Mitsuyo Hirai

Removal Kinetics of Hydrogen Sulfide, Methanethiol and Dimethyl Sulfide by Peat Biofilters

The biological degradation rates of odorous sulfur compounds, such as hydrogen sulfide (H2S), methanethiol (MT) and dimethyl sulfide (DMS) on peat biofilters were measured. First, peat was acclimated with each gas alone, then the removal rate was measured 2 h after the sulfur load was changed by altering the inlet concentration and space velocity (SV = aerated volume at standard state/packed volume of peat). A Michaelis-Menten type equation was applied and the maximum removal rate (Vm) and saturation constant (Ks) were calculated. For single gases, these constants were as follows: Vm(H2S) = 5.0 g-S/d kg-dry peat, Ks(H2S) = 55 ppm, Vm(MT) = 0.9 g-S/d kg-dry peat, Ks(MT) = 10 ppm, Vm(DMS) = 0.38 g-S/d kg-dry peat, Ks(DMS) = 10 ppm. Second, after acclimation by each gas alone, different gases were supplied and the removal rate was measured using the same method described above. Third, mixed gases were passed through the peat acclimated by a single gas, and kinetic analysis was carried out. H2S and MT were degraded on peat irrespective of the acclimating gas, and their maximum removal rates were unaffected by the presence of DMS. DMS was degraded only in DMS acclimated peat. The removal rate of DMS in mixed gas experiments on DMS acclimated peat decreased significantly 2 h after changing the inlet conditions of the peat, followed by a low constant removal rate after 7–8 h. The same phenomenon was observed in MT when MT and H2S mixed gases were supplied to MT acclimated peat.

Degradation characteristics of hydrogen sulfide, methanethiol, dimethyl sulfide and dimethyl disulfide by Thiobacillus thioparus DW44 isolated from peat biofilter

A bacterium, capable of the degradation of hydrogen sulfide (H2S), methanethiol (MT), and dimethyl sulfide (DMS), as well as dimethyl disulfide (DMDS), was isolated on a thiosulfate plate from a suspension of DMDS-acclimated peat. The isolate was identified as Thiobacillus thioparus on the basis of its morphological, physiological and chemotaxonomical characteristics. The specific uptake rates (g-S · cell−1 · h−1) of these sulfur compounds in the basal medium were determined as 7.49 × 10−14 for H2S, 3.45 × 10−14 for MT, 4.14 × 10−15 for DMS and 1.23 × 10−14 for DMDS. When this strain was inoculated in sterilized fibrous peat, the maximum removal rates (Vm; g-S · kg-dry peat−1 · d−1) of each gas singly by the peat biofilter were obtained by the application of the Michaelis-Menten equation; Vm (H2S) = 5.52, Vm (MT) = 1.16, Vm (DMS) = 0.50 and Vm (DMDS) = 1.02. The specific uptake rates estimated for these compounds by this strain on the fibrous peat were similar to those in the basal medium. This strain also simultaneously degraded H2S, MT and DMS in a mixture of the three gases, although the removal ratio of DMS in the mixed gases decreased compared with that in the case of the single gas. The removability of DMS was inhibited by the presence of MT, but accelerated by the presence of H2S.

Characteristics of a newly isolated fungus, Geotrichum candidum Dec 1, which decolorizes various dyes

A fungus, Geotrichum candidum Dec 1, newly isolated from soil as a dye-decolorizing microorganism, decolorized 18 kinds of reactive, acidic and dispersive dyes and 3 model compounds on a solid medium, showing a broad spectrum of decolorization. Except for dispersive dyes, all the dyes used on the solid medium were also decolorized even in a liquid medium, although the decolorizing rates varied depending on the dye structure. By repeated addition of one dye, Reactive blue 5, about 12 g/l of the dye was degraded without significant decline of activity, showing the resistant property of Dec 1 to a high concentration of the dye. An energy source and oxygen were essential for the expression of decolorizing activity; the optimal temperature was 30°C. A crude extracellular enzyme solution, in which the decolorizing activity was more than 100 times that of the Dec 1 culture broth, showed peroxidase activity, indicating that some peroxidases are responsible for dye-decolorization.

Enhanced removal efficiency of malodorous gases in a pilot-scale peat biofilter inoculated with Thiobacillus thioparus DW44

A newly isolated autotrophic bacterium, Thiobacillus thioparus DW44, which is capable of degrading sulfur-containing gases, was inoculated into a pilot-scale peat biofilter to treat the exhaust gas from a night soil treatment plant. Hydrogen sulfide (H2S), methanethiol (MT), dimethyl sulfide (DMS) and dimethyl disulfide (DMDS) in the exhaust gas were efficiently removed for six months. Average removal ratios were 99.8% for H2S, 99.0% for MT, 89.5% for DMS and 98.1% for DMDS at a space velocity of 46 h−1 during the period of operation. No acclimation period was needed to reach such a high efficiency in the removal of the gases, indicating that the ability of this bacterium to remove these gases was occurred immediately after its inoculation to the peat. Ammonia (NH3) in the exhaust gas was neutralized with SO42−, which is the final product of the oxidation of H2S, MT, DMS and DMDS by the bacterium. No remarkable decline of pH, which often causes a deterioration in bacterial activity, was observed, mainly because of the reaction of SO42− with NH3. This study is the first report on the application of an isolated microorganism to a practical deodorizing system. The inoculation of T. thioparus DW44 into the pilot-scale peat biofilter could overcome such disadvantages of the conventional peat biofilter as a long acclimation period to reach a constant gas removability and the low removability of DMS, and resulted in enhanced removal efficiency of malodorous gases.

