Fermentative hydrogen and methane co-production from anaerobic co-digestion of organic wastes at high loading rate coupling continuously and sequencing batch digesters

The anaerobic co-digestion of the most abundant organic wastes was investigated for enhancing biogas production rate and quality. The used feedstock was composed of fruit and vegetable waste (FVW), waste-activated sludge (WAS), olive mill wastewater (OMW) and cattle manure (CM). A considerable methane yield of 340 L/kg volatile solid (VS) inlet was obtained using single-stage anaerobic sequencing batch reactors (ASBRs). However, VS biodegradation becomes difficult at high organic loading rate (OLR). Therefore, a continuously stirred tank reactor (CSTR) was integrated to the ASBR for waste pre-digestion. The dark fermentation leads to the improvement of organic matter solubilisation and bio-hydrogen productivity, reaching 0.73 L/L/day (H2 content of 49.8%) when pH decreased to 5.8. Therefore, methane productivity increased from 0.6 to 1.86 L/L/day in the methanogenic reactor with a better VS biodegradation (91.1%) at high OLR. Furthermore, the bio-hythane production was performed through a controlled biogas recirculation from the dark fermentation stage into the methaniser to reach 842.4 L/kg VS inlet. The produced biogas was composed of 8% H2, 28.5% CO2 and 63.5% CH4. Therefore, two-stage anaerobic co-digestion with coupled CH4 and H2 recuperation may be an important contribution for pollution control and high-rate bioenergy recovery (21.1 kJ/g VS inlet) from organic wastes.