Valuing the subsurface pathogen treatment barrier in water recycling via aquifers for drinking supplies

A quantitative microbial risk assessment (QMRA) was performed at four managed aquifer recharge (MAR) sites (Australia, South Africa, Belgium, Mexico) where reclaimed wastewater and stormwater is recycled via aquifers for drinking water supplies, using the same risk-based approach that is used for public water supplies. For each of the sites, the aquifer treatment barrier was assessed for its log₁₀ removal capacity much like for other water treatment technologies. This information was then integrated into a broader risk assessment to determine the human health burden from the four MAR sites. For the Australian and South African cases, managing the aquifer treatment barrier was found to be critical for the schemes to have low risk. For the Belgian case study, the large treatment trains both in terms of pre- and post-aquifer recharge ensures that the risk is always low. In the Mexico case study, the risk was high due to the lack of pre-treatment and the low residence times of the recharge water in the aquifer. A further sensitivity analysis demonstrated that human health risk can be managed if aquifers are integrated into a treatment train to attenuate pathogens. However, reduction in human health disease burden (as measured in disability adjusted life years, DALYs) varied depending upon the number of pathogens in the recharge source water. The beta-Poisson dose response curve used for translating rotavirus and Cryptosporidium numbers into DALYs coupled with their slow environmental decay rates means poor quality injectant leads to aquifers having reduced value to reduce DALYs. For these systems, like the Mexican case study, longer residence times are required to meet their DALYs guideline for drinking water. Nevertheless the results showed that the risks from pathogens can still be reduced and recharging via an aquifer is safer than discharging directly into surface water bodies.     

Health-based targets for greywater reuse in residential schools in Madhya Pradesh,India

In line with developments in the water reuse sector, this paper applied quantitative microbial risk assessment (QMRA) techniques to seven greywater reuse systems used for recycling shower water for toilet flushing. The objective of the study was to establish a scientific basis for health-based greywater targets for India. It involved qualitative risk assessments and quantitative microbiological analysis using Enterococci, thermotolerant coliforms (TTC) and coliphage indicator organisms. Four conclusions are drawn from this study. Firstly, the systems indicated a low risk and high quality, and secondly that low levels of risk were present in systems, resulting in the recommendation of guideline of 5000 cfu/100 mL rather than 10 000 cfu/100 mL for greywater utilised for direct toilet flushing. Thirdly, disability adjusted life years (DALYs) are a useful indicator of risk for evaluating the performance of a greywater reuse system in addition to chemical/microbiological indicators DALYs, and finally that TTC are a useful surrogate microbial indicator for analysis of greywater in developing countries with limited analytical facilities.     

Influence of stormwater control measures on water quality at nested sites in a small suburban watershed

ABSTRACT

Stormwater control measures (SCMs) are designed to mitigate the deleterious impacts of urban runoff on the water quality of receiving waters. To assess the cumulative effects of SCMs at the watershed scale, we monitored longitudinal changes in storm discharge and stream water chemistry at high temporal resolution in a suburban headwater stream in Charlotte, NC. SCMs significantly decreased or stabilized instream concentrations of reactive solutes (nitrate, soluble reactive phosphorus, and dissolved organic carbon) relative to the upstream control site. However, SCM outflows minimally influenced concentrations of less reactive solutes (major ions) which increased with urbanization. Additionally, instream concentration variability correlated with antecedent moisture conditions – representative of watershed storage availability – highlighting the role that SCM storage availability plays in the timing of solute delivery to the stream. Our results show that SCMs decrease instream concentrations of biogeochemically reactive solutes but the mitigation potential is temporally dynamic and influenced by antecedent conditions.     

Assessment of the integrated urban water quality model complexity through identifiability analysis

Urban sources of water pollution have often been cited as the primary cause of poor water quality in receiving water bodies (RWB), and recently many studies have been conducted to investigate both continuous sources, such as wastewater-treatment plant (WWTP) effluents, and intermittent sources, such as combined sewer overflows (CSOs). An urban drainage system must be considered jointly, i.e., by means of an integrated approach. However, although the benefits of an integrated approach have been widely demonstrated, several aspects have prevented its wide application, such as the scarcity of field data for not only the input and output variables but also parameters that govern intermediate stages of the system, which are useful for robust calibration. These factors, along with the high complexity level of the currently adopted approaches, introduce uncertainties in the modelling process that are not always identifiable. In this study, the identifiability analysis was applied to a complex integrated catchment: the Nocella basin (Italy). This system is characterised by two main urban areas served by two WWTPs and has a small river as the RWB. The system was simulated by employing an integrated model developed in previous studies. The main goal of the study was to assess the right number of parameters that can be estimated on the basis of data-source availability. A preliminary sensitivity analysis was undertaken to reduce the model parameters to the most sensitive ones. Subsequently, the identifiability analysis was carried out by progressively considering new data sources and assessing the added value provided by each of them. In the process, several identifiability methods were compared and some new techniques were proposed for reducing subjectivity of the analysis. The study showed the potential of the identifiability analysis for selecting the most relevant parameters in the model, thus allowing for model simplification, and in assessing the impact of data sources for model reliability, thus guiding the analyst in the design of future monitoring campaigns. Further, the analysis showed some critical points in integrated urban drainage modelling, such as the interaction between water quality processes on the catchment and in the sewer, that can prevent the identifiability of some of the related parameters.     

