CN110818205A - System and process for reducing concentration of pollutants in steel comprehensive wastewater - Google Patents

Abstract

The invention relates to a system and a process for reducing the concentration of pollutants in steel and iron comprehensive wastewater, wherein the system comprises a regulating tank, a high-density sedimentation tank, a biological aerated filter, a denitrification biological filter, a high-efficiency dissolved air flotation tank, a filter and an ozone catalytic oxidation tank which are sequentially connected through a wastewater pipeline; the invention can thoroughly convert pollutants in the wastewater into non-pollutants, achieves the aim of reducing the concentration of the pollutants, meets the requirements on the special discharge limit of the water pollutants in Table 3 of the discharge standard GB13456-2012 of the pollutants for the water in the iron and steel industry, and completely meets the water quality index of the inlet water for the desalting and recycling by the double-membrane method, thereby prolonging the service life of the desalting and recycling facility.

Description

A system and process for reducing the concentration of pollutants in iron and steel comprehensive wastewater

technical field

The invention relates to the technical field of industrial wastewater treatment, in particular to a system and a process for reducing the pollutant concentration of iron and steel comprehensive wastewater.

Background technique

Iron and steel enterprises are major water users, producing a large amount of production wastewater. The indicators of SS, COD, ammonia nitrogen, total nitrogen, fluoride, cyanide and other indicators in the wastewater are easy to exceed the standard and cannot be directly discharged. The use of desalination and reuse of industrial wastewater is the development trend of the industry, but this method does not remove pollutants, but transfers the pollutants to concentrated brine, and the reuse of concentrated brine will inevitably cause secondary pollution. In addition, the double-membrane method for desalination has strict requirements on the influent water, and the quality of the influent water is good, which can greatly improve the service life of the desalination equipment. Therefore, it is best to reduce the concentration of pollutants before the wastewater enters the double-membrane desalination system.

SUMMARY OF THE INVENTION

The invention provides a system and a process for reducing the concentration of pollutants in comprehensive iron and steel wastewater, which can completely convert the pollutants in the wastewater into non-pollutant substances, achieve the purpose of reducing the concentration of pollutants, and meet the requirements of "Water Pollutant Discharge Standard for Iron and Steel Industry GB13456". -2012 "Table 3 of the special discharge limit requirements for water pollutants, and fully meet the double-membrane desalination and reuse influent water quality indicators, in order to improve the service life of desalination and reuse facilities.

In order to achieve the above object, the present invention adopts the following technical solutions to realize:

A system for reducing the concentration of pollutants in iron and steel comprehensive wastewater, including a regulating tank, a high-density sedimentation tank, a biological aeration filter, a biological denitrification filter, a high-efficiency dissolved air flotation tank, a filter tank and an ozone catalysis tank connected in sequence through a wastewater pipeline oxidation pool; where:

A liftable aerator is arranged in the regulating tank;

The high-density sedimentation tank is provided with a drug dosing device, and the high-density sedimentation tank is provided with a sediment discharge port connected to the sludge treatment system through a pipeline;

The aeration biological filter is provided with a fixed aerator, and the fixed aerator is connected to the air suspension fan through a pipeline;

The denitrification biological filter is provided with an inert gas inlet and a carbon source dosing device; the denitrification biological filter is provided with a water inlet at the bottom and a water outlet at the upper part, and at least two layers of filter layers are arranged in the tank body, including a filter layer arranged in the lower layer. Oxygen bacteria inhibition layer and denitrification layer arranged on the upper layer;

The waste water pipeline upstream of the high-efficiency dissolved air flotation tank is provided with a tubular reactor, and the tubular reactor is provided with a phosphorus removal agent addition port and a flocculant addition port; the high-efficiency dissolved air flotation tank is divided into water inlet area, In the water distribution area and separation area, the water inlet of the water inlet area is connected with the water outlet of the tubular reactor, and the air flotation device is installed in the water inlet area; the top of the water distribution area is equipped with a slag scraper, and the lower part of the water distribution area is equipped with a corrugated inclined plate , the bottom is provided with a mud discharge port; the bottom of the separation zone is provided with a mud scraper and an automatic mud discharge valve; There is an automatic mud valve on it.

