Class Session 24>

I. Global Fresh Water Usage

Throughout history, the world's lakes, streams, and rivers have provided important resources and services including water for drinking, washing, agriculture, energy production, transportation, recreation, and waste disposal. Population growth and rising requirements for energy and food are placing greater demands on both the quantity and quality of fresh water supplies. During the past three centuries, the amount of water withdrawn from freshwater resources by mankind has increased by more than 35 fold. Even more recently, total world freshwater used more than tripled between 1950 and 1980 and now stands at an estimated 4,340 cubic kilometers per year, about eight times the flow of the Mississippi River.

Total global fresh water usage in 1940 was around 900 cubic kilometers. Forty year later, in 1980, it was 4,340 cubic kilometers. Per capita freshwater usage, during the same period, has gone from 450 cubic meters annually to 800 cubic meters annually. In summary, world water demand has been growing faster than population. World per capita per year water use stands at 800 cubic meters per year, nearly 50% higher than it was in 1950.

II. Water Pollution
Sources of water pollution are typically grouped into two categories-point and non- point. Point sources are discrete discharges from pipes and other conduits such as sewage treatment plants or industrial facilities. Point sources o f water pollutants are typically classified as either industrial or municipal. Non-point sources of water pollution are not as discretely identified as are the point sources; examples include, but are not limited to, urban stormwater runoff, agricultural runoff, and acid rain.

The pattern of contribution by source type seems to be changing. Throughout the 1960's and the 1970's, point sources contributed the most to water pollution. Currently, however, because of the Clean Water Act, which mostly focuses on point sources, non-point sources are becoming increasingly important. Today, it's clear that non-point sources contribute the most to water pollution. Non-point pollution is responsible for 65% of the contamination in the nation's rivers, 76% of the contamination in the nation's lakes, and 45% of the contamination in the nation's estuaries. Much attention is now being given to the pollutant loads attributed to stormwater runoff, especially in urbanized areas. Urban runoff contributions include heavy metals, conventional pollutants, and petroleum products.

There are three principal types of water pollution: physical pollutants, chemical pollutants, and biological pollutants.

Physical pollutants include: thermal discharges; radioactive substances; sediment, particles and other matter from eroded soil, sand, and minerals; sewage plant sludge, and detergent foams.

Chemical pollutants include: synthetic organic chemicals and synthetic inorganic chemicals used in industrial facilities, agriculture and household products; dissolved mineral solids such as nitrogen and phosphorus resulting from fertilizer runoff, laundry detergents, and sewage treatment plant effluents, and; heavy metals such as chromium, mercury, cadmium, and lead.

Biological pollutants include: human and animal wastes that can carry diseases through viruses, parasites, and bacteria; fungi, and; oxygen-demanding pollutants which are natural or unnatural substances that deplete the available dissolved oxygen content in the water, usually through some form of bacterial decomposition.

Water Treatment
Water technologies include municipal wastewater treatment systems, industrial wastewater treatment technologies and drinking water treatment.

In the U.S. we have developed elaborate systems for treating sewage. Overall, sanitary sewage treatment involves settling, filtering, aerating, clarifying, and disinfecting and is based on three levels of treatment: primary, secondary, and tertiary.

Primary treatment uses physical processes to remove the solids and consists of mechanical filtration and screening. Typically, primary treatment removes 50-45% of the suspended solids and 25-40% of the biochemical oxygen demand (BOD).

Secondary treatment supplements primary treatment with a set of biological processes similar to the natural bacterial decomposition of organic wastes. Secondary treatment removes 90% of both the suspended solids and BOD. Additionally, about 50% of the nitrogen and 30% of the phosphorus are removed. Higher removal efficiencies for these nutrients can only be accomplished by tertiary treatment technologies. Tertiary treatment is a dual approach-the first removes nutrients by physical, biological, and chemical means; and the second removes microorganisms by physical- or chemical-disinfection techniques.

