CN106007040B

CN106007040B - Heavy metal wastewater treatment system and method

Info

Publication number: CN106007040B
Application number: CN201610594167.4A
Authority: CN
Inventors: 逯安国; 樊小林; 杜东清; 曹军
Original assignee: Hangzhou Zhenshui Fluid Technology Co ltd
Current assignee: Hangzhou Zhenshui Fluid Technology Co ltd
Priority date: 2016-07-23
Filing date: 2016-07-23
Publication date: 2022-09-06
Anticipated expiration: 2036-07-23
Also published as: CN106007040A

Abstract

The invention discloses a heavy metal wastewater treatment system and a heavy metal wastewater treatment method, wherein the system comprises a system control unit, a system state detection unit, a pretreatment system, an ultrafiltration system and a NF system, the pretreatment system comprises an adjusting tank, an air floatation tank, a sand filter tank, a carbon filter tank and a heavy metal adsorption device, and a backflow dissolved air assembly is arranged in the air floatation tank; the ultrafiltration system comprises an ultrafiltration filter and ultrafiltration equipment, the ultrafiltration equipment consists of a plurality of ultrafiltration tubes, and a backwashing component is arranged in the ultrafiltration system; the NF system comprises an RO booster pump, a security filter, an RO device and a cleaning component; the system state detection unit comprises a pressure gauge, a flowmeter, a conductivity meter, a pH value detector and a temperature detector, the system control unit comprises a processor module and a control terminal assembly, the control terminal assembly comprises an electromagnetic valve, a pneumatic butterfly valve and an electric butterfly valve, the processor module adjusts the flow rate and the flow direction of wastewater in the wastewater treatment system, and the wastewater is filtered step by arranging the multiple filtering devices to realize a good filtering effect.

Description

Heavy metal wastewater treatment system and method

Technical Field

The invention relates to the technical field of sewage treatment, in particular to a heavy metal wastewater treatment system and method.

Background

In the electroplating industry, a lot of industrial waste water containing a large amount of heavy metal ions is generated, and the waste water can seriously pollute the environment around a factory if the waste water is discharged without treatment. Therefore, many wastewater treatment systems in the prior art, especially for heavy metal wastewater treatment systems, for example, chinese patent with patent publication No. CN105016510A, disclose a set of wastewater treatment systems for heavy metal-containing wastewater, wherein the main method of the above systems is precipitation and adsorption, although the structure is simple, the degree of wastewater treatment achieved is not satisfactory, and the quality of treated water is not good. If the treated sewage is to be obtained more cleanly, a plurality of new processes and equipment are required to be added, and the structural level of the whole sewage treatment system is inevitably complicated. Due to the complex structural level, the difficulty of system maintenance is greatly increased, system inspection and operation are inconvenient, dead spots are easy to generate in the system, when a problem occurs in a certain link, the whole system needs to be shut down and restarted, and the cost is huge. In addition, in order to adjust the ion concentration in the sewage, clean water is often injected into the sewage treatment system to assist the normal operation of the sewage treatment system, so that a large amount of clean water is consumed, and the sewage treatment benefit is reduced.

Disclosure of Invention

Aiming at the problem that the treatment of wastewater containing heavy metals is not thorough in practical application, the invention aims to provide a heavy metal wastewater treatment system and a wastewater treatment method based on the system.

The heavy metal wastewater treatment system comprises the following specific scheme:

a heavy metal wastewater treatment system, which comprises a system control unit, a system state detection unit, a pretreatment system, an ultrafiltration system and an NF system which are sequentially arranged, wherein,

the pretreatment system comprises a regulating tank, an air floatation tank, a sand filter tank, a carbon filter tank and a heavy metal adsorption device which are sequentially arranged, wherein a backflow air dissolving assembly for circularly utilizing the wastewater in the air floatation tank to perform air dissolving purification on the wastewater is arranged in the air floatation tank;

the ultrafiltration system comprises at least two groups of ultrafiltration filters and ultrafiltration equipment which are arranged in parallel, the ultrafiltration equipment consists of a plurality of ultrafiltration tubes which are arranged in parallel, the water inlet ends of the ultrafiltration tubes are communicated with the water outlet of the ultrafiltration filter, the water outlet end of the ultrafiltration tubes is communicated with the NF system, and a backwashing component for cleaning the ultrafiltration equipment by using the wastewater filtered by the ultrafiltration system is arranged in the ultrafiltration system;

