The objective of this study was to develop, optimize, and apply a novel approach to
concentrate and isolate organic carbon using reverse osmosis (RO) followed by
electrodialysis (ED). Electrodialysis is a membrane separation process employing ion-
exchange membranes which allows separating charged from neutral constituents. Due to
an electric potential and a concentration gradient as the driving forces of separation,
organic molecules can be isolated from inorganic salts without altering characteristics of
dissolved organic carbon (DOC). Issues associated with ED separation are related to
potential migration of charged low-molecular weight organics through the membrane or
losses due to adsorption onto the membrane surface. A 1-stage lab-scale RO-unit, an ED
membrane test unit, and an ED-stack (Electrosynthesis, Inc.) were employed to perform
experiments with single organic compound solutions varying in molecular weight,
surface water samples, and treated wastewater samples. Five different ion-selective
membrane pairs were investigated in the membrane test unit to determine the best-suited
ED membrane for laboratory-scale operation. To investigate the fate of bulk organics and
specific target compounds, cations, anions, dissolved organic carbon (DOC) and UV
absorbance were measured. Conductivity, pH, and current were measured online during
each ED-experiment.
Lessons learned from this study are that RO separation to concentrate organics
from NOM and EfOM samples can achieve DOC recoveries larger than 90 percent. Losses of DOC into the RO permeate varied for NOM samples between 7 and 8 percent
and for EfOM samples between 1 and 2 percent, respectively. During the ED-membrane
selection process, a monovalent-selective membrane combination (Asahi Glass, Inc.)
showed the best DOC rejection of all membranes investigated. The DOC rejection of
NOM and EfOM concentrates during ED-treatment varied between 96 and 97 percent. It
was found that charged low-molecular weight compounds (molecular weight less than
200 Dalton) can only be partly rejected during ED and therefore contributed to the DOC
loss. Fouling of humic substances onto the ED membrane was reversible during a
subsequent rinsing procedure with 0.1 N HCl-solution. With overall DOC rejection rates
of more than 90 percent the RO/ED-approach can be a valuable alternative to the
conventional XAD-8/-4 resin approach to concentrate and isolate organics from water
samples. This approach recovers more and different fractions as compared to XAD-resin
methods and avoids sample contamination and DOC alteration. The approach is faster
and capable of processing higher volumes of samples low in initial DOC (such as
groundwater samples).
Includes 19 references, tables, figures.
| Edition : | Vol. - No. |
| File Size : | 1
file
, 580 KB |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 18 |
| Published : | 11/01/2002 |
