Recovery optimization for brackish groundwater desalination: Fid-Bau Portal

Recovery optimization for brackish groundwater desalination

Subramani, Arun / Carolis, James De / Bdruzzaman, Mohammad / Jacangelo, Joseph / Kinser, Karla / Pearce, William

The City of San Diego intends to develop local groundwater sources to supplement their drinking water supply with a target of 10000 AF/yr by 2010. Due to high salinity, many of the City's groundwater sources require desalination before it can be used to supplement drinking water supply. Since the City's potential groundwater desalination project's location is in inland areas, RO (reverse osmosis) concentrate disposal options are limited. Recovery of the primary RO process at this location is limited to 65-75 % due to the presence of high silica concentrations (60 mg/l) in the San Pasqual Basin groundwater. In this study, different methods were implemented to increase the overall feed water recovery of the desalination process. The application of an antiscalant (Pre-treat plus Y2K) at a dosage of 4 mg/l was found to be the best performing pretreatment chemical in maximizing the primary RO performance. An optimum recovery of 75 % was achieved for the primary RO. Doubling the antiscalant dosage was not efficient in increasing the feed water recovery of the primary RO process. To reduce the volume of concentrate generated from the primary RO, a VSEP (Vibratory Shear Enhanced System) was utilized. After pretreatment (acid and antiscalant) of primary RO concentrate, an overall feed water recovery of more than 93 % was achieved by using VSEP. The product water quality from the VSEP was similar to the primary RO permeate. To determine the feasibility of using ICD (intermediate chemical demineralization) of the concentrate generated from primary RO and VSEP, chemical treatment using lime and caustic was performed. Chemical treatment of the concentrate resulted in the removal of more than 90 % of scaling precursors such as barium, calcium, magnesium, and silica from both primary RO and VSEP concentrate. Results suggest that the use of SWRO (secondary seawater RO) after chemical treatment of primary RO and VSEP concentrate can lead to recoveries greater than 98 %. Hence, zero liquid discharge goals can be achieved by further processing the concentrate.