The EBR overcomes the shortcomings of conventional bioreactors by directly supplying excess electrons to the reactor and microbes, using a low applied voltage: 1 to 3 volts is all that is required for the EBR (1-volt supplies approximately 1 trillion, trillion electrons). These electrons replace the electrons normally supplied by excess nutrients and chemicals, at a considerable savings. The provided electrons make the reactors more controllable, economical, and robust than past generations of biological treatment systems. Moreover, they provide readily available electrons for microbial growth and contaminant removal, resulting in better performance in less time and space and with greater efficiency.
Pilot System
The PLC-controlled pilot system is completely contained and designed for flow rates of 0.5 to 3 LPM.
Experience had shown that conventional selenium removal methods including the EPA’s best demonstrated available technology (BDAT) — iron co-precipitation — had not been able to meet the discharge limit (0.02 mg/L). The EBR pilot system removed all examined metals and inorganics to below discharge criteria; >93% to >99% removals were obtained.
All metals, except for molybdenum, were present in the influent wastewaters at concentrations above the allowable discharge limit. Selenium was removed from influent values averaging 2.73 mg/L to an average 0.002 mg/L in the system effluent. Discharge criteria were met within 16 hours in the first EBR treatment stage.
Significant changes in influent selenium concentration and temperature had no effect on EBR system performance. Nutrient costs were significantly decreased through conversion and use of toxic floatation organics in the EBR process.
Conclusions
- The EBR technology successfully removed high selenium concentrations (2.0-3.5 mg/L) from difficult floatation-affected wastewaters to discharge criteria using short HRTs and to ultra-low levels (≤ 0.002 mg/L) using longer HRTs.
• Selenium and other metals are precipitated in the EBR system in stable elemental and sulfide forms, significantly reducing the sludge volume and providing a potential for recovery at the end of reactor life.
- Reduction of various other metals occurred concurrently with selenium reduction:
• Antimony, cadmium, copper, lead, molybdenum, silver, and zinc.
- In addition to metals removal, various inorganic species were removed by the EBRs:
• Nitrate-N, nitrite-N, WAD cyanide, total cyanide.
- Preliminary metallurgical tests using EBR effluent waters showed that treated waters may significantly increase the floatation recovery of precious and base metals.
- The initial EBR evaluation indicates over 25% lower capital costs and up to 50% lower operational costs than conventional bioreactors and other treatment methods.
- The EBR system produces more controllable and stable bioreactor environments.
- Power requirements for a full-scale facility can be supplied by a small solar grid, because of the low DC voltage potential needed for the EBRs.
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