Wastewater treatment plants for single-family houses, complexes, enterprises
From the user to the treatment plant the water is transported through the underground water supply network.
Wastewater moves on …… to the nearby pumping station, from which it either flies under pressure, or re-propels …. to the purification plant. The role of pumps is to give the water the energy needed to transport. There are many types of pumps and the most commonly used are – air, propeller, spindle.
The most common method for wastewater treatment is the three-stage with additional sludge treatment.
The primary purpose of purification is to remove solids, suspended pollutants, organic material, salts (phosphorus and nitrogen).
The three stages of purification are:
The formed slurry of the three stages is treated separately.
In mechanical purification, water is purified from rough pollutants – stones, tree branches, textiles, drowned animals. This is done by capturing with bars. After the bars, sand holder are often placed to hold the sand and other particles with a density greater than that this of the water. If required, at this level is placed an oil trap (depending on the water quality). The oils are released as a surface slurry. The pollutants from the sand holders, the bars and the oil traps are disposed of but being previously dehydrated.
Wastewater flows through bars where solid pollutants are trapped. The waste is dewatered, landfilled and burned. The bars are of varying size, from 100 to 0.2 mm depending on the desired level of retention. The automated bars with a bars spacing of 3-6 mm are used in the wastewater treatment plants. They are immersed in about 6 meters and the grid mechanically moves like a strip. The contaminated pollutants are removed using a knife. Drum sieves and cycle-driven bars are also used for finer separation. The drum is finely perforated (0.2 mm). The water is fed into the center of the drum and filtered. Along the drum is a rotating screw that transports the water.
The main objective is to remove the dissolved organic material by means of microorganisms (MO). They help to reduce nitrogen and phosphorus. The most typical process in the case of bionic is the process of activated sludge (AU), carried out in aerated pools and then settlers. Oxygen (aeration), which is used by the MO for oxidation of the biological material, is delivered to the aerated pools, thus obtaining the energy required for their biological existence and reproduction. As organic degradation products, carbon dioxide releases freely into the atmosphere, water and new biomass (new bacteria). The biomass is suspended in the water as a large part is precipitated, the microorganisms are grouped and, because they are heavier than the water, settle down to the bottom of the pools in the form of slime (activated sludge). The active sediment consists of a large part of living and dead microorganisms in order to keep the level of AU constant, periodically part of it is extracted from the ponds. It contains in large quantities molecularly bound nitrogen and phosphorus.
It is the addition of chemicals in order to improve the sedimentation of sediments in sedimentation basins. Another option is to conduct the floccation process (aeration of the water in order for the suspended substances together with the bubble gas to rise above the water and thus to be removed). The complete process is completed by filtration, again in order to remove the microorganisms and suspended substances. In many countries water disinfection (destruction of pathogenic micro-organisms) is also required as a mandatory level.
Organic matter that is in the water cannot be removed mechanically, as these compounds are in a dissolved form. The use of microorganisms naturally present in water is used to remove the hardly degradable and dissolved particles. Microorganisms are grouped into large flocs which are then removed by sedimentation. Biological purification is a natural, natural process that accelerates in sewage treatment plants, this is achieved by concentration of microorganisms in a pool. In addition to micro-organisms, the algae, which naturally multiply in the plants themselves, play a major role. To exist and to multiply, micro-organisms need a suitable environment where nutrients are present. They break down these substances and receive energy. This process can be carried out in an aerobic or anaerobic environment. In the first case, organic matter is oxidized with oxygen to carbon dioxide and water. Anaerobic processes are called rot. To exist, microorganisms need chemicals containing carbon, nitrogen, phosphorus, and others.
The principle of conversion of organic matter is as follows:
Nutrients + microorganisms + oxygen = formation of cell mass (new microorganisms) + energy + residual products (carbon dioxide + water)
Oxygen is supplied through the air, but in order to intensify the process, additional aeration facilities are provided. Micro-organisms are very sensitive to factors such as temperature and pH.
Here are some of the most common facilities for carrying out processes at the biological level:
The main task is to remove phosphorus as well as residual suspended substances by flocculation. The process is carried out using precipitating chemicals, which together with phosphorus form a precipitate. The chemical slurry formed is separated by sedimentation or flotation or filtration.
The precipitating chemicals contain metal ions which react with phosphorus and phosphates and form precipitates. The metal ions react with the hydroxides from the water to form a hydrous precipitate. They in turn play the role of flocoantes (combining particles into larger, easier to settle).
The most commonly used chemicals are iron trichloride, iron-aluminum sulphate, polymers. The precipitation can be adjusted by means of pH.
There are several implementation schemes:
- Directly after the warning basins
- Before the active sludge process
- After the average precipitates, after the activated sludge
Equipment for carrying out the activated sludge process
In this process, microorganisms live and multiply in aerated pools where nutrients are transported with waste water. Aeration is achieved by purging oxygen. Microorganisms form sludge, which is later removed in sedimentation plants. Micro-organisms multiply, grow and die. In order to keep their quantity constant, sludge is pumped from time to time. Oxygen concentration is an important parameter. Since, if oxygen is insufficient, microorganisms would not develop fully, and hence the process would not be effective.
BIOLOGICAL EDUCATION OF NITROGEN
One of the main problems that the presence of nitrogen in the wastewater causes is the eutrophication process (re-rotation) of the water basins. On the other hand, nitrogen in the form of ammonium ions further leads to the oxidation of ammonium ions to nitrate and causes oxygen deficiency.
The most important level of nitrogen reduction is biological. With the help of bacteria, nitrogen is released into the environment in the form of gas. To achieve this two processes are needed – nitrification and denitrification. Accordingly, the bacteria involved are nitrifying and denitrifying.
NITRIFICATION AND DENITRIFICATION
Ammonium ions + oxygen = nitrate + water (aerobic) ——->
Nitrate ions organic source (C) + carbon dioxide + water, anozone (stirring without aeration).
The process of nitrification requires an oxygen, aerobic process. Basically, the process consists of two separate processes, first the ammonium anions are converted into nitrite (with the help of Nitrosomonas class bacteria) and then nitrite (NitroBacteria). These bacteria develop very slowly and are very sensitive to different poisons. Denitrification is carried out in an anoxic medium. This is an environment where there is no dissolved oxygen in the water, but there is one in a bound form. After the use of oxygen in a bonded form, it is drawn from the bound nitrates, which are converted into nitrite and then into nitrogen. In order to carry out the process an energy source is also optimally available for the bacteria, for this purpose carbon is added under easily degradable form – methanol or ethyl alcohol. After completion of the process, there is usually an aerated area where residues of methanol can be removed.
Used since 1960, the purpose is to separate the suspended particles from the biological or chemical level.
It is carried out as the water is passed through a bed of sand or other suitable material where the suspended particles are seized. The filter is washed periodically with water. The rinsing water is then fed to an inlet at the wastewater treatment plant. Sometimes you also need a gas purge.