Wastewater treatment methods using chemical, biological and mechanical means. Methods and technology of wastewater treatment.
Wastewater is water polluted as a result of human activity and discharged through a sewer to a place of accumulation for further processing and treatment. Moreover, waste waters are considered to be waters formed (contaminated) both at industrial enterprises and subsequently formed as a result of human household activities. Such water contains a lot of pathogenic microorganisms, salts of heavy metals, pesticides, nitrates and nitrites, as well as many harmful chemical and biological compounds. Therefore, in order to conserve the Earth's water resources, a special treatment scheme was developed. Wastewater, which is aimed at dumping already neutralized clarified water into reservoirs and soil. This attitude towards ecology allows us to save fresh water on the planet for future generations.
Clogged drains occur with long-term power outages while the plant is still evacuating wastewater, resulting in raw wastewater coming out with activated sludge. The automation and the compressor in some installations are directly above the water level, and of course, as the water level rises, short circuit with all the ensuing consequences. It's all true about the "economic benefits and benefits" of bringing compressors and automation to compressors. That the surplus can be dumped into the Milkov River.
Methods of neutralization (purification) of effluents
Waste water, depending on the type and type of impurities in it, is today purified by several methods. Moreover, both a specific method and a combined treatment technology can be used, if necessary for the qualitative neutralization of wastewater. The most commonly used cleaning methods are:
The flow of technology complies with European standards. The process stream is designed using a low sludge treatment process including denitrification and biological phosphorus removal. The city of Focsani, the capital of the Vrancea district, has about 1000 inhabitants.
The process stream is designed using a low sludge treatment process including nitrification, denitrification and biological phosphorus removal. Characteristics of the water entering the wine-making station. Induced chemical charges and wastewater temperature.
- Mechanical water treatment(settling and filtering). This is the easiest and cheapest way to purify water.
- Chemical wastewater treatment(mixing wastewater with chemical neutralizing agents). As a result of adding reagents to water, reactions occur that completely or partially neutralize harmful impurities in effluents.
- Physical and chemical treatment of contaminated water(UV treatment or ozonation of wastewater).
- Biological wastewater treatment. In this case, a certain amount of bacteria is loaded into the aquatic environment, which feed on specific pathogenic microorganisms, reducing their number in the water to zero.
Wastewater treatment plants and special systems for wastewater treatment
The most effective and in demand in the process of neutralizing wastewater are such installations and devices:
Standards for treated water leaving the station before the lagoon is unloaded. The wastewater treatment plant has two parallel processing lines. Pre-treatment structure with grids consisting of sparse grills and thin grills 2 sand and grease removal basins. Low activity activated sludge treatment process including nitrification, denitrification and removal of biological phosphorus, consisting of: untreated water pumping stations and sludge recycling 2 aeration basins with anaerobic, anoxic and aerated areas. For treating sludge from primary decanters and overflow sludge from aerators, including: Gravity concentrator for separate thickening of primary and excess sludge. Methantane - Anaerobic fermentation of concentrated sludge Fertilized sludge storage area Mechanical dewatering station with belt presses Suspension of dry inert sludge under hemispherical conditions Dry sludge storage at the station.
- Temporary reservoir to hold rainwater.
- Natural disinfection by solar ultraviolet.
- UFS - self-cleaning filter unit.
- Sand traps.
- Grease traps.
- Settling ponds.
- Septic tanks and membrane structures.
Consider more principle action of each device.
Filtration plant
Treated waters must comply with the values of quality indicators. Installations for measuring water flows to wastewater treatment plants. The maintenance and repair of treatment facilities, as well as the duties of personnel, are contained in the operation manuals for treatment facilities.
Coordination of tracking activities, elimination of sequential wastewater treatment processes according to specified parameters is accompanied by specialized personnel. It is possible to intervene in the bad sector without disrupting the entire cleanup process.
Why do you need a new refinery? Quality indicators of the old sewer plant they say: dirty water enters it, and clean water must come out. Over time, even if pure water flows into the rivers, they died. Even the small rivers that crossed the cities had fish. Now all the rivers in the country are polluted. As if in a vessel with clean water poured sugar jar. The water will remain clear, but life cannot be developed in it.
