Solar Evaporation of Landfill Leachate: A Clean Kill in Humid Climates and a Narrow Survivor in Arid Ones

Solar evaporation ponds are periodically proposed as a simple, low-energy way to make landfill leachate disappear. This paper tests that proposal for a stated flow of 20 cubic metres per day with a total dissolved solids concentration of 5,200 mg/L, and finds it wanting in most places. SIMULATED, NOT MEASURED: all results are from climate and mass-balance calculations in the accompanying code. Evaporation removes water only. It removes 0 percent of the salt mass, which enters at 104 kg per day, or 38.0 tonnes per year, and remains in full in a smaller, stronger liquid. Evaporating 90 percent of the volume leaves 2.0 cubic metres per day at 52,000 mg/L that still requires lawful disposal. In a humid Great Lakes climate the pond evaporation rate of 0.71 m per year is less than precipitation of 0.82 m per year, giving net evaporation of −0.11 m per year: a pond gains volume rather than losing it, which is a clean kill for that climate at any pond size. In a semi-arid climate with net evaporation of 0.80 m per year the required lined area is 9,125 square metres at a modelled cost of $3.51 per cubic metre treated. In an arid southwestern climate with net evaporation of 1.69 m per year the area is 4,313 square metres at $1.66 per cubic metre. Evaporation therefore survives only where net evaporation is high, lined land is available at low cost, and a lawful route exists for the concentrate. It is a volume-reduction step, never a treatment that makes the problem disappear.