Water pollutants can be natural and human-related. Although water pollution caused by natural factors could be alarming, pollution caused by human activities is more widespread. There are four major sources of water pollution caused by human activity: municipal services (waste water, sewage), sea / river / lake transportation, industry and agriculture. Sources of water pollution could be grouped into two: point and scattered sources.


Pollution from one source is the environmental pollution caused by establishments’ and municipalities' treatment facilities. Since the place of discharge is known, it can be controlled if necessary.


Pollution from scattered sources is the pollution discharged from various points and it spreads to wide areas. Agricultural leakage, mines' waste, scattered city wastes and construction remains are some examples. Especially in Turkey, soil erosion is a major source of scattered water pollution. It is hard to control this kind.


Municipal waste


In general, this is waste water discharged from houses and commercial establishments. Domestic waste water consists of many small resources spread over a wide area. Municipalities collect these waste water via sewer lines and deliver sewage water to treatment facilities. Thus waste is collected at one point, treatment facility, and now that it can be controlled. Water pollution caused by sewage water is alarming in developing countries which have no healthy sewage system and treatment facilities.

It is hard to keep pollutants under control those are dispersed by wind.  Salt on the roads, untreated waste, construction remains and exhaust gases converted to acid rain are some examples for pollutants dispersed by the wind. Asbestos, chlorides, copper, cyanides, hydrocarbons, lead, organic wastes, phosphate and zinc can be dispersed by the wind and contaminate the water. It is municipalities’ responsibility to deal with such pollution.




Industrial waste


Food Industry

Textile Industry

Paper and Cellulose Industry

Chemical Industry

Oil Industry

Coal Mines

Synthetic Rubber / Plastic Industry

Metal Industry



Maritime/ Waterway Transportation


There are two types of pollution sources in maritime transportation: Waste water / septic tank of ships and petroleum and petroleum products transported in tankers.


Cesspits of ships/boats: This issue is a problem with all watercraft. In general, septic tanks are discharged directly into the sea and they pollute the sea water, just like domestic waste water does. If not controlled in marinas, this situation can lead to serious problems.


Oil pollution: This occurs as a result of collision of oil tankers and discharge of bilge water. In İstanbul, there has been 6 tanker accidents in the last 34 years, causing tons of oil to contaminate the waters of the Bosphorus.  This alone can give an idea of how widespread this pollution is.


After unloading the oil, tankers fill their warehouses with sea water (bilge) in order to maintain the balance. Before they anchor in the ports, they discharge this water into the sea. The case is same for boats.


Oil forms a thin layer on water and light hydrocarbons evaporate immediately. Heavy hydrocarbons, however, do not easily degrade  and do not evaporate, they remain on the surface for a long time in form of tar balls.


The most visible effect of oil pollution is the death of sea birds. The air between birds' feathers, which keeps their body temperature, is replaced by oil. Birds cannot fly and cannot maintain body temperature, so they fall sick. Oil pollution has serious implications for other marine organisms also. In 1957, in a small bay in Mexico City, all plants and animals lost their lives due to a diesel oil leakage accident. 


Agricultural Pollution:  Agriculture is the main cause of water pollution from scattered source. Agricultural practices cause a variety of substances creating water pollution. Pesticides leaking into water have negative effects on aquatic organisms and human beings. Fertilizer leaks enrich the water in nutrients. Animal waste and plant residues cause high BOD (biochemical oxygen demand) and mud in water then enrich it in nutrients (eutrophication). This causes an increase in water organisms and cause pollution on water surface.


Soil erosion in agricultural land increases the amount of solid material that can precipitate in water. In addition, some agricultural chemicals, which are not readily soluble in water, mix into the water by adhering to these solid particles. Therefore preventing soil erosion also means preventing water pollution.



The processes carried out in the treatment plants of wastewater are similar in nature to the treatment mechanism that occurs spontaneously. In these facilities, the waste water is the same regardless of whether it is directly into a stream, lake or sea. Precipitation and disintegration events take place. There are three types of treatment: primary, secondary and tertiary.


Primary Treatment (Primary or Mechanic)


This is the first phase of treatment. Sewage water enters the precipitation basin through the separation tank through grids which holds accidentally falling things (toothbrushes, combs, etc.).

Here, bacteria come into play to make organic solids clump and collapse. Approximately 80% of the solid material in the basin precipitates. Collected sludge is decomposed by anaerobic organisms in the decay ponds and emits gases such as methane, hydrogen sulfide and ammonia. This fluid sludge can be sprayed or dried on the cultivated areas. Dried sewage sludge can be used as fuel, fertilizer and soil filler.


In plants doing just primary treatment, liquid waste from the basin come to the chlorination section. At this phase, chlorine is added to kill the existing bacteria. Chlorinated liquid waste can be discharged into rivers, lakes or sea. However, this liquid still has 70% of the organic matter contained in sewage water. So the treatment is not complete. In order to obtain re-usable water, it is necessary to pass through all treatment phases.


Secondary Treatment (Secondary or Biologic)


The sludge and liquid formed in the precipitation basin during the the primary treatment are then subjected to the attack of aerobic bacteria. Liquid is decomposed by aerobic microorganisms in aeration tank and pass to the precipitation basin. The liquid collected at the top is chlorinated and discharged to sea, lake or rivers. Precipitated sludge is sent back to the aeration tank. Aerobic disintegration reduces the volume of the sludge. Therefore, the amount of solid waste to be destroyed is reduced.


Tertiary Treatment


Mechanical and biological treatment are commonly applied methods. However, tertiary treatment is also necessary for re-use of water. The level of nitrogen, phosphorus and organic matter must be reduced to the level of normal potable water. This is not so common since the cost of tertiary treatment plants where this process can occur is very high. However, it is possible to perform the same operation naturally. In the natural tertiary treatment method, the water remained in the secondary treatment is not discharged into sea, but to soil. The water passing through the soil layers is cleaned and reaches to an underground water bed, then soil's clean water is returned to soil again.