Influence of pH, EDTA/Fe(II) ratio, and microbial culture on Fe(II)-mediated autotrophic denitrification

Fe(II)-mediated autotrophic denitrification with four different microbial cultures under different pH and EDTA/Fe(II) conditions was investigated in batch bioassays. Initially, the highest nitrate removal (72%) was achieved with an activated sludge inoculum. The use of pure cultures of Pseudogulbenkiania strain 2002 and Thiobacillus denitrificans resulted in a 55 and 52% nitrate removal, respectively. No denitrification was observed for a mixed culture dominated by Thiobacillus thioparus and T. denitrificans. A longer enrichment on Fe(II) and the supplementation of thiosulfate as additional electron donor were needed to stimulate the denitrifying activity of the Thiobacillus-mixed culture. A second subculture on Fe(II) as sole electron donor resulted in higher denitrification efficiencies for all microbial cultures. In particular, nitrate removal reached up to 84% with a specific nitrate removal rate of 1.160 mM·(g VSS·day)^-1 in the bioassays seeded with the Thiobacillus-mixed culture. All cultures were favored by decreasing the EDTA/Fe(II) molar ratio from 2.0 to 0.5. The most significant denitrification enhancement was observed for the Pseudogulbenkiania species, indicating a lower tolerance to EDTA. The two pure cultures effectively maintained denitrification at pH 7.0 and were more sensitive to a pH decrease. Conversely, the optimal pH was 6.0 for the Thiobacillus-mixed and activated sludge cultures.

Identify biosorption effects of Thiobacillus towards perfluorooctanoic acid (PFOA): Pilot study from field to laboratory

The concentration of Perfluoroalkyl acids (PFAAs) and the bacterial community composition along the Xiaoqing River were explored with HPLC-MS/MS and Illumina high-throughput sequencing in present study. The results showed that perfluorooctanoic acid (PFOA) was the predominant PFAAs in all sediment samples, and high level of PFOA could lead to an evident increase in the abundance of Thiobacillus. Thiobacillus was identified with the survival ability in high concentrations of PFOA accordingly. Therefore, Thiobacillus thioparus and Thiobacillus denitrificans were selected as receptors to design indoor biosorption experiment. The growth curves under different PFOA concentrations and residual rates of PFOA in the processes of cultivation were analyzed. The results showed that upwards concentrations of PFOA below 5000 ng/L led to an obvious increase in the growth rate of T. thioparus. Whereas PFOA promoted the growth of T. denitrificans in a relatively limited range of concentration, and the effect was not obvious. The addition of different concentrations of PFOA had no apparent effects on pH values in the media of both T. thioparus and T. denitrificans. The concentrations of PFOA in liquid media reduced after the process of bacteria culturing. The removal rates of T. thioparus and T. denitrificans to PFOA were 21.1-26.8% and 13.5-18.4%, respectively. The current findings indicated that T. thioparus could play a significant role as potential biosorbent with the ability to eliminate PFOA effectively in aquatic environment, which would provide novel information for PFOA ecological decontamination and remediation.

Bioelectrochemical denitrification on biocathode buried in simulated aquifer saturated with nitrate-contaminated groundwater

Nitrate contamination in aquifers has posed human health under high risk because people still rely on groundwater withdrawn from aquifers as drinking water and running water sources. These days, bioelectrochemical technologies have shown a great number of benefits for nitrate remediation via autotrophic denitrification in groundwater. This study tested the working possibility of a denitrifying biocathode when installed into a simulated aquifer. The reactors were filled with sand and synthetic groundwater at various ratios (10, 50, and 100 %) to clarify the effect of various biocathode states (not-buried, half-buried, and fully buried) on nitrate reduction rate and microbial communities. Decreases in specific nitrate reduction rates were found to be correlated with increases in sand/medium ratios. A specific nitrate reduction rate of 322.6 mg m(-2) day(-1) was obtained when the biocathode was fully buried in an aquifer. Microbial community analysis revealed slight differences in the microbial communities of biocathodes at various sand/medium ratios. Various coccus- and rod-shaped bacteria were found to contribute to bioelectrochemical denitrification including Thiobacillus spp. and Paracoccus spp. This study demonstrated that the denitrifying biocathode could work effectively in a saturated aquifer and confirmed the feasibility of in situ application of microbial electrochemical denitrification technology.