the NF system comprises an RO booster pump, a security filter, a primary RO device and a secondary RO device which are sequentially communicated, wherein the primary RO device and the secondary RO device are respectively provided with a cleaning component for cleaning the primary RO device and the secondary RO device by utilizing the waste water filtered by the secondary RO device;

the system state detection unit comprises a pressure gauge and a flow meter which are arranged on each communicating pipeline, and a conductivity meter, a pH value detector and a temperature detector which are arranged in the NF system;

the system control unit comprises a processor module and a control terminal assembly, the control terminal assembly comprises electromagnetic valves, pneumatic butterfly valves and electric butterfly valves which are arranged in the communication pipelines, the processor module receives detection values of the system state detection unit to control the movement of the control terminal assembly, and the flow rate and the flow direction of wastewater in the wastewater treatment system are adjusted.

Further, between air supporting pond and the sand filter pond between heavy metal adsorption device and the ultrafiltration filter between ultrafiltration equipment and the RO booster pump and be provided with pond in the middle of the first-class RO equipment and the second grade RO equipment between pond in the middle of the second, pond in the middle of the third, pond in the middle of the fourth respectively, all be equipped with the liquid level height detection device with processor module signal connection in the pond in the middle of a plurality of, all be equipped with inlet tube and outlet pipe and control inlet tube, the control terminal subassembly of outlet pipe break-make on the lateral wall in a plurality of middle ponds.

Further, the backward flow dissolves the gas subassembly and includes the air supporting backwash pump that communicates each other and dissolves the gas pitcher, the end of intaking of air supporting backwash pump is used for carrying the clear water to dissolving in the gas pitcher with the bottom side wall intercommunication in air supporting pond, the drainage end that dissolves the gas pitcher sets up with the waste water input port in air supporting pond is adjacent, air supporting pond and air supporting backwash pump, dissolve and be provided with pneumatic butterfly valve between gas pitcher and the air supporting pond.

Furthermore, at least two raw water pumps for pumping the wastewater in the first intermediate water tank into the sand filter are arranged between the first intermediate water tank and the sand filter in parallel, and an electric butterfly valve or a pneumatic butterfly valve is arranged at the water inlet end and the water outlet end of each raw water pump.

Furthermore, the backwashing component comprises an ultrafiltration backwashing pump of which the water inlet end is communicated with the third intermediate water tank, and the water outlet end of the ultrafiltration backwashing pump is respectively communicated with the water outlet ends of the ultrafiltration pipes so as to flush the ultrafiltration pipes and the pipelines communicated with the ultrafiltration pipes by using the wastewater in the third intermediate water tank.

Further, one-level RO equipment, second grade RO equipment include with the RO high-pressure pump that the security personnel's filter is linked together, and with many reverse osmosis membrane that the RO high-pressure pump is linked together, many the reverse osmosis membrane constitutes a plurality of reverse osmosis modules that connect in parallel each other and set up, and is a plurality of reverse osmosis module series each other sets up and the output with pond in the middle of the fourth is linked together, and is a plurality of reverse osmosis membrane's outlet end all is provided with the sample valve.

Furthermore, the cleaning assembly comprises a cleaning water tank, the cleaning water tank is communicated with a backwater pool of the system and used for obtaining the cleaning wastewater filtered by the secondary RO equipment, the cleaning water tank is communicated with a cleaning water pump and a cleaning filter, the cleaning wastewater in the cleaning water tank is communicated with the water inlet ends of the reverse osmosis pipes after passing through the cleaning water pump and the cleaning filter, and a pneumatic butterfly valve or an electric butterfly valve is arranged among the cleaning water tank, the cleaning water pump, the cleaning filter and the reverse osmosis pipes.

Further, the heavy metal adsorption device comprises an acidic resin adsorption device and an alkaline resin adsorption device which are communicated with each other.

