Operational experience with indirect potable reuse at the Flemish Coast
Abstract
The Intermunicipal Water Company of the Veurne region (IWVA) reuses wastewater effluent for groundwater recharge of an unconfined dune aquifer since July 2002. The ‘Torreele’ reuse plant has a production capacity of 2,500,000 m3/y. Due to the sensitive environmental nature of the dune area, the quality of the infiltration water is subject to stringent standards. The combination of membrane filtration techniques proved capable of producing this quality and enabled a sustainable groundwater management of both dune water catchments owned by the IWVA.
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Fate of organic micropollutants during brackish water desalination for drinking water production in decentralized capacitive electrodialysis
2023, Water ResearchCapacitive electrodialysis (CED) is an emerging and promising desalination technology for decentralized drinking water production. Brackish water, often used as a drinking water source, may contain organic micropollutants (OMPs), thus raising environmental and health concerns. This study investigated the transport of OMPs in a fully-functional decentralized CED system for drinking water production under realistic operational conditions. Eighteen environmentally-relevant OMPs (20 µg L−1) with different physicochemical properties (charge, size, hydrophobicity) were selected and added to the feed water. The removal of OMPs was significantly lower than that of salts (∼94%), mainly due to their lower electrical mobility and higher steric hindrance. The removal of negatively-charged OMPs reached 50% and was generally higher than that of positively-charged OMPs (31%), whereas non-charged OMPs were barely transported. Marginal adsorption of OMPs was found under moderate water recovery (50%), in contrast to significant adsorption of charged OMPs under high water recovery (80%). The five-month operation demonstrated that the CED system could reliably produce water with low salt ions and TOC concentrations, meeting the respective WHO requirements. The specific energy consumption of the CED stack under 80% water recovery was 0.54 kWh m−3, which is competitive to state-of-the-art RO, ED, and emerging MCDI in brackish water desalination. Under this condition, the total OPEX was 2.43 € m−3, of which the cost of membrane replacement contributed significantly. Although the CED system proved to be a robust, highly adaptive, and fully automated technology for decentralized drinking water production, it was not highly efficient in removing OMPs, especially non-charged OMPs.
A main reverse osmosis (RO) limitation is the operational costs (including energy filtration costs), which are significantly affected by energy costs and the expense of membrane maintenance. Both costs are affected by influent characteristics, including feedwater temperatures (T), electrical conductivity (EC), and recovery set points. A fuzzy logic advanced control system optimizes the RO operational costs considering feedwater EC and T as input values, and the RO recovery setpoint as a control action. Verification results show that, once calibrated, the simulation of the control system can save more than one million euros per year in large RO facilities (>30.000m3·day-1). Which represents a reduction of 0.11€·m-3 of influent treated water.
Modeling the energy consumption of potable water reuse schemes
2021, Water Research XPotable reuse of municipal wastewater is often the lowest-energy option for increasing the availability of fresh water. However, limited data are available on the energy consumption of potable reuse facilities and schemes, and the many variables affecting energy consumption obscure the process of estimating energy requirements. By synthesizing available data and developing a simple model for the energy consumption of centralized potable reuse schemes, this study provides a framework for understanding when potable reuse is the lowest-energy option for augmenting water supply. The model is evaluated to determine a representative range for the specific electrical energy consumption of direct and indirect potable reuse schemes and compare potable reuse to other water supply augmentation options, such as seawater desalination. Finally, the model is used to identify the most promising avenues for further reducing the energy consumption of potable reuse, including encouraging direct potable reuse without additional drinking water treatment, avoiding reverse osmosis in indirect potable reuse when effluent quality allows it, updating pipe networks, or using more permeable membranes. Potable reuse already requires far less energy than seawater desalination and, with a few investments in energy efficiency, entire potable reuse schemes could operate with a specific electrical energy consumption of less than 1 kWh/m3, showing the promise of potable reuse as a low-energy option for augmenting water supply.
Secondary treated domestic wastewater in reverse electrodialysis: What is the best pre-treatment?
2019, Separation and Purification TechnologyAlthough Reverse Electrodialysis (RED) is most commonly known as a selective separation technology used for the production of sustainable energy, it can also serve as a valuable pre-desalination tool. By coupling RED to Reverse Osmosis (RO) for seawater desalination: (1) sustainable energy is produced in the RED process and (2) seawater is partially desalinated prior to RO thus, decreasing the energy demand. In this study, secondary-treated wastewater is proposed as the low salinity source in RED and suitable pre-treatment techniques for this effluent are investigated. Although it is generally accepted that RED is less prone to fouling than typical pressure driven membrane processes, results showed that pre-treatment is a key to ensure efficient operation of the wastewater-seawater RED. Both 100 µm filtration and rapid sand filtration proved to be suitable, with an increase in pressure drop of only 0.09–0.18 bar and a permselectivity decrease of only approximately 20% during 40 days of continuous operation. Conversely, River bank filtration did not perform better than the non-pretreated sample. As such, 100 µm filtration and rapid sand filtration are considered suitable, robust, and cost efficient pre-treatment options for wastewater fed RED, enabling the improvement of the hybrid process of RED-RO seawater desalination.
