WO2019130053A1

WO2019130053A1 - Wastewater treatment system and method for combined ozone and biological filters

Info

Publication number: WO2019130053A1
Application number: PCT/IB2018/001465
Authority: WO
Inventors: Yanhua Yang; Hua Ji
Original assignee: Suez Groupe
Priority date: 2017-12-27
Filing date: 2018-12-26
Publication date: 2019-07-04
Also published as: CN107902851A

Abstract

Disclosed is a wastewater treatment system and method for an advanced treatment of refractory organic matters in wastewater. The wastewater treatment system comprises an ozone treatment device (1) and a biological filter (2). An ozone dosing device (3) of the ozone treatment device (1) prepares ozone by electric discharge using air or pure oxygen as a raw material. A mixed gas including ozone and excess air or oxygen discharged therefrom is introduced into an ozone-oxygen contact tank (7) such that the wastewater to be treated is subjected to ozone oxidation treatment and oxygen absorption, and an effluent is introduced into the biological filter (2), so that the biological filter (2) does not need to provide an aeration device to increase oxygenation for microorganisms. The wastewater treatment system and method fully utilize the supersaturated dissolved oxygen in the effluent of the ozone treatment device (1) to replace the aeration system of the subsequent biological filter (2), and have the advantages of high mass transfer efficiency, high biological activity, high volume load, high removal rate, and the like. The filter (2) has a simple structure and high backwashing efficiency, which significantly reduces operating costs. For the removal of refractory COD, the economics of the overall process are greatly improved.

Description

Wastewater treatment system and method for combined ozone and biological filters

TECHN1CAL FIELD

[0001] The invention relates to a wastewater treatment system for combined ozone and biological filters, and more particularly to a wastewater treatment system for combined ozone and biological filters for deep treatment of refractory organics. The invention also relates to a wastewater treatment method for combined ozone and biological filters for deep treatment of refractory organics.

BACKGROUND

[0002] ln recent years, with the improvement of environmental protection awareness, wastewater discharge standards have also been continuously improved. Wastewater discharge parameter mainly includes chemical oxygen demand (COD), which is an amount of reducing matters to be oxidized in water samples measured by a chemical method, that is, oxygen equivalent of substances (generally organics) that can be oxidized by strong oxidants in wastewater, wastewater treatment plant effluent and contaminated water; total organic carbon (TOC), which is indicative of a total amount of organics in water samples; biochemical oxygen demand (BOD) (generally referred to as five-day biochemical oxygen demand), which is indicative of a content of aerobic pollutants such as organics in water, illustrating a total amount of dissolved oxygen in water consumed by organics in the water which undergo oxidative decomposition to be inorganic or gaseous due to the biochemical action of microorganisms. At present, mostly, the COD and TOC concentrations in organic industrial wastewater after biochemical treatment is difficult to meet the requirements of subsequent deep treatment or final discharge. Therefore, it is necessary to further remove refractory organics by strong oxidation and activated carbon adsorption etc.

[0003] Ozone oxidation is one of the most effective technical methods at present. It has the advantages of high removal efficiency, stable performance, no by-products such as solid waste, and high degree of automation. However, its investment and operating costs are high. To reduce the amount of added ozone, a combined process of combining ozone oxidation with biological aerated filter. l [0004] The combined process of ozone and biological filter utilizes the pre-oxidation of ozone to partially oxidize refractory organics in the wastewater, change the molecular structure of the organics, improve the biodegradability of the wastewater, and then utilize the biodegradation of the subsequent biological aerated filter to achieve the purpose of reducing and removing such organics.

[0005] The biological aerated filter is provided with an air pipe and an air diffusion device for aeration. The treated wastewater enters the biological filter, passes through a biofilm formed by the microorganisms on the surface of the biological filter material, and the organics in the wastewater are further degraded by the microorganisms in the biofilm. While the wastewater passes through the biological filter material, the air pipe aerates to the biological filter material. The air rises from the gap of the biological filter material, and contacts with the wastewater. The oxygen in the air is transferred to the wastewater, providing dissolved oxygen to aerobic microorganisms in the bio film to maintain their activity. Under the metabolism of microorganisms, the refractory organics in the wastewater are degraded.

[0006] Although there are many successful cases of effective ozone and biological aerated filter applications, for example, Suez (formerly Deliman) is the first to use combined process of ozone contact and biological aerated filter Biofor® C to treat industrial wastewater.

