Batch and continuous biohydrogen production using mixed microbial culture.

摘要

In this research, biological hydrogen production via dark fermentation using mixed cultures was studied in batch, repeated batch and continuous systems. The preparation of active and stable microflora, increase of hydrogen production yields and rates, and evaluation of sustainability and revivability of continuous hydrogen production were the main objectives of this research.;The effect of addition of four metabolites, including ethanol, lactic acid, butyric acid and acetic acid, by a fractional factorial design revealed the positive impact of lactic acid on hydrogen production. Although no significant hydrogen production was observed when lactic acid was used as the sole carbon source for hydrogen production, the addition of 10 mM lactic acid to a starch-containing substrate could enhance both hydrogen production rates and yields by approximately 1.9 and 1.6 times, respectively.;Continuous hydrogen production was compared in continuously stirred tank reactors (CSTR) with and without a gravity settler at mesophilic temperature. The observed inverse relationship between hydrogen yield and biomass yield implied that biomass yield is minimized with maximization of hydrogen yield. The revivability of a continuous hydrogen production system after a period of feed interruption was studied in a CSTR bioreactor. After the feed interruption, butyric acid formation completely stopped and the hydrogen yield decreased from 1.36 to 0.29 mol H2/ mol glucose with ethanol, acetic acid, and lactic acid as the predominant soluble metabolites. Hydrogen production yield later increased to 0.7 mol H2/mol glucose by adjusting the organic loading rate and pH. The microbial community analysis showed complete elimination of Clostridium affiliated strains after the re-startup of the reactor.;Key words: biological hydrogen production, dark fermentation, mixed culture, heat pre- treatment, CSTR, PCR-DGGE;Batch experiments showed that, depending on the type of inocula, the heat pretreatment temperature had a direct effect on hydrogen production yield, hydrogen production rate and microbial community. The maximum yields of 2.3 and 1.6 mol H2/mol glucose were achieved for 65°C pretreated anaerobically digested sludge and activated sludges, respectively. Pretreatment of anaerobically digested sludge at 95°C lowered the yield up to 15% while the same pretreatment for the activated sludge led to the complete suppression of hydrogen production. Biological hydrogen production with two types of microflora, activated sludge and anaerobically digested sludge, was compared at mesophilic (37°C) and thermophilic (55°C) conditions. Hydrogen production using activated sludge proved to be higher at thermophilic conditions, with cumulative hydrogen approximately six times more than that of mesophilic temperature. However, in anaerobically digested sludge, hydrogen yield at thermophilic temperature was 15% lower than that of mesophilic temperature. Repeated batch experiments at 37°C showed that hydrogen production with activated sludge was not stable due to the presence of lactic acid bacteria in the microflora according to PCR-DGGE analysis.