Forecasting point-of-consumption chlorine residual in refugee settlements using ensembles of artificial neural networks

Waterborne illnesses are a leading health concern in refugee and internally displaced person (IDP) settlements where waterborne pathogens often spread through household recontamination of stored water. Ensuring sufficient chlorine residual is important for protecting drinking water against recontamination and ensuring water remains safe up to the point-of-consumption. We used ensembles of artificial neural networks (ANNs) to probabilistically forecast the point-of-consumption free residual chlorine (FRC) concentration and to develop point-of-distribution FRC targets based on the risk of insufficient FRC at the point-of consumption. We built ANN ensemble models using data from three refugee settlements and found that the risk-based FRC targets generated by the ensemble models were consistent with an empirical water safety evaluation, indicating that the models accurately predicted the risk of low point-of-consumption FRC despite all ensemble forecasts being underdispersed even after post-processing. This demonstrates the usefulness of ANN ensembles for generating risk-based point-of-distribution FRC targets to ensure safe drinking water in humanitarian operations.

Design, performance, and demand for a novel in-line chlorine doser to increase safe water access

Financially sustainable strategies are needed to increase access to safe drinking water in low-income settings. We designed a novel in-line chlorine doser that employs the Venturi principle to automatically add liquid chlorine at the point of water collection (tap outflows). The Venturi does not require electricity or moving parts, and users do not have to change the way they typically collect water. We field-tested the Venturi and assessed its technical performance and sales viability at water kiosks in Kisumu County, Kenya. We offered kiosk owners 6-month service packages to lease or lease-to-own the device; 27% of kiosks given a sales pitch committed to a service package. All but one kiosk paid in full during the 6-month service period and more than two-thirds purchased the device with payments totaling >$250 USD per kiosk. Kiosk customers could choose to purchase chlorinated or unchlorinated water from separate taps; 66% reported buying chlorinated water. Kiosk taps fitted with the Venturi had detectable free chlorine residual 97.6% of the time. The technical performance of the Venturi and effective demand from kiosks indicate high potential for the Venturi to increase safe water access in low-income communities.

Residual-chlorine concentration impacts the ecology of biofilms in drinking water pipes and their water quality response

<p>Drinking water distribution systems (DWDS) are an engineered system designed to protect water quality during delivery from treatment works to consumers’ taps. Biofilms form on the vast internal surfaces of DWDS, impacting water quality by their activity and/or mobilisation into the bulk-water. Disinfection-residuals are often maintained in drinking water to mitigate planktonic microbial contamination (and associated water quality/health risks). However, the impact of residual-disinfection upon biofilms, and the subsequent unintended risk they may present to water quality, is unclear.</p> <p>To address this, an internationally-unique, temperature-controlled, full-scale DWDS test facility, fed with water from the local DWDS, was used to grow biofilms (for 28 days). The facility enables three simultaneous conditions to be run in replicate pipe loops (each ~200m long, 79mm internal diameter, PE100 pipe). Conditions studied were Low-, Medium- and High-chlorine regimes. Various water quality parameters were monitored throughout, biofilms were sampled every two weeks (n=5). Physical, chemical and molecular analyses were applied to characterise the matrix (structure and composition) and microbial communities (via analysis of bacterial 16S rRNA and fungal ITS genes) of biofilms developed under the different chlorine regimes. After growth, a “mobilisation” test was conducted simulating hydraulic changes that occur in DWDS. Biofilms from each chlorine regime were exposed to increasing shear stresses to determine any water quality degradation as a consequence of biofilm mobilisation.</p> <p>High-chlorine residual concentration during development reduced biofilm bacterial concentrations but increased inorganics and selected for unique bacterial and fungal communities. Ultimately the biofilms developed under a High-chlorine residual resulted in the greatest decrease in water quality, in response to mobilisation, and the Low-chlorine regime resulted in biofilms which had the lowest impact on water quality. These unanticipated findings suggest chlorine-boosting should be considered carefully and may actually exacerbate water quality issues. The derived understanding could impact the long-term management of DWDS water quality and biofilm, whilst challenging the current mind-set of continuous residual-disinfection control strategies.</p>

Comparison between constant and variable chlorine decay models applied to urban water supply network

Monitoring of chlorine residual in water distribution systems is necessary not only for ensuring potable water quality but also prevent emergence of disinfection by-products due to excess chlorination. Modelling work for chlorine residual was carried out for water supply distribution network of a town using both second order and first order reaction rate models. For the development of the model, the bulk reaction decay rate was determined in the laboratory using bottle testing while the wall decay rate was determined by calibration of the water quality model using field residual chlorine concentration measurements. The model results show that there is no significant difference in the residual chlorine between the two models or the cost saving that result in terms chlorine usage for the range of initial chlorine dosages anticipated. Constant rate chlorine model is more conservative and offers additional safety in terms of chlorine residual present. Significant differences only occur at excess chlorine residual concentration within the distribution system above the intended maximum residual to be attained. Further research that relates the chlorine dose with the water quality characteristics is necessary to make a more general evaluation.

