Impact of environmental conditions on Moving Bed Bio-Reactor (MBBR) performance in Atlantic salmon Recirculating Aquaculture Systems (RAS)

The main focus of this PhD is biological treatment of recirculating water in land-based salmon farms. Norway is the world's largest salmon producer, with a target for a five-fold increase in salmon production by 2050, thus fostering the need for rapid development in salmon production. Typically, salmon are reared from eggs to a weight of at least 50-100 g (called smolt) in land-based farms. These smolts are then transferred to sea cages, where they are grown to approximately 4-5 kg, before being harvested. Of late, there has been increased interest in rearing salmon up to 1kg (post-smolt) on land, in salinities ranging from freshwater to seawater, since it has been observed that larger salmon survive better after transfer to the sea. Traditionally, land-based fish farms consisted of fish tanks with continuous water flow. However, in the recent years, there has been a shift to Recirculating Aquaculture Systems(RAS) where most of the water is treated and recirculated to the fish tanks. This enables superior water quality control, and significantly reduces water consumption. One of the functions of the RAS is to remove organic loading and ammonia produced by the fish, which can otherwise accumulate in the recirculating water. This is achieved using a biological filter which converts organic load to suspended solids (which can be removed via particle separation) and ammonia to nitrate (relatively much less toxic to the fish than ammonia). This PhD program will focus on the performance of the RAS biofilter, specifically the AnoxKaldnes Moving-Bed Biofilm Reactor (MBBR), under various RAS conditions like varying water salinity. The best RAS operating strategies will be proposed for growing smolt and post-smolt in land-based fish farms. Results from these studies will strengthen the knowledge base for increased production of salmon in closed systems, thereby improving sustainability and fish welfare.

Achieved: - Improved start-up protocol for RAS MBBR - Strongly reduced the risk when changing from fresh water to saline water in RAS MBBR - Better understanding of microbiota in RAS MBBR - Improved MBBR design in RAS

This PhD study will be conducted as a complementary activity to CtrlAQUA SFI - Centre for Research-Based Innovations in Closed-containment Aquaculture (Senter for forskningsdrevet innovasjon innen lukket akvakultur). The broad objective of CtrlAQUA is: To develop technological and biological innovations to make closed-containment aquaculture systems (CCS), a reliable and economically viable technology, for use in strategic parts of the Atlantic salmon production cycle, thus contributing significantly to solving the challenges limiting the envisioned growth in aquaculture. Nofima is the host institution for CtrlAQUA. This study will complement the activities in the CtrlAQUA Dept. of Technology & Environment and Dept. of Fish Production & Welfare. The doctoral degree will be conferred by NTNU, under Dept. of Chemistry (academic partner at CtrlAQUA) in the Faculty of Natural Sciences & Technology. There has been increased interest in rearing salmon up to 1kg(post-smolt) in CCS before transfer to sea, in salinities ranging from freshwater to seawater. This leads to a need for studying the specific water quality requirement and recirculating aquaculture system water treatment (RAS) process performance for optimal production of post-smolts. A typical RAS consists of particle separation, biofilter, CO2 degasser and oxygenation. This PhD program will focus on the Moving Bed Bio-Reactor (MBBR) biofilter performance based on nitrification, biological oxygen demand(BOD) reduction and denitrification. The PhD program will investigate the impact of varying RAS operating conditions on MBBR efficiency, like changing salinities, advanced oxidation and BOD. The aim is to propose the best operating strategies for MBBR performance in RAS for post-smolt production. Results from these studies will strengthen the knowledge base for increased production of salmon in closed systems, thereby improving sustainability, sea lice issues, and fish welfare.