No 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-trimethylbenzene, 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 Ͼ xylene Ͼ trimethylbenzene, with 95, 80, and 70% maximum conversions, respectively. In addition, and despite the different removal levels achieved in the three bioreactors, 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 Nexcess regime, favorable to the colonization of the filter beds by nitrifying species, which particularly affected the xylene and trimethylbenzene biodegradation.

The microbial communities established in three laboratory-scale compost matrix biofilters fed with toluene were characterized. The biofilters were operated for 7 weeks at inlet concentrations of toluene ranging over 250-500 ppm with daily irrigation, using a nutrient solution containing variable concentrations of nitrogen, supplied as urea, and other inorganic salts. The indigenous microflora of the compost included toluene-degrading species, making inoculation unnecessary. The numerically predominant toluene-degrading strains were isolated from the most diluted positive wells of most-probable-number counts on mineral medium with toluene as sole carbon source and identified by rRNA 16S gene sequencing. On the basis of sequence similarity, all the isolated strains were assigned to the species Pseudomonas putida, although some variations were observed in their respective sequences. It is concluded that the mode of biofilter operation including a daily supply of non-carbon nutrients created an environment favoring the constant numerical predominance of this fast-growing toluene-degrading species.

The study presented in this paper dealt with the operation of a laboratory-scale upflow biofilter, packed with compost-based filter material. The airborne contaminant studied was toluene, maintained at a constant inlet concentration of 1.7 g‚m -3 . The input air was conveyed upward through the filter column at a flow rate of 1 m 3 ‚h -1 . The objective of this work was the study of the impact of increasing concentrations of nitrogen contained in the nutrients solution and, hence, the establishment of a new correlation between this parameter and the overall degradation performance. Depending on the nitrogen concentration employed, two biodegradation regimes have been identified. Over the optimal range of nitrogen concentrations [2.0-8.0 g of N‚L -1 ], the maximum level of elimination capacity achieved was =100 g‚m -3 ‚h -1 . This value is in line with theoretical considerations that suggest that an optimal nitrogen concentration of =2.6 g of N‚L -1 is required to achieve the same performance (100 g‚m -3 ‚h -1 ).