Uma revisão sobre: tratamento biológico de drenagem de mina — cenário atualizado, perspectivas e recomendações de futuros trabalhos / Biological treatment of mine drainage — scenario updated, perspectives, and recommendations for future works

RESUMO Rochas contendo sulfetos metálicos podem ser oxidadas em um processo catalisado por procariotos quimiolitoautotróficos ou Fe3+. A atividade mineradora acelera esse processo ao gerar resíduos contendo sulfetos metálicos com grande superfície de contato. O lixiviado resultante, conhecido como drenagem de mina (DM), é rico em sulfato, íons hidrogênio e contaminantes químicos inorgânicos como ferro (Fe), zinco (Zn), cádmio (Cd), manganês (Mn), níquel (Ni), arsênio (As) e alumínio (Al). Para remover tais poluentes, atualmente, o principal tratamento utilizado é a adição de reagentes alcalinos. Entretanto, esse método tem limitada eficiência, alto custo e gera grandes volumes de resíduos sólidos tóxicos de relativa solubilidade. Bactérias redutoras de sulfato (BRS) podem oxidar matéria orgânica com geração de sulfeto. Algumas vias metabólicas do processo consomem H+neutralizando o pH. O sulfeto produzido pode reagir com contaminantes inorgânicos e precipitá-los, permitindo sua recuperação da fase líquida. O uso de subprodutos industriais e urbanos contendo diferentes fontes de carbono como doadores de elétrons no tratamento de DM tem sido investigado. Este artigo sumariza dados sobre as variáveis relevantes para a atividade microbiana durante o tratamento biológico de DM, analisando o atual cenário de pesquisas com fontes alternativas de carbono. Discute-se ainda novas fontes de matéria orgânica ainda não aplicadas para tratamento biológico de efluentes e que, sob aspectos de sustentabilidade, dos pontos de vista sustentável e econômico, podem ser usadas no tratamento de resíduos.

ABSTRACT Rocks containing metal sulfides be can oxidized biologically or chemically. Chemolithoautotrophics prokaryotes and Fe3+ catalyze this process. The mining activities also accelerate the process for creates metal sulphides tailings with a big contact surface. The leached formed is called Mine Drainage (MD) whose composition is rich in sulphate, hydrogen ions and inorganic chemical contaminants such as Fe, Zn, Mn, Cd, Ni, As e Al. Currently, in order to remove these pollutants, the main treatment used is the addition of alkaline reagents. However, the method has limited efficiency, high cost with input reagents and generates wide amounts of toxic solid residues with high solubility. The sulphide reducing bacterias (RSB) can oxidize organic matter generating sulphide. Some metabolic pathways consume H+ neutralizing the pH. The sulphide formed can react and precipitate inorganic pollutants, allowing their recuperation from the liquid phase. The use of industrial and urban by-products containing different carbon sources have been investigated as an electron donor in the MD treatment. The diverse microbial consortia synergic acting can present bigger efficiency in the presence of mixed carbon sources, besides lower cost in relation to the pure matter. Here will be detailed the biological treatment about which and how the variables of the system can influence the microbial activity and relevant molecules to the treatment. After is described the current situation of the research about alternative carbon sources. New carbon sources whose are a by-product of the expanding industry presenting good feature to anaerobic degrading are suggested. The by-product potential is described from the point of view of sustainability, and waste management.

Uso do fosfogesso como fonte de sulfato para bactérias redutoras de sulfato em um reator contínuo de leito fluidizado / Phosphogypsum as sulfate source for sulphate-reducing bacteria in a continuous fluidized-bed reactor

