Specific Degradation Rate Research Articles

Effect of operating parameters on molinate biodegradation

The effect of operating conditions during molinate degradation by the defined mixed bacterial culture DC, previously described as able to mineralize molinate, was evaluated in a batch reactor. Parameters such as the rate of molinate degradation, the dissolved organic carbon (DOC) consumption and the accumulation of molinate degradation products were monitored along the culture growth. The effect of conditions such as temperature, pH, aeration rate, salinity, and presence of additional carbon and/or nitrogen sources, was tested independently. Degradation of molinate in river water was also evaluated. Culture DC was able to grow and to mineralize molinate at all the conditions assayed. Temperature was the factor with the strongest influence on bacterial growth and molinate mineralization. The lowest and the highest rate values of growth (0.010 and 0.110 h −1) and of molinate degradation (0.027 and 0.180 g molinate g −1 cell dry wt h −1) were obtained at 15 and 35 °C, respectively. In cultures with approximately 187 mg l −1 of molinate, 2-oxo-molinate was the major molinate degradation product accumulated in the medium, in concentrations below 0.133 mg l −1. Degradation of molinate was also evaluated in a continuous stirred tank reactor (CSTR). Operating the CSTR at a hydraulic retention time (HRT) of 83 h, fed with medium containing molinate concentrations ranging from 1 to 3 mM, culture DC degraded the herbicide with specific degradation rates similar to those obtained in the batch systems.

Degradation of 4-aminobenzenesulfonate by alginate encapsulated cells of Agrobacterium sp. PNS-1

Studies were carried out on 4-aminobenzenesulfonate (4-ABS) degradation by free and alginate entrapped cells of Agrobacterium sp. PNS-1. Degradation rate in batch reactors with free cells was marginally higher than Ca-encapsulated cells. Comparison of Ca 2+ and Ba 2+ as gelling agents showed that 4-ABS removal rate was significantly less with Ba-alginate entrapped cells. Specific degradation rates, using linear regression analysis and based on the initial biomass in the beads, varied from 49.7 mg/mg biomass/h to 92.0 mg/mg biomass/h for Ca-alginate encapsulated cells for different initial 4-ABS concentrations ranging from 200 to 800 mg/L. UV spectra of the aliquots drawn at different time intervals from batch reactors did not show accumulation of any intermediate during degradation. Ca-alginate immobilized cells could be repeatedly reused upto five cycles without any loss of activity. Studies with packed bed reactors, operated in a semi-continuous mode, showed that this could be used for 4-ABS degradation.

Effect of medium composition on pentachlorophenol removal by Amylomyces rouxii in solid-state culture

Pentachlorophenol (PCP) degradation by fungi was studied in solid state cultures (SSC); these cultures can be used in different bioremediation strategies. We assessed the effect of medium composition and PCP initial concentration on growth of Amylomyces rouxii and PCP degradation. This fungus displayed a high degradation rate on PCP when tyrosine was added to the culture medium, 0.030 mg PCP mg −1 biomass h −1, as compared against a culture without tyrosine (0.017 mg PCP mg −1 biomass h −1). Besides, results showed that growth and specific degradation were higher at high initial PCP concentration; at 100 mg PCP l −1, 100% of initial PCP was degraded at 72 h, and 50% of PCP was degraded when initial PCP was 12.5 mg l −1. In these cultures, specific degradation rates were 0.081 and 0.026 mg PCP mg −1 biomass h −1, respectively.

Enhanced biodegradation of phenol by a microbial consortium in a solid?liquid two phase partitioning bioreactor

