Enhanced ammonia nitrogen filtration using NaOH-activated Manihot utilissima peel carbon: Application in recirculating aquaculture systems for Nile tilapia

Abstract

This study investigates the potential of NaOH-activated carbon from Manihot utilissima peels as an ammonia nitrogen filter in Recirculating Aquaculture Systems (RAS) for Nile tilapia (Oreochromis niloticus). Carbon was synthesized via carbonization at 300 °C and chemical activation with NaOH, resulting in a highly porous structure with a surface area of 1725 m²/g. By Week 4, ammonia concentrations decreased significantly from 12.30 ± 0.18 μg g⁻¹ in the control to 7.46 ± 0.06 μg g⁻¹ in the 20 g treatment (P5), accompanied by lower glutamine synthetase (GS_ase) activity (398.33 ± 2.89 to 258.33 ± 10.41 μmol mg⁻¹ h⁻¹). Ammonia excretion rates (J_Amm) ranged from 2.23 ± 0.15 mmol g⁻¹ h⁻¹ in P1 to 3.07 ± 0.12 mmol g⁻¹ h⁻¹ in P5 under fed conditions and decreased during fasting. Growth performance improved, with the specific growth rate (SGR) increasing from 1.61 ± 0.22 %/day to 3.59 ± 0.03 %/day, feed conversion ratio (FCR) improving from 1.79 ± 0.26 to 0.75 ± 0.03, and 100 % survival in P5. These results highlight the efficacy of cassava peel-derived activated carbon as a sustainable filtration material for enhancing water quality and productivity in RAS aquaculture.