Mine Waters and Effluents Part 5 - Zero Liquid Effluent Discharge

Many water treatment processes are excellent at removing contaminants from water, but where do these contaminants ultimately go?

Some common technologies, such as Reverse Osmosis and Ion Exchange, transfer the contaminants to a concentrated liquid stream called ‘brine’. This brine stream is small in volume but difficult and costly to treat due to the high contaminant load.

Other technologies take an alternative approach and precipitate the contaminants into a solid form. This is beneficial because solids are easily separated from liquids, making them cheaper to dispose than brines.

Many water treatment processes use a combination of brine-producing and precipitation technologies – as discussed in Part 3 of this series.

Brine minimisation in water treatment is a common pursuit due to the following advantages:

  1. Higher water recovery – less water escaping with the brine allows more treated water production.

  2. Lower brine handling costs – smaller brine volumes are cheaper to treat or dispose.

  3. Reduced environmental footprint – smaller brine volumes require less resources for treatment and disposal.

Creek in New Caledonia contaminated by brines from local mining operations. Source: Wikimedia Commons

The ultimate goal of producing no liquid brine is called Zero Liquid Effluent Discharge (ZLED), which has historically been difficult and costly to accomplish.