Abstract
Membrane-aerated biofilm reactor (MABR) technology is an exciting alternative to conventional activated sludge, with promising results in bench and pilot-scale systems. Nevertheless, there is still a lack of long-term and full-scale data under different operational conditions. This study aims to report the performance of a full-scale hybrid MABR located in the North of Europe. Influent, effluent, and exhaust data were collected for 1year (September 2019 to September 2020) using online sensors/gas-analyzers and off-line laboratory analysis. Next, oxygen transfer rate (OTR), oxygen transfer efficiency (OTE), and nitrification rates (NR) were quantified as process indicators. Finally, multivariate methods were used to find patterns among monitored variables. Observations revealed that lower airflows achieved higher OTE at the same values of OTR and OTR was strongly correlated to ammonia/um concentration in the MABR tank (NHx,eff). The dynamics between oxygen concentration in the exhaust (O2,exh) and NHx,eff indicated that a nitrifying biofilm was established within 3weeks. Average NR were calculated using four different methods and ranged between 1 and 2gNm-2d-1. Principal component analysis (PCA) explained 81.4% of the sample variance with the first three components and cluster analysis (CA) divided the yearly data into five distinctive periods. Hence, it was possible to identify typical Nordic episodes with high frequency of heavy rain, low temperature, and high variations in pollution load. The study concludes that nitrification capacity obtained with MABR is robust during cold weather conditions, and its volumetric value is comparable to other well-established biofilm-based technologies. Moreover, the aeration efficiency (AE) obtained in this study, 5.8kg O2 kW h-1, would suppose an average reduction in energy consumption of 55% compared to fine pore diffused aeration and 74% to the existing surface aeration at the facility.
Highlights
Wastewater treatment plants located in areas with large seasonal variations in temperature, such as the Nordic region, face challenges related to low water temperatures (T) and substantial influent dilution during the colder months to successfully achieve nutrient removal
This study presents results from one year of operation of a full-scale hybrid Membrane-aerated biofilm reactor (MABR) in an existing enhanced biological phosphorus removal (EBPR) type of configuration located in the Nordic region (Denmark)
Regarding aeration efficiency (AE), results up to 19.6 kg O2 kW−1 h−1 have been estimated for laboratory-scale MABRs, which meant a reduction in energy consumption of 83.7% compared to conventional fine bubble diffusers (3.19 kg O2 kW−1 h−1 at 27.89% oxygen transfer efficiency (OTE)) (Castrillo et al, 2019)
Summary
Wastewater treatment plants located in areas with large seasonal variations in temperature, such as the Nordic region, face challenges related to low water temperatures (T) and substantial influent dilution during the colder months to successfully achieve nutrient removal. There is an ongoing trend toward stricter effluent requirements and more sustainable operation, putting pressure on finding technological solutions that can simultaneously accommodate those demands. Nitrification robustness is essential for facilities with stringent nitrogen effluent requirements during cold weather conditions. Nitrification has a high temperature sensitivity; for every 10 °C drop in temperature, the maximum specific growth rate for nitrifiers halves, and the minimum solids retention time doubles (Henze et al, 2008). Operating at longer solids retention times can increase the biological nutrient removal performance during cold weather periods. Operating at longer solids retention times —15–30 days for oxidation ditches, common in Northern Europe— requires more extensive infrastructure and often results in higher energy consumption and poorly settling sludge (Rittman and McCarty, 2012). Conventional co-diffusional biofilms typically suffer from mass transfer limitations, resulting in higher dissolved oxygen concentration requirements and higher energy requirements (Metcalf and Eddy, 2014)
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