Human activity, like any other living thing, without fail is accompanied by the release of a considerable amount of waste. In modern conditions, almost all of them are carried away into the distance by the waters of sewage rivers. Finally, it is almost impossible to imagine our civilization without a huge number of factories and other enterprises, which also produce wastewater in large quantities.
About the process of disposal of waste
Wastewater treatment is a process after which the wastewater is suitable for technical use or return to the environment without harming the latter. In short, the method depends on the further use of the liquid. For example, the wastewater from the sinks is not the same as the contents of the drain holes, where the contents of the toilet bowl go down.
Why is this so important?
In April 1993, more than 400,000 people in Milwaukee ended up in a hospital bed as a result of falling into the drinking water of cryptosporidia. After this incident, which received a powerful response in WHO, the world community began to be much more careful about the fluid that flows from under the faucets under the guise of "drinking water". This opinion only strengthened after the publication of some cases of epidemics in India, as a result of which hundreds of people died. But the matter was in the usual E. coli, trapped in the water from poorly treated drains! So, wastewater treatment is an extremely important process that preserves the life and health of people.
Any pollutants radically change the taste, color and smell of a liquid, not to mention its suitability for use in food or technical purposes. The most dangerous are industrial effluents, since they often contain such concentrations of heavy metals and other substances that are tens and hundreds of times higher than the most “optimistic” MPCs. Of course, in this case, it all depends on the specific production, which discharges wastewater. The sewage system of an average city in comparison with them may seem like a “spring”, since at least there are no radioactive isotopes or a huge amount of heavy metals in it.
Dangerous pollution that makes water unsuitable for drinking and use for domestic purposes, can be classified as physical, chemical, biological factors. Separately worth the release of radioactive isotopes. Accordingly, the classification of pollution will be identical to the reasons that cause them:
- Mechanical factors. Characterized by a sharp increase in the smallest mechanical suspension in the liquid.
- Chemical. In the water, the content of any chemical compounds is increased. It does not matter if these substances can have a negative impact on the health of the human body.
- Biological and bacteriological (domestic wastewater). A very dangerous type of pollution, as in this case the water content of microorganisms is exceeded. At the very beginning of the article we have already said what it is fraught with.
- Thermal pollution. This is the name of the discharge into the rivers and other water bodies of water from cooling ponds at thermal power plants and nuclear power plants. You should not treat this species frivolously, since such phenomena lead to a massive death of endemics adapted to the low water temperatures that are characteristic of our area.
- Radioactive. Radioactive isotopes are found in water and bottom sediments. This happens when the wastewater system is defective in some industrial plants or nuclear power plants.
Characteristics of the main types of waste
In our conditions, the most common stocks of three types:
- Impurities of inorganic origin, including even non-toxic compounds.
- Substances of organic origin.
- Mixed drains.
Waste of metallurgical industries is very dangerous, as they contain a huge amount of heavy metals and other toxic compounds. They change the physical properties of water. In those waters where this poison falls, all living things perish, including trees and other vegetation along the banks. Organics are dumped by oil refineries and similar industries. In the effluent there is not only relatively safe oil, but also extremely toxic phenols and similar substances. In addition, it should not be disregarded livestock enterprises.
They throw out a huge amount of organic matter. The latter causes a sharp deterioration in the organoleptic properties of water. In reservoirs where wastewater of enterprises goes, there is a sharp development of microscopic algae, flowering, the oxygen content drops to a minimum in liquids. Fish and other aquatic organisms die. Manufacture of electronics, including etching of printed circuit boards and the release of radio products of various types, produces mixed-type drains. They contain dyes, heavy metals, acetone, phenols and other compounds.
Risk of oil entering the water
Currently, scientists around the world are sounding the alarm, as a huge amount of oil enters the World Ocean. It forms on the surface of the water the thinnest film, which sometimes can be seen only by rainbow stains. This not only leads to a significant deterioration in the organoleptic properties of the liquid, but also to a sharp decrease in the supply of oxygen, which enters the ocean through diffusion. Again, hydrobionts suffer, and the lack of this substance especially affects corals, the number of which in the seas and oceans catastrophically decreases every year. Only 10 mg of oil and oil products make the water absolutely unsuitable for drinking and living creatures.
Extremely dangerous phenols, which we have repeatedly mentioned above. They are present in the drains of almost all industrial enterprises. This particularly applies to those of them who are engaged in the production of coke. In the presence of these substances there is a massive death of the inhabitants of ponds, rivers, seas and oceans, and the water itself acquires an extremely unpleasant, putrid odor.
What substances are in them?
Wastewaters of the following composition fall into the sewage treatment plant:
- Proteins - 28%.
- Carbohydrates - 17.5%.
