Wastewater from populated areas is formed as a result of human activity - household wastewater (fecal waste, food residues, detergents, soil particles, household waste, etc.) and in the industrial sector - industrial wastewater (process waste, raw material residues, etc. .p.).
Domestic wastewater
Domestic wastewater in each locality is uniform, namely:
wastewater from the toilet (containing fecal matter, paper, detergents), baths, washing clothes (containing large amounts of synthetic surfactants), cooking, washing dishes, cleaning the room, etc. A study of the type and amount of wastewater for each type of named expense item showed that on average, kitchen needs (cooking, washing dishes) account for 15-20% of wastewater from a family, bath and shower 20-25%, toilet flushing - up to 35 %, washing clothes - up to 20%. Toilet and kitchen drains account for up to 75% of household wastewater pollution.
For the population living in sewered buildings, in the absence of gas supply and centralized hot water supply, the average water disposal rate does not fall below 100 liters per person per day. In buildings equipped with centralized hot water supply, this norm exceeds 250 liters per person per day. These standards include all types of domestic wastewater (excluding industrial wastewater from industrial enterprises).
Pollutants in wastewater are in the form of suspensions, colloids and solutions. Up to 40% of pollution consists of mineral substances: soil particles, dust, mineral salts such as phosphates, ammonium nitrogen, chlorides, sulfates, etc.
Organic pollution is very diverse and is formed due to the influx of human and animal waste, and the influx of food residues and raw materials into the water. Organic contaminants include fats, proteins, carbohydrates, fiber, alcohols, organic acids, etc.
The content of organic pollutants in wastewater is determined by indirect indicators: COD (chemical oxygen demand) and BOD (biological oxygen demand). COD expresses the amount of oxygen required to completely chemically oxidize organic pollutants found in wastewater. BOD expresses the amount of oxygen required for the biological oxidation of organic matter by bacteria under aerobic conditions (without oxygen consumption for nitrification). Biological oxygen demand for domestic wastewater ends in approximately 20 days (BODtotal), and the value of 5-day consumption for domestic wastewater (BHKs) is, as a rule, 65-70% of BODtotal, which in practice can significantly reduce the time determination of this indicator, and with a sufficient degree of accuracy determine the amount of organic contaminants.
The amount of contaminants in household wastewater per person is determined mainly by physiological indicators and is approximately (in grams per person per day):
BODfull 75
Suspended solids 65
Ammonium nitrogen 8
Phosphates 3.3 (of which 1.6 g is due to detergents)
Chlorides 9
Thus, the concentration of pollution depends only on the amount of water disposal, which corresponds to the degree of improvement of housing.
The temperature of wastewater is determined by climatic conditions, the source of water supply, the degree of improvement of residential and public buildings (availability of gas, centralized hot water supply, etc.), and industrial enterprises. Temperature significantly affects the efficiency of wastewater treatment. So. for example, the same effect of removing suspended solids, all other conditions being equal, in winter is achieved with a settling time 30% longer than in summer. The efficiency of biological treatment decreases when the wastewater temperature decreases below 9°C; According to current regulations, water with a temperature below 6° C cannot be supplied for biological treatment.
A special type of pollution in household wastewater is bacterial. Wastewater contains a large number of bacteria, including pathogenic ones, and viruses. Pathogenic bacteria are adapted to exist in the body of humans, animals, and birds. Getting into wastewater (or directly into a reservoir), some of these bacteria die due to the lack of a specific substrate or optimal temperature. Some bacteria retain their pathogenic activity in wastewater or reservoir water. Wastewater may contain tuberculosis bacteria and leptospira. Brucella, tularemia bacteria, Vibrio cholera, etc. All these bacteria survive in water for varying periods of time. Therefore, Escherichia coli was chosen as an indicator of fecal water pollution. The concentration of cells of coliform bacteria in water determines the degree of contamination of water by bacteria and its suitability for use as drinking water or for cultural and domestic purposes.
In addition to bacteria, the wastewater contains helminth eggs: human roundworm, whipworm, etc.
Helminth eggs are highly resistant and persist in the environment for a long time. Active chlorine in doses usual for wastewater disinfection does not affect helminth eggs. Helminth eggs die under the influence of direct sunlight (from drying out), under the influence of high temperatures. It has been established that ascaris eggs die at 50-55 0 C after 5-10 minutes, at 60 ° C - after 5 minutes, at 70 ° C - after 10 seconds.
The composition of wastewater from populated areas includes ingredients coming from industrial enterprises. Unlike domestic wastewater, the composition of industrial wastewater is more diverse and depends on the type of production and the technological processes used.
