: This paper presents fundamental and theoretical aspects of biological waste gas treatment technologies as well as examples of applications to di †erent compounds. The three most widely used technologies are described, namely bioÐltration, bioscrubbing and trickling bioÐltration, focusing more extensively on bioÐltration which is the most studied and most extensively used process. A description of the di †erent technologies from technological and economic points of view, including an analysis of models used in waste gas biotreatment is given. Results presented in the literature concerning the removal of aliphatic, aromatic and mixtures of contaminants are reviewed. Carrier materials, inocula selected and alternatives proposed for regulating moisture content, pH values or for controlling pressure drop are considered. New technologies and reactor design studied at laboratory-scale are mentioned.1998 SCI (

Three identical biofilters, run under the same conditions but inoculated with different mixed cultures, were fed a mixture of toluene, ethylbenzene, and o‐xylene (TEX) gases. Inert porous perlite was used as support material, in contrast to the more conventional biofiltration systems where natural supports are used. Biodegradation started in all three biofilters a few hours after inoculation, without previous adaptation of the inocula to the toxic mixture. Despite acidification of the systems to pH values below 4·5, the elimination capacities reached were fully satisfactory. The best performing biofilter, in which bacteria were dominant, showed an elimination capacity of 70 g TEX m−3 h−1 with a near complete removal of the mixture up to an influent concentration of 1200 mg TEX m−3 at a gas residence time of 57 s. Most of the ingoing carbon was recovered as carbon dioxide in the outgoing gas. In the other biofilters fungi dominated and performance was slightly worse. With single substrates, the elimination capacity was higher for toluene and ethylbenzene than for the TEX mixture, whereas o‐xylene removal was slowest in all cases. Also when feeding the mixture to the biofilters, o‐xylene was removed most slowly.

Environmental problems associated with the use of fossil fuels as well as their expected scarcity in the near future requires a search for new alternative fuels produced from renewable sources. Bioethanol is a biofuel that can be obtained from biomass and waste as feedstocks through fermentation. Two major routes allow conversion of the feedstocks to fermentable substrates, i.e. the hydrolytic route and the thermochemical route. In the hydrolytic route, the feedstock undergoes a pretreatment stage first, aimed at facilitating the subsequent hydrolytic treatment. Chemical, physical or biological pretreatments can be applied. Lignocellulosic feedstocks are mainly composed of cellulose, hemicellulose and lignin. The pretreatment attacks the lignin and hemicellulose polymers and makes cellulose more accessible in the next, hydrolytic, stage. The hydrolytic treatment uses enzymes to convert the cellulose polymer to simple, fermentable, sugars, mainly glucose. Simple sugars obtained from hemicellulose and cellulose are then fermented by yeasts to bioethanol. In the thermochemical alternative, the feedstock is gasified, yielding syngas – a mixture largely composed of CO, CO2 and H2 – which can be fermented anaerobically, usually by clostridia, to ethanol or other products. In both cases, downstream processes are then applied to recover and purify the biofuel. The different stages involved in both alternatives are described, and both processes are compared in terms of their main characteristics and development stage. © 2015 Society of Chemical Industry

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Haloalkane dehalogenase catalyzes the hydrolytic cleavage of carbon-halogen bonds in short-chain haloalkanes. Two tryptophan residues of the enzyme (Trp125 and Trp175) form a halide-binding site in the active-site cavity, and were proposed to play a role in catalysis. The function of these residues was studied by replacing Trp125 with phenylalanine, glutamine or arginine and Trp175 by glutamine using site-directed mutagenesis. All mutants except Trpl25+Phe showed a more than 10-fold reduced k,, and much higher K, values with 1,2-dichloroethane and 1,Zdibromoethane than the wild-type enzyme. Fluorescence quenching experiments showed a decrease in the affinity of the mutant enzymes for halide ions. The *H kinetic isotope effect observed with the wild-type enzyme in deuterium oxide was lost in the active mutants, except the Trpl25-+Phe enzyme. The results indicate that both tryptophans are involved in stabilizing the transition state during the nucleophilic substitution reaction that causes carbon-halogen bond cleavage.