Los Angeles, Houston, and Phoenix are three of the biggest cities in the U.S, and also the most water-constrained. In order to survive increasingly unpredictable temperatures over the next century, these cities–and others like them–will need to get creative with their water use. In honor of UN World Water Day, Dow Water and Process Solutions has offered some tips (PDF) for city planners and entrepreneurs on how to save water. Below, we look at some of the highlights.
- Reverse osmosis, a low-cost method for desalinating seawater that removes large molecules and ions by applying pressure to one side of a filtration membrane, is extremely energy-inefficient (desalinating just four gallons of seawater could suck up as much power as running a light bulb for an hour). Dow suggests using brine waste to pressurize incoming seawater–a technique that allows system operators to recover up to 99% of lost energy.
- Reverse osmosis can also be used for wastewater treatment and recycling. Singapore, for example, uses the technique to pruify and sell its wastewater to industry. The water is also used for drinking and sold as bottled water under the brand name NEWater.
- Ion exchange, a technique that involves the exchange of ions between a solid and a liquid, can remove contaminants from water for a variety of industries. More specifically, it can be used demineralize water for fossil and nuclear power plant boiler feedwater, cooling tower water, and feedwater for industrial plants. In Black Canyon City, Arizona, ion exchange is used to remove arsenic from drinking water. The technique has produced 3.5 million gallons of potable water for the city since 2006.
- Ultrafiltration, a membrane separation process that separates particulate matter from soluble components in water, can remove bacteria, viruses, colloids and silt. The technique is already widely used in municipal potable water plants, and can purify up to a trillion pounds of water per year at a cost of one one-thousandth of a cent per pound.