What are MBR membranes and their combined processes?
What is MBR process?
Membrane Bioreactor ( Membrance Bioreactor Reactor, referred to as MBR) is a new process of biological treatment of wastewater by the combination of membrane separation and biological treatment technology.
There are many kinds of membranes, according to the separation mechanism, there are reaction membranes, ion exchange membranes, permeable membranes, etc.; according to the classification of the nature of the membrane, there are natural membranes (bio-membranes) and synthetic membranes (organic membranes and inorganic membranes); according to the classification of the structure of the membrane type, there are flat plate type, tubular, spiral and hollow fibre type and so on.
MBR process in the domestic research status
Since the 80’s, the membrane bioreactor is getting more and more attention, becoming one of the hot spots of research. At present, the technology has been used in the United States, Germany, France and Egypt and other countries, the scale from 6m3 / d to 13000m3 / d varies.
China’s research on MBR is less than ten years, but the progress is very rapid. Domestic research on MBR can be broadly divided into several aspects:
(1) to explore different biological treatment processes and membrane separation unit combination form, biological reaction treatment process from activated sludge method to expand to the contact oxidation method, biofilm method, activated sludge and biofilm combined with the composite process, two-phase anaerobic process;
(2) Research on factors, mechanisms and mathematical models affecting the treatment effect and membrane contamination, explore suitable operating conditions and process parameters, reduce membrane contamination as much as possible, and improve the treatment capacity and operational stability of membrane modules;
(3) Expand the scope of application of MBR, MBR research objects from domestic wastewater to expand to high-concentration organic wastewater (food wastewater, beer wastewater) and difficult to degrade industrial wastewater (petrochemical wastewater, printing and dyeing wastewater, etc.), but the treatment of domestic wastewater is the main.
What are the characteristics of MBR process?
Compared with traditional biochemical water treatment technology, MBR has the following main features:
1, efficient solid-liquid separation, the separation effect is much better than the traditional sedimentation tank, the water quality is good, the effluent suspended solids and turbidity is close to zero, can be directly reused, to achieve the sewage resources.
2, the high efficiency of the membrane retention effect, so that microorganisms are completely retained in the bioreactor, to achieve the reactor hydraulic retention time (HRT) and sludge age (SRT) of the complete separation, flexible and stable operation control.
3、Because MBR will be the traditional wastewater treatment of aeration tank and two sedimentation tanks into one, and replace all the process facilities of tertiary treatment, so it can greatly reduce the footprint, saving civil investment.
4, conducive to the retention and propagation of nitrifying bacteria, high nitrification efficiency of the system. Through the change of operation mode, it can also have the function of ammonia removal and phosphorus removal.
5, because the age of mud can be very long, thus greatly improving the degradation efficiency of difficult to degrade organic matter.
6、The reactor operates under high volume load, low sludge load and long sludge age, the remaining sludge production is very low, because the sludge age can be infinitely long, theoretically zero sludge discharge can be realised.
7, the system realises PLC control, convenient operation and management.
What are the components of MBR process?
The commonly mentioned membrane – bioreactor is actually a general term for three types of reactors:
Aeration Membrane Bioreactor (AMBR);
Extractive Membrane Bioreactor (EMBR);
③ solid-liquid separation membrane – bioreactor (Solid/Liquid Separation MembraneBioreactor, SLSMBR, abbreviated MBR).
1. Aeration membrane
Aeration Membrane – Bioreactor (AMBR) using breathable dense membrane (such as silicone rubber membrane) or microporous membrane (such as hydrophobic polymeric membrane), plate or hollow fibre-type components, in keeping the partial pressure of the gas is lower than the bubble point (Bubble Point) in the case of bubble-free aeration can be achieved to the bioreactor.
The process is characterised by improved contact time and oxygen transfer efficiency, which is conducive to the control of the aeration process, and is not affected by the factors of bubble size and residence time in traditional aeration.
2.Extraction membrane
Extractive Membrane – Bioreactor, also known as EMBR (Extractive Membrane Bioreactor). Because of the high acidity and alkalinity or the presence of toxic substances to organisms, some industrial wastewater is not suitable for direct contact with microorganisms to deal with; when the wastewater contains volatile toxic substances, if you use the traditional aerobic biological treatment process, pollutants are easy to volatilise the aeration airflow with the volatility of the gas lift phenomenon occurs, not only is the treatment effect is very unstable, but also cause atmospheric pollution.
In order to solve these technical difficulties, the British scholar Livingston research and development of the EMB. wastewater and activated sludge is separated by the membrane, wastewater in the membrane flow, and contains some kind of specialised bacteria activated sludge in the membrane flow, wastewater and microorganisms are not in direct contact with the organic pollutants can be selectively through the membrane is the other side of the microorganisms degradation.
