Very few of us ever think about what becomes of the things that we send down the drain or flush in toilets. The wastewater enters sewer systems and flows to rivers, lakes, or the sea, either treated or untreated, since Icelanders still have some way to go to meet European directives on wastewater treatment. At the University of Iceland, research is being conducted on novel wastewater treatment methods that take into account local conditions and the potential to use nutrients in certain wastewater as fertiliser for vegetable cultivation.
Wastewater discharge standards are becoming increasingly stringent globally, as untreated wastewater can have adverse effects on the environment and even contribute to the spread of diseases among people.
“EU directives on wastewater treatment require three main stages: primary (physical) treatment, secondary (biological) treatment, and disinfection (tertiary) treatment. In Iceland, most collected municipal wastewater is treated only with primary physical treatment; therefore, the treated wastewater generally does not meet EU discharge standards. However, biological processes fail to perform efficiently under Icelandic conditions, mainly due to the cold climate, high wastewater inflow rates with low organic concentrations, and dispersed populations. Therefore, there is an urgent need to develop a technically and economically feasible non-biological secondary wastewater treatment process that can be effectively adopted in Iceland,” says Bing Wu, Professor of Environmental Engineering at the University of Iceland, who is developing such a wastewater treatment process.
“My research focuses on innovative water and wastewater treatment, resource recovery, and renewable energy through advanced membrane technology and environmental biotechnology. My research activities include developing technically and economically feasible and environmentally sustainable processes, conducting laboratory and pilot-scale testing, and exploring theoretical fundamentals to solve challenges in the ‘Water-Food-Energy’ nexus and strengthen climate resilience,” says Bing.
Direct Membrane Filtration Can Be Used for Nutrient Recovery
The method at the centre of her research is called Direct Membrane Filtration (DMF). “Direct membrane filtration of wastewater without involving any biological treatment step has been considered a promising alternative solution for secondary wastewater treatment. In a DMF system, a semi-permeable microfiltration or ultrafiltration membrane (0.01-0.1 µm pore size) acts as a barrier to retain particulates, colloidal matter, and pathogens while allowing water and smaller substances to pass through. Compared to conventional biological treatment processes, DMF offers several advantages, including simplicity of design and maintenance, low capital costs, the ability to handle fluctuating inflow rates and low temperatures caused by seasonal changes, production of superior treated water quality free of solids and pathogens, and reduced sludge production, which lowers post-treatment costs. Thus, DMF processes offer potential solutions for Icelandic municipal wastewater treatment,” Bing points out.
In addition, Bing notes that direct membrane filtration is suitable for certain industrial wastewater treatment applications. “For example, we are working on membrane separation of microalgal cultivation wastewater for nutrient recovery. In this concept, residual nutrients such as phosphorus, ammonium, nitrate, trace elements, and water in microalgal cultivation solutions can pass through the ultrafiltration membrane and be readily collected as irrigation water for cultivated plants,” says Bing.
Bing’s research and development take place in laboratories with the aim of scaling up the solutions in the future. “We have developed several laboratory-scale DMF configurations using different membrane modules and materials and optimised their operating conditions for the treatment of Icelandic municipal wastewater and microalgal wastewater. Membrane fouling is a major concern in DMF processes because certain substances in wastewater block membrane pores and deposit on membrane surfaces, creating additional hydraulic resistance that reduces water permeability. Our research focuses on examining membrane fouling mechanisms and identifying suitable strategies for controlling membrane fouling. To further improve treated water quality and support future scale-up, studies on the removal of micropollutants and microplastics from municipal wastewater, as well as comprehensive techno-economic feasibility analyses and life cycle assessments of DMF systems, are being undertaken,” Bing explains, with microplastic pollution being a growing problem worldwide.
Lower Wastewater Treatment Costs and Reduced Environmental Impact
Asked about the results of her research, Bing says that her research group has conducted studies comparing various laboratory-scale process designs, including gravity-driven versus pressure-driven configurations and inorganic membranes versus organic membranes.
“We have also integrated novel membrane fouling control techniques into the DMF system to reduce membrane fouling. The experimental results showed that the DMF process could achieve lower municipal wastewater treatment costs and reduced environmental impact compared with conventional biological processes, while also achieving excellent treated water quality under cold-climate conditions, free of solids and microplastics,” she says.
The favourable DMF configuration that Icelandic utility companies may potentially adopt will be further scaled up. “This project is funded by the EU Marie Skłodowska-Curie Actions as one of the projects in an Industrial PhD Network and is being carried out in collaboration with Veitur. Through pilot-scale DMF systems, we will further improve DMF performance for Icelandic municipal wastewater treatment and explore fundamental research on membrane-foulant-micropollutant interactions during DMF operation,” Bing says about the continuation of the research.
Working with local company on Using Fertiliser from Microalgal Cultivation for Vegetable Production
Bing and her research group are also collaborating with the Icelandic microalgal company Algalíf to assess the feasibility of recovering liquid fertiliser from membrane-based microalgal cultivation solutions for hydroponic vegetable cultivation. The project is funded by the Rannís Technology Development Fund and is in collaboration with Prof. Sigurður Brynjólfsson (University of Iceland) and Prof. Ragnheiður I Þórarinsdóttir (Agricultural University of Iceland).
“The outcomes of this research can lead to a sustainable membrane process for wastewater treatment through lower operating costs associated with reduced membrane fouling and lower chemical consumption. This is critically significant because highly efficient municipal wastewater treatment guarantees the safe discharge of treated water into rivers and oceans, benefiting environmental conservation and promoting sustainable economic development in Iceland. Furthermore, membrane-based resource recovery from industrial wastewater could help Icelandic companies achieve a circular economy and increase profitability,” Bing concludes.
Working with Bing on her projects are undergraduate and graduate students at the University of Iceland, including Selina Hube, Sif Guðjónsdóttir, Ihtisham ul Haq Shami, Megan Elizabeth Wiegmann, Magnea Freyja Kristjánsdóttir, Yuting Huang, and Dagmar Ólafsdóttir. The research team has collaborated on this work with Professor Tzyy Haur Chong’s research team at Nanyang Technological University in Singapore and Professor Michael Burkhardt and his team at the Eastern Switzerland University of Applied Sciences.