A heating device is also provided in the conditioning tank, and the heating device is an electric heating device or a steam heating device.

The drug dosing device in the high-density sedimentation tank is one of lime dosing device, calcium chloride dosing device, sodium carbonate dosing device, sodium bicarbonate dosing device, PAC dosing device and PAM dosing device. one or more.

The air suspension fan adopts frequency conversion control.

The air flotation device is composed of a dissolved air tank, a circulating pump and a releaser. The dissolved air tank is provided with an air inlet, a circulating water inlet and a dissolved air water outlet. The circulating water inlet and the circulating water outlet on the water inlet area pass through the circulating water pipeline. A circulating pump is installed on the circulating water pipeline, and the dissolved gas water outlet is connected with the releaser in the water inlet area.

The filter tank is a sand filter tank or a V-type filter tank.

A backwash water outlet is set on the waste water pipeline downstream of the filter tank, and the backwash water inlet of the aeration biological filter tank, the denitrification biological filter tank and the filter tank are respectively connected through the backwash water pipeline; The biological filter tank and the filter tank are respectively provided with a backwash drain outlet, which is connected to the adjustment tank through a backwash drain pipe.

A process for reducing the concentration of pollutants in comprehensive iron and steel wastewater, comprising the following steps:

1) The comprehensive iron and steel wastewater first enters the regulating tank, which is used to adjust the water volume, balance the water quality, and prevent sludge precipitation; oxygenate the wastewater through aeration, and oxidize the ferrous iron in the wastewater to ferric iron, so that it can be used in the follow-up. In the high-density sedimentation tank, the total iron is removed by adding lime to form ferric hydroxide precipitation to meet the requirements of wastewater desalination and reuse; in the regulating tank, the wastewater is heated as needed to avoid the effect of subsequent biochemical treatment due to low water temperature. Double-membrane desalination water production rate;

2) The effluent from the adjustment tank enters the high-density sedimentation tank; in the high-density sedimentation tank, it is necessary to add drugs according to the water quality of the wastewater, including adding lime to remove hardness to meet the requirements of wastewater desalination and reuse; adding lime and calcium chloride Remove fluoride to meet the standard requirements of fluoride in effluent; add sodium carbonate or sodium bicarbonate to supplement the alkalinity to meet the alkalinity required for the ammoniation reaction and the alkalinity requirements for subsequent ammonia nitrogen removal; add PAC and PAM to form flocs , to remove SS; the sludge produced by the high-density sedimentation tank enters the sludge treatment system for treatment;

3) The effluent from the high-density sedimentation tank enters the biological aerated filter; the COD in the wastewater is removed in the biological aerated filter, and ammonia nitrogen is converted into nitrate;

4) The effluent from the aerated biological filter enters the denitrification biological filter; the denitrification biological filter adopts the upper effluent method, and the wastewater first passes through the aerobic bacteria inhibition layer to reduce DO, and then passes through the denitrification layer; when the wastewater passes through the denitrification layer, the other The carbon source is an electron donor to undergo denitrification reaction, and the nitrate is converted into nitrogen and discharged; the function of adding an inert gas is to expand the filter material, and the biologically-generated aging sludge flows out along the water flow;