Linking TFT-LCD wastewater treatment performance to microbial population abundance of Hyphomicrobium and Thiobacillus spp

This study investigated the linkage between performance of two full-scale membrane bioreactor (MBR) systems treating thin-film transistor liquid crystal display (TFT-LCD) wastewater and the population dynamics of dimethylsulfoxide (DMSO)/dimethylsulfide (DMS) degrading bacteria. High DMSO degradation efficiencies were achieved in both MBRs, while the levels of nitrification inhibition due to DMS production from DMSO degradation were different in the two MBRs. The results of real-time PCR targeting on DMSO/DMS degrading populations, including Hyphomicrobium and Thiobacillus spp., indicated that a higher DMSO oxidation efficiency occurred at a higher Hyphomicrobium spp. abundance in the systems, suggesting that Hyphomicrobium spp. may be more important for complete DMSO oxidation to sulfate compared with Thiobacillus spp. Furthermore, Thiobacillus spp. was more abundant during poor nitrification, while Hyphomicrobium spp. was more abundant during good nitrification. It is suggested that microbial population of DMSO/DMS degrading bacteria is closely linking to both DMSO/DMS degradation efficiency and nitrification performance.

[Study on sulfur-based autotrophic denitrification with different electron donors]

Sulphur-based autotrophic denitrification was applied to treat the low concentration nitrate-contaminated water. Different electron donors, namely, elemental sulfur, sulfide and thiosulfate, were used in three continuous reactors to compare the denitrification performance. When treating the low concentration nitrate-contaminated water (13 mg x L(-1)), the thiosulfate system showed the best performance and the sulfide system was the worst. The thiosulfate system was less sensitive to low temperature than the other two. At temperatures higher than 20 degrees C, the sulfur system was greatly influenced by mass transfer efficiency and HRT. It removed 81% of nitrate and 79% of TN when HRT was no less than 2 h, but could only achieve a low nitrate and TN removal rate of 47% and 51% when HRT was shorter than 2 h. No obvious nitrite accumulation was observed and the average effluent nitrite was 0.53 mg x L(-1). The sulfide system could only remove 47% of nitrate and 41% of TN with 0.29 mg x L(-1) nitrite in the effluent at the HRT of 4 h. Meanwhile, the thiosulfate system had a high removal rate of 99% for nitrate and 90% for TN, with a low content of effluent nitrite of 0.080 mg x L(-1), and the HRT could be shortened to 0.5 h. The molecular biological analysis showed that different bacteria predominated in the three reactors, and that Thiobacillus denitrificans existed abundantly in the sulfur system, while the functional bacteria in the sulfide and thiosulfate systems could not be identified yet. A new species of sulfur-based autotrophic denitrification bacterium may have been found.

Effects of sulphur and Thiobacillus thioparus on cow manure aerobic composting

A simulated aerobic composting experiment was used to explore the effects of sulphur and Thiobacillus thioparus during six manure composting treatments. The addition of sulphur led to a decrease of the pH level within the range 6-6.3, which was lower than the control treatment (CK). The concentration of ammonium nitrogen in T1 (0.25% sulphur), T2 (0.5% sulphur), T3 (0.25% sulphur + T. thioparus) and T4 (0.5% sulphur + T. thioparus) were much higher than the ammonium N in CK. The results indicated that addition of sulphur could increase the concentration of ammonium N and reduce loss of nitrogen. However, excess sulphur had a negative effect on temperature and GI. Addition of T. thioparus could increase concentration of available S, alleviate these negative influences and reduce compost biological toxicity.