A device that passes waste water through its filters and thereby purifies it. Filters should be self-cleaning, but in practice, industrial enterprises use standard gratings and sieves instead of self-cleaning filters, which require manual raking or using special devices.
Nowadays, the rules of quality have changed and it is not enough to simply purify water, but it must be removed from the water and dissolved substances in order for the water resulting from purification to have life. How is the cleaning process carried out? Ammonium as such is present in water, and we aim to turn it into nitrogen gas, an inert, non-toxic gas found in air at a ratio of 75%. Moreover, nitrogen is not a greenhouse gas.
There is no bacteria that converts ammonium from water into nitrogen gas. But nitrites are just as toxic as ammonium. Typically, wells in the country are contaminated with nitrates from animal husbandry. They reach the ground, in the ground, and then in the well. When water boils, it increases the concentration of nitrate in it because the pure water evaporates and the nitrates remain.
Such an installation works on the principle of separating debris and large impurities from the liquid. Moreover, gratings and filtering nets in such an installation can have a completely different structure (crushing, screw, stepped, in the form of plates or rods). The smallest fraction of the grate of such a device is 2 cm. All garbage collected on grates or nets is immediately sent for recycling or disposal. If screens with a crushing structure are used, then debris impurities are neutralized directly in the treated water.
In conclusion, we must take care of 3 families of bacteria to achieve the phenomenon of extracting solutes from water. If families of bacteria are poorly taken care of to take on certain substances that they can convert, the purification plant will not work.
Bacteria can only fulfill their mission if they have good conditions for life. We, however, must also put them in bad conditions to make them do what we want, caring but that they are fulfilling their mission. Some bacteria convert ammonium into nitrogen gas, while others accumulate phosphorus. We compress it and make it into soil that contains a lot of phosphorus or phosphates, which are biological fertilizers.
In addition to meshes and gratings, drum sieves can take part in mechanical wastewater treatment. The fraction of cells in a sieve is up to several tenths of a millimeter. These devices have a finer fraction compared to gratings and are designed to remove impurities from the water in the form of gravel, sand, small glass fragments, etc. The drum, rotating in the water, absorbs all foreign impurities into its cavity.
The graph in which green represents the concentration of phosphate in the processing line at the entrance to the station represents the increase in the level of phosphate in the first stage, because the bacteria enter the conditions unsuitable for development, in the first area with active dirt they fight for survival and thus, they release phosphorus - the opposite effect, expected. In the second part, the bacteria assimilate many of the phosphates so that their concentration drops significantly below the level found at the entrance to the treatment plant.
Constant monitoring of the balance of these bacteria works by laboratories of wastewater treatment plants. About 42 tons of bacteria are used. Their number must correspond to the amount of poison entering the station. In the first building, remove large water suspensions. The water is passed through gratings that keep these large slurries. In the desacator, the section of the channel increases, the water reduces its speed, it relaxes and the suspensions are applied gravitationally. Fats, which are highly toxic to bacteria, must be removed from the water by blowing air, which brings the fats to the surface.
sand traps
The next stage in water purification is mechanical. After the water passes through the drum screens and grates, the effluents are sent further to the sand traps. Here, the devices additionally screen out the smallest particles of impurities in the form of sand. In sand traps, water can move both horizontally and vertically. The cleaning effect of this is not reduced. Sand traps work thanks to the force of gravity, which settles all the small particles of sand to the bottom. At the same time, it is worth knowing that the higher the flow rate of water, the weaker the force of gravity. And this means that for the high-quality work of the sand trap, the speed of the movement of effluents must be reduced.
This is done in a fat separator. It was previously believed that meteoric waters are usually clear and can be evacuated directly into the river. False because meteoric waters are wiping out streets and exercising hydrocarbon sewers. These hydrocarbons are highly toxic to the aquatic environment. When it rains, the flow of water is very high. The precipitated water is separated into a holding tank and then purified.
There are two main decanters because the continuity of cleaning must be ensured in case one of them is revised and the other remains inactive. The primary decanter is a basin in which the water is clarified and after a while the dirt is collected at the bottom of the basin. Whatever water is in this main decanter, it is still cloudy and the suspensions in it do not separate by gravity. This suspension is the main food source for bacteria.
