FAQ's about Water Pollution?
What is water pollution? Water pollution is any chemical, physical or biological change in the quality of water that has a harmful effect on any living thing that drinks or uses or lives (in) it. When humans drink polluted water it often has serious effects on their health. Water pollution can also make water unsuited for the desired use.
What are the major water pollutants? There are several classes of water pollutants. The first are disease-causing agents. These are bacteria, viruses, protozoa, and parasitic worms that enter sewage systems and untreated waste.
A second category of water pollutants is oxygen-demanding wastes; wastes that can be decomposed by oxygen-requiring bacteria. When large populations of decomposing bacteria are converting these wastes it can deplete oxygen levels in the water. This causes other organisms in the water, such as fish, to die. A third class of water pollutants is water-soluble inorganic pollutants, such as acids, salts and toxic metals. Large quantities of these compounds will make water unfit to drink and will cause the death of aquatic life. Another class of water pollutants are nutrients; they are water-soluble nitrates and phosphates that cause excessive growth of algae and other water plants, which deplete the water's oxygen supply. This kills fish and, when found in drinking water, can kill young children. Water can also be polluted by a number of organic compounds such as oil, plastics and pesticides, which are harmful to humans and all plants and animals in the water. A very dangerous category is suspended sediment, because it causes depletion in the water's light absorption and the particles spread dangerous compounds such as pesticides through the water. Finally, water-soluble radioactive compounds can cause cancer, birth defects and genetic damage and are thus very dangerous water pollutants.
Where does water pollution come from? Water pollution is usually caused by human activities. Different human sources add to the pollution of water. There are two sorts of sources, point and nonpoint sources. Point sources discharge pollutants at specific locations through pipelines or sewers into the surface water. Nonpoint sources are sources that cannot be traced to a single site of discharge. Examples of point sources are: factories, sewage treatment plants, underground mines, oil wells, oil tankers and agriculture. Examples of nonpoint sources are: acid deposition from the air, traffic, pollutants that are spread through rivers and pollutants that enter the water through groundwater. Nonpoint pollution is hard to control because the perpetrators cannot be traced.
What is water purification? Water purification generally means freeing water from any kind of impurity it contains, such as contaminants or micro organisms. Water purification is not a very one-sided process; the purification process contains many steps. The steps that need to be progressed depend on the kind of impurities that are found in the water. This can differ very much for different types of water.
In which ways is polluted water treated? Before the purification process begins some contaminants, such as oil, can be settled in a settling tank. They can then be removed easily, after they have reached the bottom of the tank. Removal of dangerous microorganisms Often polluted water has to be freed from microorganisms. The water is than disinfected, usually by means of chlorination.
Microorganisms are not only a threat to water; they can also be an advantage when it comes to water purification processes. They can convert harmful contaminants to harmless substances. This biological purification process usually takes a long time and it is only used for water that is polluted with contaminants that the microorganisms, usually bacteria, can convert. Physical/ chemical techniques
When treatment by microorganisms is not an option we often use different treatment techniques, called physical/ chemical treatment techniques. Chemical treatment often deals with the addition of certain chemicals, in order to make sure that the contaminants change structure and can then be removed more easily. Fertilizers such as nitrates are removed this way. Removal of contaminants can also be done through more difficult specific chemical processes. It takes a lot of education to fully understand these purification steps. Physical treatment usually deals with purification steps such as filtration.
How can bacteria be removed from water? Bacteria and other microorganisms are removed from water through disinfection. This means that certain substances are added to kill the bacteria, these are called biocides. Sometimes disinfection can also be done with UV-light.
What is aerobic water treatment? When bacteria are used for water purification there are two sorts of transfer; one of these is aerobic transfer. This means, that bacteria that are oxygen dependent are converting the contaminants in the water. Aerobic bacteria can only convert compounds when plenty of oxygen is present, because they need it to perform any kind of chemical conversion. Usually the products they convert the contaminants to are carbon dioxide and water.
What is anaerobic water treatment? When bacteria are used for water purification there are two sorts of conversion; one of these is anaerobic transfer. This means, that bacteria that are NOT oxygen dependent are converting the contaminants in the water. Anaerobic bacteria can only convert when oxygen levels are low, because they use other sorts of substances to perform chemical conversion. Anaerobic bacteria do not just develop carbon dioxide and water during conversion, but also methane gas. This can be used to keep the machinery that supports the purification going. The anaerobic conversion of a substance requires more steps than aerobic conversion, but the final result is often less satisfactory. After anaerobic conversion usually aerobic bacteria (bacteria that do use oxygen) still need to finish the process, because the water is not clean enough yet.
How are fertilizers removed from water? Fertilizers such as phosphate are removed through addition of another chemical, usually iron. The substances than become solid precipitates, that can be filtered from the water. The removal of ammonium and nitrates is a little bit more complicated; it is a purification process that takes both aerobic and anaerobic conversion to remove them. In the aerobic conversion stage there are two bacterial species involved. Nitrosamines bacteria that convert ammonia to nitrite and Nitrobacteria bacteria that converts nitrite to nitrate after that. Although nitrate does not represent a direct health threat to most fish, high levels are still undesirable. Apart from encouraging abnormal extensive algal growth, it is now believed that high nitrate levels are implicated in some fish diseases. This means that the process cannot be stopped here. The anaerobic bacteria take over; they convert nitrate to atmospheric nitrogen gas. This process only occurs in the absence of oxygen. The first stage is the reverse of the nitrification process, it converts nitrate back to nitrite. The second stage of gentrification converts nitrite to nitrogen gas (N2). This gas can be freely released into the atmosphere without causing environmental damage.