Evaporation ponds are an ancient technology used around the world to produce salt for human usage, but modern industries can produce extremely concentrated brine. In coastal areas, the rejected brine may be disposed of directly into the ocean (itself a problematic practice), but inland areas present even more challenges, both from economic and environmental standpoints. Hazardous brine disposal practices must be developed that are both sensitive to long-term environmental effects and economic feasibility.
Evaporative Ponds - Advantages and Disadvantages
Compared to other methods for brine treatment and disposal, evaporation ponds have significant advantages. In particular, they are:
- Easy to construct
- Require relatively little maintenance and minimal operator attention
- Require no mechanical equipment except for the pump that conveys wastewater to the pond
- Frequently the least costly means of disposal, particularly in arid regions.
Naturally, there are some factors that affect suitability for some locations, including:
- Evaporation ponds can require large tracts of flat land, depending on local climate. Cost and suitability of land should be considered against the cost of transportation and the risk of environmental damage with alternate disposal methods
- Evaporation ponds can be expensive to construct, but their ongoing operation has minimal cost. Ponds that are well constructed, using high quality materials, can be operated for decades before major maintenance is required. Over time, evaporation ponds are the most environmentally sensitive and among the least expensive disposal options.
- Poorly constructed and monitored evaporation ponds pose significant risks to the local environment, particularly through seepage into nearby groundwater supplies or spills that poison the local environment. This risk can be minimized, even eliminated, through careful design and monitoring of secondary containment and leak detection protocols as well as responsible adherence to maintenance schedules.
Why Aren’t Evaporative Ponds Used More Widely?
Despite the advantages of evaporation ponds, one survey of drinking water plants in the US reported that only 6% currently use that technology, while 10% use deep well injection, 23% send their reject brine to municipal wastewater treatment plants, and a whopping 48% dump brine concentrate directly into nearby surface water.
Plants that produce drinking water through technologies like Reverse Osmosis (RO) and phase change processes are becoming more and more common as the demand for fresh drinking water and purified water for industrial processes rapidly increases. Since inland plants don’t have access to the ocean for easy (though problematic) disposal of highly concentrated brine waste, evaporation ponds are a sensible situation in regions where the climate is arid or semi-arid and receives an abundance of solar energy. If abundant and relatively cheap land is available, this becomes a highly efficient method of dealing with produced brine.
On the other hand, if the primary goal of processing seawater or brackish water is the extraction of fresh water suitable for drinking or industrial uses, then evaporation ponds shouldn’t necessarily be the first preferred option for disposal. In these cases, use of intermediary treatment like brine concentrators would permit the recovery of a significant portion of additional water from the waste stream, leaving as little as 6% of liquid to be evaporated in brine ponds. This option maximizes freshwater recovery while minimizing the disposal complexity of the ultimate dried product.
