Mechanism of cell proliferation during starvation in a continuous stirred tank anaerobic reactor treating food waste.

Anaerobic digestion is a mature technology; however, the mechanism of cell proliferation during starvation has not yet been clarified. In this study, a continuous stirred tank reactor (CSTR) treating food waste was exposed to deliberate starvation for 12 days. The cell density and the variability of digestate characteristics during starvation were monitored. Starvation increased cell density from 2.8 × 1010 to 7.9 × 1010 cells mL-1 within 2 days and reduced the residual substrate. This increase in cell density was suggested owing to a switch of the anaerobic digester microorganisms' substrate preference to the complex fractions because the easily digestible fractions were exhausted. The prolonged starvation of more than approximately 3-6 days induced an increase in the free ammonia concentration to an inhibitive level of more than 0.10 g-N L-1 for anaerobic digestion microorganisms due to the excessive ammonification of residual nitrogen, thereby resulting in a drastic decrease in cell density. Our results demonstrated that a deliberate starvation operation in an appropriate timeframe applied to a CSTR treating food waste is beneficial to proliferate cells and, at the same time, reduce residual substrate.