Biological aerated filter Biofor® C is an upward flow biological filter with heavy-duty filter material developed by Deliman Company of France. It has been widely recognized in the industry and has the characteristics of small footprint and high volume load, but with compared with the downward flow V-type filter, the structure is more complicated, the effluent suspended substances and turbidity are higher, the backwashing strength demand is high, the equipment configuration is complicated, the backwashing efficiency is not as good as the V-type filter, the backwashing duration, the wastewater amount and the energy consumption are significantly higher than the V-type filter, so the running cost and maintenance workload are also large.

[0007] Therefore, there is a need for an improved wastewater treatment system for combined ozone and biological aerated filter.

SUMMARY [0008] The invention introduces a oxygen-based mix gas of oxygen and ozone prepared by electric discharge using air or oxygen as a raw material into an ozone contact tank to be treated, and then uses supersaturated dissolved oxygen in an ozone-treated effluent to replace an aeration system, introduces the ozone-treated effluent into a biological filter for biological filtration degradation, thereby advanced removing refractory organic matters in the wastewater, and removing aeration system of the prior art for providing sufficient air to microorganisms in the biological filter, simplifying the structure, reducing costs with respect to prior art wastewater treatment systems.

[0009] According to aspect of the invention, a wastewater treatment system for an advanced treatment of refractory organic matters in wastewater is provided, the wastewater treatment system comprises an ozone treatment device and a biological filter, the ozone treatment device comprises an ozone dosing device which prepares ozone by electric discharge using air or pure oxygen as main raw material, wherein the ozone treatment device further comprises an ozone-oxygen contact tank, the wastewater to be treated is introduced into said ozone-oxygen contact tank, a mixed gas including ozone and excess air or oxygen discharged from the ozone dosing device is also introduced into the ozone-oxygen contact tank such that the wastewater to be treated is subjected to ozone oxidation treatment and oxygen absorption, and an effluent of the ozone treatment device is introduced into the biological filter, so that the biological filter does not need to provide an aeration device for microbial oxygenation.

[0010] Preferably, the effluent of the ozone treatment device is introduced into the biological filter from a top of the biological filter, and passes the biological filter from top to bottom in a downward flow.

[0011] Preferably, the ozone treatment device further comprises an ozone tail gas treatment device for treating excess ozone from the ozone-oxygen contact tank.

[0012] Preferably, a part of the wastewater to be treated is pumped to the ozone dosing device via a pipe, and mixed with the ozone and excess air and oxygen in the ozone dosing device, a mixture of ozone and oxygen and part of the wastewater is introduced into the ozone-oxygen contact tank through a pipe using the pressure of the excess air and oxygen and the ozone in the ozone dosing device and the hydraulic pressure of the part of the wastewater that is introduced, to treat the wastewater to be treated in the ozone-oxygen contact tank.

[0013] Preferably, the pipe is connected to a lower portion of the ozone-oxygen contact tank, and a lower end of the pipe to the lower portion of the ozone-oxygen contact tank is provided with a diffuser made of porous material.

[0014] Preferably, the wastewater treatment system further comprises a residual ozone control device located between the ozone treatment device and the biological filter for the effluent of the ozone treatment device, which is used to destroy residual ozone in the effluent of the ozone treatment device, and the effluent of the ozone treatment device is treated by the residual ozone control device and then introduced into the biological filter.

[0015] Preferably, the residual ozone control device further comprises an ozone detecting meter.

[0016] Preferably, the residual ozone control device is a time-controlled flow valve configured to allow ozone-treated wastewater to stand for 10-20 minutes after an end of ozone treatment and then is opened to introduce the ozone-treated wastewater into the biological filter, or is an elongated outlet pipe or water reservoir, the ozone-treated

wastewater remains in the outlet pipe or the water reservoir for 10-20 minutes before being introduced into the biological filter, when the detecting meter detects that a residual ozone concentration in the effluent of the ozone treatment device does not meet the requirements of the biological filter, the time that the ozone-treated wastewater is allowed to stand after the end of ozone treatment or the time that the ozone-treated wastewater remains in the outlet pipe or the water reservoir is prolonged.

[0017] Preferably, the biological filter comprises a filtration system and a backwash system, the backwash system is used to reverse clean the filtration system after filtering out a certain amount of dirt.

[0018] Preferably, the filtration system comprises a V-type influent distribution channel, a biodegradation zone and a gas-water distribution chamber from top to bottom, the V-type influent distribution channel is connected to a top of a filter unit, the V-type influent distribution channel is a V-type water tank with an open top, including a V-type water distribution weir.

[0019] Preferably, the biodegradation zone comprises a biological filter material and a biological filter material support layer supporting the biological filter material, the biological filter material is heavy clay ceramsite or quartz sand filter material adhered with

microorganisms for removing organic matters in the wastewater.