Characters of chloramine decay in large looped water distribution system – the case of Tianjin, China

In the water distribution system of a large city, chloramine could experience rapid decay as residence time extends, which may further threaten drinking water safety. A correlation analysis was conducted between the total chlorine residual of four sites on the distribution system and the water quality of the corresponding water treatment plant with data from 2016 to 2018 for the city of Tianjin. The results showed that the total chlorine residuals of all sites were negatively correlated with the temperature of the treated water, while the total chlorine residual of pipeline water did not uniformly correlate with that of the treated water. Further, a chloramine decay calculation study showed that pipe wall-induced decay contributes a lot of chloramine losses by conducting Total Chloramine Decay Model (TCDM) calibration with the monitored data. Hence, increasing the total chlorine residual of treated water, especially in the hot season, may not effectively maintain the disinfectant concentration at an ideal level.

Comprehensive Risk Assessment of Health-Related Hazardous Events in the Drinking Water Supply System from Source to Tap in Gaza Strip, Palestine

Background. The traditional approach in the management of the quality drinking water, and relying on end-product testing, has proven ineffective in protecting public health. Therefore, the transition to a systematic approach in drinking water supply systems management from the source to the consumer tap was taken as a water safety plan (WSP). Objective. The study aims to investigate the health-related hazardous events in order to decide on the best risk-reduction strategies in the supply of drinking water in the Gaza strip. Methods. A semiquantitative matrix method for risk assessment was applied. Also, chlorine residual, electrical conductivity, and nitrate concentration further tested in 109 water wells, 109 small-scale water desalination plants, 197 tanker trucks, and 384 households distributed over five governorates of the Gaza strip. Results. The mean of the measured chlorine residual values was less than the recommended national and international limits (0.2–1 mg/liter). The mean of electrical conductivity at catchment points and household municipal water taps was 2165.1 μS·cm−1 and 2000 μS·cm−1, respectively. Furthermore, zero percent of water samples met the recommended criteria, indicating that the groundwater in the Gaza strip is nonpotable. Only 12.8% and 8.8% of water samples met the permissible levels at catchment areas and municipal water at household, respectively, indicating sever health impacts on the public. Moreover, the most hazardous events were related to high levels of groundwater salinity, the low level of disinfection, the effect of electricity outages on the efficiency of the desalination process, and leakage of water from the tanker truck tank reservoirs. Therefore, urgent interventions are required to improve the quality of water and to mitigate the possible health effects. Conclusion. The prioritization of hazardous events that are proportional to the degree of their attributed risk could help guide in making the right risk-reduction decisions. Urgent interventions are required to improve the quality of water and to mitigate the possible health effects.

Impact of Chlorine and Chloramine on the Detection and Quantification of Legionella pneumophila and Mycobacterium Species

ABSTRACT Potable water can be a source of transmission for legionellosis and nontuberculous mycobacterium (NTM) infections and diseases. Legionellosis is caused largely by Legionella pneumophila, specifically serogroup 1 (Sg1). Mycobacterium avium, Mycobacterium intracellulare, and Mycobacterium abscessus are three leading species associated with pulmonary NTM disease. The estimated rates of these diseases are increasing in the United States, and the cost of treatment is high. Therefore, a national assessment of water disinfection efficacy for these pathogens was needed. The disinfectant type and total chlorine residual (TClR) were investigated to understand their influence on the detection and concentrations of the five pathogens in potable water. Samples (n = 358) were collected from point-of-use taps (cold or hot) from locations across the United States served by public water utilities that disinfected with chlorine or chloramine. The bacteria were detected and quantified using specific primer and probe quantitative-PCR (qPCR) methods. The total chlorine residual was measured spectrophotometrically. Chlorine was the more potent disinfectant for controlling the three mycobacterial species. Chloramine was effective at controlling L. pneumophila and Sg1. Plotting the TClR associated with positive microbial detection showed that an upward TClR adjustment could reduce the bacterial count in chlorinated water but was not as effective for chloramine. Each species of bacteria responded differently to the disinfection type, concentration, and temperature. There was no unifying condition among the water characteristics studied that achieved microbial control for all. This information will help guide disinfectant decisions aimed at reducing occurrences of these pathogens at consumer taps and as related to the disinfectant type and TClR. IMPORTANCE The primary purpose of tap water disinfection is to control the presence of microbes. This study evaluated the role of disinfectant choice on the presence at the tap of L. pneumophila, its Sg1 serogroup, and three species of mycobacteria in tap water samples collected at points of human exposure at locations across the United States. The study demonstrates that microbial survival varies based on the microbial species, disinfectant, and TClR.