Comparison of Vertical and Horizontal Composting Reactors for Co-treatment of MSW and Sewage Sludge

Purpose: This study investigated the co-composting of municipal solid waste (MSW) and sewage sludge (SS) in lab-scale vertical and horizontal reactors to compare their performance and identify optimal operational parameters for enhanced bio-safety. Method: The study compared the reactor configurations using two distinct aeration flow rates (22 and 66 L·min⁻¹) and two sizes of wood chip bulking agents (10 mm and 20 mm), resulting in eight experimental runs. Results: All eight treatments achieved the required thermophilic temperature (>55 ºC for at least 2 days). However, the Horizontal reactor method resulted in a shorter overall composting period. Notably, the treatment with the lowest aeration rate and largest bulking agent size (AVCCP2: Vertical, 22 L·min⁻¹, 20 mm) achieved the longest sustained thermophilic phase of 7 days. This optimal thermal condition confirmed the complete removal of pathogenic microorganisms (Salmonella spp., enteric viruses, and viable helminth eggs) and led to the fastest rate of C/N ratio reduction. Conclusion: The pilots AVCCP2 and AHCCP2 (Horizontal, 22 L·min⁻¹, 20 mm) demonstrated the maximum efficiency, primarily due to their long sustained thermophilic duration. AVCCP2 showed the best performance in terms of sanitization and pathogen control, achieving Class A compost standards and confirming the potential of vertical reactors for real-scale application with enhanced bio-safety. Highlights ● Vertical and horizontal in-vessel co-composting of municipal solid waste (MSW) and sewage sludge (SS) were comparatively investigated. ● Optimization of aeration rate and bulking agent size was essential for efficient process progression. ● Aerating at a lower rate significantly prolonged the thermophilic phase, ensuring effective pathogen removal. ● A higher reduction rate of the C/N ratio was observed in treatments utilizing the smaller particle size of the bulking agent. ● The increase in pH value was notably greater in the vertical reactors compared to the horizontal reactors.