Our selection of open access publications on water reuse – September 2023
Our selection this quarter includes open-access articles published in Water Research, Science of the Total Environment, Environmental Science and Ecotechnology, Utilities Policy, and John Wiley and Sons Inc. on the use online sensors for predicting microbial water quality in on-site water reuse systems; how to select indicator contaminants of emerging concern when reusing reclaimed water for irrigation; research on new technologies such as electrochemical systems with constructed wetlands and hybrid membrane biofilm reactors finding application in water reuse; what are the perational drivers of water reuse efficiency for Portuguese wastewater service providers and more… Enjoy reading!
New Methodologies for Water Quality Monitoring
Title: Predicting microbial water quality in on-site water reuse systems with online sensors
Authors: Reynaert E., Steiner P., Yu Q., D’Olif L., Joller N., Schneider M.Y. and Morgenroth E.
In: Water Research
Abstract: Widespread implementation of on-site water reuse is hindered by the limited availability of monitoring approaches that ensure microbial quality during operation. In this study, we developed a methodology for monitoring microbial water quality in on-site water reuse systems using inexpensive and commercially available online sensors. An extensive dataset containing sensor and microbial water quality data for six of the most critical types of disruptions in membrane bioreactors with chlorination was collected. We then tested the ability of three typological machine learning algorithms – logistic regression, support-vector machine, and random forest – to predict the microbial water quality as “safe” or “unsafe” for reuse. The main criteria for model optimization was to ensure a low false positive rate (FPR) – the percentage of safe predictions when the actual condition is unsafe – which is essential to protect users health. This resulted in enforcing a fixed FPR ≤ 2%. Maximizing the true positive rate (TPR) – the percentage of safe predictions when the actual condition is safe – was given second priority. Our results show that logistic-regression-based models using only two out of the six sensors (free chlorine and oxidation–reduction potential) achieved the highest TPR. Including sensor slopes as engineered features allowed to reach similar TPRs using only one sensor instead of two. Analysis of the occurrence of false predictions showed that these were mostly early alarms, a characteristic that could be regarded as an asset in alarm management. In conclusion, the simplest algorithm in combination with only one or two sensors performed best at predicting the microbial water quality. This result provides useful insights for water quality modeling or for applications where small datasets are a common challenge and a general advantage might be gained by using simpler models that reduce the risk of overfitting, allow better interpretability, and require less computational power.
Title: Selection of indicator contaminants of emerging concern when reusing reclaimed water for irrigation — A proposed methodology
Authors: Verlicchi P., Grillini V., Lacasa E., Archer E., Krzeminski P., Gomes A.I., Vilar V.J.P., Rodrigo M.A., Gäbler J., Schäfer L.
In: Science of the Total Environment
Abstract: Organic and microbial contaminants of emerging concern (CECs), even though not yet regulated, are of great concern in reclaimed water reuse projects. Due to the large number of CECs and their different characteristics, it is useful to include only a limited number of them in monitoring programs. The selection of the most representative CECs is still a current and open question. This study presents a new methodology for this scope, in particular for the evaluation of the performance of a polishing treatment and the assessment of the risk for the environment and the irrigated crops. As to organic CECs, the methodology is based on four criteria (occurrence, persistence, bioaccumulation and toxicity) expressed in terms of surrogates (respectively, concentrations in the secondary effluent, removal achieved in conventional activated sludge systems, Log Kow and predicted-no-effect concentration). It consists of: (i) development of a dataset including the CECs found in the secondary effluent, together with the corresponding values of surrogates found in the literature or by in-field investigations; (ii) normalization step with the assignment of a score between 1 (low environmental impact) and 5 (high environmental impact) to the different criteria based on threshold values set according to the literature and experts’ judgement; (iii) CEC ranking according to their final score obtained as the sum of the specific scores; and (iv) selection of the representative CECs for the different needs. Regarding microbial CECs, the selection is based on their occurrence and their highest detection frequency in the secondary effluent and in the receiving water, the antibiotic consumption patterns, and recommendations by national and international organisations. The methodology was applied within the ongoing reuse project SERPIC resulting in a list of 30 indicator CECs, including amoxicillin, bisphenol A, ciprofloxacin, diclofenac, erythromycin, ibuprofen, iopromide, perfluorooctane sulfonate (PFOS), sulfamethoxazole, tetracycline, Escherichia coli, faecal coliform, 16S rRNA, sul1, and sul2.
Innovative Technologies for Water Reuse
Title: Water treatment and reclamation by implementing electrochemical systems with constructed wetlands
Authors: Mosquera-Romero S., Ntagia E., Rousseau D.P.L., Esteve-Núñez A., and Prévoteau A.