- Fatty acids - 10%.
- Oils, fats - 27%.
- Detergents - 7%.
As you can see, the main share of pollutants is organic. In industrial conditions, it is pointless to discuss any composition of wastewater, since in each case it is its own. In particular, in some cases, the allegedly purified "water" is discharged directly into the river (!), Which in appearance and composition resembles used motor oil.
Main sources of pollution
As a rule, industrial and social facilities, as well as livestock and poultry farms are to blame for environmental pollution. Solid wastes generated by the open-cast mining of mineral deposits are very dangerous, as well as drains generated in the wood processing process. Water and rail transport give a lot of waste of biological origin. When released into water sources, they cause them to be seeded with Escherichia coli or helminth eggs. It is especially dangerous when there is a medical facility upstream.
General information about the cleaning process
Processing includes the following methods:
- Mechanical. This includes filtration, which is used by all wastewater treatment plants, as well as sedimentation.
- Physical. This electrolysis, aeration, wastewater treatment by ultraviolet radiation.
- Chemical methods. Special formulations are used to precipitate and disinfect substances that may be contained in the effluent.
- Biological sewage treatment. In this case, plants that assimilate organic matter are used, as well as some types of protozoa, snails, and fish.
Before the start of processing, preparatory work is carried out. More precisely, the analysis of wastewater. Specialists of chemical laboratories determine which pollutants they contain. It helps to choose the best strategy for neutralizing them. The general procedure of wastewater treatment includes screening of: particulate matter, bacteria, algae, plants, inorganic impurities and organic matter. Removal of solid particles is the easiest step. It includes filtration and sedimentation by settling. It is much harder to clean sewage from thin suspensions that do not linger with conventional filtering materials.
One of the most simple and cheap methods, which, nevertheless, provides a high degree of purification, is the use of activated carbon. Filters with this material are used in almost all enterprises whose management is serious about environmental protection.
How does activated carbon work?
The main advantage of coal is its high absorption capacity. Simply put, on the surface of the particles of this substance there is such a number of pores that they can trap such amount of water polluting compounds, which is several times larger than the volume of coal itself. It is the process of trapping, binding of contaminating reagents and is called absorption. It should be noted that in order to purify drinking water, coal was used before our era. Active research and production of this material began during the two world wars. Factors affecting absorption are particle size, surface area, structure of the substance to be bound, acidity of the medium (pH-factor), temperature, which wastewater has.
What kind of substances can bind activated carbon?
Charcoal absorbs many substances, ranging from non-ferrous metals to complex organic compounds (for example, phenols). Of course, it will not protect against radioactive compounds, but it is possible to remove the main types of inorganic and organic impurities with its help.
Coagulation of pollutants
In some cases, for cleaning, special liquids can be used, which include particles of colloidal substances. What are they needed for? Everything is simple - microscopic particles, combining with molecules of pollutants, cause them to precipitate. The phenomenon is known as coagulation. In some wastewater treatment plants, electrolysis is also used. The method is similar to the previous one, since the ions produced by this process also contribute to the deposition of contaminants.
On the contrary, modern researchers are increasingly proposing methods that use massive molecules that can more efficiently bind and precipitate pollutants. This process is called flocculation.
As we have said, wastewater treatment may involve the use of negatively charged ions. Historically, aluminum sulphate is used for this purpose, as well as lime. These compounds cause a drastic change in the pH of the water, which leads to the death of pathogenic microorganisms, which are contained in many in the drains. In some cases, ferric-based substances can be used. Some chemists believe that such methods could be used by the Egyptians two thousand years before our era. Potassium permanganate also perfectly precipitates organics.
More about the method of settling
Whatever it was, but the associated organic matter falls in the form of flakes or gel. These sewage sludge can be easily caught using a simple mechanical filter. This method works best with relatively dense particles (such as silt and other heavy organic impurities), while lighter particles (such as microscopic algae) are better removed by sedimentation. The precipitation vat must be large enough so that its filling proceeds as slowly as possible. This is due to the fact that the normal course of the process requires at least four hours. After the organic and inorganic impurities settle to the bottom, the water can be considered conditionally purified, suitable for technical use. This method is more commonly used in pretreatment of effluent.
Then comes the turn of aeration. Water enters the giant tanks, where the compressed air under high pressure, discharged into the liquid through sprayers. Have you ever seen how a compressor works in a regular aquarium? In this case, the same thing happens. Aeration allows you to saturate water with oxygen and precipitate the remaining organic impurities. After this treatment, the liquid is most often supplied to special ponds, planted with higher aquatic vegetation (biological wastewater treatment). And only then the water is considered suitable for use for technical purposes. It can be watered planting vegetables and fruits, as well as discharged into natural water bodies.