Membrane aerated biofilm reactor (MABR) as energy efficient biofilter on RAS

Offentlig prosjektsammendrag

Aquaculture is currently the fastest expanding global animal food production sector and is a key future contributor to food security. Land-based recirculating aquaculture system (RAS) has been a sustainable alternative to traditional open net-pens for growing fish due to documented net-pens challenges with disease, fish escapes, nutrient emissions, and sea lice. RAS offers about 90 – 99% water reuse with less pollution to the environment, and no fish escape. In 2019, DNB reported RAS was growing faster than expected and estimated there was around 500,000 metric tons of new planned RAS farms by 2026. This estimate was twice the estimates made two (2) years ago by same institution. However, RAS is highly energy dependent, and presents a challenge for realizing the Norwegian salmon farming industrial goal set to increase production to five mill tons in 2050 with defined set of environmental sustainability goals. Higher energy demand presents high economic cost to fish producers making it unattractive to investors who can drive the industry to achieving this goal. Therefore, an objective of increasing energy efficiency in RAS is of importance. Currently, more energy is used for injecting air into biofilters to provide oxygen demand, and for moving bio media in moving bed bioreactors (MBBR) to treat fish wastewater before recycled to fish tanks. As much as 70% of this oxygen is unutilized or wasted by getting out of water before used through raising air bubbles to the surface. Therefore, air is injected at the bottom of biofilter tanks which requires relatively high pressure resulting in higher energy needs. Heat is also transferred to the water during compressed air injection to these biofilters which must be removed using water chillers especially when growing salmonids. MABR is expected to lower energy utilization, ensure efficient oxygen delivery, minimal or no heat addition to biofilter, provides smaller footprint while offering lower capital investment to RAS.