Waste gas biofiltration: advances and limitations of current approaches in microbiology.

As confidence in gas biofiltration efficacy grows, ever more complex malodorant and toxic molecules are ameliorated. In parallel, for many countries, emission control legislation becomes increasingly stringent to accommodate both public health and climate change imperatives. Effective gas biofiltration in biofilters and biotrickling filters depends on three key bioreactor variables: the support medium; gas molecule solubilization; and the catabolic population. Organic and inorganic support media, singly or in combination, have been employed and their key criteria are considered by critical appraisal of one, char. Catabolic species have included fungal and bacterial monocultures and, to a lesser extent, microbial communities. In the absence of organic support medium (soil, compost, sewage sludge, etc.) inoculum provision, a targeted enrichment and isolation program must be undertaken followed, possibly, by culture efficacy improvement. Microbial community process enhancement can then be gained by comprehensive characterization of the culturable and total populations. For all species, support medium attachment is critical and this is considered prior to filtration optimization by water content, pH, temperature, loadings, and nutrients manipulation. Finally, to negate discharge of fungal spores, and/or archaeal and/or bacterial cells, capture/destruction technologies are required to enable exploitation of the mineralization product CO(2).

Macrokinetic and quantitative microbial investigation on a bench-scale biofilter treating styrene-polluted gaseous streams.

We performed a macrokinetic and quantitative microbial investigation of a continuously operating bench-scale biofilter treating styrene-polluted gases. The device was filled with a mixture of peat and glass beads as packing medium and inoculated with the styrene-oxidizing strain, Rhodococcus rhodochrous AL NCIMB 13259. The experimental data of styrene and microbial concentrations, obtained at different biofilter heights, were used to evaluate the pollutant concentration profiles as well as the influence of styrene loading on biomass distribution along the packing medium. Styrene and biomass concentration profiles permitted detection of a linear relationship between the amount of biomass grown in a given section of the biofilter and that of pollutant removed, regardless of the operating conditions tested. Biomass development in the bed appeared to: depend linearly on pollutant concentration at an inlet styrene concentration of <0.10 g m(-3) in the gaseous stream; achieve a maximum value (7. 10(7) colony forming units per gram of packing material) within a wide styrene concentration range (0.10 to 1.0 g m(-3)); and fall sharply beyond this inhibition threshold. The process followed zeroth-order macrokinetics with respect to styrene concentration, which is consistent with zeroth-order microkinetics with either fully active or not fully active biofilm. The maximal volumetric styrene removal rate was found to be 63 g m(packing material) (-3) h(-1) for an influent pollutant concentration of 0.80 g m(-3) and a superficial gas velocity of 245 m h(-1).

Treatment of benzene-contaminated airstreams in laboratory-scale biofilters packed with raw and sieved sugarcane bagasse and with peat.

Three identical upflow laboratory-scale biofilters, inoculated with the benzene-degrading strain Pseudomonas sp. NCIMB 9688 but filled up with different packing media (PM), specifically raw sugarcane bagasse, sieved sugarcane bagasse and peat, were employed to eliminate benzene from waste air. Biofilters performances were evaluated by continuous runs in parallel at different influent benzene concentrations, sequentially stepped up through three different superficial gas velocities (31, 61, and 122 m h(-1)). The peat-packed biofilter exhibited the best performances over the whole experimentation, ensuring removal efficiency of 100% for influent benzene concentrations < or = 0.05 g m(-3), regardless of the superficial gas velocity, and up to 0.4 g m(-3) at 31 m h(-1). Maximum elimination capacities of biofilters packed with raw and sieved sugarcane bagasse and with peat were 3.2, 6.4 and 26 g mPM(-3) h(-1) at 6.1, 12 and 31 g mPM(-3) h(-1) loading rates, resulting in 52, 53 and 84% removals, respectively. The bacterial concentration distribution along the medium was shown to depend on the benzene loading rate and a correlation between specific benzene elimination rate and biomass concentration was established for biofilters packed with sieved sugarcane bagasse and peat. The macrokinetics of the process were also studied using the profiles of benzene and biomass concentrations, collected under different conditions over the height of both biofilters, and a zeroth-order kinetic model was shown to describe successfully the degradation process.