Population Changes of Eubacteria, Sulfate-Reducing Bacteria and Methanogenic Archaea in an Anaerobic Reactor Processing Ethanol Distillery Vinasse

Abstract The microbiological characterization by molecular techniques (DGGE and quantitative PCR) of Archaea, Bacteria domain and sulfate-reducing bacteria (SRB) from a laboratory scale Up-flow Anaerobic Sludge Blanket (UASB) processing sugar cane vinasse was performed during the operational phase with increasing organic loads. The organic load removal efficiency was between 97% and 75% for volumetric organic loads (VOL) in the range of 0.6 to 15.4 kgCOD.m-3.d−1 and for higher VOL (until 27.0 kgCOD.m-3 .d−1) the removal efficiency decreased to 48%. Archaea represented the majority of the estimated population (107 copies of 16S RNA ribosomal gene. mL-1) followed by bacteria (106 copies of 16S RNA ribosomal gene. mL-1) and sulfate-reducing bacteria (SRB) (105 copies of dsrB gene. mL-1). There was a significant difference between the populations of Archaea and SRB with increasing VOL. DGGE profiles show differences among populations with increasing VOL, especially with respect to sulfate-reducing bacteria. The presence of SRB together with a high sulfate removal percentage (97%) of about 15 kgCOD.m-3d-1h, indicates the establishment of a sulfidogenic process.

Influência da razão DQO/[SO 4 2- ] e da concentração de Na + na remoção de matéria orgânica e sulfato em reator UASB / Influence of COD/[SO4 2-] ratio and Na+ concentration on organic matter and sulfate removal in UASB reactor

RESUMO O tratamento anaeróbio de efluentes industriais ricos em sulfato e sódio pode ser limitado por vários fatores, dentre os quais a relação DQO/sulfato, a concentração de SO4 2- e a concentração de sódio. Entre os fenômenos investigados estão a competição entre bactérias redutoras de sulfato e arquéias metanogênicas por substrato, a concentração de sulfeto gerado na sulfetogênese e a inibição por cátions. Este trabalho apresentou e discutiu os resultados da operação de um reator UASB, com volume útil de 10,5 L e vazão de 16,0 L.dia-1. Utilizou-se glicose, acetato e metanol (DQO≈2.000 mg.L-1), sob razão DQO/sulfato variando de 0,20 a 6,15, concentração de sulfato de 0,3 a 10,0 g.L-1 e concentração do cátion Na+ de 0,70 g.L-1 a 5,40 g.L-1. A eficiência de remoção de DQO foi mantida acima de 80%, e a concentração de sulfato removida ficou limitada a cerca de 800 mg.L-1 durante o período experimental. A atividade metanogênica específica do lodo (AME) foi de 0,630 gCH4-DQO.gSSV-1 até carga de sulfato de 0,300 gSO4 2-.L-1 e (razão DQO/sulfato de 6,15), declinando até atingir 0,168 gCH4-DQO.gSSV-1 (queda de 70%) na última fase com 10,000 gSO4 2-.L-1 (razão DQO/[SO4 2-] de 0,24) e concentração de Na+ de 5,41±0,10 g.L-1. O aumento crescente das concentrações de sódio e sulfato, mantendo-se a concentração de matéria orgânica constante, permitiu constatar a inibição da metanogênese por sódio e sulfeto, mesmo em concentrações abaixo das consideradas inibidoras individualmente. O efeito do sódio na estrutura do grânulo foi determinante na inibição da metanogênese observada.

ABSTRACT The anaerobic treatment of industrial wastewater presenting high concentrations of sulfate and sodium may be limited by several factors, including the ratio COD / [SO4 2-], the concentration of SO4 2- and the concentration of Na+. The competition between sulfate reducing bacteria and methanogenic archaea for substrate, the concentration of sulfide generated in sulfidogenesis, and the inhibition by cations are among the main phenomena that have been investigated. This paper presented and discussed the results of a UASB reactor with a volume of 10.5 L and flowrate of 16.0 L.day-1, subjected to increasing COD/sulfate ratio whereas influent COD was kept constant. Glucose, acetate and methanol (≈2,000 COD mg.L-1) were the carbon sources, and the COD/sulfate ratio ranged from 0.20 to 6.15 for sulfate concentrations of 0.3 to 10.0 g.L-1, Na + concentrations of 0.70 g.L-1 to 5.40 g.L-1. The COD removal efficiency was maintained above 80%, and the sulfate removal was limited to 800 mg.L-1 throughout the experimental period. The specific methanogenic activity (SMA) was 0.630 gCH4-DQO.gSSV-1 for 0.300 gSO4 2-.L-1 (COD/sulfate of 6.15), decreasing to 0.168 (70% decrease) in the last phase (COD /sulfate of 0.24) at concentrations of 10.000 gSO4 2-.L-1 and of Na+ 5.41±0.10 g.L-1. The progressive increase of sulfate and sodium concentrations at constant influent COD resulted in methanogenesis inhibition by sodium and sulfide, even at concentrations bellow the inhibition limits, if individually considered. The effect of sodium in the granule structure was determinant for methanogenesis inhibition.