1、Water pollution,It covers 71% of the earths surface and makes up 65 % of our bodies. Without the seemingly invaluable compound comprised of hydrogen and oxygen, life on Earth would be non-existent,Water is Essential for Life,Three fourths of the surface of the Earth is covered with water. Nearly 98%
2、 of the water on Earth, though, is seawaterunfit for drinking and not even suitable for most industrial purposes. Something less than 2% of the water is frozen in the polar ice caps, leaving less than 1% available as fresh water.,Water: Unusual Properties,Many chemical substances are soluble in wate
3、r. Thus, they are easily dispersed and eventually are scattered to nearly infinite dilution in the ocean. Those properties of water that make it uniquely suited for the support of life also make it easy to pollute.,Natural Water Isnt All H2O,Rainwater carries dust particles from the atmosphere to th
4、e ground. Rainwater also dissolves a little oxygen, nitrogen, and carbon dioxide as it falls through the atmosphere. During electrical storms, lightning causes nitrogen, oxygen, and water vapor to combine to form nitric acid.,As water moves along or beneath the surface of the Earth, it dissolves min
5、erals and matter from decaying plants and animals. The principal positive ions (cations) in natural water are sodium (Na+), potassium (K+), calcium (Ca2+), magnesium (Mg2+), and sometimes iron (Fe2+ or Fe3+). The negative ions (anions) are usually sulfate (SO42-), bicarbonate (HCO3-), and chloride (
6、Cl-).,hard water,Water containing these calcium, magnesium, and iron ions is called hard water. The positive ions react with the negative ions in soap to form a scum that clings to clothes and leaves them dingy looking.,Water pollution,Water pollution is any chemical, physical or biological change i
7、n the quality of water that has a harmful effect on any living thing Water pollution caused by human activities is a large set of adverse effects upon water bodies such as lakes, rivers, oceans, and groundwater Pollutants in water include a wide of chemicals, pathogens 病原体, and physical chemistry or
8、 sensory changes.,Water pollution,Water pollution is the leading worldwide cause of deaths and diseases, and that it accounts for the deaths of more than 14,000 people daily. Effects of water pollution include poisonous drinking water, poisonous food animals, unbalanced river and lake ecosystems, de
9、forestation and many other effects,Sources of water pollution,The used water of a community is called wastewater, or sewage. If it is not treated before being discharged into waterways, serious pollution is the result. There are two sorts of sources, point and nonpoint sources. Point sources dischar
10、ge pollutants at specific locations through pipelines or sewers 下水道into the surface water. Nonpoint sources 非点(污染)源are sources that cannot be traced to a single site of discharge.,Factories Agriculture Transportation Household,Sources of water pollution,Domestic sewage,Domestic sewage refers to wast
11、e water that is discarded from households. Also referred to as sanitary sewage. Domestic sewage contains a wide variety of dissolved and suspended impurities:a. organic materials-food and vegetable waste b. plant nutrients- chemical soaps, washing powders c. disease-causing microbes微生物,Household Che
12、micals,Example: substances used for houses clean: Soap and synthetic detergents Wax Paints and paint removers Bleaches Disinfectants消毒剂 Polishes,Agricultural Run off,Fertilizers: nitrate , phosphates Pesticides: phenol, chlorine diphenyl Eutrophication富营养作用: nutrients artificially supplemented resul
13、ts in an abnormal increase in the growth of water plants,Industrial Pollution,Industrial effluent of many kinds of waste, is discharged into streams, lakes, or oceans, which in turn disperse the polluting substances. The pollutants include grit, asbestos石棉, phosphates and nitrates, mercury, lead, ca
14、ustic soda and other sodium compounds, sulfur and sulfuric acid, oils, and petrochemicals. Example: Chrome plating on bumpers, grills, and ornaments is a source of pollution,Pollutants from various industries,The textile industry dumps conditioners, dyes, bleaches, and water effluents containing oil
15、s, dirt, and other organic debris. Meat-packing plants dump blood, the contents of entrails 内脏, and other animal wastes. Other food-processing plants discharge fruit and vegetable skins, seeds, leaves, stems, and other vegetable wastes. Refineries 精炼厂 release dyes, oils, acids 盐水, sulfur compounds,
16、and other wastes. Chemicals plants produce a variety of waste materials.,Oil spills,Oil spills from tankers at sea or leaks from underground storage tanks on land are very difficult to control Oil spills at sea decrease the oxygen level in the water and cause grave harm to the creatures living in th
17、e sea. On land crude is transported through pipelines or tankers which can get damaged and spew out crude oil over the land,Oil spills are very difficult to control as oil tends to spread very fast,affecting a large area in a very short time.,Groundwater and its contamination,Groundwater are contami
