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First of all, MBBR "embedded transformation" can embed the MBBR system into the original activated sludge system, and combine it with the existing process to upgrade the original pool without increasing the capacity of the original plant. It saves space and has relatively small investment and operating costs. .
Secondly, the MBBR upgrading and renovation also has the characteristics of sustainable upgrade. For example, a sewage treatment plant in the north underwent a second standard upgrade by changing the original main treatment process A2/O+MBBR to Bardenpho+MBBR. The effluent was upgraded from Class A to surface level IV standard without the need for new advanced treatment facilities. That is to say, the average TN value of the effluent is 10 mg/L.
Coupled with its good nitrogen and phosphorus removal effects, the MBBR process has long become one of the important technologies for domestic standard improvement and transformation.
However, if we want to apply the MBBR process to the standard improvement and transformation process and run it successfully, we must solve two key issues that affect the treatment effect of the MBBR process during the later operation:
How to choose the appropriate media to maximize the efficiency of the reactor?
How to solve the problem of media accumulation and blockage during MBBR operation?
One of the key factors for the successful application of MBBR is the suspension medium with a specific gravity close to water and a large specific surface area. Its performance is related to the difficulty of film hanging, the amount of biomass in the reactor, and the level of treatment efficiency.
Proper selection of media can make the reactor more efficient. Generally speaking, the selection of MBBR media should follow the following four principles:
The surface roughness of the medium should be large, so that it is easy for organic matter to stay, and microorganisms can easily breed and film; it should be hydrophilic, so that hydrophilic microorganisms can easily adhere to its surface; it should also have a certain electrostatic effect, because under normal circumstances, microorganisms Negatively charged, the medium is positively charged and is easy for microorganisms to adhere to.
The specific gravity is close to water and it is easy to move with the water flow; it has a large specific surface area and can maintain a high concentration of biomass; the shape and size of the medium should be designed to have a good flow pattern.
The media must be wear-resistant and have a long service life; the media must not be biodegradable and must be corrosion-resistant.
Media investment accounts for a part of the system construction cost, so it is particularly important to choose reasonable and economical media.
Currently, there are many types of MBBR media used at home and abroad: according to the material, they mainly include plastic, polyurethane (PU), ceramsite and other new material media; according to the configuration, they mainly include cylinder, cube, spherical, short tube media, etc.
The media properties of different materials are quite different, and media with the same material and different configurations also have differences in various parameters. Therefore, the water treatment efficiency of MBBR with different media is different. The medium determines the processing effect of MBBR to a large extent, so understanding the medium is crucial.
As one of the most common media in MBBR, PE media has the advantages of high economic efficiency, good treatment effect, and easy suspension in the reactor. It has been widely used to treat domestic sewage, catering wastewater, industrial wastewater and landfill seepage. Filtrate and other practical projects.
MBBR with PE as the medium has good removal effects on chroma, chemical oxygen demand, ammonia nitrogen, total nitrogen, nitrate nitrogen, total organic carbon, Mn2+ and volatile phenols in sewage and wastewater.
For example, if a researcher uses short-tube PE with a filling rate of 50% and a specification of φ10×0.7mm as an MBBR medium to treat rural domestic sewage at room temperature, the system has an average removal rate of COD, NH+4-N, TN and TP respectively. Reaching 85%, 85%, 60% and 70%.
As a professional OEM factory and exporter of MBBR carriers, NIHAO HDPE MBBR carriers are used by many large environmental companies, some of which are the world's top 500. It is the basis of cooperation to provide excellent materials. In addition, as the material is purer and has high impact strength, its service life can reach 20 years and it is not easy to be broken by the mixer.
PP media is mostly used in MBBR combination processes, such as MBBR and A/O combination processes, MBBR-MBR combination processes, UASB-MBBR-RBBR processes, etc. It is mainly used for denitrification and organic matter removal.
If a researcher combines MBBR with traditional A/O process to treat rural domestic sewage, high-density K1 type PP media is used in both the anoxic zone and the aerobic zone. When the filling rate is 50%, COD, NH+4-N and TN The average removal rates were 92.4%, 93.8% and 73.4% respectively.
It is worth mentioning that most PP media are rarely used in actual projects due to problems such as light density, brittle materials, and short service life.
Polyvinyl chloride (PVC), polyvinylidene fluoride (PVDF), etc. can also be used as media in MBBR.
For example, a sewage treatment plant in Shenyang uses PVC cylindrical media MBBR to treat municipal sewage in food processing areas. When the filling rate is 25% to 30% and the HRT is 4.4 hours, the removal rate of COD and suspended particulate matter (SS) reaches more than 90%.
Although PVC and PVDF media have better removal efficiency for some pollutants, they are more expensive than PE, so they are mostly used in the treatment of industrial wastewater.
PU foam media has good mechanical strength and high porosity, which can provide a large attachment area for microorganisms to grow quickly and stably, and can effectively remove organic pollutants and various nutrients in sewage and wastewater.
At the same time, its price is affordable and can reduce water treatment costs. It is a promising MBBR water treatment medium.
When PU foam is used as a medium, MBBR has a good removal effect of organic matter and nitrogen pollutants in low carbon to nitrogen ratio (C/N) wastewater, organic wastewater and petroleum processing wastewater.
If researchers use PU media to treat low C/N sewage, when the HRT is 14 hours, the removal rate of TOC and NH+4-N in the water by MBBR reaches 90% and 65% respectively.
