Journal
AQUACULTURE INTERNATIONAL
Volume 27, Issue 5, Pages 1485-1501Publisher
SPRINGER
DOI: 10.1007/s10499-019-00402-5
Keywords
Denitrification; MBBR; Moving bed biofilm reactor; Nitrate removal; ORP control; RAS; Recirculating aquaculture system
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Funding
- BMBF [AZ: 13FH004I3]
- European Union [321553]
- ERASMUS grant
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This study examined the performance of three independently operated denitrifying moving bed biofilm reactors (MBBRs) in a zero-exchange marine recirculating aquaculture system (RAS) stocked with European seabass (Dicentrarchus labrax). A semi-automated control strategy was applied to foster spontaneous denitrification. Process automation consisted of a pulsed carbon supply and an inflow of nitrate-rich, aerated process water controlled by the oxidation-reduction potential (ORP) in the MBBR. Carbon dosing frequency was adjusted manually if the process produced unwanted products (i.e., nitrite or ammonia). OPR-controlled inflow stimulated bacterial activities in the MBBRs until inflow reached the pre-set maximum at a hydraulic retention time (HRT) of 0.75 h. This allowed for a quick start-up of the denitrification processes in spite of high initial variability of process water inflow and of nitrate removal efficiency (NRE). A start-up with glycerol did not induce a stable denitrification process; however, after the process had been established with acetate, glycerol promoted efficient denitrification with NRE close to one. The successive application of the two carbon sources resulted in a high nitrate removal rate (NRR) of 2 kg nitrate-N m(-3) day(-1) in the biofilters. This diminished the concentration of nitrate-nitrogen (nitrate-N) in the RAS (volume 9 m(3)) from 176 to 36 g m(-3) in 42 days with biofilters comprising only 1% of the RAS volume. The implications for the development of an automated denitrification process are discussed.
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