Protein skimmer effluent from a seabass (Dicentrarchus labrax) RAS system as source for biofloc production

The present study evaluates the use of biofloc technology (BFT) for treatment of organic waste originated from an intensive recycling aquaculture system (RAS) with European sea bass, Dicentrarchus labrax. Two types of substrate were fed to 35 l reactors for the growth of bioflocs: the effluent of a protein skimmer (PSE), used to extract organics from the fish tanks based on foam fractionation, and PSE pre-treated through anaerobic digestion (ADPSE). The C:N ratio of the substrate was adjusted to 15 by adding sucrose. After thirty days of continuous feeding, the biofloc reactors were analysed on TAN, NO2, NO3, pH, VS, microorganisms and floc formation. The protein content and fatty acid profile of the produced bioflocs were compared between the two treatments. The reactors fed with ADPSE produced bioflocs that could serve as filter feeders nutrition. This was tested using different concentrations of the ADSPE bioflocs (0%, 20% and 80%) mixed with 50% Isochrysis spp. and 50% Chaetoceros spp. as possible feed for oysters (2,1mm). The protein skimmer was especially efficient in the removal of organics with a 48% removal of daily-added VS and an enrichment factor of 15,2. Anaerobic digestion of the PSE produced a methane yield of 283 mlCH4/gVS and showed a removal efficiency of 91%. Both PSE and ADPSE proved to be appropriate substrates for biofloc growth although the biofloc production on PSE is characterised by gel formation, poor biofloc quality and a high oxygen demand during startup. The reactors fed with PSE showed a significantly higher nitrite level (183±62mg/l) and a higher VS concentration (9,3±1,01gVS/l) compared to ADPSE fed reactors (resp. 29±31mg/l; 8,0±0,9gVS/l). The protein fraction differed significantly between treatments with 36,3±0,62% protein in PSE fed bioflocs and 21,9±0,63% in ADPSE fed bioflocs. This study could serve as a starting point for further research on the suitability of bioflocs, grown on different types of RAS waste, as feed for filter feeders.

Promotor(s) & Supervisor: Nancy Nevejan, Daan Delbare

ISCED Categories

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0511 - Biology", "0831 - Aquaculture", "0713 - Offshore and renewable energy