Jupiter Water Utilities (Town) owns and operates a 30 million gallon per day (MGD) drinking water treatment facility comprising of nanofiltration (NF), reverse osmosis (RO), and anion exchange (AX). The Town also owns pilot-scale NF and RO units that are utilized for pretreatment optimization, membrane selection, contaminant of emerging concern rejection studies, among other uses. The objective of this study was to utilize the NF and RO pilot unit to optimize pretreatment, which could then be implemented in the Town’s full-scale systems to recover chemical costs. The Town’s current full-scale NF pretreatment comprises of sand filtration, cartridge filtration, pH adjustment to 6.5 via sulfuric acid, and a 2.0 mg/L scale inhibitor dose, and full-scale RO pretreatment comprises of cartridge filtration and a 2.0 mg/L scale inhibitor dose. Sulfuric acid is added to NF raw water to increase the solubility calcium carbonate. Scale inhibitor is added in the NF and RO raw water to prevent calcium carbonate and other sparingly soluble salts from precipitating out on the membrane surface. The purpose of this study was to monitor membrane performance and water quality while the NF pilot unit experienced a decreased dose of sulfuric acid and scale inhibitor, and RO pilot unit experienced a decreased dose of scale inhibitor. Four treatment conditions were examined with the NF pilot and two treatment conditions were examined with the RO pilot. Water quality and membrane performance (normalized permeate flow (NPF), pressure drop (PD), normalized salt passage (NSP), specific flux (JSP), and water flux (JW)) were monitored throughout the study. Results indicate that in the NF pilot, scale inhibitor dosage can be decreased without compromising productivity or water quality based on 1000 hours of pilot simulation at pH 6.5 and pH 6.7. However, the RO pilot could not withstand optimum productivity with a lower scale inhibitor dosage. Additional testing may be necessary to find the lowest scale inhibitor and sulfuric acid dosage for optimum membrane lifespan and cost savings.
This presentation is available to AMTA Members only.
- Carlyn Higgins
- Hazen and Sawyer
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