AU2020101137A4

AU2020101137A4 - Wastewater treatment system by in site chemically-oxidized dynamic membrane

Info

Publication number: AU2020101137A4
Application number: AU2020101137A
Authority: AU
Inventors: Xuewen Liu
Original assignee: Binzhou University
Current assignee: Binzhou University
Priority date: 2020-06-25
Filing date: 2020-06-25
Publication date: 2020-08-13
Anticipated expiration: 2028-06-25

Abstract

The present invention discloses a non-biodegradable wastewater treatment system by in site chemically-oxidized dynamic membrane. The system includes a hydrogen peroxide overhead tank , an iron-containing ore powder mixing tank, a pH adjustment overhead tank, a circulation tank , a circulation pump, a membrane/membrane module, a recovery tank and a detection and control device for parameters such as flow rate (L), temperature (T), pressure (P) and pH. Outlets of the hydrogen peroxide overhead tank, the iron-containing ore powder mixing tank and the pH adjustment overhead tank are all connected to the circulation tank; an outlet of the circulation tank is connected to the circulation pump; an outlet of the circulation pump is connected to a circulation side of the membrane/membrane module, and an outlet pipeline of the circulation pump is provided with the detection and control device for parameters such as flow rate (L), temperature (T), pressure (P) and pH; an outlet on the circulation side of the membrane/membrane module is connected to the circulation tank; the circulation side of the membrane/membrane module is provided with a sewage outlet at the bottom; the sewage outlet is connected to the recovery tank; water discharged on a discharge side of the membrane/membrane module is discharged from the system. 1/4 DRAWINGS 2. Iron-containing ore powder 3. pH . ~~~~~~~~~~----------------- mixing tank adjustment Pressure overhead tank 1. Hydrogen peroxideL L L ove ead 8. Flow rate (L), tank temperature (T) and pressure (P) detection and Sewage control device Flow TemperPressu rate ature re L T P i .................. - Dynamic - -:membrane, shown: in FIG. 2 - p...... ................... . Sewage 4. 5. 6. 7. circulation Circulation Membrane/membrane Recovery tank pump module tank FIG. 1

Description

1/4

DRAWINGS

2. Iron-containing ore powder 3. pH . ~~~~~~~~~~----------------- mixing tank adjustment Pressure overhead tank

1. Hydrogen peroxideL L L ove ead 8. Flow rate (L), tank temperature (T) and pressure (P) detection and Sewage control device Flow TemperPressu rate ature re L T Pi .................. - Dynamic - -:membrane, shown: - p...... in ................... FIG. 2

. Sewage

4. 5. 6. 7. circulation Circulation Membrane/membrane Recovery tank pump module tank

FIG. 1

WASTEWATER TREATMENT SYSTEM BY IN SITE CHEMICALLY-OXIDIZED DYNAMIC MEMBRANE TECHNICAL FIELD

The present invention belongs to the technical field of non-biodegradable wastewater treatment, and relates to a dynamic membrane water treatment process, in particular to a dynamic membrane filtration system featuring in site formation, continuous transformation, catalytic reaction and adsorption, which couples dynamic membrane and Fenton oxidation processes.

BACKGROUND

In China, the freshwater resources per capita are low and the pollution of freshwater resources is becoming increasingly serious. Some freshwater resources are eutrophic due to N, P and other pollutants, and some have seriously exceeded the standards for the contents of heavy metals. There are dozens of pollutants, some of which are carcinogenic, teratogenic and mutagenic, threatening water safety. The conventional water treatment process involves multiple units such as coagulation, precipitation, anaerobic/aerobic biological treatment, filtration, oxidation and disinfection. Physical or physicochemical methods are used to remove turbidity and total suspended solids (TSS), and biological methods are used to degrade and remove most of the organic matter and reduce the chemical oxygen demand (CODCr) and 5-day biochemical oxygen demand (BOD5). Chemical or physicochemical methods such as ozone oxidation and catalytic oxidation are used to remove the remaining non-degradable organic matter and bacteria to meet the water production requirements. The above process is cumbersome. Some physical treatment units separate the pollutants without decomposition, so the pollutants need to be treated for a second time. Some treatment units decompose the pollutants without separation, which is only suitable for the treatment of soluble low-molecular-weight organic pollutants.

