Wastewater treatment plants remove petroleum products and suspended solids, purifying storm water to the requirements that are required to discharge them into reservoirs of any category or directly on the terrain. The cleaning devices are designed to be very diverse, because the requirements for cleanliness are also different from each other. A storm water treatment plant can use the method of sorption, physico-chemical or mechanical treatment of runoff, but it must always neutralize and purify water from all harmful impurities.
Nature of pollution
The result of a variety of precipitation is storm water. This also includes melt water when snow and ice melt in spring. Storm sewage appears occasionally, their flow rate and quality are extremely uneven. Together with them, the remnants of activities of drains, fountains, street watering, close to them in quality characteristics, are removed. Storm waters are always contaminated with mineral and organic substances contained in the atmosphere, on the ground and on objects that they wash.
During periods of rains and spring snowmelt, the most diverse and always plentiful pollution is washed off from the territories of industrial enterprises and settlements. Storm water cannot be reduced, or at least not reduced, by their quantity. But to reduce their pollution is quite within the power of man. First of all, storm water should be treated. And, of course, it is necessary to increase the culture of production and eliminate the loss of products. It will not work to stop the rain, snow or hail that falls on the surface of the earth, but on the earth itself, it is imperative to follow the order in any activity.
Stormwater Discharge
Atmospheric waters that are not contaminated with oil products or crude oil are diverted from the territory of enterprises using closed or open drains. Treatment of storm sewage is not always done, it depends on their chemical composition. If an oil refinery, rain, snow and hail absorb those petroleum products that are necessarily present on the entire surface of this territory in varying quantities.
Therefore, a simple removal of precipitation is a violation of environmental standards. Storm water must be pretreated. All production runoff and all stormwater must first go through a closed sewer network to a treatment plant where water will be freed from oil products, and only after this procedure can it be returned to the reservoir.
Atmospheric water treatment
From the bunded tanks, you can immediately send storm water to the sewer. Industrial and storm sewers lead the drain to drives arranged in the form of earth tanks, divided into sections. Further, the process depends on the origin, i.e. the classification of wastewater. They are household, industrial, atmospheric (rain). The degree of their pollution, as well as the sanitary requirements, will dictate plans for further activities: either perform a simple discharge of storm water into the reservoir, or send them to treatment facilities, where pollution can be removed mechanically, chemically or biologically.
Petroleum products are removed, for example, by sulfuric acid treatment, and therefore, immediately after it, it is impossible to dump such water into the sewer - it is excessively acidic. The next step will be its neutralization. To do this, there are special pools with a volume that allows approximately eight hours of washing water to complete the reaction. To neutralize sulfuric acid, lime is added to the water. The gypsum sludge formed as a result of the reaction absorbs all the residual 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, stormwater runoff contains a huge amount of ammonia - up to 18,000 mg per liter. Such waters infect not only water bodies and soil, near such drains one can literally suffocate from toxic air.
All water that has been used in industry or by the population, necessarily contains a variety of pollution, and therefore must be treated. If the industrial enterprise does not have environmentally harmful industries, then the wastewater from there will be considered conditionally clean. For example, if the company uses water to cool something. Like storm melt water from this territory, it is most often diverted directly to a body of water, since it is not sanitary hazardous. 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, most often a separate sewage system is installed, where conditionally clean and atmospheric water flows through its network of canals and pipes, and polluted industrial and household water flows through a different one. These are two completely independent sewage networks. The first is storm (rain), and the second is household.
Almost always conditionally clean water is reused in production. It is isolated from common wastewater and allowed to flow back through the independent network to production sites. Moreover, in this case, conditionally pure waters are not combined with atmospheric waters. The exceptions are situations when the amount of conditionally pure production water is too small. Then they are diverted directly to the reservoir through a storm network.
Application Settings
Stormwater treatment plants are used for industrial effluents, including oily. In their work, technological schemes are used, where there are several different cleaning methods after studying the types of water pollution. Used special equipment. The scheme of the whole event should ensure a minimum discharge of pollutants into the water body, in no case exceeding the permissible concentrations.
For example, such is the LIOS water treatment plant. With its help, treated storm sewage is used in production in a circle, which significantly reduces the enterprise’s expenses for wastewater and water supply. The productivity of the station is up to twenty liters of treated water per second, it can serve a catchment area of up to two hectares, and if you use an accumulating capacity with it, the catchment can increase to one hundred and twenty hectares.
How is cleaning
Drains, as already mentioned, are usually divided into household, which appear due to the vital activity of people, industrial and atmospheric. To apply this or that installation for storm water treatment, it is necessary to determine all the features of pollution in this territory. They can be organic, which contain inclusions of plant and animal origin (drains from farms, fields, etc.). Here you can observe a variety of organic chemical compounds, even polymeric ones.
