Evaluation of Potential Beneficial Reuse of San Ardo Produced Water

The goal of this DOE, Aera Energy LLC, and Kennedy/Jenks Consultants funded project was to evaluate the potential for treatment and beneficial reuse of produced water from an oilfield in San Ardo, California. A 10 – 30 gpm reverse osmosis (RO) pilot plant was constructed and operated for nine months. The key constituents of concern include total dissolved solids (7000 mg/l TDS), temperature (190 ° F), boron (25 mg/l), ammonia (20 mg/l ammonia as N), and organics (75 mg/l TOC). Although water quality requirements vary with the type of end use, treated water quality goals for this pilot were set at 400 mg/l TDS, 1 mg/l boron, 5 mg/l ammonia as N, and 1 mg/l organics. Highlights of the project include an evaluation of a recently developed boron rejection membrane for boron removal at a lower pH than for a conventional brackish water membrane. The lower pH (9.5 versus >10.5) could result in significant savings on the caustic requirement.All of the water quality goals, except for ammonia, were achieved during the pilot study using both the conventional and the new boron rejection membrane systems. Because ammonia and boron have conflicting pH requirements for removal by RO, a separate ammonia removal step was necessary to meet the ammonia treatment goal. Analysis of the low and high pH clean-in-place (CIP) solutions used following membrane cleanings, as well as evaluation of transmembrane pressure drop after cleaning, showed that most of the pressure drop was caused by inorganic scaling from magnesium and silica, rather than organic fouling. Although the new boron rejection membrane successfully removed more boron at a lower pH than the conventional brackish water membrane, this membrane was more prone to scaling.