Volatile fatty acid (VFA) profile is an important parameter in anaerobic reactors because it enables the assessment of metabolic pathways. Volatile fatty acids were monitored during sulfate reduction in a UASB (upflow anaerobic sludge blanket) reactor treating 2 g/L sulfate concentration and with the organic loading increasing from 3.5 kg COD/m 3 d to 5.9 kg COD/m 3 d, for a 1-day residence time. In the absence of recirculation, the best outcome (65% reduction) was noticed with the lowest organic loading (3.55 kg/m 3 d). When recirculation was applied, sulfate reduction yields increased to 89%, corresponding to a sulfate removal rate of 1.94 kg SO 4 2À /m 3 d. The reactor performance was discussed in relation to microbial diversity and metabolic pathways. At high organic loading, two metabolic pathways account for lactate degradation: (i) lactate is oxidized to acetate and carbon dioxide by the incomplete-oxidizer SRB (sulfate-reducing bacteria) Desulfomonas, Desulfovibrio, Desulfolobus, Desulfobulbus and Desulfotomaculum spp.; (ii) lactate is converted to acetate by fermenting bacteria such as Clostridium sp. High propionate concentrations imply that there are low sulfate reduction efficiencies.
The use of sulfate-reducing bacteria (SRB) in passive treatments of acidic effluents containing heavy metals has become an attractive alternative biotechnology. Treatment efficiency may be linked with the effluent conditions (pH and metal concentration) and also to the amount and nature of the organic substrate. Variations on organic substrate and sulfate ratios clearly interfere with the biological removal of this ion by mixed cultures of SRB. This study aimed to cultivate a mixed culture of SRB using different lactate concentrations at pH 7.0 in the presence of Ni, Mn and Cu. The highest sulfate removal efficiency obtained was 98 %, at a COD/sulfate ratio of 2.0. The organic acid analyses indicated an acetate accumulation as a consequence of lactate degradation. Different concentrations of metals were added to the system at neutral pH conditions. Cell proliferation and sulfate consumption in the presence of nickel (4, 20 and 50 mg l(-1)), manganese (1.5, 10 and 25 mg l(-1)) and copper (1.5, 10 and 25 mg l(-1)) were measured. The presence of metals interfered in the sulfate biological removal however the concentration of sulfide produced was high enough to remove over 90 % of the metals in the environment. The molecular characterization of the bacterial consortium based on dsrB gene sequencing indicated the presence of Desulfovibrio desulfuricans, Desulfomonas pigra and Desulfobulbus sp. The results here presented indicate that this SRB culture may be employed for mine effluent bioremediation due to its potential for removing sulfate and metals, simultaneously.
Among the greatest challenges to the full implementation of biological sulfate reduction are the cost and availability of the electron source. With the development of the biofuel industry, new organic substrates have become available. Therefore, this work sought to compare the performance of a sulfidogenic process utilizing either lactate or glycerol as the substrate for sulfate-reducing bacteria (SRB) growth. Although sulfate reduction is energetically more favorable with lactate, glycerol is a less expensive alternative because excess production is forecasted with the worldwide development of the biodiesel industry. Continuous experiments were performed in a fluidized bed (FB) reactor containing activated carbon as a carrier for a mixed bacterial population composed of sulfate-reducing and fermentative bacteria. During the lactate-fed phases, incomplete oxidation of lactate to acetate by SRB was the dominant metabolic pathway resulting in as much as 90 % sulfate reduction and high acetate concentrations (2.7 g L(-1)). Conversely, in the glycerol-fed phases, glycerol degradation resulted from syntrophic cooperation between sulfate-reducing and fermentative bacteria that produce butyrate along with acetate (1.0 g L(-1)) as oxidation products. To our knowledge, this is the first report of butyrate formation during sulfate reduction in a glycerol-fed continuous-flow reactor. Sulfate concentrations were reduced by about 90 % (from 2,000 to 100-300 mg L(-1)) when glycerol was being fed to the reactor. Since the FB reactor was able to stand a change from lactate to glycerol, this reactor is recommended as the preferred option should glycerol be selected as a cost-effective alternative to lactate for continuous sulfate reduction.
RESUMO ABSTRACT The aim of this study was to characterize and evaluate the tratability of wastewater produced in the campus of the Federal University of Ouro Preto (UFOP). The physical-chemical) and anaerobically (50% efficiency, AME = 0,0579 gDQO CH4 /gSSV.d).