RESUMO O fosfogesso (FG) é um dos principais subprodutos da produção de ácido fosfórico para fertilizantes. Esse sólido é constituído principalmente de sulfato de cálcio di-hidratado, podendo conter também metais tóxicos e acidez residual (pH 2-3). A disposição em pilhas próximas às usinas é o principal método de disposição, entretanto isso não soluciona os problemas ambientais, uma vez que pode haver lixiviação das pilhas de resíduo pela água da chuva, contaminando o solo e os corpos d'água. Portanto, a disposição do FG é um desafio para a indústria de fertilizantes. O FG pode ser utilizado como fonte de sulfato para a produção de sulfeto em reatores anaeróbios, utilizando bactérias redutoras de sulfato (BRS). O sulfeto gerado pode ser utilizado posteriormente para a produção de enxofre elementar ou usado na precipitação de metais de transição. No presente trabalho, avaliou-se a viabilidade do uso do FG como fonte de sulfato para as BRS em um reator contínuo de leito fluidizado alimentado com glicerol p.a. como substrato, e estudou-se a influência da variável tempo de detenção hidráulica (TDH) real no processo de biorredução do sulfato. Este último foi determinado em 15 ± 2,6 e 9,7 ± 1,2 h, respectivamente, para os valores teóricos de 10 e 8 horas, a partir do uso de cloreto de lítio como traçador. Para a razão DQO/SO4 2- igual a 1,9, obteve-se remoção de sulfato de 73 ± 11 e 75 ± 12%, respectivamente, para os TDHs 15 ± 2,6 e 9,7 ± 1,2 h. As taxas de remoção específicas de sulfato foram de 0,106 ± 0,04 e 0,179 ± 0,07 gSO4 2-/gSSV.d, respectivamente, para os TDHs 15 ± 2,6 e 9,7 ± 1,2 h.

ABSTRACT Phosphogypsum (PG) is one of the major byproducts of phosphoric acid production for fertilizers. It consists mainly of calcium sulfate dihydrate and may also contain toxic metals and residual acidity (pH 2-3). Generally, this waste is disposed in stacks near plants; however, this does not solve the environmental problems as there may be leaching of the waste piles by rainwater, contaminating the soil and water bodies. Therefore, PG disposal is a challenge for the fertilizer industry. This waste can be used as a sulfate source for sulfide production in anaerobic reactors using sulfate-reducing bacteria (SRB). The sulfide generated can be used later for the production of elemental sulfur or used in the precipitation of transition metals. This work evaluated the feasibility of using PG as a sulfate source for SRB in a continuous fluidized-bed reactor fed with glycerol p.a. as carbon source, and the hydraulic retention time (HRT) effect in the sulphate bioreduction process. The latter was determined at 15 ± 2.6 and 9.7 ± 1.2 h, respectively, for the theoretical values of 10 and 8 hours, from the use of lithium chloride as tracer. Sulfate removal at DQO/SO4 2- ratio of 1.9 was 73 ± 11 and 75 ± 12%, respectively, for HRT of 15 ± 2.6 and 9.7 ± 1.2 h. Specific sulfate removal rates were 0.106 ± 0.04 and 0.179 ± 0.07 gSO4 2-/gSSV.d, respectively, for HRT 15 ± 2.6 and 9.7 ± 1.2 h.

Anaerobic microbiota: spatial-temporal changes in the sediment of a tropical coastal lagoon with ephemeral inlet in the Gulf of Mexico / Microbiota anaerobia: cambios espacio-temporales en el sedimento de una laguna costera tropical con boca efímera en el Golfo de México

