Optimizing pH Regulation Strategies in Two-Phase Anaerobic Co-Digestion System of Food waste and Paper Waste: Alkaline Addition and Sludge Recirculation

Abstract

 This study evaluated the performance of a temperature-phased two-phase anaerobic digestion system treating food waste and paper waste under two different pH regulation strategies: alkaline addition and sludge recirculation. Alkaline regulation, using Na₂CO₃ solution supplementation, exhibited the following characteristics: (1) effectively maintained the pH in acidogenic phase within the optimal range of 5.5–6.0, (2) promoted acetate-type and butyrate-type fermentation pathways, (3) enriched dominant acidogens such as Caproiciproducens and Thermoanaerobacterium. However, it also resulted in lower microbial diversity and reduced functional redundancy. In contrast, compared to alkaline regulation, sludge recirculation (1) increased hydrogen and methane production by approximately 6% and 11%, respectively, (2) enhanced organic removal efficiency and COD gasification efficiency to produce more bio-hythane, (3) stabilized the acidogenic phase by mitigating acid accumulation and (4) significantly improved microbial diversity, adaptability, and system robustness. These findings highlight the trade-offs between pathway selectivity and ecological resilience and provide practical insights into the design of pH regulation strategies for improving the efficiency and stability of TPAD systems in the future.