Two phase partitioning bioreactors (TPPBs) operate by partitioning toxic substrates to or from an aqueous, cell-containing phase by means of second immiscible phase. Uptake of toxic substrates by the second phase effectively reduces their concentration within the aqueous phase to sub-inhibitory levels, and transfer of molecules between the phases to maintain equilibrium results in the continual feeding of substrate based on the metabolic demand of the microorganisms. Conventionally, a single pure species of microorganism, and a pure organic solvent, have been used in TPPBs. The present work has demonstrated the benefits of using a mixed microbial population for the degradation of phenol in a TPPB that uses solid polymer beads (comprised of ethylene vinyl acetate, or EVA) as the second phase. Polymer modification via an increase in vinyl acetate concentration was also shown to increase phenol uptake. Microbial consortia were isolated from three biological sources and, based on an evaluation of their kinetic performance, a superior consortium was chosen that offered improved degradation when compared to a pure strain of Pseudomonas putida ATCC 11172. The new microbial consortium used within a TPPB was capable of degrading high concentrations of phenol (approximately 2000 mg l(-1)), with decreased lag time (10 h) and increased specific rate of phenol degradation (0.71 g phenol g(1) cell h). Investigation of the four-member consortium showed that it consisted of two Pseudomonas sp., and two Acinetobacter sp., and tests conducted upon the individual isolates, as well as paired organisms, confirmed the synergistic benefit of their existence within the consortium. The enhanced effects of the use of a microbial consortium now offer improved degradation of phenol, and open the possibility of the degradation of multiple toxic substrates via a polymer-mediated TPPB system.

Kinetics of BTEX biodegradation by a coculture of Pseudomonas putida and Pseudomonas fluorescens under hypoxic conditions

Pseudomonas putida and Pseudomonas fluorescens present as a coculture were studied for their abilities to degrade benzene, toluene, ethylbenzene, and xylenes (collectively known as BTEX) under various growth conditions. The coculture effectively degraded various concentrations of BTEX as sole carbon sources. However, all BTEX compounds showed substrate inhibition to the bacteria, in terms of specific growth, degradation rate, and cell net yield. Cell growth was completely inhibited at 500 mg l(-1) of benzene, 600 mg l(-1) of o-xylene, and 1000 mg l(-1) of toluene. Without aeration, aerobic biodegradation of BTEX required additional oxygen provided as hydrogen peroxide in the medium. Under hypoxic conditions, however, nitrate could be used as an alternative electron acceptor for BTEX biodegradation when oxygen was limited and denitrification took place in the culture. The carbon mass balance study confirmed that benzene and toluene were completely mineralized to CO2 and H2O without producing any identifiable intermediate metabolites.

Real-time quantification of microbial degradation of copepod fecal pellets monitored by isothermal microcalorimetry

This study introduces isothermal microcalorimetry as a method to describe microbial degradation of copepod fecal pellets through measurements of the metabolic heat-flow produced by the degrading microbial community. We monitored the heat-flow for 20 to 24 h from samples of 300 to 1500 fecal pellets from a laboratory-cultivated calanoid copepod, Acartia tonsa Dana, fed on the chryptophyte Rhodomonas salina in excess. The microbes grew at 0.095 to 0.24 h -1 . Specific degradation rates were calculated using 3 different literature values of the carbon:volume ratio of fecal pellets. The mean ± SD specific degradation rates, Rd, were estimated at 0.023 ± 0.015 h -1 (for carbon:volume ratio of 0.39 pg C μm -3 ) and at 0.047 ± 0.038 h -1 (for carbon:volume ratio of 0.25 pg C μm -3 ), defined as the proportion of fecal pellet carbon completely oxidised to CO2 h -1 . The lowest car- bon:volume ratio (0.085 pg C μm -3 ) resulted in >100% fecal pellet carbon degradation within 20 h. These degradation rates are very high, presumably reflecting a fully active bacterial population. The limiting factor for microbial growth was not inorganic nutrients (N and P), but labile dissolved organic carbon (DOC). We compared heat-flow in situations with and without oxygen, and found it to be 1 order of magnitude lower under anoxic conditions. This indicates the presence of anaerobic or facultative bacteria associated with the fecal pellets. Possible applications of the methodology are discussed.

Enhanced kinetics of genetically engineered Burkholderia cepacia: the role of vgb in the hypoxic metabolism of 2-CBA.

