Water contamination are all chemicals and micro-organisms which are present in natural waters, but are not their natural ingredients or, they are natural ingredients but are present in increased quantities. Water pollution include also warmed water - thermal pollution.
The most common contaminants of water are: pesticides, detergents, dyes, phenols, hydrocarbons of petroleum (aliphatic and aromatic), surfactants, aromatic amines, chlorinated biphenyl, salts (nitrates, chlorides, phosphates, sulfates), heavy metals (lead (Pb), copper (Cu), mercury (Hg), cadmium (Cd), arsenic (As), and others) radioisotopes. Among living organisms the biggest role in the pollution of water has bacteria Escherichia coli.
Contamination may be in the form of dissolved water (gases, liquids, solids) of colloidal or suspensions.
Water pollution can be categorised by its origin: natural (indigenous) and anthropogenic (allochtonous).
Even roughly to the Middle Ages pollution of natural origin were dominating. They are mainly related to the life and dying of aquatic plant and animal organisms. They are caused by the washing out of certain substances from rocks and soils.
With the development of urban and industrial centers, people began to dispose more and more harmful substances to the ground waters. Currently, the main sources of water pollution are: municipal sewage (including, detergents, pathogenic micro-organisms) and industrial waste water (including salts of heavy metals, sulfur compounds and nitrogen). As a result of agricultural activities there are disposed into ground water:
- fertilizers used to in excess,
- organic and improperly used pesticides.
Mining industry disposes into groundwater large quantities of very highly saline mine water.
Agriculture is also a serious problem, especially the way the use of organic fertilizers. In many farms manure is used after harvest of cereals in root crops and then plowed underground. The soil remains so until spring without stubble cover, and the soluble nitrogen and phosphorus compounds penetrate deep into the soil, providing a source of groundwater pollution.
Significant amounts of water pollution also come from water and land transportation. Water being traffic routes, and water present in the vicinity of roads and highways contain increased amounts of lead compounds, nitrogen oxides, hydrocarbons.
Harmful substances get into waters also due to the deposition of pollutants from the air.
Eutrophication also contributes significantly to the pollution of water. One can say that it is both a cause and an effect of water pollution.
Substances that can pollute ground water cause a change in the color, taste and turbidity. This negatively affects the quality of water and drinkability. Pathogenic microorganisms, which are contained in the water, can cause severe food poisoning.
Almost all the pollution produced by man is toxic to most aquatic organisms. As the concentration of pollutants of water increases, the amount of fish in water reservoirs decreases.
Eutrophication is related to the pollution of surface waters. This is a process of enriching the waters in reservoirs with with biogenic elements (nitrogen (N), phosphorus (P) and other) are most likely due to disposal of untreated water. As an effect of increasing the amount of nutrients in the environment, the rapid propagation of microorganisms (mainly algae, blue-green algae, bacteria) occurs. The visible effect is so called water bloom. The increase in the number of microorganisms increases the biological oxygen demand. Dissolved oxygen in the water is consumed by the decomposition of organisms dead remains. Water changes its color and smell. They become more cloudy. There occur characteristic variation in the concentration of oxygen and pH in the upper water layers. Areas of water, where oxygen supplies have been exhausted, begin to arise. They are referred as the oxygen deserts. All aerobic organisms begin to die out. By contrast, anaerobic microorganisms begin to dominate. At the bottom of the water container, mud begin to accumulate, which leads to decrease the depth of the container. As a result of eutrophication of the lake can be converted into a swamp or bog.
Surface waters are now polluted most often due to disposal of municipal and industrial wastewater into rivers. Thus, the most effective form of protection of water is wastewater treatment. However, this requires the construction of expensive wastewater treatment plant. In sewage treatment plants the neutralization of harmful substances is carried out most frequently in three stages.
In the first, mechanical step - solids are removed by means of grates and sieves and grinding devices. Suspensions are removed in settling tanks and sand traps.
The second stage of wastewater treatment involves the removal of organic substances by a set of micro-organisms (bacteria, unicellular fungi, protozoa), forming the so-called activated sludge. After the decomposition of all organic contaminants into carbon dioxide and water, protozoa are used to remove bacteria and fungi from waste water.
The third step is the elimination of phosphates and nitrates from the wastewater. This uses the denitrifying bacteria or algae, which convert the nitrate (NO3) to the atmospheric nitrogen (N2). Phosphates can be removed from the wastewater chemically, by reaction with metal salts, which produces a precipitate of insoluble in water phosphate salts.
In some processes of wastewater treatment also the fourth stage is carried out. After which stage the waste water can be used as industrial water. In this process, waste water is purified by means of numerous physical and chemical processes:
- coagulation - combining colloid particles into larger groups, resulting in a residue called coagulum,
- flocculation - transforming hardly precipitating particles, that are suspended in the water, into larger groups,
- filtration - separation of liquid from solid particles,
- adsorption - a process taking place at the border of the two phases, whereby the concentration of unwanted substances becomes higher on border than the concentration of the substance in the volume of the phase.
Industrial waste water, which contains mainly inorganic contaminants are treated in a slightly different way. This method uses the following physicochemical methods: sedimentation, filtration, coagulation, chemical precipitation.
Certainly we are not and will never be able to completely prevent the contamination of water. However, we should take measures to reduce further water pollution. As mentioned earlier, the most effective form of reducing further contamination of surface water is proper treatment of municipal and industrial wastewater. Currently in Poland the number of sewage treatment plants is still too low as compared to demand. Not all Polish sewage wastewater treatment plants carry out the purification in three stages, after which the wastewater could be discharged into water bodies. To keep Polish rivers clean, new water treatment plants should be built and old ones should be modernised. Unfortunately, this requires enormous financial investment, which Poland can not afford. I think that in this situation, you must count on the help of other countries.
The section effects of water pollution, I wrote about the dangerous phenomenon called eutrophication
. The prevention from this phenomenon should comprise isolating the the flow of waters containing high concentrations of biogenic elements from natural bodies of water. It is therefore necessary to completely disable the outflow of untreated wastewater into rivers, lakes, seas, etc. In the case of water flowing from the fields, this effect can be achieved through the use of special agricultural treatments.
To prevent from further pollution of surface water, it is necessary also to systematically monitor their condition. Evaluation of water status can be made on the basis of a number of physical, chemical and biological tests.
Groundwaters are now contaminated by a very small extent. Therefore, they require special protection. To prevent pollution of these waters, it is essential to avoid discharging any sewage, even treated. The current Polish water law already contains such a prohibition. In order to maintain cleanliness of groundwater hazardous waste landfills must be also properly located and operated.