Abstract:Sulfate-reducing bacteria (SRB) and methanogenic archaea (MA) share common niches in coastal sediments during the terminal phases of the anaerobic mineralization of organic matter. The purpose of this study was to analyze the spatial - temporal variation of SRB and MA in the sediments of a tropical coastal lagoon with ephemeral inlet (La Mancha, Veracruz, Gulf of Mexico) and its relationship with environmental changes. A total of 24 sediment samples were collected during the dry (April, May), rainy (July, September) and Northern (November, February) seasons in the period 2013-2014. Microbiological analyses included the quantification of the viable SRB and MA with different substrates, as well as mineralization experiments to determine the effect of sulfate on acetate oxidation. The analyzed environmental variables in the sediments included: temperature, pH, Eh, salinity, sulfates, H2S, volatile solids, carbohydrates, and granulometric characteristics. Major changes occurred between the dry and rainy seasons. During the dry season, sulfate-reducing abundance was significantly greater with lactate (8.3x105 - 1.2x107 cells / g) and propionate (1.8x105 - 6.6x106 cells / g) as substrates, while the MA that use methanol were dominant (4.2x105 - 9.1x106 cells / g). In contrast, during the rainy season, hydrogenophylic (2.6x105 - 8.3x106 cells/g) and acetoclastic (5.4x105-6.4x106 cells / g) MA increased significantly and SRB decreased in the analyzed substrates. An apparent competition for acetate was observed, with a greater oxidation in the media with sulfates in the dry season (0.06 mM acetate / g sediment / day), and a greater oxidation in the media without sulfates in the rainy season (0.02 mM acetate / g sediment / day). SRB and MA were present throughout the sediment column, however SRB dominated in the first centimeters of the sediment while MA were abundant in deeper layers. In conclusion, SRB and MA together played a role in the mineralization of organic matter in the sediments of La Mancha lagoon, with sulfate-reduction dominating in the dry season (closed inlet) and methanogenesis during the rainy season (open inlet). Changes in rainfall and river input in this lagoon significantly affect salinity and sulfate content, the main factors that regulate the dynamics of SRB and MA in the sediments. Rev. Biol. Trop. 64 (4): 1759-1770. Epub 2016 December 01.

Resumen:Las bacterias sulfatorreductoras (BSR) y las arqueas metanogénicas (AM) comparten nichos comunes en los sedimentos costeros durante las fases terminales de la mineralización anaerobia de la materia orgánica. El objetivo del presente estudio fue analizar la variación espacio-temporal de las BSR y AM en los sedimentos de una laguna costera tropical con una boca efímera (La Mancha, Veracruz, Golfo de México) y su relación con los cambios ambientales. Un total de 24 muestras de sedimentos fueron recolectadas en las temporadas de secas (abril, mayo), lluvias (julio, septiembre) y nortes (noviembre, febrero) en el periodo 2013 - 2014. Los análisis microbiológicos incluyeron la cuantificación de las BSR y AM viables con diferentes sustratos, así como experimentos de mineralización para determinar el efecto de los sulfatos en la oxidación del acetato. Las variables ambientales analizadas en los sedimentos incluyeron la temperatura, pH, Eh, salinidad, sulfatos, H2S, sólidos volátiles, carbohidratos y las características granulométricas. Los principales cambios se presentaron entre las estaciones de secas y lluvias. En la temporada de secas la abundancia sulfatorreductora fue significativamente superior con lactato (8.3x105 - 1.2x107 células / g) y propionato (1.8x105 - 6.6x106 células / g) como sustratos, mientras que las AM que emplean metanol dominaron (4.2x105 - 9.1x106 células / g). Por el contrario, en la época de lluvias aumentaron significativamente las AM hidrogenofílicas (2.6x105-8.3x106 células / g) y acetoclásticas (5.4x105-6.4x106 células / g), disminuyendo las BSR con los sustratos analizados. Se determinó una competencia aparente por el acetato. Su oxidación fue mayor en los medios con presencia de sulfatos en las temporadas de secas (0.06 mM acetato / g sedimento / día), mientras que aumentó en los medios sin sulfatos en la época de lluvias (0.02 mM acetato / g sedimento / día). Las BSR y las AM estuvieron presentes a lo largo de la columna sedimentaria; sin embargo, las BSR dominaron en los primeros centímetros del sedimento y las AM abundaron a mayor profundidad. En conclusión las BSR y AM participaron de manera conjunta en la mineralización de la materia orgánica en los sedimentos de la laguna de La Mancha, dominando la sulfatorreducción en la temporada de secas (boca cerrada) y la metanogénesis en la época de lluvias (boca abierta). Los cambios en el aporte fluvial y la precipitación en esta laguna afectaron significativamente la salinidad y el contenido de sulfatos, siendo los principales factores que regularon la dinámica de las BSR y AM en los sedimentos.

