Sewerage wastewater treatment. Industrial sewerage: how to clean. How activated charcoal works
Wastewater generated in the course of human life, entering water bodies, becomes one of the most serious sources of pollution that negatively affects human health. To reduce the pollution of water bodies, a set of measures is applied to cleaningWastewater- removal of contaminants. Drains, depending on their origin, are divided into the following types:
- Household or household-fecal, which include receipts from residential development and public buildings;
- Production - formed in technological processes and removed from the territories of industrial enterprises;
- Rain, collected during rainfall, snowmelt and washing of territories.
Households are contaminated with all sorts of organic impurities, including food debris, and carry a huge amount of bacteria, both neutral and pathogenic. The main task of processing such wastewater is the extraction of large and small inclusions, the oxidation of organic matter contained in them, in order to reduce the burden on the environment and disinfection.
Industrial effluents, also depending on the nature of their formation, may contain a variety of organic ingredients, such as dairy effluent, mineral inclusions and other compounds harmful to life. Liquid waste generated at metalworking enterprises contains metals, including heavy ones, which, if ingested, can have a negative impact on human health.
Rain runoffs wash away organic impurities, suspended particles (sand, clay, etc.) and oil products from the territories.
Effluent of various origins contains a variety of pollutants. The discharge of rainwater into water bodies without treatment leads to serious pollution, adversely affects human health, can accumulate in the inhabitants (fish) and, accordingly, enter the body with food.
For cleaning, various methods are used, which depend on the nature of the formation of liquids, their composition and quantity. Let's consider the methods of treatment of household water, because. they make up the largest part of stocks.
Domestic wastewater treatment methods
Wastewater entering the treatment plant goes through several stages of processing:
- mechanical;
- biological;
- disinfection.
For the mechanical stage, the following equipment is used: gratings, sand traps, sedimentation tanks, filters. The first structure that drains fall on is gratings. They are a set of rods installed vertically or with an inclination on which large inclusions are retained. The recommended clearance between the bars is 16 mm. The retained debris is removed from the screens manually (for small stations) or with a mechanical rake. The collected garbage is collected in a special container, then taken to a landfill.
The following equipment is used for the mechanical stage: gratings, sand traps, sedimentation tanks, filters The next stage is settling in sand traps, which are rectangular or round in terms of structures. When entering the sand trap, the speed of movement decreases, and heavy ingredients, mainly of mineral origin (sand), settle. These particles carry all pollutants. Sand settles to the bottom of the sand trap, is moved by scrapers or washed off into the lower part of the pit, then removed by pumps or water jets to the sand platform. After drying, the sand must be disinfected and can be used, including for planning work.
After preliminary treatment, water enters the primary settling tanks, which, depending on the direction of movement in them, are divided into horizontal, radial and vertical. The choice is determined by the performance of the structures. With low productivity, vertical ones can be used, with medium productivity - horizontal ones, for large stations radial ones are used. The principle of operation of settling tanks is the same - with a decrease in the speed of movement, impurities of various sizes are released. The speed of movement in settling facilities is determined by regulatory documents. Impurities settle to the bottom, then by scrapers, liquid jets or under the action of their own weight they move to the pits, then they are pumped for further processing. There are various methods of settling intensification, first of all, it is a reagent treatment, when chemicals are added that contribute to the coarsening of suspended particles. Larger particles settle faster. Another way is thin-layer settling, when a set of shelves is placed in the sump and the process goes faster by reducing the settling height.
Secondary clarifiers are related to mechanical cleaning designs, but are located after the biological treatment stage, which will be discussed in the next section. Secondary, as well as primary, are divided into horizontal, radial and vertical, but not suspended solids are released in them, but activated sludge, which is formed in aerotanks or biofilters.
The next stage is settling in sand traps, which are rectangular or round in terms of structures. Filtration is used for deep purification from contaminants. This process completes the technological scheme and is used in cases of stringent requirements for the quality of runoff discharged into water bodies. Post-treatment is carried out on filters of different designs, the choice of which depends on the performance of facilities and pollution. Filtration is carried out through various media, mainly natural materials of various sizes, the most popular of which is quartz sand.
Biological treatment
Settled effluents enter aerotanks - biological oxidation plants. In aeration tanks, water is mixed with activated sludge - flaky compounds of bacteria, air is also supplied here in the form of small bubbles. Bacteria in the presence of air actively absorb organic ingredients, they are oxidized and the amount of activated sludge increases. The mixture flows into the secondary settling tank, where the sludge settles, then part of the sludge is taken away for processing, part is returned to the aeration tank. With low productivity, instead of aerotanks, biofilters are used - tower-type structures filled with a special load and ventilated from below. Bacteria settle on the load. The liquid, moving from top to bottom through the load, comes into contact with bacteria in the presence of air and is intensively cleaned.