Application of Vitreoscilla hemoglobin (VHb) technology to 2-CBA degradation by Burkholderia cepacia strain DNT under hypoxic conditions was studied in continuous culture chemostats. Dechlorination abilities of both recombinant (VHb gene (vgb) containing) and untransformed cells were investigated at various dilution rates to ensure complete degradation of 2-CBA. As the dilution rate increased from 0.025 to 0.25 h(-1), the ratios of chloride release to degraded 2-CBA concentration decreased from 0.95 to 0.72 and from 0.89 to 0.39 for recombinant and untransformed cells, respectively. A nonstoichiometric relationship between chloride release and 2-CBA degradation was more pronounced for untransformed cells. Recombinant cell densities were 0.1-0.2. g L(-1) greater than untransformed cell densities for a range of dilution rates. As the dilution rate increased, the oxygen uptake rate (OUR) and the substrate utilization rate (SUR) decreased for both strains. The OUR/SUR ratio increased as the dilution rate increased for both strains but was much higher for the recombinant strain compared to untransformed cells. The specific 2-CBA degradation rate of recombinant cells was greater than that of untransformed cells (1.17 vs. 0.46 mg CBA (mg) day(-1), and half-saturation constants for recombinant cells were lower than those of untransformed cells (0.18 and 0.32 mg CBA L(-1), respectively). The pseudo-first-order degradation constants, k(1CBA) and k(1ACE), were higher for recombinant cells (6.5 L (mg cells)(-1) day(-1) and 95.6 L (mg cells)(-1) day(-1), respectively) than those of untransformed cells (1.44 L (mg cells)(-1) day(-1) and 73.7 L (mg cells)(-1) day(-1), respectively).

EDTA-dependent bacterial strain

A novel ethylenediaminetetraacetate (EDTA)-degrading bacterial strain (LPM-4) with a specific requirement for EDTA as the sole nitrogen source was isolated. According to 16S rDNA sequencing, this isolate belonged to the α-proteobacteria group and was closely related to uncultured bacteria available from the GenBank (NCBI) database. The cells consumed glucose added to EDTA-containing medium only after EDTA exhaustion. Mass cell yield ( Y x/s) from EDTA and glucose amounted to 22.4 and 25.5%, respectively; the energy cell yield ( η x/s) from both substrates was 32%. Suspensions of washed cells of this isolate degraded EDTA and complexes Ba−, Mg−, Ca−, and Mn−EDTA at constant rates ranging from 0.310 to 0.486 mmol EDTA/(g dry cells h). Specific degradation rate of the more stable complex Zn−EDTA was 0.137±0.016 mmol EDTA/(g dry cells h) within the first 10 h of incubation and then declined.

Simultaneous removal of atrazine and nitrate using a biological granulated activated carbon (BGAC) reactor

AbstractThe objective of this research was to characterize the performance of granulated activated carbon (GAC) as a carrier for Pseudomonas ADP in a non‐sterile continuous fluidized bed reactor for atrazine degradation under anoxic conditions. The GAC was compared with two non‐adsorbing carriers: non‐adsorbing carbon particles (‘Baker product’) having the same surface area available for biofilm growth as the GAC, and sintered glass beads. The initial atrazine degradation efficiency was higher than 90% in the reactors with the non‐adsorbing carriers, but deteriorated to 20% with time due to contamination by foreign denitrifying bacteria. In contrast, no deterioration was observed in the biological granulated activated carbon (BGAC) reactor. A maximal atrazine volumetric and specific degradation rate of 0.820 ± 0.052 g atrazine dm−3 day−1 and 1.7 ± 0.4 g atrazine g−1 protein day−1 respectively were observed in the BGAC reactor. Concurrent atrazine biodegradation and desorption from the carrier was shown and an effluent concentration of 0.002 mg dm−3 (below the EPA standard) was achieved in the BGAC reactor. The advantages of the BGAC reactor over the non‐adsorbing carrier reactors can probably be explained by the adsorption–desorption mechanism providing favorable microenvironmental conditions for atrazine–degrading bacteria. Copyright © 2004 Society of Chemical Industry

