Aquaponics represents a sustainable and resource-efficient approach to integrated fish and crop production; h owever, its productivity and long-term stability are often limited by the accumulation of ammonia and the inefficiency of nitrification, which compromise water quality, fish health, and plant performance. Conventional biofiltration systems are often expensive and inaccessible to smallholder farmers, underscoring the need for low-cost, scalable alternatives. Rope bed biofilm reactors (RBBRs) have been explored in wastewater treatment but remain underexplored in aquaponics applications. This study, therefore, aimed to design, fabricate, and evaluate a low-cost RBBR using jute ropes as biomedia, with a focus on enhancing nitrification efficiency and overall system performance. The experimental system consisted of a 20-litre reactor (14-litre of working volume) integrated into a recirculating aquaponics setup containing Nile tilapia (Oreochromis niloticus) and insulin plants (Costus igneus ). The RBBR was operated at different flow rates to achieve variable hydraulic retention times (HRTs). Trials were conducted for 45 days in three replications, with systematic monitoring of key operational parameters including water temperature, pH, dissolved oxygen, chemical oxygen demand (COD), ammonia, nitrate, alkalinity, turbidity, as well as fish growth and plant biomass accumulation.
The RBBR demonstrated substantial improvements in water quality and system stability compared to the control. Ammonia removal efficiency reached 70% within a 6-hour HRT, while in the control setup, ammonia levels continued to rise, indicating poor nitrification. Turbidity levels were reduced to 32 NTU compared to 65 NTU in the control, which minimized sludge deposition and maintained cleaner plant beds. Enhanced biological filtration and effective ammonia conversion led to improvements of more than 40% in plant growth and fish performance compared with the control system. The findings indicate that the RBBR is an economical, scalable, and effective approach for enhancing nitrification efficiency, water quality, and the productivity of aquaponics fish and plants. The reactor addresses a significant issue in recirculating aquaculture by reducing ammonia levels, turbidity, and enhancing biological stability. The fundamental design, utilisation of low-cost locally available bio media makes it adaptable for resource-constrained small farmers.