Study On Biogasification Of Cassava Dregs By Anaerobic Fermentation

As a kind of organic solid waste, cassava dregs had contaminated environment for its large output and putrescibility. Anaerobic digestion process was the optimal treatment method when we considered friendly environment and utilization of waste. So we determined the composition of cassava dregs, studied on the acidification characteristics of cassava dregs and on this basis, optimized the parameters of methane production by one-stage anaerobic fermentation.The moisture content of wet cassava dregs was 87.6%, the average ash in dried dregs was 2.1%, and volatile solids were 98%. These indicated that cassava dregs had high composition of biomass, in which starch was 57.12%, cellulose was 28.49%, and there were a spot of fat and protein. Cassava dregs were high carbohydrate and low protein biomass, the average C/N was 49.It was proved that cassava dregs were prone to acidification. On the condition of high solid content ratio(8%),Valatile fatty acid(VFA) was accumulated rapidly, as a result, there was a sudden drop of the pH value at the initial stage of fermentation and what's more, the pH was stable at low data. That's to say, the acidification characteristics of cassava dregs were not profit to methane production.Although the acidification characteristics of cassava dregs, it was feasible for cassava dregs to self-regulate the start of methanation, the main factors were the vaccination ratio and solid content ratio. With the condition of no pH regulation, methane production could be advantageous by anaerobic fermentation when vaccination ratio was 70% and solid content ratio was 49.6%, at the moment, the gas production rate and maximum methane production was 249.5ml/gVS and 48.6% respectively.The experiment results showed that intermediate temperature of 35℃was beneficial to methanation of cassava dregs by anaerobic fermentation. The gas production ratio and maximum methane production were higher than 25℃and 55℃, 247.8mL/g(VS) and 49.2% respectively.By experiments of pH regulation to fermentation system, it confirmed that when vaccination ratio was down-regulated from 70% to 50%, solid content was still 8%, the total gas production , gas production ratio and maximum methane production were 4280mL, 232.4 mL/g(VS) and 49.7%. Neither the decrease of vaccination ratio nor the improvement of solid content went against the methanation. On the basis of this, the optimum technical conditions for methane production were that pH value was controlled to 6 at hydrolysis and acid production phase, to 7 at mid-late period of methane production, the final gas production ratio was 254.6mL/gVS and the maximum methane production was 50.9%.Finally, two better technology routes on one-stage anaerobic fermentation were proposed on the basis of the above experimental results.The first, without external pH value regulation, the best technology route was that vaccination ratio 70%, solid content ratio 8%, fermentation temperature 35℃. the maximum gas production rate was 249.5ml/gVS at this condition.The second, with external pH value regulation, pH value was controlled to 6 at hydrolysis and acid production phase, to 7 at mid-late period of methane production , the best technology route was that vaccination ratio 50%, solid content ratio 8%, fermentation temperature 35℃. the maximum gas production rate was 254.6ml/gVS at this condition.