Reverse Osmosis Desalination Is ocean water a viable source of drinking water? ** General Note ** - Times for each slide are estimates. If there’s extra time remaining, give more time for groups to complete the group activity (slide 19) 7 minutes – Go around the classroom asking students if they think ocean water could be a viable source of drinking water and why or why not. They just need to give an educated guess Jenny Meyer

What is desalination? A process that removes dissolved minerals (including salt) from seawater, brackish water (water that has more salinity than freshwater but less than seawater), and wastewater Ocean water = 35,000 ppm of salt Brackish water = 1,000 – 10,000 ppm of salt Fresh water = less than 1,000 ppm of salt 300 million people worldwide rely on desalination for their fresh water needs 1 minute to cover slide material http://www.freedrinkingwater.com/water_quality/quality1/1-make-seawater-drinkable.htm http://www.ngwa.org/media-center/briefs/documents/brackish_water_info_brief_2010.pdf https://www.chemistryworld.com/news/solar-powered-desalination-produces-energy/1010102.article

What is osmosis? A process in which a solute (ex. salt) is dissolved in a solvent (water) and the solvent moves through a semipermeable membrane into a solution of higher solute concentration (water with higher amounts of dissolved salt). The concentration of the solute on the two sides of the membrane tends to equalize. 2 minutes to cover and explain slide material https://www.merriam-webster.com/dictionary/osmosis http://science.howstuffworks.com/reverse-osmosis1.htm http://www.buzzle.com/articles/osmosis-vs-diffusion.html

What is osmotic pressure? The pressure that must be applied to the solution to prevent the flow of water across the semipermeable membrane Equation: π = MRT π = osmotic pressure (atm) M = molar concentration of dissolved species (mol/L) R = ideal gas constant (0.082057 L atm mol-1 K-1 ) T = temperature (K) 2 minutes to cover and explain slide material http://www.chem.purdue.edu/gchelp/howtosolveit/Solutions/osmoticpressure.html https://lookfordiagnosis.com/mesh_info.php?term=osmotic+pressure&lang=1

Given that the average molarity of seawater is 0 Given that the average molarity of seawater is 0.479 M and a temperature of 293 K, calculate the osmotic pressure. Equation: π = MRT π = osmotic pressure (atm) M = molar concentration of dissolved species (mol/L) R = ideal gas constant (0.082057 L atm mol-1 K-1 ) T = temperature (K) 5 minute for students to complete question

Answer π = MRT π = 0.479 mol/L * 0.082057 L atm mol-1 K-1 * 293 K 2 minutes to go over answer and answer any questions

What is reverse osmosis? Unsurprisingly, reverse osmosis is the opposite of osmosis The solvent (water) filters out of a high concentrate solution (saltwater) into a lower concentrate solution (freshwater) Pressure must be applied to the saltwater side of the tank to push the water through the membrane. Therefore, reverse osmosis (RO) makes desalination possible 60% of desalinated water was treated by RO in 2008 2 minute to cover and explain slide material http://science.howstuffworks.com/reverse-osmosis.htm http://puretecwater.com/reverse-osmosis/what-is-reverse-osmosis https://www.youtube.com/watch?v=26eyaXYIBuI

How much pressure must be applied in RO? Review: Pressure = Must apply enough pressure on the saltwater side of the tank to counteract the natural osmotic pressure as well as enough pressure to push the water through the filter 30-250 psi for fresh and brackish water 600-1000 psi for seawater 350 psi of natural osmotic pressure 2 minute to cover and explain slide material http://idahowatersolutions.com/reverse-osmosis-faqs/#1 http://science.howstuffworks.com/reverse-osmosis2.htm http://www.daerospace.com/HydraulicSystems/HydraulicFluidProp.php

When was reverse osmosis developed? 1950s - Researchers began to look for ways that ocean water could be desalinated Was a high priority technology goal during the Kennedy administration 1959 – Researchers at UCLA created a functional synthetic RO membrane from cellulose acetate polymer. It could reject salt and pass fresh water at realistic flow rates and pressures 1965 – First RO desalination plant in Coalinga, CA 1 minute to cover slide material Cellulose acetate polymer filter http://www.medline.com/product/08-UM-Cellulose-Acetate-Membrane-Filter-by-Sartorius/Z05-PF104736 http://science.howstuffworks.com/reverse-osmosis3.htm http://engineering.ucla.edu/first-demonstration-of-reverse-osmosis/ http://www.biocompare.com/20027-Membrane-Filters-Mixed-Cellulose-Esters/4223737-Cellulose-Acetate-Membrane-Circle-OE-67-0-45-m-pore-size-47-mm/?pda=20027|4223737_4_0|||

What does the reverse osmosis process look like with today’s technology? A video describing the reverse osmosis process at a desalination plant in Sydney, Australia 4 minutes – run time of YouTube clip https://www.youtube.com/watch?v=aVdWqbpbv_Y

