1. Water Treatment for Solar Panel Cleaning using Membrane Distillation
Coral R. Taylor, P.E. and Sage R. Hiibel, Ph.D.
Department of Civil and Environmental Engineering ~ University of Nevada, Reno
Project Overview
Bench- and Pilot-Scale DCMD Systems
Nevada Solar & Water Express
The NV Solar Nexus Water Team’s objective is to develop sustainable and advanced water/wastewater approaches to support the water needs of solar energy development and to use solar energy to process water. As part of this, a mobile water treatment trailer, the Nevada Solar & Water Express, is being developed that can treat water at various solar facilities.
Figure 1: Treatment and reuse of water for cleaning solar panels powered by solar heat.
Bench-Scale
Used to evaluate treatment performance of commercially available membranes
Maximum water flux and contaminant rejection
Minimum fouling and scaling
Experimental data for development and validation of computational DCMD model
Figure 3: Schematic2 and lab setup of the bench-scale DCMD system.
Pilot-Scale
Used to treat solar panel wash waters and other wastewaters at solar energy facilities
Novel stacked flat-sheet design
Increased membrane surface area with small footprint
Improved thermal profile over hollow-fiber systems
Modular design for adjustable treatment throughput
Figure 4: Side view and expanded gasket schematics of the small pilot-scale DCMD module.
Mobile water treatment trailer for use on-site at solar energy facilities in Nevada
Will include a variety of state of the art and standard water treatment technologies
NEXUS technologies
DCMD, solar distillation, solar water heater
Traditional technologies
Advanced oxidation, UV disinfection, filtration, etc.
Modular workspace design for flexibility
Will also serve as an educational demonstration unit to raise STEM awareness
Photovoltaic panels will provide a portion of electrical needs
Figure 7: Profile and plan views of the Nevada Solar & Water Express mobile water treatment trailer.
Used Wash
Water
Membrane Distillation
Gasket
Feed Side
Membrane
Distillate Side
Solar Heat
Plan View
Profile
View
Panel
Cleaning
Water
Treated
Water
Distillate
Feed
Chiller
Circulating Pumps
Membrane Module
Data Acquisition Computer
Heated Bath
Flux Balance
Conductivity Meter
Flow Meters
Direct Contact Membrane Distillation
Emerging treatment technology for brackish and some industrial wastewaters
Temperature-driven membrane separation process
Hot ‘dirty’ water circulated on feed side
Cold ‘clean’ water circulated on distillate side
Temperature difference creates partial vapor pressure difference (Dpvap) across membrane
Dpvap drives transport of water vapor through microporous, hydrophobic membrane
Provides high rejection of non-volatile contaminants and high water recoveries
Figure 2: Schematic of DCMD1
Key Advantages
Low operating pressures
Low operating temperatures
Waste heat or solar heat sources can be used
Driving force not function of concentration
Maintains efficiency at high salt concentrations
Feed Side
Distillate Side
Membrane
Preliminary Results
Wide variety of membranes evaluated for water flux and hydrophobicity (Table 1)
Hydrophobicity based on contact angles (Fig. 5) obtained with tensiometer (Fig. 6)
0.2 mm pore-size membranes (3M PP 0.2, PP 0.2, QM022) are more hydrophobic
Presence of surfactants in feed water dramatically decreases membrane hydrophobicity (<90° in all cases, data not shown) resulting in pore flooding and high salt passage
Acknowledgements
This material is based upon work supported by the National Science Foundation under Grant No. IIA
Thanks to Mark Lattin, Development Technician III at University of Nevada, Reno, and Peter Faught, Experimental Testing/Prototype Engineer at University of Nevada, Las Vegas, for assistance with trailer design and fabrication.
Figure 5: Schematic of the contact angle between a wetted surface and a water drop3. Contact angles less than 90° indicate a hydrophobic surface.
Table 1: Hydrophobicity of commercially available membranes tested.
Membrane
Contact Angle
3M ECTFE
110.3°
3M PP 0.2
121.2°
PP 0.2
134.3°
3M PP 0.45
122.6°
PTFE 0.45
134.2°
QM011
125.5°
QM022
134.9°
Figure 6: Lab setup of tensiometer. Shown with tilting cradle for testing slanted solar panel surfaces.
References
1Adham, S. et al. (2013). Desalination,
2Rao, G. et al. (2015). Desalination,
3www.ramehart.com/contactangle.htm