Wastewater treatment plants remove oil products and suspended solids, purifying storm water to the requirements for discharging them into water bodies of any category or directly onto the terrain. Cleaning devices have been developed in a variety of ways, because the requirements for cleanliness also differ from each other. A storm water treatment plant can use the method of sorption, physico-chemical or mechanical treatment of wastewater, but it must always neutralize and purify water from all harmful impurities.
The nature of pollution
Storm water is the result of a variety of atmospheric precipitation. Melt waters can also be attributed here, when snow and ice melt in spring. Storm sewage appears sporadically, its consumption and quality are extremely uneven. Together with them, the remnants of the activity of drainages, fountains, watering the streets, close to them in terms of quality, are also removed. Stormwater is always polluted with mineral and organic substances contained in the atmosphere, on the ground and on the objects that they wash.
During periods of rain and spring snowmelt from industrial areasenterprises and settlements are washed off a variety of and always abundant pollution. Stormwater cannot be reduced or reduced in any way in terms of quantity. But to reduce their pollution is quite within the power of a person. First of all, storm water must be cleaned. And, of course, it is necessary to improve the culture of production, to eliminate the loss of products. It will not be possible to stop the rain, snow or hail that falls on the surface of the earth, but on the earth itself, it is imperative to observe order in any activity.
Storm water drainage
Atmospheric waters that are not contaminated with oil products or crude oil are drained from the territory of enterprises using closed or open drains. Storm sewage is not always treated, it depends on their chemical composition. If an oil refinery, rain, snow and hail absorb those oil products that are necessarily present on the entire surface of this territory in various quantities.
Therefore, the simple removal of precipitation is a violation of environmental standards. Storm water must be pretreated. All production runoff and all storm water must go through a closed sewer network first to the treatment plant, where the water will be freed from oil products, and only after this procedure can it be returned to the reservoir.
Atmospheric water treatment
From bunded containers, you can immediately send storm water to the sewer. Industrial and storm sewers leadrunoff into storage tanks arranged in the form of earthen tanks, divided into sections. Further, the process depends on the origin, that is, the classification of wastewater. They are household, industrial, atmospheric (stormwater). The degree of their contamination, as well as the sanitary requirements imposed, will dictate plans for further activities: either simply discharge storm water into a reservoir, or send it to a sewage treatment plant, where it will remove pollution mechanically, chemically or biologically.
Petroleum products are removed, for example, by sulfuric acid cleaning, and therefore such water cannot be discharged into the sewer immediately after it - it is excessively acidic. The next step is to neutralize it. For this, there are special basins with a volume that allows approximately eight hours of residence time for the washing water to complete the reaction. Lime is added to the water to neutralize sulfuric acid. The gypsum sludge formed as a result of the reaction absorbs all the remains of oil products and many other contaminants. It is regularly removed from the pool.
Composition
Industrial storm water contains up to fifteen percent of various process condensates. This includes hydrogen sulfide, which is formed from ten to three hundred milligrams per liter. In addition to hydrogen sulfide, storm water runoff contains a huge amount of ammonia - up to 18,000 mg per liter. Such waters infect not only reservoirs and soil, near such drains you can literally suffocate from poisonous air.
All water that has been used by industry or the publicnecessarily contains a variety of contaminants, and therefore must be cleaned. If an industrial enterprise does not have environmentally harmful industries, then wastewater from there will be considered conditionally clean. For example, if the company uses water to cool something. As well as storm melt water from this area, it is most often directly discharged into a reservoir, since it is not dangerous in sanitary terms. But household and fecal, that is, domestic water, as well as showers and bath-laundries and, of course, almost all other industrial ones, are always very heavily polluted.
Sewer networks in enterprises
In production, a separate sewerage system is most often installed, where conditionally clean and atmospheric waters go through their own network of channels and pipes, and polluted industrial and household waters go through another. These are two completely independent sewer networks. The first is storm water (rain), and the second is household.
Almost always conditionally pure water is reused in production. It is isolated from the general industrial waste water and allowed through an independent network back to the production sites. Moreover, in this case, conditionally pure waters are not combined with atmospheric waters. Exceptions are situations when the amount of conditionally pure industrial water is too small. Then they are discharged directly into the reservoir through the storm network.
Applying settings
Storm water treatment plants are used for industrial wastewater, includingoily. In their work, technological schemes are used, where there are several different cleaning methods after studying the types of water pollution. Special equipment is used. The scheme of the entire event should ensure a minimum discharge of pollutants into the water body, in no case exceeding the permissible concentrations.
For example, this is the LIOS water treatment plant. With its help, treated storm sewage is used in production in a circle, which significantly reduces the cost of the enterprise for water disposal and water supply. The capacity of the station is up to twenty liters of purified water per second, it can serve a catchment area of up to two hectares, and if you use an accumulation tank with it, the catchment can increase to one hundred and twenty hectares.
How cleaning works
Drainage, as already mentioned, is usually divided into domestic, which appear due to human activity, industrial and atmospheric. To apply this or that installation for storm water treatment, it is necessary to determine all the features of the pollution of the given territory. They can be organic, which contain inclusions of plant and animal origin (runoff from farms, fields, etc.). Here you can observe a variety of organic chemical compounds, even polymer ones.
