Dong-Yeol Lee

Continuous H2 and CH4 production from high-solid food waste in the two-stage thermophilic fermentation process with the recirculation of digester sludge.

A thermophilic two-stage fermentation process using 10% total solids (TS) food waste was tested at varying organic loading rates (OLRs). The system was configured to produce H(2) and CH(4) in conjugation with the chemical oxygen demand (COD), nitrogen removal, and adjustment of the pH by returning sludge as an alkali buffer from the sludge storage tank for denitrification. The pH in the H(2) fermentation reactor was maintained in the range of 5.4-5.7 using sludge recirculation (Q(r)/Q(i) ratio 1). The average H(2) (11.1l-H(2) l(-1)-fed d(-1)) and CH(4) (47.4l-CH(4) l(-1)-fed d(-1)) production rates were achieved at OLRs of 39 (H(2) fermentation reactor) and 4.16 gCOD l(-1)d(-1) (CH(4) fermentation reactor), respectively. These results suggest that long-term stability of the continuous two-stage process can be successfully achieved by recirculation of high-alkalinity sludge of 6.7-7.5 g l(-1) as CaCO(3), without any added external chemical buffer.

Fermentative hydrogen production from tofu-processing waste and anaerobic digester sludge using microbial consortium.

The combination of tofu-processing waste and anaerobic digester sludge was studied for its fermentative H(2) production capacity in batch and continuous modes using a thermophilic mixed culture. Heat-treatment (110 degrees C, 30 min) in the presence of 0.5% HCl increased the soluble carbohydrate content of the tofu waste from 2.2 to 10.4 g/l. Anaerobic digester sludge was added to the tofu waste for supplementary nutrients with the optimal mixing ratio of 20% (v/v) under batch conditions. In continuous experiments, the effects of HRT(hydraulic retention time) and pH were investigated for the ranges of 2-6h and 5.0-6.0, respectively. The maximal H(2) production rate (12.0 l H(2)/l/day) and yield (2.3 mol H(2)/mol glucose equivalent) were obtained at HRT 4h and pH 5.5 while maintaining the head space gas at 50-60% (v/v) of H(2) without CH(4). This study indicates that the combination of tofu-processing waste and digester sludge can be considered to be one of the most promising forms of organic waste for continuous H(2) production.

Continuous H2 production by anaerobic mixed microflora in membrane bioreactor

The characteristics of H(2) production by anaerobic mixed microflora in a submerged membrane bioreactor (MBR) were investigated. For comparative purposes, a continuous stirred tank reactor (CSTR) was operated in parallel under the same conditions. The experimental results showed that 35-day stable and continuous H(2) fermentation was successfully achieved, the MBR revealing an H(2) content of 51% and the CSTR, 58%. No methane gas was detected during the experiments for the long solids retention time (SRT) of 90 days. The MBRs H(2) production rate was 2.43-2.56 l H(2) l(-1)d(-1), which was about 2.6 times higher than that (0.95-0.97 l H(2) l(-1)d(-1)) of the CSTR, reflecting the MBRs higher H(2) productivity.