NAMS 2002 Workshop - ICOM 2008

Nanofiltration and Reverse Osmosis II - Imaging and Characterization – 5
Tuesday July 15, 11:00 AM-11:30 AM, Maui
Removal of Emerging Organic Contaminants by High-Pressure
Membranes: Mechanisms, Monitoring, and Modeling
J. Drewes (Presenting), Colorado School of Mines, Golden, CO, USA
C. Bellona, Carollo Engineers, Broomfield, CO, USA
M. Sonnenberg, Colorado School of Mines, Golden, CO, USA
The rejection of emerging organic micropollutants is an important issue where
recycled water is used to augment drinking water supplies. The focus of this
research study was to explore alternatives of an integrated membrane system
involving nanofiltration (NF) and ultra-low pressure reverse osmosis (ULPRO) in
place of conventional reverse osmosis (RO) representing a more cost-effective
system because of potentially lower pressure requirements and the greater
selectivity for organic micropollutants as compared to removal of total dissolved
solids (TDS).
The organic micropollutants studied in this research included disinfection byproducts
(e.g., trichloroacetic acid, chloroform, bromoform, Nnitrosodimethylamine),
pesticides, endocrine disrupting compounds (e.g., 17²estradiol,
testosterone, bisphenol A), pharmaceutical residues (e.g., ibuprofen,
naproxen, gemfibrozil, carbamazepine, primidone), and chlorinated flame
retardants. These compounds have a broad range of physicochemical properties,
and are associated with potential adverse effects for human health and aquatic
life. Uncertainty regarding the rejection of certain solutes, justifies the
development of modeling approaches to predict the removal of contaminants by
RO and NF. A successful predictive model would eliminate the need for pilotscale
evaluation of trace organic contaminant removal, and eliminate uncertainty
regarding permeate water quality. After pre-screening over 15 potential NF and
ULPRO products during laboratory-scale membrane rejection experiments, three
candidate membranes were selected and pilot tested using a 68 L/min
membrane pilot skid for at least 1,300 hours on microfiltered feed water at two
full-scale facilities. State-of-the-art membrane characterization tools were used to
describe the fouling behavior of NF/ULPRO membranes and determine the role
of fouling on operation (e.g., flux decline) and rejection.
Past studies on modeling membrane performance have resulted in several
methods and sets of equations that can be used to model the rejection of
inorganic and organic solutes. However, simple yet robust solution-diffusion
models do not directly apply to membranes in which pore phenomena including
physical sieving and Donnan exclusion are important for solute rejection.
Transport equations developed to describe the transport of electrolytes through