| Anaerobic fermentation, which could obtain organic waste degradation and renewable energygeneration (hydrogen or methane) simultaneously, attracted widespread attention in recent years.Hydrogen is a completely clean energy fuel which generates only water in the combustion process.Hydrogen could be directly converted to electrical energy through the fuel cell, which has highenergy conversion efficiency. Methane is a high energy fuel. Although the product of methanecombustion is carbon dioxide, methane generated from anaerobic fermentation of biomass iscarbon neutral essentially. Hydrogen and methane are the products of the different stages of theanaerobic fermentation. The purpose of this study is step by step recovery hydrogen and methanefrom organic waste. In order to distinguish it from the traditional anaerobic fermentationtechnology, called the two-phase anaerobic fermentation hydrogen and methane producingtechnology. Two-phase anaerobic fermentation hydrogen and methane producing technology couldnot only achieve higher energy recovery theoretically, but also offer the possibility of directcoupling of anaerobic fermentation technology and fuel cell technology, which might extend theapplication of anaerobic fermentation technology significantly.Scholars have conducted a lot of research on the two-phase anaerobic fermentation hydrogenand methane producing technology. However, how to achieve stable and efficient production ofhydrogen and methane with cheap organic wastes as substrate is still a main problem. At the sametime, study on the kinetics and Flora dynamics of the two-phase anaerobic fermentation hydrogenand methane producing process are also needed.In this research, the fermentation characteristics of cattle manure, pig manure, food waste,and potato peels were investigated firstly, and then the optimal substrate composition for hydrogenproduction were determined by using mixture design experiments. The influences of the mixingratio of substrates, substrate concentration and hydraulic retention time (HRT) on anaerobichydrogen fermentation process were explored one by one, and the optimal factor level combinationwas determined by response surface methodology. Potential inhibitors of the hydrogen productionprocess under optimal conditions were analyzed and the tolerance limits of different inhibitorswere explored. Under different organic loading rate conditions, the performances of single-phasesystem and two-phase system were compared in terms of gas production, raw material conversionand stability of integrated contrast, the kinetic and flora dynamics of single-phase system and thetwo-phase system were also investigated. The main research results are as follows:1) The methane yield of cattle manure, pig manure, food waste, and potato peels were266.63,363.00,517.11and438.33mL/g, respectively. Food waste, and potato peels produce methane faster but easily got acidified, cattle manure and pig manure produce methane slower with pHstable in the fermentation process. The mixing of similar nature substrates showed antagonism inhydrogen production process. While mixing of different nature substrates showed significantsynergies, the hydrogen production rate and degradation rate of substrates have a greater increasethan the single substrates. The optimized composition of substrates was cattle manure: pig manure:food waste: potato peels for53.58:0:46.42:0, under which the hydrogen yield was26.28mL/g, VSdegradation was27.60%, the final pH was5.26.2) The effects of mixing ratio of cattle manure and food waste, substrate concentration andHRT on anaerobic hydrogen fermentation process was explored by single factor experiment, andthen Box-Behnken design was applied to analysis interactive effects of the three factors on thevolumetric hydrogen production rate, hydrogen yield, VS reduction rate, pH value and stability ofprocess, and the quadratic models for these indicators about three factors were obtained. By usingmulti-objective optimization, the optimum process parameters are determined as follows: themixing ratio of50%, substrate concentration of80g/L, HRT of2d. Under optimal conditions,volumetric hydrogen production rate, hydrogen yield, VS reduction rate, pH value and stabilitywere1.09L/(Ld),30.22mL/g,25.85%,5.21and0.62.3) Potential inhibitors of cattle manure and food waste mixed anaerobic hydrogenfermentation were fats, sodium chloride, lactic acid and ammonia. The lactic acid showed thestrongest inhibition of hydrogen production process, hydrogen production soon stopped with thelactic acid concentration of2g/L, VS reduction rate and final pH decreased to10%and4.0. Lipid,sodium chloride and ammonia showed promotion of hydrogen production at low concentrations,but inhibition at high concentration. The inhibitory concentration of the fats, sodium chloride andammonia were16g/L and9g/L and2.58g/L.4) The two-phase system could withstand higher organic loading rate than single-phasesystem, and achieved higher volumetric methane production rate and VS reduction rate. However,single-phase system has higher energy recovery rate. The maximum organic loading rate forsingle-phase system was5.6g/(Ld), and got the highest volumetric methane production rate of1.57L/(Ld), with average methane yield, VS reduction rate, and energy recovery of to290.79mL/g,45.27%and41.77%, respectively. The maximum organic loading rate for methaneproduction phase of the two-phase system was9g/(Ld). The highest volumetric methaneproduction rate of1.85L/(Ld) was obtained at the HRT of10d and organic loading rate of7.2g/(Ld), at which average methane yield, VS reduction rate and energy recovery rate were256.28mL/g,51.76%and38.19%, respectively.5) Based on the equation of Contois and Chen-Hashimoto, the kinetic model describing effectof HRT on the concentration of the substrate was formulated. The kinetic parameters for thesingle-phase and two-phase system were μmvalues of0.167and0.293, K value of0.204, and0.403, R value of0.465and0.409, respectively. The μmand K of the two-phase system are greater than the single-phase system, which means the two-phase system have higher he microorganismsgrowth rate than the single-phase system; The R value of two-phase system is less thansingle-phase system, indicating that the two-phase the system capacity of raw material degradationis also higher than the single-phase system. Upon examination, the model can well predict theconcentration of the material under different HRT.6) PCR-DGGE and scanning electron microscopy(SEM) were applied to resolve the microbialcommunity structure and dynamics at different organic loading rate of single-phase and two-phasesystem. The results indicated that the microbial community structure of hydrogen production phaseis relatively simple, dominant microorganisms are Clostridium proteoclasticum, Pseudomonasmendocina, Olsenella sp, Acetobacterium sp. and uncultured rumen microorganisms. Single-phasesystem and methane production phase of two-phase system microbial have similar communitydynamics. At stable runtime, high microbial diversity was observed, dominant microorganisms areMethanosaeta and Methanococcus, considerable numbers of Olsenella sp, Fibrobacters sp.,Clostridium sp, Parabacteroides sp. and Megasphaera sp., also exist. When shortening thehydraulic retention time, the system got acidified, and the non-dominant species graduallytransformed into the dominant species. |
