The principle of MBBR Process is to use the basic principle of biofilm process, by adding a certain number of suspended carriers to the reactor, improve the biomass and biological species in the reactor, so as to improve the treatment efficiency of the reactor. Because the density of packing is close to that of water, it is completely mixed with water during aeration, and the environment for microorganism growth is gas, liquid and solid.
The collision and shear of the carrier in water make the air bubble smaller and increase the utilization of oxygen. In addition, each carrier has different biological species inside and outside, some anaerobic or facultative bacteria grow inside, and aerobic bacteria grow outside, so each carrier is a micro reactor, which makes nitrification and denitrification exist at the same time, thus improving the treatment effect.
I. principle and characteristics of MBBR Process
1. Principle of MBBR Process
The principle of MBBR Process is to increase the biomass and species in the reactor by adding a certain number of suspended carriers to the reactor, so as to improve the treatment efficiency of the reactor. Because the density of packing is close to that of water, it is completely mixed with water during aeration, and the environment for microorganism growth is gas, liquid and solid. The collision and shear of the carrier in water make the air bubble smaller and increase the utilization of oxygen. In addition, there are different kinds of organisms inside and outside each carrier, some anaerobic or facultative bacteria grow inside, and the outside is aerobic bacteria, so each carrier is a micro reactor, which makes nitrification and denitrification exist at the same time, thus improving the treatment effect.
MBBR Process has the advantages of both traditional fluidized bed and biological contact oxidation process. It is a new and efficient sewage treatment method. The carrier is in the fluidization state by the enhancement of aeration and water flow in the aeration tank, and then the suspended activated sludge and the attached biofilm are formed. This makes the whole reactor space used by the moving bed biofilm, and the attached biofilm is fully utilized The advantages of phase and suspended phase make them complement each other. Different from the previous packing, the suspended packing can contact with sewage frequently and many times, so it is called "moving biofilm".
2. Advantages of MBBR
Compared with the activated sludge process and the fixed packing biofilm process, MBBR has not only the high efficiency and flexibility of the activated sludge process, but also the characteristics of the traditional biofilm process, such as resistance to impact load, long sludge age and less excess sludge.
(1) filler characteristics
Most of the fillers are made of polyethylene, polypropylene and its modified materials, polyurethane foam and so on. The specific gravity is close to the water, mainly cylindrical and spherical, easy to film, no agglomeration, no blockage, and easy to remove film.
(2) good denitrification capacity
The nitrification and denitrification can take place in a single reactor, which has a good effect on the removal of ammonia nitrogen.
(3) good organic matter removal effect
The sludge concentration in the reactor is higher, which is 5-10 times higher than that of the conventional activated sludge process, and can be as high as 30-40g / L. The treatment efficiency of organic compounds is improved, and the impact load resistance is strong at the same time.
(4) easy to maintain and manage
There is no need to install packing bracket in the aeration tank. It is convenient to maintain the packing and the aeration device at the bottom of the tank. At the same time, it can save investment and floor space.
3. MMBR disadvantages
(1) the packing in the reactor is in the fluidization state depending on the lifting effect of aeration and water flow. In the actual project, the phenomenon of local packing accumulation is easy to occur. In order to avoid packing accumulation, the layout of aeration pipeline and the structure of reactor need to be improved. The structure of the reactor determines its hydraulic characteristics to a great extent. In practical engineering, when the length depth ratio of a single reactor is about 0.5 and the length is not more than 3m, it is conducive to complete movement of the filler. In the actual engineering design, a large number of tests should be carried out to optimize the reactor structure and hydraulic characteristics, reduce energy consumption, and further improve the economic benefits of MBBR.
(2) the outlet water of reactor is often equipped with grid plate or grid to avoid the loss of packing, but it is easy to cause blockage. In the actual project, movable grid plate can be set up, regular manual cleaning can be carried out, and air back blowing device can also be set up to prevent blocking.
II. Identification index of MBBR filler
1. Adhesion of biofilm
Adhesion capacity of biofilm - the most important index to evaluate the quality of fillers: biological adhesion = protected surface area (related to the design and operation state of fillers) × biological adhesion per unit surface area (related to the performance of fillers)
2. Filler performance
Performance of packing - the most important index to evaluate the biological adhesion of packing
(1) surface performance of packing
1. Surface structure: it is generally considered that the surface roughness is large and the film hanging speed is fast.
2. Surface potential: generally, microorganisms are negatively charged, and the surface of filler is positively charged, which is suitable for microbial growth.
3. Hydrophilicity: the microorganism is a hydrophilic particle, and the filler has a good hydrophilicity, which is suitable for the growth of microorganism.
