1. Project Goals and Approach Experimental Sequence
Predicting RO Removal of Toxicologically Relevant Unique Organics
Lauren Breitner, Dr. Kerry J. Howe, Dr. Andrea F. Corral
Background
Water reuse, specifically direct potable reuse (DPR), is continuing to be seen as a viable option for communities with extreme water scarcity. The need for investigating the removal of CECs has become crucial for further DPR considerations. Reverse osmosis (RO) has been demonstrated to remove many CECs. However, RO removal efficiency can be affected by many factors, including the physical-chemical properties of the CEC, membrane properties, process operating conditions, and feedwater characteristics. A useful relationship between these variables can be achieved by using a quantitative structure activity relationship (QSAR) model. This study aims to conduct laboratory-scale experiments of trace organic rejection to develop an integrated process and QSAR model to predict the rejection rates of a wide range of compounds via RO treatment.
Model Development
Process Model
Rejection: Permeate Concentration:
Mass Transfer Coefficients:
Using a numeral integration across the length of a RO element, then across multiple elements in a stage for overall plant performance, the above can be calculated. This approach also takes concentration polarization into account via a boundary layer model.
Membranes Selected
Process Model
(kW and kS for salts)
QSAR Model
Combined Model Organic Removal Efficiency
Operating Conditions
(Pf, Cf, T, v, , , , etc.)
Membrane Properties
(Permeate flow,
salt rejection)
Literature Removal Data
kS for organics
Experimental
Data
Membrane Chemistry
Intrinsic Interactions between Organics and Membrane, ΔGintr
Selection of Organics
Manufacturer
Product
Type 1
Permeate Flow 2 (m3/d)
NaCl Rejection (%)
Dow Filmtec
SW30XHR SW
23.0
99.82
Toray
TM800M
26.5
99.8
Hydranautics
ESPA2-LD BW
37.9
99.6 GE
AG LF
39.7
99.5
TMG(D)
45.8
99.7
BW30HR
48.0 AP
ULP
47.2
95.0
NF 270
47.0
97.0 3
Project Goals and Approach
Develop a model to predict the removal efficiency of organic compounds of potential health concern (PPCPs, EDCs, etc.) by reverse osmosis for potable reuse applications. The model will account for organic compound characteristics, membrane properties, and operating conditions.
Experimental Methods
Experimental Conditions and Variables
Experimental Sequence
Bulk Average kw and ks Values
Variable
Notes
Organic compound
25 to 30 compounds
Membrane product
8 membranes
Feed pressure
7.5, 15, and 22.5 bar (109, 218, and 326 psi).
Feed flowrate
Cross-flow velocity = 0.18 m/s
Temperature
20 C
Permeate pressure
0 bar
TDS concentration
2,000 mg/L NaCl
Spacer thickness
28 mil pH
Depends on final compound selection
Solution composition
DI water, NaCl, H3BO3, NaHCO3 (buffer), organics, acid or base for pH adjustment
Experimental Setup
Measured Parameters
Preliminary tests are being completed currently to understand any variations in experimental data that can be attributed to the experimental setup or sampling procedures. Experiments have been performed with ethanol and sodium chloride to gain an understanding of these variations.
Rejection based on the following test conditions:
Feed pressure: 100 psi
Ethanol feed concentration: 8 mg/L
Sodium Chloride feed concentration: 2,000 mg/L
Note: Rejection is measured as conductivity rather than concentration of NaCl. This may lead to a slightly higher rejection of ions than shown above.
Preliminary Results
Parameter
Feed
Permeate
Concentrate
Flow rate 
Pressure
Temperature
Conductivity
Organic concentrations
H3BO3 concentration pH
Step
Notes
Cleaning and compaction
Insert new membranes, operate for 24 hours, recycle permeate and concentrate, change water periodically, measure baseline water flux.
NaCl rejection
Operate 24 hours, recycle permeate and concentrate, measure permeate flux and conductivity for NaCl rejection.
Organic equilibration
Operate 72 hours, recycle permeate and concentrate, allow organic concentrations to equilibrate (allows for adsorption).
Sampling
Each permeate measured individually, starting with membrane 1. Change operating conditions (e.g. pressure), wait 1 – 2 hours, repeat sampling.
Bench-scale Experimental Setup
5-Chamber RO Test System
The University of New Mexico gratefully acknowledges the WateReuse Research Foundation’s financial, technical, and administrative assistance in funding and managing the project through which this information was discovered, developed, and presented.
The comments and views detailed herein do not necessarily reflect the views of the WateReuse Research Foundation, its officers, directors, employees, affiliates, or agents.