[0020] According to another aspect of the invention, a wastewater treatment method is provided using combined technology of ozone treatment and biological filter filtration to treat wastewater, an ozone treatment device for ozone treatment comprises an ozone dosing device which prepares ozone by electric discharge using air or pure oxygen as main raw material, wherein the ozone treatment device further comprises an ozone-oxygen contact tank, the wastewater to be treated is introduced into said ozone-oxygen contact tank, a mixed gas including ozone and excess air and oxygen discharged from the ozone dosing device is also introduced into the ozone contact tank such that the wastewater to be treated is subjected to ozone oxidation treatment and air or oxygen absorption, the method utilizes supersaturated oxygen dissolved in the ozone-treated wastewater discharged from the ozone treatment device, introduces the ozone-treated wastewater discharged from the ozone treatment device into the biological filter without a need of aeration treatment to further increase oxygenation for microorganisms.

[0021] The wastewater treatment system according to the invention fully utilize the supersaturated dissolved oxygen in the effluent of the ozone-oxygen contact tank to replace the aeration system of the subsequent biological filter, and have the advantages of high mass transfer efficiency, high biological activity, high volume load, high removal rate, and the like. The filter has a simple structure and high backwashing efficiency, which significantly reduces operating costs. For the removal of refractory COD, the economics of the overall process are greatly improved.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Fig. 1 is a schematic view of an embodiment of a general principle of a wastewater treatment system in accordance with the present invention.

[0023] Fig. 2 is a diagram of 02, COD and BOD of each section of Fig. 1.

[0024] Fig. 3 is a schematic view of a wastewater treatment system in accordance with a preferred embodiment of the present invention. [0025] Fig. 4 is an operational diagram of the wastewater treatment system of the embodiment shown in Fig. 3.

[0026] Fig. 5 is a schematic view of a backwash device of the wastewater treatment system of the embodiment shown in Fig. 3.

[0027] Fig. 6 is an operational diagram of the wastewater treatment system of the embodiment 1 .

[0028] Fig. 7 is an operational diagram of the wastewater treatment system of the embodiment 2.

DETA1LED DESCRIPTION

[0029] The general principles of the invention are described below in accordance with embodiments of the invention with reference to the drawings.

[0030] Fig. 1 is a schematic view in accordance with an embodiment of the present invention. The wastewater treatment system according to this embodiment of the present invention mainly comprises an ozone treatment device 1 and a biological filter 2. The ozone treatment device 1 of this embodiment of the present invention comprises an ozone dosing device 3, an ozone-oxygen contact tank 7, and an ozone tail gas treatment device 6 schematically indicated by an arrow in Fig. 1.

[0031] Usually, the ozone dosing device 3 uses oxygen or air as a raw material to prepare ozone by electric discharge. The ozone dosing device 3 is connected to the ozone-oxygen contact tank 7. A mixed gas discharged from the ozone dosing device 3 comprising generated ozone and excess air or oxygen is directly introduced to the ozone-oxygen contact tank 7. Wastewater 4 to be treated, which is schematically indicated by an arrow, is also introduced into the ozone-oxygen contact tank 7, and reacts with ozone. The ozone oxidizes various organics and other reducing matters in the wastewater to degrade it. After oxidizing the wastewater, excess ozone is treated by the ozone tail gas treatment device 6, while excess air and oxygen are also dissolved in the wastewater. The ozone-oxygen contact tank 7 is connected to the biological filter 2. The wastewater discharged from the ozone-oxygen contact tank 7 after being treated by ozone is introduced into the biological filter 2. The biological filter 2 with an addition of microorganisms therein further removes refractory organics in the wastewater, so that the wastewater reaches the final discharge requirement. The effluent 5 schematically indicated by an arrow is discharged or collected.

