Harmonization of biogas, greenhouse gases, water quality, and energy consumption in sidestream systems using computational assessment
Abstract
Graphical summary of the study. Four anaerobic digestion configurations - conventional anaerobic digestion, thermal hydrolysis combined with conventional digestion, an anaerobic membrane bioreactor configuration, and the fully integrated configuration - are evaluated by plant-wide simulation across food-waste mixing ratios. Four indicators (specific methane production, sidestream load to mainstream, greenhouse gas emissions and energy footprint) are normalised and combined into a single composite Sustainability WWTP Index. This study evaluated the sustainability of four anaerobic digestion (AD) configurations, namely conventional anaerobic digester (CAD), thermal hydrolysis coupled with CAD (THP + CAD), CAD integrated with an anaerobic membrane bioreactor (AnMBR), and a fully integrated THP + CAD + AnMBR system. Process simulation and response surface methodology (RSM) were applied to assess system performance under varying food waste (FW) ratios. the sustainability WWTP Index (SWI) was developed by integrating specific methane production (SMP), sidestream load to mainstream (SLM), greenhouse gas (GHG) emissions and energy footprint (ENF). Advanced configurations enhanced methane production at moderate FW ratios. However, synergy decreased at 50% FW, where THP + CAD + AnMBR's SMP (11.5) fell below the CAD baseline (11.8). THP + CAD achieved the most consistently favourable SWI balance, maintaining a 100% above-median frequency up to 25% FW. The AnMBR-based systems exhibited higher volatility and increased the GHG footprint by approximately 4.5%. Ammonia rose with food waste addition, yet free ammonia stayed below inhibitory levels in all scenarios. Optimization indicated that for the THP + CAD + AnMBR configuration, a 0.35 bypass ratio and a 50-day SRT maximized the SWI. These findings show that AD configuration performance depends on the operating regime, which the SWI makes explicit.