At present, membrane separation has become a hotspot in water treatment research. The preparation and application techniques of existing microfiltration membranes (MFM, pore size > 0.05 pm) and ultrafiltration membranes (UFM, pore size 2-50 nm) are maturing. The inorganic ceramic membrane has good chemical stability, resists organic solvents and strong acid/alkaline solutions, and avoids microbial degradation. It is often used for separation under the conditions of strong oxidation, high pH and high temperature in many industries. Dynamic membrane separation (DMS) is a novel membrane separation process developed on the basis of solid-phase membrane separation (SPMS). The dynamic membrane includes a base membrane and a separation layer. The base membrane is a porous material for carrying the dynamic membrane, and includes macro-porous industrial filter cloth, stainless steel wire mesh and ordinary screen, and micro-porous sintered polyvinyl chloride (PVC) tube and inorganic filter membrane. As the core of the dynamic membrane, the separation layer is a filter cake layer attached on the base membrane to perform the separation function. It is formed by precipitating certain solid or colloidal particles on the surface of the base membrane by means of cross-flow filtration (CFF) or dead-end filtration (DEF). There are many types of particles used to form the dynamic membrane, such as clay minerals and powdered activated carbon (PAC). Some substances in the treated waste liquid are also used to precipitate on the base membrane to form the dynamic membrane. For example, activated sludge in sewage is used to form a biodynamic membrane. The membrane processes all are designed to trap and separate, that is, to separate and remove the pollutant particles based on their size. Since the pollutants are concentrated on the circulation side without decomposition and degradation, the separated substances need to be treated for a second time.

The Fenton process (an advanced oxidation process) has significant advantages in the treatment of non-biodegradable pollutants. H202 produces hydroxyl radicals (OH) with high reactivity and high redox potential (up to 2.8 V) under the action of iron-containing catalysts. The non-degradable organic matter are oxidized and decomposed into low-molecular-weight organic matter or even inorganic matter, thus completely removing the non-degradable organic matter that cannot be handled by conventional wastewater treatment processes. However, for large-particle organic pollutants, due to the small contact area, the reaction efficiency and pollutants removal rate are low.

The patent Application No. 201110304246.4 discloses a dynamic membrane purification reactor and method for removing ammonia nitrogen and organic matter in reclaimed water. The ozone oxidation treatment of pollutants is independently performed, and then the adsorbing particles such as activated carbon and diatomite are added to form a dynamic membrane for filtration. The ozone oxidation and dynamic membrane filtration are performed separately. The removal of organic matter depends on the biological oxidation of breeding microorganisms, and the particles forming the dynamic membrane are used for adsorption rather than catalytic oxidation. These principles are different from the present invention.

In the patent Application No. 201310090838X, the sewage treatment method couples an organic membrane with an electro-Fenton process (EFP). The organic membrane serves as a cathode for the EFP, and no dynamic membrane is involved. In the patent Application No. 2014102125035, a Fenton reactor is combined with a ceramic membrane tube. The ceramic membrane tube is used to form a cavity, which only utilizes the excellent oxidation resistance of the ceramic membrane tube. The quartz sand filter provided at the rear part makes it clearer that the patent does not involve the dynamic membrane process and is different from the present invention. The patent Application No. 2013103936358 discloses a method for non-degradable wastewater treatment by subjecting iron precipitated by a biomembrane and a recovered hydrogen peroxide solution to a Fenton reaction. The biomembrane is a continuous thin layer formed by microorganisms attached together. This method does not involve the dynamic membrane process, and is different from the present invention.

Other similar patents use biomembranes, which are biomembrane reactor systems with similar structure. The SPMS process is used to trap and separate the remaining sludge to be discharged from the system, replacing the original separation equipment such as secondary sedimentation tank. The pollutants in the sewage are still treated by biological degradation with activated sludge. These patents do not involve the dynamic membrane process and differ from the present invention. In addition, as for patents related to photocatalytic dynamic membranes, their principles are completely different from the present invention.