[0032] The ozone-oxygen contact tank 7 may dissolve ozone and oxygen into the wastewater by a bubbling method or a jet method for further ozone treatment and subsequent supply of oxygen to the biological filter. As shown in Fig. 1 , the wastewater 4 is divided into two parts, one part enters the ozone-oxygen contact tank 7 to be treated, and the other part is brought upward to the ozone dosing device 3. A mixture of the part of wastewater 4 introduced into the ozone dosing device and ozone and oxygen in the ozone dosing device 3 is introduced into the ozone-oxygen contact tank 7 via a pipe in a downward flow from the top to the bottom of the ozone-oxygen contact tank 7 under a gas pressure of ozone and oxygen in the ozone dosing device 3 and a hydraulic pressure of the part of wastewater 4 introduced into the ozone dosing device 3. A porous diffuser 10 is disposed at the end of the pipe located at the bottom of the ozone-oxygen contact tank 7. The gas-liquid mixture of ozone, oxygen, and the part of wastewater 4 that is introduced into the ozone dosing device 3 passes through the porous diffuser 10 to form uniformly distributed small bubbles in the ozone-oxygen contact tank 7 to promote ozone and oxygen to diffuse and dissolve into the wastewater. After ozone, oxygen and wastewater enter the ozone-oxygen contact tank, ozone, oxygen and wastewater pass to the lower portion of the ozone-oxygen contact tank 7, so that ozone and oxygen can further contact the wastewater from bottom to top, further diffuse and dissolve into the wastewater, and finally excess ozone and oxygen are discharged from the ozone contact tank to the ozone tail gas treatment device 6. The part of wastewater 4 that is introduced into the ozone dosing device 3 may not enter the ozone-oxygen contact tank first in an upward flow as shown in Fig. 1 , it may be introduced into the ozone dosing device 3 in a downward flow, then ozone and oxygen in the dosing device 3 are introduced to the bottom of the ozone-oxygen contact tank 7 in an upward flow. The method of dissolving ozone and oxygen in the wastewater in the ozone-oxygen contact tank 7 according to this embodiment of the present invention is not limited to the above, and any gas distribution method which is advantageous for the wastewater to dissolve ozone and oxygen can be employed.

[0033] According to actual experiences of the inventors and experimental results, an ozone content in the gas discharged from the ozone dosing device is about 10%, and the remaining 90% is basically pure oxygen or air. In the usual engineering application, the amount of added ozone is tens to hundreds of milligrams per liter, which means that at least hundreds of milligrams per liter of pure oxygen is added to the water, and tens of milligrams per liter of COD need to be removed by the ozone-oxygen contact tank, thus knowing that the dissolved oxygen in the ozone-oxygen contact tank is supersaturated. The experimental and engineering results show that the dissolved oxygen concentration in the ozone-oxygen contact tank can be as high as 30~40mg/l, which is several times higher than the normal saturated dissolved oxygen. Therefore, the ozone-oxygen contact tank is also equivalent to a pure oxygen aeration tank. The wastewater discharged from the ozone-oxygen contact tank can reach a higher oxygen concentration than that subjecting aeration in the conventional aerated biological filter without further aeration and oxygenation for increasing microorganism activity.

[0034] In Fig. 1 , in order to facilitate the description of the concentration change of 0₂,

COD and BOD in the wastewater during the wastewater treatment process in the wastewater treatment system according to the embodiment of the present invention, the ozone-oxygen contact tank 7 and the biological filter 2 are schematically divided into four sections, labeled 1 1 , 12, 13 and 14. Section 1 1 represents start dosing and rapid reaction section of ozone, section 12 represents an equilibrium reaction section of ozone, section 13 represents a transition section after the completion of the ozone treatment and before introducing into the biological filter, and section 14 represents a section of biological filter.

[0035] Fig. 2 is a diagram of a concentration of 0₂, COD and BOD of each section after the gas discharged from the ozone dosing device 3 for preparing ozone using oxygen as a raw material (the main component is generated ozone and residual oxygen) is introduced into the wastewater treatment system of Fig. 1. Fig. 2 shows that with ozone dosing, at section 1 1 , the chemical oxygen demand COD is rapidly decreasing, ozone is rapidly oxidizing various organics and other reducing matters to degrade them, and with ozone dosing, pure oxygen dosing also increases, the oxygen concentration increases rapidly, and the biochemical oxygen demand BOD also increases. At section 12, the reaction is equilibrated and the solubility of oxygen is saturated, so the COD, oxygen concentration and BOD are all balanced. At section 13, the ozone-treated wastewater is discharged from the ozone-oxygen contact tank but has not yet introduced into the biological filter 2. During this process, COD and BOD remain basically unchanged, and some of the oxygen dissolved in the wastewater is lost, but the overall loss is not large, that is to say, when introducing into the biological filter 2, the concentration of oxygen in the wastewater remains at a higher level. Section 14 is a biological filter section, and the ozone-treated wastewater is further treated in the biological filter. Both COD and BOD continue to decrease until below a subsequent deep treatment or final discharge requirements.