Streptomyces lunalinharesii 235 prevents the formation of a sulfate-reducing bacterial biofilm

ABSTRACT Streptomyces lunalinharesii strain 235 produces an antimicrobial substance that is active against sulfate reducing bacteria, the major bacterial group responsible for biofilm formation and biocorrosion in petroleum reservoirs. The use of this antimicrobial substance for sulfate reducing bacteria control is therefore a promising alternative to chemical biocides. In this study the antimicrobial substance did not interfere with the biofilm stability, but the sulfate reducing bacteria biofilm formation was six-fold smaller in carbon steel coupons treated with the antimicrobial substance when compared to the untreated control. A reduction in the most probable number counts of planktonic cells of sulfate reducing bacteria was observed after treatments with the sub-minimal inhibitory concentration, minimal inhibitory concentration, and supra-minimal inhibitory concentration of the antimicrobial substance. Additionally, when the treated coupons were analyzed by scanning electron microscopy, the biofilm formation was found to be substantially reduced when the supra-minimal inhibitory concentration of the antimicrobial substance was used. The coupons used for the biofilm formation had a small weight loss after antimicrobial substance treatment, but corrosion damage was not observed by scanning electron microscopy. The absence of the dsrA gene fragment in the scraped cell suspension after treatment with the supra-minimal inhibitory concentration of the antimicrobial substance suggests that Desulfovibrio alaskensis was not able to adhere to the coupons. This is the first report on an antimicrobial substance produced by Streptomyces active against sulfate reducing bacteria biofilm formation. The application of antimicrobial substance as a potential biocide for sulfate reducing bacteria growth control could be of great interest to the petroleum industry.

The level of Inhibition of Microbial Functional Group Activities by Some Oxidizing Agents Commonly used as Biocides in Oil field Operations.

Aim: To determine the level of inhibition of microbial functional group activities such as the ability to reduce sulfate to sulfide by sulfate reducing bacteria (SRB), reduce nitrate to nitrite by the heterotrophic nitrate reducing bacteria (hNRB), and oxidize sulfide and reduce nitrate by sulfide oxidizing, nitrate reducing bacteria (so-NRB) by some oxidizing biocides like chlorine, bromine and ozone. Methodology: Samples of the oxidizing biocides were obtained from Microcheck and the inhibition of some functional group activities in produced and injection water samples were determined using CSB-K medium. Results: Ozone was found to be more effective than chlorine and bromine in the inhibition of functional group activities at lower concentrations. Conclusion: More research effort is required to see if ozone can work in synergy with other biocides to improve on its efficiency.

Sulfate reducing bacteria as secondary and necessary pathogens in black band disease of corals / Bacterias reductoras de sulfato como patógenos secundarios y necesarios en la enfermedad de la banda negra de coral

Black band disease (BBD) is a complex, polymicrobial disease that consists of cyanobacteria, sulfide-oxidizing and sulfate-reducing bacteria (SRB), and heterotrophic bacteria. The cyanobacterium Roseofilum reptotaenium has been implicated as the primary pathogen of BBD, but other consortium members may be secondary pathogens that are necessary to the development of the disease. It is known that populations of the sulfate-reducing bacterium Desulfovibrio are present in BBD and that these populations generate sulfide within the band as a byproduct of dissimilatory sulfate reduction. It is also known that exposure of healthy corals to sulfide leads to cell lysis and coral tissue death. Previous work showed that when freshly collected BBD, which easily infects healthy corals, is exposed to sodium molybdate, a specific inhibitor of sulfate reduction, infection does not occur. In this study we examined the effect of sodium molybdate on infection of corals by a unialgal culture of R. reptotaenium. Coral fragments of Montastraea cavernosa and Siderastrea siderea were transferred into two experimental aquaria, one a control with only artificial seawater (ASW) and the second containing ASW and 2mM sodium molybdate. Small mats of cultured R. reptotaenium were inoculated onto the surface of experimental coral fragments. Both M. cavernosa (n = 6) and S. siderea (n=4) became infected and developed BBD-like infections in the control tank, while there were temporary attachments to, but no successful infection of M. cavernosa (n=3) or S. siderea (n=2) in the experimental tank containing sodium molybdate. The results of this study reveal that a secondary pathogen is essential to the infection process and development of BBD in scleractinian corals. Specifically, SRB such as Desulfovibrio are required for the development of BBD on the coral host. This is the first step in understanding the roles of secondary pathogens in a complex, polymicrobial coral disease.

