Passive biological systems such as sulfate-reducing biochemical reactors have shown promise for treatment of mine drainage because of their low cost, minimal maintenance, and constructability in remote locations. However, few criteria exist for their design and operation. In particular, the impact of the choice of carbon substrate is poorly understood. This study represents the first to directly compare the effect of simple and complex organic substrate on microbial communities present in pilot-scale biochemical reactors treating mine drainage. Three organic substrates were evaluated: ethanol (ETOH), hay and pine wood chips (HYWD), and corn stover and pine wood chips (CSWD). Microbial community compositions were characterized by cloning and sequencing of 16S rRNA and apsA genes corresponding to the sulfur cycle. Quantitative polymerase chain reaction was applied to quantify Desulfovibrio-Desulfomicrobium spp. and methanogens. Results revealed differences in microbial compositions and relative quantities of total and sulfate-reducing bacteria among reactors. Notably, the greatest proportion of sulfate-reducing bacteria was observed in the ETOH reactors. HYWD and CSWD reactors contained similar bacterial communities, which were highly complex in composition relative to the ETOH reactors. Methanogens were found to be present in all reactors at low levels and were highest in the lignocellulose-based reactors. Interestingly, higher proportions of aerobic Thiobacillus spp. were detected in two reactors that experienced an oxygen exposure during operation. This study demonstrates that both substrate and environmental stress influence both microbial community composition and diversity in biochemical reactors treating mine drainage. While there were no significant differences in performance observed over the time scale of this study, potential long-term implications of the differing microbial communities on performance are discussed.

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Here, we introduce a new technique called embedded passivated-electrode insulator-based dielectrophoresis (EπDEP) for preconcentration, separation, or enrichment of bioparticles, including living cells. This new method combines traditional electrode-based DEP and insulator-based DEP with the objective of enhancing the electric field strength and capture efficiency within the microfluidic channel while alleviating direct contact between the electrode and the fluid. The EπDEP chip contains embedded electrodes within the microfluidic channel covered by a thin passivation layer of only 4 μm. The channel was designed with two nonaligned vertical columns of insulated microposts (200 μm diameter, 50 μm spacing) located between the electrodes (600 μm wide, 600 μm horizontal spacing) to generate nonuniform electric field lines to concentrate cells while maintaining steady flow in the channel. The performance of the chip was demonstrated using Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacterial pathogens in aqueous media. Trapping efficiencies of 100% were obtained for both pathogens at an applied AC voltage of 50 V peak-to-peak and flow rates as high as 10 μl/min.

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