Kinetics of protein substrate degradation by HslUV

The HslUV protease–chaperone complex degrades specific protein substrates in an ATP-dependent reaction. Current models propose that the HslU chaperone, a AAA protein of the Clp/Hsp100 family, binds and unfolds substrates and translocates the polypeptide into the catalytic cavity of the HslV protease. These processes are being characterized using substrates that are targeted to HslUV with a carboxy-terminal fusion of the natural substrate SulA or the carboxy-terminal 11 amino acid residues thereof. In a tandem fusion of green fluorescent protein with SulA, HslUV degrades the SulA moiety but not green fluorescent protein. Wild type and mutant Arc repressor variants are degraded; over a range of substrate stabilities, the specific rate of degradation and its dependence on substrate stability is similar to that of ClpXP. For a hyperstable Arc variant having an intermolecular disulfide bond, the rate of degradation by HslUV is an order of magnitude slower than by ClpXP. Similarity in degradation rates for a subset of substrates by HslUV and ClpXP suggests a similarity in mechanism of the apparent rate-limiting steps of unfolding and translocation by the chaperone components HslU and ClpX. The fall-off in degradation by HslUV for the more stable substrates that are degraded by ClpXP is consistent with the two systems acting on different spectra of biological substrates.

Effect of Fe 0 quantity on the efficiency of integrated microbial-Fe 0 treatment processes

Batch experiments were conducted with different reaction systems to investigate how the treatment efficiency of integrated microbial-Fe 0 processes is affected by the amount of Fe 0 added. Abiotic experiments with hexavalent chromium and carbon tetrachloride mixtures corroborated that different pollutants could compete for reactive sites on the iron surface, which would hinder specific degradation rates when the available Fe 0 surface area is relatively small (e.g., 11 m 2 l −1). In such cases, reductive precipitation of chromium could occlude reactive sites and significantly inhibit removal efficiency. Microbial participation in the cleanup process was also influenced by the amount of Fe 0 added. Increasing the Fe 0 dose (and thus the available surface area) had a stimulatory effect possibly due to a higher production of cathodic H 2, which can be used as electron donor for reductive biotransformation of many pollutants. However, high Fe 0 doses had an inhibitory effect due to a corrosion-induced increase in pH beyond the optimum range of the bacteria. This suggest that there may be a system-specific, optimum quantity of Fe 0 that satisfies availability requirements to preclude contaminant competition for reactive sites and biological requirements for H 2 production while minimizing inhibitory increases in pH. Results also confirmed extensive RDX mineralization in bioaugmented (but not in abiotic) Fe 0 systems, and support the notion that permeable reactive iron barriers performance might be enhanced by the participation of some microorganisms.

In vitro degradation studies of calcium phosphate glass ceramics prepared by controlled crystallization

Calcium phosphate glass ceramics with incorporation of small additions of two nucleating agents, MgO and K 2O were prepared in the metaphosphate and pyrophosphate region, using an appropriate two-step heat treatment of controlled crystallization defined by differential thermal analysis results. Identification and quantification of crystalline phases precipitated from the calcium phosphate glass were performed using X-ray diffraction and Rietveld analysis. The β-Ca 2P 2O 7 (β-DCP), KCa(PO 3) 3, β-Ca(PO 3) 2 and Ca 4P 6O 19 phases were detected in the glass ceramics. In order to evaluate the degradation of the glass ceramics prepared, degradation studies were carried out during 42 days in Tris-HCl solution at 37 °C, pH 7.4, using granules in the range of 355–415 μm. The materials presented a weight loss ranging up to 12%. The ions leached during the immersion mainly originated from the KCa(PO 3) 3 phase, probably due to the presence of K + ion in the calcium metaphosphate, and the residual glassy phase. The structural changes at the surface of materials during degradation have been analyzed by Fourier transform infrared spectroscopy and X-ray diffraction. Results showed that significant surface changes occurred with immersion time, with the decrease of KCa(PO 3) 3, β-Ca 2P 2O 7 and β-Ca(PO 3) 2 phases occurring at different periods of immersion. This study has demonstrated an easy way to prepared calcium phosphate materials with specific calcium phosphate phases and crystallization, and therefore specific degradation rates.

