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The MBBR process (moving bed biofilm reactor) is an efficient biological treatment technology with the advantages of flexible operation, resistance to shock loads, and low residual sludge. It has been widely used in the field of sewage treatment. However, the film-laying efficiency in the initial stage of the MBBR process is slow, which affects the rapid start-up and stable operation of the system. In order to shorten the film hanging time and improve the film hanging efficiency, the following measures can be taken:
Filler is the core component of the MBBR process. Its material, shape, specific surface area and other factors have a significant impact on the film hanging efficiency. Generally speaking, choosing fillers with light materials, high strength, large specific surface area, and high void ratio is more conducive to the attachment and growth of microorganisms. Commonly used MBBR fillers include fillers made of polyethylene, polypropylene, ceramics and other materials.
Inoculated sludge can provide the initial microbial flora for the MBBR system and accelerate the formation of biofilm. The source of inoculation sludge can be activated sludge, secondary effluent, municipal sewage, etc. The dosage of inoculated sludge is generally 5% to 10% of the sludge volume in the sewage treatment system.
Nutrients are necessary for the growth and reproduction of microorganisms. In the early stage of the MBBR process, it is necessary to ensure that nutrients (such as COD, N, and P) in the wastewater are sufficient to meet the growth needs of microorganisms. Generally speaking, the ratio of COD/N/P is 100:5:1.
Aeration can provide dissolved oxygen to microorganisms and promote their respiratory metabolism. In the early stage of the MBBR process, the aeration intensity should be appropriately high to facilitate the rapid growth of aerobic microorganisms. Generally speaking, the dissolved oxygen concentration is controlled at 2~3mg/L.
Before the biofilm of the MBBR system is mature, the amount of water inlet should be gradually increased to avoid impact loads affecting the film hanging effect. Generally speaking, the water intake should not be increased by more than 10% every day.
Closely monitor the operating parameters of the MBBR system, such as DO, pH, COD, etc., and adjust operating conditions in a timely manner to ensure stable operation of the system.
In the early stage of the MBBR process, flocculants can be added appropriately to promote microbial flocculation and aggregation, which is beneficial to the formation of biofilm.
It takes a certain amount of time to hang the film in the initial stage of the MBBR process, usually 7 to 15 days. Therefore, the operating time of the system should be extended as much as possible to ensure adequate formation of biofilm.
Filler is a key component of the MBBR process, and its performance directly affects the processing effect and operating efficiency of the system. Therefore, when selecting MBBR biological filler, the following factors should be considered:
Material: The material of MBBR biological filler should have good corrosion resistance, aging resistance, high mechanical strength, low density and other characteristics. Commonly used MBBR biofiller materials include polyethylene (PE), HDPE, polypropylene (PP), ceramics, fiberglass, etc.
Shape: The shape of the MBBR biological filler should be conducive to the attachment and growth of microorganisms and make full use of the reactor space. Commonly used MBBR biofiller shapes include cylindrical, spherical, rhombus, honeycomb, etc.
Specific surface area: The larger the specific surface area of MBBR biological filler, the more microbial attachment area it can provide, which is beneficial to improving the processing efficiency of the system. Generally speaking, the specific surface area of MBBR biological filler should not be less than 100m2/m3.
Porosity: The porosity of MBBR biological filler should be moderate, which not only ensures the mechanical strength of the filler, but also provides enough space for the growth of microorganisms. Generally speaking, the void ratio of MBBR biological filler should be between 50% and 70%.
Biofilm cultivation is a crucial step in MBBR processes, aiming to establish a uniform, dense, and highly active biofilm on the filler material. Two primary methods are employed for biofilm cultivation: static cultivation and dynamic cultivation.
Static cultivation involves halting influent flow and utilizing aeration techniques to encourage the attachment of microorganisms from the inoculated sludge to the filler material, promoting biofilm formation. This method offers several advantages:
Simplicity: Static cultivation is a straightforward approach, requiring minimal operational adjustments.
Effective Initial Biofilm Formation: The static environment favors microbial attachment and biofilm development.
Suitable for Small-Scale Systems: Static cultivation is well-suited for smaller MBBR systems due to its ease of implementation.
However, static cultivation also has limitations:
Extended Cultivation Period: The lack of influent flow prolongs the biofilm cultivation process.
Potential for Nutrient Limitations: Static conditions may restrict nutrient diffusion, potentially hindering microbial growth.
