EBR for metals removal

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Coal Mining: EBR Metals Removal Case Study

In the pilot-test waters, metals that were not targeted for removal, but still removed by the EBR system included molybdenum (7.8 μg/L), nickel (113 μg/L), antimony (2.8 μg/L), uranium (18.2 μg/L), and zinc (64 μg/L). Most metals were removed to below 1 μg/L. Nickel was reduced to an average of 2 μg/L while effluent zinc concentration was non-detectable.
The on-site test was performed with average influent water temperatures of 14ºC to a low of 1ºC, demonstrating the effectiveness of EBR at low temperatures. It is worth noting that effluent TSS concentration were low, illustrating that the EBR process is capable of removing metals to low levels while not producing excess solids or biomass (i.e., the EBR process does not require a solids management post-treatment).

EBR bioreactor for metals removal from coal mining waters

Flotation-Influenced Waters: EBR Metals Removal Case Study

An underground mining operation producing copper, lead, zinc, silver and gold uses three floatation circuits for metal recovery. Suppressants (e.g., cyanides) and collectors (e.g., xanthates) are added at each step to recover only the desired products. Water and solids from the floatation circuit are discharged to a tailing pond, where solids are allowed to settle and water is re-circulated to the circuits. Constant water reuse practice without treatment has resulted in a steady degradation in water quality, which cannot be discharged to the environment and has significantly reduced floatation recoveries. The concentration of metals (i.e., selenium, antimony, cadmium, copper, lead, molybdenum, silver, and zinc) and chemical reagents, such as collectors and suppressants, is increasing over time. High concentrations of complex organic compounds and other contaminants (over 700 mg/L COD; TDS of over 4,000 mg/L; selenium 2.0-3.5 mg/L) renders this wastewater difficult to treat using conventional biological, chemical and/or physical processes.
The EBR pilot system removed all examined metals and inorganics to below discharge criteria; >93% to >99% removals were obtained. All values are given as total metals, i.e., samples were not filtered prior to analysis.

EBR bioreactor for metals removal from flotation mining waters

Heap Leaching: EBR Metals Removal Case Study

The waters generated from a closed heap leaching operation contain a broad spectrum of contaminants that either exceed the discharge standards or are considered a nuisance chemical by the US Environmental Protection Agency (EPA). Cadmium (Cd), copper (Cu), and zinc (Zn) all significantly exceed the discharge limits and are not removed by the existing Conventional Bioreactor (CBR) facility. The EBR pilot system removed all three metals to below the discharge criteria; Cd was reduced from an average influent concentration of 0.135 mg/L to below the detection limit of 0.001 mg/L, while Cu and Zn were removed from average influent concentrations of 0.061 mg/L and 2.26 mg/L to 0.014 mg/L and 0.04 mg/L, respectively.
Due to their aesthetic effects on water quality, such as water discoloration, staining, and taste, aluminum (Al) and manganese (Mn) are listed on the secondary US EPA pollutants list. Both metals are not removed by the existing CBR facility, but were removed from average influent levels of 0.34 mg/L (Al) and 57 mg/L (Mn) to 0.04 mg/L and 29 mg/L, respectively, in the EBR effluent.

Nickel (Ni), not listed by the US EPA as a primary or secondary pollutant, is present in the mining waters at average concentrations of 0.83 mg/L. Ni drinking water standards in other countries, for example the EU, are as low as 0.02 mg/L. The pilot EBR system removed nickel to an average concentration of 0.007 mg/L.
In addition to meeting metals discharge criteria, the EBR system produced low levels of total suspended solids (TSS). High TSS levels are commonly associated with anaerobic biotreatment effluents and often require post-treatments or polishing steps prior to discharge, which can add significant capital and operating expenses. The pilot EBR system generated on average 13 mg/L TSS; the discharge standard is 20 mg/L.

EBR bioreactor for metals removal from heap leaching mining waters

FGD Waters: EBR Metals Removal Case Studies

The EBR pilot system was tested on two coal-fired power plant sites for treatment of FGD waters.
During the first on-site trial, the average total mercury concentration of 0.616 μg/L in the influent exceeded the proposed ELG limit of 0.119 μg/L. However, average dissolved mercury concentrations met the ELG limit, indicating that mercury ions were effectively removed from the solution in the phys-chem treatment up-stream but the resulting total suspended solids were not effectively captured. The EBR treatment retained the mercury associated with the suspended solids from the phys-chem system and both total and dissolved mercury were below detection limits throughout the EBR system.
In addition to the parameters specified by the proposed ELG rule, the influent water contained elevated concentrations of chromium, molybdenum, zinc, and uranium. All metals were removed to below detection by the EBR system.

During the second trial, the average total mercury concentration of 0.518 μg/L in the influent exceeded the proposed ELG limits. However, at 0.028 μg/L, average dissolved mercury concentrations met both ELG limits, indicating that mercury ions were effectively removed from the solution in the phys-chem treatment but the resulting total suspended solids were not effectively captured. The EBR treatment removed the mercury associated with the suspended solids from the phys-chem system and both total and dissolved mercury met ELG limits in the system effluent.
The average arsenic in the pilot system influent was 21 μg/L and 17 μg/L, for total and dissolved fractions, respectively; both above the ELG limits. The EBR pilot system reduced arsenic concentrations to below both ELG limits; average total As in the EBR effluent was 4.0 μg/L, with an average dissolved As of 3.6 μg/L.
Other metals removed by the pilot EBR system included Cd, Co, Ni, Sb, V, and Zn.