Efeitos da relação DQO/SO4-2 e dos doadores de elétrons na riqueza microbiana de reatores utilizados no tratamento de águas residuárias ácidas ricas em sulfato

Abstract

Biological sulfate reduction is widely used for treating sulfate-containing wastewaters. In this research, the biological reduction of sulfate was evaluated according to the chemical oxygen demand (COD)/sulfate (SO4-2) ratio and electron donors using batch reactors operated over 88 days. The reactors were fed with synthetic acidic wastewater at pH 4.0 and the electron donors were ethanol, sodium lactate and cheese whey analyzed individually on the COD/SO4-2 ratio of 1 and 2. On the COD/SO4-2 ratio of 1, the COD and sulfate removal raised high levels to all electron donors, above 68% for COD and 73% for sulfate. However, on the COD/SO4-2 ratio of 2, only lactate resulted in high removals rates of COD and sulfate (71 ± 17% and 90 ± 6%, respectively). MPN technique was used for sulfate-reducing bacteria (SRB) quantification and the results demonstrated that the SRB population increased 102 times in the presence of ethanol and 103 in the presence of lactate, on the COD/SO4-2 ratio of 1.0. However, the SRB population decreased with the increase in the COD/SO4-2 ratio for ethanol and lactate while cheese whey has not promoted the growth of SRB in any COD/SO4-2 studied. The biomass was characterized using denaturing gradient gel electrophoresis (DGGE). For the Bacteria Domain and SRB group, a high microbial richness and low similarity were obtained compared to the inoculum while in the Archaea Domain no major changes could be observed when compared to even inoculum or among the evaluated conditions. The phylogeny of the sulfate-reducing group showed predominance of Desulfovibrio species for all substrates studied, whereas all species were found to conduct the incomplete oxidation of organic matter. However, on COD/SO4-2 ratio of 1.0 and lactate, SRB species such as Desulfacinum were found, responsible to perform a key role in the complete oxidation of organic matter.