A heavy metal wastewater treatment method is based on the heavy metal wastewater treatment system and comprises the following steps:

s1, adding the wastewater containing large heavy metals into a regulating reservoir, adding a flocculating agent into the regulating reservoir, and flocculating the particulate matters in the wastewater together by using the flocculating agent;

s2, discharging the wastewater containing the flocculating agent into an air floatation tank, and lifting particulate matters in the wastewater to the surface of the air floatation tank by utilizing bubbles in the air floatation tank to be separated out;

s3, discharging the wastewater purified by the air flotation tank into a first intermediate water tank, discharging the wastewater into a sand filter tank and a carbon filter tank when the liquid level reaches a preset height, and in order to prevent the wastewater from being blocked when discharged from the first intermediate water tank, arranging two sets of raw water pumps between the first intermediate water tank and the sand filter, wherein one set is selected when in use;

s4, obviously reducing large particle substances of the wastewater filtered by the sand filter and the carbon filter, then discharging the wastewater into a resin absorption device, further removing the particle substances in the wastewater by utilizing acidic and alkaline solutions, and then discharging the wastewater into a second intermediate water tank;

s5, when the liquid level height of the second intermediate water tank reaches a preset height, the processor module controls the control terminal assembly to discharge the wastewater into the ultrafiltration filter from the second intermediate water tank, the wastewater is discharged into the ultrafiltration equipment after primary filtration, the ultrafiltration membrane is used for further filtering particulate pollutants in the wastewater, the filtered wastewater is discharged into a third intermediate water tank, and when the liquid level height of the third intermediate water tank reaches a preset value, the wastewater in the third intermediate water tank is discharged into the NF system;

s6, pressurizing the wastewater to meet the osmotic pressure condition of the RO equipment, further filtering the wastewater by the RO equipment, and discharging the wastewater into a reuse water pool after filtering by the primary RO equipment and the secondary RO equipment;

in the above steps S5 and S6, when the work efficiency of the ultrafiltration tube or the reverse osmosis tube is significantly reduced, the clean water for cleaning the ultrafiltration device, the primary RO device, and the secondary RO device is supplied from the third intermediate water tank and the fourth intermediate water tank, respectively.

Further, in the steps S2 and S3, the water in the dissolved air tank comes from the water body at the bottom of the air flotation tank, and when the filtering effect in the sand filter tank and the carbon filter tank is not good, the air compressor is used for filling water to the bottoms of the sand filter tank and the carbon filter tank, so as to realize backwashing of the sand filter tank and the carbon filter tank.

The invention has the following beneficial effects:

(1) by arranging the multiple filtering devices, the wastewater containing heavy metal ions is filtered step by step, and finally a good filtering effect is realized;

(2) by arranging a series of intermediate water tanks and cleaning the equipment in the previous step by using the wastewater in the intermediate water tanks, the whole system does not consume external clean water, and the economic benefit of wastewater treatment is improved;

(3) by arranging the multiple backwashing devices, when the filtering effect of a certain device is poor, the system state detection unit sends a detection result to the processor module, and then the processor module controls the control terminal assembly to adjust the conduction mode of the pipeline, so that the device with poor filtering effect is cleaned;

(4) by arranging the multiple pipeline structures in parallel at the key part, when one filtering line is interrupted, other filtering lines can be used for filtering the wastewater, so that the whole wastewater treatment system is prevented from being shut down integrally due to local faults;

(5) by arranging the detection devices such as pressure meters, flowmeters and the like on the communicating pipelines, the running state of the wastewater treatment system is automatically monitored in real time, the time for field maintenance of maintainers is saved, and the maintenance efficiency is ensured.

Drawings

FIG. 1 is a schematic diagram of a front section of a pretreatment system;

FIG. 2 is a schematic view of a back end portion of the pretreatment system;

FIG. 3 is a schematic diagram of an ultrafiltration system;

FIG. 4 is a schematic diagram of a primary RO device;

FIG. 5 is a schematic diagram of a secondary RO device;

FIG. 6 is a schematic view of a cleaning assembly;

FIG. 7 is a schematic flow diagram of the wastewater treatment process of the present invention.

