Typical characteristics for wastewaters from the mining sector are:
- Low BOD-content
- Ammonium- and/or nitrate-nitrogen from explosive residues
- Thiocyanate (SCN) and cyanide (CN-) and cyanate (OCN-)
- Elevated concentrations of metals
- Low temperature
Necessary treatment usually includes degradation of SCN and CN followed by nitrogen removal and sometimes chemical treatment for removal of metals. Cyanide is toxic for the microorganisms, especially towards nitrifiying bacteria and therefore needs to be degraded before nitrification can take place.
MBBR in mining applications
With MBBR-technology, it is easy to design for a multi-step process which allows for the development of unique micro floras in the different process steps and makes it possible to protect subsequent nitrification steps from the toxicity of the various compounds, for example cyanide.
The MBBR-process is also easy to combine with chemical post-treatment directly with the effluent, since no sludge recycle is required.
Some mining wastewaters contain selenium, mainly in the soluble forms (selenate and selenite). Selenate and selenite can be reduced to elementary selenium by biological treatment under anoxic conditions. Since elementary selenium is insoluble, this offers a way to remove selenium by utilizing biological treatment.
AnoxKaldnes has worked extensively with development of optimized treatment solutions for the mining industry over the past years. The studies performed include treatment of wastewater that contains SCN and CN followed by subsequent nitrification of the released nitrogen and low-temperature studies (down to 2 °C) of nitrification and denitrification.