Hee Wook Ryu

Biological Deodorization of Hydrogen Sulfide Using Porous Lava as a Carrier of Thiobacillus thiooxidans

Biological deodorization of hydrogen sulfide (H2S) was studied using porous lava as a carrier of Thiobacillus thiooxidans in a laboratory-scale biofilter. Three different samples of porous lava, A, B, and C, which were obtained from Cheju Island in Korea, were used. The water-holding capacities of samples A, B and C were 0.38, 0.25, and 0.47 g-H2O/g-lava, respectively. The pHs and densities of the lava samples ranged from 8.25-9.24 and 920-1190 kg/m3, respectively. The buffering capacities, expressed as the amount of sulfate added to lower the pH to 4, were 60 g-SO4(2-)/kg-lava for sample A, 50 g-SO4(2-)/kg-lava for B, and 90 g-SO4(2-)/kg-lava for C. To investigate the removal characteristics of H2S by the lava biofilters, T. thiooxidans was immobilized on the lava samples. Biofilters A and C showed a removal capacity of 428 g-S.m(-3).h(-1) when H2S was supplied with 428 g-S.m(-3).h(-1) of inlet load at a space velocity (SV) of 300 h(-1). At the same inlet load and SV, the removal capacity of biofilter B was 396 g-S.m(-3).h(-1). The H2S critical loads of biofilters A, B and C at a SV of 400 h(-1) were 396, 157 and 342 g-S.m(-3).h(-1), respectively. It is suggested that natural, porous lava is a promising candidate as a carrier of microorganisms in biofiltration.

Degradation characteristics of toluene, benzene, ethylbenzene, and xylene by Stenotrophomonas maltophilia T3-c.

Abstract Stenotrophomonas maltophilia T3-c, isolated from a biofilter for the removal of benzene, toluene, ethylbenzene, and xylene (BTEX), could grow in a mineral salt medium containing toluene, benzene, or ethylbenzene as the sole source of carbon. The effect of environmental factors such as initial toluene mass, medium pH, and temperature on the degradation rate of toluene was investigated. The cosubstrate interactions in the BTEX mixture by the isolate were also studied. Within the range of initial toluene mass (from 23 to 70 μmol), an increased substrate concentration increased the specific degradation of toluene by S. maltophilia T3-c. The toluene degradation activity of S. maltophilia T3-c could be maintained at a broad pH range from 5 to 8. The rates at 20 and 40°C were 43 and 83%, respectively, of the rate at 30°C. The specific degradation rates of toluene, benzene, and ethylbenzene by strain T3-c were 2.38, 4.25, and 2.06 μmol/g-DCW/hr. While xylene could not be utilized as a growth substrate by S. maltophilia T3-c, the presence of toluene resulted in the cometabolic degradation of xylene. The specific degradation rate of toluene was increased by the presence of benzene, ethylbenzene, or xylene in binary mixtures. The presence of toluene or xylene in binary mixtures with benzene increased the specific degradation rate of benzene. The presence of ethylbenzene in binary mixtures with benzene inhibited benzene degradation. The presence of more than three kinds of substrates inhibited the specific degradation rate of benzene. All BTEX mixtures, except tri-mixtures of benzene, ethylbenzene, and xylene or mixtures of all four substrates, had little effect on the degradation of ethylbenzene by S. maltophilia T3-c. The utilization preference of the substrates by S. maltophilia T3-c was as follows: ethylbenzene was degraded fastest, followed by toluene and benzene. However, the specific degradation rates of substrates, in order, were benzene, toluene, and ethylbenzene.

Microbial refinement of kaolin by iron-reducing bacteria

Abstract Low-grade kaolin contains Fe(III) impurities, which cause the detraction of refractoriness and whiteness of porcelain and pottery. Microbial refinement of low-grade kaolin to remove Fe(III) by iron-reducing bacteria was investigated. The removal of Fe(III) impurities could be performed by the indigenous microorganisms in kaolin, but could be enhanced by the inoculation of iron-reducing bacteria. Maltose, sucrose, and glucose could be used as substrates. The removal efficiency of Fe(III) increased with increasing sugar concentrations in the range of 1–5% (w/w, sugar/clay). After the microbial refinement, the whiteness of the kaolin increased from 64.49 to 71.50, and the redness decreased remarkably from 7.41 to 2.55. Fe(III) impurities were selectively removed from the kaolin without changing or losing the mineralogical composition of the kaolin by the microbial refinement.