Tertiary treatment may include any of the following technologies: distillation, reverse osmosis, electrodialysis, chemical precipitation, ion exchange, or carbon adsorption. Tertiary treatment removes up to 99% of the BOD and up to 94% of the phosphorus. Nitrogen removal efficiencies are determined by the specific treatment technology and range from 95-98%.

III. Sewage Treatment
First, many wastewater treatment facilities in the U.S. are equipped only with primary and secondary treatment technologies and so nitrogen and phosphorus often go untreated. A second problem is the number of sewage treatment plants and the amount of sewage in the US has increased rapidly in urban areas since 1950. A third problem is that the drain systems that carry sewage and storm water are often combined. These systems are usually designed to handle the dry weather flow of these two combined sources and, during times of heavy rains, the volume of storm water causes overflow of the system and much of the raw sewage can then go untreated into waterways.

IV. Industrial Wastewater
Industrial wastestreams are much more complex in their pollutant characteristics. Therefore, they are more difficult and costly to treat using any one form or even a combination of control technologies. Each type of industrial process results in differing types of wastestreams. In brief, industrial wastewaters that are corrosive are neutralized; suspended solids can be removed through sedimentation, flotation, or screening; and colloidal solids are treated by chemical coagulation, neutralization coagulation, or adsorption. Inorganic dissolved solids can be removed using various control technologies including evaporation, dialysis, ion exchange, and reverse osmosis. Organic dissolved solids can be treated using various forms of aeration, trickling filtration, wet combustion, and anaerobic (without oxygen) digestion.

V. Drinking Water
Tastes and odors in drinking water result from algae and microorganisms, as well as inorganic and organic chemicals. Technologies for treating drinking water also vary, determined by the particular pollutant that requires removal. A general treatment scheme for drinking water include coagulant mixing, settling, filtration, and disinfection. The coagulant is mixed to remove the suspended particles that cause turbidity, taste, color, and odor. Settling allows the coagulated solids to be removed. Filtering removes even smaller particles that were not removed by the settling phase. Finally, disinfectants are added to kill disease-causing viruses, parasites, and bacteria.

Chlorination and powdered/granular carbon have varying degrees of success in removing unwanted tastes and odors. Activated carbon is also used to remove organics, trihalomethanes and their precursors, and chlorine. Particulate matter is removed by coagulation and filtration. Inorganics are difficult to remove, usually requiring a detailed treatment process that involves oxidation, precipitation, and ion exchange along with the standard settling and filtration technologies. Disinfection technologies for re moving pathogenic substances include chlorination, bromination, ultraviolet light radiation, and ozonation.

Different types of water pollutants result in varying effects. An important point to remember about the different types of water pollution is that, while each type tends to affect human health and the environment in a specific way, both human and natural systems are normally stressed by a combination of pollutants at the same time. This combined stress can lead to synergistic effects which can be greater or less than the specific effects of the different individual pollutant combined. Impacts include:

Human Health
Waterborne disease-causing or disease-carrying agents can kill or cause illness in both animals and humans. Consumption of, or contact with, the polluted water can prove to be a human health hazard. Shellfish can become contaminated and, therefore, inedible.

Recreation
The aesthetic qualities of water - how it looks, how it smells, and how it "feels" can be affected by the presence and concentration of water pollution. These aesthetic affects determine whether people will want to recreate on or near the water.

Animal Life
Oxygen-demanding wastes reduce oxygen levels and can result in fish kills. Nutrients also reduce oxygen and can lead to excess algae growths. This, in turn, can reduce the amount of and depth of light penetration into the water. Sediments and other particulate matter also reduce light. Their bottom deposits also smother and prevent fish eggs from hatching or even being laid. Thermal pollution raises the temperature of the water and reduces its oxygen-absorbing capacity. These effects, solely or in combination, affect whether crustaceans, fish and other undersea animal life flourish.

Plant Life
Water quality, speed, & flow determine whether or not sea grasses and other plants can establish themselves. Plants such are these are important for they often serve as breeding grounds for many different types of aquatic species. Pollutants, or combinations of pollutants can stress aquatic plant and reduce photosynthetic activity.