Management of waste water is a challenging issue in many municipal and industrial sectors. The oil and gas industry produces a massive amount of waste water during production. The production of one barrel of oil results in approximately nine barrels of water that is contaminated with salt, heavy metals, and organic compounds. The development of methods for cost-efficient disposal and re-use of produced water without damage to the environment is a critical need for the oil and gas industry. Also, re-use of the water for agricultural purposes will be helpful because the agricultural sector is a primary consumer of increasingly scarce freshwater (accounting for 63% of U.S. surface water withdrawals, according to the U.S. Geological Survey).
In this project sponsored by the US Department of Energy, Drs. Shabgard, Cai and Parthasarathy are working on the development of a novel, zero-liquid discharge freeze system to remove dissolved salt from contaminated water. Freeze-desalination processes are well suited for these situations because pure ice crystals can be produced even in highly concentrated brine. However, current freeze-desalination technologies have some deficiencies that hinder their widespread use. A new method of eutectic freeze desalination will be used with a cooling approach that maximizes efficiency. Thus, the need for energy-intensive evaporation methods is avoided. The density differences between water, ice, and salty brine are used to separate the components. The system will operate under atmospheric pressure and be capable of treating highly concentrated/contaminated water. If successful, the treated water will be suitable for agricultural use, providing an abundant new water source. The goal is to develop a zero-liquid discharge (ZLD) freeze-desalination system capable of treating water with total dissolved solids (TDS) values up to 250,000 mg/l (milligrams per liter). For comparison, the TDS content of seawater is approximately 35,000 mg/l.
The proposed system offers a sustainable solution for the increasing water demand in industrial and oil and gas sectors by recycling the otherwise wasted water, without putting pressure on increasingly scarce fresh water resources also in demand by local communities for agricultural and municipal purposes. Also, the environmental concerns related to disposing of highly contaminated water are avoided by the use of the proposed ZLD desalination system.