Pollution can be of a mineral nature, with impurities of inorganic compounds. For example, storm meltwater carries with it a lot of soil. Waters polluted with various s alts also require special purification. The third type is biological pollution, these are microorganisms that develop in drains and quickly master any reservoir. The environment of storm water is very nutritious for them. Surely everyone saw how quickly overgrown reservoirs that do not have a channel. This is what is popularly called "blooming water". It is no longer possible to use such reservoirs.
Cleaning methods: mechanical and chemical
Mechanical method of cleaning with the help of special installations includes sedimentation of water sediment, their filtration, flotation, that is, cleaning from solid particles and organic residues. For this, special sedimentation tanks, huge various sieves, as well as traps for sand and oil are used.
The principle of chemical wastewater treatment is that pollutants are forced to react to reagents added to the water. The result is a precipitate that is settled and removed. Water is most well purified in this way, since the amount of substances that do not dissolve in it is significantly reduced.
Physical-chemical and biological cleaning methods
Physico-chemical method is used to detect and remove finely dispersed substances of inorganic and organic origin. The activities are lengthy but very effective. Coagulation (coagulation, enlargement, thickening of solids), oxidation, sorption, electrocoagulation, electrolysis are used. These methods can also remove toxic impurities.
The biological method is also not complete without chemistry andbiochemistry. Water treatment plants using this method are especially popular. They include biological filters, aerotanks, biological ponds, methane reactors. You can use any of the proposed methods, but there are always three main stages of wastewater: filtration of solid particles and impurities, aeration and slow filtration, enrichment and regeneration.
Wastewater Treatment Plants
Cleaning can occur using the simplest - gravity method. The catchment area of such treatment facilities is up to twenty hectares, that is, they operate locally and are used mainly in summer cottages and small towns. Gravity cleaning is a line of filters: sand separator, gasoline oil separator, sorption filter.
Productivity - a maximum of one hundred and fifty liters per second of surface runoff water. So that the load on the treatment plant is not excessive, a distribution well is used, which directs the standard amount of storm water to local areas. If the intensity of storm water exceeds the calculated amount, then some part of the runoff goes to the bypass line.
Benefits
There are no rotating and moving elements in gravity structures, so there is no need to change any units or components. The operation of such facilities is fully automated, the cleaning of the runoff surface takes place without the involvement of manual labor, thus ensuring the safety of workers and not even requiring their constant presence.
Missing andopen water surfaces, non-pressure, self-flowing mode of operation, does not require electricity consumption. Not a single element rises above the surface of the earth, there are only hatches closed hermetically so that ammonia and hydrogen sulfide odors do not spread. Installation work is quite simple and carried out in the shortest possible time. The groundwater level does not affect underground placement. In this way, the natural environment is preserved and the surrounding landscape is not disturbed.
Storage tank
The area of collection of sewage storm water from treatment facilities with a storage tank is up to seven hundred hectares, this type is considered the most effective. Melt water and rain runoff are cleaned using local devices for collecting runoff and directing water to a storage tank, which provides a uniform supply of water for cleaning, and the intensity of precipitation can be any. The operating mode at such facilities is optimized, the installation cost is also relatively low.
Accumulation tanks up to three hundred cubic meters are made of fiberglass, reinforced concrete or metal. The design can be different - open and closed. For residential areas, the second option is preferable, and open tanks are also used at construction sites and industrial areas.
How storm water is collected
Small debris, sand, oil products and other pollution are washed away from the earth's relief by melt water or rain streams that carry it all into water bodies: rivers, lakes, ponds, seas and oceans. As a result, instead of a pond orlakes, after a short time, a swamp overgrown with duckweed and algae is formed, smelling strongly of ammonia from the decomposition of the garbage brought in. Therefore, it is customary to treat storm drains before the waters enter the reservoirs.
For this, there are local installations specially designed for each locality that purify storm water, which, after cleaning, is discharged either into drainage collectors or into open water bodies. Local installations are available in a wide variety of models, with a capacity of ten to ninety liters of storm water per second. During the primary treatment, suspended solids and oil products are removed, then the water settles, after which it is brought back to life by coalescing (a floating bed layer is used) and filtering through a sorption bed.
Design
Since there are a lot of wastewater treatment plants and their design sometimes differs dramatically, let's consider one of them - PVO-SV. It consists of a number of elements. The first section is a mud trap, it is here that the remains of oil products settle. The largest particles remain in the receiving tank - small stones, sand, silt, garbage. To remove all this, a settling chamber is installed in the tank. Most of the contaminants and almost all of the solid particles remain on the sump plates, and the released oil products float on the surface, because they are lighter than water.
The second section is a floating filter loading. The water coming here is still heavily polluted with oil products, which are init in the form of an emulsion. When the flow passes through the loading layer, the dispersed system is destroyed, and oily contaminants are separated from the wastewater. The third section is a sorption filter, this is the last stage of cleaning to obtain standard indicators. The filter consists of a flask, zerlite or coal. The fourth section of the installation is a collector for clean water.
