Methane production by anaerobic co-digestion of food waste and waste paper

Using food waste and waste paper as anaerobic co-digestion materials,batch mesophilic(35℃) experiments were carried out to investigate the effects of material proportion(100:0,83:17 and 62:38)and pH adjustments at the acidification stage(unadjusted vs.7.2) on the stability and performance of anaerobic digestion.Compared to the pure food waste without pH adjustment,adjusting the pH to 7.2 at the acidification stage avoided the inhibition of volatile fatty acids(VFAs),but maintained the stability and good digestion performance.For the two digestions of material proportion(83:17 and 62:38)with pH adjustment to 7.2 at the acidification stage,the stable pHs for methane production were 7.4～8.0,total VFA concentrations were 500～900 mg·L-1,propionic acid concentrations were 100～550 mg·L-1,and no ethanol production was detected.The cumulative methane production(calculated from volatile solids.where 1 g VS equals 1.1 g COD) was 347 and 247 mL·g-1 respectively,and methane contents were 70%～80%,highest at 81.6%.The COD removal rates were 93.2% and 80.5% and the COD of methane production were 90.0% and 64.0% of total added COD,respectively.The optimal conditions for anaerobic mesophilic co-digestion for methane production were a food waste to waste paper ratio of 83:17 with pH adjustment to 7.2 at the acidification stage.