| Summary: | 博士 === 逢甲大學 === 土木及水利工程研究所 === 90 === This study aimed at the hydrogen production of sewage sludge that digested the carbohydrate (glucose and sucrose). To achieve this purpose, the experimental approach was initially focused on the starting-up of hydrogen-producing digesters (continuously stirred tank reactor, CSTR), then the performance of the reactors and finally the influences of enrichment of seed sludge.
The procedure for starting-up CSTR reactors for acclimating anaerobic hydrogen-producing microorganisms with sewage sludge was investigated. Initially, the feeding and mixing were in a mode of semi-continuous type; hydraulic retention time (HRT) was in an order of 20, 15, 10, 5, 2.5 and 2 days. When the pH declined to a low value (pH 5.18), it was adjusted to 6.7 with sodium hydroxide (1N). At the same time, the semi-continuous type operation was changed to a continuous type. Finally, the pH was continuously regulated around 6.7. The results indicate that this procedure could cultivate seed sludge for hydrogen production from sewage sludge and obtain a large hydrogen production in less than 60 days. This seed sludge had a hydrogen yield of 1.63 mol-H2/mol-glucose and specific hydrogen production rate (SHPR) of 321 mmol-H2/g VSS-d at the HRT of 13.3 h; hydrogen yield was 4.45 mol-H2/mol-sucrose and SHPR was 707 mmol-H2/g VSS-d.
The influence of substrate on anaerobic hydrogen producing reactors seeded with sewage sludge was employed with batch tests. The results indicated that a substrate inhibition phenomenon results from higher glucose concentration, but not in higher sucrose concentration. The varieties of substrate and initial concentration influence the fermentation for hydrogen production.
Using thermal pretreatment, or a low or high pH environment to obtain dominant microbes for hydrogen production from sludge is a feasible method. Based on the experimental results, hydrogen production from sludge with thermal, acid or base enrichment is higher than that of the control. The hydrogen production potential of the sludge with acid or base enrichment enhanced 200 and 333 folds than that of the control when the enrichment pH was 10 and 3, respectively. The enrichment is due to the shortening of microorganisms'' lag-time which occurs at a proper cultivation pH level.
Two CSTR reactors were started up by using sewage sludge for producing hydrogen from sucrose or glucose. The substrate was fed in a continuous mode from HRT 13.3 hrs to 10, 8, 6, 5, 4, 3, and 2 hrs. The hydrogen gas production and hydrogen percentage increased when HRT decreased at long HRT and decreased with a HRT decreased at short HRT (2 hrs). Under steady state conditions, for reactor fed with glucose and sucrose, respectively, the SHPR ranged from 60 to 516 and 82 to 886 mL-H2/g VSS-hr; the yield ranged from 0.39 to 1.65 mol-H2/mol-glucose and 1.42 to 4.52 mol-H2/mol- sucrose. Kinetic models were developed to describe and predict the experimental results from the H2-producing cultures. The major volatile fatty acid (VFA) produced was butyric acid (HBu) with acetic acid and propionic acid at less quantities. The major solvent product was ethanol, whose concentration was only 15% of that of HBu, indicating that the metabolic flow favors H2 production. The model study also suggests that product formation in the continuous hydrogen-producing cultures was essentially a linear function of biomass concentration. H2 content, SHPR and yield were HRT and substrate-dependent. For each substrate two stages of HRT-dependent relationships for these three parameters were obtained. For glucose-degradation hydrogenation, the critical HRT values of the two-stages relation were 6 hrs for these three parameters. For sucrose-degradation hydrogenation, the critical HRT values of the two-stages relation were 5, 4 and 4 hrs for H2 content, SHPR and yield, respectively.
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