Abstract Biological acid mine drainage treatment depends significantly on inoculum origin, pH, COD/sulfate ratio, and carbon source. In this study, the performance and microbial diversity of anaerobic batch reactors used for sulfate reduction was evaluated. A medium COD/sulfate ratio of 1.14 ± 0.10 was used, and the evaluation was performed in two steps: Phase 1, based on the inoculum source (autochthonous, AUT, and non-autochthonous, N-AUT); and Phase 2, based on the carbon source (lactate, ethanol, and formate) and low pH. In Phase 1, the sulfate removal using both AUT and N-AUT biomasses were similar, 53% and 59%, respectively. In Phase 2, ethanol and lactate as electron donors yielded similar sulfate removal efficiencies of 42% and 44%, respectively, at neutral pH. When the initial pH was reduced from 4 to 3, sulfate removal using formate remained nearly constant at 34%, whereas it reduced from 43% to 30% with lactate, and dropped significantly from 18% to 7% with ethanol. Denaturing gradient gel electrophoresis analyses for sulfate-reducing bacteria revealed their presence in all samples. Microbial activity and sulfate removal obtained for AUT cultures indicated that they possess the potential for use in local acid mine drainage decontamination processes.

ABSTRACT This work aimed at evaluating the effect of recirculation ratio on the degree of mixing in the flow of a structured bed reactor. Stimulus-response assays were carried out with hydraulic retention times of 6 h and 12 h, subjected to recirculation ratios of 0, 1, 2, 3, and 4. The assays were undertaken with dextran blue as a tracer and without aeration. The results fitted a compartment model, allowing the determination of the mixed-flow and plug-flow volumes inside the reactor. The model application showed that recirculation ratios between 1 and 3 do not increase the mixed-flow volume of the reactor. Higher mixed-flow volumes were obtained at recirculation rates higher than 4 for both 6 h and 12 h of hydraulic retention times. The results obtained in this research are important for future applications of this reactor configuration, promoting a mixed flow in the reactor with a minimum recirculation ratio.

Este trabalho descreve o desenvolvimento e validação de um método de detecção de aldicarbe e seus metabólitos por cromatografia líquida de alta eficiência (HPLC) em amostras líquidas sem pré-tratamento. O sistema HPLC foi equipado com coluna C-18 e fase móvel composta de água e acetonitrila empregando gradiente de eluição linear. O detector UV foi operado em 210 nm. Metomil foi utilizado como padrão interno. Água e meio sintético foram utilizados como solventes. O método foi linear de 0,49-15,0 mg L-1 (r² > 0,9985), 0,1-5,0 mg L-1 (r² > 0,9974) e 0,1-5,0 mg L-1 (r² > 0,9987) para o aldicarbe, sulfóxido de aldicarbe e sulfona de aldicarbe, respectivamente. A linearidade do método foi confirmada pelo teste F (ANOVA) através dos testes de ajuste do modelo linear, validade da regressão e eficiência da regressão. Os limites de detecção na água e em meio sintético foram de 0,391/0,440 mg L-1, 0,069/0,192 mg L-1 e 0,033/0,068 mg L-1 para o aldicarbe, sulfóxido de aldicarbe e sulfona de aldicarbe, respectivamente. O tempo total de análise foi de 22 minutos. Na aplicação do método, avaliou-se a degradação do aldicarbe no reator anaeróbio horizontal de leito fixo (RAHLF) em diferentes condições operacionais (metanogênese, sulfetogênese e desnitrificação).

This study describes the development and validation of a high-performance liquid chromatography (HPLC) method for detecting aldicarb and its residues in liquid samples without pretreatment. The HPLC system was equipped with a C-18 column and the mobile phase was composed of a mixture of water and acetonitrile using a linear gradient elution. The UV detector was utilized at 210 nm. Methomyl was used as an internal standard. Water and synthetic medium were used as solvents. The method was linear from 0.49-15.0 mg L-1 (r² > 0.9985), 0.1-5.0 mg L-1 (r² > 0.9974) and 0.1-5.0 mg L-1 (r² > 0.9987) for aldicarb, aldicarb sulfoxide and aldicarb sulfone, respectively. The linearity of the method was confirmed by the ANOVA F-test through adjustment of the linear model, validity of the regression and efficiency of the regression tests. The limit of detection in water and synthetic medium were of 0.391/0.440 mg L-1, 0.069/0.192 mg L-1 and 0.033/0.068 mg L-1 for aldicarb, aldicarb sulfoxide and aldicarb sulfone, respectively. Total time of analysis was of 22 min. In the application of the method, the aldicarb degradation in horizontal-flow anaerobic immobilized biomass (HAIB) reactor was evaluated under different conditions (methanogenic, sulfidogenic and denitrifying).