A critical review of anaerobic biofilm reactors for the renewable biogas production from food waste

The search for better biogas-producing methods has led to greater attention to studying advanced bioreactor technologies. Among these, biofilm reactors are gaining attention due to improved stability and effectiveness with their distinctive capabilities to promote microbial growth. This review paper presents the use and development of several types of biofilm reactors, such as anaerobic moving bed reactor and upflow anaerobic sludge blanket reactors, treating food waste (FW) to produce biohydrogen and biomethane. Under ideal conditions, the biohydrogen and biogas produced by the anaerobic biofilm reactor are 0.31-280 mL CH4/g chemical oxygen demand (COD) and 18-86 mL H2/g COD, respectively. In the process of dark fermentation, the pH can vary between 5.5 and 6.5; the pH in anaerobic digestion should be between 6.8 and 7.5, the hydraulic retention time period should be between 2 and 10 days, and the organic loading rates can be from 5 to 20 kg COD/m3. In properly managed facilities, at least 70-90 % of COD and volatile solids are typically removed. Advantageous numbers can create additional challenges, as large systems are easily affected by clogging, competing flows, and a greater diversity of reactions to the products they process. This review integrates recent advances and case studies to highlight key operational strategies and design improvements of anaerobic biofilm. The objective is to provide an overview of technological development with a critical aspect on how anaerobic biofilm reactors can be effectively configured and managed for efficient conversion of FW into valuable biofuels.