Acid-tolerant Acclimation Of Inoculum And Its Application In Solid State Anaerobic Digestion

To further improves stability of solid state anaerobic digestion(SS-AD)and avoid acid inhibition,carried out acid-tolerant acclimation by gradient adding acetic acid(HAc)to inoculums.Changes of biogas yield and enzymes activities in acclimation process,differences of tolerance of low pH value and high volatile fatty acid(VFA)concentration and microbial community structure between two inoculums and dynamic effects of adding ratio of acid tolerant inoculum on the performance of yielding biogas and characteristic of digestate for spent mushroom substrate(SMS)SS-AD were studied.The main contents are as follows:(1)Characteristics of yielding biogas and changes of enzyme activity of inoculums in HAc acclimation process.The entire acclimation process was divided into four stages: 7.24,6.74,6.24 and 6.0 based on pH value.Measured methane content and volume of biogas every day and adapted pH value until stably yield biogas.Measure dehydrogenase,CMCase and Co F420 activities of sample at the end of each acclimation stage to reflect changes of microorganism metabolic activity.The results show that there were shocks at methane concentration and pH value at each of early acclimation phase,while these values would turn to the normal value as inoculum adapted to acid pressure,finally methane concentration reached at 57%.Dehydrogenase activity appeared first rise and then decrease as the reaction progressed.The Co F420 activity of initial inoculum was low,reached peak at pH value of 7.24 and increased to 16.92 μmol/L in the end of acclimation,while CMCase activity reached peak at pH value of 6.74 after acclimation decreased to 494.11μg G/g by higher HAc concentration.(2)Tolerance and microbial community structure of inoculums were studied.Tolerance experiments of pH value and VFA concentration were carried out for the two inoculum samples respectively and comparison of microbial community structure by 16 SrRNA high-throughput sequence.The results showed that acid tolerant inoculum had a good methane production under pH value of 5.5 and VFA concentration of 4250 mgHAc/L.Contrast with initial inoculums,acclimation can significantly improve inoculum acid resistance.The analysis of archaeal community showed that acclimation can improve microbial abundance and make Methanosarcina become dominant archaea group,while dominant position of Methanoculleus and Methanospirillum didn’t be affected by the acclimation.Neither of the two genus utilize acetic acid,and higher relative abundance of the two genus in the initial inoculum showed that lower acetic acid conversion ability.The analysis of bacterial community showed that relative abundance of Clostridium III decreased after acclimation,which is associated with cellulose degradation,while relative abundances of Peptococcus and Sedimentibacter increased.There were decrease in community diversity of archaea and bacteria after acclimation.(3)The effects of adding ratio of acid-tolerant inoculum on the biogas yield of SS-AD of SMS.In all treatments,the conditions of SS-AD were same with F/I ratio(based on volatile solid)of 3 and 5 and inoculation by the way of mixing different proportion of acid tolerant inoculum with initial inoculum.The results showed that reactors with adding proper acid tolerant inoculum had faster methane production rate and increase to methane content during early stage of SS-AD.There was significantly differences(p<0.05)on biogas yield to change of adding ratio of acid tolerant inoculum,reactors with adding 75% acid tolerant inoculum obtained the highest cumulative biogas and methane yield with F/I of 3 and 5.When F/I was 5,peak at daily methane yield to reactors without adding acid tolerant inoculum was slightly later and then rapidly declined and appeared an obvious acid inhibition phenomenon,while as long as reactors with adding acid tolerant inoculums made biogas production focus on the first half of SS-AD and avoid acid inhibition phenomenon.(4)The effects of adding ratio of acid-tolerant inoculum on characteristics of digestate of SS-AD of SMS.At predetermined times(day 8,20,29,and 48),each of the treatments of F/I of 3 would terminate one reactor following to take out and mix all materials thoroughly,after that the samples were analyzed for digestate characteristics.VFA/alkalinity ratio generally almost increased with increasing acid tolerant inoculum after material mixed,along with the fermentation,the ratio was decreased,while the trend of pH value was opposite.There was no obvious difference berween CMCase and Co F420 activity of all reactors,which were related to biogas yield performance.