Microbial community analysis in the autotrophic denitrification process using spent sulfidic caustic by denaturing gradient gel electrophoresis of PCR-amplified genes

Spent sulfidic caustic (SSC) produced from petrochemical plants contains a high concentration of hydrogen sulfide and alkalinity, and some almost non-biodegradable organic compounds such as benzene, toluene, ethylbenzene and xylenes (BTEX). SSC is mainly incinerated with auxiliary fuel, leading to secondary pollution problems. The reuse of this waste is becoming increasingly important from economic and environmental viewpoints. To denitrify wastewater with low COD/N ratio, additional carbon sources are required. Thus, autotrophic denitrification has attracted increasing attention. In this study, SSC was injected as an electron donor for sulfur-based autotrophic denitrification in the modified Ludzack-Ettinger (MLE) process. The efficiencies of nitrification, COD, and total nitrogen (TN) removal were evaluated with varying SSC dosage. Adequate SSC injection exhibited stable autotrophic denitrification. No BTEX were detected in the monitored BTEX concentrations of the effluent. To analyse the microbial community of the MLE process, PCR-DGGE based on 16 S rDNA with EUB primers, TD primers and nirK gene with nirK primers was performed in order to elucidate the application of the MLE process to SSC.

[Regulation of hydrogen sulfide level by acidophobic bacteria of Thiobacillus genus in technogenic reservoirs of sulfur mining regions]

An increase of acidophobic thione bacteria quantity in Rozdil and Yavoriv reservoirs of sulfur mining regions during 2005-2009 years, which correlates with a decrease of hydrogen sulfide content in water surface layers, was shown. The ability of acidophobic bacteria of Thiobacillus genus, isolated from "Yavorivske" lake, to oxidize effectively hydrogen sulfide added into Beijerinck medium instead of thiosulfate, was discovered. It was established, that hydrogen sulfide oxidizing efficiency by Thiobacillus sp. Yav-8, Yav-11 and Yav-14 strains is the highest (78.48-84.56%) when its content in cultivation medium was increased twice: to 2584 mg/l. An increase of sulfur quantity in sodium sulfide form from to six times as compared with its standard content in sodium thiosulfate form in the Beijerinck medium does not lead to the increase of hydrogen sulfide oxidizing efficiency by cells.

Treatment of leather industry wastewater by aerobic biological and Fenton oxidation process

Degradation of leather industry wastewater by sole aerobic treatment incorporating Thiobacillus ferrooxidans, Fenton's reagents, and combined treatment was investigated in this study. The sole treatment by Fenton's oxidation involving the introduction of 6g FeSO(4) and 266 g H(2)O(2) in a liter of wastewater at pH of 3.5 and 30 degrees C for 30 min at batch conditions reduced COD, BOD(5), sulfide, total chromium and color up to 69%, 72%, 88%, 5%, 100% and T. ferrooxidans alone showed maximum reduction to an extent of 77, 80, 85, 52, 89, respectively, in 21 d treatment at pH 2.5, FeSO(4) 16 g/L and temperature of 30 degrees C. The combined treatment at batch conditions involving 30 min chemical treatment by Fenton's oxidation followed by 72 h biochemical treatment by T. ferrooxidans at batch conditions gave rise up to 93%, 98%, 72%, 62% and 100% removal efficiencies of COD, BOD, sulfide, chromium and color at pH of 2.5 and 30 degrees C. Decrease in photo absorption of the Fenton's reagent treated samples, as compared to the banks, at 280, 350 and 470 nm wave lengths was observed. This may be the key factor for stimulating the biodegradation by T. ferrooxidans.

Growth kinetics of Hyphomicrobium and Thiobacillus spp. in mixed cultures degrading dimethyl sulfide and methanol

The growth kinetics of Hyphomicrobium spp. and Thiobacillus spp. on dimethyl sulfide (DMS) and methanol (in the case of Hyphomicrobium spp.) in an enrichment culture created from a biofilter cotreating DMS and methanol were studied. Specific growth rates of 0.099 h(-1) and 0.11 h(-1) were determined for Hyphomicrobium spp. and Thiobacillus spp., respectively, growing on DMS at pH 7. These specific growth rates are double the highest maximum specific growth rate for bacterial growth on DMS reported to date in the literature. When the pH of the medium was decreased from pH 7 to pH 5, the specific growth rate of Hyphomicrobium spp. decreased by 85%, with a near 100-fold decline in the yield of Hyphomicrobium 16S rRNA gene copies in the mixed culture. Through the same pH shift, the specific growth rate and 16S rRNA gene yield of Thiobacillus spp. remained similar. When methanol was used as a substrate, the specific growth rate of Hyphomicrobium spp. declined much less over the same pH range (up to 30%) while the yield of 16S rRNA gene copies declined by only 50%. Switching from an NH(4)(+)-N-based source to a NO(3)(-)-N-based source resulted in the same trends for the specific growth rate of these microorganisms with respect to pH. This suggests that pH has far more impact on the growth kinetics of these microorganisms than the nitrogen source. The results of these mixed-culture batch experiments indicate that the increased DMS removal rates observed in previous studies of biofilters cotreating DMS and methanol are due to the proliferation of DMS-degrading Hyphomicrobium spp. on methanol at pH levels not conducive to high growth rates on DMS alone.