[0036] In the environment of high dissolved oxygen, the activity of microorganisms is greatly improved, the rate of biodegradation is significantly accelerated, and the biological reaction time is greatly reduced. The high concentration difference produced by high dissolved oxygen has a strong penetration rate to penetrate a thick biofilm to the surface of the biological filter material, so that internal aerobic bacteria can fully function. So under the condition of high dissolved oxygen, BOD (biochemical oxygen demand) removal load of the biological filter is significantly improved. High dissolved oxygen can significantly enhance the metabolism of biofilm, the activity of mildew is enhanced, the metabolism of matter and energy is accelerated, the amount of excess sludge is small, and the frequency of backwash of biological filter is reduced. Therefore, the wastewater discharged from the ozone-oxygen contact tank can be directly introduced into the biological filter without aeration, thereby meeting the oxygen concentration requirement of the biological filter.

[0037] The biological filter according to this embodiment of the invention comprises a tank body, an influent distribution device located at the top of the tank body, a biological filter material located in an upper layer inside the tank body, a filter plate and filter heads located below the biological filter material, and a backwash device connected with the tank body. The influent distribution device, the biological filter material, the filter plate and the filter heads divide the biological filter into a top influent distribution zone, a biodegradation zone formed by the biological filter material layer, and a gas-water distribution chamber located below the filter plate and the filter heads .

[0038] Conventional aerated biological filters usually require an upward flow influent mode from the bottom of the biological filter because if aeration in a downward flow mode, the air bubbles rise and the downward flow easily form a gas barrier, and the filtration rate is low (less than 3m/h). The low filtration rate will result in a larger tank body area of the filter.

Moreover, the upward flow mode will easily wash the filter bed into a fluffy state. Therefore, the filtration interception effect and the effluent quality will be affected.

[0039] According to the wastewater treatment system of the embodiment of the present invention since the aeration is not required, a simple downward flow influent mode can be adopted. The wastewater discharged from the ozone-oxygen contact tank 7 is introduced from the top of the biological filter 2, thereby simplifying the structure, saving costs, reducing footprint, and improving wastewater treatment rate.

[0040] Moreover, in order to ensure that the residual ozone concentration dissolved in the wastewater discharged from the ozone-oxygen contact tank 7 does not affect the

microorganisms in the subsequent biological filter 2, in section 13 of the present embodiment, that is, between the ozone-oxygen contact tank 7 and the biological filter 2, a residual ozone control device is also provided for suppressing the residual ozone concentration in the ozone-treated wastewater before entering the biological filter 2 to prevent the residual ozone in the wastewater introduced into the biological filter 2 from harming the microorganisms in the biological filter 2, reducing the activity of the biological filter, and to prevent the residual ozone from eroding the filter material and the filter plate etc..

[0041] The residual ozone control device can be implemented by controlling the ozone concentration in the following manner:

[0042] 1. Controlling a residence time or distance between the wastewater discharge port after ozone treatment and the inlet port of the biological filter, so that the ozone naturally decomposes, and the residence time is at least 10-20 minutes;

(0043] 2. Accelerating the decomposition of residual ozone by physical means, such as providing a mechanical stirring device;

[0044] 3. Controlling the residual ozone concentration by chemical means, such as adding a reducing agent such as hydrogen peroxide to remove ozone;

[0045] 4. Installing a detecting meter to monitor the residual ozone concentration, such as a redox potential probe.

[0046] One embodiment of the residual ozone control device may be a time-controlled flow valve. Since the half-life of ozone is very short, the ozone in the ozone-treated wastewater can be eliminated by allowing the ozone-treated wastewater to stand for 10-20 minutes to naturally decompose the ozone. By using a time control flow valve, for example, the valve can be set to be open in 10-20 minutes after the end of the ozone treatment, the ozone concentration in the wastewater flowing out from the control flow valve is low, and cannot affect the activity of the biological filter.

[0047] The embodiment may install a detecting meter to further monitor the residual ozone concentration. The detecting meter may be installed upstream of the valve. When the detected residual ozone concentration is too high to meet the requirements of the biological filter, the standing time of the wastewater can be appropriately extended until the residual ozone concentration meets the requirements and then the time control flow valve may be opened again.

[0048] Another embodiment of the residual ozone control device may be an elongated outlet pipe. It takes the ozone-treated wastewater 10-20 minutes to pass through the elongated outlet pipe by controlling the flow rate of the ozone-treated wastewater so that the ozone in the wastewater is naturally decomposed. The wastewater is then introduced into the biological filter. The elongated outlet pipe may also be replaced by a water reservoir. The ozone-treated wastewater is placed in the water reservoir for 10-20 minutes to naturally decompose the ozone in the ozone-treated wastewater. The wastewater is then introduced into the biological filter.