Purified liquids contain a large number of bacteria, including pathogens, so they must be decontaminated before being discharged into a reservoir. For disinfection are used:
- sanitation with chlorine-containing reagents;
- ozonation;
- ultraviolet irradiation.
Each method has its own advantages and disadvantages. Chlorination involves the use of chlorine - a toxic substance, so working with it requires special care. The liquid after chlorination must be kept for at least half an hour to remove chlorine compounds. For this, contact tanks are used.
Purified liquids contain a large number of bacteria, including pathogens, so they must be decontaminated before being discharged into a reservoir. Such tanks, with high productivity, occupy significant areas. Ozonation is an expensive energy-intensive procedure and is carried out in sealed structures. UV disinfection is limited in performance.
In the process of processing domestic wastewater, primary sludge is released in the primary settling tanks, after the aerotanks, activated sludge is released in the secondary settling tanks.
Recycling and subsequent disposal of the resulting sludge is one of the most serious tasks of sewage. The complexity of the task is determined by their large volume and properties. As a rule, sediments are hard-to-filter suspensions of organic origin. Their volume, depending on the composition and technological scheme, is 0.5 - 10% of the flow rate supplied to the treatment facilities. Their humidity is 90 - 99%, most of the moisture is in a bound state. The bacteria and helminths contained in them require serious disinfection before further use.
Recycling and subsequent disposal of the resulting sludge is one of the most serious tasks of sewage. The main tasks are the reduction of humidity, stabilization, disinfection.
To transfer the main part of organic matter into a mineral form, methane digestion and aerobic stabilization are used. Methane fermentation is carried out in digesters, where, under the action of high temperature, the sludge is mineralized, and gas is released - methane, which can also be used at treatment facilities for their own needs. The difficulty lies in the contamination of the gas with impurities. During fermentation, in addition to mineralization, the issue of disinfection is solved.
Aerobic stabilization is used to mineralize the active or. The process is an active aeration of sludge in structures similar to aeration tanks. The next step in the processing of sludge is their dehydration. For dehydration, natural methods are used (drying on sludge beds) and mechanical methods (on belt or chamber filter presses, centrifuges, vacuum filters). Before dehydration, to transfer moisture from a bound form to a free one, it is treated with reagents or flocculants. Dehydrated sludge with a moisture content of 70 - 80% (depending on the method of dehydration) is fed for further processing - disinfection - mainly by thermal methods.
After disinfection, the sediment is suitable for use as a valuable fertilizer.
Wastewater treatment plant
Sewerage wastewater treatment This is a set of required activities. Its implementation is regulated by the current legislation and which is necessary both for the purpose of protecting the environment and for the renewal of water resources. Modern purification technologies using various methods in their nature make it possible to ensure maximum purity of the liquid returned to nature.
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What is meant by waste water?
Sewer wastewater is called:
- all liquid waste from human life and activities, the so-called domestic waste;
- industrial effluents, water used directly in production, as well as for cooling systems;
- atmospheric precipitation that enters the sewer through the storm sewer system.
According to the types of pollution, wastes are classified as follows:
- Minerals containing:
- salt;
- sand;
- clay, etc.
- chemical organics;
- polymers.
As a rule, sewage drains are a combination of all types of pollution, which makes it necessary to carry out their multi-stage purification.
The cost of sewerage wastewater treatment
| Name of service | Price |
| Maintenance of heat substations (independent scheme) | from 6 000 rub/month |
| Maintenance of heat substations (dependent scheme) | from 10 000 rub/month |
| Maintenance of UUTE | from 3 000 rub/month |
| Installation UUTE | from 250 000 rub |
| Hydraulic tests (pressurization) | from 7 000 rub |
| Chemical flushing of the heat exchanger | from 8 000 rub |
What methods are used to clean sewage?
A variety of contaminants makes it necessary to treat sewage wastewater according to a combined scheme using the following methods.
- Mechanical.
It is used to remove large particles and insoluble residues and serves as a preparatory step for subsequent biological cleaning.
Sorting of this group of waste can be done in the following ways:
- straining;
- filtration;
- upholding;
- centrifugal filtration.
The combination of these methods used in practice can significantly increase the efficiency of mechanical cleaning.
This method is used, as a rule, for the treatment of industrial effluents and consists in the addition of chemical reagents that contribute to the transformation of soluble components into insoluble ones for their subsequent removal by a mechanical method.
The action of reagents can also be directed to such reactions as:
- neutralization;
- oxidation;
- recovery.
In practice, due to its high cost, the chemical method in its pure form is used extremely rarely.
Being a combination of the use of physical and chemical properties of liquids and trace elements, this group of methods is considered the most effective for treating a wide range of wastewater, including industrial waste.
There are the following cleaning methods:
- electrochemical;
- coagulation;
- sorption;
- ion exchange;
- extraction, etc.