Ceramsite is a biological carrier with clay as the main raw material. Its appearance is mostly round or elliptical spheres, irregular gravels, and its surface is rough and honeycomb-like, which can provide an environment suitable for microorganisms to attach, fix and grow. , can absorb harmful elements, bacteria and mineralized water in water, and is mostly used in biological filters.
It is worth mentioning that there are currently few cases of ceramsite media being used in MBBR, and the existing cases are mostly focused on the treatment of simulated domestic sewage, production and hospital wastewater.
Some researchers used lightweight ceramsite with a filling rate of 50% as the MBBR medium to treat hospital wastewater. When the HRT was 42 hours and the mixed liquid suspended solids concentration was 5000 mg/L, the COD removal rate of the system reached 83%.
Of course, in addition to various plastics, PU foam media, and ceramsite media, many new MBBR media have appeared in recent years, such as biodegradable polymers, self-made inorganic active porous materials, fiber synthetic materials, Arundoba, loofah, etc. Good processing results were achieved.
Among them, biodegradable polymers not only serve as attachment carriers for microorganisms, but also serve as carbon sources. For example, if the biodegradable polymer polycaprolactone (PCL) is used as the MBBR medium, when the HRT is 18.5 h, the average TN removal rate is 74.6%, and simultaneous nitrification and denitrification are achieved under low C/N conditions.
To sum up, the most suitable MBBR media for different types of sewage and wastewater are also different:
Compared with plastic, PU media is porous and can store more microorganisms. However, when denitrification MBBR is used to treat actual urban sewage plant tail water, MBBR with PE as the media has better effect.
MBBR using PU as the medium has a better removal effect of TOC and NH+4-N than biodegradable polymer materials, but the removal effect of TN is not as good as biodegradable polymer materials.
Therefore, in practical applications, the media should be screened and optimized. In recent years, modifying MBBR media to improve its hydrophilicity and bioaffinity has become a current research hotspot. However, it must be noted that media modification is still a research category and cannot yet reach the engineering category.
Generally speaking, in order to prevent media loss and take into account the size of the media, grilles with smaller apertures will be installed at the water crossing and outlet ends of each section. As a result, it is easy to be stuck by suspended sludge and media, causing water to fail to flow away normally and causing blockage.
Once the grille at the water crossing is clogged and the water level rises to overflow, the media will be lost and enter subsequent pipes.
Whether it is the sludge return pipe, the mixed liquid return pipe, or the sedimentation tank pipe, etc., it will be blocked by the media, and the entire system has to stop running and is on the verge of collapse.
Set up an aeration or backflush device: Setting up an aeration device at the grille can effectively prevent the grille from clogging. In this way, any suspended sludge or media at the grille will be blown away to avoid clogging.
Setting up a backflush device at the return point of the mixed liquid is also an effective measure to prevent grid clogging. In actual operation, the grid at the return flow of the mixed liquid is often blocked.
Of course, if the design of the backflush device is not considered in the early stage of the design, the backflush can be carried out manually. Although manual backflush must be carried out every time there is a blockage, which brings a certain workload to the staff and the pump must be dismantled every time. Installing the pump is also inconvenient, but the problem can be effectively solved.
Set up automatic cleaning devices: Regular automatic cleaning devices can also prevent grates from getting clogged.
Add mesh fence: Cover the media as a whole with a mesh. Even if it is clogged, it will not cause media loss. There will be no problem of media entering the pipe and causing pipe blockage. The system will recover quickly as long as the blockage is cleared. grille, the system can operate normally.
Add a liquid level gauge: Install a high liquid level gauge in each pool. If the grid is blocked, the water level will inevitably rise. When the water level rises to the high liquid level, the system will stop water inflow, which can prevent the water level from overflowing, media loss and pipe blockage. In this way, after the blocked grille is manually cleaned, the system can immediately return to normal operation.
Among the above measures, adding mesh fences and installing liquid level gauges cannot fundamentally solve the problem of grid blockage. They can only prevent media loss and pipe blockage caused by media loss, reduce the workload of staff, and make The system resumes normal operation immediately.
Setting up aeration and backflushing or automatic cleaning devices at the grille can greatly reduce the probability of grille clogging. Of course, we can consider combining them to ensure nothing goes wrong.
In actual operation, if the media in the MBBR cannot be guaranteed to be in a uniform fluidization state, media accumulation will easily occur.
Therefore, the key to solving this problem is to optimize the structure and hydraulic characteristics of the reactor and improve the layout of the aeration pipeline to achieve a uniform fluidization state of the medium with lower energy consumption.
For example, some researchers have shown through experimental studies on the hydraulic characteristics and biological activity of MBBR that when the length-to-depth ratio of the reactor is about 0.5, it is conducive to good movement of the medium, and the mixing in the reactor is sufficient, and a wide range of media will not be generated. accumulation phenomenon.
There is also research on introducing baffles into MBBR to force the medium to circulate and move, improving the structure and operation mode of the reactor so that it has good hydraulic characteristics and aeration and oxygenation performance, and can be started with a small gas volume. , save energy and improve the efficiency of the reactor.
The structure of the reactor determines its hydraulic characteristics to a large extent. The accumulation of media at the bottom corners of the reactor is prevented by designing the bottom corners of the reactor into slopes.
