Biofiltration of n-butyl acetate with three packing material mixtures, with and without biochar

Two cost-effective packing materials were used for n-butyl acetate removal in lab-scale biofilters, namely waste spruce root wood chips and biochar obtained as a byproduct from a wood gasifier. Three biofilters packed with spruce root wood chips: without biochar (SRWC), a similar one with 10% of biochar (SRWC-B) and that with 10% of biochar impregnated with a nitrogen fertilizer (SRWC-IB) showed similar yet differing maximum elimination capacities of 206 ± 27, 275 ± 21 and 294 ± 20 g m-3 h-1, respectively, enabling high pollutant removal efficiency (>95% at moderate loads) and stable performance. The original biochar adsorption capacity was high (208 ± 6 mgtoluene g-1), but near 70% of it was lost after a 300-day biofilter operation. By contrast, the exposed impregnated biochar drastically increased its adsorption capacity in 300 days (149 ± 7 vs. 17 ± 5 mgtoluene g-1). Colony forming unit (CFU) and microscopic analyses revealed significant packing material colonization by microorganisms and grazing fauna in all three biofilters with an acceptable pressure drop, up to 1020 Pa m-1, at the end of biofilter operation. Despite a higher price (14 vs. 123 €m-3), the application of the best performing SRWC-IB packing can reduce the total investment costs by 9% due to biofilter volume reduction.

Removal of dimethyl sulphide via a bio-scrubber under anoxic conditions

The removal performance of dimethyl sulphide (DMS) by anoxic laboratory-scale bio-scrubber was studied under different operation conditions for 315 days. DMS removal in bio-scrubber system was performed by controlling and changing the operation parameters, including inlet concentration, empty bed residence time (EBRT) and spraying density (SD) of irrigation. Best conditions in the system were achieved for SD of 0.18 m³/m² h within EBRT of 40 s at an inlet gas concentration of 150 mg/m³ in which 93% of waste gas stream was removed in the bio-scrubber column and bio-degradation in the bio-reactor tank led to 89% of DMS removal from the transferred bio-reactor, while 91.5% of input chemical oxygen demand (COD) was successfully removed. The use of closer values of the average experimental yield to the theoretical value (Y_NO3/NO3 -) of 0.74 led to the production of elemental sulphur (S°) and other sulphur forms rather than sulphate (SO₄^2-) , which was also was recognized as a pale-yellow coloured substance of S° that appeared within the biomass.

Biodegradation of airborne acetone/styrene mixtures in a bubble column reactor

The ability of a bubble column reactor (BCR) to biodegrade a mixture of styrene and acetone vapors was evaluated to determine the factors limiting the process efficiency, with a particular emphasis on the presence of degradation intermediates and oxygen levels. The results obtained under varied loadings and ratios were matched with the dissolved oxygen levels and kinetics of oxygen mass transfer, which was assessed by determination of k_La coefficients. A 1.5-L laboratory-scale BCR was operated under a constant air flow of 1.0 L.min^-1, using a defined mixed microbial population as a biocatalyst. Maximum values of elimination capacities/maximum overall specific degradation rates of 75.5 gC.m^-3.h^-1/0.197 gC.gdw^-1.h^-1, 66.0 gC.m^-3.h^-1/0.059 gC.gdw^-1.h^-1, and 45.8 gC.m^-3.h^-1/0.027 gC.gdw^-1.h^-1 were observed for styrene/acetone 2:1, styrene-rich and acetone-rich mixtures, respectively, indicating significant substrate interactions and rate limitation by biological factors. The BCR removed both acetone and styrene near-quantitatively up to a relatively high organic load of 50 g.m^-3.h^-1. From this point, the removal efficiencies declined under increasing loading rates, accompanied by a significant drop in the dissolved oxygen concentration, showing a process transition to oxygen-limited conditions. However, the relatively efficient pollutant removal from air continued, due to significant oxygen mass transfer, up to a threshold loading rate when the accumulation of acetone and degradation intermediates in the aqueous medium became significant. These observations demonstrate that oxygen availability is the limiting factor for efficient pollutant degradation and that accumulation of intermediates may serve as an indicator of oxygen limitation. Microbial (activated sludge) analyses revealed the presence of amoebae and active nematodes that were not affected by variations in operational conditions.