Industrial Stormwater Systems
- Stormwater treatment areas with airports, depots and storage tanks
- The use of reagent flotators
- The use of pressure filters
- Absorbent boom use
Surface wastewater from airports, depots, and storage tanks and similar areas is significantly contaminated with petroleum products. Wastewater treatment of runoff containing oil is difficult because the oil is emulsified. While large droplets of oil float well or settle on the bottom, emulsified oil is retained in the suspended state.
Even prolonged settling does not offer an adequate level of treatment. The solution is the use of flotators. Flotation is based on the removal of contaminants from the pop-up bubbles. Surfacing bubbles capture particle contaminants, including oil and petroleum products, and raise them to the surface, forming there a layer of film or foam, which is swept by a special mechanism to the oil collection chute pipe. Next, the pipe flow is directed into the reservoir of oil.
Depending on the method of producing gas bubbles in the liquid, the flotation can be:
- mechanical: bubbles are formed by dispersing air with mechanical mixing devices;
- pressure or vacuum: bubbles are separated from supersaturated solutions of gases in water at atmospheric pressure and vacuum, respectively;
- pneumatic: bubbles are formed by passing pressurized air through porous materials (plate filters, ceramic membranes, etc.);
- electroflotation: flotation by bubbles of electrolytic gases produced by the electrolysis of water.
In most cases, the removal of petroleum products is due to pressure flotation process. In setting pressure flotation, a booster pump, a compressor (or ejector), a tank for saturation of water with air (saturator), and a device for the introduction of water-air mixture are used.
Setting pressure flotation is different in that it is a stable formation of water-air mixture (at a constant flow of treated water) and requires extensive use of reagents.
Foam flotation separation system
Before sending wastewater to flotators, it is necessary to remove the main amount of the surfaced oil and sedimentation of suspended solids.
Flotation systems are generally used with recirculation. Thus, after removal of petroleum, wastewater is sent to flotators mixed with 50% of treated wastewater previously saturated with air. The use of such a scheme eliminates the chance of the additional oil emulsifying.
The effectiveness of wastewater treatment containing oil and petroleum products is significantly enhanced by the use of the reagent.
Thus, at a dose of 50 mg of alumina / l, the residual oil content decreases to 15-20 mg / l instead of 30-40 mg / L without the use of the reagent.
There are many types of filters, differing in purpose, structure and operation principle.
For tertiary treatment of stormwater which is significantly polluted with oil products, pressure filters are most commonly used.
A pressure filter is a vertical or horizontal tank, calculated for pressure up to 0.6 MPag.
The filter is used for fine filtration of granular load (quartz sand, expanded clay, anthracite, activated carbon, zeolite, etc..).
Pollutants stick to the filter material and are retained in the pores of the filter material.
In ground stormwater treatment plants supplied by Bioxica, clarification pressure filters of vertical type FCV are used.
Clarification filter of FCV type
The FCV type filter consists of a body, welded from a steel sheet, low distributor unit (LDU) and top distribution unit (TDU), piping, valves, and devices for sampling. The filter housing of FCV type is a cylinder with welded elliptic stamped bottoms. The body has two ports: upper and lower. Through the upper port, the initial loading of the filter material, inspection and repair of the upper distributor unit and periodic inspection of the surface of the filter material are made. Through the lower hole, the installation and repair of LDU is made.
Three legs are welded to the lower bottom of filter FCV for setting the filter on the foundation.
In the center of the upper and lower bottoms of the filter the flanges are welded to which the conduits are connected from outside and distribution units inside.
UDU of filter FCV is an overflow hole of plate shape positioned within the filter housing in the center.
LDU is a "false bottom" with drainage slotted caps mounted therein.
Water enters the filter FCV under the pressure of 0.6 MPag and passes through a bed of granular filter material. All mechanical impurities contained in the water are delayed in the filter FCV, and the clarified water is going to lower collection and distribution system (LDU) and is discharged from the filter. Water clarification in filter FCV is the result of sticking to the grains of filter material suspended solids from the water, which are retained on the surface and in the pores of the filter material.
The working cycle of filter FCV 3,0-0,6 consists of three stages: clarification, backwash and rinse. Filter FСV 3,0-0,6 designed to be installed only indoors, but also for operation at a positive temperature.
In some cases, to improve the treatment of surface wastewater with a high concentration of oil, it is possible to install absorbent-barrier booms in the storage tank in order to reduce the burden on the rest of the process.
There are a lot of absorbent-barrier boom designs, but all of them are floating barrage in the form of a flexible hose of various lengths and diameters with strings or carbines to connect circuits. They possess the necessary positive buoyancy even in a state of complete saturation with petroleum products.
Absorbent booms are universal in application and can absorb all kinds of oil products.
The sorption properties of absorbent booms are achieved using materials with sorption capacity of 8-15 kg / 1kg Bon (depending on the viscosity of the collected oil or petroleum products).
At the end of their life, absorbent booms and cartridges are disposed of by burning in designated facilities.
Depending on the absorbent-barrier booms design, reuse after pressing or cartridge replacement is possible.