Enrichment And Characterization Of Mixed Hydrogen Production Flora From Digested Sludge

In order to enrich hydrogen production bacteria and remove hydrogen consuming bacteria, four processes (heat-shock, acid, base and chloroform, respectively) were conducted in batch tests to evaluate their suitability in the construction of mixed hydrogen production flora from digested sludge. The experimental results showed that chloroform process irreversibly killed lots of hydrogen production bacteria, while heat-shock, acid and base processes could efficiently adjust flora structure and enrich hydrogen production bacteria. For fermentative hydrogen production from glucose, the digested sludge pretreated by heat-shock (121℃,8min), acid (pH=4), and base (pH=10) resulted in an increase of 216%,141% and 128% in hydrogen yield respectively. The result of 16S rRNA gene sequence analysis indicated that Enterobacter was the preponderant bacteria in the mixed hydrogen production flora constructed after heat-shock, acid or base enrichment processes.Then experients were conducted to investigate hydrogen production performance by this mixed flora at various initial pH, fermentative temperatures, inoculation volumes and substrate types respectively. Different initial pH had little influence on the fermentative system. Hydrogen yield was 1.18mol H2/mol glucose when fermentative temperature was controlled at 37℃, which was the favorite fermentative temperature. At the optimal inoculation volume of 10%, the hydrogen yield, biomass and substrate degradation were high. The hydrogen production on four monosaccharides was investigated, and hydrogen yields on the four momosaccharides were in the order as follows:gluctose> fructose> galactose> xylose, meanwhile substrate concentration of 10-20g/L was suitable for hydrogen fermentation.Finally, Sodium cellulose sulfate (NaCS)/Ploy-dimethyl-dially-ammonium chloride (PDMDAAC) capsules were used to immobilize this mixed hydrogen production flora. Compared to free cells the hydrogen evolution was increased more than 30% after immobilization, meanwhile the biomass was increased from 1.5g/L to 3.2g/L. Operation at a temperature of 40℃resulted in the most efficient hydrogen production, and the most favorable substrate concentration was 20g/L. The NaCS/PDMDAAC capsules showed excellent stability during 15 repeated-batch runs. The hydrogen yield maintained 1.73-1.81mol H2/mol glucose, and the biomass was notably increased. Thus the fermentation cycle was shortened from 48 hour to 24 hour, resulting in an increase of 198.6% in hydrogen production rate. And the soluble metabolites contained high percentage of butyric acid and acetic acid.