RO Today (cont’d) A video giving a closer look at a RO membrane assembly 3 minutes – run time of YouTube clip https://www.youtube.com/watch?v=VGYgbPKSZs4

Where is reverse osmosis most frequently used? The Middle East Only receives 20-40 cm of water per year Oil rich which keeps energy prices low 70% of Saudi Arabia’s water comes from desalination but only 50% of that amount uses RO California and Florida 11 minutes – 1 minute to cover slide material, 10 minute runtime of YouTube clip https://www.youtube.com/watch?v=3Skuk8DeXpE https://water.usgs.gov/edu/drinkseawater.html http://www.natureasia.com/en/nmiddleeast/article/10.1038/nmiddleeast.2014.273

Given that 200 million KWH/day are used in desalination plants worldwide and 300 million people use that water, how much natural gas would be consumed per person through desalination? 10 minutes for students to complete problem

Answer 1 KWH = 3.311 cubic feet of natural gas 200 million KWH = 662,200,000 cubic feet of natural gas 2.2073 cubic feet of natural gas per desalination customer per day Average annual natural gas consumption per customer = 528 thousand cubic feet (California, 2015) 1446.58 cubic feet per day If an entire community served by desalinated seawater, the annual power usage for a household would increase by 10% 2 minutes to go over answer and answer any questions http://www.convertunits.com/from/kWh/to/hundred+cubic+foot+of+natural+gas https://www.eia.gov/dnav/ng/ng_cons_num_a_epg0_vp5_mcf_a.htm https://www.amtaorg.com/wp-content/uploads/7_MembraneDesalinationPowerUsagePutInPerspective.pdf

What are the main disadvantages of RO desalination? High energy needs Plants uses 200 million KWH/day worldwide 3-10 KWH are needed to produce 1 cubic meter of freshwater compared to 1 KWH for conventional freshwater Roughly 2/3 of the energy is used to supply the necessary water pressure Cost 1,000 gallons of RO desalinated water costs $2.5 - $5 per 1000 gallons compared to $2 for conventional fresh water 2 minute to cover slide material http://www.lenntech.com/processes/desalination/energy/general/desalination-costs.htm https://www.technologyreview.com/s/533446/desalination-out-of-desperation/ https://www.pri.org/stories/2015-05-15/desalination-expensive-energy-hog-improvements-are-way

Disadvantages (cont’d) Disposal of brine Brine – the wastewater from the RO process that has a high salt concentration (generally twice as much as the intake water) Brine is disposed back into the ocean. Long term effects on marine life are not understood Can be mixed back in the open seawater with high speed jets so salinity levels are back to normal within 100 feet of the release point. Inefficiency of the RO process 55-75% of the intake water is discharged as brine 1 minute to cover slide material http://www.sandiegouniontribune.com/opinion/commentary/sdut-desalination-carlsbad-marine-life-cartamil-2015nov28-htmlstory.html http://www.lenntech.com/processes/desalination/brine/general/brine-disposal.htm http://pacinst.org/publication/desal-marine-impacts/

What maintenance is performed on a RO plant? Preventive maintenance Instrument calibration, pump adjustment, chemical feed inspection and adjustment, leak detection and repair, and structural system repair Fouling Caused when membrane pores are clogged by salts or other particulates Membranes must be cleaned or backwashed about every 4 months Cartridge filter elements must be replaced about every 8 weeks Membrane lifespan is about 2-3 years 1 minute to cover slide material https://www.oas.org/dsd/publications/Unit/oea59e/ch20.htm

Could a RO desalination be powered by renewable energy? Since the largest obstacle for RO desalination is high energy needs, could this be avoided by using renewable energy? A RO desalination system designed to be powered by wind or solar energy Read the following article: https://www.technologyreview.co m/s/601419/to-make-fresh-water- without-warming-the-planet- countries-eye-solar-power/ 12 minutes – 1 minute to cover slide material, 4.5 minute YouTube clip, 6.5 minutes to read article https://www.youtube.com/watch?v=26eyaXYIBuI

Group activity: Research a new technology that could improve RO desalination or desalination in general and present findings The technology could be one that improves efficiency or decreases negative environmental impacts 45 minutes – 30 minutes of group work, 15 minutes to present results

Examples of new technologies Shock electrodialysis https://www.technologyreview.com/s/524606/new-desalination-technique-also- cleans-and-disinfects-water/ Microbial capacitive desalination http://www.colorado.edu/today/2015/02/24/cu-boulder-technology-could-make- treatment-and-reuse-oil-and-gas-wastewater-simpler Desalination pipe in Santa Monica, CA http://www.businessinsider.com/solar-powered-desalinization-tube-2016-8 5 minutes – have students click on one of the links and read the corresponding article