Louise Bibeau

Biofiltration of air contaminated with toluene on a compost-based bed

Many studies have focused on problems created by emissions to the atmosphere of gaseous effluents containing volatile organic compounds (VOCs). Over the more recent decades, such studies have led to the development of various bioreactors such as the bioscrubber, the biotrickling filter and the biofilter. This paper presents the results of a study on the biofiltration of airborne toluene, the biofilter employed being operated at the laboratory-scale for a continuous period of 3 months. The focus of this particular study has been the development of a new compost-based filter-bed material, which consists of an association between matured compost and a proprietary organic binder that is intended to prolong the period of the beds efficient operations. No inoculum was added to the filter-bed material. During the experimental program, the performance of two different bed irrigation solutions was examined, the most effective nutrient supply solution then being used, along with toluene input levels varying from 0.6–2.6 g/m3, and toluene polluted air flow rates ranging from 0.4–1 m3/h, equivalent to empty bed residence times of 65–165 s. The results of this program have demonstrated removal efficiencies approaching 95%, while maximum elimination capacities of 55 g/m3 h, for an inlet load of 65 g/m3 h, have been achieved, supporting the view that the compost-based filter material tested in this work functions as a promising biofilter medium in this application. Finally, in order to present the biofilter performance observed under the best operating conditions, a simplified representation based on Ottengrafs model has been developed from the experimental results and is included here.

A study of the impact of particle size and adsorption phenomena in a compost-based biological filter

Abstract The removal of toluene by biofiltration has been investigated. The first objective was to study the impact of the filter bed pellet size on the biodegradation performance. Three different pellet sizes (5.0, 10 and 20 mm diameter) were evaluated with an air flowrate of 1.0 m 3 h −1 , toluene inlet concentrations between 1.8 and 3.9 g m −3 and with variable nitrogen concentrations in the irrigation solutions (0.0– 7.0 g of N l −1 ). It was shown that pellet size and specific surface area were major limiting factors for the biodegradation process. Thus, for the optimal N-concentration (2.0– 3.0 g of N l −1 ), the maximum elimination capacities, decreasing with pellet size, but increasing with specific surface area, were achieved: 180 g m −3 h −1 (5.0 mm , 590 m −1 ) , 90 g m −3 h −1 (10 mm , 280 m −1 ) , and 45 g m −3 h −1 (20 mm , 120 m −1 ) . The second objective was the determination of the adsorption isotherm (22°C) for toluene on the wet filter bed. Toluene inlet concentrations between 0.0 and 3.2 g m −3 were introduced in a bench-scale biofilter. The experimental adsorption isotherm was modeled by either a Langmuir model (K 1 =344.8 μg g −1 of moist bed, K 2 =16.7 g m −3 ) or a Freundlich approach ( k f =19.4 μg g −1 of moist bed, n =0.92).

Treatment of Air Polluted with Xylenes using a Biofilter Reactor

Biofiltration of air polluted by VOCs is now beingrecognized by the industrial and research communitiesto be an effective and viable alternative for theclassical environmental technologies. While a numberof biological aspects of the biofiltration process arewell understood, the effect of certain engineeringparameters such as temperature, pressure drop,bacterial count, etc., remained ambiguous especiallywhen several isomers have to be removedsimultaneously. In this paper are reported theresults of purification of air containing vapors ofxylenes in a laboratory-scale biofilter reactor. Thelatter is a packed bed of peat balls particlesspecifically designed and produced for this purpose. Three types of micro-organisms strains werescrutinizingly selected and immobilized on thefiltering material. Xylenes entering the biofilter ata relatively high inlet load (110 g m-3 h-1)are removed with an elimination capacity of60 g m-3 h-1 (at steady state). Theexperimental results obtained on the reduction ofxylenes were satisfactorily represented by thegeneralized Ottengrafs model.

Degradation of toluene, xylene, and trimethylbenzene vapors by biofiltration: A comparison

Abstract This paper presents a comparative study of the biodegradation of three aromatic volatile compounds in a compost-based biofilter: toluene, xylene, and 1,2,4-trimethyl-benzene, used in the course of this work for the first time in the field of biofiltration. Hence, three identical biofiltration units have been operated at the laboratory scale. During the experiments, nitrogen (as urea) was supplied at various concentrations to each reactor, via irrigated nutrient solutions. A comparative analysis of the results showed that the biodegradability scale followed the degree of substitution around the aromatic ring: toluene > xylene > trimethylbenzene, with 95, 80, and 70% maximum conversions, respectively. In addition, and despite the different removal levels achieved in the three biore-actors, it was established that from a reaction viewpoint, the degradation of the three compounds seemed to follow similar metabolic pathways involving methylcatechol isomers. Finally, by varying the nitrogen input concentrations in the three reactors, three degradation regimes have been highlighted: an N-limitation regime and an N-optimum regime, common to the three solvents, and an N-excess regime, favorable to the colonization of the filter beds by nitrifying species, which particularly affected the xylene and trimethylbenzene biodegradation.