A Simultaneous Denitrification and Fermentation Process for Nitrate Removal in a Whiteleg Shrimp (<i>Litopenaeus vannamei</i>) Recirculating Aquaculture System: Using Endogenous Carbon from a Biofilm

Abstract

During the process of circulating aquaculture, high concentrations of nitrate will accumulate. A simultaneous denitrification and fermentation process is described to remove nitrate from a recirculating aquaculture system using endogenous carbon on a biofilm. 15N isotope technology was used to assess the nitrate removal, mainly through heterotrophic denitrification. The nitrate removal rate could be as high as 98.97%, with a final concentration of nitrate below 1 mg/L. The denitrification process obeys a Michaelis–Menten-type enzyme kinetic model, with a half saturation constant of 99.91 mg/L and a maximum nitrate removal rate of 0.39 mg L−1 h−1 at 28 °C. The functional genes narG and narH for nitrate removal were obtained from Nitrospirae spp. at proportions of 39.13% and 26.16%, respectively. The acetate, propionate and iso-valerate produced by anaerobic fermentation provided the principal electron donors for denitrification.

Keywords

• heterotrophic denitrification
• ¹⁵N-tracer technique
• recirculating aquaculture system
• <i>Nitrospira</i>
• endogenous carbon from the biofilm