Optimization Of Temperature-separated Two-stage Anaerobic Fermentation Process With Hydrogen And Methane Production

Traditional solid waste disposal methods cannot efficiently transform the valuable energy in sludge and food waste biomass.Anaerobic fermentation technology can realize the stabilization of organic solid waste and simultaneously transform the organic content of biomass into hydrogen and methane.The two-stage anaerobic fermentation has a higher energy yield than the single stage anaerobic fermentation,and can be operated more steadily.In this study,the operation conditions for a temperature-separated two-phase anaerobic fermentation process were optimized.Six pretreatment methods for hydrogen-producing seed sludge were investigated.Results show that the pretreatment methods of 2-Bromoethanesulfonic acid sodium salt(BESA),acid,continuous aeration and repeated aeration performed effectively.The repeated aeration pretreatment sludge had a highest hydrogen yield of 86.9 mLH2/g-VSadded.The pretreatment of the seed sludge enriched and acclimated hydrogenproducing bacteria to the mixed substrates,and thus shortened the hydrogen production lag time.Hydraulic retention time(HRT)had little effect on the VS removal rate in the methane production phase(21.0%~27.0%).The methane yield in the methane production stage,the VS removal rate and the total energy yield of the two-stage system increased with the HRT.Under the HRT of 12 d,the methane energy yield was 7.70 kJ/g-VSadded,the VS removal rates of the two-stage system was 63.8%,total energy yield of the two-stage system was 8.80 kJ/g-VSadded.Carbohydrates were found to be the main substrates for hydrogen production,while volatile acids produced in hydrogen production stage and protein were main substrates for methane production.Sludge return rates of 1:1,1:2,and 2:1 were tested and it was found that the methane yield in the methane production stage and the total energy yield of the twostage system were enhanced by decreasing the sludge return rates.The sludge return can complement alkalinity for the hydrogen production stage,but also carried methanogens to inhibite hydrogen-producing reaction.According to the total energy yield of the two-stage system,the optimized sludge return rate was 1:2,at which the methane energy yield and total energy yield were 8.60 kJ/g-VSadded and 9.70 kJ/gVSadded,respectively.According to the additional alkalinity,the optimized sludge return rate was 1:1,at which the additional alkalinity of hydrogen production phase was 1.331 g-K2HPO4/L/d.