Comparison of four different types of biomedia during start-up in a recirculating aquaculture system with rainbow trout

• Published in: Journal of water process engineering 2024-12, Vol.68, p.106549, Article 106549
• Main Authors: Mnyoro, Mang'era Samwel, Munubi, Renalda N., Chenyambuga, Sebastian W., Pedersen, Lars-Flemming
• Format: Article
• Language: English
• Subjects: Alternative bio media; Biofiltration; Ceramic beads; Coconut husks; Polyurethane foam
• ISSN: 2214-7144; 2214-7144
• DOI: 10.1016/j.jwpe.2024.106549

Towards modern development of fish production technology, recirculating aquaculture system (RAS) application has become prominent. One of the main functional parts of RAS is biofilters. Biomedia type and surface area are among the factors determining the effectiveness of a biofilter. This experiment was done to test and compare the nitrification performance of similar sized coconut husks, granulated leftover polyurethane foam, ceramic beads and a commercial available bioelement simultaneously operated in a 20 m3 semi-commercial RAS during startup. Volumetric total ammonia nitrogen (TAN) and nitrite conversion rates (VTR and VNR respectively) were measured biweekly for the first 6 weeks, followed by the assessment of bacterial activity at week 8. Significant highest TAN removal was found in biofilters with granulated polyurethane foam (310 ± 21 g TAN/m3/d) while coconut husks, ceramic beads and plastic media removed from 160 to 175 g TAN/m3/d. Biofilters stocked with polyurethane foam achieved higher VNR (257 ± 22.2 g NO2-N/m3/d) than coconut husks, ceramics beads and plastic bioelements (140 ± 10; 125 ± 8 and 90 ± 5.2 g NO2-N/m3/d respectively. The 0′ order nitrification kinetics for VTR (k0v) averaged 202, 371, 417 and 539 g/m3/d for plastic beads, ceramic beads, coconut husks, and polyurethane foam granulates, and a similar order was found when estimating nitrite removal. After week 7, bacterial activity associated with the different types of biofilter was assessed using an assay based on the degradation of added hydrogen peroxide. The lowest H2O2 degradation rate constant (k), was found in biofilters with commercial plastic (0.76 ± 0.1 h−1). Intermediate activities were found in biofilters with ceramic beads and coconut husks (1.0 ± 0.01 h−1 and 1.4 ± 0.1 h−1) while polyurethane foam had the highest H2O2 rates (2.3 ± 0.3 h−1). Polyurethane foam appears to be an excellent biomedium in RAS while coconut husks and ceramic beads revealed a better performance compared to a commercial biocarrier. •Polymeric foam granulates proved superior in nitrification performance in a freshwater RAS during startup.•Coconut shells and ceramic beads performed similarly to commercial PP bioelements during startup.•Hydrogen peroxide degradation showed significantly different bacterial activity between the types of bioelements tested.