Abstract / Description Hong Kong confronts an acute municipal solid waste crisis, generating 10,548 tonnes daily, of which 3,300 tonnes (30%) constitutes organic fraction municipal solid waste (OFMSW). With only 6.4% food waste recycled and landfills projected to reach full capacity in 2026, anaerobic digestion (AD) technology offers a validated circular economy solution to simultaneously address waste diversion and renewable energy generation. Technical Process: AD systems convert organic waste through five sequential biological stages operating in oxygen-free environments. Stage I employs mechanical (milling, grinding), chemical (HCl pretreatment at 100°C achieving 120% efficiency gains), and biological methods to enhance substrate accessibility while removing contaminants via trommel screens and ballistic separators. Stage II (hydrolysis) utilizes enzymatic cellulosome complexes to depolymerize complex carbohydrates, proteins, and fats into monomers. Stage III (acidogenesis) converts hydrolyzed substrates into volatile fatty acids and alcohols, with pH monitoring via SCADA systems. Stage IV (acetogenesis) transforms organic acids into acetate, hydrogen, and carbon dioxide. Stage V (methanogenesis) employs archaeal communities to produce biogas (60-70% methane, 30-40% CO₂) with biochemical methane potential reaching 308.3 L CH₄/kg volatile solids under mesophilic (30-40°C) or thermophilic (50-60°C) conditions. Biogas Upgrading: Raw biogas undergoes desulfurization (H₂S removal), moisture extraction, and CO₂ separation to achieve pipeline-grade biomethane (97.5-99.2% purity) requiring 0.3-0.5 kWh/m³ energy input. Dual outputs include renewable natural gas convertible to compressed natural gas (CNG) and nutrient-rich digestate retaining 50% nitrogen and 86.4% phosphorus for agricultural applications. Performance Metrics: Systems achieve 78% greenhouse gas reductions (from 568 to 125 g CO₂-eq/kg waste). Hong Kong's O·PARK1 demonstrates commercial viability: 200 TPD capacity producing 14M kWh/year electricity (3,000 households) and 20 tonnes/day compost while avoiding 42,000 tonnes CO₂-eq annually. Critical operational constraints include maintaining methane leakage below 0.3% (industry average: 2-10%), managing feedstock contamination (oils 16.98-38.92%, microplastics 0.69-2.4%), and achieving municipal waste sorting compliance above 70%.
Winkey et al. (Mon,) studied this question.