The reference symbols: 1. a pre-treatment system; 11. a regulating tank; 111. a raw water pool; 112. a metering pump; 113. a coagulant; 114. a flocculant; 115. a pipeline mixer; 12. an air floatation tank; 13. a backflow dissolved air assembly; 131. a dissolved air tank; 132. an air floatation reflux pump; 14. a first intermediate pool; 15. a sand filter; 16. a carbon filter; 17. a heavy metal adsorption device; 171. an acidic resin adsorption unit; 172. an alkaline resin adsorption unit; 173. a water ejector; 18. a second intermediate pool; 19. a raw water pump; 20. a butterfly valve; 21. a pressure gauge; 22. a flow meter; 23. an ultrafiltration filter; 24. ultrafiltration equipment; 241. an ultrafiltration tube; 25. an ultrafiltration backwash pump; 26. a third intermediate pool; 27. an RO booster pump; 28. a security filter; 29. an RO high-pressure pump; 30. a primary RO device; 31. a secondary RO device; 301. a reverse osmosis tube; 32. a fourth intermediate pool; 33. a produced water recycling pool; 34. cleaning the filter; 35. cleaning the water pump; 36. and (5) cleaning the water tank.

Detailed Description

The invention aims to provide a heavy metal wastewater treatment system which can effectively reduce the workload of managers of a wastewater treatment system and improve the management efficiency of the wastewater treatment system.

The present invention will be described in further detail with reference to examples and drawings, but the embodiments of the present invention are not limited thereto.

A heavy metal wastewater treatment system comprises a system control unit, a system state detection unit, a pretreatment system 1, an ultrafiltration system and an NF system which are sequentially arranged, wherein,

the pretreatment system 1 comprises a regulating tank 11, an air floatation tank 12, a sand filter tank, a carbon filter tank and a heavy metal adsorption device 17 which are arranged in sequence, wherein a backflow air dissolving component 13 for circularly utilizing waste water in the air floatation tank 12 to dissolve and purify the waste water is arranged in the air floatation tank 12.

As shown in fig. 1 and fig. 2, in the above solution, the adjusting tank 11 includes a raw water tank 111 for containing heavy metal ions, a flow channel is provided between the raw water tank 111 and the flotation tank 12, wherein, in order to coagulate particulate matter in the water body, a flocculant 114 and a coagulant 113 are injected into the flow channel, a channel mixer 115 is communicated with the channel for mixing the flocculant 114, the coagulant 113 and the raw water, during the actual operation, the coagulant 113 and the flocculant 114 include polyaluminium chloride and a nonionic polymeric flocculant 114, and the additives are respectively stored in a container and are injected into the flow channel by a quantitative metering valve.

The backflow dissolved air module 13 is mainly used for injecting the water body at the bottom of the dissolved air tank into the bottom of the dissolved air tank again after new dissolved air is dissolved, adsorbing particulate matters in the water body by means of bubbles dissolved in the water body, and lifting the particulate matters to the surface of the water body. The arrangement can reduce the use amount of the water outside the system. In further detail, the backflow dissolved air assembly 13 includes an air flotation reflux pump 132 and a dissolved air tank 131 that are communicated with each other, a water inlet end of the air flotation reflux pump 132 is communicated with a bottom side wall of the air flotation tank 12 to convey clean water into the dissolved air tank 131, a water discharge end of the dissolved air tank 131 is adjacent to a wastewater inlet of the air flotation tank 12, and pneumatic butterfly valves are disposed between the air flotation tank 12 and the air flotation reflux pump 132, and between the dissolved air tank 131 and the air flotation tank 12.

The sand filter belongs to a multi-media filter, is a pressure type filter, and utilizes refined quartz sand filter materials filled in the filter, when inlet water flows through a filter layer from top to bottom, suspended matters and mucilaginous particles in the water are removed, so that the turbidity (NTU) and the pollution index (SDI) of the water are reduced. The sand filter 15 is mainly made of cobblestones and quartz sand, the cobblestones are used as a bottom supporting layer, and the cobblestones are filled from thick to thin (from bottom to top) until the lower end socket is filled.

The carbon filter is also called an activated carbon filter, and is a pressure type filter. The filling material is high-quality shell activated carbon, and the bottom layer is quartz sand.

