Enhancement of the solid-state anaerobic digestion of rice straw by liquor supplementation

Abstract

Solid-state anaerobic digestion (SS-AD) has gained attention in recent years because it is robust, cheap and easy to operate. However, at high loads, the SS-AD is often plagued by acidification and poor methane yields. Mesophilic and thermophilic SS-AD at the different substrate to inoculum ratios (S/I) aided by liquor supplementation was studied in batch mode. Results demonstrated that the liquor supplementation reinvigorated the failed or inhibited SS-AD processes giving methane yields as high as 260.3 ± 5 mL CH4/g VS and improved process stability evidenced low VFA accumulation (˂1 g/L). The achieved methane yield was 85% of the biochemical methane potential achieved under unlimiting batch assay. This study, therefore, revealed that the methane yield in an SS-AD of lignocellulosic biomass can be significantly boosted at high loads by simply adding recycled water or sludge supernatant especially in an inhibited SS-AD process.