Limited Biofilm Diversity: The static environment may favor specific microbial communities, potentially limiting biofilm diversity.
Dynamic cultivation involves continuous influent flow while maintaining aeration to promote biofilm growth. This method offers several benefits:
Shorter Cultivation Period: The continuous flow accelerates biofilm development, reducing the cultivation timeframe.
Enhanced Nutrient Supply: Continuous influent provides a constant supply of nutrients, supporting microbial growth.
Promotes Biofilm Diversity: The dynamic environment encourages the establishment of diverse microbial communities.
However, dynamic cultivation also presents challenges:
Increased Operational Complexity: Continuous influent flow necessitates careful monitoring and adjustments to maintain optimal conditions.
Potential for Biofilm Detachment: The fluid shear forces introduced by influent flow may cause biofilm detachment, affecting treatment efficiency.
Not Suitable for All Systems: Dynamic cultivation may not be ideal for smaller systems due to the increased operational complexity.
Biofilm acclimation is the process of adapting the microbial community on the biofilm to the specific characteristics of the wastewater being treated. This involves exposing the biofilm to gradually increasing influent concentrations and ensuring optimal environmental conditions for the target microbial populations. Effective biofilm acclimation is crucial for achieving efficient and stable wastewater treatment.
Strategies for Biofilm Acclimation:
Gradual Influent Load Increase: Introduce the wastewater gradually, allowing the biofilm to adapt to the increasing pollutant load.
Nutrient Balancing: Ensure adequate nutrient availability for the target microbial communities involved in the treatment process.
Optimal Environmental Conditions: Maintain appropriate pH, temperature, and dissolved oxygen levels to support the desired microbial populations.
Monitoring and Adjustments: Continuously monitor biofilm performance and make adjustments to influent flow, nutrient dosing, and environmental conditions as needed.
Biofilm carriers play a pivotal role in MBBR processes, directly influencing treatment performance and operational efficiency. When selecting MBBR biofilm carriers, consider the following factors:
Material:
Durability: Choose carriers made from corrosion-resistant, high-strength materials like polyethylene (PE), polypropylene (PP), or ceramics.
Density: Opt for lightweight carriers to minimize system load and enhance aeration efficiency.
Shape:
Surface Area: Select carriers with a high surface area to maximize microbial attachment and biofilm growth.
Void Space: Choose carriers with appropriate void space to balance mechanical strength and microbial growth space.
Performance Considerations:
Biofilm Stability: Ensure carriers provide a stable surface for biofilm attachment and prevent detachment under operational conditions.
Hydraulic Characteristics: Consider the carrier's impact on hydraulic flow and ensure it does not impede treatment efficiency.
Cost-Effectiveness: Evaluate the cost-performance ratio of different carrier options based on treatment requirements and budget constraints.
Nutrient availability plays a pivotal role in biofilm formation and microbial growth in MBBR processes. Ensuring a balanced supply of essential nutrients (COD, N, P) is crucial for promoting rapid and effective biofilm development. Here are key strategies for optimizing nutrient conditions in MBBR systems:
Maintain Optimal COD/N/P Ratio: Aim for a COD/N/P ratio of 100:5:1 to provide sufficient carbon, nitrogen, and phosphorus for microbial growth.
Monitor Nutrient Concentrations: Regularly measure influent and effluent nutrient levels to assess nutrient availability and potential imbalances.
Consider Nutrient Supplementation: Supplement wastewater with additional nutrients if influent concentrations are inadequate.
Employ Nutrient Cycling Techniques: Utilize techniques like internal carbon recycling or sidestream nutrient recovery to optimize nutrient utilization.
Adapt Nutrient Management to Wastewater Characteristics: Tailor nutrient management strategies to the specific wastewater being treated.
Monitor Biofilm Activity and Adjust Nutrient Dosing: Assess nutrient utilization by monitoring biofilm activity indicators and adjust nutrient dosing accordingly.
Consider Nutrient Removal Processes: Incorporate nutrient removal processes like biological denitrification or chemical phosphorus precipitation if nutrient levels become excessive.
Utilize Nutrient Modeling Tools: Employ nutrient modeling tools to gain insights into nutrient dynamics and optimize nutrient management strategies.
By implementing these strategies, wastewater treatment plants can effectively manage nutrient conditions, promote biofilm formation, enhance microbial growth, and optimize the performance of their MBBR systems, ensuring sustainable and efficient wastewater treatment.
