| The molasses wastewater from sugar refinery is a kind of wastewater with hingh content of organic matters, especially rich in carbonhydrates and nitrogen. It is hard to degrade by using of conventional treatment, however, because of its good biochemical performance, a two-phase "UASBH-CSTRMet" anaerobic fermentation system using molasses as substrate has been investigated. The resource utilization is important significant to the purifying environment and alleviating the energy shortage.In this study, hydrogen could be continuously produced from the two-phase hydrogen fermentation of molasses wastewater in UASB and effluents from hydrogen fermentation were converted into methane in cstr reactor. The strategy on the start-up of UASB was investigated first in the paper. A hydrogen fermentation system could start up successfully after 25d in UASB by increasing the influent COD stage during the start-up process. Inoculated with qerobic activated sludge, UASB started up at an influent COD 2000mg/L and pH 7.0 under a temperature of 37℃. Meanwhile CSTR reactors operated from artificial preparation of simulated molasses wastewater in former 35 days.then the effluent containing mainly with acetate was began to fed to the second CSTR reactor for methane production. After 65d, a methane fermentation microorganism system had bred in CSTR reactor. Which indicating the two-phase anaerobic system had been established achievely.When the influent COD increased from 2000mg/L(VLR 3.4kg/m3.d) to 4000 mg/L(VLR 11.5kg/m3.d), experiment studied the influence of hydraulic retention time(HRT) on acidogenic phase, so as to determine the optimal operation condition. The performance cha racteristics varied with the different HRT in CSTR. HRT were changed on 12、10、8、7、6h. Results show that:the optimal HRT condition for acidogenic phase was 6h, and under this condition, hydrogen production rate of 7.6L.d-1 and cotent of 69.2% was obtained, the COD removal could reach the highest 42.4%. under HRT condition for methanogenic phase was 18h, the number and activity of methane fermentation microorganism was growing along with the reaction time, the COD removal could reach 48.8%,with a methane yield of 7.89 L.d-1 and content of 42.4%.With optimal operation condition of acidogenic phase and methanogenic phase, the influence of volume loading rate(VLR) on system energy recovery efficiency was discussed. Results indicated that:at VLR27 kg/m3.d, the maximum hydrogen yield of 10.8 L.d-1 and content of 57.7%, with a COD average removel about 48%,and ethanol-type fermentation occurred in UASB. Then the influent COD increed to 10000mg/L, the acidogenia phase could not endure an VLR as high as 34 kg/m3.d, more VFAs were detected in the effluent. However, the methane phase in CSTR showed a better self-adjusting ability to shocking loading rate than that of UASB. With the increase of VLR, the performance characteristics in CSTR were becoming better and better, the maximum methane production rate of 19.3 L.d-1 and content of 76.4% was gained,with 77.8% COD was resealed in the form of methane and carbon dioxide. VFAs in effluent kept at 213mg/L, while the degradation rate of ethanol was fastest, acetic acid and butyrate took the second place, propionic acid was slowest.In conclusion, the two-phase anaerobic system can greatly improve energy recovery efficiency and COD removel rate. The maximum energy recovery efficiency of 65.5% was gained, in which the percentages of hydrogen and methane energy recovery efficiency were 15.8% and 49.6%.The removel of organic matters promoted to 88.3%, with the COD content of 930～1340mg/L in effluent. The results revealed that two-phase anaerobic system is the effective combination of wastewater treatment and energy recovery, but further research was deserved in this system especially the acidogenic phase. |
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