Abstract
About 60,000-70,000 tons of 2-chlorotoluene, which shows high toxicity in aquatic ecosystems, are produced worldwide and used in a tremendous field of applications. However, clear proofs of biodegradation were only presented for Comamonas testosteroni KT5 and Rhodococcus sp. OCT10. Hence, this study aims on the isolation of additional strains and their characterization in pilot-scale biotrickling filters. Three strains named OCT2, OCT9, and OCT14 of the genus Rhodococcus were isolated, able to mineralize gaseous 2-chlorotoluene like the previously isolated strain Rhodococcus sp. OCT10. The performance levels of these strains were tested in four biotrickling filters each containing 18.8 L of polyurethane foam package, showing elimination capacities of carbon (C) of 30.9 (OCT2), 30.1 (OCT9), 32.2 (OCT10), and 3.9 g C·m-3·h-1 (OCT14) at an average crude gas level of 397.6 mg C·m-3 and an empty bed residence time (EBRT) of 22.6 s. Since OCT10 showed the highest performance levels, this strain was characterized in a second biotrickling filter configuration at long-term conditions of 985 days, varying crude gas levels, EBRT and nutrient supply. Chloride balancing showed a recovery of 94.4\% of 2-chlorotoluene eliminated out of the gas phase, pointing out mineralization of 2-chlorotoluene. German emission limit values were met at crude gas levels up to 750 mg C·m-3 at EBRTs of 120 s or higher. The maximum elimination capacity was 51.2 g C·m-3·h-1 at a specific freight of 51.9 g C·m-3·h-1 and an EBRT of 254 s. Performance levels were strongly boosted by addition of ammonia as nutrient and stabilized at efficiency levels higher than 90\% at a feed rate of 4 g ammonium sulfate per week and 100 L of package volume. Repetitive monitoring of the established 2-chlorotoluene degrading community by BOX-PCR fingerprinting revealed a high long-term stability of OCT10, underlining its suitability in this kind of application.
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