Optimization of media composition for the production of biohydrogen from waste glycerol

Abstract

Glycerol Box-Behnken design a b s t r a c tEnterobacter aerogenes has a known ability to convert glycerol during a fermentative process to yield hydrogen and ethanol as the main products. A Box-Behnken design and response surface methodology were used to determine the optimal concentration of some media constituents and oxygen to maximize the yield of biohydrogen. Results indicated that the concentration of the salts studied: NH 4 NO 3 , FeSO 4 , and Na 2 HPO 4 and; the presence of oxygen in the pre-culture significantly influence the production of biohydrogen. Optimal conditions were determined to be 7.5% O 2 in the inoculum transfer step, ratio of inocula 18%, 8 g/L of Na 2 HPO 4 , 0.00625 g/L of FeSO 4 and 1.5 g/L of NH 4 NO 3 . These optimal conditions resulted in a measured yield of 0.85 mol H 2 /mol glycerol at a substrate concentration of 15 g/L and a maximum predicted yield of 0.95 mol H 2 /mol glycerol at a substrate concentration of 21 g/L. These results were obtained using lower concentrations of salts than in previous studies, corresponding to a 76% cost savings. These experimental results also demonstrated the importance of optimizing the amount of oxygen present in the biological system rather than maintaining complete anaerobic conditions.

Biorefinery for Glycerol Rich Biodiesel Industry Waste

“…Improvements in H 2 production from glycerol have been reported by changing the nitrogen source: (1) 0.542 mol/mol glycerol with 1 % w/v ammonium chloride and (2) 0.748 mol/mol glycerol with sodium nitrate, and (3) 0.646 mol/mol glycerol with ammonium nitrate [52]. Similar enhancement in H 2 yield from glycerol was observed previously as well with ammonium sulphate [53]. Biological hydrogen production on a regular basis can be achieved where ever feasible, by continuous culture digestions, especially using immobilized bacterial cultures.…”

Optimization of selected salts concentration for improved biohydrogen production from biodiesel-based glycerol using Enterobacter aerogenes

“…Prior to taking inoculum from the inoculum bottles, an argon-oxygen gas mixture (7.5% O 2 ) was used to over-pressurize the inoculum bottles while maintaining the semi anaerobic conditions identified in previous work [14] has being beneficial to the production of hydrogen by E. aerogenes. 9.4 mL of inoculum was then transferred from an inoculum bottle into the experiment bottles containing 50 mL of glycerol-containing MMSM.…”

“…The screening of salts was done by varying the concentration of MG and CA by 50% above and below the concentrations reported in literature (MG 200 mg/L, CA 10 mg/L [14]), and including a concentration of 0 mg/L. The concentrations studied were 0, 100, 200, 300 mg/L for MG and 0, 5, 10, 15 mg/L for CA.…”

“…Optimization II: ratio of Na 2 HPO 4 to KH 2 PO 4 In order to study the effect of two phosphate salts commonly used as buffer, potassium and sodium salts, experiments were performed by maintaining a constant molar amount of phosphate equivalent to the level used in previous studies (8.0 g/L Na 2 HPO 4 and 4.0 g/L KH 2 PO 4 [14]), while varying the ratio of Na 2 HPO 4 (PH) to KH 2 PO 4 (KP). The levels of PH and KP were adjusted to obtain five different mass ratios PH/KP: 0 (PH only), 0.43, 0.67, 0.84 and 1 (KP only).…”

“…The optimized conditions obtained from previous work [14] and through the optimization studies described in the earlier sections (Sections 2.3.1 and 2.3.2) were used to study the conversion of crude glycerol obtained from a biodiesel production company. Crude glycerol was vacuum filtered using filter paper P8 and P4 purchased from Fisher Scientific before being mixed with deionized water in order to obtain a concentration of 18.5 g/L of crude glycerol (corresponding to 15 g/L of glycerol).…”