The Saline Solution

Desalination as an alternative to Hawaii’s Thirst

By Alex Watanabe, Hunter Hunt and Sara Robinow

What is Desalination?

• ““The removal of salt or other The removal of salt or other chemicals from something, such as chemicals from something, such as seawater or soil. Desalinization can seawater or soil. Desalinization can be achieved by means of be achieved by means of evaporation, freezing, reverse evaporation, freezing, reverse osmosis, ion exchange, and osmosis, ion exchange, and electrodialysis.” (dictionary.com)electrodialysis.” (dictionary.com)

Popular Methods of Desalination

• Reverse Osmosis• Multistage Flash Distillation

• Solar Distillation• Ion exchange• Electrodialysis

• FreezingQuickTime™ and a

TIFF (Uncompressed) decompressorare needed to see this picture.

Reverse Osmosis

•Forces saline water through a membrane and the salt gets left behind

•Lower energy consumption

•Higher up front investment

•Can operate with fluctuating demand for water

Multistage Flash Distillation

• Most widely used method

• Process: Heat saline water to a very high temperature and pass it through vessels of decreasing pressure to collect the

maximum amount of water vapor

Feedwater salinity• It costs 3 to 5 times as much to

desalt salt water than brackish water

Energy Cost•50%-75% of the cost of water

is for the cost of energy

Economies of Size

•The more water you desalinate, the less it costs

Cost Variables

CostCost

• $0.30-$2.10 per kL depending on process, $0.30-$2.10 per kL depending on process, not including disposal or distributionnot including disposal or distribution

• To build a brackish water treatment facility, it To build a brackish water treatment facility, it would cost about $40-$50 million.would cost about $40-$50 million.

• To build a seawater treatment facility, it would To build a seawater treatment facility, it would cost more than $100 million.cost more than $100 million.

Costs and Energy Consumption

•For every 326,000 gal. of water (1 acre foot) it would take app. 29,500

kilowatt hours of electricity to desalinate.

•A modern plant capacity is 112,000 AF/year for 3, 304,000,000 kilowatt

hours/year

Efficiency in terms of Production Cost of Power

• Wind Power= $0.0004/ kilowatt hours• Hydroelectric=$0.008/ kWh• Nuclear power= $0.0172/ kWh• Solar Power= $0.0217/ kWh• Coal Power= $0.0221/ kWh• Natural Gas= $0.0751/ kWh• Petroleum= $0.0809/kWh

Annual Power Cost

• Hawaii power plants use petroleum

• For a modern capacity desalination plant, Hawaii’s cost per year:

-$63,000,000

• Hawaii consumes 26,535.1 AF/year

Solar Still Experiment

• 1st design:– 1 liter of salt water was poured into a large

container. When the water evaporated, it was collected by the roof and funneled into a smaller concentric container.

• Results:– Day 1: 35 mL water collected– Day 2: 12 mL water collected– Average return: 2%

Solar Still Experiment

• Second Design:– 500 mL of salt water was placed in the smaller

concentric container and when evaporated, dripped into the outside larger container (opposite of the first design).

• Results:– Day 1: 35 mL of water collected– Day 2: 26 mL of water collected– Day 3: 35 mL of water collected– Averaged return: 6%

What We Learned:

• The efficiency of solar distillation depended upon uncontrollable variables such as temperature, weather, and rate of evaporation

• It is likely that if continued, we could have designed a much more efficient still.

Consequences

– As previously discussed, the price of desalination (includes pumping, desalinating, etc.) make it one of the most expensive sources of water.

– Also previously discussed, it would be expensive and power consuming to run a desalination plant.

– Environmental consequences: Desalination produces a waste product that is a highly concentrated salty brine. Also sometimes containing chemicals and toxic metals, this liquid waste is released directly into the ocean, which can potentially cause damage to the costal marine environment. Also, marine life will be killed if they are sucked into the plant itself.

– Conservation: Relying on turning salt water into fresh water could weaken the conservation of the fresh water that we already have.

Is It Worth It?

Well…

The Answer is incredibly speculative and subjective.

The Factors

• How much will it cost?

• Do we need it?

• How fast are we depleting our current water supply?

• What will it consume cost or energy wise?

• What method will we use?

Pros• An almost inexhaustible water supply.

• Non damaging to the certain aspects of the environment (freshwater lens, less consumption from artesian systems)

• Clean healthy water

Cons• It is expensive• Some methods are inefficient• High overhead• Damaging to other aspects of the

environment (high salt waste byproduct)• Some animals get sucked in and killed

(damage/clog filters, expensive to replace)

Conclusions

• Hawaii’s environment is ideal for a desalination system, although there is a lack of space.

•It would solve Hawaii’s water problem, but it would be very expensive