For example, wastewater from ferrous and non-ferrous metallurgy factories is contaminated with a large amount of suspended minerals and contains non-ferrous metals and iron, sulfates, chlorides, resins and oils, sulfuric acid, and ferrous sulfate. Oil refineries and oil fields discharge oil and oil products, chlorides, suspended solids, and possibly the presence of iron and hydrogen sulfide. Wastewater from coke-chemical enterprises poses a great danger, since in addition to suspended substances it contains resins, oils, phenols, ammonia, cyanides, thiocyanates, and a large amount of salts of inorganic acids. One type of highly polluted wastewater that is difficult to treat is wastewater from pulp and paper mills, which contains dissolved organic substances, fiber, kaolin, etc. Machine-building and automobile factories discharge cyanide, chromium, oils and petroleum products, and scale. The main pollutants of textile enterprises are dyes and synthetic surfactants.
Wastewater from an industrial enterprise contains specific contaminants that must be removed before mixing with the wastewater of another enterprise or populated area.
Indeed, increasing the volume of water containing a particular ingredient will make its removal much more difficult and cost much more than in situ treatment.
For this reason, wastewater from industrial enterprises must be subjected to local treatment, the main purpose of which is:
Maximum reduction in losses of raw materials with wastewater;
Reducing clean water consumption;
Reducing wastewater discharge in terms of volume and quantity of pollutants into water bodies;
Reducing the volume of off-site treatment facilities and capital investments in their construction.
Many of the components of wastewater from industrial enterprises are contained in such quantities that, due to their high toxicity, their combined treatment with domestic wastewater is impossible.
In this regard, “Rules for the reception of industrial wastewater into the sewerage systems of populated areas” /1/ have been developed, aimed at preventing violations in the operation of treatment facilities and the safety of their operation through the correct organization of the reception of industrial wastewater into the sewerage network of populated areas. The “Reception Rules” were developed on the basis of the “Rules for the Protection of Surface Waters” /2/ to calculate permissible concentrations of pollutants in industrial wastewater, taking into account the requirements for the quality of treated water in specific local conditions.
The “Reception Rules” contain requirements for the quantity and composition of industrial wastewater accepted by city sewerage systems for joint disposal and treatment with household wastewater.
When determining the concentration of pollutants discharged into the sewerage system, it is necessary to take into account the conditions for the discharge of treated water into reservoirs, the efficiency of removing these substances at treatment plants, and the ratio of the amount of domestic and industrial wastewater. Concentrations of substances that are not removed at treatment facilities are determined based on the ratio of the volumes of domestic and industrial wastewater and maximum permissible concentrations (MPC) in water bodies.
One example of the influence of industrial enterprises on the composition of urban wastewater is the wastewater of the city of Cherepovets. Cherepovets has more than thirty large industrial enterprises, including the Cherepovets Metallurgical Plant, the Cherepovets Steel Rolling Plant, the Ammofos Production Association, the Promstroykomplekt reinforced concrete plant, a silicate brick plant, a carriage depot, a locomotive depot, a plywood furniture plant, a furniture factory, food industry enterprises (dairy plant, bakery plant, meat processing plant, brewery, distillery, fish factory), shipbuilding shipyard, light industry enterprises, etc.
For example, a metallurgical plant, in addition to the usual pollution, discharges petroleum products (up to 17 mg/l), cyanides (on average about 2 mg/l), thiocyanates (more than 10 mg/l), phenols (0.45 mg/l), copper , iron, zinc; a plywood furniture plant discharges formaldehyde in concentrations of more than 90 mg/l; dairy and meat processing plants discharge a large amount of organic substances - according to BOD_45_0 from 900 to 1160 mg/l; Oil depot wastewater contains an average of 282 mg/l of petroleum products, etc. As a result, the wastewater of the city of Cherepovets has a qualitative composition unfavorable for treatment, and the city wastewater treatment plants cannot currently provide the required quality of treated wastewater.
Waste water– water contaminated as a result of its use in everyday life and production, as well as atmospheric water discharged from the territories of populated areas and industrial enterprises.
|
Types of waste |
Composition of contaminants |
Pollution concentration |
|
Economically – household |
The composition is monotonous: organic in undissolved, colloidal and dissolved states |
Depends on the norm consumption, i.e. degrees dilution of contaminants water supply network |
|
Production: - contaminated - conditionally clean |
The composition is varied: organic, mineral and their mixture |
Depends on the character production, type of product products, features technological process production |
|
Atmospheric (superficial): - rain - thawed |
The composition is monotonous: predominantly mineral, small quantity organic |
Depends on location precipitation equipment, duration and precipitation intensity |
B.s.v. By nature, pollution is divided into:
- fecal(from the toilets)
- economic(from sinks, washbasins, bathtubs, showers, laundries, baths, catering establishments, public buildings, household premises of industrial enterprises)
Industrial wastewater.