Degradation characteristics of microcystins by isolated bacteria from Lake Kasumigaura

Research Article| February 01 2003 Degradation characteristics of microcystins by isolated bacteria from Lake Kasumigaura Takeshi Saitou; Takeshi Saitou 1Agricultural Science, University of Tsukuba, 1-1-1 Tennoudai, Tsukuba, Ibaraki 305-0006, Japan Search for other works by this author on: This Site PubMed Google Scholar Norio Sugiura; Norio Sugiura 2Institute of Agricultural and Forest Engineering, University of Tsukuba, 1-1-1 Tennoudai, Tsukuba, Ibaraki 305-0006, Japan Tel: +81-298-53-4715 Fax: +81-298-53-4715; E-mail: cyasugi@sakura.cc.tsukuba.ac.jp Search for other works by this author on: This Site PubMed Google Scholar Tomoaki Itayama; Tomoaki Itayama 3Advanced Technology Research Centre, Mitsubishi Heavy Industries, Co., Ltd, 1-8-1 Sachiura, Kanawa-ku, Yokohama 236-8515, Japan(Present address) National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba, Ibaraki 305-0053, Japan Search for other works by this author on: This Site PubMed Google Scholar Yuhei Inamori; Yuhei Inamori 4National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba, Ibaraki 305-0053, Japan Search for other works by this author on: This Site PubMed Google Scholar Masatoshi Matsumura Masatoshi Matsumura 5Institute of Applied Biochemistry, University of Tsukuba, 1-1-1 Tennoudai, Tsukuba, Ibaraki 305-0006, Japan Search for other works by this author on: This Site PubMed Google Scholar Journal of Water Supply: Research and Technology-Aqua (2003) 52 (1): 13–18. https://doi.org/10.2166/aqua.2003.0002 Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Cite Icon Cite Permissions Search Site Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAll JournalsThis Journal Search Advanced Search Citation Takeshi Saitou, Norio Sugiura, Tomoaki Itayama, Yuhei Inamori, Masatoshi Matsumura; Degradation characteristics of microcystins by isolated bacteria from Lake Kasumigaura. Journal of Water Supply: Research and Technology-Aqua 1 February 2003; 52 (1): 13–18. doi: https://doi.org/10.2166/aqua.2003.0002 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex A microcystin degradative bacteria was isolated from natural lakes and its phylogenetic position was confirmed. The 16 s rRNA of the bacteria exhibited 98.5% homology with the 16 s rRNA of Sphingomonas stygia belonging to the alpha subdivision on proteobacteria. The bacteria could degrade microcystins as a sole carbon source, therefore the bacteria utilizes microcystin. The bacteria could degrade microcystins LR, YR and RR, and their specific degradation rates were 0.66 h−1, 1.25 h−1 and 1.90 h−1, respectively. The degradation activity and growth rate of the bacteria was decreased under alkaline pH conditions. 16 s rRNA, microcystin, Sphingomonas This content is only available as a PDF. © IWA Publishing 2003 You do not currently have access to this content.

Kinetics of phenol oxidation by Candida tropicalis: effects of oxygen supply rate and nutrients on phenol inhibition.

The kinetics of phenol degradation was estimated in a fed-batch reactor system. Effects of oxygen and nutrient excess or limitation as well as the presence of several essential ions on the phenol- and oxygen-specific uptake rates achieved simultaneously in a bioreactor were shown. Candida tropicalis was grown on phenol as the only carbon and energy source. Applying the best fit of polynomial function, the maximum specific uptake rates of phenol and oxygen, the critical concentrations of phenol, the half-saturation constants and inhibition constants were determined. Linear relationship between specific phenol uptake rate and the exogenous respiration rate was found regardless of the kind and presence of essential nutrients. At oxygen limitation both the phenol uptake rate and the cell affinity to phenol decreased more strongly compared with those under nutrient limitation. Oxygen in excess resulted in a significant increase of cell tolerance toward phenol. The presence of essential nutrients increased the specific phenol degradation rate and led to complete phenol oxidation.