As the bioreactor unit and wastewater recycling unit on both sides of the extraction membrane are independent of each other, the water flow of each unit has little influence on each other, and the nutrients and microbial survival conditions in the bioreactor are not affected by the quality of wastewater, which makes the water treatment effect stable. The operating conditions of the system, such as HRT and SRT, can be controlled in the optimal range to maintain the maximum rate of pollutant degradation.
3.Solid-liquid separation membrane
Solid-liquid separation membrane – bioreactor is the most widely researched class of membrane – bioreactor in the field of water treatment, is a membrane separation process to replace the traditional activated sludge method in the secondary sedimentation tank of water treatment technology. It refluxes solid organic matter back into the reactor through a membrane module, and then discharges the treated organic water. The type of membrane separation bioreactor can be classified according to the location of the membrane module and bioreactor there are integrated membrane bioreactor, discrete membrane bioreactor, composite membrane bioreactor.
In the traditional wastewater biological treatment technology, the mud-water separation in the secondary sedimentation tank is completed by gravity, and its separation efficiency depends on the sedimentation performance of activated sludge, the better the sedimentation, the higher the mud-water separation efficiency. The settling property of sludge depends on the operating condition of the aeration tank, and the operating condition of the aeration tank must be strictly controlled to improve the settling property of sludge, which limits the scope of application of the method. Due to the requirement of solid-liquid separation in the secondary sedimentation tank, the sludge in the aeration tank can not maintain a high concentration, generally around 1.5~3.5g/L, thus limiting the biochemical reaction rate. Hydraulic retention time (HRT) and sludge age (SRT) are interdependent, and increasing the volumetric load and reducing the sludge load often form a contradiction. The system also produces a large amount of residual sludge during operation, and its disposal cost accounts for 25% to 40% of the operating cost of the wastewater treatment plant. The traditional activated sludge treatment system is also prone to sludge expansion, the effluent contains suspended solids, the effluent water quality deterioration.
In view of the above problems, MBR combines the membrane separation technology in separation engineering with the traditional wastewater biological treatment technology, which greatly improves the solid-liquid separation efficiency; and due to the increase of the concentration of activated sludge in the aeration tank and the emergence of effective bacteria (especially the dominant flora) in the sludge, it improves the rate of biochemical reaction; at the same time, it reduces the amount of residual sludge generated by lowering the F/M ratio (or even 0), which basically solves the problems existing in the traditional activated sludge method. At the same time, by reducing the F/M ratio to reduce the amount of residual sludge production (even 0), it basically solves many outstanding problems existing in the traditional activated sludge method.
What are the types of MBR processes?
According to the combination of membrane module and bioreactor, membrane-bioreactor can be divided into three basic types: split, integrated and composite. (The following discussions are all about solid-liquid separation type membrane-bioreactors)
1. Separation type
The membrane module and the bioreactor are set up separately.
The mixed liquid in the bioreactor is pressurised by the circulating pump and then pumped to the filtration end of the membrane module. Under pressure, the liquid in the mixed liquid passes through the membrane and becomes the treated water of the system; solids and macromolecules are retained by the membrane, and then flow back to the bioreactor along with the concentrated liquid.
2. Integral type
The membrane module is placed inside the bioreactor. Inlet water into the membrane – bioreactor, where most of the pollutants are removed by the activated sludge in the mixture, and then filtered out of the water by the membrane under external pressure.
This form of membrane – bioreactor due to the elimination of the mixed liquid circulation system, and by the pumping out of water, energy consumption is relatively low; occupies a more compact than the split type, in recent years in the field of water treatment has received special attention. But the general membrane flux is relatively low, easy to membrane contamination, membrane contamination is not easy to clean and replace.
3. Composite
The form also belongs to the one-piece membrane – bioreactor, the difference is in the bioreactor with packing, thus forming a composite membrane – bioreactor, changing some of the characteristics of the reactor.
What are the combined MBR processes?
In order to achieve better purification of wastewater, the A2O process and MBR process are often combined to form a new system.
1.A2O-MBR process
Coking wastewater is produced in the process of coking, high-temperature dry distillation, gas purification and recovery, etc. It contains volatile phenols, polycyclic aromatic hydrocarbons (PAHs), oxygen, sulphur and nitrogen heterocyclic compounds and other characteristics, as well as a high COD value, a high phenol value and a high content of ammonia nitrogen.
Although the A2O process is one of the most effective and widely used methods for treating coking wastewater. However, the effluent from this process is difficult to meet the national comprehensive wastewater discharge standards.The emergence of the combined A2O-MBR process utilises the advantages of the membrane process to further improve the effluent quality.