La enfermedad de la Banda Negra (BBD) es una enfermedad polimicrobiana compleja, que consiste en las cianobacterias, sulfuro oxidante y bacterias reductoras de sulfato (SRB) y bacterias heterotróficas. La cianobacteria Roseofilum reptotaenium se considera como el principal patógeno de BBD, pero otros miembros del consorcio pueden ser patógenos secundarios que son necesarios para el desarrollo de la enfermedad. Se conoce que las poblaciones de la bacteria reductora de sulfato Desulfovibrio están presentes en BBD y que estas poblaciones generan sulfuro dentro de la banda como un subproducto de la reducción del sulfato. También se conoce que la exposición de los corales sanos a sulfuro conduce a la lisis celular y la muerte del tejido de coral. Trabajos previos muestran que cuando recién colectado el tejido con BBD, que infecta fácilmente corales sanos, se expone al molibdato de sodio, un inhibidor específico de la reducción del sulfato, la infección no se produce. En este estudio analizamos el efecto del molibdato de sodio sobre la infección de los corales en un cultivo unialgal de R. reptotaenium. Fragmentos de coral de Montastraea cavernosa y Siderastrea siderea se transfirieron a dos acuarios experimentales, uno control con solo agua de mar artificial (ASW) y el segundo que contenía ASW y molibdato de sodio 2mM. Pequeñas esteras de cultivo R. reptotaenium se inocularon en la superficie de fragmentos experimentales de coral. Tanto M. cavernosa (n=6) y S. siderea (n=4) se infectaron y desarrollaron infecciones BBD- como en el tanque de control, mientras que había adjuntos temporales, sin infección exitosa en M. cavernosa (n=3) o S. siderea (n=2) en el tanque experimental con molibdato de sodio. Los resultados de este estudio revelan que un patógeno secundario es esencial para el proceso de infección y el desarrollo de BBD en corales escleractíneos. Específicamente, SRB como Desulfovibrio son necesarios para el desarrollo de BBD en el coral hospedero. Este es el primer paso en la comprensión de las funciones de los patógenos secundarios en una enfermedad polimicrobiana compleja de coral.

Study on application of biological iron sulfide composites in treating vanadium-extraction wastewater containing chromium (VI) and chromium reclamation.

In this study, the Cr(VI)-resistant properties and regeneration characteristics of biological iron sulfide composites were investigated, which consist of sulfate reducing bacteria (SRB) and its in situ synthesized nanosized iron sulfides. Then the application of the composites in treating vanadium-extraction wastewater containing high concentration Cr(VI) and reclaiming Cr were performed. It was found that SRB in composites still survived after being used to treat vanadium-extraction wastewater, which could reduce reaction products Fe3+ and sulphur into Fe2+ and S2- by using them as the electron acceptors and thus regenerating biological iron sulfide composites. The SRB also could be resistant to 600 mgl-1 Cr(VI) and reduce it gradually. Based on the Cr(VI)-resistant properties and regeneration characteristics of the composites, a reduction-regeneration recirculation process for treating vanadium-extraction wastewater and reclamation of Cr was developed. The results indicated that the contaminants in effluent reached the Chinese discharge standard of pollutants for vanadium industry (GB 26452-2011), i.e. the concentration of total Cr(TCr) was less than 0.912 mgl-1, Cr(VI) was less than 0.017 mgl-1 and V was less than 0.260 mgl-1. After 10 cycles of treatment, the Cr2O3 content in sludge reached 41.03%, and the ratio of Cr2O3/FeO was 7.35. The sludge reached the chemical and metallurgical (hydrometallurgy) grade of chromite ore and could be reclaimed.

