Introduction to MBR and Seven Combined Processes

Membrane Bioreactor (MBR) is a new process for wastewater biological treatment that combines membrane separation and biological treatment technology.

There are various types of membranes, classified according to their separation mechanisms, including reaction membranes, ion exchange membranes, permeation membranes, etc; According to the nature of membranes, there are natural membranes (biofilms) and synthetic membranes (organic and inorganic membranes); According to the structural types of membranes, there are flat, tubular, spiral, and hollow fiber types.

Research status of MBR process in China

Since the 1980s, membrane bioreactors have received increasing attention and become one of the research hotspots. At present, this technology has been applied in more than ten countries, including the United States, Germany, France, and Egypt, with scales ranging from 6m3/d to 13000m3/d.

The research on MBR in China has been less than a decade, but progress has been very rapid. The research on MBR in China can be roughly divided into several aspects:

(1) Exploring the combination forms of different biological treatment processes and membrane separation units, the biological reaction treatment process has expanded from activated sludge method to contact oxidation method, biofilm method, compound bench process combining activated sludge and biofilm, and two-phase anaerobic process;

(2) Research on factors, mechanisms, and mathematical models that affect treatment efficiency and membrane fouling, exploring appropriate operating conditions and process parameters, minimizing membrane fouling as much as possible, and improving the treatment capacity and operational stability of membrane components;

(3) Expanding the application scope of MBR, the research object of MBR has expanded from domestic sewage to high concentration organic wastewater (food wastewater, beer wastewater) and difficult to degrade industrial wastewater (petrochemical wastewater, printing and dyeing wastewater, etc.), but mainly focuses on the treatment of domestic sewage.

What are the characteristics of MBR process?

Compared with traditional biochemical water treatment technologies, MBR has the following main characteristics:

1. The separation effect of solid-liquid separation is much better than that of traditional sedimentation tanks. The effluent quality is good, and the suspended solids and turbidity of the effluent are close to zero, which can be directly reused, achieving sewage resource utilization.

2. The interception effect of the membrane enables microorganisms to be completely trapped in the bioreactor, achieving complete separation of hydraulic retention time (HRT) and sludge age (SRT), and flexible and stable operation control.

3. Due to the integration of traditional sewage treatment aeration tanks and secondary sedimentation tanks in MBR, and the replacement of all process facilities for tertiary treatment, it can significantly reduce the floor area and save civil engineering investment.

4. It is conducive to the interception and reproduction of nitrifying bacteria, and the system has high nitrification efficiency. By changing the operating mode, it can also have the functions of ammonia and phosphorus removal.

5. Due to the fact that the mud age can be very long, the degradation efficiency of difficult to degrade organic compounds is greatly improved.

6. The reactor operates at high volume load, low sludge load, and long sludge age, resulting in extremely low excess sludge production. Due to the infinite sludge age, theoretically zero sludge discharge can be achieved.

7. The system achieves PLC control, making operation and management convenient.

What are the components of MBR process?

The commonly mentioned membrane bioreactors are actually a collective term for three types of reactors:

① Aeration Membrane Bioreactor (AMBR);

② Extractive Membrane Bioreactor (EMBR);

③ Solid/Liquid Separation Membrane Bioreactor (SLSMBR).

Aeration membrane

Aeration membrane - The bioreactor (AMBR) uses a breathable dense membrane (such as silicone rubber membrane) or a microporous membrane (such as hydrophobic polymer membrane), with plate or hollow fiber components, to achieve bubbleless aeration into the bioreactor while maintaining gas partial pressure below the Bubble Point.

The characteristic of this process is that it improves contact time and oxygen transfer efficiency, which is conducive to the control of the aeration process and is not affected by factors such as bubble size and residence time in traditional aeration.

Extraction membrane

Extractive Membrane Bioreactor, also known as EMBR (Extractive Membrane Bioreactor). Due to high acidity or the presence of toxic substances to organisms, some industrial wastewater should not be treated by direct contact with microorganisms; When wastewater contains volatile toxic substances, if traditional aerobic biological treatment processes are used, pollutants are prone to volatilization with the aeration airflow, resulting in gas extraction. Not only is the treatment effect unstable, but it also causes atmospheric pollution.

