A Utilities Path to Implementing Disruptive Emerging Technologies: From Demonstration to the Full-Scale Implementation of MABR Technology

INTRODUCTION VCS is Denmark's third largest and oldest water utility with more than 150 years of operational experience and a strong tradition of innovation, with a focus on implementing triple-bottom-line sustainability practices and emerging technologies to manage the water-energy nexus. The utility 8 water resource recovery facilities (WRRFs). In 2009 IT initiated the Beyond Energy Neutrality program, aimed at improving resiliency and sustainability through turning their largest facility, the Ejby Mølle WRRF with a 410,000 population equivalent (PE) capacity from a large electrical power consumer to a net producer of electricity and heat energy.This biological nutrient removal facility meets very stringent nutrient limits (6 mg/L total nitrogen and 0.5 mg/L total phosphorus) prior to its discharge into a small, local river. By 2014, the Ejby Mølle was net energy positive as the result of implementing several innovative technologies, including ammonia-based aeration control, sidestream deammonification, optimized combined heat power capacity from sludge digestion, and induced biomass granulation through hydrocyclones, which also improved process resiliency during wet weather events (Nielsen and Sandino, 2020). DEMONSTRATION TESTING - UNDERSTANDING MABR'S POTENTIAL The Beyond Energy Neutrality program continued to investigate ways to further provide sustainable water resource recovery at the Ejby Mølle WRRF. Between 2017 and 2020, VCS conducted an industry-first demonstration program focused on how membrane aerated biofilm reactors (MABR) might deliver further energy savings, while reducing greenhouse gas emissions and requiring a much smaller facility footprint, which would be of great importance to other large facilities in need to increase capacity or achieve higher levels of treatment within constraint sites. This emerging technology relies on membranes capable of gas transfer to deliver oxygen to a AOB-rich biofilm that is attached to the membrane. The direct supply of oxygen to the biomass growing in the biofilm makes the theoretical oxygen transfer efficiency, a key parameter for efficient and low energy aeration, close to 100%. The testing program aimed at answering several questions that need to be addressed regarding the applicability of this emerging technology in full-scale and of the installation of MABR modules purchased from two different manufacturers in the last anaerobic zone ahead of the aeration ditches at Ejby and in remote containers next to the tanks, and their operation during a three-year period (Figure 1). FULL-SCALE IMPLEMENTATION — BETTING ON DISRUPTION Based on the encouraging results and further understanding of the anticipated operational and maintenance requirements of the technology gathered from the demonstration testing stage, VCS decided to implement MABRs at their Søndersø¸ WRRF. This 20,000 PE nutrient removal facility was built in 1990 and is configured with two treatment trains running in parallel, each consisting in two oxidation ditches operated under alternate aerobic/anoxic conditions (BioDenitro process). During heavy precipitation events, the maximum incoming flow is more than four times the yearly average incoming flow, when the facility is under stress and its performance worsens, resulting in ammonia peaks discharged in the effluent. Given this challenge, VCS decided to couple the MABR with induced granulation capabilities via heavy biomass selection using hydrocyclones, based on their earlier positive experience at their Ejby Mølle facility. A key component in the road to the full-scale implementation of this emerging and potentially disruptive technology was VCS's ability to secure funding from the LIFE programme, the European Union's funding instrument for the environment and climate action. Essentially, the programme financed 50% of the implementation costs at Søndersø. Improvements at Sonderso included the retrofit completed in 2023 of one of the two oxidation ditches with seven MABR modules, becoming one of the largest facilities with this technology currently operating in the world (Figure 2). Results to date show an average aeration energy saving of 25% compared to the control train. The MABR units are showing an average oxygen transfer rate of 11 g O2/m2/d (Figure 3). Nitrification rates from the MABRs are averaging 2.4 g N/m2/d, corresponding to approximately one fourth of the total nitrogen load to the treatment plant. Normalizing these nitrification rates per volume of reactor used, the MABRs are successfully removing 0.5 kg N/m3/d, which is 25 times more intensive than the existing activated sludge train. These results indicate that the incorporation of this emerging technology does in fact provide significant additional capacity, while reducing energy consumption and maintaining low N2O emissions (Uri-Carreño et al, 2023). RELEVANCE This paper will show how a water utility has successfully embarked in transforming by adopting emerging technologies that have a very high disruptive potential. MABR is one of these them, promising significant process intensification and energy reduction while also resulting in a very low carbon footprint for biological nutrient removal applications. This paper is intended to illustrate the role water utilities can play on moving a promising emerging technology in the water resource recovery industry, a much-needed step in meeting the umprecendented challenges we are facing.