Aerobic degradation of ethyl-tert-butyl ether by a microbial consortium: Selection and evaluation of biodegradation ability

A microbial consortium that degrades ethyl-tert-butyl ether (ETBE) as the sole source of carbon and energy under aerobic conditions was selected from a gasoline-polluted soil. This consortium consists of a variety of microorganisms with a predominance of filamentous morphology. Degradation of ETBE was found to be solely related to bacterial activity. After prolonged cultivation followed by successive transfers, the consortium's degradation ability was improved and reached a specific degradation rate of 95 mg/g(protein)/h (about 146 mg/g(dry wt)/h). This exceeds the previously reported rates in the literature for ETBE-degrading microorganisms as pure or mixed cultures. Furthermore, a stoichiometric balance of chemical oxygen demand (COD) removal and oxygen uptake with ETBE removal provides indirect evidence of complete degradation. The consortium's activity was not inhibited by high ETBE concentrations (< or = 1,600 mg/L), and large inoculum sizes (> or = 120 mg(protein)/L) were desirable for a faster and complete degradation of ETBE. The enriched consortium was also able to completely degrade methyl-tert-butyl ether (MTBE), tert-amyl methyl ether (TAME), and tert-butyl alcohol (TBA). both alone and in mixture with ETBE, without any measurable release of major degradation intermediates. In each case, MTBE and TAME exhibited the most significant resistance to degradation while TBA was rapidly degraded.

Biodegradation of Methyl tert -Butyl Ether and Other Fuel Oxygenates by a New Strain, Mycobacterium austroafricanum IFP 2012

A strain that efficiently degraded methyl tert-butyl ether (MTBE) was obtained by initial selection on the recalcitrant compound tert-butyl alcohol (TBA). This strain, a gram-positive methylotrophic bacterium identified as Mycobacterium austroafricanum IFP 2012, was also able to degrade tert-amyl methyl ether and tert-amyl alcohol. Ethyl tert-butyl ether was weakly degraded. tert-Butyl formate and 2-hydroxy isobutyrate (HIBA), two intermediates in the MTBE catabolism pathway, were detected during growth on MTBE. A positive effect of Co2+ during growth of M. austroafricanum IFP 2012 on HIBA was demonstrated. The specific rate of MTBE degradation was 0.6 mmol/h/g (dry weight) of cells, and the biomass yield on MTBE was 0.44 g (dry weight) per g of MTBE. MTBE, TBA, and HIBA degradation activities were induced by MTBE and TBA, and TBA was a good inducer. Involvement of at least one monooxygenase during degradation of MTBE and TBA was shown by (i) the requirement for oxygen, (ii) the production of propylene epoxide from propylene by MTBE- or TBA- grown cells, and (iii) the inhibition of MTBE or TBA degradation and of propylene epoxide production by acetylene. No cytochrome P-450 was detected in MTBE- or TBA-grown cells. Similar protein profiles were obtained after sodium dodecyl sulfate-polyacrylamide gel electrophoresis of crude extracts from MTBE- and TBA-grown cells. Among the polypeptides induced by these substrates, two polypeptides (66 and 27 kDa) exhibited strong similarities with known oxidoreductases.

Degradation of methanethiol in a continuously operated upflow anaerobic sludge-blanket reactor.