5) The effluent of the denitrification biological filter enters the high-efficiency dissolved air flotation tank; the waste water first enters the tubular reactor, and the phosphorus removal agent and flocculant are added to the tubular reactor to make the impurities in the waste water form separable flocs; waste water After entering the water inlet area, the flocs come into contact with the air bubbles with a diameter of 30-50um released from the dissolved gas water to form a low-density "air flotation body", while removing oil and suspended solids in the wastewater, and the flocs coalesce in the water distribution area. It is scum, which is scraped to the slag collection tank by the slag scraper, and then discharged into the sludge treatment system; the flocs with a slower rising speed and water flow downward through the corrugated inclined plate to further coalesce, and the low-density flocs float up to the sludge. On the water surface, the high-density flocs settle to the bottom, and the sand deposited in the water distribution area is discharged through the sand discharge port; the sediment deposited in the water inlet area and the sludge deposited at the bottom of the separation area are scraped by the scraper to the sludge discharge end, and passed through the discharge port. The automatic sludge discharge valve is regularly and quantitatively discharged into the sludge treatment system;

6) The effluent from the high-efficiency dissolved air flotation tank enters the filter tank to remove suspended solids and reduce turbidity;

7) The effluent from the filter tank enters the ozone catalytic oxidation tank, part of the COD in the wastewater is degraded in the high-density sedimentation tank and aerated biological filtration, and the remaining part is removed in the ozone catalytic oxidation tank; The BOD reaches the standard, and the COD of the system effluent is less than or equal to 30mg/L.

In the present invention, as the pretreatment process of the double-membrane desalination process, the effluent of the system enters the double-membrane desalination system, and step 5) is omitted at this time, or the effluent of the denitrification biological filter is directly sent to the subsequent treatment device through the surpassing pipeline.

Compared with the prior art, the beneficial effects of the present invention are:

1) The process and system settings are reasonable, which can adapt to the comprehensive iron and steel wastewater quality, and can simultaneously remove SS, COD, ammonia nitrogen, total nitrogen, fluoride, hardness, turbidity, chroma, total iron, oil and other pollutants in the wastewater.

2) The treated wastewater can meet the requirements of the special discharge limit index of water pollutants in Table 3 of "Water Pollutant Discharge Standard for Iron and Steel Industry GB13456-2012", and can be used as a pretreatment process for double-membrane desalination;

3) The removal rate of pollutants in wastewater is greatly improved, among which the removal rate of ammonia nitrogen can reach more than 95%, the removal rate of COD can reach more than 90%, and the removal rate of total nitrogen can reach more than 90%.

Description of drawings

FIG. 1 is a schematic structural diagram of a system for reducing the concentration of pollutants in comprehensive iron and steel wastewater according to the present invention.

Detailed ways

The specific embodiments of the present invention will be further described below in conjunction with the accompanying drawings:

As shown in Figure 1, a system for reducing the concentration of pollutants in comprehensive iron and steel wastewater according to the present invention includes a regulating tank, a high-density sedimentation tank, a biological aeration filter, a denitrification biological filter, a high-efficiency Dissolved air flotation tank, filter tank and ozone catalytic oxidation tank; of which:

A liftable aerator is arranged in the regulating tank;

The high-density sedimentation tank is provided with a drug dosing device, and the high-density sedimentation tank is provided with a sediment discharge port connected to the sludge treatment system through a pipeline;

The aeration biological filter is provided with a fixed aerator, and the fixed aerator is connected to the air suspension fan through a pipeline;

The denitrification biological filter is provided with an inert gas inlet and a carbon source dosing device; the denitrification biological filter is provided with a water inlet at the bottom and a water outlet at the upper part, and at least two layers of filter layers are arranged in the tank body, including a filter layer arranged in the lower layer. Oxygen bacteria inhibition layer and denitrification layer arranged on the upper layer;

The waste water pipeline upstream of the high-efficiency dissolved air flotation tank is provided with a tubular reactor, and the tubular reactor is provided with a phosphorus removal agent addition port and a flocculant addition port; the high-efficiency dissolved air flotation tank is divided into water inlet area, In the water distribution area and separation area, the water inlet of the water inlet area is connected with the water outlet of the tubular reactor, and the air flotation device is installed in the water inlet area; the top of the water distribution area is equipped with a slag scraper, and the lower part of the water distribution area is equipped with a corrugated inclined plate , the bottom is provided with a mud discharge port; the bottom of the separation zone is provided with a mud scraper and an automatic mud discharge valve; There is an automatic mud valve on it.

