Characteristics Of Biofilm And Process Of Fixed Bed With Stirring In Biogas Producing

This study aimed to solve the problems in scale dairy farm such as the great output of cattle manure, the low processing efficiency and low gas production of tradition biogas fermentation. A new biogas production technology based on the stirred fixed bed was developed to elucidate its operational mechanisms and improve the utilization of cattle manure.The effect of total solid (TS), temperature, carbon and nitrogen ratio, stirring speed, pH and hydraulic retention time on biogas production using cow dung as feedstock was investigated. According to the analysis of response response surface method logy and desirability function, the optimum conditions for biogas yield was as follows, materials density 8%, temperature 39 ℃, carbon and nitrogen ratio 25:1 and hydraulic retention time 10d. Under this condition, the property of biofilm and gas yield were also evaluated. Results indicated that biofilm is accumulating at the first HRT of 10d in the fermentation, whereas it become as a relative stable film at the second HRT of 15d.The diversity and dynamic change of bacterial and archaea were analyzed by 16S rRNA cloning technology. The results showed that fermentation liquid and biofilm bacterial populations includes:Pseudomonas (26%-18%), Clostridium(21%-13%), Bacteroidetes (16%-12%)and uncultured bacteria(31%-25%). Among them, Pseudomonas reduced at the first HRT in the fermentation liquid. The microbial component diversity of biofilm were stable. Clostridium were reduced in the bioflm of the first HRT. The microbial component diversity of fermentation liquid were stable. Bacteroides were increasing in the fermentation liquid and bioflm at the first HRT. The predominant bacterial populations were stable in the fermentation liquid and biofilm at second HRT. Results showed that archaea were consisted of Methanosarcina, Methanoculleus, Methanosaeta, Methanoplanus, Methanobacterium, Nitrosocaldus and uncultured archaea in the various periods of fermentation liquid and biofilm. There were also differences in diversity between the fermentation liquid and biofilm.The redundancy analysis (RDA) was used to analyze the correlation between the microbialcommunity structure, characteristics of biofilm and methane production rate during with different aeration rate. The results showed that moisture, chemical oxygen demand(COD), moisture and extracellular polymeric substances(EPS) had high correlation to bacterial populations, while EPS, total organic carbon and COD had high correlation to archaea.The COD affect significantly formation of biofilm. RDA results also revealed that the bacterial and archaeal community structure of biofilm changed with the fermentation time, and were stable at the second HRT of fermentation.These results showed that the stirred fixed bed technology can operate steady and form biofilm which would promote the production of biogas. It also could be found that the biofilm was unstable at the first HRT and were stable at the second HRT.