The point of this study was to find out how well anaerobic digestion (AD) can clean up wastewater from making fish crackers (Krepoh). Specifically, they wanted to find the best hydraulic retention time (HRT), rate system performance, and make sure it could be used on a large scale in communities. First, batch experiments were done with HRTs of 7, 14, 21, and 30 days to find the best time for biogas production. Next, a 19-liter continuous AD system was used to compare single-phase and single-phase with medium setups for treatment efficiency and biogas stability. Finally, a 500-liter system with a 400L working volume was tested to make sure it could be used in real life. Results indicated that the 14-day HRT produced the highest biogas yield (3,248 mL), outperforming shorter and longer HRTs. The continuous system achieved COD reduction of 65.18%, TSS reduction of 70.42%, and stable biogas production of 5.32±0.52 L/day. The larger system was still about as efficient as the smaller one. It cut COD by 57.87%, TSS by 70.42%, and EC by 28.11%, and it made high-quality biogas (400–500 L/day) with 59.49% methane that could be used for cooking in homes. System stability was demonstrated through pH normalization from acidic to neutral levels. These findings validate AD as an effective, scalable solution for wastewater treatment, offering renewable energy generation, waste reduction, and environmental benefits at the community level.