However, during summer, when the maximum temperature reached 38-40 °C, the indicator bacteria removal was maximum by 99.9%, Salmonella reduction by 96.9% and Escherichia coli by 99.3%. The pathogen removal efficacy of VF increases with the increase in temperature, as shown by linear regression analysis, which implied that temperature had a significant contribution to the pathogen removal efficiency of VF. Pearson coefficient of correlation (r) derived an important relationship between the seasonal temperature and treatment efficiency, pathogen removal efficacy and microbial numbers during vermifiltration.

Evaluating the effectiveness of management practices on hydrology and water quality at watershed scale with a rainfall-runoff model

The adverse influence of urban development on hydrology and water quality can be reduced by applying best management practices (BMPs) and low impact development (LID) practices. This study applied green roof, rain barrel/cistern, bioretention system, porous pavement, permeable patio, grass strip, grassed swale, wetland channel, retention pond, detention basin, and wetland basin, on Crooked Creek watershed. The model was calibrated and validated for annual runoff volume. A framework for simulating BMPs and LID practices at watershed scales was created, and the impacts of BMPs and LID practices on water quantity and water quality were evaluated with the Long-Term Hydrologic Impact Assessment-Low Impact Development 2.1 (L-THIA-LID 2.1) model for 16 scenarios. The various levels and combinations of BMPs/LID practices reduced runoff volume by 0 to 26.47%, Total Nitrogen (TN) by 0.30 to 34.20%, Total Phosphorus (TP) by 0.27 to 47.41%, Total Suspended Solids (TSS) by 0.33 to 53.59%, Lead (Pb) by 0.30 to 60.98%, Biochemical Oxygen Demand (BOD) by 0 to 26.70%, and Chemical Oxygen Demand (COD) by 0 to 27.52%. The implementation of grass strips in 25% of the watershed where this practice could be applied was the most cost-efficient scenario, with cost per unit reduction of $1m3/yr for runoff, while cost for reductions of two pollutants of concern was $445 kg/yr for Total Nitrogen (TN) and $4871 kg/yr for Total Phosphorous (TP). The scenario with very high levels of BMP and LID practice adoption (scenario 15) reduced runoff volume and pollutant loads from 26.47% to 60.98%, and provided the greatest reduction in runoff volume and pollutant loads among all scenarios. However, this scenario was not as cost-efficient as most other scenarios. The L-THIA-LID 2.1 model is a valid tool that can be applied to various locations to help identify cost effective BMP/LID practice plans at watershed scales.

A review of virus removal in wastewater treatment pond systems

Wastewater treatment ponds (lagoons) are one of the most common types of technologies used for wastewater management worldwide, especially in small cities and towns. They are particularly well-suited for systems where the effluent is reused for irrigation. However, the efficiency of virus removal in wastewater treatment pond systems is not very well understood. The main objective of this paper is to critically review the major findings related to virus removal in wastewater treatment pond systems and to statistically analyze results reported in the literature from field studies on virus removal in these systems. A comprehensive analysis of virus removal reported in the literature from 71 different wastewater treatment pond systems reveals only a weak to moderate correlation of virus removal with theoretical hydraulic retention time. On average, one log10 reduction of viruses was achieved for every 14.5-20.9 days of retention, but the 95th percentile value of the data analyzed was 54 days. The mechanisms responsible for virus removal in wastewater treatment ponds were also reviewed. One recent finding is that sedimentation may not be a significant virus removal mechanism in some wastewater ponds. Recent research has also revealed that direct and indirect sunlight-mediated mechanisms are not only dependent on pond water chemistry and optics, but also on the characteristics of the virus and its genome. MS2 coliphage is considered to be the best surrogate for studying sunlight disinfection in ponds. The interaction of viruses with particles, with other microorganisms, and with macroinvertebrates in wastewater treatment ponds has not been extensively studied. It is also unclear whether virus internalization by higher trophic-level organisms has a protective or a detrimental effect on virus viability and transport in pond systems. Similarly, the impact of virus-particle associations on sunlight disinfection in ponds is not well understood. Future research should focus on the interactions of viruses with particles and with other organisms, as well as the development of a model for virus removal in pond systems that can be used for design purposes, and to inform future editions of the WHO Guidelines for Wastewater Use in Agriculture.

Presence and persistence of wastewater pathogen Escherichia coli O157:H7 in hydroponic reactors of treatment wetland species

Treatment wetlands (TWs) efficiently remove many pollutants including a several log order reduction of pathogens from influent to effluent; however, there is evidence to suggest that pathogen cells are sequestered in a subsurface wetland and may remain viable months after inoculation. Escherichia coli is a common pathogen in domestic and agricultural wastewater and the O157:H7 strain causes most environmental outbreaks in the United States. To assess attachment of E. coli to the TW rhizosphere, direct measurements of E. coli levels were taken. Experiments were performed in chemostats containing either Teflon nylon as an abiotic control or roots of Carex utriculata or Schoenoplectus acutus. Flow of simulated wastewater through the chemostat was set to maintain a 2 hour residence time. The influent was inoculated with E. coli O157:H7 containing DsRed fluorescent protein. Root samples were excised and analyzed via epifluorescent microscopy. E. coli O157:H7 was detected on the root surface at 2 hours after inoculation, and were visible as single cells. Microcolonies began forming at 24 hours post-inoculation and were detected for up to 1 week post-inoculation. Image analysis determined that the number of microcolonies with >100 cells increased 1 week post-inoculation, confirming that E. coli O157:H7 is capable of growth within biofilms surrounding wetland plant roots.