Comparison of nitrate-removal efficiency and bacterial properties using PCL and PHBV polymers as a carbon source to treat aquaculture water

Abstract

Nitrate (NO3−) accumulation in recirculating aquaculture systems (RASs) with high stocking densities presents a problem for reared animals and the environment. The use of a biodegradable polymer as organic carbon for heterotrophic denitrification exhibits good performance for NO3− removal from wastewater. A comparison of NO3−–N removal efficiency and bacterial properties using polycaprolactone (PCL) and poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) as carbon sources to treat aquaculture water was conducted for a 102-day period. The results indicated that the NO3−–N removal rates of 0.27 ± 0.07 and 0.19 ± 0.05 g/L per day, respectively, could be achieved with influent concentrations ranging from 81.1 to 132.75 mg/L and a flow rate of 1 L/h. The removal of NO3−–N versus consumed PCL (1:1 w/w) was significantly higher than that versus consumed PHBV (0.3:1 w/w) (P < 0.05). The concentrations of effluent nitrite-nitrogen and total ammonium nitrogen were maintained at an acceptable level. The bacterial community structures between the two types of reactors varied significantly. Acidovorax and Denitratisoma were the top two genera of the bacterial community in the biofilm in the PCL beads with a dominance of 26.83% and 6.67%, respectively. In the PHBV beads, Acidovorax at 17.95% and Bdellovibrio at 6.37% were the top two genera. The PCL-denitrification reactor developed in this study showed better potential than the PHBV-denitrification reactor in removing NO3− from aquaculture water. Keywords: Denitrification, Polycaprolactone, Poly (3-hydroxybutyrate-co-3-hydroxyvalerate), Recirculating aquaculture system, Nitrate