How scale and technology influence the energy intensity of water recycling systems-An analytical review
2019, Journal of Cleaner ProductionMany cities are moving towards increased use of recycled water to meet water demand due to freshwater scarcity, population growth, urbanisation and climate change. Water recycling requires substantial energy. Water utilities are facing serious challenges providing cost-effective and reliable water services under rising energy cost. Energy is further linked with global climate change through carbon intensive Greenhouse Gases (GHGs) emissions. However, few studies have attempted to understand the energy use of water recycling systems and how energy intensity of those systems varies with scale and technology. In this paper, we undertook a comprehensive and systematic literature and data review to understand the energy intensity of water recycling systems. We used four “cases”: (1) Centralised Potable (2) Centralised Non-Potable, (3) Decentralised Potable and (4) Decentralised Non-Potable systems to structure our work. Our analysis demonstrates how energy intensity of water recycling systems decreases with increasing size for a wide range of scale and for different treatment technologies. The treatment energy intensity for centralised systems having capacity less than 5 MLD varies from 0.48 to 2.0 kWh/kL for non-potable and 0.75 to 2.0 kWh/k for potable; for capacities between 5 and 200 MLD varies from 0.2 to 0.9 kWh/kL for potable and from 0.25 to 0.75 kWh/kL for non-potable; and for any capacity greater than 200 MLD, the treatment energy intensity is less than 0.8 kWh/kL for potable and 0.55 kWh/kL for non-potable systems. But current centralised water recycling systems have a treatment energy intensity from 0.65 to 1.4 kWh/kL for Potable for capacity from 21 to 378 MLD and from 0.6 to 1.0 kWh/kL for non-potable systems for 6 to 350 MLD. In the case of decentralised systems, smaller systems consume higher energy than centralised systems but larger decentralised Systems (mid-size) have lower energy intensity. Though the treatment energy intensity of a centralised system is low, the reuse of treated water for non-potable water requires a dual pipe system which involves a good amount of pumping energy due to the long distance between the treatment plant and the users. Pumping energy, in this case, can vary from 0.19 to 1.43 kWh/kL. The selected treatment technology and train have also influence on the energy use. The present trend of water recycling is to produce high-quality recycled water for all non-potable reuse using Advanced Water Treatment but all non-potable water uses do not necessarily require such high quality water. Little attention has been given to introducing ‘fit for purpose’ water reuse using appropriate technologies and larger decentralised (distributed) water recycling systems that have the potential to reduce energy intensity for cost-effective urban water services.
Efficiency and sustainability of urban wastewater treatment with maximum separation of the solid and liquid fraction
2019, Comprehensive BiotechnologyThe high CO2 footprint of conventional activated sludge (CAS) schemes acts as an economical and environmental incentive to totally revise existing systems. Indeed, sewage treatment through the CAS process with low loading and high solids retention time (sludge retention time (SRT) = 25 days) requires significant energy input for carbon and ammonium oxidation, that is, 22 kg CO2 equivalents per inhabitant equivalent (IE) per year. Excess sludge production is usually disposed off to the environment (landfill) in small- and medium-scale facilities, rendering an additional global warming equivalent of 40–100 kg CO2 IE−1 year−1. These emissions can be minimized in larger-scale facilities by anaerobic digestion of the excess sludge, which furthermore recovers an equivalent of 7–10 kg CO2 IE−1 year−1 as energy. Innovative schemes are based on a first concentration step of the chemical oxygen demand (COD), P, and heavy metals; followed by anaerobic digestion of the produced sludge; and a final aerobic step for N oxidation and residual COD degradation. A first option is to concentrate biologically, with a highly loaded activated sludge tank with low SRT (5 days), requiring an equivalent of 6 kg CO2 IE−1 year−1. A second option is to use physicochemical concentration techniques. In practice, it is possible to implement a chemically enhanced primary treatment (CEPT) step at an equivalent energy input of 3 kg CO2 IE−1 year−1. This can be upgraded with dissolved air flotation (DAF) for an additional 3 kg CO2 IE−1 year−1. A nitrifying trickling filter or an oxygen-limited autotrophic nitrification/denitirification (OLAND) process can perform the final polishing, at an additional equivalent of only 4 kg CO2 IE−1 year−1. In the proposed schemes, anaerobic digestion hence plays a key role, recovering an energy equivalent of as much as 10 kg CO2 IE−1 year−1.