Adaptation Of Microbes In Solid-state Anaerobic Digestion(SS-AD) Of Corn Stover Inoculated With Liquid AD Effluent

To improve the qualification accuracy of the microbes in solid state anaerobicdigestate employed fluorescent in situ hybridization (FISH), ultrasonic pretreatmentmethod of samples was optimized. Using effluent of liquid state anaerobic digestion (L-AD)as inoculum for solid state anaerobic digestion (SS-AD) of corn stover, the effects ofinoculum size and initial moisture content on the adaptability of microbial population andSS-AD performance were studied. The main contents are as follows:1. Optimization of ultrasonic pretreatment for the solid state digestate. In order toimprove the qualification accuracy of the microbes in solid state anaerobic digestate byFISH, orthogonal array and single factor methods were used to investigate the effect ofultrasonic treatment time and power on distribution of microbial cells and hybridizationrate of FISH. The results showed the optimal ultrasonic power was200W and pretreatmenttime was100S, espectively. Under this condition, quantities of microbes, brightness andthe abundance of the samples observed with fluorescence microscope were significantlyimproved.2. Microbial adaptability of different inoculums in SS-AD of corn stover. L-ADeffluent and SS-AD residues were used as inoculums for SS-AD of corn stover,respectively, and the inoculum size was the same based on the concentration of microbialpopulations. The results indicated start-up speed and gas production of the digesters withL-AD effluent as inoculum were significantly better than that of the digester using SS-ADresidues as inoculums. PH value in the reactors using SS-AD residues as inoculumsdecreased dramatically during the startup stage of digestion and caused acid inhibition tomethanogens and result in failure of the reactors.3. Effects of inoculum source and inoculum size on the performance of SS-AD. L-ADeffluent and SS-AD residues were used as inoculums for SS-AD of corn stover,respectively. Feedstock to inoculum ratios (F/I ratio, based on volatile solid) were1,3and5. The results showed that reactors using L-AD residue as inoculum started more quicklythan that inoculated with SS-AD residue. Accumulative biogas yields of the reactorsinoculated with L-AD residue at F/I ratios of1,3and5had no remarkable difference.When using SS-AD residue as inoculum, reactors with F/I ratio of1performed well and the accumulative biogas yield was66.9L/kg-VS while the reactors at F/I ratios of3and5failed due to excessive acidification.4. Analysis of the key features in inoculum impacting SS-AD performance. Residuesof L-AD were used for inoculum, and F/I ratio was3. Before inoculation, part of theinoculum was sterilized by autoclave. Thus, the ratios of feedstock to inoculum withmicrobial activity were4and5, respectively. The results show the total gas production rateand methane content of the reactors with F/I of3,4and5had no significant difference(P>0.05). The total biogas production of the reactors with F/I ratio of3, while40%or25%of the inoculum were sterilized were80.1L/kg/vs and77.9L/kg/vs, which were similar tothat of the reactors with F/I of3without inoculum sterilization.5. Effects of the initial moisture content on the change of microbial population inSS-AD. The relationship between microbial structure and characteristics of substrate wasanalyzed. The results showed that different moisture content leaded to different startingspeed of AD, methane production cycle and total gas production. The less of moisturecontent was, the earlier AD started and the longer methane production cycle was. Theoptimum moisture content was TS=20%.