To address these technical challenges, British scholar Livingston has developed EMB. Wastewater and activated sludge are separated by a membrane, and wastewater flows inside the membrane, while activated sludge containing certain specific bacteria flows outside the membrane. Wastewater does not come into direct contact with microorganisms, and organic pollutants can be selectively degraded by microorganisms on the other side through the membrane.

Due to the independent nature of the bioreactor units and wastewater circulation units on both sides of the extraction membrane, the water flow in each unit has little interaction with each other. Nutrients and microbial survival conditions in the bioreactor are not affected by wastewater quality, resulting in stable water treatment efficiency. The operating conditions of the system, such as HRT and SRT, can be controlled within a relatively optimal range to maintain a high rate of pollutant degradation.

Solid-liquid separation membrane

Solid liquid separation membrane bioreactor is a type of membrane bioreactor that has been extensively and deeply studied in the field of water treatment. It is a water treatment technology that uses membrane separation process to replace the secondary sedimentation tank in traditional activated sludge method. It reflux solid organic matter into the reactor through membrane components, and then discharge the treated organic water. The types of membrane separation bioreactors can be classified according to the position of membrane components and bioreactors, including integrated membrane bioreactors, separated membrane bioreactors, and composite membrane bioreactors.

In traditional wastewater biological treatment technology, the separation of sludge and water in the secondary sedimentation tank is completed by gravity, and its separation efficiency depends on the settling performance of activated sludge. The better the sedimentation, the higher the separation efficiency of sludge and water. The settling ability of sludge depends on the operating conditions of the aeration tank, and improving the settling ability of sludge requires strict control of the operating conditions of the aeration tank, which limits the applicability of this method. Due to the requirements for solid-liquid separation in the secondary sedimentation tank, the sludge in the aeration tank cannot maintain a high concentration, usually around 1.5-3.5g/L, which limits the biochemical reaction rate. The hydraulic retention time (HRT) and sludge age (SRT) are interdependent, and there is often a contradiction between increasing volumetric load and reducing sludge load. During the operation of the system, a large amount of excess sludge is generated, and its disposal cost accounts for 25% to 40% of the operating cost of the sewage treatment plant. Traditional activated sludge treatment systems are also prone to sludge bulking, resulting in suspended solids in the effluent and deteriorating water quality.

In response to the above issues, MBR organically combines membrane separation technology in separation engineering with traditional wastewater biological treatment technology, greatly improving the solid-liquid separation efficiency; And due to the increase in the concentration of activated sludge in the aeration tank and the emergence of particularly effective bacteria (especially dominant bacterial groups) in the sludge, the biochemical reaction rate has been increased; At the same time, by reducing the F/M ratio to reduce the production of excess sludge (even to 0), many prominent problems in traditional activated sludge methods have been basically solved.

What are the types of MBR processes?

According to the combination of membrane components and bioreactors, membrane bioreactors can be divided into three basic types: split type, integrated type, and composite type. (The following discussions are all solid-liquid separation membrane bioreactors)

Split type

Separate the membrane components from the bioreactor.

The mixed liquid in the bioreactor is pressurized by a circulating pump and 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; Solid substances, macromolecular substances, etc. are intercepted by the membrane and returned to the bioreactor with the concentrated solution.

Integrated

Place the membrane module inside the bioreactor. The influent enters the membrane bioreactor, where most of the pollutants are removed by the activated sludge in the mixed solution, and then the effluent is filtered by the membrane under external pressure.

This form of membrane bioreactor eliminates the need for a mixed liquid circulation system and relies on suction for effluent, resulting in relatively low energy consumption; The land occupation is more compact than the split type, and has received special attention in the field of water treatment in recent years. However, the membrane flux is generally relatively low, making it prone to membrane fouling. After membrane fouling, it is not easy to clean and replace.

Composite

Formally, it also belongs to an integrated membrane bioreactor, but the difference is that adding fillers inside the bioreactor forms a composite membrane bioreactor, which changes certain characteristics of the reactor.

What combination processes do MBR have?