A heating device is also provided in the conditioning tank, and the heating device is an electric heating device or a steam heating device.

The drug dosing device in the high-density sedimentation tank is one of lime dosing device, calcium chloride dosing device, sodium carbonate dosing device, sodium bicarbonate dosing device, PAC dosing device and PAM dosing device. one or more.

The air suspension fan adopts frequency conversion control.

The air flotation device is composed of a dissolved air tank, a circulating pump and a releaser. The dissolved air tank is provided with an air inlet, a circulating water inlet and a dissolved air water outlet. The circulating water inlet and the circulating water outlet on the water inlet area pass through the circulating water pipeline. A circulating pump is installed on the circulating water pipeline, and the dissolved gas water outlet is connected with the releaser in the water inlet area.

The filter tank is a sand filter tank or a V-type filter tank.

A backwash water outlet is set on the waste water pipeline downstream of the filter tank, and the backwash water inlet of the aeration biological filter tank, the denitrification biological filter tank and the filter tank are respectively connected through the backwash water pipeline; The biological filter tank and the filter tank are respectively provided with a backwash drain outlet, which is connected to the adjustment tank through a backwash drain pipe.

A process for reducing the concentration of pollutants in comprehensive iron and steel wastewater, comprising the following steps:

1) The comprehensive iron and steel wastewater first enters the regulating tank, which is used to adjust the water volume, balance the water quality, and prevent sludge precipitation; oxygenate the wastewater through aeration, and oxidize the ferrous iron in the wastewater to ferric iron, so that it can be used in the follow-up. In the high-density sedimentation tank, the total iron is removed by adding lime to form ferric hydroxide precipitation to meet the requirements of wastewater desalination and reuse; in the regulating tank, the wastewater is heated as needed to avoid the effect of subsequent biochemical treatment due to low water temperature. Double-membrane desalination water production rate;

2) The effluent from the adjustment tank enters the high-density sedimentation tank; in the high-density sedimentation tank, it is necessary to add drugs according to the water quality of the wastewater, including adding lime to remove hardness to meet the requirements of wastewater desalination and reuse; adding lime and calcium chloride Remove fluoride to meet the standard requirements of fluoride in effluent; add sodium carbonate or sodium bicarbonate to supplement the alkalinity to meet the alkalinity required for the ammoniation reaction and the alkalinity requirements for subsequent ammonia nitrogen removal; add PAC and PAM to form flocs , to remove SS; the sludge produced by the high-density sedimentation tank enters the sludge treatment system for treatment;

3) The effluent from the high-density sedimentation tank enters the biological aerated filter; the COD in the wastewater is removed in the biological aerated filter, and ammonia nitrogen is converted into nitrate;

4) The effluent from the aerated biological filter enters the denitrification biological filter; the denitrification biological filter adopts the upper effluent method, and the wastewater first passes through the aerobic bacteria inhibition layer to reduce DO, and then passes through the denitrification layer; when the wastewater passes through the denitrification layer, the other The carbon source is an electron donor to undergo denitrification reaction, and the nitrate is converted into nitrogen and discharged; the function of adding an inert gas is to expand the filter material, and the biologically-generated aging sludge flows out along the water flow;

5) The effluent of the denitrification biological filter enters the high-efficiency dissolved air flotation tank; the waste water first enters the tubular reactor, and the phosphorus removal agent and flocculant are added to the tubular reactor to make the impurities in the waste water form separable flocs; waste water After entering the water inlet area, the flocs come into contact with the air bubbles with a diameter of 30-50um released from the dissolved gas water to form a low-density "air flotation body", while removing oil and suspended solids in the wastewater, and the flocs coalesce in the water distribution area. It is scum, which is scraped to the slag collection tank by the slag scraper, and then discharged into the sludge treatment system; the flocs with a slower rising speed and water flow downward through the corrugated inclined plate to further coalesce, and the low-density flocs float up to the sludge. On the water surface, the high-density flocs settle to the bottom, and the sand deposited in the water distribution area is discharged through the sand discharge port; the sediment deposited in the water inlet area and the sludge deposited at the bottom of the separation area are scraped by the scraper to the sludge discharge end, and passed through the discharge port. The automatic sludge discharge valve is regularly and quantitatively discharged into the sludge treatment system;

