Volatile Fatty Acids Production From Rice Straw By Anaerobic Fermentation

Rice straw was a very rich crop straw. Volatile fatty acids as the production from rice straw by hydrolysis acidification, can be used to product methane, and can also be used as the chemical industry raw materials. The research take rice straw raw materials for anaerobic fermentation, investigated the influencing factors and process conditions in fermentation process, established anaerobic fermentation system of rice straw to promote the resource utilization.The following contents were studied:(1) Paly a preliminary research on rice straw hydrolysis acidification with the different load, alkaline pH conditions;(2) Effects of different sludge and different initial pH on rice straw anaerobic hydrolysis acidification in startup process;(3) Effect of using the excess sludge and maintaining pH conditions on rice straw anaerobic hydrolysis acidification in startup process;(4) Effect of using the fermentated sludge and maintaining pH conditions on rice straw anaerobic hydrolysis acidification in startup process;(5) A preliminary study of rice straw hydrolysis acidification in continuous operation mode.The results indicated that:(1) the load and pH has a great effect on the yield, both VFAs and unit quality rice straw acid production of the load of1.334g/g was respectively4385mg/L、2.19g/g, the degradation of hemicellulose、cellulose、acid detergent lignin(ADL)was respectively32.69、22.53and6.40%, the VFAs and rice straw degradation were significantly higher than others when pH was8.0, the VFAs was4409mg/L, the degradation of hemicellulose、cellulose、ADL was respectively28.60、47.32and22.69%.(2) The experiment of different sludge and different initial pH showed that, hydrolysis acidification with excess sludge had more SCOD, VFAs production, and more degradation of rice straw, when the initial pH was9.0the VFAs was3787.03mg/L, the degradation of hemicellulose、cellulose、ADL was respectively63.84、43.65and19.55%.(3) In the experiment used excess sludge, production of SCOD、VFAs with alkaline conditions were significantly higher, in which when pH was8.0had the highest concentration of VFAs was6632.59mg/L, HAc/VFAs with pH rise, propionic acid/VFAs were significantly higher than others when on the condition of pH was7.0、6.0, acidic conditions conducive to butyrate producing.Alkaline conditions more conducive to the degradation of rice straw, when pH was8.0the total degradation was highest,was62.08%, degradation of hemicellulose、ADL degradation rate with pH rise, cellulose degradation rate of pH was5.0～8.0with pH rise, pH8.0～10.0when rise with the pH reduce. (4) In the experiment used fermentated sludge, production of SCOD、VFAs under alkaline conditions were also significantly higher, in which when pH was8.0had the highest concentration of VFAs was7714.35mg/L, HAc/VFAs with pH rise, the propionic acid concentration of pH was6.0、7.0、8.0were significantly higher than others, acidic conditions conducive to butyrate producing, Alkaline conditions more conducive to the degradation of rice straw, the total degradation o of pH was9.0was highest, was75.44%, degradation of hemicelluloses、ADL degradation rate changed with pH rise, cellulose degradation rate of pH was5.0～9.0with pH rise, reduced when pH was10.0;(5) In the process of rice straw continuous hydrolysis acidification, input rice straw make the SCOD, VFAs concentration has been on the decline, the refluxing of sludge enabling SCOD rise, had little effect on the VFAs, adding excess sludge and continue input rice straw could make SCOD, VFAs concentration maintained respectively at about7000、4000mg/L; adding rice straw was in favor for acetic acid ratio.; pH has little effect on SCOD and acetic acid ratio, when pH was8.0had a higher concentrations of the VFAs than pH was9.0.(6) The production of VFAs with the excess sludge as start sludge, was a little higher; Because of the bigger pH buffer range, higher HAc/VFAs and more faster durable of VFAs, the fermentated sludge was more appropriate as the start sludge.Therefore, through anaerobic fermentation system with a certain load、pH and sludge conditions could make rice straw hydrolysis acidific effectively. Select fermentated sludge with maintaining pH at alkaline conditions, was a suitable start condition for rice straw to Hydrolysis acidification; Control the pH at8.0～9.0, rice straw continuous anaerobic fermentation could have stabilize production VFAs with process to the sediments and adding raw sludge reflux, so as to realize the resource utilization of rice straw.