It should be noted that the complex application of the physicochemical method allows not only to obtain an almost pure liquid at the outlet, but also to fully automate the entire process.
These purification methods are based on special bacteria capable of processing human waste products with a degree of purity of the liquid at the outlet up to 95%.
By type of bacteria can be:
- aerobic, which require air to live;
- anaerobic, living without access to oxygen.
The use of bacteria is considered the most promising direction in the purification of polluted wastewater, but this method is not suitable for processing wastewater from industrial enterprises.
However, in the residential sector and in the urban economy, this method is used quite widely.
It is used in the case when liquid purification is not possible, as well as for liquid waste immediately after the relevant processes have been carried out. The essence of the method is to spray a contaminated liquid over a burning fuel torch.
Calculate the cost of sewage treatment for you
In order to select the optimal treatment method, sewage effluents in a particular area are subjected to a thorough analysis to determine their composition, on the basis of which the most effective combination of methods is developed.
The purification processes themselves take place at specialized stations, which are a complex system of tanks, sedimentation tanks, filtration modules, etc. The composition of the equipment is also determined by the composition of specific waste.
Thus, sewerage wastewater treatment is a process that involves the use of a variety of methods and technologies. The general reduction of water resources increases the importance of this area, and state regulation is an additional incentive for improving technologies in this area.
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What do you know about sewers? Filling in the gaps
If you ask the majority of the population what sewage is, it will not cause difficulties with the answer, regardless of their place of residence. A resident of London, Paris, Moscow, Vologda or an urban-type settlement somewhere near Krasnoyarsk understands perfectly well what is at stake, although he has little idea of what happens to wastewater outside a residential building or production workshop.
I will fill this gap in your knowledge by describing and illustrating the operation of the entire system, and will talk about wastewater accounting, and the treatment of hazardous and domestic wastewater. So, go! I promise it will be interesting.
We study wastewater
I think it is not worth explaining that the water from the bathroom of the apartment and the effluents of galvanic production differ significantly in a number of ways. Accordingly, the methods of disposal will also be different, primarily in terms of chemical and bacteriological composition. Let's find out what the options are.
Stock Pedigree
- In most cities and towns, there are various industrial enterprises that are connected to the citywide sewerage system. The sector of the national economy that deals with toxic or aggressive substances often has its own treatment facilities. In both cases, their waste is referred to as industrial effluent;
- As for domestic wastewater, first of all they pose a danger of biological contamination: the organic matter contained in them is a breeding ground for numerous bacterial colonies. Such effluents are purposefully sent to treatment facilities located outside settlements;
Captain Obviousness suggests: in the absence of a central sewage system, sewage transport is used, or wastewater is disposed of locally after separation of solid fractions.
- Do not forget about natural runoff - rain and melt water must also go somewhere from the paved avenues and streets of our cities. For these purposes, storm sewers function, which are often discharged into a nearby reservoir without any treatment.
Important: I will reassure all environmentalists - there are no violations here, since rain sewers and drains only dump water that has spilled onto the ground in a natural way.
The degree of its pollution is not so critical and does not pose a threat to the local ecology.
Structural analysis
We have more or less dealt with domestic wastewater, let's move on to industrial wastewater. And here the situation is much more complicated.
Stocks can be:
- With mineral pollution;
- polluted with organic matter;
- Combining both types of pollution.
The degree of contamination is also important, on which the cleaning method primarily depends - you must admit that different amounts of impurities, for example, 100 mg/l compared to 10,000 mg/l, require a fundamentally different approach.
In the above example, it is far from the worst option. But, you see, with such a composition, wastewater cannot be discharged into a reservoir or onto filtration fields.
How to calculate stocks
It is logical to start reasoning with private households - water enters the system from a well or city water supply, and its consumption is easily determined by water meters. If the drainage is made into the city sewer, then the owner of a private house is billed for the consumed water and services for the disposal of domestic wastewater.
The situation with industrial enterprises is much more complicated. After all, a number of them have both their own water intakes - reservoirs, lakes and rivers, as well as treatment facilities. In addition, the volume of wastewater correlates non-linearly with the amount of water used. For example, due to the fact that water in the production cycle turns into steam, respectively, without getting into the drains.
And yet, part of the waste is still discharged by enterprises into the city sewer networks. And since disposal is expensive, the utility bills each one. True, the accounting of sewage flows is carried out not according to the readings of water meters, but with the help of special devices that read volumes of wastewater close to real.
Why "close to real"? Let's figure it out.
Non-pressure systems
The sewage flow meter, designed for installation in a gravity sewer, operates on the principle of measuring the actual liquid level in a known section. Receiving real-time wastewater parameters, it is easy to determine the average flow per unit of time.
