Assessing the Diversity and Metabolic Potential of Psychrotolerant Arsenic-Metabolizing Microorganisms From a Subarctic Peatland Used for Treatment of Mining-Affected Waters by Culture-Dependent and -Independent Techniques.

Arsenic contamination in water by natural causes or industrial activities is a major environmental concern, and treatment of contaminated waters is needed to protect water resources and minimize the risk for human health. In mining environments, treatment peatlands are used in the polishing phase of water treatment to remove arsenic (among other contaminants), and peat microorganisms play a crucial role in arsenic removal. The present study assessed culture-independent diversity obtained through metagenomic and metatranscriptomic sequencing and culture-dependent diversity obtained by isolating psychrotolerant arsenic-tolerant, arsenite-oxidizing, and arsenate-respiring microorganisms from a peatland treating mine effluent waters of a gold mine in Finnish Lapland using a dilution-to-extinction technique. Low diversity enrichments obtained after several transfers were dominated by the genera Pseudomonas, Polaromonas, Aeromonas, Brevundimonas, Ancylobacter, and Rhodoferax. Even though maximal growth and physiological activity (i.e., arsenite oxidation or arsenate reduction) were observed at temperatures between 20 and 28°C, most enrichments also showed substantial growth/activity at 2-5°C, indicating the successful enrichments of psychrotolerant microorganisms. After additional purification, eight arsenic-tolerant, five arsenite-oxidizing, and three arsenate-respiring strains were obtained in pure culture and identified as Pseudomonas, Rhodococcus, Microbacterium, and Cadophora. Some of the enriched and isolated genera are not known to metabolize arsenic, and valuable insights on arsenic turnover pathways may be gained by their further characterization. Comparison with phylogenetic and functional data from the metagenome indicated that the enriched and isolated strains did not belong to the most abundant genera, indicating that culture-dependent and -independent methods capture different fractions of the microbial community involved in arsenic turnover. Rare biosphere microorganisms that are present in low abundance often play an important role in ecosystem functioning, and the enriched/isolated strains might thus contribute substantially to arsenic turnover in the treatment peatland. Psychrotolerant pure cultures of arsenic-metabolizing microorganisms from peatlands are needed to close the knowledge gaps pertaining to microbial arsenic turnover in peatlands located in cold climate regions, and the isolates and enrichments obtained in this study are a good starting point to establish model systems. Improved understanding of their metabolism could moreover lead to their use in biotechnological applications intended for bioremediation of arsenic-contaminated waters.

Treatment of heavy metal polluted industrial wastewater by a new water treatment process: ballasted electroflocculation.

This laboratory study investigated the parameters efficiency of the new technology: ballasted electro-flocculation (BEF) using aluminum (Al) electrodes to remove cadmium and zinc from industrial mining wastewater (MWW). The principle of the BEF process is based on the use of micro-sand and polymer together to increase the weight of the flocs and the rate at which they settle is radically changing the electrocoagulation-electroflocculation settling methodology. Based on the examination of the operation parameters one by one, the best removal percentage was obtained at a current intensity of 2A, a the flow rate of 20L/h, a micro-sand dose of 6g/L, a polyéthylèneimine (PEI) polymer dose of 100mg, the contact times of 30min, a stirring speed of 50 RPM, a monopolar configuration of the electrodes, and an electrodes number of 10. The results showed that the flow rate and the current density have a preponderant effect on the variability of the quality of the settled water. In comparison, filterability was found to be more sensitive to number of electrodes, micro sand dosages and current density. It was dependent on the ratio of microsand to PEI polymer dosage, and improved when this ratio increased. Response surface methodology was applied to evaluate the main effects and interactions among stirring speed, polymer dose, current intensity, and electrodes number. The removal of Cd and Zn from industrial MWW was done for very low cost of 0.1TND/m3 equivalent to 0.04€/m3. The investigation of BEF process proposes a highly cost-effective wastewater treatment method if compared to Actiflo TM and electrocoagulation.

Electrochemical oxidation of cyanide on 3D Ti-RuO2 anode using a filter-press electrolyzer.

The novelty of this communication lies in the use of a Ti-RuO2 anode which has not been tested for the oxidation of free cyanide in alkaline media at concentrations similar to those found in wastewater from the Merrill Crowe process (100 mg L-1 KCN and pH 11), which is typically used for the recovery of gold and silver. The anode was prepared by the Pechini method and characterized by SEM. Linear sweep voltammetries on a Ti-RuO2 rotating disk electrode (RDE) confirmed that cyanide is oxidized at 0.45 < E < 1.0 V vs SHE, while significant oxygen evolution reaction (OER) occurred. Bulk oxidation of free cyanide was investigated on Ti-RuO2 meshes fitted into a filter-press electrolyzer. Bulk electrolyzes were performed at constant potentials of 0.85 V and 0.95 V and at different mean linear flow rates ranging between 1.2 and 4.9 cm s-1. The bulk anodic oxidation of cyanide at 0.85 V and 3.7 cm s-1 achieved a degradation of 94%, with current efficiencies of 38% and an energy consumption of 24.6 kWh m-3. Moreover, the degradation sequence of cyanide was also examined by HPLC.