Sulfate reducing bacteria (SRB) can be used as an alternative biotechnology to promote passive treatment of industrial effluents. Treatment efficiency however depends on pH and metals content of the effluent and also on the quantity of organic matter available. As COD/sulfate ratio varies, sulfate consumption changes. It is commonly assumed that the ideal COD/sulfate ratio is around 0.67. The aim of this work was to optimize the growth and sulfate reduction capacity of mixed bacterial cultures. Samples were cultured using modified Postgate C medium. Metals (Cu, Mn and Ni) were added to the medium in order to study bacterial resistance. Maximum sulfate reducing (98%) was achieved for lactate containing medium, pH 7.0. However, with ethanol containing medium sulfate removal was of about 50%. Acetate production was observed in all cases. Results shown that lactate was more efficient than ethanol for sulfate biological reduction and pH neutralization.
Doutor em Agronomia (solos, nutrição de plantas)/ESALQ-USP. Programa de pós-graduação em Qualidade Ambiental da Universidade Federal de Uberlândia. (lucasazevedo@ufu.br). Resumo Este trabalho teve como objetivo avaliar o potencial da Eleocharis acutangula no tratamento do efluente de uma central de processamento de alimentos vegetais, por meio de leito cultivado em escala laboratorial. Analisou-se a influência do substrato e das plantas na remoção de DQO, sólidos totais, turbidez, nitrogênio, fósforo e estabilização do pH. O experimento foi montado em duas caixas de vidro em casa de vegetação e teve duração de onze meses. O substrato utilizado foi cascalho de rio e apenas um dos leitos recebeu E. acutangula. O leito com as macrófitas reduziu 87,9% de fósforo, 80,8% de nitrogênio e 92,69% de DQO em relação ao efluente bruto. Quanto ao controle, o leito experimental reduziu 54,5% de fósforo, 33,0% de nitrogênio e 81,4% de DQO. De acordo com os parâmetros após o tratamento em ambos os leitos, o efluente se tornou apto para disposição final, conforme os padrões da Resolução do CONAMA Nº 430/2011 (BRASIL, 2011) e Deliberação Conjunta COPAM-CERH Nº 01/2008 (MINAS GERAIS, 2008). Considerando as reduções observadas, o estudo mostrou que a espécie tem potencial no tratamento de águas residuais.Palavras-chave: efluente industrial, leito cultivado, rizofiltração. AbstractThe objective of this work was to evaluate the potential of the Eleocharis acutangula in the treatment of the wastewater of a central of vegetable foods processing through a laboratory scale wetland. Was analyzed the influence of the substrate and the species on the removal of COD, total solids, turbidity, nitrogen, phosphorus and pH stabilization. The experiment was set upin two glass boxes in a greenhouse and lasted for eleven months. The substrate used was river gravel and only one of the beds received E. acutangula. The bed with the macrophytes reduced 87.9% of phosphorus, 80.8% of nitrogen and 92.69% of COD in relation to the raw effluent. Regarding the control, the experimental bed reduced 54.5% of phosphorus, 33.0% of nitrogen and 81.4% of COD. According to the analyzed parameters, after the treatment in both beds the effluent became fit for final disposal, according to the standards of CONAMA Resolution N° 430/2011 (BRASIL, 2011) and COPAM-CERH Joint Resolution N° 01/2008 (MINAS GERAIS, 2008). Considering the reductions observed, the study showed that the species has potential in the treatment of wastewater.
As veredas, uma fitofisionomia encontrada no Cerrado responsável pela manutenção de cursos d’água de bacias hidrográficas, são consideradas áreas de preservação permanente. Portanto, seus limites, vegetações naturais e qualidade dos recursos devem ser preservados. O objetivo deste trabalho foi avaliar a qualidade dos sedimentos em cinco áreas alagadas de veredas na região de Uberlândia (MG), sendo três rurais e duas urbanas, por meio da análise de dezoito elementos metálicos. Os elementos avaliados foram importantes para a análise de qualidade, pois através dos métodos estatísticos utilizados foi possível diferenciar as áreas alagadas com base na composição química dos sedimentos. As alterações no uso e ocupação do solo decorrentes de atividades antrópicas, foram um dos principais fatores na diferenciação das características dos sedimentos dentre as veredas monitoradas. A área com maior quantidade de elementos em não conformidade com as legislações vigentes foi uma das veredas urbanas. O cádmio, cromo, cobre e zinco foram os metais encontrados em concentrações acima dos valores de referência de qualidade estabelecidos em Minas Gerais. Esse estudo também mostrou que as veredas com mais intervenções, exercem maior pressão na qualidade dos sedimentos do que nos ambientes preservados.
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