[Domestication study about desulfuration microorganism from oxidation ditch by low concentration SO2]

An excellent desulfuration microorganism with a quick growth and propagation, high activation, high efficiency of removing SO2 is obtained from oxidation ditch of a city sewage treatment plant by inductive acclimatization over 6 d with low concentration SO2 gas (100-2 000 mg/m3). The desulfurition microorganism get their energy sources for growth from transforming SO2 (SO3(2-)) to SO4(2-). The predominant bacterium of the desulfuration microorganism has the same characteristic with Thiobacillus ferrooxidans (T. ferrooxidans), which showed that it was Gram negative, short rod bacteria with a single polar flagellum under a microscopic examination, and obtained its nourishment through the oxidation of inorganic compounds. The technology process condition of domestication and desulfuration of microorganism are particular studied, and the results showed that aerating time, SO2 flux and time to provide nutriment contained N, P, K to microorganism were very important. They have an ability with degradation rate of 160g/ (m3 x h) and degradation efficiency over 50% to transform sulfite to sulfate in liquid phase. The bacteria have a 98% of removing efficiency and over 80% of biodegradation efficiency for the 5 500 mg/m3 SO2 gas and the outlet concentration of SO2 is lower than 100 mg/m3, and also have a 95% of removing efficiency for 15 000 mg/m3 SO2 gas in the packed tower reactor with Raschig ring at 3s contact time.

[Biofilm on a metal surface as a factor of microbial corrosion]

Main attention was given in the present review to the research methods, phases of biofilm's forming, exopolymer compounds of bacteria as main biofilm forming factor. A microbial corrosion as a result of interaction between the biofilm and metal surface was considered. The interaction was displayed in biomineralization. The future trends of biofilms study were bound with research of their architecture. That architecture was determined by the structure and function of biofilms compounds: biopolymers and biominerals.

[Characteristic of autotrophic denitrification in bioaugmented anaerobic system]

An autotrophic denitrification process using reduced sulfide as electron donor in anaerobic system is proposed as an efficient and cost effective alternative to conventional heterotrophic denitrification for low C/N ratio wastewaters and for simultaneous removal of sulfide and nitrate. A suspended culture of Thiobacillus denitrificans bacteria was fast and efficiently established in anaerobic system. 5 series bioaugmented anaerobic systems with different N/S ratio synthetic influent were set up. Sulfide, nitrate, sulfate, and nitrite concentration in the effluent at every 3 hours were measured after 15 day. The primary objective was to investigate the characteristic of autotrophic denitrification and sulfide oxidation, and to reveal the mechanism of autotrophic denitrification process using reduced sulfide as electron donor in bioaugmented anaerobic system. 90% removal efficiency of sulfide was observed after 3 hours and removal efficiency of sulfide had no reference to N/S ratio. The rate of sulfide oxidation was 20-24 g x (m3 x h)(-1), which was 10 times higher than that have been reported in the literatures. Maximum removal efficiency of nitrate was 65% after 6 hours, which enhanced with increasing N/S ration of influent. The result showed bacteria reduced nitrate to nitrite at first step, and resulted in accumulation of nitrite to 93 mg x L(-1) to the large extent. Accumulated nitrite was disappear on low influent N/S ratio condition after 6 hours, and need 21 hours on high influent N/S ratio condition. So, complete sulfide and nitrate removal was achieved during 6 hours. The results revealed that the sharp decreasing of sulfide concentration attributed to the reaction between sulfide and biosulfur particles to form polysulfide anions. In addition, biosulfur produced in 3 hours was the main source of electron donor for reducing nitrate.