SUMMARY

In the treatment of non-degradable wastewater, the total removal rate of an independent Fenton process on soluble low-molecular-weight pollutants is low, which is about 30-50%. An independent membrane separation (i.e. microfiltration (MF) and ultrafiltration (UF)) process is difficult to completely filter out the soluble low-molecular-weight pollutants, only achieving a total removal rate of 50-80%. If nanofiltration (NF) and reverse osmosis membranes are used, multiple pretreatment units are required, resulting in redundant processes and high operating costs. The present invention couples the heterogeneous Fenton oxidation and dynamic membrane processes to form a new system to cooperatively treat the non-degradable wastewater. This system integrates Fenton oxidation, dynamic membrane filtration, dynamic membrane particle adsorption and base membrane filtration steps, greatly simplifying the process units. It maintains the advantages of the two processes, and has significant effect on the removal of total suspended solids (TSS), chromaticity, chemical oxygen demand (CODCr), 5-day biological oxygen demand (BOD5) and benzene series, etc.

The present invention adopts the following technical solution: Raw materials (solution and powder) are added to a hydrogen peroxide overhead tank (1), an iron-containing ore powder mixing tank (2) and a pH adjustment overhead tank (3), respectively. The ingredients are fed in proportion to a circulation tank (4) holding non-biodegradable wastewater. The proportions of the ingredients are adjusted to meet the operating requirements of a membrane/membrane module (6). Then a circulation pump (5) is started to supply a liquid to the membrane/membrane module (6). A circulating liquid return valve is turned on to start circulating filtration operation. The operating parameters such as flow rate (L), temperature (T), pressure (P) and pH are adjusted by a detection and control device (8). In the initial 0-10 min, the effluent has poor quality, and is returned to the circulation tank (4). The normal production of water is started after the effluent meets the quality standard. A flushing cycle is determined according to the drop of a permeation flux. After the flushing, waste dynamic membrane particles together with the trapped and adsorbed pollutants form iron-containing sludge. The iron-containing sludge is discharged into a recovery tank (7) for further treatment. The system composition is shown in FIG. 1.

The iron-containing ore powder is selected from hematite powder, limonite powder, magnetite powder, iron oxide powder or iron filings according to the actual situation. The mesh number of the ore powder particles is determined based on the pore size of a base membrane to avoid clogging the pores of the base membrane. The ore powder particles are used to form a filter cake filtration type dynamic membrane. The structure of the dynamic membrane and the base membrane is shown in FIG. 2, and the membranes maintain continuous high-permeation flux operation.

No stirring device is provided in the circulation tank. Instead, the diameter of a return water outlet on a circulation side is adjusted, so that the circulation liquid hydraulically agitates, which saves energy.

The circulation pump is a water pump that allows the particles to pass, such as a slurry pump, whose allowable particle diameter is larger than the particle size of the iron-containing ore powder.

The membrane/membrane module comes in many forms, such as tubular membrane, plate membrane, multi-channel membrane and external pressure hollow fiber membrane. Because it involves particle filtration, it is generally not suitable to adopt a rolling membrane module, so as to avoid clogging the channel. The base membrane must be a MF or UF membrane resistant to pressures (0-0.5MPa) and strong oxidants, such as alumina ceramic MF membrane and titanium dioxide ceramic UF membrane.

The present invention has the following beneficial effects: The present invention couples the heterogeneous Fenton oxidation and dynamic membrane processes to form a new system to cooperatively treat the non-degradable wastewater. This system integrates Fenton oxidation, dynamic membrane filtration, dynamic membrane particle adsorption and base membrane filtration steps, greatly simplifying the process units. It maintains the advantages of the two processes, and significantly improves the removal rate of TSS, chromaticity, CODCr, BOD5 and benzene series to 80-100%. In addition, this system has simple operation and low operation costs.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of a wastewater treatment system by in site chemically oxidized dynamic membrane.

FIG. 2 is a structural diagram showing a local section of a dynamic membrane and a base membrane of a membrane/membrane module (6).

FIG. 3 is a diagram showing a gradient pore size of a dynamic membrane.

FIG. 4 is a diagram showing the morphology of a particle surface of a dynamic membrane after a reaction.

DETAILED DESCRIPTION

The present invention is described in further detail below with reference to the technical solutions and examples of the present invention.

