Technical Research On Combined Fermentation Of Methane And Ethanol With Rice Straw

Since solid digestate from straw biogas plant still remained high fiber and organic matter content,the recycle of these residual organic carbons can enhance the utilization and energy conversion efficiency of materials.For the developed anaerobic digestion(AD)and cellulosic ethanol technology,the biogas and ethanol coproduction with rice straw can solve the difficult of solid digestate utilization in AD,and feedstock cost issue in cellulosic ethanol.This can coproduce bioenergy and achieve a complete degradation of biomass.The effect of acid/alkali pretreatment conditions including acid/alkali concentration,temperature and time on rice straw degradation and sugars conversion efficiency was investigated.The results showed that the higher the alkali concentration and temperature were,the better the hemicellulose and lignin removal were.The maximum hemicellulose and lignin removal were 89.45% and 88.92%,respectively.Acid pretreatment mainly focused on hemicellulose in rice straw,and the maximum hemicellulose removal was 75.58%.It was found that glucose conversion rate and the organic matter content were greater with alkali rather than acid pretreatment.Suitable conditions for hydrolysis using NaOH pretreatment were 2%,60 h and 60 ?.With these conditions the glucose conversion rate was 55.5%.In addition,as for combined ozone and aqueous ammonia pretreatment,with the increase of ozone amount,glucose concentration was firstly increased,and then decreased.While the ozone amount was 0.75g/g,the glucose and reducing sugars reached maximum.Compared with untreated,the reducing sugars concentration for 4h of aqueous ammonia pretreatment increased by 82.06%.And it was not obviously improved as for 6h and 8h of aqueous ammonia pretreatment.Therefore,the suitable parameters of ozone and aqueous ammonia pretreatment were 0.75g/g ozone amount and 6h of aqueous ammonia soaking time.The combined anaerobic deigestion and ethanol fermentation was used for degrading the rice straw and enhancing bioenergy production.Four processes(direct anaerobic digestion,coproduction of ethanol and methane,sequential fermentation of ethanol and methane,and coproduction of methane and ethanol)were designed to compare the biogas production,methane production and ethanol production.And based on lignocelluloses content and sugars concentration,degradation process of lignocelluloses was studied.The results indicated coproduction or sequential fermentation of ethanol and methane had some advantages,which its energy output was increased by 17.12% and 49.36%,respectively.However,taking into account the new utilization ways of solid digestate,the coproduction of methane and ethanol was chosen to study the effect of acid/alkali or ozone and aqueous ammonia pretreatment on saccharification efficiency of solid digestate during enzymatic hydrolysis,and optimized the anaerobic digestion conditions and pretreatment paramters in coproduction process of methane and ethanol.Acid and alkali pretreatment was used to study the anaerobic digestion conditions and pretreatment parameters of cellulosic ethanol during methane and ethanol coproduction.It was found that mesophilic and low solid concentration AD had an obvious degradation of cellulose in rice straw.Moreover,the cellulose loss in pretreatment was low,and glucose conversion was high.Thus,the anaerobically digested fibers at mesophilic and low solid concentration AD obtained a better ethanol production.The comparison of acid and alkali pretreatment proved under mild temperature,alkali pretreatment had an advantage on ethanol production of anaerobically digested fibers.The suitable conditions were 3% NaOH,60? and 6h.The recovery rate of cellulose was more than 80%,and glucose conversion was highest,58.66%.The ethanol production achieved to 87g/kg for anaerobically digested fibers of mesophilic and low solid concentration.It enhanced the ethanol yield effectively.During methane and ethanol coproduction process,the organic carbon in solid digestate can be effectively used by ozone and aqueous ammonia pretreatment.The mass and energy balance anlysis of methane and ethanol coproduction process showed that using solid digestate from anaerobic digestion at 55?,17% solid concentration and 24 days to produce ethanol can reached the highest net energy balance,6416 kJ/kg.Under these conditions,the methane and ethanol production per kg rice straw were 142.8g and 65.2g,respectively.It is proved that anaerobic digestion combined with ethanol fermentation to produce methane and ethanol is an effective biorefinery process,which can realize the combination and continuous utilization of organic carbon.