The heavy metal adsorption device 17 includes two acid resin adsorption devices 171 and a basic resin adsorption device 172 that communicate with each other. Wherein the approximate chemical reaction formula is:

Fe3++3HR→FeR+3H+Ni2++2HR→NiR+2H+；

when the raw water enters the A ion exchanger, various cations contained in the water react with H + on the ion exchange resin as described above, and as a result of the above reaction, various cations (Fe3+, Ni2+, etc.) in the water are adsorbed on the ion exchange resin, while the H + on the ion exchange resin enters the water, the cations in the water almost only contain H +, and react with various anions in the water to generate various acids.

The mechanism of ultrafiltration is the combined effect of mechanical sieving on the membrane surface, membrane pore retardation and adsorption on the membrane surface and membrane pores, mainly sieving and filtering. As for the ultrafiltration system, as shown in fig. 3, the ultrafiltration system comprises at least two groups of ultrafiltration filters 23 and ultrafiltration devices 24 arranged in parallel, the ultrafiltration device 24 is composed of a plurality of ultrafiltration tubes 241 arranged in parallel, the water inlet ends of the ultrafiltration tubes 241 are communicated with the water outlet of the ultrafiltration filter 23, the water outlet end is communicated with the NF system, and the ultrafiltration system is provided with a backwashing component for cleaning the ultrafiltration device 24 by using the wastewater filtered by the ultrafiltration system.

Because the fault rate of the ultrafiltration tube 241 is high, by arranging two groups of ultrafiltration filters 23 and ultrafiltration equipment 24, when one group of equipment fails, the other group of equipment can be continuously used, and the normal operation of the system is ensured.

The backwashing component comprises an ultrafiltration backwashing pump 25 with a water inlet end communicated with the third intermediate water tank 26, and the water outlet end of the ultrafiltration backwashing pump 25 is respectively communicated with the water outlet end of the ultrafiltration pipe 241 for flushing the ultrafiltration pipe 241 and a pipeline communicated with the ultrafiltration pipe 241 by using the wastewater in the third intermediate water tank 26. The body of the ultrafiltration tube 241 is cleaned by the filtered water body, so that the requirement for external clean water can be reduced.

As shown in fig. 4 and 5, the NF system includes an RO booster pump 27, a cartridge filter 28, a primary RO device 30, and a secondary RO device 31, which are arranged in series, and each of the primary RO device 30 and the secondary RO device 31 is provided with a cleaning unit for cleaning the primary RO device 30 and the secondary RO device 31 by using waste water filtered by the secondary RO device 31.

One-level RO equipment 30, second grade RO equipment 31 include the RO high-pressure pump 29 that is linked together with security personnel's filter 28 to and many reverse osmosis tube 301 that are linked together with RO high-pressure pump 29, and many reverse osmosis tube 301 constitute a plurality of reverse osmosis module that connect in parallel each other and set up, and a plurality of reverse osmosis module establish ties each other and the output is linked together with fourth middle pond 32, and the water outlet end of a plurality of reverse osmosis tube 301 all is provided with the sampling valve.

As shown in fig. 6, the cleaning assembly includes a cleaning water tank 36, the cleaning water tank 36 is communicated with a water return tank of the system for obtaining the cleaning wastewater filtered by the secondary RO device 31, the cleaning water tank 36 is communicated with a cleaning water pump 35 and a cleaning filter 34, the cleaning wastewater in the cleaning water tank 36 is communicated with the water inlet ends of the reverse osmosis pipes 301 after passing through the cleaning water pump 35 and the cleaning filter 34, and a pneumatic butterfly valve 20 or an electric butterfly valve is arranged between the cleaning water tank 36, the cleaning water pump 35, the cleaning filter 34 and the reverse osmosis pipes 301.

The system state detection unit comprises a pressure gauge 21 and a flow meter 22 which are arranged on each communication pipeline, and a conductivity meter, a pH value detector and a temperature detector which are arranged in the NF system;

the system control unit comprises a processor module and a control terminal assembly, the control terminal assembly comprises electromagnetic valves, pneumatic butterfly valves and electric butterfly valves which are arranged in the communication pipelines, and the processor module receives detection values of the system state detection unit to control the movement of the control terminal assembly and adjust the flow rate and the flow direction of wastewater in the wastewater treatment system.