[0049] The above embodiment may also install a detecting meter to further monitor the residual ozone concentration. The detecting meter may be installed downstream of the outlet pipe or the outlet of the water reservoir. When the detected residual ozone concentration at the outlet is too high to meet the requirements of the biological filter, the standing time of the wastewater can be appropriately extended until the residual ozone concentration meets the requirements and then the wastewater is discharged into the biological filter. In embodiments using an elongated outlet pipe and a water reservoir as the residual ozone control device, a mechanical agitation device may be provided or a reducing agent may be added to further remove ozone.

[0050] The residual ozone control device is not limited to the specific embodiment described above, and any embodiment capable of reducing or removing the residual ozone concentration in the ozone-treated wastewater should be within the scope of the present application.

[0051] Fig. 4 is a recording of dissolved oxygen change of the ozone biological filter according to the embodiment of the present invention of Fig. 1 . The Figure shows dissolved oxygen concentration at the inlet of the ozone-oxygen contact tank, the outlet of the ozone-oxygen contact tank, the inlet of the biological filter and the outlet of the biological filter. Specifically, the dissolved oxygen concentration at the outlet of the ozone-oxygen contact tank is up to 30-40 mg / L, and the dissolved oxygen concentration at the inlet of the biological filter is as high as 20-25 mg / L, which can meet the oxygen concentration requirements of the microorganisms in the biological filter.

[0052] Fig. 3 is a schematic view of a wastewater treatment system in accordance with a preferred embodiment of the present invention. The ozone treatment device in this embodiment is the same as the ozone treatment device 1 in the embodiment shown in Fig. 1 , and will not be described in detail here, except that the biological filter in Fig. 1 is embodied as a V-type biological filter here. Only the ozone-oxygen contact tank 8 and the V-type biological filter 9 are shown schematically in Fig. 3. The main difference between this preferred embodiment and the embodiment shown in Fig. 1 is that this preferred embodiment uses combined ozone and V-type biological filter.

[0053] A specific structure of the V-type biological filter is shown in Fig. 5. The V-type biological filter unit consists of two parts: a filtration system and a backwash system. The backwash system is used to backwash the filtration system after the filtration system filters out a certain amount of contaminants to remove the filtered contaminants to prevent the filtration system from being clogged and to ensure the filtration performance of the filtration system.

[0054] The filtration system comprises a rectangular water tank, and is divided into three zones including a V-type influent distribution channel 901, a biodegradation zone 913, and a gas-water distribution chamber 914 from top to bottom. The V-type influent and sweeping channels are located at the top of both sides of the tank and are connected to the top of the filter unit, and the wastewater discharged from the ozone treatment device is thereby introduced. The biodegradation zone comprises a biological filter material and a biological filter material support layer supporting the biological filter material. The biological filter material is a heavy clay ceramsite filter material adhered with a large amount of aerobic microorganisms for removing COD. The filter material has a height of about 1.5 meters high and a diameter of 1 mm to 5mm. The filter material has a porous structure and therefore has a high specific surface area, which is helpful for the adhesion of microorganisms. Below the biological filter material support layer is a gas-water distribution chamber 914. The gas-water distribution chamber 914 comprises a filter plate located below the biological filter material support layer and a plurality of filter heads evenly disposed on the filter plate. The heavy clay ceramsite filter material is, for example, BIOLITETM clay filter material. The biological filter material is used to intercept large particle suspensions and biodegrade the organics.

[0055] A quartz sand filter material (not shown) may be disposed between the biological filter material-the biological filter material support layer and the filter plate-the filter heads, for further filtration. The quartz sand filter material is supported by a quartz sand filter material support layer. The quartz sand filter material may be composed of different grades of gravel having a size of 8mm~40mm. Quartz sand filter material is mainly used to further intercept fine suspensions, obtaining better effluent quality.

[0056] When the wastewater treatment system according to the embodiment of the present invention is in operation, the effluent passing through the ozone-oxygen contact tank flows into the V-type biological filter through the V-type water tank which is opened at the top of the V-type biological filter 9. The V-type water distribution channel ensures uniform distribution of water flow on a filter bed and consistent filtration rate. Microorganisms adhere to the filter bed composed of biological filter material to form a fixed biofilm. The water flows through the filter bed from top to bottom, undergoes biodegradation under the action of biofilm and oxygen, and is physically filtered through ceramsite or quartz sand filter material, and then passes through the filter plate and the filter heads. An anti-blocking design of the filter heads can greatly reduce the risk of clogging of the filter bed. Finally, the filtered water is discharged from the tank body through the filtered water outlet pipe. With the operation of the wastewater treatment of the embodiment of the present invention, the suspensions in the influent is first retained by the filter material. And as time passes, the suspensions accumulate, causing head loss and even filter bed penetration, which deteriorate the treated effluent suspensions. Timely removal of the trapped suspensions is required. Therefore, the

wastewater treatment system according to this embodiment of the invention also comprises a backwash system for assisting in the removal of suspensions when backwashing is required.