(2) hydraulic properties
1. Porosity: the volume occupied by the filler, with high porosity.
2. Shape and size: the flow pattern that affects the water flow and air flow.
(3) fluidization performance: it is related to the density of filler. The density of the packing should be 0.97-1.03, and fluidization can be achieved with less aeration or agitation.
3. Identification of film maturity
The biofilm is evenly distributed on the surface of the carrier, the closer it is to the surface of the carrier, the denser it is, on the contrary, the looser it is, and the color of the carrier becomes darker, which indicates that the carrier film has entered the mature stage.
The structure of biofilm is compact, the species of microorganism are diverse, the number of fixed ciliates, Campanula and Dendrolimus are mostly, a small number of rotifers and swimming ciliates show the maturity of biofilm.
II. Research status of MBBR
MBBR was developed and applied in the mid-1990s. It has the advantages of both traditional fluidized bed and biological contact oxidation, and is a new and efficient sewage treatment method. Up to now, MBBR has been applied in small-scale, pilot scale and productive experiments of domestic and industrial wastewater treatment in foreign countries, and good results have been achieved. Among them, captor process in the United States and LINPOR process in Germany are currently two relatively mature porous suspension carrier systems. The polyurethane foam block was added to the complete mixing reactor for microbial growth. It was used to treat municipal sewage. The removal and nitrification of BOD were studied.
The results showed that nitrifying bacteria preferentially attached to the carrier, the nitrifying activity reached 0.33mgn/h · block carrier (the carrier volume was 8cm3 / block), in 4h, BOD could be completely removed, and then nitrification occurred, nitrification could be completed in 10h. In the past 10 years, mobile bed biofilm technology has been developed in Norway. Now more than 100 sewage treatment plants based on this technology have been put into use or under construction in 17 countries. They are mainly used to remove organic matters and ammonia nitrogen from municipal sewage or industrial wastewater.
The research and development of a new carrier for microorganisms is one of the key technologies for the treatment of wastewater by mobile biofilm, whose performance directly affects the treatment effect and investment cost of wastewater. With the improvement of fillers as a breakthrough, researchers have been promoting the development of mobile biofilm technology. Most of the suspended carriers are made of polyethylene, polypropylene and its modified materials, polyurethane foam and so on. The specific gravity is close to that of water. After the biofilm is grown, it is easy to reach the whole pool in normal aeration intensity.
The shape of the suspended packing is usually spherical, cylindrical or granular. It is generally considered that the spherical has good hydraulic properties and is the most ideal shape. However, due to the limitation of production technology, sometimes it is difficult to make the material into a ball; and when the length diameter ratio of cylindrical packing is 1, it is close to the ball, so the general choice of suspended packing is cylindrical. In addition, the specific surface area of the fillers filled in the biofilm reactor is more than 100-500m2 / m3. There are two kinds of suspension fillers made of polyethylene: one is φ 10 × 7 (mm), the specific surface area is 335m2 / m3, the other is φ 15 × 15 (mm), the specific surface area is 235m2 / m3; the other is made of polypropylene, the density is 0.94g/cm3, the shape is corrugated cylinder, the size is φ 15-20 (mm) × 20-30 (mm).
In recent years, many scholars in China have also studied MBBR technology, but most of them are still in the experimental stage. The key technology lies in the research of the suspended packing. For example, the patented product of Tongji University is φ 50 × 50 (mm) cylindrical suspended packing, with the specific surface area of 278m2 / m3, and the material is modified polyethylene; the suspended packing reported by Li Feng is made of polypropylene plastic, with the specific surface area of 350m2 / m3, which is φ 50 × 50 (mm). Generally speaking, the external dimension of the carrier used in China is larger than that of foreign countries, which is mainly limited by the whole process and outlet grid.
Generally speaking, the research of suspended packing is just in the beginning in China, and the application of new suspended packing in sewage treatment engineering has a wide development space. At present, the commonly used fillers in China are honeycomb fillers, soft fillers, semi soft fillers, composite fillers and other fixed fillers, but these fillers often encounter problems such as blocking, agglomeration, uneven distribution of air and water, which affect the biological treatment effect. In addition, the above fillers need to be installed on the auxiliary support, which causes a lot of inconvenience to the installation and replacement of fillers, and makes the project investment and operation management cost relatively higher.
From the point of view of economy, practicality and high efficiency, high-performance new fillers should have the characteristics of low price, long service life and easy to hang film in terms of material quality; in terms of structure, the designed specific surface area should be as large as possible, and some functional areas can be manufactured to adapt to the growth of anaerobic and aerobic microorganisms with different requirements, and also take into account the characteristics of easy to take off film. At the same time, the cost of suspended packing should be reduced as much as possible, and its advantages should be brought into full play to make it more widely used in sewage treatment.
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