Removal characteristics of dimethyl sulfide, methanethiol and hydrogen sulfide by Hyphomicrobium sp. 155 isolated from Peat Biofilter

Abstract Methylotrophic strain I55, capable of removing dimethyl sulfide (DMS), methanethiol (MT), dimethyl-disulfide (DMDS), hydrogen sulfide (H 2 S) and dimethyl sulfoxide (DMSO) was isolated from DMSO enrichment culture by inoculating DMS-acclimated peat. This bacterium was identified as Hyphomicrobium sp. by an electron microscope and substrate requirement study. Optimal removal of DMS was observed at pH 6.8, and the maximum removal rate was 1.2 × 10 −14 (g-S·h −1 ·cell −1 ). When strain I55 was inoculated to peat, the specific DMS removal rate estimated was almost equal to that measured in a liquid test of pure I55. The overall maximum removal rate of DMS in a peat biofilter seeded with strain I55 was 0.59 (g-S·kg-dry peat −1 ·d −1 ), which was 1.5 times larger than that of the peat biofilter seeded with digested sludge of night soil in a previous experiment. In a mixed gas supply of DMS, MT and H 2 S, the removal rate of H 2 S and MT were not affected by the co-existence of the other gases, but DMS removal was inhibited by the presence of H 2 S and MT.

Comparison of organic and inorganic packing materials in the removal of ammonia gas in biofilters

Two organic and two inorganic packing materials were compared with regard to the removal of ammonia gas in a biofilter inoculated with night-soil sludge. By gradually increasing the inlet load of ammonia, the complete removal capacity, which was defined as the inlet load of ammonia that was completely removed, and the maximum removal capacity of ammonia, which was the value when the removal capacity leveled off for each packing material, were estimated. Both values which were based on a unit volume of packing material, were higher for organic packing materials than inorganic ones. By using kinetic analysis, the maximum removal rate of ammonia, V(m), and the saturation constant, K(s), were determined for all packing materials and the values of V(m) for organic packing materials were found to be larger. By using the kinetic parameters, the removal rates for ammonia were compared among the four packing materials, and the organic packing materials showed superior performance for the removal of ammonia in the concentration range of 0-300 ppm as compared to inorganic packing materials.

REMOVAL CHARACTERISTICS OF HYDROGEN SULPHIDE AND METHANETHIOL BY THIOBACILLUS SP. ISOLATED FROM PEAT IN BIOLOGICAL DEODORIZATION

Thiobacillus sp. HA43 as a dominant strain was isolated from a H2S-acclimated peat biofilter seeded with aerobically-digested sludge of night soil. Strain IIA43 degraded both H2S and methanethiol (MT) without lag-time, but degraded neither dimethy sulphide (DMS) nor dimethyl disulphide (DMDS). The removal characteristics for sulphur compounds (H2S, MT, DMS and DMDS) by strain HA43 well reflected the removal behaviour of the H2S-acclimated peat biofilter where this strain was isolated. The specific H2S and MT uptake rates of strain HA43 in batch culture were determined as 1.22 × 10−12 and 8.53 × 10−14 g-S·cell−1·h−1, respectively. The maximum removal rates (Vm = g-S·kg-dry peat−1·d−1) for H2S and MT by peat biofilter inoculated by strain HA43 were obtained as follows: Vm(H2S)− 11.3, Vm(MT) = 0.21 in sterilized peat; Vm(H2S) = 12.4, Vm(MT)− 0.27 in non-sterilized peat; Vm(H2S) = 33.0, Vm(MT) = 0.27 in peat with aerobically-digested sludge of night soil. The peat biofilter inoculated with strain HA43 enhanced the maximum removal rate for H2S 6-fold compared with the biofilter without strain HA43.

Comparison of the biological H2S removal characteristics among four inorganic packing materials

Four inorganic packing materials were evaluated in terms of their availability as packing materials of a packed tower deodorization apparatus (biofilter) from the viewpoints of biological H2S removal characteristics and some physical properties. Among porous ceramics (A), calcinated cristobalite (B), calcinated and formed obsidian (C), granulated and calcinated soil (D), the superiority of these packing materials determined based on the values of non-biological removal per unit weight or unit volume of packing material, complete removal capacity of H2S per unit weight of packing material per day or unit volume of packing material per day and pressure drop of the packed bed was in the order of A approximately equal to C > D approximately equal to B, which is correlated with the maximum water content, porosity, and mean pore diameter.

Oxidation of dimethyl sulfide byPseudomonas acidovorans DMR-11 isolated from peat biofilter

SummaryPseudomonas acidovorans DMR-11, capable of oxidizing dimethyl sulfide (DMS), was isolated from peat biofilter. DMS as a sole carbon or energy source was not degraded, but it was co-degraded in the medium containing organic carbon sources. The removal rate of DMS in heat-treated glucose medium was 1.12×10−17 mole/h cell at 30 °C. Dimethyl sulfoxide (DMSO) was the only product of DMS oxidation and was formed stoichiometrically. DMS was reversibly evolved in excess of DMSO. The cell free extract of strain DMR-11 oxidized DMS in presence of NADPH.

Studies of the oxidation mechanism of sulphur-containing gases on wet activated carbon fibre

Abstract The oxidation mechanism of hydrogen sulphide (H2S), methanethiol (MT), and dimethyl sulfide (DMS) on wet activated carbon fibre (ACF) at room temperature was elucidated from the results of flow system experiments using a packed column with single and mixed gas supplies. Oxidation of MT and DMS in mixed gases with H2S was explained by the occurrence of a hydroxyl radical (·OH) generated from the ferrous cation and hydrogen peroxide (H2O2) through oxidation of H2S on the wet ACF.