Study on implementation of anaerobic digestion and composting technologies for kitchen waste management: A case study in Macau

Background: Macau, a key tourist and commercial hub, is grappling with substantial kitchen waste due to its growing population and tourism sector. The rapid increase in kitchen waste has significant environmental, social, and economic impacts, necessitating effective waste management strategies. Objective: This study aims to address the significant technical challenge of inefficient kitchen waste management in Macau by developing innovative, scalable solutions. Specifically, the study introduces a tailored application of the Continuous Stirred Tank Reactor (CSTR) process and a combined desulfurization approach, which have not been extensively tested under Macau's unique environmental and economic conditions. This innovative approach optimizes resource utilization, minimizes environmental impacts, and aligns with sustainable development goals. Methods: The study evaluates and selects the Continuous Stirred Tank Reactor (CSTR) process from various anaerobic digestion technologies (UASB, CF, USR, dry fermentation) for its adaptability and efficiency. It incorporates a combination of biological and chemical desulfurization methods to ensure high-quality biogas production. Results: ● Biogas Production and Trend Analysis: The anaerobic digestion process demonstrated a steady increase in biogas production, reaching a peak of 150 cubic meters per day on the 22nd day. This trend indicates a stable microbial adaptation phase, followed by an optimal biogas yield phase. Methane content was consistently maintained at an average of 65 %, which aligns with industry standards for renewable energy applications. Compared to previous studies, the methane yield stability in this study indicates an effective microbial balance and process optimization.● Compost Quality and Agricultural Viability: The compost produced exhibited a high organic matter content of approximately 75 % and an optimal pH of 7.2, making it suitable for agricultural applications. Nutrient analysis revealed elevated levels of nitrogen (2.1 %), phosphorus (1.8 %), and potassium (2.3 %), ensuring soil enrichment benefits. Compared with conventional composting methods, the dual-treatment process used in this study enhanced nutrient preservation and minimized degradation losses. These findings align with prior research, further validating the agricultural applicability of the compost product. Conclusions: This study demonstrates that anaerobic digestion and composting are not only viable solutions for Macau's kitchen waste management but also offer tailored innovations. The integration of dual desulfurization methods within the Continuous Stirred Tank Reactor (CSTR) system enhances methane yields and biogas quality. Mechanistically, the CSTR facilitates uniform substrate mixing and stable microbial activity, optimizing the hydrolysis and methanogenesis stages, while the combined biological and chemical desulfurization effectively reduces hydrogen sulfide levels, ensuring biogas purity. Additionally, the composting process promotes aerobic microbial activity, enhancing nutrient mineralization and humification. The nutrient-rich compost thus aligns with sustainable waste management goals in Macau's high-density urban context.