Pr.s.v. are divided into:
Contaminated (min. impurities, organic impurities and mixtures thereof)
Conditionally clean.
To develop a rational water disposal scheme and assess the possibility of reusing industrial wastewater, its composition and water disposal regime are studied.
Number of pr.s.v. Roughly can be determined by the specific water consumption per unit of reference. raw materials or a unit of finished product.
Surface wastewater.
S.s.w., or surface runoff, includes rain and melt water, as well as water from watering the territory of enterprises, streets, runoff from fountains, and drainage water.
For p.s.v. characterized by great unevenness of its flow into the sewer system. The composition of p.s.v. includes min. pollution and, to a lesser extent, organic. A special group should include surface runoff generated in the territories of industrial enterprises. These waters wash away waste and waste from the relevant industries and, in some cases, are close in composition to industrial ones.
10. Classification of drainage systems. Composition of structures. All-alloy drainage system. Separate drainage system. Semi-separate drainage system. Sewer basin. Separation chambers.
Water disposal (sewage) is a complex of engineering structures and measures that ensure the reception, transportation, purification and disinfection and release of wastewater into a reservoir, as well as the disposal of resulting sediments
Classification of sewage systems for residential areas.
Sewerage– a set of engineering structures and measures that ensure the reception, collection, disposal of wastewater, its purification and neutralization before disposal or discharge into a reservoir.
Classification:
1) – export(liquid pollution is collected in cesspools and periodically transported by horse-drawn or automobile transport to sewage disposal fields for treatment) - in small settlements, when the use of another type of sewage system is difficult
– alloy(wastewater is transported through underground pipelines to treatment facilities, where it is purified and then discharged into reservoirs)
2) - gravity(90% of all sewers)
- pressure(with the installation of pumping stations)
3) - internal(consists of plumbing fixtures, outlet pipes, risers and outlets)
- outdoor (street)- a system of underground pipelines that receives wastewater from yard networks and transports it to pumping stations, treatment plants and reservoirs.
Composition of sewer network structures.
The sewerage system consists of:
Int. building sewerage devices
External intra-quarter channel. networks
External street canal. networks
Pumping stations and pressure pipelines
Treatment facilities
Devices for releasing purification. wastewater into water bodies.
Sewer networks are built primarily by gravity. To do this, they are laid according to the terrain, dividing the entire sewered area into sewer basins. Bk– part of the territory limited by watersheds. Canal plots. networks collecting wastewater from 1 or several wastewater treatment plants – collectors (main, sewerage pools, suburban collectors). Large size collectors – channels. Treatment- structures intended for cleaning the station. waters and processing of their sludge.
Trace sequence:
1. Treatment facilities.
2. Main collector.
3. Sewer basin collectors.
4. Street networks.
5. Intra-block networks.
All-alloy sewerage system:
All-alloy SK.(K1+K2+K3) All types of wastewater are collected and transported to treatment facilities through a single sewer. networks. Storm drains can be installed to release part of the water into the reservoir during heavy rainfalls, which makes it possible to reduce the diameter of the collector and the productivity of treatment facilities. The construction of a waste water treatment plant without storm drains is difficult, because... During periods without rain, the hydraulic conditions of the collectors are worse due to low filling; the structures operate at only 1/3 of their productivity. Capital costs for the construction of treatment facilities designed to handle storm water flows are also high.
Separate sewerage system.
-
full separate sk- at least 2 networks. Network for drainage of domestic wastewater – domestic, for atmospheric wastewater – rainwater, manufactured. Water can be discharged into domestic or rainwater.
- incomplete separate sk– an underground rainwater network is not installed, and the drainage of atmospheric water into the reservoir is carried out through open trays and ditches.
Phalf-separated sk – the first portions of the dirtiest rainwater and water from melting snow go to wastewater treatment plants, and cleaner stormwater goes to storm drains.
Combined SC .
One part of the serviced facility is equipped with a complete separate system, the other with an all-alloy system. It is used when, during the expansion of cities that have a general alloy system (loaded only with domestic and industrial waters), new drainage collectors are built. Thus, in different areas of the city, along with the common one, separate or incomplete separate sewerage systems arise.
Sewer basin:
TO 
analysis networks are built primarily by gravity. To do this, they are laid according to the terrain, dividing the entire sewered area into sewer basins. BC- part of the territory limited by watersheds. Sections of the sewer network that collect wastewater from 1 or several wastewater treatment plants are called collectors, large-sized collectors – channels.
Separation chamber.
