The Humification Process And Its Regulatory Mechanism During Biogas Residue Aerobic Composting

With the development of urbanization and the improvement of people's living standard and the awareness of environmental protection in China,a deal of large and medium-sized biogas projects is widespread with anaerobic digestion technonlogy being applied widely,so that it is a serous problem to dispose its residues.Landfill is a traditiobal method to treat residues,but it would influence the normal growth of plants,due to it might contain harmful substances,such as heavy metals,organic pesticides,and pathogenic bacteria.Although the residue is dehydrated,its moisture content is relatively higher,which is about 80%.Besides,a large number of ligncellulose is another reason that is difficult to be utilized.Aerobic composting has been considered as an economical method to treat organic solid wastes,which not only reduces environmental pollution,but recycles resources back into the soil.Biogas residues after anaerobic digestion and dehydration were used as the research object,to improve aerobic composting efficiency and product quality,variations in the physicochemical properties,the degradation of ligncellulose,the humic substance?HS?formation,the microbial community composition and function metabolic during the aerobic composting mixed with cattle manure and food waste were studied.Meanwile,exploring the process of humus formation by microorganisms in compost using different carbon sources.The results provide a therotical reference to the practical production and application of biogas residues compost in the future.The main results were described as follows:?1?Biogas residues were mixed with cattle manure and food wastes for aerobic composting,which were the dregs after anaerobic fermentation of sludge,straw and vinegar,respectively.The results showed that the activities of cellulose enzyme and phoyphenol oxidase were higher,dehydrogenase and urease were lower in straw biogas residue composting?STR?,and germination index?GI?was 135.29%,its compost had reached full maturity.Besides,the total nutrient?N+P₂O₅+K₂O?content was the highest?5.4%?,especially K₂O content?2.69%?in STR compost,which provided sufficient nutrients for plants growth.A short duration of high temperature that was lower?50??in vinegar biogas residue composting?VIR?,which might contain potentially pathogenic bacteria.The moisture content was the highest at the end of sludge biogas residue composting?SLR?,was 47.45%;the activities of dehydrogenase and urease were more than STR and VIR,indicated that organic matter degraded incompletely and had a lower maturity.Its humification coefficients were lower than STR and VIR.It was proved that SLR was not decomposed completely after 30days of aerobic composting.In addition,Cr content of SLR compost was 144.65 mg·kg^-1,approached to the standard limit level that was 150 mg·kg^-1,which was used into the soil long-term resulting in the accumulation of Cr,contaminating the soil and harming the normal growth of plants.Therefore,the effect of straw biogas residue composting was the best among three biogas residues.?2?The experiments were designed with different proportions of straw biogas residue and cattle manure,variations of ligncellulose degradation,humic degree and microbial cell viability during aerobic composting were studied.Results showed that the increase of the proportion of biogas residue increased the composting temperature,maximum temperature upped to 66?,promoted the degradation of organic matter and ligncellulose,and the humification degree of composting.The fluorescenc intensity of humus and cell viability increased with the proportion of biogas residue increased.When the proportion of biogas residue was 60%,the degradation rate of organic matter,reduction of cellulose,humus coefficients?HR,HI,DHA and DP?and cell viability reached the peak,which was 17.47%,22.83%,24.85%,22.97%,92.43%,15.03 and 95.3%,respectively,the degree of humicfication was highest.?3?1%white rot fungi inoculated into biogas residue composting when the temperature was above 50?,changes of organic matter,nitrogen?total nitrogen,NO₃^--N?,ligncellulose,humic substances composition,microbial community and metabolic diversity were explored.Inoculate white rot fungus promoted the degradation rate of organic matter,cellulose and hemicellulose,increased total nitrogen,NO₃^--N and HS content.The degradation rate of organic matter was 24.75%.Firmicutes,Actinobacteria,Proteobacteria and Bacteroidetes were the dominant bacteria in initial of composting,Firmicutes was dominant in the thermophilic phase.Inoculating white rot fungus reduced the?diversity of microbial community,increased the quantities of thermophilic microorganisms and relative abundance of the microbial sequences related to amino acid metabolism that was the major metabolic pathways of microorganisms.The reason could be growth of microbes in Chloroflexi were inhibited.Thus,the microbial activity in the compost was improved and the composting process was accelerated.Based on the Network analysis,Actinomadura and Chelativorans were related to hemicellulose and lignin,and Verrucosispora could promote the formation of FA.The degradation of organic matter was accelerated and the maturity degree of composting was improved by the synergistic of various microorganisms in during composting.?4?To explore the composition,structure and formation process of HS,liquid culture experiments were designed that sodium carboxymethyl cellulose?C?,lignin?L?and glucose?G?were used as carbon sources and inoculated compost microorganisms.Based on spectroscopy analysis,it was found that humic acid?HA?containing CH with substituents,CNH,NH₂ and aromatic was formed mainly in G;fulvic acid?FA?containing CH and NH₂was formed in C;HA containing C-H with substituents,CNH,NH₂,and aromatic was formed in L;while FA containing P-O and CNH was formed in Control.Oxidation,dehydrogenation,substitution of substituent and polycondensation might occur during the formation of HS,and finally humus with complex structure was formed.?5?The effects of compost on cadmium-polluted soil and growth of Chinese cabbage were studied.Results showed that compost reduced bioavailability of cadmium,the reasons were that cadmium?Cd?contents that exchangeable and combined with carbonate were decreased and residual form cadmium content increased.Meanwhile,the contents of organic matter,available phosphorus?AP?,available K?AK?were increased by compost.The Cd absorption of Chinese cabbage was concentrated in the root,its concentration reached 189.01mg·kg^-1DW.The concentration of Cd was reduced in the root and overground part by compost.Compost was applied,synthesis of chlorophyll was not promoted under Cd stress(100mg·kg^-1),the activities of superoxide dismutase?SOD?,catalase?CAT?and peroxidase?POD?were enhanced.The activity of SOD in both compost and Cd?CdC?was more 4.16 times than in only Cd treatment.Thus,which reduced the production of reactive oxygen species?ROS?and the accumulation of malonaldehyde?MDA?,and reduced the membrane lipid peroxidation damage of Chinese cabbage.Therefore,the application of compost reduced the toxicity of Cd to plants.