Characteristics of nitrogen removal and microbial distribution by application of spent sulfidic caustic in pilot scale wastewater treatment plant

Since spent sulfidic caustic (SSC) produced from petrochemical industry contains a high concentration of alkalinity and sulfide, it was expected that SSC could be used as an electron donor for autotrophic denitrification. To investigate the nitrogen removal performance, a pilot scale Bardenpho process was operated. The total nitrogen removal efficiency increased as SSC dosage increased, and the highest efficiency was observed as 77.5% when SSC was injected into both anoxic tank (1) and (2). FISH analysis was also performed to shed light on the effect of SSC dosage on the distribution ratio of nitrifying bacteria and Thiobacillus denitrificans. FISH results indicated that the relative distribution ratio of ammonia-oxidizing bacteria, Nitrobacter spp., Nitrospira genus and Thiobacillus denitrificans to eubacteria varied little with the pH of the tanks, and SSC injection did not give harmful effect on nitrification efficiency. These results show that SSC can be applied as an electron donor of autotrophic denitrification to biological nitrogen removal process effectively, without any inhibitory effects to nitrifying bacteria and sulfur-utilizing denitrifying bacteria.

Removal of hydrogen sulfide by immobilized Thiobacillus thioparus in a biotrickling filter packed with polyurethane foam

In the work described here, a biotrickling filter with Thiobacillus thioparus (ATCC 23645) immobilized on polyurethane foam is proposed for the removal of hydrogen sulfide contained in air. The effect of surface velocity of the recirculation medium (5.9-1.2 m/h), sulfate concentration inhibition (3.0-10.7 g/L), pH (6.0-8.2), empty bed residence time (EBRT) (150-11 s) for constant loads of 11.5 and 2.9 g S/m(3)/h, and pressure drop of the system were investigated. The total amount of biomass immobilized on the carrier was 8.2+/-1.3x10(10) cells/g. The optimal values of the operating variables were: pH between 7.0 and 7.5, surface velocity of 5.9 m/h and sulfate concentration below 5 g/L. The critical EC value was 14.9 g S/m(3)/h (removal efficiency of 99.8%) and the EC(max) was 55.0 g S/m(3)/h (removal efficiency of 79.8%) for an EBRT of 150 s. For loads of 2.89+/-0.05 and 11.5+/-0.1 g S/m(3)/h, the removal efficiency was higher than 99% for an EBRT over 90 s.

Assessment of the addition of Thiobacillus denitrificans and Thiomicrospira denitrificans to chemolithoautotrophic denitrifying bioreactors

The aim of the present study was to assess the impact of adding cultures of Thiobacillus denitrificans and Thiomicrospira denitrificans to two upflow anaerobic sludge bed (UASB) reactors: one inoculated with granular sludge and the other filled only with activated carbon (AC). The performances of the bioreactors and the changes in biomass were compared with a non-bioaugmented control UASB reactor inoculated with granular sludge. The reactors inoculated with granular sludge achieved efficiencies close to 90% in nitrate and thiosulfate removal for loading rates as high as 107 mmol-NO3 -/l per day and 68 mmol-S2O3 2-/l per day. Bioaugmentation with Tb. denitrificans and Tm. denitrificans did not enhance the efficiency compared to that achieved with non-bioaugmented granular sludge. The loading rates and efficiencies were 30-40% lower in the AC reactor. In all the reactors tested, Tb. denitrificans became the predominant species. The results strongly suggest that this bacterium was responsible for denitrification and sulfoxidation within the reactors. We additionally observed that granules partially lost their integrity during operation under chemolithoautotrophic conditions, suggesting limitations for long-term operation if bioaugmentation is applied in practice.

[Monosaccharide composition of exopolymer complex in Thiobacillus thioparus and Stenotrophomonas maltophilia]

The bacteria of Thiobacillus thioparus and Stenotrophomonas maltophilia are capable to form a thick biofilm complicated as to its structure on the surface of low-carbon steel. This biofilm formation on any surface occurs under the adhesion of the cells of the plankton growth model with the help of synthesis of muciferous exopolymers with adhesive properties. Hence the monosaccharide composition of the exopolymer complex in the form of polyol acetates was studied by chromate-mass-spectrum method. A significant difference in the composition of exopolymer monosaccharides with the presence of steel model in the medium and without it was established; a change in the monosaccharide composition of mono- and binary culture in the conditions of plankton and biofilm growth was also observed.