污水厂再生水用于城市绿化的健康风险评价研究

针对深圳市3个污水处理厂再生水水体中的有毒有害化学物质,采用基于蒙特卡罗( Monte - Carlo)模拟的概率统计方法对再生水回用于城市绿化途径所造成的人体健康风险进行了定量评价.结果表明,深圳市A、B、C污水处理厂再生水中化学物质所致人体终身健康风险与个体健康风险均远小于国际公认可接受的最大风险水平,各污水厂的再生水可直接回用于城市绿化.     

The influence of context and perception when designing out risks associated with non-potable urban water reuse

Perceptions and cognitive bias in relation to reuse water can influence the responses to risk and reward. Much has been written on community perspectives and risk perceptions with regard to recycled water for non-potable use. This paper is distinct in that it focuses on the scheme proponents and those involved in designing and delivering schemes. An analysis of five case studies in Australia across a range of diverse settings revealed that the levels of treatment for various end-uses were in excess of the Australian Guidelines for Water Recycling. The evidence shows that the water industry has a fairly narrow view when identifying risks, and has an insurance type response to mitigating the risk. The overarching drivers for this are either the mitigation of the perceived risk associated with using reuse water, or the lack of an adaptive response to changes in the circumstances.     

Geochemical contamination of urban water by concrete stormwater infrastructure: applying an epoxy resin coating as a control treatment

Urban drainage systems that use concrete gutters, pits and pipes have been adopted worldwide by drainage engineers. This study tested the hypothesis that treating a concrete pipe with a coating of epoxy resin is an effective method to reduce the concrete mineral leaching and associated contamination of water carried within the pipe. Four 20 litre samples of rainwater were individually circulated through the untreated and epoxy treated portions of the pipe for 100 minutes. After recirculation through the untreated portion of the pipe pH increased by almost two units, electrical conductivity doubled and there were significant increases in bicarbonate, calcium and other ions. In contrast, rainwater circulated through the epoxy treated portion of the pipe showed a minimal pH increase (0.32 pH units) but no other significant increases in any other water chemistry attributes. The epoxy resin greatly reduced mineral contamination of recirculated water, supporting the hypothesis.     

Characterization of drinking water treatment for virus risk assessment

Removal or inactivation of viruses in drinking water treatment processes can be quantified by measuring the concentrations of viruses or virus indicators in water before and after treatment. Virus reduction is then calculated from the ratio of these concentrations. Most often only the average reduction is reported. That is not sufficient when treatment efficiency must be characterized in quantitative risk assessment.We present three simple models allowing statistical analysis of series of counts before and after treatment: distribution of the ratio of concentrations, and distribution of the probability of passage for unpaired and paired water samples.Performance of these models is demonstrated for several processes (long and short term storage, coagulation/filtration, coagulation/sedimentation, slow sand filtration, membrane filtration, and ozone disinfection) using microbial indicator data from full-scale treatment processes.All three models allow estimation of the variation in (log) reduction as well as its uncertainty; the results can be easily used in risk assessment. Although they have different characteristics and are present in vastly different concentrations, different viruses and/or bacteriophages appear to show similar reductions in a particular treatment process, allowing generalization of the reduction for each process type across virus groups.The processes characterized in this paper may be used as reference for waterborne virus risk assessment, to check against location specific data, and in case no such data are available, to use as defaults.     

Assessment of rainfall influence over water quality effluent of an urban catchment: a data driven approach

Experience has shown the important influence of rainstorm water in the arrival of pollutants to receiving water bodies. This paper presents an identification of rain gauge stations and rainstorm variables with influence over water quality parameters such as Temperature, Conductivity, pH and COD, measured in the effluent of an urban catchment. Fourteen rainfall events registered by eight rain gauge stations within or in the proximity of the studied catchment (El Salitre Basin, Bogotá, Colombia) were analysed by the use of correlation tests and Kernel Classificatory methods. Some sensitive water quality parameters to rainfall (maximum rainfall height, mean of height, total height; during a rainstorm event) were identified (pH, temperature, conductivity and settleable solids). Correlations were significant mainly for two rain gauge stations in the proximity (about 5 km) of the effluent and two others near the eastern mountains of the city (zone with high slopes).     