[0057] The backwash system comprises a backwash water intake pipe 907 and an air intake pipe 904, which are connected to the gas-water distribution chamber at the bottom of the filter. Water and gas are distributed by the filter heads. The backwash water intake pipe 907 is connected with a backwash water pump 908 and a backwash water tank 909. The air intake pipe 904 is connected with a blower 905. The backwash system further comprises a backwash water outlet pipe 902 for discharging the backwashed wastewater. The backwash water intake pipe 907, the air intake pipe 904 and the backwash water outlet pipe 902 are connected to the gas-water distribution chamber through a backwash gas-water distribution tank located in the middle of the gas-water distribution chamber, and communicate with the gas-water distribution chamber through a gas-water distribution aperture.

[0058] During the filtration process, the water level in the filter is controlled by an effluent regulating valve, so that the filtering water level is basically constant, which ensures that the effluent quality is stable, and there is substantially no water drop of the influent.

[0059] When the V-type filter is periodically backwashed, the main steps of backwashing are as follows: ( 1) Stop the influent, keep the filtered water regulating valve open, and continue to filter until the liquid level in the tank drops to the surface of the filter material; (2) Start the blower and open the air intake valve. The backwashing gas first enters the gas-water distribution zone via the air intake pipe. An air cushion layer is formed under the filter plate to fluff the filter material. The suspensions on the filter material are stripped by the friction between the filter materials. The gas backwashing lasts for about 30 seconds to 1 minute; (3) lntroduce backwashing water which is combined with the backwashing gas to carry out the gas-water mix flushing, and start the backwash water pump. High-strength flushing may remove the suspensions retained in the filter bed and the aged biofilm. The gas-water flushing lasts for about 6 minutes; (4) Turn off the backwashing gas, and use only the backwashing water to flush to further remove residual particulates. The wastewater generated by

backwashing overflows into a backwashing wastewater channel at the top of the filter tank and finally flows into a backwashing wastewater tank. After the backwashing, the filter returns to the operating mode.

[0060] Water is keeping flowing into the V-type water of the V-type biological filter channel during backwashing, so that by a surface-assisted sweeping of the raw water influent, the biofilm and suspension backwashed to the water surface from the filter material can be discharging through a backwashing wastewater pipe more quickly, greatly reducing backwashing time and saving water. A wedge-shaped buffering effluent weir at the top of the backwashing wastewater channel can effectively avoid the loss of the filter material.

[0061] The following is application examples in practice according to this preferred embodiment of the invention.

[0062] Example 1 :

[0063] The effluent of the secondary sedimentation tank in a petrochemical enterprise wastewater treatment plant has a COD of 60-100 mg/L. The combined technology of ozone and V-type biological filter is used to treat the wastewater. The treatment target of COD is less than 50 mg/L. The effluent quality of the V-type filter was monitored for 51 days. As shown in the Figure below, the average rate of COD in the V-type biological filter was 30%, and the dissolved oxygen in the effluent was still higher than 10 mg/1.

J0064] Fig. 6 is an operation record of the V-type biological filter in this example.

[0065] Example 2:

[0066] The secondary air-floating water from a wastewater treatment plant in a chemical industrial park has a TOC of 20-30 mg/L. The combined technology of ozone and V-type biological filter is used to treat the wastewater. The target of TOC is less than 20 mg/L. The effluent quality of the V-type biological filter was monitored for 30 days. The ozone dosage was 9~ 12 g03/gATOC, and the V-type filter rate was 7~8m h. The V-type biological filter removes more than 10 mg/1 of COD and 5 mg/1 of TOC on average. The dissolved oxygen in the influent and effluent is shown in the table below.

[0067] The actual engineering operation is as follows. The average TOC removal of the V-type biological filter is l0mg/l or more, and the V-type biological filter is backwashed every 2 days, indicating that the mud production is low, the amount of the backwashing wastewater is small, and the energy consumption is low.

[0068] Fig. 7 is an operation record of the V-type biological filter in this Example 2.

[0069] It should be noted that the described embodiments are merely exemplary and are not intended to limit the invention, and that the features of the various embodiments may be used in combination to obtain further embodiments of the present invention. The scope is only limited by the appended claims. Many variations and modifications of the described embodiments are possible without departing from the scope of the invention.