2.A2OA-MBR process
A2O/A-MBR process is commonly used in denitrification and phosphorus removal, the process is based on the A2O process and then set up a level of anoxic tank, wastewater through the carbon membrane to complete the biological denitrification and phosphorus removal, and then the use of the second anoxic tank for the endogenous denitrification, to further remove the TN, and then the use of membrane tanks to ensure the role of aerobic aeration of the effluent.
3.AO-MBR process
In the AO-MBR system, the wastewater that is separated from suspended solids and debris flows into the adjustment tank to equalise the water quality and quantity, and then enters the sedimentation tank for solid-liquid separation. The clear liquid from the upper stream flows into the MBR treatment tank, which is designed as an AO system: in the front section, the influent stream water is fully mixed to carry out biological denitrification for nitrogen removal, and in the back section, biological degradation and nitrification are carried out, while alkali is added, and the treated wastewater is discharged directly.
4.3A-MBR process
3A-MBR process is a membrane bioreactor technology and the traditional anaerobic, anoxic, aerobic process combined with a new process, often used in the de-nitrogenation and de-phosphorisation of wastewater purification, highlighting the characteristics of biological phosphorus denitrification process and promote each other, so that the entire system of phosphorus denitrification and the removal of organic matter in the efficiency of the maximum effect.
Technical characteristics
Fully improve the high concentration of activated sludge in the membrane reaction pool, promote the formation of dominant nitrifying bacteria communities, improve nitrification efficiency, so that ammonia and nitrogen removal is complete; through automatic control, optimize the membrane bioreactor sludge discharge time, reasonable control of the age of the mud, improve the concentration of slow-growing nitrifying bacteria, denitrifying bacteria and other specialised biochemical bacteria in the system, improve the effect of organic matter and phosphorus removal and denitrification; to achieve aerobic sludge discharge, to avoid secondary release of phosphorus. Improve the phosphorus removal rate.
5.A(2A)O-MBR process
A(2A)O-MBR process adopts the process flow in the order of anaerobic, the first anoxic, the second anoxic, aerobic and membrane tank. Characterised by two anoxic zones in the A2O-MBR process, the function of the two anoxic zones is regulated by controlling the influent and return points.
The water intake method adopts two points of water intake in the anaerobic zone and the first anoxic zone. The reflux method adopts three-stage two-point reflux, the first stage is the mixed liquid of membrane pool refluxed to the front of aerobic zone; the second stage is the mixed liquid of aerobic zone refluxed to the first anoxic zone and the second anoxic zone; and the third pole is the mixed liquid of the first anoxic zone mixed flowed to the anaerobic zone.
6.SBR-MBR process
SBR-MBR process is a combination of SBR and MBR to form a process with the advantages of both, SBR is an improved activated sludge treatment process, the use of membrane components of the retention and filtration, the reaction of the microorganisms in the reaction can be maximally reproduced, conducive to the growth of nitrifying bacteria, sludge biological activity, adsorption and degradation of organic substances with high capacity.
SBR-MBR process has five systems of influent, anaerobic, aerobic and sedimentation, SBR and MBR work to provide conditions for biological dephosphorisation and nitrogen removal, and can also be controlled according to the need to deal with different wastewaters, the use of membrane separation of drainage water, to improve the efficiency of wastewater purification, but also saves time.