18、nated with heavy metals, persistent organic pollutants, and nutrients Pesticides : Run-off from farms, backyards, and golf courses Leachate沥出液from landfill sites Untreated or inadequately treated municipal sewage :organic material , microbial pathogen Nutrients :phosphorus and nitrogen Synthetic org
19、anics :industrial chemicals and pesticides,Chemicals in drinking water,Chemicals in drinking water can be both naturally occurring or introduced by human interference Fluoride Arsenic Petrochemicals Chlorinated solvents Salts,Different types of water pollution,Microbiological : Disease-causing (path
20、ogenic) microorganisms, like bacteria, viruses and protozoa原生动物. Chemicals : A whole variety of chemicals from industry, such as metals, solvents and acids,Oxygen-depleting Substances Many wastes are biodegradable, they can be broken down and used as food by microorganisms like bacteria. Too much bi
21、odegradable material can cause the serious problem of oxygen depletion in waters,Aerobic bacteria,Aerobic bacteria that live in water use oxygen gas dissolved in the water when they consume their “food“ Aerobic microorganisms-which use dissolved oxygen- convert the nitrogen, sulfur, and carbon compo
22、unds present in the wastewater into odorless- and relatively harmless- oxygenated forms like nitrates, sulfates and carbonates,Anaerobic bacteria,Once the oxygen is depleted, other (anaerobic) bacteria that do not need dissolved oxygen take over Anaerobic microorganisms produce toxic and smelly ammo
23、nia, amines, and sulfides, and flammable methane (swamp gas),Biochemical oxygen demand, or BOD,BOD is the amount of oxygen required by micro-organisms to decompose the organic substances in sewage.The more organic material there is in the sewage, the higher the BOD.,Nutrients,Water-soluble nitrates
24、and phosphates that cause excessive growth of algae and other water plants, which deplete the waters oxygen supply.,Suspended matter,Particulate matter, consist of much larger- but still very small- particles which are just suspended in the waterThey will eventually settle out and form silt or mud a
25、t the bottom :sediments,Water-borne disease,Pathogens which include virus, bacteria, protozoa, and parasitic worms are disease-producing agents found in the faeces of infected persons. Hepatitis 肝炎, cholera霍乱, dysentery痢疾, diarrhoea腹泻, skin irritation , and typhoid伤寒症are common water-borne diseases,
26、How do we prevent water pollution?,In urban areas, the wastewater from homes, businesses and factories is collected by a system of underground pipes- sewers which carry it to one or more central treatment facilities. Homes in non-urban areas that are not connected to a sewer are usually required by
27、their town to have on-site treatment systems.,Wastewater treatment plants,Consists of a train of individual unit processes, with the output (effluent) of one process becoming the input (influent) of the next process.Biological plants are more commonly used to treat domestic or combined domestic and
28、industrial wastewater from a municipality.Physical/chemical plants are more often used to treat industrial wastewaters directly, because they often contain pollutants which cannot be removed efficiently by microorganisms,A typical treatment plant,The first stages will be made up of physical processe
29、s that take out easily removable pollutants. The remaining pollutants are generally treated further by biological or chemical processes,physical process,A physical process usually treats suspended, rather than dissolved pollutants flocculation Filtration :Ultrafiltration, and reverse osmosis adsorpt
30、ion on activated charcoal Air or steam stripping,Desalination of seawater by reverse osmosis.,A common set of processes,Preliminary treatment : grinders, bar screens, and grit channels. To remove large or hard solids that might clog or damage other equipment.,Primary settling basins,The water flows
31、slowly for up to a few hours, to allow organic suspended matter to settle out or float to the surface.,Secondary treatment,to remove the remaining dissolved or colloidal organic matter using usually biological method. The most common type of biological treatment process : Activated sludge process,Ac
32、tivated sludge process,consists of two parts, an aeration tank and a settling tank. The aeration tank contains a “sludge“ : containing mostly bacteria, as well as protozoa, fungi, algae, etc. The wastewater enters the tank and mixes with the culture, which uses the organic compounds for growth- prod
33、ucing more microorganisms- and for respiration, which results mostly carbon dioxide and water.,The sludge is carried by the flow into the settling tank. The sludge collected at the bottom of the settling tank is then recycled to the aeration tank to consume more organic material. Since the amount of
34、 microorganisms, or biomass, increases as a result of this process, some must be removed on a regular basis for further treatment and disposal,Final process: Disinfection,Destruction of harmful (pathogenic) microorganisms, i.e. disease-causing germs :sterilization The most commonly used disinfectant is chlorine, in the form of a liquefied gas, or an alkaline solution called sodium hypochlorite,A more powerful disinfectant is ozone The other commonly used method of disinfection is ultraviolet light,