Separation chambers are arranged with complete separate and semi-separate drainage systems. Their locations and purposes are different. With a complete separate system, separation chambers are arranged:
On the rainwater network in separate places of the water collector or in front of treatment facilities to discharge part of the rainwater during intense rains into the reservoir;
at facilities for self-purification of storm water, if different degrees of purification are necessary.
With a semi-separate drainage system:
On the rain network before connecting it to all-alloy collectors to discharge part of the rain. water during intense rains into a reservoir;
In front of treatment facilities for the temporary discharge of some household waste, industrial waste. and rain stations water into control tanks for subsequent supply to treatment facilities.
The concept of “wastewater” includes precipitation and other waters clogged during human activity. They can drain either independently or through a specially created sewer system that drains liquid from populated areas and industrial enterprises.
A centralized sewer system is a series of engineering structures designed to receive, remove wastewater and deliver it to the treatment site. Cleaning and disinfection are carried out outside populated areas and enterprises.
Wastewater classification:
· Atmospheric, formed during precipitation.
· Domestic, discharged from bathtubs, toilets and other flushing structures of residential, industrial and industrial premises.
· Industrial, coming after the use of water at the stages of industrial production.
Each of the presented categories of wastewater contains pollutants of organic and inorganic origin:
1.Domestic wastewater is the most polluted among the three categories presented above, which is due to the high content of organic components, which are easily rotten. This includes feces, bacteria and urine. Bacteria in household waste can be either harmless or pathogenic.
2. Atmospheric effluents belong to the category of low pollutants. This is exactly what became main reason to create several chambers with storm drain and storm drainage in the main collector. Due to the chambers, rainwater is discharged along with other wastewater directly into the reservoir without preliminary treatment.
3. Industrial wastewater is divided into two categories depending on the purpose of the water used. Thus, the waters involved in the process at the cooling stage are slightly polluted. If water is the active reagent, then the qualitative composition of the contaminants can be very different and is determined by the type of production.
Alloy sewer The system is characterized by the fact that wastewater of any origin is processed in special treatment facilities. Only after reaching the necessary sanitary standards is the wastewater classified as treated. It is this kind of waste that is discharged into the reservoir.
Separate sewer system is more complex and is divided into:
· full,
· incomplete separate.
· separate.
Let's look at each in more detail.
Complete separate sewerage requires the creation of two separate structures of underground pipes and channels. Through one of them (domestic) contaminated water flows from domestic and industrial use; atmospheric and industrial wastewater, characterized by conditional purity, passes through the second (rain or drainage).
Wastewater coming from domestic canals is sent to special treatment facilities located outside the boundaries of populated areas. Water from rain canals does not require purification and is therefore discharged into the nearest body of water.
The diameter of the pipes of the domestic sewer system is smaller than the diameter of the pipes and channels of the rainwater drainage system. According to the structural calculations used, the amount of atmospheric water is tens of times greater than the entire volume of domestic wastewater.
Incomplete separate sewerage characterized by the presence of an exclusively domestic wastewater system.
Semi-separate sewer system
This type of system involves the creation of two drain networks. The first removes clean water from atmospheric precipitation and lightly contaminated water from industrial production; the second drains heavily polluted waters of domestic and industrial origin, as well as dirty atmospheric waters of the first rainfall.
Obviously, rainwater must be separated, which is what happens in “interceptors” specially designed for this purpose.
Combined sewerage can be laid in various areas of the village.
Among all the above-mentioned wastewater systems, the semi-separate system best satisfies sanitary requirements, since wastewater of any origin is discharged outside of cities, villages and other populated areas for the purpose of further purification.
However, semi-separate sewerage has two disadvantages:
1.The design of interceptors is far from perfect.
2. Creating two networks with interceptors requires considerable financial expenditure.
It is the second point that is the most serious reason for using more simple system sewerage. To date, the design of semi-separate sewers is not carried out.
The qualitative composition of wastewater varies greatly, so internal sewage systems are divided into:
· Rainwater, used to remove precipitation using internal gutters from the flat roofs of buildings.
· Domestic, used for the disposal of domestic wastewater. Water from industrial production can be discharged into the same system, but only if its volume and composition meets the standards that allow wastewater to be discharged through a network of this type.
· Industrial, used to remove contaminated water coming from production workshops.
The internal domestic sewage system consists of special receivers, which include:
Toilets, bathtubs and sinks,
Highways with risers,
Risers with revisions,
Wiring to risers (in a private house).
The risers must end with a ventilation pipe, in which a deflector must be included to enhance draft.
Wastewater collection
Reception of contaminated water into the sewer is carried out in accordance with specially developed sanitary standards. According to the rules, each wastewater receiver must have a hydraulic seal that prevents the penetration and spread of unpleasant sewer odor into the room.