Preferably, a first middle water tank 14, a second middle water tank 18, a third middle water tank 26 and a fourth middle water tank 32 are respectively arranged between the air flotation tank 12 and the sand filter tank, between the heavy metal adsorption device 17 and the ultrafiltration filter 23, between the ultrafiltration device 24 and the RO booster pump 27 and between the primary RO device 30 and the secondary RO device 31, liquid level height detection devices in signal connection with the processor module are arranged in the middle water tanks, and a water inlet pipe, a water outlet pipe, a control terminal assembly for controlling the connection and disconnection of the water inlet pipe and the water outlet pipe are arranged on the side wall of each middle water tank.

In order to enhance the reliability of the system, at least two raw water pumps 19 for pumping the wastewater in the first intermediate water tank 14 into the sand filter 15 are arranged between the first intermediate water tank 14 and the sand filter 15 in parallel, and an electric butterfly valve or a pneumatic butterfly valve is arranged at both the water inlet end and the water outlet end of the raw water pump 19.

Based on the above system design, the wastewater treatment method of the present invention, as shown in fig. 7, comprises the following steps:

s1, adding the wastewater containing large heavy metals into the adjusting tank 11, then adding a flocculant 114 into the adjusting tank 11, and utilizing the flocculant 114 to coagulate the particulate matters in the wastewater together;

s2, discharging the wastewater containing the flocculating agent 114 into the air flotation tank 12, lifting particulate matters in the wastewater to the surface of the air flotation tank 12 by utilizing bubbles in the air flotation tank 12, and then separating out;

s3, discharging the wastewater purified by the air flotation tank 12 into a first intermediate water tank 14, discharging the wastewater into a sand filter tank and a carbon filter tank when the liquid level reaches a preset height, and in order to prevent the wastewater from being blocked when discharged from the first intermediate water tank 14, arranging two sets of raw water pumps 19 between the first intermediate water tank 14 and a sand filter 15, wherein one set is selected when in use;

s4, obviously reducing the large particle substances of the wastewater filtered by the sand filter 15 and the carbon filter, then discharging the wastewater into a resin absorption device, further removing the particle substances in the wastewater by utilizing acid and alkaline solutions, and then discharging the wastewater into a second intermediate water tank 18;

s5, when the liquid level height of the second intermediate water tank 18 reaches a preset height, the processor module controls the control terminal assembly to discharge the wastewater from the second intermediate water tank 18 into the ultrafiltration filter 23, the wastewater is discharged into the ultrafiltration equipment 24 after primary filtration, the ultrafiltration membrane is used for further filtering particulate pollutants in the wastewater, the filtered wastewater is discharged into the third intermediate water tank 26, and when the liquid level height of the third intermediate water tank 26 reaches a preset value, the wastewater in the third intermediate water tank 26 is discharged into the NF system;

s6, pressurizing the wastewater to meet the osmotic pressure condition of the RO equipment, further filtering the wastewater by the RO equipment, and discharging the wastewater into a reuse water pool after filtering by the primary RO equipment 30 and the secondary RO equipment 31;

in the above steps S5 and S6, when the operation efficiency of the ultrafiltration tube 241 or the reverse osmosis tube 301 is significantly reduced, the clean water for cleaning the ultrafiltration device 24, the primary RO device 30, and the secondary RO device 31 is supplied from the third intermediate water tank 26 and the fourth intermediate water tank 32, respectively.

In steps S2 and S3, the water in the dissolved air tank 131 comes from the water body at the bottom of the air flotation tank 12, and when the filtering effect in the sand filter and the carbon filter is not good, the air compressor is used for filling water to the bottoms of the sand filter and the carbon filter, so as to realize backwashing of the sand filter and the carbon filter.

The above is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above-mentioned embodiments, and all technical solutions belonging to the idea of the present invention belong to the protection scope of the present invention. It should be noted that modifications and embellishments within the scope of the invention may occur to those skilled in the art without departing from the principle of the invention, and are considered to be within the scope of the invention.

