Bioenergy Potential of Anaerobic Co-Digestion of Aquaponics Effluent and Cattle Manure

Mathematical modeling is a key tool for describing and predicting the dynamic behavior of anaerobic digestion. Studies combining the co-digestion of aquaponics effluent (AE) and cattle manure (CM) with kinetic modeling remain scarce, particularly regarding the estimation of the apparent kinetic constant of hydrolysis constants and energy conversion indicators. Accordingly, this study aimed to evaluate the bioenergy potential of co-digesting aquaponics effluent (AE) and cattle manure (CM), with an emphasis on kinetic modeling and energy conversion. The experiments were carried out in a bench-scale Indian-type anaerobic biodigester. Different AE, CM, and water (W) (0:1, 1:0, 1:1, 1:3, 3:1 W:CM, and 1:1, 1:3, and 3:1 AE:CM) ratios were tested to identify the most efficient substrate combination for biogas production. The 1:3 AE:CM ratio achieved the best performance, with the Gompertz model providing the best fit for cumulative production and the first-order model accurately estimating k. This ratio yielded the highest cumulative biogas production (72.2 L kg−1 substrate), shorter lag phase, higher production rate, and greater energy conversion efficiency. Comparative analysis revealed that 1:3 AE:CM outperformed both 1:3 A:CM and CM alone, highlighting the positive influence of aquaponics effluent on microbial activity and process stability. These results demonstrate that anaerobic co-digestion of AE and CM, particularly at the 1:3 ratio, is a viable and efficient strategy for renewable energy generation in rural areas, while promoting waste valorization and enhancing environmental and energy sustainability.