PROBLEM OVERVIEW 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 constantly degrading water quality, which cannot be discharged

to the environment and 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 concentration 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.

ELECTRO-BIOCHEMICAL TECHNOLOGY All biological and chemical metal and inorganic reduction/removal methods are based on redox reactions.

Electrons are needed for contaminant transformations, and conventional treatments rely on chemicals and

nutrients to provide these electrons. The Electro-Biochemical Reactor (EBR) technology reduces the amount

of chemical needed by directly supplying excess electrons to the reactor and microbes, using a low applied

voltage. 1 to 3 volts is all that is required, (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 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. Using selenium as an example, in the EBR biological treatment system, the selenium oxidation state

is not as crucial as it is in other treatment processes. Selenate is reduced to selenite, which in turn is reduced

to elemental selenium, which is virtually insoluble.

The pilot system is completely contained and designed for flow rates of 0.5 to 3 LPM, and PLC-controlled.

The EBR technology, while using only slightly modified standard treatment equipment, improves conventional

biological treatment process resulting in about 25% savings in capital costs and up to 50% savings in

operational costs.

RESULTS Conventional selenium removal methods including the EPA’s

best demonstrated available technology (BDAT) – iron co-

precipitation – had not b e e n 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. 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 cost were significantly decreased through conversion

and use of toxic flotation organics in the EBR process.

CONTACT INOTEC www.inotec.us

Jack Adams, Ph.D. President and CTO

(801) 712‐2760 - jack.adams@utah.edu

Parameter [mg/L]

Average Influent

Average Discharge

% Removal

Antimony 0.15 <0.001 >99.3%

Cadmium 0.014 <0.0002 >98.0%

Copper 0.41 <0.005 >98.7%

Lead 0.30 0.0008 99.7%

Molybdenum 0.10 <0.0005 >99.5%

Selenium 2.73 0.002 99.9%

Silver 0.041 <0.0001 >99.8%

Zinc 0.46 <0.03 >93.5%

Nitrate-N 3.3 <0.1 >97.1%

Nitrite-N 0.9 <0.02 >97.8%

Cyanide WAD 0.26 <0.005 >98.1

Cyanide TOTAL 0.47 <0.005 >98.9

EBR technology starts with the best aspects of proven microbial and chemical systems and

takes them to the next level of performance and cost-effectiveness