Treatment of Wastewater for Reuse in a Cooling Tower
By Katariina Majamaa, Steve Gluck, Ph.D., Javier Suarez, and Nanette Hermsen
Water and energy resources are connected and under increasing stress globally. In the United States, water withdrawals for irrigating crops and for cooling thermoelectric power plants are relatively evenly split at around 40% of the total each. Thermoelectric-power generation water withdrawals were an estimated 201 billion gallons per day (Bgal/d) in 2005 (1). Globally, approximately 11,900 Bgal (45 billion cubic meters [Bm3]) of water are consumed per year for energy production globally (2). Advanced wastewater treatment and reuse offers an attractive and cost-efficient option for industrial processes such as boiler and cooling water. Diverting wastewater effluent from return flows to consumptive uses reduces the need for water withdrawal. Typical treatment schemes to produce high-quality industrial water from wastewater involve membrane technologies, including membrane bioreactors (MBR), ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO) as an alternative to aggressive chemical treatments to manage scaling, corrosion, and biofouling. Membrane technologies require certain features that help them operate successfully despite the technical challenges presented by purifying wastewater. The recent developments in membrane technology research in the general industry have substantially addressed the cost of water treatment. These advances include improved features such as fouling resistance, higher productivity, higher solute rejection, and advanced module components. In addition to tertiary treatment, RO or NF systems effectively reduce total dissolved solids (TDS), ammonium, and sulfate concentrations in the cooling tower blowdown water for further reuse as general makeup water and as a key operation for zero liquid discharge.
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