The feasibility of anaerobic treatment of wastewater containing volatile organic sulfur compounds was investigated using biomass originating from an anaerobic wastewater treatment facility treating brewery wastewater. Interest focused mainly on the degradation of methanethiol (MT), an extremely volatile and malodorous sulfur compound. Formation of hydrogen sulfide from methanethiol, dimethyl sulfide (DMS), and dimethyl disulfide (DMDS) was observed. Batch experiments showed that methanethiol was predominantly used by methanogenic bacteria as the sole source of energy and carbon. Methane was formed on MT degradation, and in the presence of 2-bromoethanesulfonic acid (BES), a specific inhibitor of methanogens, MT conversion was strongly inhibited. During the MT degradation, DMS and DMDS were the other primary compounds found. Relatively small quantities of DMS were present; whereas the DMDS concentrations could accumulate as a result of the relatively fast rate at which methanethiol autoxidizes in the presence of minor amounts of molecular oxygen. It was shown that DMS and DMDS could be biologically degraded, resulting in the formation of methane and hydrogen sulfide. In a continuous experiment using a laboratory-scale upflow anaerobic sludge-blanket (UASB) reactor with a volume of 2.0 L, the feasibility of anaerobic treatment of methanethiol was tested. The reactor was operated at a hydraulic residence time (HRT) of 6 hours, temperature of 30 degrees C, and pH of 7.3 to 7.6. The maximal MT conversion efficiency in the continuous experiment was reached after approximately 70 days and exceeded 97% at an influent concentration of 6 mM, corresponding to a MT loading rate of 25 mM/d. The specific MT degradation rate, as determined after 40 days of operation in the UASB, measured 1.1 +/- 0.1 mM MT/g volatile suspended solids.d. These results show that anaerobic treatment of MT-containing waste streams is an interesting alternative for currently used physicochemical treatment methods.

Strategies for augmenting the pentachlorophenol degradation potential of UASB anaerobic granules

Anaerobic degradation of pentachlorophenol (PCP) is an example of a process that may benefit from enrichment or bioaugmentation. In one approach, enrichment acceleration was attempted by applying an on-line control-based selective stress strategy to a native anaerobic upflow sludge bed (UASB) system; this strategy linked PCP loading rate to methane production. As a result, the reactor biomass potential for PCP complete dechlorination reached a rate of 4 mg g(-1) volatile suspended solid (VSS) day(-1) within a period of 120 days. In another approach, a pure culture, Desulfitobacterium frappieri PCP-1, a strictly anaerobic Gram-positive bacterium, was used to augment the granular biomass of the UASB reactor. This also resulted in a specific degradation rate of 4 mg PCPg(-1) VSS day(-1); however, this potential was attained within 56 days. Fluorescent in situ hybridization (FISH) showed that the PCP-1 strain was able to rapidly attach to the granule and densely colonize the outer biofilm layer.

Ortho pathway of benzoate degradation in Pseudomonas putida: induction of meta pathway at high substrate concentrations

The growth of Pseudomonas putida ATCC 49451 on various concentrations of sodium benzoate was examined under batch cultivation. At low initial concentrations (≤400 mgl −1), cell growth rate was described by the Monod model with parameters of maximum specific growth rate, μ m = 0.66 h −1 and saturation constant, K s = 10 mgl −1. At higher initial concentrations (≥500 mgl −1), product inhibition on specific growth and degradation rates was observed; specific growth rate decreased as sodium benzoate was degraded. A change in degradation pathway was observed with different initial concentrations of sodium benzoate. With initial concentrations up to 200 mgl −1, catechol was oxidized via the ortho ring cleavage with the induction of catechol 1,2-dioxygenase. The ortho pathway metabolites namely, catechol, cis, cis-muconate and muconolactone, were identified using gas chromatography/mass spectrometry (GC/MS) after trimethylsilyl (TMS) derivatization. When higher initial concentrations of sodium benzoate were used (≥300 mgl −1), the culture media showed absorbance at 375 nm (A 375) during the later stage of degradation after approximately 200 mgl −1 of sodium benzoate has been transformed. This was attributed to the accumulation of 2-hydroxymuconic semialdehyde (HMSA), which is an intermediate metabolite of the meta ring fission of catechol. It is concluded that cells grown on high enough concentrations of sodium benzoate simultaneously induced catechol 1,2-dioxygenase and catechol 2,3-dioxygenase, thus activating both the ortho and the meta catechol cleavage pathways. It was further found that catechol, a metabolic intermediate of sodium benzoate, did not effectively support the growth of P. putida when used as a sole substrate. Instead, a dark brown polymerization product was formed. We infer that the induction of the meta pathway is a consequence of the accumulation of 1,2-dihydro-1,2-dihydroxybenzoate (DHB) in the media.

Degradation Characteristics of Toluene, Benzene, Ethylbenzene, and Xylene by Stenotrophomonas maltophilia T3-c

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.