Study On Bio-hydrogen Production Of Different Fermentation Types In CSTR Reacter

Biological hydrogen production process by anaerobic fermentation is a new, low energy consuming and clean technology which includes the utilization of renewable energy resources which are inexhaustible with the production of high quality fuel gas. There are mainly three fermentation types in dark fermentation hydrogen production:ethanol-type fermentation, butyric acid-type fermentation and propionic acid-type fermentation, this study used a continuous flow stirred tank reactor (CSTR) to compare hydrogen production capability of them. The effect of organic loading rate on operation of continuous flow anaerobic activated sludge fermentation system for hydrogen production was investigated too.Each kind of fermentation was performed by different microbial populations, and each population turned into a climax community in different stages of fermentation types, depending on living environment such as pH and redox potential value(ORP). It was demonstrated that under the same hydraulic retention times (HRT=6 h) and influent chemical oxygen demand (COD=5000 mg/L) at 35℃, ethanol-type fermentation, butyric acid fermentation and propionic acid-type fermentation were formed with pH and ORP of 4.2～4.4 and -280～-320mV, 4.6-4.8 and -200--240mV,5.2-5.6 and -180～-210mV, respectively.The maximum specific hydrogen production rate of the anaerobic sludge fermentation system reached 4.92 mol/kg mixed liquid volatile suspended solid (MLVSS)/day, (mol·kg MLVSS-1d-1), in ethanol-type fermentation. The average specific hydrogen production rate of the anaerobic sludge fermentation system reached 3.80 mol-kg MLVSS-1d-1, in ethanol-type fermentation, while 1.28 mol-kg MLVSS-1d-1 in butyric acid-type fermentation, and 0.02 mol-kg MLVSS-1d-1 in propionic acid-type fermentation. The hydrogen production capability of anaerobic activated sludge in ethanol-type fermentation was 3 times greater than that of butyric acid-type fermentation and 190 times that of propionic acid-type fermentation. It indicated that ethanol-type fermentation bacteria have the largest H2-production capability, butyric acid type fermentation bacteria take the second place, and propionic acid-type fermentation bacteria have the least H2-poduction capability.The effect of organic loading rate on operation of continuous flow anaerobic activated sludge fermentation system for hydrogen production was obviously. At some range, hydrogen production increased with the raise of OLR, while too large of OLR went against to hydrogen production. When influent COD concentration rose to 6000 mg/L with HRT of 6h (OLR 24 kg /(m3·d)), the anaerobic activated sludge fermentation system reached the maximum hydrogen production of 17.8L/d. With OLR of 6-24 kg/(m3·d), the total amount of ethanol and acetic acid was accounted for above 85% of the total liquid products, indicating that ethanol-type fermentation occurred in the CSTR. At this stable state, continuous flow anaerobic activated sludge had high activity with MLVSS/MLSS of above 80%. Hydrogen production increased with the raise of OLR. When OLR reached 36 kg/(m3·d), the organic wastewater fermentation type changed from ethanol-type fermentation to mixed acids fermentation, the activity of microorganism in anaerobic activated sludge was inhibited and hydrogen production declined fast.OLR also had effect on the environment in the reactor (pH, ALK, ORP), the activity, amount and metabolize character of microorganism in anaerobic activated sludge. All of the above factors determined the run state, fermentation type and hydrogen production capability of continuous flow anaerobic activated sludge fermentation system together.