6) The effluent from the high-efficiency dissolved air flotation tank enters the filter tank to remove suspended solids and reduce turbidity;

7) The effluent from the filter tank enters the ozone catalytic oxidation tank, part of the COD in the wastewater is degraded in the high-density sedimentation tank and aerated biological filtration, and the remaining part is removed in the ozone catalytic oxidation tank; The BOD reaches the standard, and the COD of the system effluent is less than or equal to 30mg/L.

In the present invention, as the pretreatment process of the double-membrane desalination process, the effluent of the system enters the double-membrane desalination system, and step 5) is omitted at this time, or the effluent of the denitrification biological filter is directly sent to the subsequent treatment device through the surpassing pipeline.

The aeration biological filter adopts air suspension fan aeration, and performs frequency conversion control according to the effluent DO situation to save power consumption.

The denitrification biological filter adopts an inert gas to drive out DO to improve the denitrification effect; and an external carbon source is used to carry out the denitrification reaction. The filter material that inhibits the growth of bacteria is arranged in the lower layer, and the added carbon source will not be consumed due to the growth of aerobic bacteria, saving about one third of the carbon source. Using the upper effluent method, the wastewater passes through the denitrification layer, and the carbon source is used as an electron donor to undergo a denitrification reaction, and the nitrate is converted into nitrogen and discharged. At the same time, due to the entry of inert gas, the filter material expands, and the biologically-generated aging sludge flows out along the water flow, reducing the probability of filter material blockage and prolonging the backwash cycle. If the effluent of the system enters the double-membrane desalination system, the process of denitrification biological filter can be canceled or the setting can be overridden by overtaking the pipeline.

The high-efficiency dissolved air flotation tank is used to remove the difficult-to-settlement biological sludge produced by the denitrification process, and reduce the subsequent filtration pressure; remove the oil in the wastewater, protect the subsequent double-membrane desalination system, and prevent the oil from causing membrane fouling. Since the biological sludge contains air bubbles, it is difficult to settle. The incoming water first enters the tubular reactor, and the flocculation agent is added to the tubular reactor to form separable flocs. After mixing with part of the dissolved gas water, the flocs are coalesced. , dense. The sediment deposited in the water inlet area and the sludge deposited at the bottom of the separation area are scraped by the scraper to the sludge discharge end, and discharged into the sludge system regularly and quantitatively through the automatic sludge discharge valve, which does not affect the normal operation of the equipment.

The air flotation device uses air as the air source, which is mixed with the water pressurized by the circulating pump in the dissolved air tank to form dissolved air water, which is released to the water inlet chamber through the releaser. It can remove oil and suspended solids in wastewater at the same time, protect the water quality of the subsequent double-membrane demineralization, and prolong the filter backwash cycle.

The ozone catalytic oxidation tank plays the role of reducing the COD and chromaticity of the effluent. Part of the COD in the wastewater is degraded in the high-density sedimentation tank and aerated biological filter, and the remaining part is removed in the ozone catalytic oxidation tank; in order to achieve a higher removal effect by denitrification, prevent excessive or incomplete addition of carbon sources. Biological utilization, through the ozone catalytic oxidation tank can play a role in ensuring that the effluent COD and BOD does not exceed the standard.

The above description is only a preferred embodiment of the present invention, but the protection scope of the present invention is not limited to this. The equivalent replacement or change of the inventive concept thereof shall be included within the protection scope of the present invention.

