1. Introduction to MBBR Process

The MovingBed Biofilm Reactor (MBBR) process originated in Norway in the late 1980s and is currently a mature sewage biochemical treatment technology internationally. It aims to enhance the deep denitrification and phosphorus removal of biochemical tanks, achieve economic and sustainable stable standards, and is widely used in sewage plant upgrading and capacity improvement. Since the first application of MBBR in the STENSHOLT municipal sewage treatment plant project in Norway in 1989, thousands of municipal and industrial wastewater treatment facilities have been built in more than 50 countries, achieving good results. This process uses suspended packing as a growth carrier for microorganisms, and achieves efficient treatment of wastewater through sufficient fluidization of the suspended packing. This process fully absorbs the advantages of biological contact oxidation and biological fluidized bed, overcomes the disadvantages of low mass transfer efficiency, poor treatment efficiency, and high fluidization power, and applies the basic principles of biofilm process to fully utilize the advantages of activated sludge process, achieving the operation of activated sludge mode in biofilm process. The MBBR process is divided into suspended packing process (MBBR) and activated sludge suspended packing composite process according to the form of microbial existence. The municipal sewage treatment scale of MBBR in China exceeds 20 million tons/day, which is a typical process for upgrading high emission standards.

The MBBR process is a biofilm process that operates on activated sludge. The basic principle is to add a certain amount of suspended packing material with a density close to water to the aeration tank. As the sewage flows through the packing material, a biofilm gradually forms on the inner and outer surfaces of the packing material, increasing the variety and quantity of microorganisms in the reactor and purifying the sewage.

The MBBR process is usually divided into pure film MBBR and mud film blended MBBR. Early MBBR specifically referred to the pure membrane MBBR process, which was an improvement of fluidized bed technology by using suspended packing with a density close to water to replace traditional heavy packing, saving energy consumption in packing fluidization. Pure membrane MBBR, the system does not have sludge reflux, and microorganisms mainly exist in the form of attachment on the suspended packing.

The mud film blending MBBR process combines activated sludge method with biofilm method, aiming to enhance the treatment effect of activated sludge system in situ. Mud film blending MBBR contains both suspended and attached microorganisms, requiring sludge reflux. The upgrading and renovation of domestic sewage treatment plants are often combined with existing processes, using mud film blended MBBR. The mud film blending MBBR process is a dual sludge age sewage treatment technology that combines MBBR process with activated sludge process, combining the advantages of both activated sludge and biofilm. By relying on aeration or stirring to keep the packing in a fluidized state, suspended growth activated sludge and attached growth biofilm are formed, making full use of the entire reactor space and fully utilizing the advantages of both attached and suspended organisms. It not only has the characteristics of traditional biofilm method, such as shock load resistance, long sludge age, and low residual sludge volume, but also has the high efficiency and flexible operation of activated sludge method. It maximizes strengths and avoids weaknesses, complementing each other.

2. MBBR process principle

The MBBR process utilizes the basic principles of biofilm method, fully utilizing the advantages of activated sludge method while overcoming the disadvantages of traditional activated sludge method and fixed biofilm method.

The key technology lies in the research and development of bio fillers with a specific gravity close to water and easy to move freely with water under slight stirring. Biological fillers have the characteristics of large effective surface area and are suitable for microbial adsorption and growth. The structure of the filler is characterized by a protected internal surface area for microbial growth. The schematic diagram of MBBR process principle is shown in Figure 2-1. During aeration and oxygenation, the rising buoyancy of air bubbles pushes the packing and surrounding water to flow. When the airflow passes through the gap between the water flow and the packing, it is blocked by the packing and divided into small bubbles. In this process, the filler is thoroughly stirred and mixed with the water flow, while the air flow is sufficiently divided into small bubbles, increasing the contact and oxygen transfer efficiency between the biofilm and oxygen. Under anaerobic/anaerobic conditions, the water flow and packing material fully flow under the action of the submersible agitator, achieving the goal of full contact between the biofilm and the treated pollutants for biological decomposition. Therefore, the MBBR process breaks through the limitations of traditional biofilm processes (such as blockage and uneven water distribution in fixed bed biofilm processes, as well as fluidization limitations in biofluidized bed processes), laying a good foundation for the wider application of biofilm processes in biological treatment of wastewater.