Methodological aspects for the culture and quantification of heterotrophic sulfate-reducing bacteria / Aspectos metodológicos para el cultivo y la cuantificación de bacterias heterotróficas sulfato-reductoras

This paper presents a comparison of various methods for culture, quantification, and maintenance of sulfate-reducing bacteria (SRB) under laboratory conditions, using liquid and semisolid media for water and soil samples. Starkey, Postgate B, API and modified Baars media were used with an incubation time of 21 days in a GasPack™ anaerobic jars type. The modified Baars medium was more efficient for the quantification of SRB in both liquid and semisolid media when compared with other culture media tested, detecting differences of three orders of magnitude in soil samples and in two orders for water samples at 8 days of incubation. The semisolid modified Baars medium in Petri dishes allowed the isolation of pure cultures of SRB by the streak plate method. It was found that strains in liquid modified Baars medium remain viable for up to three months, while in the same semisolid medium were kept only one month.

Este trabajo presenta una comparación de diversos métodos para el cultivo, cuantificación, y mantenimiento de bacterias sulfato-reductoras (BSR) en condiciones de laboratorio, utilizando medios líquidos y semisólidos para muestras de agua y suelo. Se utilizaron los medios de cultivo de Starkey, Postgate B, API y Baars modificado con un tiempo de incubación de 21 días en jarras de anaerobiosis tipo GasPack™. Se determinó que para la cuantificación de SRB, tanto en medio líquido como en semisólido, el medio Baars modificado es más eficiente comparado con los demás medios de cultivo probados, detectando diferencias de tres órdenes de magnitud en muestras de suelo y de dos órdenes de magnitud en muestras de agua a los 8 días de incubación. El medio Baars modificado semisólido servido en placas de Petri permitió el aislamiento de cultivos puros de BSR mediante siembra por agotamiento. Se encontró que en el medio modificado de Baars líquido las cepas se mantienen viables hasta por tres meses mientras que en el mismo medio semisólido sólo se mantienen durante un mes.

Evaluation of microorganisms with sulfidogenic metabolic potential under anaerobic conditions

The aim of this work was to identify groups of microorganisms that are capable of degrading organic matter utilizing sulfate as an electron acceptor. The assay applied for this purpose consisted of running batch reactors and monitoring lactate consumption, sulfate reduction and sulfide production. A portion of the lactate added to the batch reactors was consumed, and the remainder was converted into acetic, propionic and butyric acid after 111 hours of operation These results indicate the presence of sulfate-reducing bacteria (SRB) catalyzing both complete and incomplete oxidation of organic substrates. The sulfate removal efficiency was 49.5% after 1335 hours of operation under an initial sulfate concentration of 1123 mg/L. The SRB concentrations determined by the most probable number (MPN) method were 9.0x10(7) cells/mL at the beginning of the assay and 8.0x10(5) cells/mL after 738 hours of operation.

Simultaneous removal of NOX and SO2 in exhausted gas through landfill leachate.

Simultaneous removal of NOx and SO2 from exhausted gas were investigated by studying co-culture of sulfate reducing bacteria and anaerobic denitrifying bacteria, separated from landfill leachate. When H2S, generated by sulfate reducing bacteria was chosen as the sole electron donor for anaerobic denitrifying bacteria, the co-culture system demonstrated a faster NO removal rate, higher stability and better permanence. When the feed gas flow rates of N2 and SO2 were maintained constant at 0.1 m3/h and 16 ml/min respectively, the maximum NO-removal rate could be achieved at over 92% with NO feed gas kept between 2-6 ml/min, while the SO2 removal rate was always above 95%. Long-term continuous removal of NO exhibited an evident periodicity of five days, however, the fluctuation range of NO-removal was decreasing. Moreover, the decrease of the gas flow rate and the increase in NO inlet concentration could contribute to a higher NO-removal rate.