Claims

1. A heavy metal wastewater treatment system is characterized by comprising a system control unit, a system state detection unit, a pretreatment system (1), an ultrafiltration system and an NF system which are sequentially arranged, wherein,

the pretreatment system (1) comprises an adjusting tank (11), an air flotation tank (12), a sand filter tank, a carbon filter tank and a heavy metal adsorption device (17) which are sequentially arranged, wherein a backflow air dissolving component (13) for circularly utilizing wastewater in the air flotation tank (12) to carry out air dissolving purification on the wastewater is arranged in the air flotation tank (12);

the ultrafiltration system comprises at least two groups of ultrafiltration filters (23) and ultrafiltration equipment (24) which are arranged in parallel, wherein the ultrafiltration equipment (24) consists of a plurality of ultrafiltration tubes (241) which are arranged in parallel, the water inlet ends of the ultrafiltration tubes (241) are communicated with the water outlet of the ultrafiltration filter (23), the water outlet end of the ultrafiltration tubes is communicated with an NF system, and a backwashing component for cleaning the ultrafiltration equipment (24) by using the wastewater filtered by the ultrafiltration system is arranged in the ultrafiltration system;

the NF system comprises an RO booster pump (27), a security filter (28), a primary RO device (30) and a secondary RO device (31) which are sequentially communicated, wherein the primary RO device (30) and the secondary RO device (31) are respectively provided with a cleaning component for cleaning the primary RO device (30) and the secondary RO device (31) by utilizing waste water filtered by the secondary RO device (31);

the system state detection unit comprises a pressure gauge (21) and a flow meter (22) which are arranged on each communicating pipeline, and a conductivity meter, a pH value detector and a temperature detector which are arranged in the NF system;

the system control unit comprises a processor module and a control terminal assembly, the control terminal assembly comprises an electromagnetic valve, a pneumatic butterfly valve and an electric butterfly valve which are arranged in each communication pipeline, the processor module receives a detection value of the system state detection unit to control the movement of the control terminal assembly and adjust the flow rate and the flow direction of wastewater in the wastewater treatment system;

a first intermediate water tank (14), a second intermediate water tank (18), a third intermediate water tank (26) and a fourth intermediate water tank (32) are respectively arranged between the air flotation tank (12) and the sand filter tank, between the heavy metal adsorption device (17) and the ultrafiltration filter (23), between the ultrafiltration equipment (24) and the RO booster pump (27) and between the primary RO equipment (30) and the secondary RO equipment (31), liquid level height detection devices in signal connection with the processor module are respectively arranged in the plurality of intermediate water tanks, and a water inlet pipe, a water outlet pipe and a control terminal component for controlling the on-off of the water inlet pipe and the water outlet pipe are respectively arranged on the side walls of the plurality of intermediate water tanks;

the backflow dissolved air assembly (13) comprises an air floatation backflow pump (132) and an air dissolving tank (131) which are communicated with each other, the water inlet end of the air floatation backflow pump (132) is communicated with the side wall of the bottom of the air floatation tank (12) and used for conveying clean water into the air dissolving tank (131), the water discharge end of the air dissolving tank (131) is arranged adjacent to a wastewater inlet of the air floatation tank (12), and pneumatic butterfly valves are arranged between the air floatation tank (12) and the air floatation backflow pump (132), and between the air dissolving tank (131) and the air floatation tank (12);

at least two raw water pumps (19) for pumping the wastewater in the first intermediate water tank (14) into the sand filter (15) are arranged between the first intermediate water tank (14) and the sand filter (15) in parallel, and an electric butterfly valve or a pneumatic butterfly valve is arranged at both the water inlet end and the water outlet end of each raw water pump (19);

the backwashing component comprises an ultrafiltration backwashing pump (25) with a water inlet end communicated with the third intermediate water tank (26), and the water outlet end of the ultrafiltration backwashing pump (25) is respectively communicated with the water outlet end of the ultrafiltration pipe (241) to flush the ultrafiltration pipe (241) and a pipeline communicated with the ultrafiltration pipe (241) by using wastewater in the third intermediate water tank (26).