(a) Aerobic reactor (b) anaerobic reactor

Figure 2-1 Schematic diagram of MBBR process principle

The core of MBBR process lies in the research and development of suspended fillers with a specific gravity close to water, which can move freely with slight stirring. It has a large specific surface area, fast film formation speed, better biological affinity, high biological activity, long service life, and efficient ammonia nitrogen removal ability, synchronous nitrification denitrification ability, and organic matter removal ability.

Adding suspended packing can greatly increase the biomass and species of organisms in the reactor. Due to the packing density being close to water, it is completely mixed with water during aeration or stirring. As the packing moves freely in the tank, it accelerates the mass transfer efficiency between microorganisms, pollutants, and oxygen, thereby improving the treatment efficiency of the reactor. The collision and shear effects of fillers in water make air bubbles finer and increase the utilization rate of oxygen.

The key to the MBBR process system is to achieve sufficient fluidization of suspended packing to enhance the treatment of pollutants. Therefore, the MBBR process includes efficient biological suspended packing, tank design, packing interception system, aeration system, packing diversion system, interception net self-cleaning system, packing addition and intelligent control system, as well as maintenance emergency measures and other systematic processes. Reasonably configure the parameters of various equipment in the system according to the nature of the sewage and the project situation, and maximize their effectiveness to achieve stable and standard effluent. This technology has strong applicability and a wide range of applications, and can be used for both organic matter removal and nitrogen and phosphorus removal; It can operate in aerobic environments, as well as anaerobic and hypoxic environments.

The fluidization of biological suspended fillers in the aeration zone mainly relies on the aeration system. In the aerobic zone, an appropriate aeration system is used to ensure the fluidization effect of the biological carrier fluidized packing material, ensuring that the fluidized packing material flows up and down, back and forth in the water body, and ensuring sufficient mixing, collision, and contact between the packing material and sewage, effectively completing the contact, exchange, adsorption and other processes of pollutants, water, and gas in three directions. The use of perforated tubes for aeration can ensure the up and down fluidization movement of biological fluidized packing and promote the membrane separation and deposition process of the packing. The specific gravity of the packing material is selected as 0.94-0.97g/cm3. During the cultivation period, a large amount of biofilm will gradually adhere to the surface of the packing material. The larger the adhesion amount, the higher the specific gravity. When the biofilm on the packing material reaches a certain thickness, its specific gravity is greater than 1. The packing material sinks from the non aeration zone to the bottom of the water tank, and the impact force at the bottom of the aeration zone is the strongest, which can quickly wash away the residual biofilm on the packing material. After membrane removal, the specific gravity of the packing material also decreases to below 1 and increases in the aeration zone. According to the characteristics of the specific gravity changes before and after membrane hanging, the filler can be agitated in the aeration zone and non aeration zone with the water flow, thus alternately completing the growth and shedding process of the biofilm, ensuring the stability and activity of the biofilm quantity, and making the process operation more stable. In order to prevent fluidized suspended packing from entering the next stage with the mixed liquid, a sieve is designed at an appropriate position in the aerobic zone for interception and separation. The screen material is made of stainless steel 304, and the type is matched with the suspended packing.

The MBBR process can be used for both newly built sewage treatment plants and for upgrading and expanding existing sewage treatment plants. It can be embedded into existing processes such as A2O, AO, oxidation ditch, SBR, etc.

3. Characteristics of MBBR process

3.1 Simultaneous enhanced denitrification and phosphorus removal:

The use of activated sludge suspended packing composite process can achieve sludge age separation of different functional microorganisms in the same reactor. The denitrifying bacteria (nitrifying bacteria) are generally long mud aged bacteria that require a longer mud age (15-25 days); Phosphorus removal bacteria (polyphosphate accumulating bacteria) are generally short mud age bacteria and require a shorter mud age (3-7 days); Excessive sludge age can lead to poor microbial activity, reduced treatment load, difficulty in aggregation due to aging, and decreased settling performance. In practice, traditional nitrogen and phosphorus removal processes have irreconcilable contradictions in sludge age. The composite process provides a carrier for the growth of nitrifying bacteria, prolongs their sludge age, and improves denitrification efficiency due to the addition of biological fillers; Simultaneously controlling the activated sludge system to have a short sludge age can enhance phosphorus removal efficiency; The sludge membrane is fully fluidized under aeration and water flow, promoting biofilm renewal and preventing excessive sludge age and decreased sludge aging treatment performance; When the water temperature is low in winter and the activated sludge system is not conducive to the growth of nitrifying bacteria, the shedding biofilm plays a continuous inoculation role in the activated sludge, maintaining the nitrification performance of the system from decreasing. The effluent TP in the biochemical section can be less than 1mg/L, the TP removal rate in the biochemical section exceeds 90%, and the ammonia nitrogen removal rate can reach over 99%.