In order to achieve better purification efficiency of wastewater, A2O process and MBR process are often combined into a new system.

A2O-MBR process

Coking wastewater is generated during processes such as coking, high-temperature distillation, gas purification, and recovery. It contains volatile phenols, polycyclic aromatic hydrocarbons, oxygen, sulfur, nitrogen heterocyclic compounds, as well as high COD value, high phenol value, and high content of ammonia nitrogen.

Although the A2O process is one of the more effective and widely used methods for treating coking wastewater. However, the effluent from this process is difficult to meet the national comprehensive sewage discharge standards. The emergence of A2O-MBR combined process utilizes the advantages of membrane process to further improve the effluent quality.

A2OA-MBR process

The A2O/A-MBR process is commonly used for nitrogen and phosphorus removal. This process is based on the A2O process by setting up a secondary anoxic tank. After the wastewater undergoes biological nitrogen and phosphorus removal through a carbon membrane, the secondary anoxic tank is used for endogenous denitrification to further remove TN. Afterwards, the aerobic aeration of the membrane tank is used to ensure the effluent.

AO-MBR process

In the AO-MBR system, the wastewater that has been separated from suspended solids and debris flows into the regulating tank to balance the water quality and quantity, and then enters the sedimentation tank for solid-liquid separation. The upstream clear water flows into the MBR treatment tank at night, and the MBR treatment tank is designed as an AO system. In the front section, the incoming water is fully mixed for biological denitrification and denitrification, while in the rear section, biodegradation and nitrification are carried out. At the same time, alkali is added, and the treated wastewater is directly discharged.

3A MBR process

The 3A MBR process is a new process that combines membrane bioreactor technology with traditional anaerobic, anoxic, and aerobic processes. It is often used for the purification of nitrogen and phosphorus removal wastewater, highlighting the mutual promotion between the characteristics and biological phosphorus and nitrogen removal processes, achieving greater efficiency in phosphorus and nitrogen removal and organic matter removal throughout the entire system.

Technical characteristics

Fully improve the high concentration activated sludge in the membrane reaction tank, promote the formation of dominant nitrifying bacterial communities, improve nitrification efficiency, and completely remove ammonia nitrogen; By automatic control, optimizing the sludge discharge time of the membrane bioreactor, reasonably controlling the sludge age, increasing the concentration of slow-growing nitrifying bacteria, denitrifying bacteria, and other specialized biochemical bacteria in the system, and improving the effectiveness of organic matter and phosphorus and nitrogen removal; Realize aerobic sludge discharge, avoid secondary release of phosphorus, and improve phosphorus removal rate.

A (2A) O-MBR process

The process flow used in the A (2A) O-MBR process is anaerobic, stage anoxic, second stage anoxic, aerobic, and membrane tank. The gas characteristic is to set up two stages of anoxic zones in the A2O-MBR process, and adjust the function of the two stages of anoxic zones by controlling the inlet and return points.

The water inlet method adopts two points: anaerobic zone and anaerobic zone. The reflux method adopts a three stage two point reflux, where the mixed liquid in the membrane tank flows back to the front end of the aerobic system; The second stage is when the mixed liquid in the aerobic zone flows back to the anoxic zone and the second anoxic zone, respectively; The third pole is the mixing of the mixture from the anaerobic zone to the anaerobic zone.

SBR-MBR process

The SBR-MBR process is a combination of SBR and MBR, which has the advantages of both. SBR is an improved activated sludge treatment process that utilizes the interception and filtration effect of membrane components. Microorganisms in the reaction can reproduce to a large extent, which is conducive to the growth of nitrifying bacteria. The sludge has high biological activity and strong ability to adsorb and degrade organic matter.

The SBR-MBR process has five systems: influent, anaerobic, aerobic, and sedimentation. The working methods of SBR and MBR provide conditions for biological phosphorus and nitrogen removal, and can be controlled according to the needs of treating different wastewater. Membrane separation and drainage are used to improve the purification efficiency of wastewater and save time.

The above is the introduction of MBR and seven combination processes that Hongjie Water brings to everyone. We hope it can help you! 

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