[Effect of the biofilm biopolymers on the microbial corrosion rate of the low-carbon steel]

The relationship between exopolymer's specific production, relative carbohydrate and protein content in the biofilm exopolymers of the pure and mixed Thiobacillus thioparus and Stenotrophomonas maltophilia cultures and their corrosion activity was studied. Change of growth model of investigated cultures from plankton to biofilm led to an increase of specific exopolymer's production. In the biofilm formed by T. thioparus and S. maltophilia biofilm on the low-carbon steel surface one could observe an increase of relative protein content in the exopolymer complex in comparison with those in the pure culture. The development of such biofilms stimulatied the 7-fold corrosion activity.

Combined removal of sulfur compounds and nitrate by autotrophic denitrification in bioaugmented activated sludge system

An autotrophic denitrification process using reduced sulfur compounds (thiosulfate and sulfide) as electron donor in an activated sludge system is proposed as an efficient and cost effective alternative to conventional heterotrophic denitrification for inorganic (or with low C/N ratio) wastewaters and for simultaneous removal of sulfide or thiosulfate and nitrate. A suspended culture of sulfur-utilizing denitrifying bacteria was fast and efficiently established by bio-augmentation of activated sludge with Thiobacillus denitrificans. The stoichiometry of the process and the key factors, i.e. N/S ratio, that enable combined sulfide and nitrogen removal, were determined. An optimum N/S ratio of 1 (100% nitrate removal without nitrite formation and low thiosulfate concentrations in the effluent) has been obtained during reactor operation with thiosulfate at a nitrate loading rate (NLR) of 17.18 mmol N L(-1) d(-1). Complete nitrate and sulfide removal was achieved during reactor operation with sulfide at a NLR of 7.96 mmol N L(-1) d(-1) and at N/S ratio between 0.8 and 0.9, with oxidation of sulfide to sulfate. Complete nitrate removal while working at nitrate limiting conditions could be achieved by sulfide oxidation with low amounts of oxygen present in the influent, which kept the sulfide concentration below inhibitory levels.

Succession of sulfur-oxidizing bacteria in the microbial community on corroding concrete in sewer systems

Microbially induced concrete corrosion (MICC) in sewer systems has been a serious problem for a long time. A better understanding of the succession of microbial community members responsible for the production of sulfuric acid is essential for the efficient control of MICC. In this study, the succession of sulfur-oxidizing bacteria (SOB) in the bacterial community on corroding concrete in a sewer system in situ was investigated over 1 year by culture-independent 16S rRNA gene-based molecular techniques. Results revealed that at least six phylotypes of SOB species were involved in the MICC process, and the predominant SOB species shifted in the following order: Thiothrix sp., Thiobacillus plumbophilus, Thiomonas intermedia, Halothiobacillus neapolitanus, Acidiphilium acidophilum, and Acidithiobacillus thiooxidans. A. thiooxidans, a hyperacidophilic SOB, was the most dominant (accounting for 70% of EUB338-mixed probe-hybridized cells) in the heavily corroded concrete after 1 year. This succession of SOB species could be dependent on the pH of the concrete surface as well as on trophic properties (e.g., autotrophic or mixotrophic) and on the ability of the SOB to utilize different sulfur compounds (e.g., H2S, S0, and S2O3(2-)). In addition, diverse heterotrophic bacterial species (e.g., halo-tolerant, neutrophilic, and acidophilic bacteria) were associated with these SOB. The microbial succession of these microorganisms was involved in the colonization of the concrete and the production of sulfuric acid. Furthermore, the vertical distribution of microbial community members revealed that A. thiooxidans was the most dominant throughout the heavily corroded concrete (gypsum) layer and that A. thiooxidans was most abundant at the highest surface (1.5-mm) layer and decreased logarithmically with depth because of oxygen and H2S transport limitations. This suggested that the production of sulfuric acid by A. thiooxidans occurred mainly on the concrete surface and the sulfuric acid produced penetrated through the corroded concrete layer and reacted with the sound concrete below.

