Shock loading in biofilters: impact on biodegradation activity distribution and resilience capacity.

A synthetic contaminated gas was generated, representative of gaseous emissions from sludge composting. It was composed of six volatile organic compounds (aldehyde, ketones, esters, sulphur compound) in an ammoniacal matrix. The gaseous stream was purified by biofiltration, in pilot scale biofilters filled with pine bark woodchips as organic carrier for biomass colonization. After reaching a constant high efficiency, with complete removal, the system was disturbed by transient loading shocks. The impact of perturbations was assessed by both performance evaluation (i.e. contaminant removal) and microbial behaviour. The microbial community was analysed in terms of density. The resilience of functional component following a perturbation was evaluated. This work highlighted the longitudinal distribution of both biodegradation activities and biomass density.

Structural and functional responses of sewage microbial communities used for the treatment of a complex mixture of volatile organic compounds (VOCs).

AIMS: The aim of this work was to assess the impact of the applied mass loading on the selection of an efficient microbial community able to degrade a complex mixture of volatile organic compounds (VOCs). METHODS AND RESULTS: Two reactors were used and were supplied with a gaseous effluent containing 11 VOCs with different concentrations. The response of the microflora was monitored as a function of time: biodegradation activity, bacterial density and diversity. The results showed that the applied mass loading seems to have an impact on the functioning and the genetic structure of the bacterial community. CONCLUSIONS: A high mass loading seems to induce a low efficient functioning in terms of elimination efficiency and a simplification of the genetic structure of the total bacterial community with the apparition of a dominant microflora. A low mass loading seems to favour a better functioning and allows to keep a healthier bacterial diversity. SIGNIFICANCE AND IMPACT OF THE STUDY: In the treatment processes of gaseous effluents, it would be judicious to define the functioning parameters of the process to keep the diversity of important functional bacterial groups. These results provide also useful information about changes in microbial communities following natural or anthropogenic alterations in different ecosystems.

External capillary condensation and adsorption of VOCs onto activated carbon fiber cloth and felt.

Adsorption isotherms of some volatile organic compounds (VOCs), present in air at concentrations ranging from 10 to 2500 mg m(-3), were performed onto activated carbon fiber cloth and felt. The VOCs loading air were isopropanol, toluene, acetone, methyl ethyl ketone, ethyl acetate and dichloromethane. Isotherm adsorption data were generated. These experimental values were modeled by the equation of Dubinin and co-workers and by the Langmuir relation. Model parameters are discussed as a function of adsorbent materials and VOC structure. Adsorption capacity was generally found higher for the cloth than for the felt. An effect of external capillary condensation onto the felt of compounds with high surface tension was demonstrated for VOC concentrations above 1500 mg m(-3).

Link between spatial structure of microbial communities and degradation of a complex mixture of volatile organic compounds in peat biofilters.

AIMS: To investigate the relationships between the operation of the volatile organic compound (VOC) removal biofilter and the structure of microbial communities, and to study the impact on degradation activities and the structuring of microbial communities of biofilter malfunctions related to the qualitative composition of the polluted air. METHODS AND RESULTS: A microbiological study and a measurement of biodegradation activities were simultaneously carried out on two identical peat-packed columns, seeded with two different inocula, treating polluted air containing 11 VOCs. For both reactors, the spatial structure of the microbial communities was investigated by means of single-strand conformation polymorphism (SSCP) analysis. For both reactors, stratification of degradation activities in function of depth was observed. Oxygenated compounds were removed at the top of the column and aromatics at the bottom. Comparison of SSCP patterns clearly showed a shift in community structure in function of depth inside both biofilters. This distribution of biodegradation activities correlates with the spatialization of microbial density and diversity. Although the operating conditions of both reactors were identical and the biodegradation activities similar, the composition of microflora differed for biofilters A and B. Subdivision of biofilter B into two independent parts supplied with polluted air containing the complex VOC mixture showed that the microflora having colonized the bottom of biofilter B retained their potential for degrading oxygenated compounds. CONCLUSIONS: This work highlights the spatialization of biodegradation functions in a biofilter treating a complex mixture of VOCs. This distribution of biodegradation activities correlates with the spatialization of microbial density and diversity. SIGNIFICANCE AND IMPACT OF THE STUDY: This vertical structure of microbial communities must be taken into consideration when dealing with the malfunctioning of bioreactors. These results are also useful information about changes in microbial communities following natural or anthropogenic alterations in different ecosystems (soils and sediments) where structuring of microbial communities according to depth has been observed.

Biofiltration of a mixture of volatile organic compounds on granular activated carbon.