Claims (9)

1. A system for reducing the concentration of pollutants in steel and iron comprehensive wastewater is characterized by comprising a regulating tank, a high-density sedimentation tank, a biological aerated filter, a denitrification biological filter, a high-efficiency dissolved air floatation tank, a filter and an ozone catalytic oxidation tank which are sequentially connected through a wastewater pipeline; wherein:

a liftable aerator is arranged in the regulating tank;

the high-density sedimentation tank is provided with a drug feeding device and a sediment discharge port which is connected with a sludge treatment system through a pipeline;

a fixed aerator is arranged in the biological aerated filter and is connected with an air suspension fan through a pipeline;

the denitrification biological filter is provided with an inert gas inlet and a carbon source adding device; the bottom of the denitrification biological filter is provided with a water inlet, the upper part of the denitrification biological filter is provided with a water outlet, and the filter body is internally provided with at least 2 filter layers which comprise an aerobic bacteria inhibition layer arranged on the lower layer and a denitrification layer arranged on the upper layer;

a pipe reactor is arranged on a wastewater pipeline at the upstream of the high-efficiency dissolved air floatation tank, and the pipe reactor is provided with a phosphorus removing agent adding port and a flocculating agent adding port; the high-efficiency dissolved air flotation tank is sequentially divided into a water inlet area, a water distribution area and a separation area along the water flow direction, the water inlet of the water inlet area is connected with the water outlet of the tubular reactor, and the water inlet area is provided with an air flotation device; the top of the water distribution area is provided with a slag scraper, the lower part of the water distribution area is provided with a corrugated inclined plate, and the bottom of the water distribution area is provided with a sludge discharge port; the bottom of the separation area is provided with a mud scraper and an automatic mud valve; the residue scraper is connected with the sludge treatment system through a residue discharge groove, the sludge scraper is connected with the sludge treatment system through a sludge discharge pipeline, and an automatic sludge discharge valve is arranged on the sludge discharge pipeline.

2. The system for reducing the pollutant concentration in the integrated steel and iron wastewater according to claim 1, characterized in that a heating device is further arranged in the regulating tank, and the heating device is an electric heating device or a steam heating device.

3. The system for reducing the concentration of pollutants in comprehensive wastewater of iron and steel according to claim 1, wherein the drug adding device in the high-density sedimentation tank is one or more of a lime adding device, a calcium chloride adding device, a sodium carbonate adding device, a sodium bicarbonate adding device, a PAC adding device and a PAM adding device.

4. The system for reducing the concentration of pollutants in integrated steel and iron wastewater according to claim 1, wherein the air suspension fan is controlled by frequency conversion.

5. The system for reducing the concentration of pollutants in wastewater from iron and steel synthesis as claimed in claim 1, wherein the air flotation device comprises a dissolved air tank, a circulating pump and a releaser, the dissolved air tank is provided with an air inlet, a circulating water inlet and a dissolved air water outlet, the circulating water inlet is connected with the circulating water outlet on the water inlet area through a circulating water pipeline, the circulating water pipeline is provided with a circulating pump, and the dissolved air water outlet is connected with the releaser in the water inlet area.

6. The system for reducing the pollutant concentration in integrated steel and iron wastewater according to claim 1, characterized in that the filter is a sand filter or a V-shaped filter.

7. The system for reducing the concentration of pollutants in wastewater from integrated steel and iron production according to claim 1, wherein a back-washing water outlet is arranged on a wastewater pipeline at the downstream of the filter tank, and the back-washing water outlet is respectively connected with the biological aerated filter, the biological denitrification filter and a back-washing water inlet of the filter tank through back-washing water pipelines; the aeration biological filter, the denitrification biological filter and the filter are respectively provided with a backwashing water outlet and are connected with the regulating tank through a backwashing water drainage pipeline.