Contamination can be of a mineral nature, with impurities of inorganic compounds. For example, storm meltwater carries with it a mass of soil. Also, water contaminated with various salts is especially required. The third type is biological pollution, these are microorganisms developing in drains and quickly mastering any reservoir. The stormwater environment is very nutritious for them. Surely everyone saw how quickly overgrown ponds that do not have a duct. This is what is popularly called "blooming water." You can no longer use such reservoirs.
Cleaning methods: mechanical and chemical
The mechanical method of cleaning with the help of special plants includes sedimentation of water, its filtration, flotation, that is, purification from solid particles and organic residues. To do this, use special settlers, a huge variety of sieves, as well as traps for sand and oil.
The principle of chemical wastewater treatment is that pollutants are made to react to reagents added to the water. The result is a precipitate, which is defended and removed. Water is best cleaned in this way, since it significantly reduces the amount of substances that do not dissolve.
Methods for cleaning physico-chemical and biological
The physicochemical method is used to detect and remove finely dispersed substances of inorganic and organic origin. The activities are lengthy, but very effective. Coagulation (coagulation, coarsening, thickening of solids), oxidation, sorption, electrocoagulation, electrolysis are used. These methods can remove toxic impurities.
The biological method also does not do without chemistry and biochemistry. Water purification plants using this method are especially popular. They include biological filters, aeration tanks, biological ponds, methane reactors. You can use any of the proposed methods, but the effluent always passes through three main stages: filtering solid particles and impurities, aeration and slow filtering, enrichment and regeneration.
Treatment facilities
Cleaning can occur when using the simplest - gravity method. The catchment area of such treatment facilities is up to twenty hectares, that is, they operate locally and are mainly used in summer associations, small towns. Gravity cleaning is a line of filters: sand separation, gas oil separation, sorption.
Productivity - a maximum of one hundred and fifty liters per second of surface runoff water. So that the load on the treatment facilities is not excessive, a distribution well is used, which directs the standard amount of storm water to local areas. If storm water exceeds the calculated amount in intensity, then some of the runoff goes to the bypass line.
Benefits
In gravity constructions there are no rotating and moving elements, so there is no need to change any units or nodes. The work of such facilities is fully automated, cleaning the drain surface occurs without the inclusion of manual labor, thus ensuring the safety of workers and not even requiring their constant presence.
There are no open water surfaces, the operating mode is pressureless, gravity, 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 works are quite simple and are carried out in the shortest possible time. Groundwater level does not affect underground placement. Thus, the natural environment is preserved and the surrounding landscape is not disturbed.
Storage tank
The area for collecting storm water from sewage treatment plants with a storage tank of up to seven hundred hectares, this type is considered the most effective. Melt water and rainwater are treated using local devices to collect the drain and direct the water to the storage tank, which provides a uniform supply of water for treatment, and the intensity of precipitation can be any. The operating mode at such facilities is optimized, the cost of installation is also relatively low.
Storage tanks with a volume of 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 on the construction sites and in production areas, an open type of tank is also used.
How is storm water collected
Small debris, sand, oil products and other contaminants wash melt water or rain streams from the topography of the earth that carry all this into water bodies: rivers, lakes, ponds, seas and oceans. As a result, instead of a pond or lake, after a short time, a swamp overgrown with duckweed and algae forms, smelling strongly of ammonia from the decomposition of the brought garbage. Therefore, it is customary to clean storm drains before the waters enter the water bodies.
To do this, there are local installations specially developed for each area that purify storm water, which, after treatment, are discharged either into drainage collectors or into open water bodies. Local installations exist of the most various models, with a productivity from ten to ninety liters of storm water per second. During the initial treatment, suspended solids and oil products are removed, then the water settles, after which it is brought back to life by coalescing (a floating loading layer is applied) and filtering through a sorption loading.
Design
Since there are a lot of sewage treatment plants and their design sometimes differs dramatically, consider one of them - air defense-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 deposition chamber is installed in the tank. The largest part of the contaminants and almost all solid particles remain on the plates of the sump, and the released oil products float on the surface, because it is lighter than water.
The second section is a floating filter load. The water entering here is still heavily contaminated with oil products, which are in it in the form of an emulsion. When the flow passes through the loading layer, the disperse system is destroyed, and the oily contaminants are separated from the wastewater. The third section is a sorption filter, this is the last stage of purification until standard indicators are obtained. The filter consists of flask, cerlite or coal. The fourth section of the installation is a collection for clean water.