Biofilm reactor technology for low temperature anaerobic waste treatment: microbiology and process characteristics

The microbial composition, methanogenic activity and architecture of particulate and fixed biofilms within four anaerobic hybrid reactors, R1–R4, operating at psychrophilic temperatures were investigated. The reactors treated low-strength (1 g COD l⁻¹; R1) and high-strength (10 g COD l⁻¹; R2–R4) wastewaters from the food-processing sector (R1, R2 – whey; R3 – sucrose; R4 – volatile fatty acids). Successful start-up and long-term psychrophilic operation was observed for all four reactors, with COD removal efficiencies of 80–99% achieved at 12–20 °C at organic loading rates of 1.3–20 kg COD m⁻³ d⁻¹. The formation and maintenance of a well-settling granular sludge bed and an attached biofilm were shown to occur under psychrophilic conditions, an important consideration for the successful implementation of low temperature biofilm reactor technology. Culture-independent molecular techniques (terminal restriction fragment length polymorphism, clone library analysis and 16S rRNA gene sequencing) revealed that microbial population structure could be a key factor in reactor performance, with changes in the community structure of the three high-strength reactors preceding granular instability and a subsequent decline in COD removal efficiency. Biomonitoring of microbial population structure and dynamics within anaerobic reactors may, therefore, allow for the early recognition of potential operational problems.