A meta-analysis of pathogen reduction data in anaerobic digestion

Anaerobic digestion (AD)-derived digestate can be used as an organic fertilizer or for soil amendment. However, its utilization for resource recovery raises valid biosafety concerns. Despite extensive research on the capacity of AD for pathogen reduction, the variability in results poses challenges for drawing definitive conclusions. To address this lack of unification, results from 121 scientific articles were compiled, and a comprehensive meta-analysis was conducted. Findings indicate that artificial pathogen spiking leads to performance overestimation. Current most common indicators represent accurately their respective microbial groups. Clostridiaceae are barely affected by AD and may be favored by some pre-treatment technologies. The impact of operational parameters and the coupling of pre- and post-treatments with AD on pathogen reduction was also investigated. While an optimal batch duration was identified, the hydraulic retention time in (semi)continuous systems did not affect the overall pathogen reduction. Heat-based post-treatments coupled with thermophilic AD resulted in the highest pathogen reductions, fulfilling legislations. Unprecedented statistical analyses allowed categorizing quantitatively key parameters. Results confirmed that temperature is the most relevant parameter. Thermophilic conditions resulted in the highest pathogen reductions, while psychrophilic and mesophilic temperatures showed similar performances. The impact of pH on pathogen removal was confirmed, with acidic and basic values enhancing pathogen reductions. More research considering all AD products within a multicriteria optimization approach (e.g., pathogen reduction, biogas production, and digestate quality) is needed to determine optimal conditions considering all aspects. This study provides novel and relevant conclusions for AD at research and industrial scale, drawing several R&D perspectives.