2. The heavy metal wastewater treatment system of claim 1, wherein the primary RO equipment (30) and the secondary RO equipment (31) comprise a RO high-pressure pump (29) communicated with the security filter (28) and a plurality of reverse osmosis pipes (301) communicated with the RO high-pressure pump (29), the plurality of reverse osmosis pipes (301) form a plurality of reverse osmosis modules which are arranged in parallel, the plurality of reverse osmosis modules are arranged in series, the output ends of the reverse osmosis modules are communicated with the fourth intermediate water tank (32), and the water outlet ends of the plurality of reverse osmosis pipes (301) are provided with sampling valves.

3. The heavy metal wastewater treatment system according to claim 2, wherein the cleaning assembly comprises a cleaning water tank (36), the cleaning water tank (36) is communicated with a water return tank of the system and is used for obtaining the cleaning wastewater filtered by the secondary RO equipment (31), the cleaning water tank (36) is communicated with a cleaning water pump (35) and a cleaning filter (34), the cleaning wastewater in the cleaning water tank (36) is communicated with the water inlet ends of the reverse osmosis pipes (301) after passing through the cleaning water pump (35) and the cleaning filter (34), and a pneumatic butterfly valve or an electric butterfly valve is arranged among the cleaning water tank (36), the cleaning water pump (35), the cleaning filter (34) and the reverse osmosis pipes (301).

4. The heavy metal wastewater treatment system according to claim 1, wherein the heavy metal adsorption device (17) comprises two acidic resin adsorption devices (171) and an alkaline resin adsorption device (172) which are communicated with each other.

5. A heavy metal wastewater treatment method is characterized in that the heavy metal wastewater treatment system according to any one of claims 1-4 comprises the following steps:

s1, adding the wastewater containing large heavy metals into a regulating reservoir (11), then adding a flocculating agent (114) into the regulating reservoir (11), and utilizing the flocculating agent (114) to coagulate particulate matters in the wastewater together;

s2, discharging the wastewater containing the flocculating agent (114) into the air flotation tank (12), lifting particulate matters in the wastewater to the surface of the air flotation tank (12) by utilizing bubbles in the air flotation tank (12) and then separating out;

s3, discharging the wastewater purified by the air flotation tank (12) into a first intermediate water tank (14), discharging the wastewater into a sand filter tank and a carbon filter tank when the liquid level reaches a preset height, and in order to prevent the blockage of the wastewater discharged by the first intermediate water tank (14), two sets of raw water pumps (19) are arranged between the first intermediate water tank (14) and the sand filter (15), and one set is selected when in use;

s4, obviously reducing large granular substances of the wastewater filtered by the sand filter (15) and the carbon filter, then discharging the wastewater into a resin adsorption device, further removing the granular substances in the wastewater by utilizing acidic and alkaline solutions, and then discharging the wastewater into a second intermediate water tank (18);

s5, when the liquid level height of the second intermediate water tank (18) reaches a preset height, the processor module controls the control terminal assembly to discharge the wastewater from the second intermediate water tank (18) into the ultrafiltration filter (23), the wastewater is discharged into the ultrafiltration equipment (24) after primary filtration, the ultrafiltration membrane is utilized to further filter particulate pollutants in the water, the filtered wastewater is discharged into the third intermediate water tank (26), and when the liquid level height in the third intermediate water tank (26) reaches a preset value, the wastewater in the third intermediate water tank (26) is discharged into the NF system;

s6, pressurizing the wastewater to enable the wastewater to meet osmotic pressure conditions of RO equipment, further filtering the wastewater by the RO equipment, and discharging the wastewater into a reuse water pool after filtering by primary RO equipment (30) and secondary RO equipment (31);

in the above steps S5 and S6, when the work efficiency of the ultrafiltration tube (241) or the reverse osmosis tube (301) is significantly reduced, the clean water for cleaning the ultrafiltration device (24), the primary RO device (30), and the secondary RO device (31) is respectively from the third intermediate water tank (26) and the fourth intermediate water tank (32).

6. The heavy metal wastewater treatment method according to claim 5, wherein in steps S2 and S3, the water used in the dissolved air tank (131) comes from the water body at the bottom of the air flotation tank (12), and when the filtering effect in the sand filter tank and the carbon filter tank is poor, the air compressor is used for filling water to the bottom of the sand filter tank and the carbon filter tank, so as to realize backwashing of the sand filter tank and the carbon filter tank.