| Phosphonates Antiscalants, Corrosion Inhibitors and Chelating Agents | |
| Amino Trimethylene Phosphonic Acid (ATMP) | CAS No. 6419-19-8 |
| 1-Hydroxy Ethylidene-1,1-Diphosphonic Acid (HEDP) | CAS No. 2809-21-4 |
| Ethylene Diamine Tetra (Methylene Phosphonic Acid) EDTMPA (Solid) | CAS No. 1429-50-1 |
| Diethylene Triamine Penta (Methylene Phosphonic Acid) (DTPMPA) | CAS No. 15827-60-8 |
| 2-Phosphonobutane -1,2,4-Tricarboxylic Acid (PBTC) | CAS No. 37971-36-1 |
| 2-Hydroxy Phosphonoacetic Acid (HPAA) | CAS No. 23783-26-8 |
| HexaMethyleneDiamineTetra (MethylenePhosphonic Acid) HMDTMPA | CAS No. 23605-74-5 |
| Polyamino Polyether Methylene Phosphonic Acid(PAPEMP) | |
| Bis(HexaMethylene Triamine Penta (Methylene Phosphonic Acid)) BHMTPMP | CAS No. 34690-00-1 |
| Hydroxyethylamino-Di(Methylene Phosphonic Acid) (HEMPA) | CAS No. 5995-42-6 |
| Salts of Phosphonates | |
| Tetra sodium salt of Amino Trimethylene Phosphonic Acid (ATMP•Na4) | CAS No. 20592-85-2 |
| Penta sodium salt of Amino Trimethylene Phosphonic Acid (ATMP•Na5) | CAS No. 2235-43-0 |
| Mono-sodium of 1-Hydroxy Ethylidene-1,1-Diphosphonic Acid (HEDP•Na) | CAS No. 29329-71-3 |
| (HEDP•Na2) | CAS No. 7414-83-7 |
| Tetra Sodium Salt of 1-Hydroxy Ethylidene-1,1-Diphosphonic Acid (HEDP•Na4) | CAS No. 3794-83-0 |
| Potassium salt of 1-Hydroxy Ethylidene-1,1-Diphosphonic Acid (HEDP•K2) | CAS No. 21089-06-5 |
| Ethylene Diamine Tetra (Methylene Phosphonic Acid) Pentasodium Salt (EDTMP•Na5) | CAS No. 7651-99-2 |
| Hepta sodium salt of Diethylene Triamine Penta (Methylene Phosphonic Acid) (DTPMP•Na7) | CAS No. 68155-78-2 |
| Sodium salt of Diethylene Triamine Penta (Methylene Phosphonic Acid) (DTPMP•Na2) | CAS No. 22042-96-2 |
| 2-Phosphonobutane -1,2,4-Tricarboxylic Acid, Sodium salt (PBTC•Na4) | CAS No. 40372-66-5 |
| Potassium Salt of HexaMethyleneDiamineTetra (MethylenePhosphonic Acid) HMDTMPA•K6 | CAS No. 53473-28-2 |
| Partially neutralized sodium salt of bis hexamethylene triamine penta (methylene phosphonic acid) BHMTPH•PN(Na2) | CAS No. 35657-77-3 |
| Polycarboxylic Antiscalant and Dispersant | |
| Polyacrylic Acid (PAA) 50% 63% | CAS No. 9003-01-4 |
| Polyacrylic Acid Sodium Salt (PAAS) 45% 90% | CAS No. 9003-04-7 |
| Hydrolyzed Polymaleic Anhydride (HPMA) | CAS No. 26099-09-2 |
| Copolymer of Maleic and Acrylic Acid (MA/AA) | CAS No. 26677-99-6 |
| Acrylic Acid-2-Acrylamido-2-Methylpropane Sulfonic Acid Copolymer (AA/AMPS) | CAS No. 40623-75-4 |
| TH-164 Phosphino-Carboxylic Acid (PCA) | CAS No. 71050-62-9 |
| Biodegradable Antiscalant and Dispersant | |
| Sodium of Polyepoxysuccinic Acid (PESA) | CAS No. 51274-37-4 |
| CAS No. 109578-44-1 | |
| Sodium Salt of Polyaspartic Acid (PASP) | CAS No. 181828-06-8 |
| CAS No. 35608-40-6 | |
| Biocide and Algicide | |
| Benzalkonium Chloride(Dodecyl Dimethyl Benzyl ammonium Chloride) | CAS No. 8001-54-5, |
| CAS No. 63449-41-2, | |
| CAS No. 139-07-1 | |
| Isothiazolinones | CAS No. 26172-55-4, |
| CAS No. 2682-20-4 | |
| Tetrakis(hydroxymethyl)phosphonium sulfate(THPS) | CAS No. 55566-30-8 |
| GLUTARALDEHYDE | CAS No. 111-30-8 |
| Corrosion Inhibitors | |
| Sodium salt of Tolyltriazole (TTA•Na) | CAS No. 64665-57-2 |
| Tolyltriazole (TTA) | CAS No. 29385-43-1 |
| Sodium salt of 1,2,3-Benzotriazole (BTA•Na) | CAS No. 15217-42-2 |
| 1,2,3-Benzotriazole (BTA) | CAS No. 95-14-7 |
| Sodium salt of 2-Mercaptobenzothiazole (MBT•Na) | CAS No. 2492-26-4 |
| 2-Mercaptobenzothiazole (MBT) | CAS No. 149-30-4 |
| Oxygen Scavenger | |
| Cyclohexylamine | CAS No. 108-91-8 |
| Morpholine | CAS No. 110-91-8 |
| Other | |
| Sodium Diethylhexyl Sulfosuccinate | CAS No. 1639-66-3 |
| Acetyl chloride | CAS No. 75-36-5 |
| TH-GC Green Chelating Agent (Glutamic Acid,N,N-diacetic Acid, Tetra Sodium Salt) | CAS No. 51981-21-6 |