Example 1

Hydrogen peroxide was added to a hydrogen peroxide overhead tank (1), and its pH was maintained at 3.0-5.0 to prevent decomposition before the operation of the device. 2,000-mesh hematite powder was added to an iron-containing ore powder mixing tank (2) (the pore size of a base membrane was 0.5-3.0 pm). 10% caustic soda was added to a pH adjustment overhead tank (3). The ingredients were added in proportion to a circulation tank (4) holding pesticide wastewater with high acid concentration and high chemical oxygen demand (CODCr). After a liquid level met an operating condition, a circulation pump (5) was started to supply the liquid to a membrane/membrane module (6) to start circulating filtration operation. A membrane in the module was a 19-channel ceramic microfiltration (MF) membrane with a pore size of 0.5-3.0 Pm. The ceramic membrane was placed vertically. The wastewater entered a circulation side from the bottom and exited from an upper part. Every 19 membrane tubes made up a module. A circulating liquid return valve was turned on. The operating parameters such as flow rate (L), temperature (T), pressure (P) and pH were adjusted by a detection and control device (8). The effluent in the initial 10-15 min was returned to the circulation tank (4). After a dynamic membrane was formed, the quality of the effluent was gradually improved due to Fenton oxidation and adsorption. After the water quality met the standard, normal water production began. A permeation flux was recorded, and when the permeation flux dropped to about 70% of normal permeation flux, the normal operation time was recorded, and the dynamic membrane was flushed for 30-90 s. Then the periodic operation was implemented to discharge acceptable water. The removal rate of chromaticity and CODCr reached more than 80%. After the flushing, the waste hematite particles and the trapped and adsorbed pollutants formed iron-containing sludge. The iron-containing sludge was discharged from a sewage outlet at the bottom of the circulation side into a recovery tank (7) for further treatment.

Example 2

Hydrogen peroxide and an appropriate amount of acid were added to a hydrogen peroxide overhead tank (1), and their pH was maintained at 3.0-5.0 to prevent the hydrogen peroxide from decomposition before operation. 0.1-0.5 pm iron oxide powder was added to an iron-containing ore powder mixing tank (2) (the pore size of a base membrane was 0.05-0.5 Pm). 10% hydrochloric acid was added to a pH adjustment overhead tank (3). The ingredients were added in proportion to a circulation tank (4) holding flax production wastewater with high alkalinity. A circulation pump (5) was started to supply the liquid to a membrane/membrane module (6) to start circulating filtration operation. A membrane in the module was a plate-type ceramic microfiltration (MF) membrane with a pore size of 0.05-0.5 pm. The ceramic membrane was placed horizontally, and each ceramic membrane made up a unit. A circulating liquid return valve was turned on. The operating parameters such as flow rate (L), temperature (T), pressure (P) and pH were adjusted by a detection and control device (8). The effluent in the initial 8-10 min was returned to the circulation tank (4). After a dynamic membrane was formed in 10-15 min, the quality of the effluent was improved and met the standard due to Fenton oxidation and adsorption. Then normal water production began. When a permeation flux dropped to about 75% of normal permeation flux, the dynamic membrane was flushed for 30-90 s. Then the periodic operation was implemented. The removal rate of chromaticity, total suspended solids (TSS) and CODCr reached more than 85%. After the flushing, a small amount of iron oxide particles and the trapped and adsorbed organic matter formed sludge, and the sludge was discharged into a recovery tank (7) for further treatment.

Example 3

Hydrogen peroxide and an appropriate amount of hydrochloric acid were added to a hydrogen peroxide overhead tank (1), and their pH was maintained at 3.0-5.0 to prevent the hydrogen peroxide from decomposition. 0.05-0.08 pm nano-iron powder was added to an iron containing ore powder mixing tank (2) (the pore size of a base membrane was 0.01-0.05 pm). 10% hydrochloric acid was added to a pH adjustment overhead tank (3). The ingredients were added in proportion to a circulation tank (4) holding alkaline printing and dyeing wastewater. A slurry pump (5) was started to supply the liquid to a membrane/membrane module (6) to start circulating filtration operation. A membrane in the module was a 37-channel ceramic ultrafiltration (UF) membrane with a pore size of 0.01-0.05 pm. Every 19 ceramic membrane tubes made up a unit. A circulating liquid return valve was turned on. The operating parameters such as flow rate (L), temperature (T), pressure (P) and pH were adjusted by a detection and control device (8). The effluent in the initial 5-8 min was returned to the circulation tank (4). After a dynamic membrane was formed, the quality of the effluent was gradually improved due to Fenton oxidation and filtration and adsorption by the dynamic membrane. After the water quality met the standard, normal water production began. When a permeation flux dropped to about 70% of normal permeation flux, the dynamic membrane was flushed for 60-90 s. Then the periodic operation was implemented. The removal rate of chromaticity, TSS, CODCr and benzene series reached more than 90%. In this example, a small amount of sludge was formed, which was also discharged into a recovery tank (7) for further treatment.