3.2 High load, saving land occupation:

By adding biological fillers to the reaction tank for upgrading the original tank, there is no need to add new land. Compared to the activated sludge method, the effective biomass can be significantly increased, while compared to the biofilm method, the fluidized bed packing method significantly improves mass transfer efficiency. It is possible to increase the standard, increase the quantity, and increase the quantity simultaneously, with a maximum increase of over 100%; The load is more than 2-5 times that of traditional craftsmanship. Land occupation can save 30% -50% of land compared to activated sludge method.

3.3 Less civil engineering modifications:

The use of advanced interception and diversion systems can achieve upgrading and transformation without changing the civil structure of the biochemical pool.

Strong ability to withstand impact loads, still showing good treatment effects under harsh water quality conditions:

The impact load mainly manifests as water quality impact of conventional pollutants, water quality impact of toxic pollutants, and water quantity impact. Essentially, it is the impact of changes in the amount of pollutants carried by microorganisms per unit surface area per unit time on the treatment effect. The MBBR process has a longer sludge age in the packing area, which increases the abundance of microbial populations and is beneficial for the treatment of recalcitrant organic matter. Under adverse water quality conditions such as low temperature, high salt, and low substrate, MBBR has a long mud age and locally exists aerobic and hypoxic microenvironments, which is conducive to its adaptation to microbial screening and enrichment under adverse water quality conditions, and is conducive to the domestication of cold loving bacteria, high salt tolerant bacteria, and other enrichment. Biofilm mass transfer is slower than activated sludge, and similarly, the heat generated by biodegradation exchanges slower with water, increasing the local environmental temperature of microorganisms and facilitating the maintenance of bacterial activity. Macroscopically, MBBR still has good treatment effects under harsh water quality conditions such as low temperature, high salt, and low substrate.

3.4 Tolerance to extreme water quality such as low temperature, poor nutrition, high toxicity, and high chloride ions:

The biofilm on the packing material has a long mud age, generally exceeding 30 days, which is beneficial for the enrichment of nitrifying bacteria, especially for the screening of relevant efficient bacterial species under special water quality conditions; Wastewater treatment plants in the north are plagued by low temperatures, and MBBRzui can achieve 3 ℃ low temperature treatment; MBBR can be used for wastewater treatment with low C/N ratio or micro polluted water treatment, and can also achieve denitrification treatment with chloride ions of 5000-10000mg/L; These are all situations that are difficult to treat with activated sludge technology, and MBBR has shown excellent performance in this regard, solving related problems;

3.5 Sustainable Upgrade:

The process has strong flexibility and good scalability. Due to the different specific surface areas and filling rates of suspended fillers, there is no need to make any changes after the inlet or outlet indicators are improved. Simply replace the suspended fillers or increase the dosage to achieve a filling rate of 10-70%.

3.6 Investment Province:

The main investment in MBBR process comes from suspended fillers, and the amount of suspended fillers used is related to various factors such as water quantity, water quality, effluent standards, temperature, etc. Municipal sewage ranges from 50-800 yuan/(m3/d), with a typical value of 100-400 yuan/(m3/d); And with a service life of over 20 years, there is no need to replace or supplement suspended fillers, and there are no additional costs in the future.

3.7 Short project implementation cycle:

Generally, each group of pools lasts for 3-15 days, mainly due to minimal or no civil engineering modifications, and the supporting equipment is prefabricated, which can directly achieve on-site modular installation.

