New pilot scale concepts for water treatment with membrane technology

IntroductionGlobal water scarcity necessitates innovative approaches to water treatment. Membrane technology has emerged as a key solution, demonstrating its effectiveness across a range of applications, from seawater desalination using reverse osmosis to wastewater treatment with membrane bioreactors. This presentation will introduce three novel water treatment concepts based on membrane technology, detailing their development from initial idea to pilot-scale testing. The concepts include utilizing microfiltration/ultrafiltration (MF/UF) membranes for the efficient collection and purification of stormwater, implementing direct membrane filtration (DMF) for enhanced wastewater treatment processes, and combining forward osmosis (FO), membrane distillation (MD), and nanofiltration (NF) for a more efficient seawater desalination process. These innovative approaches promise to enhance water treatment efficiency and sustainability, addressing the critical issue of water scarcity.MF/UF for rain and stormwater harvestingThe EU-Horizon 2020 project REWAISE (Resilient Water Innovation for Smart Water Economy) aims to reduce drinking water consumption by 30%. In Sweden, where the average consumption is 140 liters per person per day, this target would bring it down to around 100 liters. Approximately 45 liters per person per day are used for purposes such as toilets and washing machines, which do not require drinking water quality. The project proposes using membrane technology to treat stormwater for these uses.Initial trials of this concept were conducted at a stormwater pond in Lund, Sweden, utilizing a unit with 5 m² of submerged ceramic membranes. Specifically, silicon carbide membranes (Liqtech, Denmark) with a 400 kDalton molecular weight cut-off were used. These membranes effectively remove microplastics and micropollutants larger than 0.2 microns from stormwater. The results showed efficient removal of micropollutants, microplastics, and some heavy metals, producing water close to EU class 'A' quality for agricultural use. Building on these successful trials, a full-scale unit was installed at the Röda Oasen apartment building in Malmö, Sweden. This unit employs 13.8 m² of ceramic silicon carbide membranes (Cembrane, Denmark) with a 200 kDalton molecular weight cut-off. Operational since February 2024, it produces about 1,300 liters of water daily for 22 toilets and 4 washing machines, using stormwater collected from the roof and an underground tank. This installation saves the property owner approximately 40% of their drinking water consumption, equating to 475,000 liters annually.Wastewater treatment with DMFThe DMF concept, an abiotic alternative for municipal wastewater treatment, employs coagulation, flocculation, and microsieving before membrane treatment. This approach achieves high carbon rejection, which enhances biogas production and paves the way for a potentially energy-neutral or energy-positive process. The concept was successfully tested on a pilot scale in Lund, Sweden, using 0.2 μm PVDF microfiltration membranes (Alfa Laval, Denmark), with coagulation, polymer addition, and 100 µm micro-screening as pre-treatment.Building on the positive pilot test results, a larger unit was installed in Fredrikstad, Norway, capable of treating over 90 m³ of wastewater per day. This installation is currently one of the largest DMF plants for wastewater treatment. These two cases demonstrate that DMF can achieve high rejection rates of carbon (COD, SS) and total phosphorus. Moreover, its significant carbon rejection capability can substantially boost biogas production, advancing the goal of energy-neutral or energy-positive wastewater treatment.Novel concept for seawater desalinationThe EU-Horizon 2020 project DESOLINATION (Demonstration of Concentrated Solar Power Coupled with Advanced Desalination System in the Gulf Region) aims to efficiently integrate a concentrated solar power (CSP) system with a membrane-based desalination system on a pilot scale in a real-world setting. Waste heat from the CSP system will power the desalination process, reducing costs—a major barrier to CSP deployment. The concept utilizes a thermo-responsive polymer as a forward osmosis (FO) draw solution, combined with nanofiltration (NF), membrane distillation (MD), and a coalescer. A key success factor is the draw solution, which must provide sufficient osmotic pressure to desalinate seawater with 3.5% salt while being compatible with the membranes and modules used. Initial trials of the individual units are currently ongoing in the pilot plant hall at Lund University, Sweden. Based on these results, a large-scale pilot will be installed at the CSP plant of King Saud University in Riyadh, Saudi Arabia.Outlook and conclusionsThese innovative water treatment concepts showcase the significant potential of membrane technology in addressing global water scarcity. By progressing from pilot studies to full-scale implementations, these projects are paving the way for more sustainable and efficient water management solutions on a global scale.AcknowledgmentsThe research is partly funded by the REWAISE “Resilient Water Innovation for Smart Economy” (Project No. 869496) and DESOLINATION (Project No. 101022686) under the European Horizon 2020 programme.References[1] Svenskt Vatten (2017). Värt att veta om vatten. https://www.svensktvatten.se/globalassets/fakta-om-vatten/dricksvattenfakta/vart-att-veta-om-vatten_2017.pdf