It should be remembered that sewer cleaning is carried out when installing inspections. Street sewerage must be ventilated, which is necessary due to the breakdown of the organic component of wastewater.
The removal of contaminated water through the industrial sewer system and its subsequent processing for purification purposes is determined by several factors: the type of production, the type of technology used, the composition and amount of contaminants, features and type of equipment.
Internal and external sewerage design
Internal drains consist of:
Funnels into which water flows from the roofs,
Outlet pipes, thanks to which water flows from the funnel into the risers,
Stoyakov,
Collection trays in which water from risers is collected.
Audits and wells.
The latter are necessary for organizing repair work.
In most cases, the organization of yard sewage requires the presence of street and intra-block networks. Their main function is to collect wastewater through intra-block networks and subsequently transport the wastewater to treatment facilities.
A modern sewer system necessarily includes treatment facilities. An exception is when the State Sanitary Inspectorate issues a permit allowing water to be discharged without prior treatment.
Using flocculation for wastewater treatment
The process of flocculation involves the formation of large aggregates by the association of smaller particles as they collide with each other. The aggregates formed in this way are quite easily removed from wastewater at the stages of mechanical treatment: flotation, filtration or sedimentation.
Technologies using flocculation appeared in the 30s of the last century. Since then they have improved significantly. Modern techniques using flocculation make it possible to treat industrial and domestic wastewater.
The operating principle of flocculants is based on a physicochemical type of interaction: at the first stage, the flocculant is adsorbed on a colloidal particle, covering its entire surface; at the second stage, flocculants form a surface network that ensures aggregation large quantity colloidal particles due to intermolecular van der Waals forces.
The formation of three-dimensional structures is another feature characterizing the action of flocculants. As a result, the efficiency and speed of treatment activities increases, since colloidal aggregates are easily removed from wastewater. The three-dimensional structure appears due to the formation of “polymer bridges” between colloidal particles with flocculants adsorbed on their surface.
Treatment stations
Stormwater is treated at special stations called LIOS. Their job is to remove pollutants in the form of suspended matter and petroleum products. Storm water is considered purified only after reaching established sanitary standards. Purified water is discharged onto the terrain or into a nearby body of water.
Each company sets its own cleaning requirements based on the types of contaminants. In some cases, it is necessary to use wastewater treatment facilities. The operation of special treatment facilities involves the use of the following types of processing:
Sorption,
Physico-chemical,
Mechanical.
The effectiveness of the methods is very high and allows you to clean wastewater from harmful substances of various types. chemical composition. They are rarely used separately. Combinations of methods are more common. LIOS should be installed if there is a need for deeper purification of wastewater from suspended matter and oil products.
LIOS provides a sufficiently high degree of purity of processed wastewater, which allows it to be discharged into fishery reservoirs for disposal. Industrial storm water is processed according to certain technological schemes. The complexity of the scheme depends on the composition and amount of contaminants. In each case, several cleaning methods are used.
Stormwater treatment work is aimed at removing as much contaminant as possible. As a result, only a small portion of harmful substances remains in the processed wastewater. The maximum amount of pollution is strictly regulated and should not exceed the established value.
A serious advantage of LIOS is the possibility of subsequent use of treated wastewater at the stages of industrial production. Cyclic use of water allows you to save a lot of money on water supply and sanitation.
Pollutant - ammonium nitrogen
When talking about ammonium nitrogen in wastewater, we mean all ammonium salts and ammonia. Discharges of wastewater containing large amounts of such ammonia pollutants lead to the transformation of water bodies into swamps. That is why cleaning from them is mandatory, which is prescribed in special regulations.
Water purified from ammonia impurities can be discharged into a reservoir or used in coke production.
Possible waste treatment methods
1. Chemical. Based on the use of special chemicals that break down pollution.
2. Waste disposal. It's about about cesspools or special tanks where all the waste goes. As they accumulate, they are removed using sewage disposal equipment. This method is considered the most common.
3. Every year there is more and more pollution. Previous treatment facilities cannot cope with such a load. This required the development of more efficient and at the same time environmentally friendly methods of wastewater treatment. One of these is the bioremediation method. The high efficiency and safety of the method allow us to consider it the most in a modern way processing of contaminated water. Moreover, many scientific studies are devoted to the development of this particular cleaning method.
Bioremediation
Biological treatment (biological treatment) is based on the use of bacteria, for which the organic substances contained in wastewater act as a nutrient mass. By processing them internally, bacteria accelerate the decomposition of runoff pollutants several times. The activity of bacteria leads to the breakdown of harmful substances and the formation of harmless ones.