3.8 Low operating costs:

Suspended packing fluidization does not require additional aeration and stirring, and normal aeration can meet the requirements of suspended packing fluidization. The continuous movement of the packing in the tank improves the mass transfer rate and efficiency between the biofilm on the packing and the pollutants and oxygen in the water, greatly improving the treatment efficiency; Simultaneously improving oxygen utilization efficiency and reducing energy consumption. The interception and diversion system is made of stainless steel material with a service life of over 15 years, and the service life of suspended packing is over 20 years. There are almost no equipment that needs maintenance in the biochemical tank, saving maintenance costs.

3.9 Low sludge production, good settling performance, and cost savings in sludge disposal:

The biofilm microbial community on the suspended packing is rich, with a long life cycle, long biological chain, and low sludge production. Using the pure membrane MBBR process, the sludge production is only 30% or less of the activated sludge process. When the microbial biomass in the biological treatment system is increased to over 10000mg/l during the upgrading process, it will not increase the solid load of the secondary sedimentation tank. And due to the low sludge production, it can save on sludge disposal costs.

3.10 Convenient and simple operation and management:

When the MBBR process is used for the renovation of existing sewage treatment plants, the original operating mode is not changed, which can continue the operational management experience of existing operators. After debugging and operation, the microbial count on the packing will change with the change of inlet load, without the need for manual adjustment, ensuring the stability of the effluent. And the process has no special maintenance requirements, and the operation and management are simple.

3.11 Non activated sludge process is prone to sludge swelling and other issues:

Adopting a pure MBBR system, as it is a pure membrane method, there is no sludge expansion problem; When using the composite process of activated sludge suspended packing, the proportion of inorganic matter in the biofilm that has aged and fallen off is high, and the density is high, making it easy to settle; Moreover, there are more extracellular polymers in biofilm compared to activated sludge, which have a contact flocculation effect, improve sludge aggregation performance, and enhance sludge settling performance.

The non fixed bed biofilm process is prone to clogging, requires backwashing, and breeds red worms

The fixed bed process often encounters problems such as uneven water distribution, the formation of dead zones, the need for regular backwashing and additional energy consumption, the need for supporting facilities, and reduced nitrification performance due to red worms. Due to the mixing of fillers and water flow throughout the entire volume of the biological tank, the possibility of blockage in the tank is fundamentally eliminated, and the tank capacity is fully utilized without the need for backwashing. Chironomid larvae, also known as red worms, belong to the metazoan group and are prone to laying eggs and breeding in areas with slow water flow and stable water quality. They mainly feed on nitrifying bacteria, which is not conducive to the safety and stability of the system. They are particularly common in fixed bed processes, and the operation of biofilm activated sludge method restricts the growth conditions of red worms from the perspective of survival conditions.

3.12 Long system lifespan:

The filling is wear-resistant and durable, and the mixer uses banana shaped mixing blades with soft contour lines that do not damage the filling; The entire mixing and aeration system is easy to maintain and manage. Due to the cutting effect of the filler on the bubbles, the oxygen transfer efficiency is improved. Perforation aeration can be used to enhance the safety of the aeration system and extend the maintenance cycle.

3.13 Suitable for upgrading and three-dimensional expansion of sewage treatment plants:

The process has high flexibility in operation. Firstly, various pool types (deep, shallow, and square) can be used without affecting the treatment effect of the process; Secondly, it is possible to flexibly choose fillers with different specific surface areas and filling ratios. When the actual inflow water quality or quantity changes during operation, simply increasing the filling rate of the filling material can ensure that the original design biological tank capacity remains unchanged while meeting the original design or upgraded effluent standards, achieving the goal of physical expansion and balancing efficient treatment with long-term expansion of treatment scale without increasing the tank capacity; Afterwards, the mobile bed biofilm process can be easily combined with the original process to form an activated sludge biofilm composite process. Traditional monitoring and control methods for regulating activated sludge systems (such as controlling sludge discharge, aeration, etc.) can be used for the regulation of the composite process, and can be flexibly adjusted according to system functions and operating conditions.

4. Manufacturer Introduction

Dalian Yudu Environmental Engineering Technology Co., Ltd. was established in 2002 and is an environmental protection enterprise specializing in MBBR process. It is one of the largest MBBR filler production enterprises in China; The enterprise with the largest export volume of MBBR fillers in China.