Bacterial contamination of automotive fuels in a tropical region: the case of Costa Rica

Microbial contamination of fuel has been the cause of several problems in transportation and storage of these products. Due to the lack of previous studies related to these problems in Costa Rica, bacterial quality was evaluated biannually in automotive fuels stored in the four oil distribution facilities of the Costa Rican Petroleum Refinery (RECOPE). In 12 oil storage tanks, for a total of 96 samples, mesophilic, heterotrophic aerobic/facultative counts (ASTM D6974-04) and identification of bacteria presented in regular gas, premium gas and diesel from the bottom and superior part of the tanks were done; in the samples containing an aqueous phase, sulfate reducing bacteria (SRB) were also quantified by the most probable number technique (MPN), according to the ASTM D4412-84 standard. The higher contamination was shown at the bottom of the tanks (populations up to 10(4) UFC/l), especially if there was accumulated water, in which case populations reached 10(8) UFC/l. The most contaminated fuel was diesel (counts up to 10(4) UFC/l), whereas the less contaminated was premium gas. The less contaminated fuels were from the facilities of La Garita and Barranca, whereas the most contaminated were from Ochomogo. Nevertheless, the quantified populations did not cause significant alteration in quality physicochemical parameters in the samples analyzed. A total of 149 bacterial strains were isolated, 136 (91.3%) Gram positive and 13 (8.7%) Gram negative. The most frequent genera were Staphylococcus (24.0%), Micrococcus (21.9%), Bacillus (18.8%) and Kocuria (11.5%) among Gram positive bacteria and Pseudomonas (7.3%) among Gram negative bacteria. The majority of these genera have been found as fuel contaminants or even as degraders of this kind of products; nevertheless, some species for which their appearance or growth in hydrocarbons have not been described were found with low frequencies. SRB were present in counts up to 10(5) MPN/l in 42.9% of water containing samples (including all from diesel tanks), indicating biocorrosion processes risk in fuel transport and storage systems. From the findings in this study it is recommended to give a frequent maintenance to fuel containers, based on continuous drainage and removal of accumulated water, antimicrobial agent addition and microbial quality monitoring in country’s fuels. Rev. Biol. Trop. 57 (3): 489-504. Epub 2009 September 30.

Se evaluó semestralmente durante dos años la calidad bacteriana de los combustibles almacenados en los cuatro planteles de la Refinadora Costarricense de Petróleo (Costa Rica). Para un total de 96 muestras se realizaron recuentos (norma ASTM D6974-04) e identificación de las bacterias presentes en gasolina regular, gasolina súper y diesel en los niveles superior e inferior de los tanques contenedores; en las muestras con fase acuosa se cuantificaron las bacterias reductoras de sulfato (SRB, norma ASTM D4412-84). La mayor contaminación se observó en el fondo de los tanques, sobretodo si se presentó una capa de agua almacenada. El diesel fue el combustible más contaminado, sin embargo, no se observó alteración importante en los parámetros fisicoquímicos de las muestras evaluadas. Se aislaron 149 cepas, 136 (91.3%) Gram positivas y 13 (8.7%) Gram negativas; los géneros más frecuentes fueron Staphylococcus (24.0%), Micrococcus (21.9%), Bacillus (18.8%), Kocuria (11.5%) y Pseudomonas (7.3%). Con bajas frecuencias se encontraron algunas especies para las que no se ha descrito su aparición o crecimiento en hidrocarburos. Las SRB se presentaron con recuentos de hasta 105 MPN/l en un 42.9% de las muestras con agua residual, principalmente en diesel, lo cual es indicativo de alerta por biocorrosión. A partir de los resultados se recomienda dar un mantenimiento frecuente a los contenedores, la adición de compuestos antimicrobianos y el monitoreo de la calidad microbiana de los combustibles del país.

