Dynamic behaviors of batch anaerobic systems of food waste for methane production under different organic loads, substrate to inoculum ratios and initial pH.

This study characterized dynamic behaviors of batch anaerobic digesters treating food waste in terms of methane production, organics destruction and process stability under different organic loads (OLs), substrate to inoculum (S/I) ratios [on volatile solid (VS) basis] and initial pH. The results showed that OL, S/I ratio and initial pH significantly affected batch anaerobic process. Methane yield was proved to be inversely proportional to OL and S/I ratio. Digester with lowest OL (5 g VS/L) obtained greatest methane yield (551.4 mL/g VS), highest organics removal (94.1%) and good stability. Enhancing OL to 10 g VS/L was recommended for satisfactory stability and higher volumetric methane productivity. When OL was designated as 10 g VS/L, digester with low S/I ratio (1/2) achieved satisfactory methane yield (539.3 mL/g VS), high organics removal (92.3%) and stable performance. When OL was relatively high (20 g VS/L), adjusting initial pH to 7.5 contributed to stable performance via enhancing buffering capacity against volatile fatty acids (VFA) disturbance. Strong VFA inhibition occurred under high OL (40 g VS/L) or great S/I ratio (2/1) or acidic initial pH (6.5). In this case, acetate was dominant VFA, followed by butyrate. However, when digester was stable, acetate was main VFA, followed by propionate. This study provided practical guidance on process configurations for batch digesters of food waste needed to achieve satisfactory performance and stability.