Modern biological treatment technologies make it possible to use aerobic and anaerobic bacteria to process wastewater. The difference between them lies in their relationship to oxygen in the air. Thus, anaerobic bacteria break down organic substances in an airless space. In contrast, aerobic bacteria exhibit their activity only in the presence of atmospheric oxygen, and their activity is higher, the more oxygen there is.
Purification by biological methods is divided into three stages:
1.Collect wastewater into vacuum separators, where water settles and contaminants are fermented. The result of the first stage of purification is “clarified water”.
2. Filtration of clarified wastewater by diluting it with soil water.
3.Diluted water is exposed to the action of aerobic bacteria, for which purpose the system is specially enriched with oxygen. Bacteria live in sludge. At the end of this stage, the water is considered purified, which allows it to be drained into the ground.
The wastewater disposal system and all structures used for these purposes are part of engineering devices, the purpose of which is to improve the city, residential or industrial complex. If we describe a liquid of this type, it can be characterized as follows. This is water that was used for some purpose, after which its properties were significantly deteriorated, and it became unsuitable for further use.
General description of the concept
Most often, wastewater becomes those liquid streams whose initial properties have been changed. Most often, such changes occur due to the fact that various impurities enter the composition. In addition, this class also includes those waters that are removed from cities and towns using sewage systems or drain from any industrial enterprise.
If we consider the type and composition of wastewater, they can be divided into three categories: domestic, industrial, atmospheric.
Description of the household type of liquid
Domestic wastewater is those streams that have been polluted as a result of practical activities and human activities. Most often, water in this category contains a high content of mineral and organic impurities. If we talk about mineral mixtures, then these are most often ammonium, chlorides, etc. Among organic substances, the presence of nitrogen-free and nitrogen-containing components is most often observed. Most often, such substances are presented in the form of proteins, fats or carbohydrates. Less often, but still, there are impurities in the form of microorganisms or viruses and bacteria that carry various diseases.
Types of industrial effluents
If we talk about industrial wastewater, the nature of the industrial enterprise that creates this wastewater plays an important role. Depending on this, they can be divided into several groups.
The first group is a liquid containing impurities of inorganic origin. These compounds contain a variety of special toxic substances. This can be wastewater from electroplating companies, construction enterprises, mineral substances production plants and others. Waste from these enterprises changes the pH structure of water. Wastewater with this structure contains heavy metal salts. These substances are considered toxic to possible inhabitants of the reservoir where waste water will be discharged.
There is a group of waters that contains inorganic compounds that are considered non-toxic. Effluents from such waters are created by factories such as cement plants, ore processing plants, and others. The waste from this industry is not considered too dangerous for those bodies of water where the water is discharged.
Another category is industrial wastewater containing organic non-toxic elements. The food industry is characterized by such waste. These can be factories for the production of dairy, meat, microbiological and other products. When this kind of liquid enters a body of water, a parameter such as oxidability increases significantly.
The last group, which is considered the most dangerous, is a liquid containing organic elements with special toxic substances. This type of waste is characterized, for example, by the oil refining industry. Also worth adding here are those factories that produce sugar or canned food.
Consumption standards
Wastewater treatment methods are also different types. The presence of several options is due to the fact that each industry needs to have its own method. Various scientific methods are used to develop a suitable purification method. Another important condition is that the enterprise must consume exactly as much water as is necessary for its operation, so as not to create excess contaminated liquid.
water consumption
The first thing that needs to be done in order to select a wastewater treatment method is to determine the very rate of liquid consumption for a plant, factory, etc. There are two ways to do this: scientific and well-founded calculations or best practice. There is also the concept of integrated water consumption by an enterprise.
However, the definition of the norm is only suitable for industry, and what to do with precipitation, which washes away all the dirt from the street, and then carries it through the sewer and is poured into certain place? To influence these factors, it is necessary to periodically dry clean the street. However, it’s worth saying right away that this will not solve the problem 100%. In any case, contaminated water from roads, which carries particles of organic matter, nutrients, petroleum products, and metal salts, will enter atmospheric groundwater.
Description of city waters
In practice, the concept of municipal wastewater is often used. This category most often combines household and industrial flows. It is worth paying attention to the fact that industrial, domestic and atmospheric waters can be drained separately or together. The most popular wastewater systems have become all-alloy and separate designs. The advantage of using the first category of system is that it will not be difficult for it to remove any types of contaminated water from the city through sewer pipes. Most often, such networks lead to treatment plants and facilities. As for separate systems, there are several pipeline networks, each of which carries a different type of fluid. For example, rain and unpolluted water can be transported through the first channel, and water with various harmful impurities can be transported through the second.
What criteria influence the choice of drainage system?
When choosing a network for treatment, the following parameters must be taken into account: wastewater substances contained within the liquid composition; the technical, sanitary, and economic components of the enterprise are assessed. It is also necessary to provide for the intensification of the activities of the selected facility.
