1. RO / NF Applications in Brackish Water Desalination: membrane characterization and hybridization with EDR
Ghazaleh Vaseghi; Neil Moe; Abbas Ghassemi; James Loya
New Mexico State University, Institute for Energy and Environment
ABSTRACT
INTRODUCTION
RESULTS
Hybridization tests
Following is the hybrid scenario which were tested:
Reverse Osmosis (RO) is one of the technologies used for desalinating brackish and saline waters to provide drinking water. RO treatment plants use semipermeable membranes and pressure to separate salts from water.
The focus of this study is in two parts. First is, studying the characterization of different types of membranes used in RO systems. A huge database collected from a full pilot-scale system, located at the Brackish Groundwater National Desalination Research Facility (BGNDRF) in Alamogordo, NM, and operated by New Mexico State University, are going to be analyzed.
Second part is to combine pressure driven systems, like RO / NF, with electric driven ones, like EDR, find out the stability of hybrid systems, and try to develop a cost model for them. In order to get to this approach we are running such systems in a pilot plant for about 300 hrs. Then, to model the hybrid system, WinFlows is used for RO and WATSYS is used for EDR. At the end of modeling, applying mass balance, we can get to the product and concentrate blowdown streams specifications. Of course, there are different scenarios of hybridization. We choose couple of these scenarios worthwhile to examine to do the experiments.
With the growth of membrane science In the last two decades, Reverse Osmosis (RO) overtook multi stage distillation MSF as the leading desalination technology, and have advanced significantly, allowing new brackish groundwater desalination facilities to use RO technology much more economically than distillation. RO systems typically use less energy than thermal distillation, leading to a reduction in overall desalination costs [3].
Nevertheless, the major problem of RO desalination plants is the generation of a concentrate effluent (brine) that must be properly managed. Disposal of such brines presents significant costs and challenges for the desalination industry due to high cost and environmental impact of brine disposal [3].
One approach that is somehow novel these days to solve this challenge is using the hybrid systems. The hybrid desalting concept is the combination of two or more processes in order to provide better solutions, a lower cost product than either alone can provide. These systems can be used for all seawater, brackish water, waste water, and ultrapure water. Higher combined recovery, lower energy costs and lower lifecycle costs can be reached by this approach.
Figure 1. Hybrid System
Figure 9. Primary Pressure (psi)
Feed
gpm
Permeate
Concentrate
Recovery % NF
33.5 gpm
24 gpm
260 uS/cm
9.5 gpm
5000 uS/cm
73%
Product
Stage1 Current
Stage 2 Current
EDR
39000 uS/cm
SO4:
27-29 kppm
Calcium Hardness:
8-9 kppm
SI(CaSO4)=10.5
LSI=1.92
< 2000 uS/cm
35 amps
18 amps
Table 1. Setpoints of Hybrid System
Figure 10. Primary Pressure (psi)
RESULTS
DK membrane characterization tests
A-value, the factor of water permeability of membrane is too low
Figure 11. Permeate Conductivity with modified B-value
Conclusions
Figure 2. Primary Pressure (psi)
Figure 3. Primary Pressure with modified A-Value
A-value multiple=1.13, B-value multiple= leads to pretty good WinFlows projection
Negative rejection of Cl- is observed in experimental data
Better rejection of divalent cations compared to monovalent cations: both experiment and WinFlows
Almost complete removal of Sulfate in experiments
B-value, the factor of salt permeability of membrane is too low
MATERIALS AND METHODS
First set of experiments are designed to test the effect of Recovery, Permeate Flow, Inlet pH, and Inlet Conductivity on Permeate and Concentrate Conductivity, Primary Pressure, and Bank one Permeate Flow. Three different levels for set points are determined, and randomized to increase the power and reliability of experiment. Comparing measured data with the predicted ones by WinFlows, we are getting to the accurate operating models for RO/NF systems. During the pilot testing, water samples are sent to Woodlands analytical lab for water chemistry determination. Then, the chemical analysis results are used to figure out ion rejections of each set of membranes. Second set of experiments are belonged to hybrid systems. Most common way of hybridization is to combine pressure driven systems, like RO/NF, with electric driven ones, like EDR. To model the hybrid system, WinFlows is used for RO and WATSYS for EDR. At the end of modeling, applying mass balance can lead to the product and concentrate blowdown streams specifications.
Figure 5. Permeate Conductivity with modified B-value
Figure 4. Permeate Conductivity (uS/cm)
REFERENCES
CONTACT
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Figure 6. Rejections of Na+ and K+
Figure 7. Rejections of Cl- and F-
<Ghazaleh Vaseghi>
<New Mexico State University, Institute for Energy and Environmenr>
Phone: (575)
Figure 8. Rejections of Mg++ and Ca++