Important: sand separated from water in this way is most often used later in construction work.
Grease trap
This type of treatment plant is usually installed next to the sand trap. The grease trap has a closed shape and is designed for some cooling of wastewater. As a result of a decrease in water temperature, all soluble fats acquire certain form and float to the surface of the water. Further, the effluents flow into the settling tanks, and the fats are removed from the grease traps.
After we force bacteria to remove dissolved substances from the water into active mud pools, as side effect this process, the water will remain clean. At the end of the day, water mixes with bacteria, but substances do not dissolve in it. Bacteria occur in families of bacteria, also called agglomerations.
In secondary decanters, these families of bacteria are separated from the water, leaving it clear and free of solutes. The resulting water is sent to a biological reservoir. Instead of this lagoon, sediment from the cleaning process was deposited, creating olfactory discomfort but polluting the groundwater.
sump
Such shallow home-made modern ponds are designed for further settling of water. Here, effluents can settle for up to 3 hours. As a result of settling, all impurities and suspended particles of debris remaining in the water are additionally removed.
In this reservoir, clean water preserves life. Also here, due to the fact that the depth of the pond is only 1 m, the water is also disinfected through the ultraviolet of the sun, destroying the viruses coming from the hospital wastewater. The sludge is 90% water, as milk is only black in color. before discarding the residue. It comes from primary sludge that is placed in a gravity concentrator, causing it to lose some of its water and secondary sludge. Both sludges are pumped into methane, where they are anaerobically fermented.
Here, other bacteria convert it into mineral, water and biological fermentation gas. This engine drives an electrical generator that covers about 20% of the power required by the station. The heat from the engine helps to heat the spaces of the buildings and heat the bacteria that need the heat to complete all these processes.
Important: the efficiency of settling with the use of such a wastewater treatment scheme is 50%. Efficiency can also be increased if the depth of the settling pond is reduced by an order of magnitude and at the same time its area is increased.
After settling, the water is clarified using special coagulants, which turn into flakes in the water, thereby filtering the effluents, further clarifying them.
In methanethane, the precipitate boils completely after about 75 days. It is stored for 20 days, most of the mineralization is resolved during this period. There is also an inconvenience in this process - the formation of hydrogen sulfide, which, upon contact with water vapor, turns into sulfuric acid. We can get rid of hydrogen sulfide by passing it through active carbon. Within no more than one week, the pores of the coal are loaded with this substance. Another method, more expensive than investment but cheaper to operate, is to use certain bacteria that, under certain conditions, absorb hydrogen sulfide from biogas.
Additional wastewater treatment plants
In addition to the systems and devices listed above, so-called membrane devices are also used in wastewater treatment. In the design of such installations there are special membrane sheets, overflow pipes and capillaries. Thanks to this design, the wastewater is divided into two parts in the membrane installation. At the same time, their pressure and compositions differ. Membrane installations can be made of polymers or ceramics.
These bacteria, in addition to heat and food, also need oxygen. If more than 10% oxygen is released, the gas ignites spontaneously. A series of sensors that monitor the percentage of oxygen in a gas. From methane, biogas enters the raw gas tank, desulfurizes there, and pure gas without hydrogen sulfide passes into another tank. From here it gets to the engines and produces electricity.
The sludge is not completely fermented, it still smells and contains a lot of water. Remove water and stabilize it. Thus, the sediment reaches the belt filters. But dirt particles are electrically connected to water. Using an electrolyte pole, remove water from the sludge. The sludge is pumped into a special sludge sludge. Here thermal dehydration continues using solar heat. There is also a final stabilization of the sludge by chemical stabilization. The oxygen in the air is sent to the greenhouse with the help of fans.
Hydrocyclones and centrifuges
These modern devices are also used for sedimentation of suspended particles in effluents. Due to the centrifugal force into which the waste water enters, all impurities are separated from the liquid and the water is considered to have passed the stage of mechanical treatment.
