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In the coke & by-product process a large amount of sewage is formed polluted with impurities of organic & inorganic origin including nitrogen compounds in form of ammonium ions, nitrite & nitrate ions.
Ammonia is a typical nervous poison for fish with haemolitic & local action, too. Nitrites reduce blood haemoglobin ability to grab and carry oxygen. Nitrates are not toxic so much, however the fish living in water with a large concentration of this nitrogen compounds gets a pale coloration of the gills. The above nitrogen compounds are toxic for human organism too. The toxic effect of nitrites is namely connected with the fact that because of their influence hemoglobin turns into methaemoglobin which is unable to bind and carry oxygen. One should remember that ammonia toxicity depends on the milieu acidity which decreases with pH reduction. Hence, ammonia compounds water purification is necessary prior to its further use.
The most effective method of nitrogen compounds removal from the sewage is biochemical purification which is done by the microorganisms team-work including a great amount of various protozoa bacteria and a number of highly organized organisms: water plants, fungi etc. which are closely linked to each other through complex interrelations.
The basic problem of biochemical water purification process from nitrogen compounds is that to oxidize ammonia compounds and restore nitrates ions special groups of microorganisms are necessary to apply. In the existing process the time the water stays in biological basins allows to oxidize practically all ammonia ions but it is not sufficient to oxidize organic nitrogen because this process speed is considerably lower then the previous one.
To remove nitrogen compounds from the sewage the word practice uses nitrification and denitrification methods envisaging the change of aerobic and anaerobic zones in one construction. However, the existing constructions allow limited application of these methods as their reconstruction presupposes the use of special equipment.
Researches in recent years show that realization of one-stage nitrification and denitrification process is possible in principle in ordinary aerotanks. It is proved that aerobic microorganisms in the active silt particles screen anaerobic denitrificators against oxygen influence, that’s why both processes can flow simultaneously.
The main condition of nitrification and denitrification process effectiveness is raising the age of active silt up to (20 – 30) days. In this case (97 – 98)% of ammonia nitrogen is removed. The index of denitrification level grows to (50 – 65)%.
The problem can be solved due to using aerotanks with prolonged aeration. They are aerotanks-displacers having from one to four corridors, water and silt are brought to the front part of construction while mixture is displaced in its rear part. Theoretically the flow regime in displacers must be a piston one without longitudinal stirring. However, according to researches a considerable longitudinal stirring exists in the corridor aerotanks. The cell-type aerotanks constructions fit the displacer regime to a greater extent.
But the water quality in water objects is formed as a result of the complex interaction of factors with different directivity, the internal water reservoir processes included, among which the exchange of solutes within “water-bottom sediments” system takes a special place. The bottom sediments of water reservoirs can be looked at from two points of view. Under certain conditions they can make the water purification process more active and on the contrary, they can turn into a secondary water pollution source when pollutants are accumulated in them and the impurity gradient is directed from the bottom sediments into the water.
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