Conditions of lag-phase reduction during anaerobic digestion of protein for high-efficiency biogas production

Abstract

Anaerobic digestion is a promising method of treating organic waste. However, when the protein content of the organic waste is high, a lag-phase that interferes with the efficiency of biogas production occurs. This study is intended to determine the conditions for reducing lag-phase and improving the efficiency of biogas production. This study focused on the determining conditions of lag-phase reduction of anaerobic digestion with high protein organic loading. The anaerobic digestion was conducted under batch conditions at mesophilic temperature (36.5 °C). The batch test was divided into Experiments I and Ⅱ. In Experiment I, the biogas potential and biogas production rate of protein was measured. In Experiment Ⅱ, the effect of feed to microorganism ratio (F/M ratio) (0.2–1.0) with regard to lag-phase was tested. Protein produced biogas and methane yield of 996–1037 and 750–801 mL gVS−1 at the F/M ratio of 1.0, respectively. Biogas production rate tends to decrease after seven days of digestion. Lag-phase could be caused from the acidification by volatile fatty acid (VFA) accumulation and the initial VFA to volatile solid ratio. To reduce the lag-phase, the VFA/Alk ratio should be maintained below 0.4. The initial VFA/VS ratio below 10% enhanced anaerobic digestion performance and digestion time reduction at a high protein loading rate. The F/M ratio was found to be a predominant factor during the protein anaerobic digestion process initiation. When the F/M ratio was within 0.4–0.6, biogas production performance was improved and the lag-phase was decreased.