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Abstract
Environment friendly, economic and efficient processes for bioenergy generation are required to fulfill the energy demands of today’s anthropogenic world. Biohythane production plays important role for a cleaner and efficient bioenergy generation. It also improves the overall gaseous energy recovery. Commercialization of biohythane process requires exploration of cheaper substrates, potential microbial cultures and efficient process designs. These factors can be easily controlled and optimized in a two stage biohythane production process as compared with a single stage biohythane process.
Optimization of the hydrogen and methane production phases improves the overall energy efficiency and biohythane productivity. Aim of the present study was to develop an efficient two stage biohythane production process by using organic wastewater.
Different wastewaters viz., distillery effluent, cheese whey, starchy wastewater and brewery wastewater, were explored as substrate for biohydrogen production using Klebsiella pneumoniae IIT-BT 08. Distillery effluent was found most suitable with a hydrogen yield of 3.47 mol H2 / Kg CODreduced. Elemental analysis showed that distillery effluent was lacking in some of the essential micronutrients required for fermentative hydrogen production. Supplementation of FeSO4, MgSO4, CuCl2, yeast extract and malt extract showed 3 fold improvement in hydrogen yield as compared with non- supplemented distillery effluent. Hydrogen yield of 7.64 mol H2 / Kg CODreduced was observed after optimizing the nutritional supplements by central composite design (CCD).
A potential acidogenic mixed consortium (AMC) was developed (2.66 mol H2 / mol glucosereduced) from anaerobic digester. Phylogenetic analysis showed dominance of Clostrium sp. A gradual acclimatization of AMC in an increasing gradient of distillery effluent showed 1.6 folds increase in the cumulative hydrogen production (142 ± 2.1 mmol / L). Modified Gompertz model showed higher hydrogen production potential of AMC (166.5 mmol H2 / L), as compared with co-culture (K. pneumoniae IIT-BT 08 and C. fruendii IIT-BT L139) (120.3 mmol H2 / L), and pure culture (K pneumoniae) (81.1 mmol H2 / L). Different organic solid wastes rich in nitrogen and minerals were explored as a co-substrate with distillery effluent to make the process economically feasible.
Groundnut deoiled cake (150.7 mmol H2 / L) and distiller’s dried grain with solubles (144.2 mmol H2 / L) were found as a better co-substrate as compared to mustard deoiled cake (109.1 mmol H2 / L) and algal biomass (116.1 mmol H2 / L). A significant reduction (> 97 %) in the substrate input cost (SIC) was attained by replacing tryptone with cheaper organic co-substrates. Methanogenic mixed consortium (MMC) was developed and methane yield of 0.78 mol CH4 / mol acetatereduced was obtained at optimum conditions.
Combination of an ethanol utilizing consortium (EUC) with methanogenic consortium (MMC) showed more than 56.3 % and 26.6 % improvement in ethanol conversion efficiency and cumulative methane production, respectively. Two stage continuous hydrogen and methane production from distillery effluent resulted in 40.31 ± 0.65 L H2 / Kg CODreduced and 127.1 ± 0.15 L CH4 / Kg CODreduced with overall CODs reduction of 85.5 % and energy recovery of 38.98 %.
Keywords: Klebsiella pneumoniae IIT-BT 08, Citrobacter fruendii IIT-BT L139, acidogenic mixed consortium, methanogenic mixed consortium, two stage biohythane, distillery effluent.
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