[Investigation of the structure of biofilms formed by sulfur cycle bacteria on metal matrices]

The structure of biofilm formed by Thiobacillus thioparus, Stenotrophomonas maltophilia on the metal matrix was investigated. Use of electron microscope-microanalysis showed that these bacteria can form biofilms 34-94 microm thick on metal different in their structure and elemental sulfur composition. A biofilm formed by mixed culture of Thiobacillus thioparus and Stenotrophomonas maltophilia had a developed interior structure and biofilm porosity. The use of the confocal laser scanning microscope permitted to show nonuniform location of the colony. Mixed cultures, in contrast to individual ones, can form conglomerates which consist of cells and exopolymers submerged in the biofilm thickness.

The role of higher polythionates in the reduction of chromium(VI) by Acidithiobacillus and Thiobacillus cultures

In this paper, we report the chromium(VI) reduction by filtrates of Acidithiobacillus and Thiobacillus cultures. Chromium(VI) reduction by filtrates of A. ferrooxidans cultures under acidic conditions was higher than that observed for A. thiooxidans. However, at pH close to 7, chromium(VI) reduction by filtrates of T. thioparus cultures was as high as that by filtrates of A. thiooxidans cultures and much higher than that observed for A. ferrooxidans cultures at the same pH. The capability of these cultures to reduce chromium(VI) was associated specifically with the fraction of cultures (cells, sulphur and associated sulphur compounds) retained by filtration through a 0.45mum filter. In the fraction that comes from A. thiooxidans culture, polythionates (S(x)O(6)(2-)) with 3-7 sulphur atoms were detected and identified (by HPLC with MS as detector). The model of vesicles containing polythionates, sulphur and water agrees with our results.

[Adhesion and colonisation of the glass surface by Thiobacillus thioparus and Stenotrophomonas maltophilia and their biculture]

The thionic bacteria Thiobacillus thioparus and its natural sattelite Stenotrophomonas maltophilia have been isolated from the soil, adjacent to the surface of Kyiv underground tunnel. The sterile glass, was used as a model surface which imitates the hydrophilic model surface. Beijerinck nutrition media were inoculated by pure and mixed culture of T. thioparus. Some differences in adhesion by mono- and mixed cultures were shown. Hemolithotrophic and heterotrophic bacteria could be interrelated and this could influence the biofilm formation. The formation of biofilm of T. thioparus mixed culture occurs more actively in comparison with the pure culture.

Oxygen transfer and consumption in a thiosulfate oxidizing bioreactor with sulfur production

AIMS

To evaluate the contribution of oxygen transfer and consumption in a sulfoxidizing system to increase the elemental sulfur yield from thiosulfate oxidation.

METHODS AND RESULTS

A 10 l thiosulfate oxidizing bioreactor with suspended cells operating under microaerophilic conditions and a separated aerator with a variable volume of 0.8--1.7 l were operated with a consortium containing mainly Thiobacillus sp. that oxidizes several sulfide species to elemental sulfur and sulfate. From the gas-liquid oxygen balance, the k(L)a was estimated under different operation conditions. A k(L)a of around 200 h(-1) favoured elemental sulfur production and can serve as scale-up criterion. It was further shown that more than 50% of the oxygen fed to the system was consumed in the aerator.

CONCLUSIONS

The performance of the sulfoxidizing system can be improved by controlling oxygen transfer.

SIGNIFICANCE AND IMPACT OF THE STUDY

The proposed method for the k(L)a determination was based on the oxygen balance, which incorporates the oxygen concentrations measured in the liquid in steady state, reducing the interference of the response time in the traditional non-steady state methods. This approach can be used to optimize reactors where microaerophilic conditions are desirable.

Anaerobic, nitrate-dependent oxidation of U(IV) oxide minerals by the chemolithoautotrophic bacterium Thiobacillus denitrificans

Under anaerobic conditions and at circumneutral pH, cells of the widely distributed, obligate chemolithoautotrophic bacterium Thiobacillus denitrificans oxidatively dissolved synthetic and biogenic U(IV) oxides (uraninite) in nitrate-dependent fashion: U(IV) oxidation required the presence of nitrate and was strongly correlated with nitrate consumption. This is the first report of anaerobic U(IV) oxidation by an autotrophic bacterium.