Performance and microbial analysis of defined and non-defined inocula for the removal of dimethyl sulfide in a biotrickling filter.

The performance and microbial communities of three differently inoculated biotrickling filters removing dimethyl sulfide (DMS) were compared. The biotrickling filters were inoculated with Thiobacillus thioparus TK-m (THIO), sludge (HANDS) and sludge + T. thioparus TK-m + Hyphomicrobium VS (HANDS++), respectively. The criteria investigated were length of the start-up period, the maximum elimination capacity, and the effects of intermittent loading rates, low pH, peak loading and very low loading rate on the DMS removal efficiency. The HANDS++ reactor exhibited the best performance considering all treatments. HANDS performed almost equally well as HANDS++, except during the determination of the EC(max), while THIO was generally the least efficient. During stable DMS loading at concentrations of 20 ppmv or lower, all reactors exhibited similar and high removal efficiencies (>99%). Denaturing gradient gel electrophoresis (DGGE) analysis showed the establishment of T. thioparus in the biofilm of all reactors, but not of Hyphomicrobium VS. Quantitative monitoring of the introduced bacterial strains was performed with a newly developed real-time PCR protocol. Initially, the inoculated strains were exclusively found in the reactors in which they were added. Afterwards, however, both strains developed in the biofilm of all three reactors, although T. thioparus attained higher cell densities than Hyphomicrobium. The presence of T. thioparus in THIO was related with the DMS loading rates that were applied, in the sense that intermittent DMS loading and very low DMS loading rates (0.5 ppmv) induced a decrease in gene copy numbers. Real-time PCR and DGGE both gave consistent results regarding the presence of Hyphomicrobium VS and Thiobacillus thioparus TK-m in the reactors. Only real-time PCR could be used to detect bacteria comprising of less than 1.4% of the total bacterial community ( approximately 10(5) copies ring(-1)).

Operational and microbiological aspects of a bioaugmented two-stage biotrickling filter removing hydrogen sulfide and dimethyl sulfide.

A two-stage biotrickling filter was developed for removing dimethyl sulfide (DMS) and hydrogen sulfide (H2S). The first biotrickling filter (ABF) was inoculated with Acidithiobacillus thiooxidans and operated without pH control, while the second biotrickling filter (HBF) was inoculated with Hyphomicrobium VS and operated at neutral pH. High DMS elimination capacities were observed in the HBF (8.2 g DMS m(-3) h(-1) at 90% removal efficiency) after 2 days. Maximal observed elimination capacities were 83 g H2S m(-3) h(-1) (100% removal efficiency) and 58 g DMS m(-3) h(-1) (88% removal efficiency) for the ABF and the HBF, respectively. The influence of a decreasing empty bed residence time (120 down to 30 sec) and the robustness of the HBF towards changing operational parameters (low pH, starvation, and DMS and H2S peak loadings) were investigated. Suboptimal operational conditions rapidly resulted in lower DMS removal efficiencies, but recovery of the HBF was mostly obtained within a few days. The H2S removal efficiency in the ABF, however, was not influenced by varying operational conditions. In both reactors, microbial community dynamics of the biofilm and the suspended bacteria were investigated, using denaturing gradient gel electrophoresis (DGGE). After a period of gradual change, a stable microbial community was observed in the HBF after 60 days, although Hyphomicrobium VS was not the dominant microorganism. In contrast, the ABF biofilm community was stable from the first day and only a limited bacterial diversity was observed. The planktonic microbial community in the HBF was very different from that in the biofilm.

Bioaugmentation of the phyllosphere for the removal of toluene from indoor air.

The removal of airborne toluene by means of the phyllosphere of Azalea indica augmented with a toluene-degrading enrichment culture of Pseudomonas putida TVA8 was studied. The 95% disappearance time [DT95%; the time in which an initial toluene concentration of 90 ppmv (339 mg.m(3)) was removed in a batch experiment] was 75 h for Azalea plants. Under the same experimental conditions, DT95% of inoculated Azalea plants decreased remarkably to about 27 h. Subsequent additions of toluene further increased the removal efficiency of the bioaugmented system (DT95% decreased by a factor of four). A decrease in DT95% was also recorded after repeated incubations of non-inoculated plants, but the toluene-removal rate was remarkably low, compared with the inoculated plants. Hence, inoculation of the leaf surface appeared essential for obtaining rapid removal rates. It was not possible to obtain comparable and sustained removal of airborne toluene by inoculating artificial plant surfaces. This is, to our knowledge, the first report on bioaugmentation of the leaf surface of plants to remove gaseous pollutants from air. The results presented are promising and could be of great practical importance in the field of indoor air pollution control.

Degradation of isobutyraldehyde and its intermediates in a compost biofilter.

This study demonstrates that at low to medium isobutyraldehyde loading rates (191 gm(-3) d(-1)-933 gm(-3) d(-1)), 100% removal efficiencies can be obtained in a compost biofilter. However, increasing the loading rate to 1500-1900 gm(-3) d(-1) caused a drop in degradation efficiency, a pH decrease and production of isobutyl alcohol and isobutyric acid. Additional batch and continuous experiments were performed to study the effect of pH and compost moisture content on the biofiltration of isobutyraldehyde, isobutyl alcohol and isobutyric acid. It was shown that the degradation rate of the three compounds decreased in the order isobutyraldehyde > isobutyl alcohol >> isobutyric acid, with no significant degradation for isobutyric acid. The isobutyl alcohol degradation rate was negatively influenced by the presence of isobutyraldehyde, while isobutyraldehyde degradation was not affected by the presence of either of the two compounds. A pH of 5.2 apparently inhibited the isobutyl alcohol degradation and lowered the isobutyraldehyde degradation rate, although adaptation of the microorganisms to low pH seemed to occur in the biofilters. Moisture content had a smaller effect on the degradation rates, although continuous experiments showed that a very high water content (55% compared to 40%) negatively affected isobutyraldehyde elimination increasingly during the course of the experiment. As a conclusion, it appears that at high loads of isobutyraldehyde, isobutyric acid is accumulated in the biofilter, resulting in a drop of pH. Consequently, isobutyraldehyde removal efficiency decreases and both isobutyl alcohol and isobutyric acid are measured in the effluent. It is suggested that next to moisture control, a pH buffer is necessary to remove high loads of isobutyraldehyde and to avoid persistence of intermediates in the effluent.