Treatment plants of different manufacturers can be compared by the price, by the cost of maintenance, by appearance and even by the country of manufacturing, but since the main task of the wastewater treatment plant is the removal of contaminants from the sewage, one of the main criteria for the selection of the wastewater treatment plant is precisely the quality of the treated wastewater. Before talking about the effectiveness of sewage treatment, it is necessary to understand what, in fact, it is necessary to clean it of? Absolutely pure water does not exist in nature, drinking water contains a lot of various impurities, mainly mineral salts, and its chemical composition in each region will be individual, and sometimes it also requires cleaning, from excessive iron, excess of calcium and magnesium salts. But after drinking or technical water is used by us, its properties change, the chemical composition is transformed, and it is this water that enters the treatment plants. For any structures in which biological treatment is carried out, there are certain standards for the concentration of substances on the inflow. They need to be normalized for a number of reasons, but first of all this is necessary in order to ensure the normal operation of the main driving force of purification – active sludge. The microorganisms that make it up are sensitive to sudden changes in the environment, and this must be taken into account in order to achieve high water purification rates. But not all contaminants are removed from the sewage system in the same way. There are substances that are a nutrient substrate for active sludge and are digested by microorganisms, becoming a material for the construction of new bacterial cells. And there are substances that can not be changed through a treatment plant.
Depending on how much of the pollutant is removed from the treatment plant, the cleaning efficiency is determined, this is one of the most important indicators of the operation of treatment plants. It is calculated as follows:
Naturally, not all contaminated waste water is equally efficiently decomposed by active sludge bacteria and are purified in the plant. For example, in BIOTAL plants with an efficiency of 98% organic pollution is eliminated, and therefore the biological consumption of oxygen (BOD) is reduced:
Microorganisms of activated sludge under aeration conditions convert organic pollutants into carbon dioxide and water. The effectiveness of wastewater treatment from suspended matter in BIOTAL plants averages:
Removal of nitrogen in the plants is due to the successive processes of nitrification and denitrification. The fresh waste water flowing into the plant contains a considerable amount of organic matter, which in the first reactor is the main substrate for the bacteria of active sludge. In the second and third reactors, organics are less and energy is being produced for the life of bacteria in the process of nitrification, oxidizing ammonium nitrogen to nitrites and nitrates. These substances, in turn, must also be eliminated from the waste water, which is why a multi-circuit recirculation of activated sludge is provided in BIOTAL plants. When the active sludge saturated with nitrates from SBR-3 enters the inlet chamber under conditions of oxygen deficiency (anoxic conditions) and the presence of fresh readily oxidized organic matter, the denitrification process begins:
Phosphorus is also a nutrient, so together with nitrogen, up to 50% of it is absorbed by microorganisms to build their cells. Phosphorus accumulates PP-bacteria (in such way you can remove up to 10% of the phosphorus from waste water). If there are strict requirements for phosphorus content to the treated water, or if the phosphorus content on the inlet is higher than the prescribed intake into the sewage system, it is necessary to install an additional dosing pump (the output is for it in the standard BIOTAL automation unit). By means of this pump, a coagulant is dosed into the contact tank of the plant, which reacts with the phosphorus in the water and binds it, forming an insoluble compound precipitating out. This makes it possible to eliminate as much as possible from the treated waste water not only organic contaminants, nitrogenous compounds, but also phosphorus.
It is not enough to simply purify water, purified water must also leave the plant without causing any harm to the environment. Thus, each owner of a treatment plant must provide a method for disposing of treated wastewater. If the quality of water allows, it is possible to organize the reuse of treated wastewater for technical purposes, what will significantly reduce the consumption of drinking water for such purposes. But often it is necessary to provide the discharge of water, for example, into a water body. Coordination of such discharge mostly depends on what kind of water it is planned to drain there. In this case, without exaggeration, the decisive factor will be what the efficiency of purification for each of the indicators is normalized.
|Household waste water||390||480||20||220||> 100 000|
|Requirements for treatment at municipal sewage treatment plants||15||80||–||15||–|
|Water quality after BIOTAL plant||< 12||< 50||< 1||< 12||< 1000|
|BIOTAL plant with post-treatment||< 6||< 30||< 1||< 6||< 1000|