Rejection of Wastewater-Derived Micropollutants in High-Pressure Membrane Applications Leading to Indirect Potable Reuse
Project: 02-01
Type: Scientific Investigation
Year Released: 2006
Program: Principal
Funding Partners: Bureau of Reclamation, California State Water Resources Control Board, West Basin Municipal Water District
Total Investment: $230,000 (Cash: $221,500, In-Kind: $8,500)
Principal Investigator: Dr. Jörg E. Drewes, Colorado School of Mines
Background
Membrane processes such as reverse osmosis (RO), ultralow pressure reverse osmosis (ULPRO), and nanofiltration (NF) are becoming increasingly widespread in water treatment and wastewater reclamation and reuse applications where a high-quality product is desired. Membrane processes are often chosen because these applications achieve high levels of removal of constituents such as dissolved solids, organic carbon, inorganic ions, and regulated and unregulated organic compounds.
Goals and Objectives
The project examines the rejection mechanisms of organic trace pollutants in NF and RO membrane applications. Specific goals of the project were (1) to determine physicochemical properties which are suitable to describe membrane–solute interactions and rejection behavior; (2) to explore the relationships among physicochemical properties of trace organics and rejection mechanisms; and (3) to develop a fundamental transport model to describe and predict the rejection of trace organics in high-pressure membrane applications, based on hindered or facilitated diffusion.
Research Approach
The study was conducted using bench and laboratory scale facilities. Findings of the study were verified at water reuse field sites in Southern California and Arizona, employing full-scale membrane facilities.
Findings and Conclusions
Findings from this study imply a rather neutral or positive effect of hydrodynamic operating conditions on the rejection of hydrophilic negatively charged and nonionic organic compounds in a Jo/k range of 1.3 to 2.4. This range corresponds to a recovery range from 10 to 25%, which is usually achieved by individual spiral-wound membrane elements employed in two- and three- stage trains at full-scale applications. These findings imply that similar rejection performances of individual spiral-wound elements can be expected regardless of where they are employed in a pilot or full-scale multistage array. However, with a system recover of approximately 77% simulating the tail-end elements at full-scale applications, concentrations of some dissolved constituents present in these permeate streams were higher than for the lead elements. This finding was expected for nonionic hydrophilic solutes with a molecular weight close to the MWCO of a membrane, because a higher concentration gradient results in a higher solute mass transport.
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