RECOVERING BOTH WATER AND SALTS FROM A SALINE INLAND GROUNDWATER

摘要

Sandoval County is located in central New Mexico approximately 20 miles north of the city of Albuquerque. In 2009,the County investigated treatment of a brackish groundwater source for potable water use. The artesian groundwater contains 12,000 milligrams per liter (mg/L) of total dissolved solids (TDS) with extremely high levels of calcium, magnesium, arsenic, and boron, as well as to radionuclides and a temperature exceeding 125o F. In addition to removing these contaminants to produce a potable water supply, the County is also seeking to produce usable byproducts from the waste streams to potentially reduce disposal costs and to offset operating costs of the proposed desalination facility. A process treatment approach was developed using a combination of coagulation, chemical softening, media filtration, ion exchange, and reverse osmosis to produce potable quality water and three distinct waste streams, two of which could produce marketable byproducts. Two months of pilot testing was conducted in the fall of 2009 to confirm the effectiveness of the treatment processes,optimize chemical usage, and identify recommended operating conditions for the various treatment steps. Pilot testing results confirmed that calcium can be effectively removed through chemical softening, preventing fouling of the downstream RO and maintaining a relatively pure calcium carbonate waste stream that can potentially be recovered, recalcinated, and reused in the treatment process. RO waste streams were found to contain primarily sodium chloride and sodium sulfate, which can be separated from each other using nanofiltration to produce high purity salt product streams. Operation of the RO unit at high pH was also found to remove 94 percent of the boron without the need for second pass RO, even at the elevated feed water temperatures. RO recoveries up to 80 percent were achieved, with the recovery limited, not by scaling potential, but by osmotic pressure and maximum allowable pressures for the RO elements. The results of the pilot testing are being used by the County to determine the best approach for moving forward with development of this new water supply for a highly arid region with few water supply alternatives.