8. A process for reducing the concentration of pollutants in integrated steel and iron wastewater based on the system of claim 1, comprising the steps of:

1) the method comprises the following steps that (1) steel comprehensive wastewater firstly enters an adjusting tank, and the adjusting tank is used for adjusting water quantity, balancing water quality and preventing sludge from precipitating; the waste water is oxygenated by aeration, and the ferrous iron in the waste water is oxidized into ferric iron so as to remove the total iron by adding lime into a subsequent high-density sedimentation tank to form ferric hydroxide sediment, thereby meeting the requirements of desalting and recycling the waste water; heating the wastewater in the adjusting tank according to the requirement, and avoiding the influence on the subsequent biochemical treatment effect and the double-membrane desalination water yield due to the over-low water temperature;

2) the effluent of the regulating tank enters a high-density sedimentation tank; in the high-density sedimentation tank, medicaments are added according to the water quality condition of the wastewater, and the method comprises the steps of adding lime to remove hardness so as to meet the requirements of desalting and recycling the wastewater; lime and calcium chloride are added to remove fluoride, so that the standard reaching requirement of the fluoride in the effluent is met; adding sodium carbonate or sodium bicarbonate to supplement alkalinity so as to meet the alkalinity required by ammoniation reaction and the alkalinity requirement in the subsequent ammonia nitrogen removal; PAC and PAM are added to form floc so as to remove SS; sludge generated by the high-density sedimentation tank enters a sludge treatment system for treatment;

3) the effluent of the high-density sedimentation tank enters an aeration biological filter; removing COD in the wastewater in the biological aerated filter, and converting ammonia nitrogen into nitrate;

4) the effluent of the aeration biological filter enters a denitrification biological filter; the denitrification biological filter adopts an upward water outlet mode, wastewater firstly passes through the aerobic bacteria inhibition layer to reduce DO, and then passes through the denitrification layer; when the wastewater passes through the denitrification layer, an external carbon source is taken as an electron donor to perform denitrification reaction, so that nitrate is converted into nitrogen to be discharged; adding inert gas to expand the filter material, and allowing aged sludge generated by organisms to flow out along water flow;

5) the effluent of the denitrification biological filter enters a high-efficiency dissolved air flotation tank; the wastewater firstly enters a tubular reactor, and a phosphorus removing agent and a flocculating agent are added into the tubular reactor to enable impurities in the wastewater to form separable flocculates; after the wastewater enters the water inlet area, the flocculate is contacted with bubbles with the diameter of 30-50 um released in the dissolved air to form a low-density 'air floating body', oil and suspended matters in the wastewater are removed at the same time, the flocculate is coalesced into scum in the water distribution area, and the scum is scraped to a scum collecting tank through a scum scraper and then automatically flows and is discharged into a sludge treatment system; the flocs with lower ascending speed and water flow downwards to be further coalesced through the corrugated inclined plate, the flocs with low density float to the water surface, the flocs with high density precipitate to the bottom, and sand deposited in the water distribution area is discharged through a sand discharge port; the silt precipitated in the water inlet area and the sludge precipitated at the bottom of the separation area are scraped to a sludge discharge end by a sludge scraper and are periodically and quantitatively discharged into a sludge treatment system through an automatic sludge discharge valve;

6) the water discharged from the high-efficiency dissolved air floatation tank enters a filter tank to remove suspended matters and reduce turbidity;

7) the effluent of the filter tank enters an ozone catalytic oxidation tank, part of COD in the wastewater is degraded in a high-density sedimentation tank and an aeration biofiltration tank, and the rest part of the COD is removed in the ozone catalytic oxidation tank; the COD and BOD in the wastewater can be ensured to reach the standard through the ozone catalytic oxidation tank, and the COD of the effluent of the system is less than or equal to 30 mg/L.

9. The process for reducing the pollutant concentration in the integrated wastewater of iron and steel according to claim 8, wherein as a pretreatment process of the double-membrane desalination process, the effluent of the system enters a double-membrane desalination system, and the step 5) is omitted or the effluent of the denitrification biofilter is directly sent to a subsequent treatment device through an overtaking pipeline.

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