Construction Of Anaerobic Composting Consortia For Degrading Cellulose And Its Application In The Biogas

More than 700 million tons of crop straw is produced every year in China, but less than 40 percent of it is used, which causes a huge waste of resources as well as contaminates the environment. The main composition of the straw is cellulose. It decomposes easily into small organic molecules in the presence of cellulase. Cellulase consists of various kinds of enzyme and the studies showed that synergistic effect of cellulase on the degradation of cellulose was much better than single cellulose. In this paper, bacterial co-cultures were constructed artificially and screened naturally referring to FPA and degradation rate of cellulose, and then applied to biogas production of crop straw, which increased the utilization of straw and improved the yield and quality of methane. This would be important for the optimal use of resources and reducing the pollution.Bacterial co-cultures were composed artificially using three existing Cellulase-producing bacteria LXD-2(Clostridium cellobioparum), CZ-3(Clostridium papyrosolvens)and N14(Cellulomonas.sp.). Through a series of experiments, the optimum inoculation order was determined: N14, then CZ-3 and LXD-2 at the same time, inoculation amount was 15% and inoculation proportion was 2: (1:1).The FPA and the degradation rate of cellulose of bacterial co-cultures were much higher than single bacterium. The FPA of bacterial co-cultures was 1.47 times that of LXD-2,1.29 times of CZ-3 and 1.14 times of N14; The degradation rate of cellulose was 1.38 times that of LXD-2, 1.57 times of CZ-3 and 1.22 times of N14.After subcluturing more than ten generations, two stable mix cultures LS and W2 capable of degrading cellulose with high efficiency were selected naturally through a number of samples from different habituating conditions, with the filter paper as substrate and indicator .The optimum fermentation conditions for LS were as follows:0.5% of microcrystalline cellulose as carbon source ; 0.15% of peptone as the nitrogen source; the adaptable temperature was 30-37℃, pH value was 7.0-7.5 and the NaCl concentration was 0.1%.K⁺ and Al³⁺ promoted the degradation of cellulose by LS while Co²⁺ inhibited the degradation. The highest FPA of LS was 1.21U when the fermentation time was 72 hours. At the end of fermentation, the degradation rate of cellulose was 22.86%, and the content of acetic acid, propionic acid, butyrate acid were 462.2ppm, 1574.3ppm, 377.3ppm respectively. And the content of cellulose and hemicellulose were reduced by 12% and 11% respectively, while the lignin content showed little change.The optimum fermentation conditions for W2 were as follows:0.5% of microcrystalline cellulose as carbon source, 0.15% of yeast powder as nitrogen source, the adaptable temperature was 30-37℃,the pH value was 7.0-8.0 and the NaCl concentration was 0.1%.K⁺ and Mg²⁺ promoted the degradation of cellulose by W2 while Mn2+ inhibited the degradation. The highest FPA of W2 was 1.23U at the time of 72 hours. At the end of fermentation, the degradation rate of cellulose was 23.38%, and the content of acetic acid, propionic acid, butyrate acid were 410.1ppm, 1808.0ppm, 313.6ppm respectively. And the contents of cellulose and hemicellulose were reduced by 14% and 13% respectively, while the lignin content showed little change.Experiments of anaerobic digestion of crop straw were conducted with the addition of LS, W2 and bacterial co-cultures. The results showed that compared with the control unit, the addition of LS, W2 and bacterial co-cultures in the anaerobic digestion of crop straw enhanced the production of methane. The daily yield of biogas by adding LS, W2 and bacterial co-cultures were 96.1ml, 98.4ml and 88.1ml respectively, which increased by 40.1%, 43.44% and 28.43% compared with the control. Meanwhile, the content of methane by adding LS, W2 and bacterial co-cultures were 73.33%, 74.14% and 72.81% respectively ,which were 1.07, 1.09and 1.06 times respectively as much as that of the control unit.