The performance of a biofilter packed with Active Carbon (AC) was evaluated. The effluent (alcohol, ketones, esters, aromatic and chlorinated compounds) treated was a representative mixture of most common industrial emissions. To achieve a better knowledge of multicomponent adsorption mechanisms, and to underline the interest of inoculating AC, a control abiotic humidified filter had been operated in the same conditions as the biofilter. For a load of 110 g VOC m(-3) AC h(-1), after 55 days of operation, the removal efficiency was higher in the biotic than in the abiotic filter (85% vs 55%, respectively). Moreover, in the biofilter, at steady state, the elimination of all compounds was almost complete except for chlorinated compounds and p-xylene (removal efficiency of 25% and 64%, respectively). The microbial colonization of AC involved a decrease of the adsorption sites accessibility and enhanced the treatment of VOCs (volatile organic compounds) having a lower affinity for activated carbon. Moreover, while aromatic compounds and MIBK were eliminated along the overall height of the biofilter, pollutants with reduced affinity for AC, such as methanol, acetone, and halogenated compounds were only treated on the second half of the reactor. Thus, the affinity for activated carbon was an important parameter controlling the biodegradation process. Nevertheless, the use of AC as packing material in biofilters treating complex mixtures of VOCs is limited. Actually, similar removal efficiency could be reached, in the same conditions, for a biofilter packed with granular peat. Furthermore, for the biofilter packed with AC, the column height necessary to remove biodegradable compounds, with reduced affinity for the support, was important.

Biofiltration of a mixture of volatile organic emissions.

Air biofiltration is now under active consideration for the removal of the volatile organic compounds (VOCs) from polluted airstreams. To optimize this emerging environmental technology and to understand compound removal mechanisms, a biofilter packed with peat was developed to treat a complex mixture of VOCs: oxygenated, aromatic, and chlorinated compounds. The removal efficiency of this process was high. The maximum elimination capacity (ECmax) obtained was approximately 120 g VOCs/m3 peat/hr. Referring to each of the mixture's components, the ECmax showed the limits in terms of biodegradability of VOCs, especially for the halogenated compounds and xylene. A stratification of biodegradation was observed in the reactor. The oxygenated compounds were metabolized before the aromatic and halogenated ones. Two assumptions are suggested. There was a competition between bacterial communities. Different communities colonized the peat-based biofilter, one specialized for the elimination of oxygenated compounds, the others more specialized for elimination of aromatic and halogenated compounds. There was also substrate competition. Bacterial communities were the same over the height of the column, but the more easily biodegradable compounds were used first for the microorganism metabolism when they were present in the gaseous effluent.

Potential of solid-phase microextraction fibers for the analysis of volatile organic compounds in air.

This work presents the usefulness of five different solid-phase microextraction fibers in the screening of volatile organic compound (VOC) traces in air samples. The performances of these fibers are compared by studying the sorption kinetics in an equimolar gaseous mixture of eleven VOCs. For each fiber, static and dynamic sampling are compared. It is shown that repeatability is better for the dynamic mode (less than 6% for dynamic sampling and 10% for static sampling). The equilibrium time and the sensitivity vary considerably from one fiber type to another. As an example, the classical polydimethylsiloxane (PDMS) coating presented the shortest equilibration time (5 min) but also the poorest sensitivity, whereas the PDMS-Carboxen showed the longest extraction time but the greatest sensitivity. The estimation of the quantity of VOCs fixed on the target fiber allows for the determination of the different affinities of the compounds with the involved sorbent and relates them with physicochemical properties of the molecules. Competitive sorption is observed for the fibers involved with the adsorption process (i.e., PDMS-divinylbenzene and PDMS-Carboxen fibers). These competitions can lead to SPME calibration problems and thus bad quantitative analysis.

Formation of artefacts during air analysis of volatile amines by solid-phase micro extraction.

Solid-phase micro extraction (SPME) is a promising technique for fast and low cost trace analysis. However, some limitations of the technique were encountered when using a PDMS (polydimethylsiloxane)/Carboxen fibre for sampling a mixture of volatile aliphatic amines in air. On the GC chromatogram, two supplementary peaks were noticed in addition to the analyte peaks, thus limiting qualitative and quantitative analysis in this particular case. This paper presents the investigations to identify the artefacts and determine the origin of their formation. First, GC-MS identification, by both electron impact and chemical ionisation modes, demonstrated that the two artefacts were unsaturated amines assumed to be formed by a dehydrogenation reaction of the target amines. This reaction was found to occur during thermal desorption of analytes in the GC injection port and to be catalysed by temperature and by metals consisting of the inox (stainless-steel) needle of the SPME device. It was also demonstrated that artefact formation was not significant when using PDMS or PDMS/divinylbenzene fibres. This difference with PDMS/Carboxen fibre can be explained by the high desorption temperature required for this fibre. Moreover, the microporosity of Carboxen induces a longer desorption time which increases the contact between analytes and inox and thereby enhances artefact formation.