Mark D. Redwood

Dehalogenation of polychlorinated biphenyls and polybrominated diphenyl ethers using a hybrid bioinorganic catalyst

The project objective was to advance the development of the H2 economy by improving biological H2 production in a sustainable way. Pseudo-continuous H2 production was achieved with improved efficiency, via the bacterial fermentation of sugars in a dual-bioreactor (‘upstream system’) comprising a dark fermentation coupled to a photofermentation. Excess biomass from the upstream system was used to recover palladium from solution, producing ‘palladised biomass’ (Bio-Pd(0)), which was useful in the construction of bioinorganic catalytic anodes for the electricity generation from bio-H2 using a polymer electrolyte membrane fuel cell (‘downstream system’). Furthermore, the catalytic usefulness of Bio-Pd(0) was confirmed in several reactions in comparison with other palladised biomasses and with Pd(0) made chemically. The upstream modules: Escherichia coli dark fermentation and Rhodobacter sphaeroides photofermentation, were investigated and developed separately, before coupling the two stages by the novel application of electrodialysis (accelerated membrane separation). The biorecovery and testing of palladium bionanocatalyst are described, before the production of fuel cell catalyst using waste biomass. The technical challenges and potential benefits of biohydrogen production are discussed and contrasted with those of competing biofuel technologies.The environmentally prevalent polybrominated diphenyl ether (PBDE) #47 and polychlorinated biphenyls (PCBs) #28 and #118 were challenged for 24 hours with a novel biomass-supported Pd catalyst (Bio-Pd(0)). Analysis of the products via GC-MS revealed the Bio-Pd(0) to cause the challenged compounds to undergo stepwise dehalogenation with preferential loss of the least sterically hindered halogen atom. A mass balance for PCB #28 showed that it is degraded to three dichlorobiphenyls (33.9%), two monochlorobiphenyls (12%), and biphenyl (30.7%). The remaining mass was starting material. In contrast, while PCB #118 underwent degradation to yield five tetra- and five trichlorinated biphenyls, no less chlorinated products or biphenyl were detected, and the total mass of degraded products was 0.3%. Although the Bio-Pd(0) material was developed for treatment of PCBs, a mass balance for PBDE #47 showed that the biocatalyst could prove a potentially useful method for treatment of PBDEs. Specifically, 10% of PBDE #47 was converted to identifiable lower brominated congeners, predominantly the tribrominated PBDE #17 and the dibrominated PBDE #4, 75% remained intact, while 15% of the starting mass was unaccounted for.

Electro-extractive fermentation for efficient biohydrogen production.

Electrodialysis, an electrochemical membrane technique, was found to prolong and enhance the production of biohydrogen and purified organic acids via the anaerobic fermentation of glucose by Escherichia coli. Through the design of a model electrodialysis medium using cationic buffer, pH was precisely controlled electrokinetically, i.e. by the regulated extraction of acidic products with coulombic efficiencies of organic acid recovery in the range 50-70% maintained over continuous 30-day experiments. Contrary to previous reports, E. coli produced H(2) after aerobic growth in minimal medium without inducers and with a mixture of organic acids dominated by butyrate. The selective separation of organic acids from fermentation provides a potential nitrogen-free carbon source for further biohydrogen production in a parallel photofermentation. A parallel study incorporated this fermentation system into an integrated biohydrogen refinery (IBR) for the conversion of organic waste to hydrogen and energy.