What is this device, and on what principle does it work?
| The design of the meter | Technical description |
| Lever | The simplest measurement method: the position of the float measures the liquid level. The float itself is connected to the measuring part of the device by a rocker arm. |
| electromagnetic | Wastewater with a high salt content is an electrolyte that interacts with the electromagnetic field of the measuring device. The actual consumption of effluents can be judged by its changes. |
| Ultrasonic | The speed of propagation of sound vibrations in air and water (an empty pipe or a filled one) depends on the level of the liquid. The device measures sound delay in real time and records the current liquid level. |
I note that such readings cannot be considered ideally accurate, since the measurement result is reliable only for perfectly clean sewer pipes.
As you understand, such a situation is impossible in principle - solid fractions in wastewater, silting, etc. will introduce distortions into the values recorded by the devices.
Pressure systems
We examined the principle of accounting for wastewater in gravity systems, and now let's find out how the meter works on a pressure sewer. Logic dictates that the principle is the same as with any measuring instrument for the water supply system.
But, unlike its “colleague in the shop”, which supplies clean water, the pump for pumping sewage is used for other purposes:
- Creates excess pressure in the sewer pipe;
- Grinds partially large fractions of wastewater.
To calculate the volume of waste, you need to know the cross section of the pipe and the flow rate. And the well-known Bernoulli's law helps to solve the problem. Let me remind you of it for those who have forgotten the school formulas - the static pressure in a fluid flow is inversely proportional to its speed.
The implementation of Bernoulli's law in practice for accounting is quite simple:
- drains are passed through a pipe of variable diameter;
- measure the pressure in its sections with different sections;
- calculate the flow rate.
Wastewater treatment plant
Let's return to our story and analyze how wastewater is cleaned, the amount of which is accurately measured directly at the utilities responsible for processing it.
City systems
Getting into the city sewer, domestic wastewater:
- Passed through primary coarse filters. These are gratings that trap large debris, sieves of various diameters and sand traps. Accumulated MSW (solid household waste) is further removed to landfills;
Sand from sand traps is used by the enterprise during the restoration work of the sewer network.
- Pass through grease traps, which collect grease from the surface of wastewater;
- Fall into settling pools. Waste water is in them for several days, and during this time heavy particles precipitate, where they are subsequently removed by scrapers. Surface contaminants are driven by a special float into a storage bin;
- After settling tanks, wastewater is subjected to biological treatment- water is forcibly aerated, bacteria that consume oxygen are activated, eating all organic matter;
- The next step is physical and chemical processing.- wastewater is passed through a molecular membrane that removes solutions of potentially hazardous substances;
- At the last stage, disinfection is carried out using ultraviolet radiation and chlorine treatment.. The purpose of their impact on wastewater is to destroy colonies of pathogenic bacteria that can cause epidemics, both among people and among domestic and wild animals.
Effluent from industrial plants
Unlike domestic wastewater treatment, industrial wastewater treatment involves a number of additional operations:
- To neutralize aggressive substances (for example, acids), appropriate reagents are used. Most often, caustic soda is used as an additive to neutralize them;
- For waste containing hydrocarbons, there is also thermal utilization. It involves the initial atomization and combustion of the water-air mixture in furnaces and burners. Under the influence of high temperatures, water evaporates, and the hazardous components of wastewater decompose into substances that are harmless to nature - carbon dioxide and water;
- Removal of toxic suspensions by centrifugation: wastewater is fed into a drum rotating at high speed, where it settles on its walls, and is subsequently removed and disposed of at special landfills.
Sewerage of a private household
All this is interesting, some readers will say, but we have our own house, and we are not connected to the city sewer system. It is for this category of readers that I will tell you how sewerage is cleaned in a private house. After all, for the majority it is quite primitive, and not everyone knows how to properly modernize it.
The most effective solution for today is a biological sewage treatment plant, which uses aerobic decomposition in its work. With its help, you can achieve a fantastic degree of wastewater treatment of 95-98%.
The compact device operates according to the already familiar principle of operation:
- Large particles and light fractions are retained in the first and second chambers of the settling tanks;
- Then the wastewater is transferred to an aeration tank equipped with a compressor. The air injected by it contributes to the rapid reproduction of colonies of aerobic bacteria that actively eat organic matter;
- The purified water at the outlet is discharged into the soil or used for watering flowers.
Captain Evidence suggests: you have to pay for everything good.
And the price of deep cleaning stations is quite high, which does not contribute to their mass distribution.
That is why septic tanks with the described principle of operation are often built with their own hands.
The proposed design is quite simple:
- In the first settling tank, wastewater stays for several days, separating into heavy and light fractions, as well as into water;
- Stratification of wastewater into fractions continues in the second settling tank;
- The water taken from the middle of the second tank enters the third for soil purification. Its device implies the natural absorption of wastewater by the soil.