Relationships between biomass, pressure drop, and performance in a polyurethane biofilter.

In biofilters for controlling volatile organic compounds (VOCs), clogging in the filter bed due to overgrowth of biomass causes the deterioration of biofilter performance. In this study, the relationships between biofilter performance, biomass concentration (X), and pressure drop (DeltaP) was qualitatively and quantitatively evaluated in a polyurethane (PU) biofilter. Benzene was used as a model VOC. The relationship between DeltaP and X at a moisture content of 80-90% was expressed as log DeltaP (mm H(2)Om(-1))=0.315+3.87 log X (g-dry cell weight (DCW) g-PU(-1)), 0.8<X<2.5. Maximum removal rate (V(m)) for benzene declined with increasing biomass concentration at more than 0.8 g-DCW g-PU(-1), and the following equation was obtained: V(m) (gm(-3)h(-1))=811-261 X (g-DCW g-PU(-1)), 0.8<X<2.5. The quantitative relationships obtained in this study can be applied to assess and optimize PU biofilter performance for long-term operation.

Removal of benzene and toluene in polyurethane biofilter immobilized with Rhodococcus sp. EH831 under transient loading

The performance of a polyurethane (PU) biofilter inoculated with Rhodococcus sp. EH831 was evaluated under different transient loading conditions, such as shutdown, intermittent and fluctuating loading. A mixture of benzene and toluene vapors was employed as model pollutants. When the biofilter was restarted after a 2 week-shutdown, during which neither clean air nor water was supplied, the benzene and toluene removal capacities were rapidly restored after a re-adaptation period of only 1 day. A comparison of the removal capacity under continuous and intermittent loading revealed that constant and periodic loading (8 h on/16 h off per day) and a 2 day-shutdown did not significantly influence the biofilter performance, although the removals of benzene and toluene were relatively unstable and lower under intermittent loading during the initial week. The result of quantitative real-time PCR showed that Rhodococcus sp. EH831 could be maintained during transient loading periods (10(10)-10(11) CFU/g-dry PU) irrespective of the different operating conditions.

Production of a desulfurization biocatalyst by two-stage fermentation and its application for the treatment of model and diesel oils.

For the production of oil‐desulfurizing biocatalyst, a two‐stage fermentation strategy was adopted, in which the cell growth stage and desulfurization activity induction stage were separated. Sucrose was found to be the optimal carbon source for the growth of Gordonia nitidaCYKS1. Magnesium sulfate was selected to be the sulfur source in the cell growth stage. The optimal ranges of sucrose and magnesium sulfate were 10−50 and 1−2.5 g L−1, respectively. Such a broad optimal concentration of sucrose made the fed‐batch culture easy, while the sucrose concentration was maintained between 10−20 g L−1 in the actual operation. As a result, 92.6 g L−1 of cell mass was acquired by 120 h of fed‐batch culture. This cell mass was over three times higher than a previously reported result, though the strain used was different. The desulfurization activity of the harvested cells from the first stage culture was induced by batch cultivation with dibenzothiophene as the sole sulfur source. The optimal induction time was found to be about 4 h. The resting‐cell biocatalyst made from the induced cells was applied for the deep desulfurization of a diesel oil. It was observed that the sulfur content of the diesel oil decreased from 250 mg‐sulfur L‐oil−1 to as low as 61 mg‐sulfur L‐oil−1 in 20 h. It implied that the biocatalyst developed in this study had a good potential to be applied to a deep desulfurization process to produce ultra‐low‐sulfur fuel oils.

