Adsorption technologies are a focus of interest for the removal of pollutants in water treatment systems. These removal methods offer several design, operation and efficiency advantages over other wastewater remediation technologies. Particularly, graphene oxide (GO) has attracted great attention due to its high surface area and its effectiveness in removing heavy metals. In this work, we study the functionalization of GO with zinc oxide nanoparticles (ZnO) to improve the removal capacity of aluminum (Al) and copper (Cu) in acidic waters. Experiments were performed at different pH conditions (with and without pH adjustment). In both cases, decorated GO (GO/ZnO) nanocomposites showed an improvement in the removal capacity compared with non-functionalized GO, even when the pH of zero charge (pHPZC) was higher for GO/ZnO (5.57) than for GO (3.98). In adsorption experiments without pH adjustment, the maximum removal capacities for Al and Cu were 29.1 mg/g and 45.5 mg/g, respectively. The maximum removal percentages of the studied cations (Al and Cu) were higher than 88%. Further, under more acidic conditions (pH 4), the maximum sorption capacities using GO/ZnO as adsorbent were 19.9 mg/g and 33.5 mg/g for Al and Cu, respectively. Moreover, the removal percentages reach 95.6% for Al and 92.9% for Cu. This shows that decoration with ZnO nanoparticles is a good option for improving the sorption capacity of GO for Cu removal and to a lesser extent for Al, even when the pH was not favorable in terms of electrostatic affinity for cations. These findings contribute to a better understanding of the potential and effectiveness of GO functionalization with ZnO nanoparticles to treat acidic waters contaminated with heavy metals and its applicability for wastewater remediation.

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Adaptive laboratory evolution typically involves the propagation of organisms asexually to select for mutants with the desired phenotypes. However, asexual evolution is prone to competition among beneficial mutations (clonal interference) and the accumulation of hitchhiking and neutral mutations. The benefits of horizontal gene transfer toward overcoming these known disadvantages of asexual evolution were characterized in a strain of Escherichia coli engineered for superior sexual recombination (genderless). Specifically, we experimentally validated the capacity of the genderless strain to reduce the mutational load and recombine beneficial mutations. We also confirmed that inclusion of multiple origins of transfer influences both the frequency of genetic exchange throughout the chromosome and the linkage of donor DNA. We built a simple kinetic model to estimate recombination frequency as a function of transfer size and relative genotype enrichment in batch transfers; the model output correlated well with the experimental data. Our results provide strong support for the advantages of utilizing the genderless strain over its asexual counterpart during adaptive laboratory evolution for generating beneficial mutants with reduced mutational load. IMPORTANCEOver 80 years ago Fisher and Muller began a debate on the origins of sexual recombination. Although many aspects of sexual recombination have been examined at length, experimental evidence behind the behaviors of recombination in many systems and the means to harness it remain elusive. In this study, we sought to experimentally validate some advantages of recombination in typically asexual Escherichia coli and determine if a sexual strain of E. coli can become an effective tool for strain development.

Acid mine drainage (AMD) is an environmental concern characterized by low pH and high concentrations of dissolved metals and sulfate. Yerba Loca Creek in Santiago, Chile, is an AMD-affected water stream that originates in a glacier and, therefore, has a season-dependent flow. This water course is characterized by low pH (3.75 ± 0.13) and high concentrations of aluminum (2.2-2.6 mg/L) and copper (4.8-6.5 mg/L). A field campaign was carried out to study the geochemical behavior around the confluence of the Yerba Loca Creek with the San Francisco River, which has a neutral pH and low concentration of dissolved metals. The results show that the geochemical parameters after the confluence are very similar to those registered for the Yerba Loca Creek, due to its great flow in relation to the San Francisco River. The pH after the mixing zone was controlled by the geochemical conditions and flow of the Yerba Loca Creek; however, the turbidity decreases and stabilizes downstream. We found that, despite the low impact of pH on the precipitation of aluminum and copper phases due to poor neutralization, the dissolved aluminum and copper concentrations are slightly decreased after the mixing zone by natural microscale removal processes or suspended solids formation. Scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDX) analysis of suspended solids indicates the presence of various oxides, hydroxy-sulfates and aluminosilicates, which have a great affinity for adsorption and co-precipitation with dissolved metals (i.e., Al and Cu). A pH-neutralization would favor the formation of more minerals and, therefore, the immobilization of the heavy metals found in these waters. These results contribute to a better understanding of the effect of the confluence of water courses related to pollution by AMD. It is possible that the seasonal variation of the flows has an impact on the composition of water and minerals formed. River (pH~7.2) [4]. At high elevations of the Yerba Loca Basin, there is a large deposit of copper porphyry, which have long influenced the surface water quality of the area, particularly in terms of pH, sulfate content and mineral concentrations [5]. In particular, in the Yerba Loca Creek acidic conditions and metal content, mainly copper (Cu) and aluminum (Al) [6], have a substantial impact on the vegetation of the area since these waters are highly toxic for most plant species [5]. Furthermore, the presence of Cu in excessive concentrations is harmful to a variety of living organisms such as microorganisms, fish and humans [7]. In the environment, Cu is commonly presented as a divalent cation and is generally more mobile in acidic conditions, while at pH above 7, it tends to form minerals like Cu carbonates and hydroxyl-carbonates [8,9]. Al is the third most abundant element in the Earth's crust and is commonly present as Al oxide and Al silicate [10,11]. At pH less than 6, Al can be leached from the soil and sediments in the water [10], but the solubility increases when pH is less than 4.5 [12...

Acid mine drainage (AMD) is a complex environmental problem, which has adverse effects on surface and ground waters due to low pH, high toxic metals, and dissolved salts. New bioremediation approach based on microbial fuel cells (MFC) can be a novel and sustainable alternative for AMD treatment. We studied the potential of MFC for acidic synthetic water treatment through pH neutralization in batch-mode and continuous-flow operation. We observed a marked pH increase, from~3.7 to~7.9 under batch conditions and to~5.8 under continuous-flow operation. Likewise, batch reactors (non-MFC) inoculated with different MFC-enriched biofilms showed a very similar pH increase, suggesting that the neutralization observed for batch operation was due to a synergistic influence of these communities. These preliminary results support the idea of using MFC technologies for AMD remediation, which could help to reduce costs associated with conventional technologies. Advances in this configuration could even be extrapolated to the recovery of heavy metals by precipitation or adsorption processes due to the acid neutralization.