In order not to make a mistake when choosing a drainage system, it is also necessary to determine a value such as the maximum permissible discharge (MAD). This term refers to the mass of elements contained in water that can be removed through the selected system and in the selected mode per unit of time. This is important to ensure the standard water quality at the control point.
Most often, pollution, etc. occurs due to the fact that wastewater from industrial enterprises is discharged here. The discharge of contaminated liquid can cause a change in some physical properties, for example, temperature, odor, etc. In addition, such places almost immediately become unsuitable for water supply to the population.
Observation of the release
Of course, there are certain conditions for releasing dirty water into a reservoir. The main criterion is the national economic significance, as well as the nature of use. After the release of contaminated liquid, the water quality in the reservoir deteriorates significantly. Therefore, release is permitted only if it does not have too much impact on life in the reservoir, and also if it does not harm future fish breeding in this place. In addition, the possibility of further use of this reservoir as a source of water to supply the population must remain.
The fulfillment of all requirements of this kind is monitored by the sanitary and epidemiological service. Another important point The problem is that the rules for preserving water bodies are not uniform. It all depends on what purpose the storage will be used in the future. Thus, there is the first group, which includes reservoirs that must remain suitable for centralized and non-centralized water supply to the population. The second type is the preservation of a reservoir for swimming, recreation and sports. Sanitary stations classify all bodies of water into one of these two groups.
Water self-purification process
Today it is known that such a process as self-purification of water in a reservoir is possible. This is understood as the occurrence of hydrodynamic, chemical, microbiological and hydrobiological reactions, as a result of which the liquid returns to its original state.
However, to achieve this result, it is necessary to comply with certain restrictions on the discharge of wastewater. First, the release of contaminated water must not disrupt the functioning of other facilities. Secondly, the waste liquid should not contain substances or impurities that could clog or even be deposited inside the pipes. If industrial wastewater does not meet these requirements, it is first purified at the station, and only then discharged into the reservoir.
Mechanical cleaning process
It is used if there are insoluble mineral or organic masses in the water. Most often, this process is a preliminary method of purifying the liquid. They resort to using this method before proceeding to the main ones. If you follow this procedure according to all the rules, you can ensure that the amount of suspended mechanical substances is reduced to 92%, and organic substances - to 23%.
Mechanical water purification systems include devices such as filters and screens. Let's say a common thing is a sand trap, which is designed to separate large mineral impurities from a liquid, in in this case sand. Here, equipment such as a homogenizer is used. This device is capable of regulating the composition and flow of wastewater.
Objects such as primary settling tanks are widespread, where, using the force of gravity, heavy mechanical impurities can be separated from the water, which settle to the bottom of the settling tank. In order to purify water coming from oil refineries, special oil traps are used. This is a special rectangular tank where oil products are separated from water. The principle of the difference in density of these compositions is used here.
It is worth noting here that the biological purification method requires additional costs, but it is used quite widely. When carrying out this procedure, all organic compounds present in the water begin to oxidize. To perform this operation, special microorganisms are used.
Purification of wastewater by biological means can be carried out both in natural conditions, that is, in fields of irrigation, filtration, etc., and in special systems, for example in a biofilter. This creates a favorable environment for the development of special microorganisms, which significantly speed up the cleansing procedure. However, creating such conditions will require additional financial costs.
Chemical and physico-chemical methods
These methods of liquid purification have become most popular and important when working with industrial wastewater. These methods can be used either separately from the others or in conjunction with mechanical or biological ones. For example, there is a neutralization procedure that is used in cases where it is necessary to purify industrial wastewater from the acids contained in it. Most often, this method is used to avoid the development of corrosion inside metal drainage systems. This also helps to avoid disruption of the biochemical processes taking place in the reservoir.
Precipitation
Sewage sludge is a suspension that is separated from contaminated liquid by mechanical, biological, chemical or physicochemical treatment.
There are several types of residues that remain after cleaning. Belonging to a particular type depends on what kind of equipment or method was used to improve the quality of the liquid. Coarse impurities remaining on the grates are classified as waste. Heavy impurities that remain in sand traps are sand. Floating impurities remaining in settling tanks are classified as fatty substances. There are also sediments dried on silt beds. There are quite a lot of these types. Discharge of wastewater into water bodies should be carried out only after removal of such sediments.