Evaluación del molibdato y nitrato sobre bacterias sulfato-reductoras asociadas a procesos de corrosión en sistemas industriales / Evaluation of molybdate and nitrate on sulphate-reducing bacteria related to corrosion processes in industrial systems

Se estudió la cinética de crecimiento de bacterias sulfato-reductoras (BSR) y la biotransformación de sulfato a sulfuro de hidrógeno bajo condiciones de laboratorio, para establecer el efecto inhibitorio de sales de molibdato y nitrato de sodio. Los microorganismos estudiados fueron aislados del agua de producción contenida en un sistema de transporte de gas natural, donde se encontraban relacionados con procesos de corrosión influenciada microbiológicamente. Con 5 mM de molibdato se obtuvo una reducción de células libres a niveles no detectables y de seis órdenes de magnitud en las biopelículas, con una disminución del sulfuro de alrededor del 100%. Con 75 mM de nitrato se observó una reducción de cuatro y dos órdenes de magnitud en las células libres y en las adheridas en forma de biopelículas, respectivamente, con una disminución del sulfuro de alrededor del 80%. La reducción de la tasa de corrosión observada sustenta la posibilidad de emplear estas sales como biocidas no convencionales no contaminantes del medio ambiente, para el control y mitigación efectiva de los procesos de biocorrosión interna de tanques de almacenamiento y de líneas de transporte en sistemas industriales de gas natural y petróleo.

The sulfate-reducing bacteria growth kinetics and the biotransformation of sulfate into hydrogen sulfide were studied under laboratory conditions, using batch and continuous assays to determine the effect of molybdate and nitrate as metabolic inhibitors. The microorganisms were isolated from water coming from a natural gas dehydration plant, where they were associated with Microbiologically Influenced Corrosion (MIC) processes, and later cultured in planktonic and sessile states. The addition of 5 mM molybdate showed a growth reduction to levels of non - detectable floating cells and a six order of magnitude reduction in biofilms, concomitant with a sulfide decrease of around 100% in all cultures inhibited by this compound. The addition of 75 mM nitrate showed a four order of magnitude reduction in free bacterial cells and a two order of magnitude reduction in adhered bacterial cells, respectively, as well as a sulfide decrease of around 80%. The decreased corrosion rate detected suggests that these inorganic salts could be nonconventional biocides for an effective and environmentally non contaminant way of controlling and mitigating internal biocorrosion processes in storage tanks and pipelines in natural gas and petroleum industrial systems.

Sulfate-reducing Bacteria and Research Progress of Cr(Ⅵ ) Reduction by Sulfate-reducing Bacteria / 微生物学通报

Sulfate-reducing bacteria (SRB) are widespread in the environment. SRB are obligate anaerobes and capable of dissimilatory reduction of sulfate. SRB have application prospects in the control of environmental pollution due to that many pollutants can be removed by SRB. The biological characteristics and metabolic mechanisms of SRB are introduced, and the application of SRB in the treatment of environmental pollution is described in this paper. The research progress of Cr(Ⅵ ) reduction and Cr(Ⅵ ) removal from wastewater by SRB is reviewed, and future direction of research on the control of Cr(Ⅵ ) pollution by SRB is also analysed.

Research Progress in Microbiol Removal of Sulfur Dioxide / 微生物学通报

SO2 is one of the main pollutants in the air. Tradational disposal methods are limited in the industrial application owing to their high cost. Some foreign scholars began to research in microbial treatment of SO2 both in laboratory test and in full-scale test in recent years and good results were achieved. This method can significantly lowering costs and acquire sulfur product and microbial biomass protein of high quality. The microbial method which is simple, effect and of low costs can satisfy needs of industry and give attention to environmental, economical and social benefits, therefore, it will have amplitude and well application prospects.

CHARACTERISTICS OF THIOBACILLUS DENITRIFICANS AND THE EFFECT ON THE GROWTH OF SRB / 微生物学通报

In this paper, a strain of Thiobacillus denitrificans was isolated from soil The optimal pH for growth was 7 0 In mixed cultivation with SRB, the number of SRB was determined The results show that Thiobacillus denitrificans can restrain the growth of SRB, and decrease the concentration of corrosive metabolic production caused by SRB The corrosion rate reduces as a result So it is propitious to prevent and cure the corrosion caused by SRB