Reverse osmosis (RO) is among the most effective available technologies for removing PFAS from contaminated water—achieving greater than 90% rejection of most PFAS compounds in a single pass. However, RO does not destroy PFAS; it concentrates these compounds into a reject stream (brine or concentrate) that contains 90-95% of the PFAS mass from the feed water in a volume representing only 10-20% of the original feed. The resulting brine disposal problem is one of the central challenges in scaling up PFAS treatment, particularly for large municipal water systems, industrial facilities, and groundwater remediation sites.
Characterizing the RO Concentrate PFAS Problem
For a water utility treating 10 million gallons per day (MGD) of PFAS-contaminated source water at 20 ppt total PFAS, an RO system operating at 80% recovery would generate 2 MGD of concentrate containing approximately 90 ppt total PFAS—a fivefold concentration factor. This concentrate must be disposed of in a manner that does not return PFAS to the environment or transfer PFAS to another environmental medium. Traditional concentrate disposal options—discharge to surface water, deep well injection, or delivery to a POTW—become problematic when the concentrate contains regulated PFAS at concentrations that violate discharge limits or impair downstream treatment.
The brine disposal challenge is compounded for inland facilities that lack access to ocean outfalls or saline receiving waters where dilution factors can render PFAS concentrations environmentally acceptable. Inland RO concentrate from municipal drinking water treatment and groundwater remediation systems may have no cost-effective direct discharge pathway, necessitating transport and off-site disposal at regulated hazardous waste facilities or, increasingly, on-site destruction.
Concentrate Management Options and Emerging Destruction Technologies
Thermal incineration in a permitted hazardous waste incinerator operating at temperatures above 1,100°C provides effective PFAS mineralization for RO concentrate and is currently the most widely used concentrate disposal method for PFAS-laden brines. However, transport costs, incineration gate fees, and limited permitted incineration capacity create logistical and cost constraints that scale poorly with the volume of concentrate generated by large systems.
On-site PFAS destruction systems for RO concentrate are an active area of development and commercial deployment. Electrochemical oxidation systems using boron-doped diamond (BDD) electrodes can achieve substantial PFAS mineralization in high-conductivity concentrate streams, operating at current densities that become more energetically favorable as concentrate ionic strength increases. Smoldering combustion and thermal hydrolysis systems are being piloted for high-volume concentrate streams. UV/sulfite advanced reduction processes have shown PFAS destruction efficiency in laboratory settings and are advancing toward pilot-scale demonstration for concentrate applications.