The greenhouse has a robot that turns the sludge to achieve uniform stabilization. Hence the sediment is rich in phosphates, being a very good fertilizer. Finally, a precipitate forms. The discipline "Environmental Chemical Engineering" is an important part of education in the field of chemical technology. It provides the basic principles of the various methods of treating wastewater that results from technological processes, as well as their methods of processing and drinking irrigation of natural waters. The main technologies and methods for removing various toxic compounds in natural waters are: humic substances, colloidal and dispersed particles, fats and oil products, toxic fluoride ions, as well as the removal of various toxic substances from wastewater: Colored substances, surfactants, halogenated hydrocarbons, heavy metal ions, etc.
Hydrocyclones, unlike centrifuges, are open (work with light impurities) and pressure (designed to separate heavy particles of debris from wastewater). This classification allows the use of installations depending on the type and degree of wastewater pollution.
In turn, the classification of the centrifuge looks like this:
- Settling;
- Filtering.
The design of filtering industrial centrifuges includes thin metal sheets with perforations for better particle settling. Also, the devices have main grids made of copper, aluminum or steel and dense fabric partitions. The type and type of filter completely depends on the intended task, that is, on the rate of separation of impurities, their size, type of effluents, liquid pressure and concentration of debris in the effluents.
Aerotank
Water treatment device for biological wastewater treatment. Here, the water is treated with special organic sludge under the influence of oxygen injected into the plant. As a result, bacteria eat harmful impurities contained in the water. Most often, this basic method of wastewater treatment is used in case of contamination with organic debris.
The principle and scheme of contaminated wastewater treatment today
Having studied all the existing devices for the neutralization of wastewater, you can consider how the neutralization of wastewater occurs. It consists of several stages:
- First, all effluents from enterprises and residential areas of the city fall into a specially mounted water collector, from where they are then transported to a treatment plant.
- The first main stage in the neutralization of industrial (industrial) effluents is mechanical treatment. That is, the passage of wastewater through special filters, nets and grates to separate large debris. Debris particles are sent to the sludge collector.
- The next stage (stage) of water purification is its pumping into a special sump, where the remaining debris particles are further settled and removed from the water. A sand trap also takes part in settling, which passes through itself the water entering the settling pond.
- Further, the settled water goes through the stage of clarification using coagulants and is sent to press filters. Here under great pressure water passes through special filters that trap any remaining particles. This stage is the final one in mechanical wastewater treatment.
- Further, depending on the initial type of wastewater pollution, water is sent for further biological, chemical or physico-chemical treatment. That is, water will be affected either by bacteria, or chemicals, or ultraviolet or ozone.
Important: the efficiency of wastewater treatment using the initial mechanical method is 60%. Further manipulations with water allow you to clean the drains by 90-98%.
Further disinfection of wastewater
In addition to wastewater treatment, it is also necessary to carry out the stage of its disinfection. The most common method is chlorination. But according to Canada's Protection Act environment» This method poses a threat to the environment, therefore, in Russia, a decision was made to additionally dechlorinate wastewater before discharging it into ponds, soil or water bodies.
In addition to chlorination, ozonation is a very effective way to disinfect wastewater. But this method is quite expensive. Used only in European countries.
An alternative and high-quality method of wastewater treatment is water treatment with ultraviolet light. Special UV lamps act on the surface of the water, disinfecting it and destroying residual pathogenic microorganisms in the liquid.
It should be noted that when water is treated with UV lamps, water does not take part in the reaction. Only bacteria and ultraviolet interact with each other. The efficiency of such water treatment is 90%.
Important: ultraviolet wastewater disinfection units do not take up much space and are fully automated. In addition, they do not pose a threat to humans.
All-consuming technical progress, unfortunately, is not always reflected in our lives in the best way. So, at present, the shortage of drinking water, and indeed clean water in general, caused by total environmental pollution, is becoming increasingly important. Although in fairness it is worth noting that humanity is trying to solve this issue, including through wastewater treatment. If in the conditions of the city such tasks are assigned to the city centralized system, then in private estates outside the territories of large settlements Owners of private houses have to rely solely on themselves.
Wastewater treatment in a modern way allows you to perform very efficient cleaning operations, from odor removal to pumping out or reusing sewage water. At this time stage, technologies offer various methods of wastewater treatment, which differ both in the method of treatment and in price. More specifically, the most effective ways wastewater treatment is divided into 3 types:
- Mechanical.