Claims

WHAT IS CLAIMED IS:

1 . A wastewater treatment system for an deep treatment of refractory organics in wastewater, comprising an ozone treatment device and a biological filter, the ozone treatment device comprising an ozone dosing device which prepares ozone by electric discharge using air or pure oxygen as main raw material, wherein the ozone treatment device further comprises an ozone-oxygen contact tank, wherein the wastewater to be treated is introduced into said ozone-oxygen contact tank, and a mixed gas including ozone and excess air or oxygen discharged from the ozone dosing device is also introduced into the ozone-oxygen contact tank such that the wastewater to be treated is subjected to ozone oxidation treatment and oxygen absorption, and wherein an effluent of the ozone treatment device is introduced into the biological filter, so that an aeration device for increasing oxygenation for microorganisms is not need in the biological filter.

2. The wastewater treatment system according to claim 1 , wherein the effluent of the ozone treatment device is introduced into the biological filter from a top of the biological filter, and passes through the biological filter from top to bottom in a downward flow.

3. The wastewater treatment system according to claim 1 , wherein said ozone treatment device further comprises an ozone tail gas treatment device for treating excess ozone from the ozone-oxygen contact tank.

4. The wastewater treatment system according to any one of claims 1 to 3, wherein a part of the wastewater to be treated is pumped to the ozone dosing device via a pipe, and mixed with the ozone and excess air and oxygen in the ozone dosing device, a mixture of the ozone and oxygen and the part of the wastewater is introduced into the ozone-oxygen contact tank through a pipe under the pressure of the excess air and oxygen and the ozone in the ozone dosing device and the hydraulic pressure of the part of the wastewater that is introduced, to treat the wastewater to be treated in the ozone-oxygen contact tank.

5. The wastewater treatment system according to claim 4, wherein the pipe is connected to a lower portion of the ozone-oxygen contact tank, and a lower end of the pipe opened into the lower portion of the ozone-oxygen contact tank is provided with a diffuser made of porous material.

6. The wastewater treatment system according to any one of claims 1 to 3, wherein the wastewater treatment system further comprises a residual ozone control device located between the ozone treatment device and the biological filter for the effluent of the ozone treatment device, which is used to destroy residual ozone in the effluent of the ozone treatment device, and the effluent of the ozone treatment device is treated by the residual ozone control device and then introduced into the biological filter.

7. The wastewater treatment system according to claim 6 wherein the residual ozone control device further comprises an ozone detecting meter.

8. The wastewater treatment system according to claim 7, wherein the residual ozone control device is a time control flow valve configured to allow ozone-treated wastewater to stand for 10-20 minutes after ozone treatment is finished and then is opened to introduce the ozone-treated wastewater into the biological filter, or is an elongated outlet pipe or water reservoir, wherein the ozone-treated wastewater remains in the outlet pipe or the water reservoir for 10-20 minutes before being introduced into the biological filter, when the detecting meter detects that a residual ozone concentration in the effluent of the ozone treatment device does not meet the requirements of the biological filter, a standing time of the ozone-treated wastewater after the end of ozone treatment or a remaining time of the ozone-treated wastewater in the outlet pipe or the water reservoir is prolonged.

9. The wastewater treatment system according to any one of claims 1 to 3, wherein the biological filter comprises a filtration system and a backwash system, the backwash system is used to backwash the filtration system after a certain amount of dirt is filtered out.

10. The wastewater treatment system according to claim 9, wherein the filtration system comprises a V-type influent distribution channel, a biodegradation zone and a gas-water distribution chamber from top to bottom, wherein the V-type influent distribution channel is connected to a top of the filter, the V-type influent distribution channel is a V-type water tank with an open top, including a V-type water distribution weir.

1 1. The wastewater treatment system according to claim 10, wherein the biodegradation zone comprises a biological filter material and a biological filter material support layer supporting the biological filter material, wherein the biological filter material is a heavy clay ceramsite or quartz sand filter material adhered with microorganisms for removing organics in the wastewater.

12. A wastewater treatment method using a technology of combined ozone and biological filter to treat wastewater, wherein an ozone treatment device for ozone treatment comprises an ozone dosing device which prepares ozone by electric discharge using air or pure oxygen as main raw material, wherein the ozone treatment device further comprises an ozone-oxygen contact tank, the wastewater to be treated is introduced into said ozone-oxygen contact tank, a mixed gas including ozone and excess air and oxygen discharged from the ozone dosing device is also introduced into the ozone contact tank such that the wastewater to be treated is subjected to ozone oxidation treatment and air or oxygen absorption, the method utilizes supersaturated oxygen dissolved in the ozone-treated wastewater discharged from the ozone treatment device, introduces the ozone-treated wastewater discharged from the ozone treatment device into the biological filter without a need of aeration treatment for further increasing oxygenation for microorganisms.