| Translating the crop residues for biogas by way of anaerobic biological can not only alleviate the problem of straw pollution but also will provide clean energy as biogas. Biogas residue can also be used as high-quality organic fertilizer to improve soil fertility. According to the physiological characteristics of two flora across the anaerobic fermentation process, the whole process can be divided into two stages as hydrolysis and acidogenic stage and methanogenic stage. And to separate them, the process is called two-phase anaerobic fermentation process. Compared with the traditional single-phase fermentation process, the two-phase anaerobic fermentation process has a higher rate of gas production, system stability and resistance to high load capacity. This paper conducts studies to address the problem of unsatisfying effect of two-phase separation. Hope to use some effective control measures to reduce the biogas yields produced by hydrolysis and acidogenic phase, improving the hydrolysis and acidogenic phase effluent COD concentration, and increasing the biogas yields produced by methanogenic phase, improving the effect of phase separation.(1) Effect of OLR on the two-phase anaerobic fermentation phase separation. Hydrolysis and acidogenic reactor use bale straw as the stationary phase, and pig slurry as the mobile phase, by gradually increase the pig slurry COD load to achieve the target of reducing biogas yields produced by hydrolysis and acidogenic phase. The results shows that because of good cushioning properties of pig slurry, though the OLR of pig slurry is very high, however the pH of hydrolysis and acidogenic phase effluent always remained at around 7.0. Daily biogas yields of the reactor increase with the improving of OLR load of pig slurry. The highest volume biogas yield of 0.748m3/(m3·d) was obtained at the OLR of pig slurry of 7.2 kgCOD/(m3·d), increase of 92.38% compare with the CK group. A large number of easily decomposable organic matter in pig slurry inhibited the hydrolysis of straw, straw acid hydrolysis rate has dropped by 7.3%. These results indicate that improving OLR of pig slurry may improve biogas yield of hydrolysis and acidogenic reactor instead of reducing it.(2) Effect of HRT on the two-phase anaerobic fermentation phase separation. Hydrolysis and acidogenic reactor use bale straw as the stationary phase, and pig slurry as the mobile phase, by Fixing COD concentration of pig slurry to change the hydraulic retention time (HRT) of pig slurry and reduce the biogas yields of hydrolysis and acidogenic phase, to achieve the purpose of phase separation. The results shows that HRT of pig slurry has a great effect on volume biogas yield but has litter effect on methane content. Low HRT of pig slurry increases the volume biogas yield, when HRT of pig slurry is Id, the volume biogas yield can up to 2.29m/(m3·d). After gas production remained stable, volume biogas yield of treatment was 1.52-1.76 m3/(m3·d) which was more than 50% and 130% higher than that of treatment with HRT of pig slurry of 3 and 5 days. The result of DGGE of water extract of digested wheat straw showed that higher OLR of pig slurry promoted the colonization of microorganisms in the straw surface and anaerobic microbial community structure and number were much more than that of treatment with lower organic loading rate of pig slurry. The above results indicated that it is feasible to use straw-bed bioreactor for biogas production with agricultural straw and livestock wastewater as fermentation materials and higher OLR of livestock wastewater with higher volume biogas yield. These results indicate that by way of reducing HRT of pig slurry cannot reach the goal of phase separation, and may improve biogas yield of hydrolysis and acidogenic reactor after 25d. (3) Effect of pH on the two-phase anaerobic fermentation phase separation. By controlling the fermentation broth to alkaline environment of pH to see the Influence to phase separation of two-phase anaerobic fermentation. The results shows that Adjusting the pH of the fermentation broth to 8.0 can increase gas production of hydrolysis and acidogenic phase, cumulative biogas production is 88960mL, increasing by 30% compared with the CK. But continued to raise the pH of the fermentation broth will have an inhibitory effect on the production of biogas. If Adjust the pH of the fermentation broth to 9.5 and 11, their cumulative gas production well reduce 33.60% and 90.13%. Adjusting the pH of the fermentation broth to 8.0 and 9.5 has little effect on methane content, both of their methane content are more than 50%, but if adjust pH to 11.0 well greatly reduce the methane content, only about 15%. Though adjusting the pH of the fermentation broth to 9.5 and 11.0 can reduce the gas production of hydrolysis and acidogenic phase, however, due to the large amount of alkali in fermentation broth, it also inhibit the gas production of methanogenic phase, the corresponding cumulative biogas production of methanogenic phase are 2780ml and 540ml, reducing by 10.03% and 82.52% compared with the CK. High alkalinity also inhibited the hydrolysis of straw, straw loss rates were reduced by 8.47% and 24.94% compared with CK. These results indicate that by way of controlling the fermentation broth to alkaline environment of pH can reduce biogas yield of hydrolysis and acidogenic reactor, but well also reduce biogas yield of methanogenic phase, is not a suitable phase separation method.(4) Effect of methane inhibitors on the two-phase anaerobic fermentation phase separation. By adding methane inhibitors into hydrolysis and acidogenic phase, to see the Influence to phase separation of two-phase anaerobic fermentation. The results shows that Chloroform has a very good inhibitory effect on gas production, the peak gas production of T1 is 50.82% lower than CK, and total gas production is 85.78% lower. T2 and T3 even have no gas throughout the experiment. Chloroform in fermentation broth has a serious inhibitory effect on the next step of methane production in methanogenic phase, the peak gas production of T1 is 89.74% lower than CK, and total gas production is 97.27% lower. T2 and T3 even have no gas throughout the experiment. These results indicate that Chloroform can not only inhibit biogas yield of hydrolysis and acidogenic reactor but also well have a severe inhibition on methanogenic phase.As can be seen from the above results, four kinds of methods used in this paper can not reach the effect of phase separation, But some of the results are also very usefull, for example:Adjusting the pH of the fermentation broth to 8.0 can increase gas production of hydrolysis and acidogenic phase; Shortening the HRT or improving the OLR can increase volume biogas yield. |
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