Transition to a water-cycle city: risk perceptions and receptivity of Australian urban water practitioners

Transition to a water-cycle city, a sustainable urban water management future, requires the implementation of centralised and decentralised systems to augment potable water supply, protect waterways and enhance urban liveability. Risk is simultaneously driving and impeding this transition. However, risk perceptions of water practitioners and how they affect practitioner receptivity to future modes of urban water supply are poorly understood. This study characterises risk perceptions and attitudes of Australian urban water practitioners towards alternative water systems and uses a receptivity framework to suggest how receptive practitioners are to these systems. Differences between cities are identified, suggesting how familiarity might influence receptivity. These results can inform strategies to enhance receptivity, including improved communication within the water industry and beyond with its various stakeholders, improved cost-projection frameworks to provide a quantitative metric of the benefits of sustainable water options, and a shift from ‘learning to manage’ to ‘managing to learn’.     

Health risk related to the presence of metals in drinking water from different types of sources

The aim of the paper is to assess health risk related to the exposure of people to contact with water contaminated with chosen metals, via ingestion and dermal routes. The results of analyses performed in 2012–2017 using water samples collected from a surface water intake point on the Dunajec, from infiltration wells and samples of treated water supplied to the water distribution system were used as the basis for calculations. Exposure assessment was performed for children and adults. It was demonstrated that treated water supplied directly into the water distribution system had superior parameters. In the case of adults, the calculated HI values were two or three times higher than for children over the entire analysed period in all three risk assessment scenarios. Health risk resulting from the presence of metals in water is mostly related to the ingestion exposure route. Dermal contact does not produce a considerable risk.     

Metabolism-modelling approaches to long-term sustainability assessment of urban water services

There is a discernible need for a holistic, long-term and sustainability approach in decision-making in water and wastewater utilities around the world. Metabolism-based modelling, which can quantify various flows within an urban water system (UWS), has shown its effective usability for a more comprehensive understanding of the impacts of intervention strategies and can be used by any water utility for future planning of UWS. This study presents the main principles of a holistic Sustainability Assessment Framework which can be simulated by using two analytical, conceptual, mass-balance-based models to quantify relevant key performance indicators (KPIs) associated with the metabolic flows of the urban water cycle. These two models are WaterMet² (WM2) and dynamic metabolism model (DMM), developed recently under the aegis of the EU TRUST (Transitions to the Urban Water Services of Tomorrow) project. There are clear differences between the two models which make them useful in different contexts and circumstantial situations. DMM is a mass-balance consistent model which quantifies and presents annually-aggregated performance values for system wide energy consumption, emissions, environmental impacts and costs for the entire UWS though it is also possible to derive corresponding indicators for individual sub-systems (e.g. water distribution and wastewater transport). WM2 is the opposite of this, it is a distributed metabolism model which simulates water related and other resource flows throughout the UWS components with a higher resolution both spatially (e.g. multiple water resources and service reservoirs) and temporally (e.g. daily and monthly), and thereby is useful in contexts where utilities would like to focus on further details of the UWS metabolism with the aim to understand and solve specific problems. Overall, these two complementary metabolism-based approaches enable any water utility to quantitatively explore and understand the influences of different external drivers and intervention strategies on future performance profiles linked to any physical, environmental and economic criteria.     

Application of an aerial catchment monitoring methodology to assist the development of drinking water safety plans

Risk-based management approaches for safeguarding the quality of public water supply, as strongly endorsed by the World Health Organisation and the Drinking Water Inspectorate, place greater emphasis on the importance of water companies knowing their catchments and their associated risks. Because of their often vast extent, and problems relating to access, it has always been a challenge for water companies to gather reliable data relating to catchment landuse and to monitor catchment activities. This paper presents a methodology that was used successfully within Cambridge Water to gain more knowledge about landuse within its catchments by chartering a helicopter and systematically photographing them. The method used is described, the results are shown and the strengths and the weaknesses of the approach are considered.     

Measurement of dissolved organic nitrogen in a drinking water treatment plant: size fraction, fate, and relation to water quality parameters

This paper investigates the characteristics of dissolved organic nitrogen (DON) in raw water from the Huangpu River and also in water undergoing treatment in the full-scale Yangshupu drinking water treatment plant (YDWTP) in Shanghai, China. The average DON concentration of the raw water was 0.34 mg/L, which comprised a relatively small portion (~ 5%) of the mass of total dissolved nitrogen (TDN). The molecular weight (MW) distribution of dissolved organic matter (DOM) was divided into five groups: > 30, 10-30, 3-10, 1-3 and < 1 kDa using a series of ultrafiltration membranes. Dissolved organic carbon (DOC), UV absorbance at wavelength of 254 nm (UV254) and DON of each MW fraction were analyzed. DON showed a similar fraction distribution as DOC and UV254. The < 1 kDa fraction dominated the composition of DON, DOC and UV254 as well as the major N-nitrosodimethylamine formation potential (NDMAFP) in the raw water. However, this DON fraction cannot be effectively removed in the treatment line at the YDWTP including pre-ozonation, clarification and sand filtration processes. The results from linear regression analysis showed that DON is moderately correlated to DOC, UV254 and trihalomethane formation potential (FP), and strongly correlated to haloacetic acids FP and NDMAFP. Therefore, DON could serve as a surrogate parameter to evaluate the reactivity of DOM and disinfection by-products FP.