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Water Scarcity Ground Gains: Unlocking Additional Water Supplies Groundwater supplies can be plenty, but are plenty contaminated ��� giving rise to new technology. By Jess Bown and Chris Cleveland W ater scarcity in the United States is a long-standing issue in the American West. Aggressive conservation programs have helped, but are frequently not enough by themselves to solve the continued pressure brought on by increasing populations, limited additional surface water supplies, and increasing regulations. With few additional surface water options, communities often look to prevalent groundwater supplies that have previously been avoided due to water-quality issues and limited, expensive treatment options. Water scarcity is not just a western issue anymore, and new solutions are needed to address this issue across the country. Widespread Groundwater Contamination Nitrate is a prevalent groundwater contaminant across the United States, with approximately 57% of all domestic groundwater wells affected, according to data from the U.S. Environmental Protection Agency.1 Currently, ion exchange (IX) is most often used to remove nitrate from drinking water. A 2006 U.S. Geological Survey study showed that volatile organic compounds (VOCs) join nitrate as some of the most common groundwater contaminants. Sixty percent of the 932 wells they tested were contaminated with various VOCs such as perchloroethylene (PCE), trichloroethylene (TCE), and dibromochloropropane (DBCP).1 VOCs are typically removed from drinking water through adsorption onto liquid-phase granular activated carbon (GAC) or through volatilization across air stripping towers. Volatilized VOCs are then scrubbed from the discharge gas using air-phase GAC. Reverse osmosis (RO) can also be implemented to remove nitrate, VOCs, and other dissolved contaminants from water. Addressing Treatment Limitations A critical limitation of IX, GAC, air stripping, and RO is that they each produce a contaminant-laden waste stream, sometimes highly saline, that must be further treated or disposed of. This can drive up operations and maintenance costs and, in some cases, all but eliminate treatment viability. Consequently, utilities need an efficient groundwater treatment solution that does not generate a high-strength waste stream. In response to this need, a natural treatment system, BIOTTTA��� (Biologically-Tailored, Two-Stage, Treatment Approach), has been under development over the last 32 wateronline.com ��� decade. The system uses bacteria indigenous to the local groundwater to convert contaminants like nitrate and VOCs to harmless end-products such as nitrogen gas, carbon dioxide, and water. It includes two fixed-bed bioreactors in series, each using a stationary bed of GAC, on which bacteria form robust biofilms. Raw water is amended with nutrients and is pumped across the anoxic, biologically active media bed. After first-stage biological treatment, the water is reoxygenated, dosed with a particle-conditioning agent, and treated across an aerobic biofilter that provides oxidizing and filtration capacity. Occasionally, the fixed-bed bioreactors are taken offline for backwashing. Backwash wastewater can be treated to remove solids (i.e., sloughed bacteria), which can be discharged to a sewer or land-applied, depending on the location. The Groundwater Treatment Future Is Now Over the past 20 years, new surface water treatment tools such as ozone, membranes, and UV have been developed to help meet water quality challenges of poorer quality sources. However, few new tools have emerged to meet groundwater treatment challenges over that time. This has left many groundwater supplies untapped due to infeasible treatment needs, challenging brine disposal options, or unreasonable costs using previous treatment approaches. For utilities seeking to combat water scarcity with previously unusable groundwater supplies, this new system is a tool worthy of investigation. BIOTTTA��� provides a new treatment technique that treats multiple contaminants, eliminates challenging brine disposal issues, and is cost-effective for water suppliers to implement. Such systems represent a new option for utilities looking for answers to water scarcity, and the key to open a once-locked water supply. ��� 1. EPA Groundwater Information Sheet ��� Nitrate/Nitrite, Clean Water Programs, 2002; USGS Circular 1292 ��� Volatile Organic Compounds in the Nations��� Groundwater and Drinking-Water Supply Wells, 2006. Chris Cleveland, P.E., is a vice president with Carollo Engineers, Inc. in their Sacramento, CA, office. He has 19 years experience developing and designing water treatment solutions for local, regional, and national water issues. Jess Brown, Ph.D., P.E., is the director of Carollo Engineers��� R&D; Practice and leads Carollo���s Biological Drinking Water Treatment Initiative. His work in biological drinking water treatment has resulted in more than 100 national and international presentations and 12 peer-reviewed publications. Water Online The Magazine