Nitrogenous waste removal in closed freshwater recirculating aquaculture systems using an innovative DHS-USB bioreactor

IF 4.8 Q1 AGRICULTURE, MULTIDISCIPLINARY

Journal of Agriculture and Food Research Pub Date : 2024-12-19 DOI:10.1016/j.jafr.2024.101577

Calvin Owuor Obondo , Robert Nesta Kagali , Paul Mwangi Njogu , Joseph Ngugi Kamau

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Abstract

This study aimed to evaluate the efficacy of a combined Down-flow Hanging Sponge and Up-flow Sludge Blanket (DHS-USB) system in managing nitrogenous waste in aquaculture and reducing the need for frequent water changes by mimicking natural nitrification and denitrification processes. The setup included a fish tank, water pumps, and an underground tank for storing filtered water. Fish growth parameters—body weight gain (BWG), standard growth rate (SGR), and feed conversion ratio (FCR)—were measured biweekly, while water quality metrics such as dissolved oxygen (DO), temperature, pH, turbidity, and electrical conductivity (EC) were monitored daily. Total Ammonium Nitrogen (TAN), nitrites, and nitrates were analysed using a UV–VIS spectrophotometer. Results showed that fish in the DHS-USB system had optimal growth, with an SGR of 1.98 and an FCR of 2.22, outperforming those in a pumice aquaponics setup. The DHS-USB system achieved reductions of 34.68 %, 17.54 %, and 43.71 % for TAN, Total Inorganic Carbon, and Total Suspended Solids, respectively. Bacterial density was highest within the DHS system (3.54 ± 0.27 ⨯ 10⁵ CFUs mL⁻¹), supporting efficient waste processing. Overall, the DHS-USB system demonstrated significant potential for sustainable aquaculture waste management, enhancing water quality without compromising fish growth.

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