Near-Synchronization Anaerobic Co-Digestion Of Vinegar Residue And Corn Stover Based On Enhanced Vinegar Residue Modification

China is the world's largest producer of vinegar.As a by-product of the vinegar-making process,the vinegar residue is quite acidic with a high moisture content and a long biodegradation period.Therefore,it needs to be carefully dealt with,otherwise it will probably lead to soil acidification and water-body pollution.Meanwhile,agriculture being a large part of its economy,China also has abundant straw,especially corn straw which has become an important biomass resource.During its anaerobic digestion process,however,the hydrolysis period is usually long and degradation rate low due to the lignocellulose in straw.To solve this issue,much attention is paid to modification technologies,one of which is acid modification.Modifiers are mostly pure chemical reagents,including sulfuric acid and nitric acid,which raise the cost of the technology as well as the risk of secondary pollution.As such,modification is necessary for corn straw.Vinegar residue is a biomass resource rich in organic acid,which is also volatile fatty acid as typified by acetic acid that can be utilized during the anaerobic digestion without causing secondary pollution.A new method of joint anaerobic digestion is thus proposed in this study to replace chemical reagents with vinegar residue,whose acidity can be used to modify the corn straw without putting in extra material;through the joint anaerobic digestion technology,the straw and vinegar residue can also be treated synergistically and used as resources in a synchronized way.The main parts of the study and the results are as follows:?1?Study on the bio-chemical methane potential of vinegar residue and strawStudies on the bio-chemical methane potential and the process of methane production of vinegar residue and straw were conducted respectively through the BMP test and kinetic model analysis.According to the results,vinegar residue showed good potential in methane production when F/M=0.25?2,with the maximum methane production rate per unit of VS being 93.79 mL/gVS;corn straw achieved the highest rate of methane production per unit of VS of 290.61 mL/g VS when F/M=2.When considering the need to increase organic loading and when F/M was 3.33,the methane production processes of vinegar residue and corn straw both went smoothly,yet the corn straw had a lag phase of 25 d,which was obviously asynchronous with vinegar residue.?2?Study on corn straw modified by vinegar residue leachate and its impact on the performance of methane productionThe batch anaerobic digestion test of corn straw modified by vinegar residue leachate under the full factorial design was carried out to examine the effects of leachate on the modification of corn straw under different temperatures and time periods,as well as the performance of methane production of modified corn straw through anaerobic digestion.The result was compared with that of hydrothermal modification.It was found out that the vinegar residue leachate could effectively facilitate the hydrolysis of hemicellulose of corn straw under 150?,where the relative percentage content could drop from 27%to 6%,decreasing by over 77.8%,and the concentration of VFAs,SCOD and reducing sugar in the hydrolysate rose considerably.When the temperature was 90? and time period 30 minutes,the maximum methane production rate per unit of VS was reached,which was 223.61 mL/g VS,an increase of 52.1%compared with that of unmodified corn straw.In addition,compared with the increase of production rate by hydrothermal pretreatment?40.12%?,this method pushed the production rate up further by 12 percentage points.?3?Study on methane production performance of vinegar residue-modified corn straw and its quasi-synchronous joint anaerobic digestionThe joint anaerobic digestion test was conducted by directly mixing vinegar residue with corn straw,the latter then modified by the former.The effects of the direct modification,the performance and systemic stability of joint anaerobic digestion after modification were studied in a systematic way,and the effect of quasi-synchronization of joint anaerobic digestion between different materials was confirmed.The results showed that the lag phase of corn straw shortened and the quasi-synchronous joint anaerobic digestion was enabled due to the direct modification by vinegar residue.When the temperature was 150?,the mixing ratio of vinegar residue was 5:1,and the duration of modification was 60 minutes,the hydrolysis rate of the hemicellulose in the mixture could reach 73.7%,the concentration of VFAs,SCOD and reducing sugar in the hydrolysate grew significantly and the methane production rate per unit of VS was 140.5 mL/gVS,raising the methane production performance by about 35.7%.When F/M=3.33,the lag phase of corn straw was as long as 25 d.Through modification,the lag phase of joint anaerobic digestion system was cut to around 15 d.?4?Study on the mechanism of corn straw modification by vinegar residue and the mechanism of conversion during the quasi-synchronous joint anaerobic digestionThe mechanism of corn straw modification by vinegar residue was studied through the analysis of the microstructure,physical and chemical structures and the makeup of hydrolyzed material.It was shown that under 150?,the microstructure of lignocellulose was effectively broken by modification;and the temperature needed for this modification was lower than hydrothermal modification due to the acidity of vinegar residue,which could contain the production of the inhibitor,and thus the impact of inhibitor was not pronounced.Besides,the mechanism of impact of different modification temperatures on methane production of the joint anaerobic digestion was studied through the analysis of the change of the concentration of SCOD,makeup of lignocellulose and concentration and makeup of VFAs during anaerobic digestion.The result demonstrated that under 150?,modification enhanced the rapid acid production in large amounts by hydrolysis of cellulose at the initial stage of anaerobic digestion.The type of hydrolysis acidification was butyric acid fermentation,so that the performance of methane production was high during anaerobic digestion due to butyric acid of high concentration.Under 180?,due to the inhibiting effect of inhibitors on microbial,butyric acid and propionic acid had low concentrations,which constrained the methane production performance during joint anaerobic digestion.?5?Study on the evolution of microbial community and its impact on material conversion and methane production performance during quasi-synchronous joint anaerobic digestionThe characteristics of bacteria and archaea community under different modification conditions were studied,and the mechanism of effects of the most significant impact factors on systematic methane production performance during quasi-synchronous joint anaerobic digestion was analyzed from the perspective of microbial community.The results showed relevance between characteristics of bacteria and archaea community and conversion of acetic acid,butyric acid and propionic acid,and methane production performance.According to the results,under 150?,dominant bacteria multiplied rapidly at the initial stage of anaerobic digestion,and thus effectively improved the breakdown and acid production of cellulose at the initial stage,which facilitated the methane production that happened afterwards.There was a positive correlation between the dominant genus Clostridium_sensu_stricto₁ and butyric acid,and negative one between the genus and propionic acid,so the type of fermentation was butyric acid fermentation where butyric acid and acetic acid played major parts.In addition,a notable increase of metabolic activity of methanobacterium consuming H2/CO2 effectively improved the methane production performance during quasi-synchronous joint anaerobic digestion.