TREATMENT OF LAUNDRY WASTEWATER FROM A
NUCLEAR POWER PLANT BY REVERSE OSMOSIS
Fu-Tien Jenq, Associate Professor
Chien-Jen Shih, Master
National Taiwan University
Taipei, Taiwan
Republic of China
INTRODUCTION
Reverse osmosis has been used in the chemical, food processing, pharmaceutical industries, and
sea water desalination for many years. Also, this process has been applied in the treatment of industrial waste [1] such as electroplating [2,3,4], pulp spent liquor [5], wastewater reclamation [6,7], oily
waste water [8], and electronic waste [9]. We can say that there are two general applications of RO.
One is the production of clean water; the other is a salt concentrate. We may obtain drinking water
from salty water or recover valuable salts from a waste solution by RO. However, in applying RO for
the treatment of laundry waste water from a nuclear power plant, we are concerned about both the
"permeate" and "retentate". We require not only a clean permeate without radioactive hazard, but
also a minimum volume of concentrate containing radioactive species in order to treat and to dispose
it easily. Due to large volume and low radioactive strength in the laundry waste water, it is necessary
to study on how to reduce its volume.
EXPERIMENTAL
A schematic diagram of the experiment unit is shown in Figure 1. The RO apparatus used in this
study is Vaponics Model VRO-1 and DDS Lab-Unit, Type 20. The Vaponics module is a spiral
wound while DDS module is a frame plate type. The raw water tested was synthesized accordingly to
the water quality found from the actual laundry waste water from nuclear power plant as shown in
Table I. During this experiment we also changed the heavy metal contents.
For Vaponics module only cellulose acetate (CA) membrane was investigated. The average transmembrane pressure was about 180 psi. The parameters studied were pH, total solids, water temperature, water recovery, and operation time. For DDS module CA membrane (CA-990, CA-992, and
CA-995) and Polyamide (HR95 and HR98) were tested. Pressure was operated from 200 psi to 600
psi.
RESULTS AND DISCUSSION
Vaponics Module
pH
The first step in this experiment was to synthesize the laundry waste water and change the pH value
in order to find out the influence of pH on the performance of RO. The result is shown as Figure 2.
High pH water will make the CA membrane hydrolyze, influence the adsorption capacity of membrane, and change the constituents form in water [10]. From Figure 2 we find that the optimum pH
seems to be about 4.5. Thus, the succeeding experiments were conducted at this pH.
7o/i7/ Dissolved Solids
As shown in Figure 1, raw laundry waste water was treated by a prefilter to remove suspended
solids in order to prevent them from clogging the membrane. During this stage of experiment, the concentration of Cr, Mg, Co, Sr, Cs in the raw water was varied and the rejection ratio was investigated.
The result is shown as Figure 3. The rejection ratio decreases with the increase of solids content in the
raw water. Solute concentration increases in raw water may increase the solute content in the permeate
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