4.4 WATER POLLUTION

What is pollution? Both surface water and groundwater can become polluted by waste from cities, factories and nearby farms. Pollution is the introduction of harmful substances into the environment. Water can become polluted so much it becomes deadly.

TYPES OF POLLUTION Pollution coming from one specific site is called point-source pollution. Example: a leak from a sewer pipe. Can be controlled because its source can be identified.

TYPES OF POLLUTION Nonpoint-source pollution is a pollution coming from many sources. More difficult to control because it does not come from a single source. Main sources include: street gutters, fertilizers, eroded soils, mine drainage, and salts from irrigation.

Health of a water system Just as you need oxygen to survive, so do fish and other organisms living in water. The oxygen dissolved in water is called the dissolved oxygen, or DO. DO levels below 4.0 ppm (parts per million) in freshwater can cause stress and possibly death for marine organisms.

Health of a water system Nitrates are naturally occurring compounds of Nitrogen (N) and Oxygen (O). Small amounts normal  however, elevated levels can be harmful. Excess of nitrates creates lower DO levels. Can come from animal waste or fertilizers.

Health of a water system Alkalinity refers to water’s ability to neutralize or buffer out an acid. Acid rain and other wastes can harm aquatic life. A pH below 6.0 is too acidic for most marine organisms. Water with a higher alkalinity can better protect organisms from acid.

Cleaning polluted water Where does the water go … When you flush the toilet? When it goes down the shower drain? The water flows through sewer pipes to a sewage treatment plant, which is a facility that cleans the waste materials out of the water.

Cleaning polluted water When water reaches a sewage treatment plant, it is cleaned in two ways: Primary Treatment: water treatment phase where dirty water is passed through a large screen to catch solid objects, such as paper, rags, and bottle caps. Then placed in large tank, where smaller particles (sludge), can sink and be filtered out. Secondary Treatment: water treatment phase where water is sent to an aeration tank, where it is mixed with oxygen and bacteria. Bacteria  use the oxygen to feed on wastes. Water sent to another settling tank and both chlorine (Cl) and ultraviolet (UV) light can be added to disinfect the water. The water is released into a water source – lake, river, ocean, etc.

Cleaning polluted water Water can also be cleaned by using a septic tank, which is a large underground tank separating solid wastes from liquids. Solids sink to bottom where bacteria break waste down and the water flows from the tank into buried pipes, called the drain field. Must be cleaned every few years in order to continue working properly.

Water in industry About 19% of water used worldwide is for industrial purposes. Manufacture goods, cool power stations, clean industrial products, extract minerals, generate energy for factories. In the USA, most water in factories is recycled at least once  about 90% of recycled water can be treated and returned to surface water.

Water in agriculture Water is important for cropland as well. The Ogallala Aquifer is the largest known aquifer in North America. Provides water for approximately 1/5 of cropland in the United States. Most of the water lost during farming (irrigation) is through evaporation and runoff.

THE OGALLALA AQUIFER

CONSERVING WATER As you can see, we use a lot of water for industrial and agricultural purposes, not to mention our household uses of water. Therefore, we need to conserve what we can. Ways in which we can do this include: Low-flow shower heads Low-flush toilet systems Use native plants (don’t need extra watering) Shorter showers No running water while brushing teeth Full dishwasher load