The conversion of organics in wastewaters into hydrogen gas could serve the dual role of renewable energy production and waste reduction. The chemical energy in a sucrose rich synthetic wastewater was recovered as hydrogen gas in this study. Using fractional factorial design batch experiments, the effect of varying pH (4.5-7.5) and substrate concentration (1.5-44.8 g COD/L) and their interaction on hydrogen gas production were tested. Mixed bacterial cultures obtained from a compost pile, a potato field, and a soybean field were heated to inhibit hydrogen-consuming methanogens and to enrich sporeforming, hydrogen-producing acidogens. It was determined that the highest rate (74.7 mL H2/(L*h)) of hydrogen production occurred at a pH of 5.5 and a substrate concentration of 7.5 g COD/Lwith a conversion efficiency of 38.9 mL H2/(g COD/L). The highest conversion efficiency was 46.6 mL H2/(g COD/L).
"Generally , the decreasing of VFAs occurs with increasing alkalinity during the hydrogen and acetate conversion by methanogens to CH 4 and CO 2 , causing the rise of pH ( Malakahmad et al . , 2014 ) . In addition , pH range of 5e6 was considered to be appropriate for H 2 production to avoid both methanogenesis and solventgenesis processes ( Ginkel et al . , 2001 ) . This finding is one of the main reasons for the low COD removal , which is in strong correlation with stable methanogenesis . The soluble metabolites compositions reflect the metabolic pathways of the anaerobic community with changing the HRT , which can be useful to improve the hythane ( H 2 þ CH 4 ) production Fig . 4 . H 2 yield "
[Show abstract][Hide abstract] ABSTRACT: Hythane (H 2 þ CH 4) production from petrochemical wastewater containing mono-ethylene glycol (MEG) via a novel stepped anaerobic baffled (SAB) reactor was investigated. The reactor was continuously operated for five months at constant hydraulic retention time (HRT) of 72 h and different organic loading rates (OLRs) of 0.33, 0.67 and 1.67 gCOD l À1 d À1. The maximum H 2 yield of 359.01 ± 33.46 ml H 2 gCOD removed À1 and H 2 production rate of 5.12 ± 0.48 l d À1 were obtained at OLR of 1.67 gCOD l À1 d À1. Nevertheless, the maximum methane yield of 159.11 ± 14.72 ml CH 4 gCOD removed À1 and methane production rate of 2.48 ± 0.22 l d À1 were recorded at OLR of 0.67 gCOD l À1 d À1. The maximum CH 4 and H 2 content of 52.08 and 49.84% were achieved at OLR of 0.33 and 1.67 gCOD l À1 d À1 , respectively. Compartment-wise hythane profiles were assessed to optimize the production rate. Microbial community analysis was conducted and showed the dominant bacteria of Proteobacteria (44.3%), Firmicutes (28.9%), Chloroflexi (8.9%), Actinobacteria (5.7%), and Bacteroidetes (5.6%).
"Additionally, the optimal pH also varies widely from 4.5  to 9.0 , depends on the nature of the inoculum source and feedstock. For instance using sucrose as carbon source authors reported pH 9.0  and pH 5.5 as optimal  values. Such discrepancy concept could be explained mainly due to the source of inoculum used for hydrogen turnout. "
"Higher concentration (above 0.5%) used in our study resulted in poor hydrogen production as shown in Fig. 2c, which is similar to other findings and indicated that the alkali concentrations between 0.2 and 0.5% showed improved biohydrogen production, whereas further increased concentration resulted in lower biogas production. This might be due to the fact that high NaOH concentration inhibited the growth of anaerobic organisms  . Hydrothermal and autoclave pretreatments did not significantly improve hydrogen production. "
[Show abstract][Hide abstract] ABSTRACT: Fermentation of de-oiled Jatropha waste (DJW) hydrolyzate was carried out at 55 °C and pH 7 to evaluate the efficacy of the DJW pretreatment methods for enhancing the hydrogen production rate. The enzyme (7.5%) treated hydrolyzate showed a peak hydrogen production rate (HPR) and hydrogen yield (HY) of 5146 mL H2/L-d and 98 ml H2/g VSadded, respectively. The HCl (2.5%), H2SO4 (0.5%), ultrasonication (45 min), and heat treatment (100 °C, 45 min) treatments gave maximal HY of 43, 24, 23, and 34 mL H2/g VSadded, respectively. Further enzyme (5%) treatment of the acid (2%) unhydrolysed biomass showed HPR of 2947 mL H2/L-d and HY of 106 mL H2/g VSadded. Besides, it was also observed that higher DJW concentrations during pretreatment, and higher butyrate levels in the fermentation process, led to increased release of reducing sugar and increased HPR, respectively. The total bioenergy production analysis revealed nearly 10-fold increase in the energy values with peak HPR and HY of 55 KJ/L-d and 1.0 KJ/g VSadded, respectively.
International Journal of Hydrogen Energy 07/2015; DOI:10.1016/j.ijhydene.2015.06.118 · 3.31 Impact Factor
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