Saline Water - Considerations for Future Water Supply. Bruce Thomson Water Resources Program UNM

Transcription

1 Saline Water - Considerations for Future Water Supply Bruce Thomson Water Resources Program UNM (bthomson@unm.edu) 1

2 Objectives Provide overview of Reverse Osmosis (RO) technology Identify differences between seawater & inland desalination Identify limitations of inland desalination on development of brackish & saline ground water resources 2

3 Saline & Brackish Water Resources in NM Brackish water - TDS > 1,000 Saline Water - TDS > 10,000 3

4 Saline & Brackish Water Resources in NM 75% of ground water in NM estimated to be brackish or saline (Reynolds, 1966) Until 2009 legislative session, deep (>2,500 ft) brackish (TDS > 1,000 mg/l) water wasn t regulated by the State Engineer. Pending legislation resulted in rush of Notices to Appropriate brackish water. Volume of Brackish Water Claimed 1.4E E E E+06 Acre-Ft 8.0E E E E E E E Jan-08 Apr-08 4

5 Notices to Appropriate Near Albuquerque (Jan. 2009) 5

6 Reverse Osmosis High pressure used to force water through semipermeable membranes Salts & other dissolved constituents will not pass through the membrane Pressure is determined by salt concentration (TDS), not by membrane characteristics Technical improvements in membranes will not reduce pressure requirements 6

7 Reverse Osmosis Terms RO Membrane Feed Water High Pressure Pump Permeate Concentrate (Brine) Energy Recovery System 7

8 Desalination Energy Costs (Thermodynamics - It s the Law) RO pressure depends on TDS: Feedwater TDS Fractional recovery Thermodynamic min. energy requirement for seawater (0% recovery) = 0.7 kwh/m 3 = 2.6 kwh/10 3 gal Energy requirement increases as recovery increases ABC WUA treatment plant uses 0.17 kwh/m 3 = 0.64 kwh/10 3 gal 8

9 Seawater vs. Groundwater Chemistry Sea water is dominated by Na + &Cl - - low fouling potential Ground water contains Ca 2+, HCO 3-, SO 2-4, and SiO 2. All have high fouling potential K+ 1% Mg2+ 5% Ca2+ 1% Mg2+ 2% K+ 1% Ca2+ 6% Cl- 20% Na+ 42% Cl- 48% Na+ 40% HCO3-9% Seaw ater TDS = 35,400 mg/l SO42-3% HCO3-0.2% Sandoval Co. Ground Water TDS = 12,500 mg/l SO42-22% 9

10 3 Principal Challenges to Inland Desalination Energy requirements Recovery Leads to membrane fouling Increases pressure requirements Concentrate disposal 10

11 Seawater vs. Inland Desal Parameter Seawater Desal Inland Desal Source of Supply Sustainability Seawater unlimited Ground water limited Water Rights? Fractional Recovery Not important Very important Water Quality Mainly Na + & Cl - Low scaling potential High Ca , CO 3, SO 4 High scale potential Concentrate disposal To ocean Deep well injection Evaporation Hazardous constituents? Others? Environmental impact Minimal Uncertain Brine disposal Aquifer impacts 11

12 Energy Considerations A 30 MGD facility treating 12,500 TDS water to 75% recovery: 750 psi Power = 192,000 kwh/day (Just for desalination) CO 2 emissions = 250,000 lbs CO 2 /day based on NM energy profile 12

13 Summary Points Inland desalination presents many challenges: Technical: Recovery, scaling, waste disposal Energy Cost Environmental impacts: Waste disposal, carbon footprint, aquifer impacts Sustainability Saline/brackish water should not be primary source of residential or municipal supply Can serve as source of emergency supply in times of drought 13

14 3.5E E E+06 New Mexico Mid Rio Grande Estancia Basin The Future Challenge: My Perspective Population 2.0E E E+06 What s the biggest challenge? 5.0E E (BBER, 2008) Year acre feet x 1000 (kaf) Average Monthly Aggregated Streamflow Baseline 2030 Dry 2030 Middle 2030 Wet 2080 Dry 2080 Middle 2080 Wet 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec (Hurd & Coonrod, 2007) 14

15 Final Thoughts State of NM needs to begin a dialog to address the question are there limits to growth? Limiting factors might be Economy and/or jobs Water Others Corollary: What would a zero population growth economy look like? 15