Earthworm cast as a promising filter bed material and its methanotrophic contribution to methane removal

The use of biocovers is a promising strategy toward mitigating CH(4) emission from smaller and/or older landfills. In this study, a filter bed material consisting of a mixture of earthworm cast and rice paddy soil in a biocover was evaluated. Although the CH(4) oxidation rate of the enriched paddy soil was 4.9 microg g-dry soil(-1) h(-1), it was enhanced to 25.1 microg g-dry soil(-1) h(-1) by adding an earthworm cast with a 3:7 ratio of earthworm cast:soil (wet weight). CO(2) was found as the final oxidation product of CH(4), and the mole ratio of CO(2) production to CH(4) consumption was 0.27. At a moisture content range of 15-40% and a temperature range of 20-40 degrees C, the CH(4) oxidation rates of the enriched mixture were more than 57% of the maximum rate obtained at 25% moisture content and 25 degrees C. By denaturing gradient gel electrophoresis analysis employing primers for the universal bacterial 16S rRNA gene, and terminal-restriction fragment length polymorphism analysis using primers for the pmoA gene, the bacterial and methanotrophic communities in the enriched mixture were mainly originate from paddy soil and earthworm cast, respectively. Both type I (mainly Methylocaldum) and type II methanotrophs (mainly Methylocystis) played important roles in CH(4) oxidation in the enriched mixture.

Microbial treatment of high-strength perchlorate wastewater

To treat wastewater containing high concentrations of perchlorate, a perchlorate reducing-bacterial consortium was obtained by enrichment culture grown on high-strength perchlorate (1200 mg L(-1)) feed medium, and was characterized in a sequence batch reactor (SBR) over a long-time operation. The consortium removed perchlorate in the SBR with high reduction rates (35-90 mg L(-1)h(-1)) and stable removal efficiency over 200-day operations. The maximum specific perchlorate reduction rate (qmax), half saturation constant (Ks), and optimal pH range were 0.67 mg-perchlorate mg-dry cell weight(-1) h(-1), 193.8 mg-perchlorate L(-1), and pH 7-9, respectively. The perchlorate reduction yield was 0.48 mol-perchloratemol-acetate(-1). A clone library prepared using the amplicons of cld gene encoding chlorate dismutase showed that the dominant (per)chlorate reducing bacteria in the consortium were Dechlorosoma sp. (53%), Ideonella sp. (28%), and Dechloromonas sp. (19%).

Leaching of Mn, Co, and Ni from manganese nodules using an anaerobic bioleaching method.

An anaerobic bioleaching of a manganese nodule by anaerobic Mn-reducing bacteria was evaluated for the leaching of metals, Mn, Co, and Ni. Insoluble Mn4+ in the nodule could be reduced to soluble Mn2+ by dissimilatory Mn-reducing bacteria that use a carbon source and Mn4+ as an electron donor and acceptor, respectively. As a result of the Mn reduction, Co and Ni could be leached from the loosed Mn matrix. Leaching experiments were carried out to optimize various process parameters, such as inoculation, pH, temperature, mineral salts, and particle size of the nodule used. The leaching efficiencies of Mn, Co, and Ni increased from 18, 7, and 10% to 77, 70, and 75%, respectively by the inoculation of the Mn-reducing enrichment culture broth. Metals could be efficiently recovered from the nodule in the ranges of pH from 5.0 to 6.5 and temperature from 30 to 45 degrees C by anaerobic bioleaching. External addition of mineral salts was not necessary for Mn, Co, and Ni leaching from the nodule. The optimum ratio of nodule to glucose was 0.1 (w/w). To obtain a leaching efficiency above 70%, the particle size of the nodules must be less than 0.6 mm.

Microbial characterization of toluene-degrading denitrifying consortia obtained from terrestrial and marine ecosystems

The degradation characteristics of toluene coupled to nitrate reduction were investigated in enrichment culture and the microbial communities of toluene-degrading denitrifying consortia were characterized by denaturing gradient gel electrophoresis (DGGE) technique. Anaerobic nitrate-reducing bacteria were enriched from oil-contaminated soil samples collected from terrestrial (rice field) and marine (tidal flat) ecosystems. Enriched consortia degraded toluene in the presence of nitrate as a terminal electron acceptor. The degradation rate of toluene was affected by the initial substrate concentration and co-existence of other hydrocarbons. The types of toluene-degrading denitrifying consortia depended on the type of ecosystem. The clone RS-7 obtained from the enriched consortium of the rice field was most closely related to a toluene-degrading and denitrifying bacterium, Azoarcus denitrificians (A. tolulyticus sp. nov.). The clone TS-11 detected in the tidal flat enriched consortium was affiliated to Thauera sp. strain S2 (T. aminoaromatica sp. nov.) that was able to degrade toluene under denitrifying conditions. This indicates that environmental factors greatly influence microbial communities obtained from terrestrial (rice field) and marine (tidal flat) ecosystems.