- Biological.
- Physical and chemical.
Features of the mechanical cleaning method
Mechanical wastewater treatment is defined as the initial stage of treatment activities. Its main task is to remove coarse impurities by using coarse filters. The range of possibilities for mechanical treatment is quite extensive; in the case of application in a domestic wastewater treatment system, up to 60% of impurities can be removed. And when used on an industrial scale, wastewater treatment by 90% is possible. This is how wastewater is treated from oil products at car washes or refineries. In addition, it should be said that mechanical cleaning methods are the cheapest. There are 3 key technological methods for the mechanical treatment of sewage water:
- upholding;
- straining;
- filtration.
The process of mechanical cleaning by straining at a special station
During mechanical treatment, sand and iron hydroxide (rust) are removed from wastewater. For these purposes, a water clarification filter is used, consisting of a glass fiber body, a filter load and a control unit, which allows automatic loosening and washing of the load.
Bacterial and biological treatment
In this regard, such a concept as anaerobic wastewater treatment is very often used. The point is that on English language the word "anaerobic" is defining for the process of decomposition of wastewater and waste, in which the main emphasis is on the absence, or rather the deficiency of oxygen.
At its core, this method is based on the functioning of the wastewater-“activated sludge” system and is distinguished by the inclusion of a complex multi-level structure. Biological wastewater treatment implies the principle of biological oxidation, which is activated as a result of a whole complex of interrelated processes of varying complexity. In this case, we are talking about the mechanism of the exchange of electrons belonging to the interacting components, and the most complex interaction of the biocenosis with the external environment.
Special “processor bacteria” are also loaded into a conventional septic tank, which process wastewater.
As the results of scientific research in this field show, a characteristic feature of complex multi-species populations, and activated sludge in particular, is the establishment of a dynamic balance in the system, the achievement of which is ensured by adding multiple relatively small deviations in the activity and quantitative composition of individual species from their average level. Such cleaning can be carried out both in natural conditions and in artificial ones. Natural facilities and biological treatment facilities include:
- A filter well, which is used at a flow rate of 1 m 3 or less, as well as a filter cassette - the flow rate is 0.5-6 m 3 per day.
- Underground filtration field - consumption is about 15 m 3 per day or more.
- Filtration trench, sand and gravel filter, used at a flow rate of 15 m 3 per day or more. The irrigation and drainage network of these structures is laid in a layer of filtering artificial soil made from imported soil. It is arranged in case of water resistance or poor soil filtration.
- Filter cassette - throughput 0.5-6.0 m 3 per day, intended for operation in weakly filtering soils (loams) with a characteristic filtration coefficient of at least 0.1 m 3 / day.
- Circulation oxidizing channel (COC) - consumption 100-1400 m 3 / day.
- Biological pond with artificial or natural aeration - consumption 1400 m 3 per day.
Aerobic treatment also involves the use of technology, which uses the so-called biofilters for wastewater treatment. We are talking about treatment facilities filled with loading material intended for filtration. According to the technology, a biological film develops on the surface of this layer. Due to the temperature difference between atmospheric air and wastewater provides continuous ventilation of air masses through the filter loading, which contributes to a constant oxygen concentration sufficient for the life of microorganisms.
The key element of the biofilter is the feed material. According to the type of this part of the filter, biological filters are divided into 2 categories:
- with flat loading;
- with bulk loading.
One of the possible designs of the biofilter
- crushed stone of strong breeds;
- slag;
- pebbles;
- expanded clay.
Physical and chemical cleaning method
It is based on the mutual reaction between the treated liquid and a special reagent: coagulant or flocculant. This component interacts with soluble compounds, which are then filtered during mechanical wastewater treatment. The pollutants remaining in a soluble form are transformed into a harmless form as a result of the application of the method of physical and chemical purification. In this case, water is purified from iron-containing components and hardness salts. However, this cleaning method does not always remove all harmful impurities.
Physical and chemical cleaning allows you to get rid of iron and various salts
We hope that the described methods and stages of wastewater treatment will help you correctly assess the situation and create a universal treatment system on your territory.