Biological hydrogen production from lignocellulosic biomass in an up-flow anaerobic sludge blanket reactor using mixed microbial cultures

The current research investigated hydrogen (H 2 ) production potential from lignocellulosic biomass via dark-fermentation in upflow sludge blanket reactors (UASBRs) using mixed anaerobic culture. The effects of hydraulic retention time (HRT) and organic loading rate (OLR), on H 2 production were examined under mesophilic conditions using linoleic acid (LA), as a methanogenic inhibitor. The dynamics of the microbial community were explored using terminal restriction fragment length polymorphism analysis. Studies with pure glucose revealed that high H 2 yield greater than 2.1 mol mol -1 glucose was obtained in control cultures operating at HRTs ranging from 12 h to 20 h with OLRs corresponding to 16 g L -1 d -1 and 10 g L -1 d -1 , respectively. Species belonging to Clostridia was observed under these conditions. A further decrease with the HRT in control cultures reduced H 2 yields up to 1.3 mol mol -1 glucose, while addition of LA showed improved H 2 yields greater than 2.0 mol mol -1 glucose at HRTs ranging from 6 to 12 h. A maximum H 2 yield of 303±20 mL g -1 COD was obtained from switchgrass-derived sugars under the optimal conditions (pH 5.0, HRT 10 h and 1.75 g L -1 of LA) determined using response surface methodology. The microbial characterization under optimal conditions showed dominance of Ruminococcaceae and Clostridiaceae with efficient suppression of methanogens. Nitrogen sparging of the UASBRs under the optimal conditions, increased H 2 yield by 15% in comparison to unsparged cultures. Sparging the bioreactors increased the abundance of Clostridium sp. and Bacillus sp. under LA treated conditions. A stable H 2 yield of 274±40 mL g -1 COD was obtained by the control cultures fed corn stover hydrolysate and operating at 18 and 24 g COD L -1 d -1 , suggesting furans and phenols could serve as methanogenic inhibitors at low levels. The dominance of Clostridium sp., Flavobacterium sp. and Eubacterium sp., were observed under these H 2 -producing conditions. The results from current research suggest that H 2 production from lignocellulosic biomass is feasible and could be applied on a large scale by maintaining proper operational conditions.

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