Dark fermentative biohydrogen production from brewery wastes

Abstract

Since brewery waste yeast is plenty and contains high nutritional value, the possibility in using for enhancing H[subscript 2] production is studied. The two sets of batch experimental set-up were carried out in CSTR operating at pH and temperature of 5.0 and 30 ํC, respectively, by means of brewery waste yeast adding and non-waste yeast adding using glucose as substrate. Factorial design experiments with a central composite design (CCD) and response surface methodology (RSM) were used for finding optimal point of glucose, brewery waste yeast and microbial sludge concentration that yielded the maximum hydrogen production rate. For explanation process reaction and design, the Monod kinetic coefficient rate of k and Ks were determined using the integrated Monod equation weighted least-square model. The modified Gompertz equation could be used to best fit the accumulative hydrogen production with correlation (R[superscript 2]) greater than 0.98. It was shown that at 7.0 g/l glucose, 11 g/l brewery waste yeast and 12 g/l of microbial sludge, the highest H[subscript 2] yield of 1.42 mol H[subscript 2]/mol glucose was obtained. Addition of brewery waste yeast into synthetic wastewater in the reactor was found to shift the specific H[subscript 2] production rate from 2.5 to 3.9 ml H[subscript 2]/g VSS.h[superscript -1]. The apparent kinetic value of k (maximum specific substrate utilization rate) was also shift from 0.52 to 1.84 d[superscript -1]. The effect of hydraulic retention time (HRT) on continuous H[subscript 2] production and its mixed anaerobic microbial community were observed in a CSTR operated with 4 HRTs, each lasting 10 days. The major bacterial composition of each HRT was analyzed by 16S rRNA gene-targeted denaturing gradient gel electrophoresis (DGGE). It was found that the H[subscript 2] production was increased after transition from 24h, 12h, 8h and 4h HRT. The experimental result clearly showed that H[subscript 2] yield as high as 2.87 mol H[subscript 2]/mol glucose was achieved at 4h HRT running, corresponding to 71.8% H[subscript 2] conversion efficiency compared to the theoretical yield. Clostridium pasteurianum sp. and uncultured bacterium Clone HPR 146 existed in the reactor might be the dominant strains that contribute to H[subscript 2] production at HRT 4h.