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06 Water Purification: Physical Treatment: Distillation.




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This article is from the Water Treatment FAQ, by Patton Turner with numerous contributions by others.

06 Water Purification: Physical Treatment: Distillation.

Distillation is the evaporation and condensation of water to purify
water. Distillation has two disadvantages: 1) A large energy input is
required and 2) If simple distillation is used, chemical contaminants
with boiling points below water (such as ethlyene gycol in automotive
antifreeze) will be condensed along with the water. Distillation is
most commonly used to remove dissolved minerals and salts from water.

The simplest form of a distillation is a solar still. A solar still
uses solar radiation to evaporate water below the boiling point, and
the cooler ambient air to condense the vapor. The water can be
extracted from the soil, vegetation piled in the still, or
contaminated water (such as radiator fluid or salt water) can be added
to the still. While per still output is low, they are an important
technique if water is in short supply

Other forms of distillation require a concentrated heat source to boil
water which is then condensed. Simple stills use a coiling coil to
return this heat to the environment. These can be improvised with a
boiler and tight fitting lid and some copper tubing (Avoid using lead
soldered tubing if possible). FEMA suggests that, in an emergency, a
hand towel can be used to collect steam above a container of boiling
water. More efficient distillations plants use a vapor compression
cycle where the water is boiled off at atmospheric pressure, the steam
is compressed, and the condenser condenses the steam above the boiling
point of the water in the boiler, returning the heat of fusion to the
boiling water. The hot condensed water is run through a second heat
exchanger which heats up the water feeding into the boiler. These
plants normally use an internal combustion engine to run the
compressor. Waste heat from the engine, including the exhaust, is used
to start the process and make up any heat loss. This is the method
used in most commercial and military desalinization plants

Inflatable solar stills are available from marine supply stores, but
avoid the WW2 surplus models, as those who have used them have had a
extremely high failure rate. Even new inflatable solar stills may only
produce from 30-16 oz under actual conditions, compared to a rating of
48 oz/day under optimum conditions.

Desanilation kits are not the same as solar stills. These kits
contain a tablet that binds the salt up. One tablet will treat X
amount of water

Jade Mountain also offers the following portable models in travel
cases:

Traveler (WC106) 1 gpd,23 lb., 24x26x10 folded $695
Base Camp (WC107) 2 gpd,51 lb., 48x48x4 folded $895
Safari (WC108) Ruggedized version of the Base Camp, 48X48X5 $1095

 

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