《大学化学》课程PPT教学课件（英文版讲稿）Chapter 16 Fresh water resources

Chapter 16 Fresh water resources 16 Fresh Water Resources Saline water in oceans: 97.29 Ice caps and glaciers: 2. 14% Available fresh water: 0669 Fresh water is a limited source

Chapter 16 Fresh water resources Fresh water is a limited source

16. 1 Water circulates through the hydrologic cycle (水文循环) The Earth's water is constantly circulating powered by the heat of the sun and the force of gravity Water evaporated from ocean precipitates(降水) into the ocean direct route Water evaporated from ocean is blown by winds until it is over the land and precipitates:(1 evaporates beck into atmosphere, (2). Infiltrate the ground, (3 ). Become part of the snow or glacier,(4). Drain to a river and back to the sea

16.1 Water circulates through the hydrologic cycle （水文循环） • The Earth’s water is constantly circulating, powered by the heat of the sun and the force of gravity. • Water evaporated from ocean precipitates (降水) into the ocean: direct route. • Water evaporated from ocean is blown by winds until it is over the land and precipitates: (1) evaporates beck into atmosphere, (2). Infiltrate the ground, (3). Become part of the snow or glacier, (4). Drain to a river and back to the sea

Precipitation Precipitation Evaporation EVaporation Runo Ocean Land 3 Infiltrate Figure 16.1 The hydrologic cycle Water evaporated at the earth s surface enters the atmosphere as water vapor, condenses into clouds, precipitates as rain or snow, and falls back to the surface, only to go through the cycle yet another time

Water table(地下水位) 热 W Normal water table Stream Water table during drought Figure 16.2 The water table in any location roughly parallels surface contouring. In times of drought, the water table falls, reducing stream flow and drying up wells. It also falls when the amount of water pumped out of a well exceeds the amount replaced as precipitated water infiltrates the ground and recharges the supply

Water table (地下水位)

Ground water and surface water Over-use of ground water leads to subside(沉降) of land H H Figure 16.3 The Leaning Tower of Pisa, built cen- turies ago, slowly acquired a deviation from the vertical of about 4.6 meters as a result of groundwater withdrawal The towers foundation has been sta- bilized by groundwater withdrawal management and the tower should remain stable for years to come

Ground water and surface water • Over-use of ground water leads to subside (沉降) of land

16.2 Collectively, we consume huge amounts of water Livestock 21(2%) Domestic 99(8%) Municipal 23(2%) Irrigation 507039%6 Commercial 36(3‰) Industrial Thermoelectric 106(8%) power499(38%) Fiqure 16.4 Water usage in the United States (1995)in billions of liters per day

16.2 Collectively, we consume huge amounts of water

1500 □ Groundwater Population 口 Surface water □ Total 250 1200 200 900 508 600 100 300 1950195519601965197019751980198519901995 Figure 16.5 Total withdrawals of fresh water increased from 1950 to 1980 largely because of expanded irri- gation systems and urban developments. After 1980, however, conservation measures reduced water usage even in the face of a growing population

16.3 Water treatment facilities make water safe for drinking Remove dirt particles and pathogens 3Ca(OH)2+ Al2(SO4)3- 2Al(OH)3+ 3 CaSO4 Slaked lime Slaked lime Aluminum Aluminum ulfate hydroxide Aluminum Aluminum suifate hydroxide (gelatinous) 8 ·的 83:8 Impurities in water Slaked lime and aluminum (2 Impurities captured Gelatinous aluminum ulfate added to water react by aluminum hydroxide hydroxide and impurities to form gelatinous aluminum as it settles. collect at bottom of basin hydroxide Figure 16.6 Slaked lime, Ca(OH)2, and aluminum sulfate, Al(SO/ react to form aluminum hydroxide, AlOH)3, which forms a gelatinous material used to capture impurities

16.3 Water treatment facilities make water safe for drinking • Remove dirt particles and pathogens

Aeration of water improves the odor and flavor of water Figure 16.7 Volatile impurities are removed from drinking water by cascading it through the columns of air within each of these stacks

Aeration of water improves the odor and flavor of water

Final step is to treat water with a disinfectants chlorine gas or ozone 400 people die every hour from diseases caused by drinking contaminated water Impure or contaminated water In UV light sources Portabl water out Water flow Figure 16.8 Small-scale water disinfecting units, such as the one shown here, hold great value in regions of the world where potable water is scarce

Final step is to treat water with a disinfectants, chlorine gas or ozone. 400 people die every hour from diseases caused by drinking contaminated water