Water & Water Purification
Dec 19, 2015
Water
• Expands when freezing – fish • Liquid at room temperature – H-bonding• High specific heat (heat capacity) ↑ - weather • High heat of vaporization – cooling ↑• High surface tension – capillary act.↑• An excellent solvent (polar)
– Sometimes good?– Sometimes bad?
Water
• Covers 72% of the earth’s surface– Average of 2.5 miles deep
• 97.6% of all water is in the oceans
• 2.07% is in ice caps and glaciers, etc
• .5% is in groundwater (.28% above 1 km)
• .009% is in fresh lakes and rivers
• .005% is in soil moisture
• .008% is in the atmosphere
Hydrologic Cycle
• 4350 billion gallons/day fall on contig. US
• 3100 billion gallons/day ↑– By evaporation– By transpiration ?
• Plants giving off water – Oak tree 110 gal/day, acre of corn 3000 gal/day
• 800 billion gal/day ↓ to oceans and groundwater
• Leaves 450 billion gal/day for our use
Water Use
• In 1900 use was 40 billion gal/day
• In 1993 use was more than 400 billion gal/day
• Today? Constantly growing and water is being reused.
• World Resources Institute – by 2025, 3.5 billion people will experience water shortages.
Aquifers (groundwater)
• In US we were removing 90 billion gal/day– Source and demand are out of balance– Ogallala Aquifer stretches from SD to TX
• Was 58 ft thick in 1930• Was 8 ft thick in 1990
• Recharging – inject treated sewage water back into aquifers drinking water is coming out of.– El Paso, TX 10 million gal/day
Aquifer Depletion
• Causes subsidence – San Joaquin Valley– More than 40 ft
• Causes sink holes – south east – more damage
• Causes sea water encroachment – both coasts
Water Pollution
• What is in pure water?
• What is clean water?– Depends on use– Some pollution is natural– Most of the worst is man-made
• Clean Water Act – 1977 – responsibility on the wastewater producer
Chlorination
• Oxidizes the cell walls of water-borne bacteria– Started in early 1900’s– Deaths from typhoid, cholera, paratyphoid,
and dysentery decreased from 35/100,000 in 1900 to 3/100,000 in 1930
• Also reacts with trace organics → chlorinated hydrocarbons (THM’s)– 50% - 100% increased risk from cancer
(rectal, colon, bladder)– Why use?
Other options
• Most common chlorination – HOCl – hypochlorous acid – chlorination of HC’s
• Can use ozone, O3
– Expensive, no residual protection, and oxidizes organics – toxic
• Chlorine dioxide, ClO2
– Less toxic organics, chlorite and chlorate ions are troubling
• Ultraviolet light, UV, - complications