Claims

1. A non-biodegradable wastewater treatment system, comprising a hydrogen peroxide overhead tank (1), an iron-containing ore powder mixing tank (2), a pH adjustment overhead tank (3), a circulation tank (4), a circulation pump (5), a membrane/membrane module (6), a recovery tank (7) and a detection and control device (8) for parameters such as flow rate (L), temperature (T), pressure (P) and pH, wherein outlets of the hydrogen peroxide overhead tank, the iron-containing ore powder mixing tank and the pH adjustment overhead tank are all connected to the circulation tank; an outlet of the circulation tank is connected to the circulation pump; an outlet of the circulation pump is connected to a circulation side of the membrane/membrane module, and an outlet pipeline of the circulation pump is provided with the detection and control device for parameters such as flow rate (L), temperature (T), pressure (P) and pH; an outlet on the circulation side of the membrane/membrane module is connected to the circulation tank; the circulation side of the membrane/membrane module is provided with a sewage outlet at the bottom; the sewage outlet is connected to the recovery tank; water discharged on a discharge side of the membrane/membrane module is discharged from the system.

2. The wastewater treatment system according to claim 1, wherein the outlets of the hydrogen peroxide overhead tank (1), the iron-containing ore powder mixing tank (2) and the pH adjustment overhead tank (3) are all connected to the circulation tank (4); the outlet of the circulation tank (4) is connected to the circulation pump (5); the outlet of the circulation pump is connected to the circulation side of the membrane/membrane module (6); the membrane/membrane module uses a solid-phase membrane, which is a microfiltration (MF) or ultrafiltration (UF) membrane resistant to the corrosion of strong oxidants such as hydrogen peroxide; the outlet on the circulation side is connected to the circulation tank (4).

3. The wastewater treatment system according to claim 2, wherein the outlets of the hydrogen peroxide overhead tank (1), the iron-containing ore powder mixing tank (2) and the pH adjustment overhead tank (3) are all connected to the circulation tank (4); a flow rate of the pH adjustment overhead tank is adjusted based on the wastewater, and the pH in the circulation tank is adjusted to suit a Fenton oxidation reaction; flow rates of the hydrogen peroxide overhead tank (1) and the iron-containing ore powder mixing tank (2) are adjusted simultaneously; ingredients are continuously fed into the circulation tank (4) at a reasonable ratio; after continuous circulating operation begins, a condition for the efficient progress of the Fenton oxidation reaction for degrading a low-molecular-weight pollutant in the wastewater is formed in the circulation tank (4) and on the circulation side of the membrane/membrane module (6).

4. The wastewater treatment system according to claim 3, wherein when the suitable condition for the Fenton oxidation reaction is formed, a flow rate and pressure of the circulation pump (5) are adjusted to reasonably match a mesh number of a powder added in the iron containing ore powder tank (2); an on-line chemical oxidation dynamic membrane is formed on a base membrane of the membrane/membrane module (6), which is used to filter a particulate or high-molecular-weight pollutant; the thickness of the dynamic membrane is affected by the filtration operating condition and sewage quality.

5. The wastewater treatment system according to claim 3 or claim 4, wherein pores of the in site chemically-oxidized dynamic membrane continuously consume the iron-containing powder with the progress of the Fenton oxidation reaction; a gradient pore size is formed from a surface layer to a deep layer of the dynamic membrane and from large pores to small pores; the gradient pore size is smaller than a pore size of the base membrane, and the removal rate of total suspended solids (TSS) in the effluent is significantly higher than that of the base membrane alone; because the sewage repeatedly flows through the dynamic membrane, the contacts are increased to better the mixing effect; therefore, the reaction efficiency is higher than that of ordinary heterogeneous Fenton oxidation; pits are formed on a surface of the iron-containing powder due to the Fenton reaction, resulting in obvious adsorption of pollutants in the wastewater, further reducing the chromaticity, TSS, chemical oxygen demand (CODCr), 5-day biological oxygen demand (BOD5) and benzene series in the effluent; a small amount of iron containing sludge is discharged into the recovery tank (7) for further treatment.