Wastewater contaminated with household waste and industrial waste and removed from populated areas and industrial enterprises by sewerage systems. Wastewater also includes water generated as a result of precipitation within the territories of populated areas and industrial facilities. Organic substances contained in wastewater, entering significant quantities into water bodies or accumulating in the soil, can quickly rot and worsen the sanitary condition of water bodies and the atmosphere, contributing to the spread of various diseases. Therefore, the issues of purification, neutralization and disposal of wastewater are an integral part of the problem of nature conservation, improvement of the human environment and ensuring the sanitary improvement of cities and other populated areas.
Classification of wastewater.
Wastewater can be classified according to the following criteria:
- production (industrial) wastewater (generated in technological processes during production or mining) are discharged through an industrial or general sewage system
- Domestic (domestic and fecal) wastewater (generated in residential premises, as well as in domestic premises in production, for example, showers, toilets) is discharged through the domestic or general sewer system
- surface wastewater (divided into rainwater and meltwater, that is, formed by the melting of snow, ice, hail), is usually discharged through the system storm sewer. May also be called "storm drains"
Industrial wastewater, unlike atmospheric and domestic wastewater, does not have a constant composition and can be separated:
- according to the composition of pollutants:
- contaminated primarily with mineral impurities
- contaminated primarily with organic impurities
- contaminated with both mineral and organic impurities
- by concentration of pollutants:
- with impurity content 1-500 mg/l
- with impurity content 500-5000 mg/l
- with impurity content 5000-30000 mg/l
- with an impurity content of more than 30,000 mg/l
- by properties of pollutants
- by acidity:
- non-aggressive (pH 6.5-8)
- slightly aggressive (slightly alkaline - pH 8-9 and slightly acidic - pH 6-6.5)
- highly aggressive (strongly alkaline - pH>9 and strongly acidic - pH<6)
- on the toxic effect and effect of pollutants on water bodies:
- containing substances that affect the general sanitary condition of the reservoir
- containing substances that change organoleptic properties (taste, smell, etc.)
- containing substances toxic to humans and animals and plants living in water bodies
Composition of wastewater
There are two main groups of pollutants in wastewater - conservative, i.e. those that hardly enter into chemical reactions and are practically not biodegradable (examples of such pollutants are salts of heavy metals, phenols, pesticides) and non-conservative, i.e. those that can, incl. undergo self-purification processes of reservoirs.
The composition of wastewater includes both inorganic (particles of soil, ore and waste rock, slag, inorganic salts, acids, alkalis); and organic (petroleum products, organic acids), incl. biological objects (fungi, bacteria, yeast, including pathogens).
Wastewater treatment methods
In rivers and other bodies of water, a natural process of self-purification of water occurs. However, it proceeds slowly. While industrial and domestic discharges were small, the rivers themselves coped with them. In our industrial age, due to the sharp increase in waste, water bodies can no longer cope with such significant pollution. There is a need to neutralize, purify wastewater and dispose of it.
Wastewater treatment is the treatment of wastewater to destroy or remove harmful substances from it. Removing wastewater from pollution is a complex process. It, like any other production, has raw materials (wastewater) and finished products (purified water).
Mechanical cleaning
Mechanical wastewater treatment is used mainly as a preliminary treatment. Mechanical treatment ensures the removal of suspended solids from domestic wastewater by 60-65%, and from some industrial wastewater by 90-95%. The objectives of mechanical treatment are to prepare water for physical, chemical and biological treatment. Mechanical wastewater treatment is, to a certain extent, the cheapest method of purification, and therefore the most in-depth wastewater treatment using mechanical methods is always advisable.
Nowadays, there are great demands placed on cleaning. This leads to the creation of highly effective methods of physical and chemical treatment, intensification of biological treatment processes, development of technological schemes with a combination of mechanical, physical, chemical and biological treatment methods and reuse of purified water in technological processes.
Mechanical purification is carried out to separate undissolved coarse impurities contained in it from wastewater by straining, settling and filtering.
To retain large contaminants and partially suspended substances, water is filtered through various grates and sieves. To separate suspended substances from wastewater that have a higher or lower density relative to the density of water, sedimentation is used. In this case, heavy particles settle, and light particles float up.
Structures in which heavy particles fall out when wastewater settles are called sand traps. They trap particles larger than 0.15 mm or a hydraulic particle size greater than 13.2 mm/s.
Structures in which lighter particles float when contaminated industrial waters settle are called grease traps, oil traps, oil traps, etc., depending on the floating substances.
Filtration is used to retain smaller particles. In filters for these purposes, filter materials are used in the form of fabrics (mesh), a layer of granular material or chemical materials with a certain porosity. When wastewater passes through the filter material, the suspension separated from the wastewater is retained on its surface or in the pore space.
Mechanical purification as an independent method is used when clarified water after this purification method can be used in production processes or discharged into reservoirs without disturbing their ecological condition. In all other cases, mechanical treatment serves as the first stage of wastewater treatment.
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