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The oxidation of methane (CH 4 ) using biofilters has been proposed as an alternative to mitigate anthropogenic greenhouse gas emissions with a low concentration of CH 4 that cannot be used as a source of energy. However, conventional biofilters utilize organic packing materials that have a short lifespan, clogging problems, and are commonly inoculated with non-specific microorganisms leading to unpredictable CH 4 elimination capacities (EC) and removal efficiencies (RE). The main objective of this work was to characterize the oxidation of CH 4 in two biotrickling filters (BTFs) packed with polyethylene rings and inoculated with two methanotrophic bacteria, Methylomicrobium album and Methylocystis sp., in order to determine EC and CO 2 production (pCO 2 ) when using a specific inoculum. The repeatability of the results in both BTFs was determined when they operated at the same inlet load of CH 4 . A dynamic mathematical model that describes the CH 4 abatement in the BTFs was developed and validated using mass transfer and kinetic parameters estimated independently. The results showed that EC and pCO 2 of the BTFs are not identical but very similar for all the conditions tested. The use of specific inoculum has shown a faster startup and higher EC per unit area (0.019 gCH 4  m -2  h -1 ) in comparison to most of the previous studies at the same CH 4 load rate (23.2 gCH 4  m -3  h -1 ). Global mass balance showed that the maximum reduction of CO 2 equivalents was 98.5 gCO 2eq  m -3  h -1 . The developed model satisfactorily described CH 4 abatement in BTFs for a wide range of conditions.

Mixtures of volatile reduced sulphur compounds (VRSCs) like hydrogen sulphide (H(2)S), methylmercaptan (MM), dimethyl sulphide (DMS) and dimethyl disulphide (DMDS) are found in gaseous emissions of several industrial activities creating nuisance in the surroundings. Hydrogen sulphide (H(2)S) decreases the removal efficiency of volatile reduced sulphur compounds (VRSCs) in biofilters but the kinetics of this effect is still unknown. Kinetic expressions that represent the rate of bio-oxidation of H(2)S, MM, DMS and DMDS are proposed. In order to observe and quantify this effect, equimolar mixtures of MM, DMS and DMDS were fed into a biotrickling filter inoculated with Thiobacillus thioparus at different H(2)S loads. Experimental results shown a good agreement with the simulations generated by the model considering the kinetic equations proposed. The estimated kinetic constants show that H(2)S and MM have a significant inhibitory effect on the bio-oxidation of DMS and DMDS, having the H(2)S the higher effect., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

The simultaneous removal of H(2)S and NH(3) was investigated using two biotrickling filters packed with polyurethane foam cubes. One biotrickling filter was inoculated with Thiobacillus thioparus ATCC 23645 for the removal of H(2)S (BTT) and the other filter with Nitrosomonas europaea ATCC 19718 for the removal of NH(3) (BNE). Three different configurations were studied by modification of the gas line and recirculation medium line. The best results were obtained with the BNE biotrickling filter after the co-immobilization of the two bacteria. A removal efficiency of 100% for 230 ppmv of NH(3) and 129 ppmv of H(2)S was reached at an EBRT of 60 seconds. The results obtained show that it is possible to co-immobilize both microorganisms using the same recirculation medium and remove successfully H(2)S and NH(3) from a gas mixture.

In this work the variation in the elimination capacity of a biofilter as a function of the gas flow and toluene concentration was studied. A bioreactor 0.75 m high x 14.5 cm diameter was used, divided into three equal stages, using compost to support the microorganisms, and sea shells to control the pH. The biofiltration of toluene was evaluated for flows between 0.12 and 0.73 m(3)h(-1) in a concentration range of 1-3.2 gm(-3). It was observed that on increasing the toluene inlet load by 90% (from 37 to 70 gm(3)h(-1)), the conversion by the biofilter varied by only 5% (from 98% to 93%). The biofiltration system used achieved elimination capacities of up to 82 gm(-3)h(-1) for a toluene load of 100 gm(-3)h(-1).

The influence of the pH in the first stage, the hydrolytic stage, of the anaerobic digestion of the organic fraction of urban solid waste in a two phase anaerobic reactor was studied. The reactor was fed with a solution of the organic fraction of urban solid residues containing 5 to 7% solids. Four reactors with a working volume of 3 L were used, the experiments were done at three controlled pHs; 6, 7, and 8, and one with free pH, the temperature was keep at 37°C in all the experiments. The higher degradation of TSS and VSS was obtained in the reactors operated at pH 7 and 8; 75% degradation of TSS and 85% degradation of VSS. The volatile fatty acids were determined at the different pH conditions, no significant differences were found, and as was expected, the acetic acid was found at the higher value among them (from 25 to 29 g/L). According to the results obtained it is possible to conclude that in the case of the hydrolytic stage of the anaerobic digestion of the organic fraction of urban solid waste it is not necessary to control the pH, the pH is kept stable by the buffer effect of the protein residues and other macromolecules present in the residue. [ABSTRACT FROM AUTHOR]

Abstract: Baeyer–Villiger bioconversion productivity of the cyclic ketone (±)-cis-bicyclo [3.2.0] hept-2-en-6-ona by the biocatalyst Escherichia coli TOP10 pQR239 in a multiphase system can be limited by mass transport. Mass transfer rates through the liquid–liquid interface depend on the volumetric mass transfer coefficient (kA) and the substrate and product partition coefficients. In situ experimental determination of the volumetric mass transfer coefficient in a partitioning bioreactor is complex. In this work, the substrate (k S ) and product (k P ) global mass transfer coefficients were determined in a modified Lewis cell in three water–ionic liquids systems. The ionic liquids used were butylmethylpyrrolidinium bis(trifluoromethylsulfonyl)imide [MeBuPyrr][BTA], trioctylmethylammonium bis(trifluoromethylsulfonyl)imide [OMA][BTA] and 1-butyl-3-metyl-imidazolium hexafluorophosphate [BMIM][PF6]. The maximum k S and k P values obtained were 4.35×10−5 and 1.21×10−5 ms−1 for water-[MeBuPyrr][BTA] system; 1.53×10−5 and 7.84×10−6 ms−1 for water-[OMA][BTA] system, respectively; and k S values up to 1.01×10−5 ms−1 were found for the water-[BMIM][PF6] system. The association among the mass transfer coefficients and the physicochemical properties (interfacial tension, viscosity and density) and the thermodynamics (partition coefficients) are analysed and discussed. Finally, the volumetric mass transfer coefficients (k S A and k P A) were calculated using interfacial areas (A) of the dispersed ionic liquid phase estimated from the “Sauter” mean drop diameter (d 32) in a one litre stirred tank partitioning bioreactor. [Copyright &y& Elsevier]