In: Environmental Science and Ecotechnology
Abstract: Seasonal or permanent water scarcity in off-grid communities can be alleviated by recycling water in decentralized wastewater treatment systems. Nature-based solutions, such as constructed wetlands (CWs), have become popular solutions for sanitation in remote locations. Although typical CWs can efficiently remove solids and organics to meet water reuse standards, polishing remains necessary for other parameters, such as pathogens, nutrients, and recalcitrant pollutants. Different CW designs and CWs coupled with electrochemical technologies have been proposed to improve treatment efficiency. Electrochemical systems (ECs) have been either implemented within the CW bed (ECin-CW) or as a stage in a sequential treatment (CW + EC). A large body of literature has focused on ECin-CW, and multiple scaled-up systems have recently been successfully implemented, primarily to remove recalcitrant organics. Conversely, only a few reports have explored the opportunity to polish CW effluents in a downstream electrochemical module for the electro-oxidation of micropollutants or electro-disinfection of pathogens to meet more stringent water reuse standards. This paper aims to critically review the opportunities, challenges, and future research directions of the different couplings of CW with EC as a decentralized technology for water treatment and recovery.
Title: Methanotrophic oxidation of organic micropollutants and nitrogen upcycling in a hybrid membrane biofilm reactor (hMBfR) for simultaneous O2 and CH4 supply
Authors: Mortensen A.T., Goonesekera E.M., Dechesne A., Elad T., Tang K., Andersen H.R., Smets B.F., Valverde-Pérez B.
In: Water Research
Abstract: Pharmaceuticals and other organic micropollutants (OMPs) present in wastewater effluents are of growing concern, as they threaten environmental and human health. Conventional biological treatments lead to limited removal of OMPs. Methanotrophic bacteria can degrade a variety of OMPs. By employing a novel bubble-free hybrid membrane biofilm bioreactor (hMBfR), we grew methanotrophic bacteria at three CH4 loading rates. Biomass productivity and CH4 loading showed a linear correlation, with a maximum productivity of 372 mg-VSS·L−1·d−1, with corresponding biomass concentration of 1117.6 ± 56.4 mg-VSS·L−1. Furthermore, the biodegradation of sulfamethoxazole and 1H-benzotriazole positively correlated with CH4 oxidation rates, with highest biodegradation kinetic constants of 3.58 L·g−1·d−1 and 5.42 L·g−1·d−1, respectively. Additionally, the hMBfR recovered nutrients as microbial proteins, with an average content 39% DW. The biofilm community was dominated by Methylomonas, while the bulk was dominated by aerobic heterotrophic bacteria. The hMBfR removed OMPs, allowing for safer water reuse while valorising CH4 and nutrients.
Water Reuse Planning and Management
Title: Operational drivers of water reuse efficiency in Portuguese wastewater service providers
Authors: Amaral A.L., Martins R., Dias L.C.
In: Utilities Policy
Publisher: Elsevier Ltd
Abstract: Identifying the service providers that perform best in key operational indicators is important for increasing the sustainability of the wastewater treatment sector. Wastewater reuse is increasingly considered as a relevant aspect in this context. The current study first identifies the Portuguese service providers in the efficiency frontier regarding wastewater reuse and proceeds to identify its main operational drivers. Reused wastewater was then successfully estimated using the selected drivers. The main policy recommendations, resulting from this study, towards wastewater reuse upsurge include fostering the aggregation of smaller SP to benefit from economies of scale, and strive for adequate infrastructure maintenance practices.
Title: Perspectives on multi-benefit water reuse systems: A confluence of water and wastewater management planning
Authors: Bunney S., Melville-Shreeve P., Chisholm A., Cotterill S.
In: Water and Environment Journal, 37 (3), pp. 561 – 572
Publisher: John Wiley and Sons Inc
Abstract: The multiple benefits of water reuse have yet to be fully realized in our urban water management systems. One pathway to optimal implementation is to plan for their integration with wider assets in water resource or drainage and wastewater management plans. This paper explores the perspectives of water resource and wastewater management planners. Qualitative data was gathered from a workshop organized by the Chartered Institution for Water and Environmental Management (CIWEM) with 25 participants from England’s Water Service Providers (WSPs), regulators (Ofwat and the Environment Agency) and consultants working within the UK water sector. The participants acknowledged that water reuse is relevant to both water resource and drainage and wastewater management planning, but that current regulatory and funding frameworks are constraining effective engagement between water resource and drainage and wastewater management planners by encouraging the development of separate plans. A general consensus of the participants was that it would be beneficial to include water reuse technology within current and future Water Resource Management Plans (WRMPs) and Drainage and Wastewater Management Plans (DWMPs). Participants suggested this could be developed through collaborative working partnerships and support from regulatory and funding frameworks that allow for the growth and development of innovative technologies and nature-based solutions. Participants also highlighted a stronger economic case could be made for water reuse technologies if the approach seeks to capture the wider benefits and not only the ‘best value’ solution. Societal acceptance and the availability of good quality data will be key to the successful adoption of any incentivized water reuse schemes.