Recent Developments for Remediating Acidic Mine Waters Using Sulfidogenic Bacteria.

Acidic mine drainage (AMD) is regarded as a pollutant and considered as potential source of valuable metals. With diminishing metal resources and ever-increasing demand on industry, recovering AMD metals is a sustainable initiative, despite facing major challenges. AMD refers to effluents draining from abandoned mines and mine wastes usually highly acidic that contain a variety of dissolved metals (Fe, Mn, Cu, Ni, and Zn) in much greater concentration than what is found in natural water bodies. There are numerous remediation treatments including chemical (lime treatment) or biological methods (aerobic wetlands and compost bioreactors) used for metal precipitation and removal from AMD. However, controlled biomineralization and selective recovering of metals using sulfidogenic bacteria are advantageous, reducing costs and environmental risks of sludge disposal. The increased understanding of the microbiology of acid-tolerant sulfidogenic bacteria will lead to the development of novel approaches to AMD treatment. We present and discuss several important recent approaches using low sulfidogenic bioreactors to both remediate and selectively recover metal sulfides from AMD. This work also highlights the efficiency and drawbacks of these types of treatments for metal recovery and points to future research for enhancing the use of novel acidophilic and acid-tolerant sulfidogenic microorganisms in AMD treatment.

Protists and bacteria interactions in the presence of oil.

Little is known about the role of protists and bacteria interactions during hydrocarbon biodegradation. This work focused on the effect of oil on protists from three different locations in Guanabara Bay and bacteria from Caulerpa racemosa (BCr), Dictyota menstrualis (BDm) and Laurencia obtusa (BLo) during a 96 h bioassay. Cryptomonadida (site 1, 2 and 3), Scuticociliatida (site 2) and Euplotes sp.1 and Euplotes sp.2 (site 3) appeared after incubation. The highest biomass observed in the controls was as follows: protist site 3 (6.0 µgC.cm-3, 96 h) compared to site 3 with oil (0.7 µgC.cm-3, 96 h); for bacteria, 8.6 µgC.cm-3 (BDm, 72 h) and 17.0 µgC.cm-3 (BCr with oil, 24 h). After treatment, the highest biomasses were as follows: protists at site 1 and BLo, 6.0 µgC.cm-3 (96 h), compared to site 1 and BLo with oil, 3.31 µgC.cm-3 (96 h); the bacterial biomass was 43.1 µgC.cm-3 at site 2 and BDm (96 h). At site 3 and BLo with oil, the biomass was 18.21 µgC.cm-3 (48 h). The highest biofilm proportions were observed from BCr 1.7 µm (96 h) and BLo with oil 1.8 µm (24 h). BCr, BLo and BDm enhanced biofilm size and reduced the capacity of protists to prey.