Use Membrane Diffusers to Avoid Aeration Dead Zones in MBBR Tanks

A typical issue that plagues the MBBR process is aeration. When the fluid is stagnant or at a slow velocity it's challenging to keep your biofilm carriers and biofilm to remain suspended and uniform in their distribution within the tank. Dead spots can then develop, compromising treatment efficiency, leading to fluctuating levels of dissolved oxygen and more frequent cleaning. The best approach is to use membrane diffusers, a proven and effective solution which can address these issues by producing very small bubble aeration that delivers superior distribution of oxygen across the entire tank while also providing an enhanced degree of mixing within the MBBR system. Properly configuring diffusers will enable operators to optimize their MBBR Biofilm Carriers movement, biofilm growth, and overall system operation.

Reasons for Aeration Dead Zones

The problem can be blamed on numerous things; it all comes down to knowing which causes the problems. An MBBR dead zone, a problem at waste water facilities all around the world, is basically an area where air and water are not getting circulated as they should throughout the whole reactor tank, or an area where there is insufficient air and or water flow. Over time, and depending on the tank design, this may result in biofilm carriers bunching together rather than free moving within the reactor.These dead zones can be caused by the uneven distribution of your diffusers If the diffusers that are in your tank are located unevenly they may be uneven airflow into your tank There may be zones of high activity while other parts of the tank will be more stagnant or inactive Low activity zones can develop dead zones Dead zones may form within the design of the tank itself Poor MBBR tank design, including walls, baffles, pipes, and internal structures, may also affect water flow through your MBBR Biochip Media . These can create circular or stagnant zones even with uniform aeration, especially if they are not considered when placement of the tank diffusers are made Insufficient air flow In addition to other factors, your tank needs a sufficient amount of airflow. Air must have sufficient momentum to distribute your carriers evenly and ensure adequate mixing throughout.If the airflow isn't adequate, too little energy may go into circulating them. The carriers may then begin to settle in the corners of the tank, further restricting water flow once they start accumulating. Biofouling within diffusers at the tank bottom is another potential issue at certain locations: biological materials, dirt, and minerals may settle into openings in the diffusers, and over time, completely clog certain parts of their surface.Uneven aeration then occurs; some parts of the tank have sufficient air supply, while other parts are poorly supplied. This makes it much easier to get dead zones. Take the food-grade processing wastewater treatment facility which realized collectors had stopped settling in the bottom one-third of the tank and found the air diffusers at the bottom had become clogged.The tank operators were able to get air flow back to a consistent, well distributed system, and it seemed to do the trick as the biofilm was soon in motion once again.Operators should keep a vigilant watch on how their carrier material, air flow and oxygen levels look so that dead zones can be identified, and dealt with, before they begin to hinder the wastewater treatment processes.

Matching Membrane Diffuser

The selection of properly sized membrane diffusers is a major factor in avoiding aeration dead zones in MBBR tank. There are several different types of diffusers and the choice of one that matches the design of the tank and treatment objectives can make a difference to mixing and oxygen distribution.The mechanism of membrane diffusers is the release of the large number of fine bubbles from flexible membranes. These bubbles ascend through the water column, causing a movement in the water column as they ascend. They are useful when correctly chosen and installed, for moving the biofilm carriers and transporting oxygen throughout the tank.The first one is the capacity for air flow. Any diffuser is designed to accommodate a certain amount of air volume without producing excessive mixing or diffusing. If the air flow is inadequate, there could be insufficient air flow to certain areas. Carriers might suffer from excessive turbulence if it is too high, influencing the stability of biofilm.The size and arrangement of the diffusers is also crucial. With larger tanks, it may be necessary to install more than a single diffuser line in order to achieve a uniform mixing pattern. Spacing should be carefully designed to allow air to flow into all parts of the reactor. Certain locations around walls, corners, and tank ends should be paid special attention as they are more prone to dead zones.Membrane material is another factor that is important. The use of high quality EPDM and silicone membranes is prevalent due to their ability to give a constant rate of bubble production and useful durability under continuous operation. A good membrane is important to provide consistent aeration over time.For instance, a municipal wastewater plant switched from an older coarse bubble aeration system to fine bubble membrane diffusers. Operators found that they could adjust the diffuser configuration to provide coverage over the entire floor of the tank and get more even movement of the carriers and fewer areas where carriers tend to accumulate. The dissolved oxygen readings also showed a more consistent reading across the reactor.Operators need to consider a variety of factors before choosing a diffuser, such as tank size, carrier fill level, airflow requirements, and treatment objectives. A diffuser that matches these conditions can be used to increase the mixing efficiency, decrease the risk of dead zones and ensure more stable biological treatment in the long term.

Installation & Layout Tips

The best membrane diffuser will not work if it is not installed in the proper location. A well-designed layout will help to circulate air through all areas of the MBBR tank and ensure that the carriers are able to move throughout the tank, while also minimizing the potential for the formation of dead zones as time goes on.A primary objective for installation is to make sure that air is evenly distributed across the bottom of the tank. The diffusers should be placed such that the bubbles rise all over the reactor and not at one point. A more balanced spread of air results in a more balanced water circulation, and fewer corners and walls become water collection points.It's also good to consider the spacing between diffuser lines. Gaps will form if diffusers are spaced too far apart and mixing is not complete. Packing too tightly can cause some parts of the house to get too much air, while other places don't get much. The spacing recommended by the manufacturer is a good guideline; it may be necessary to make adjustments based on the tank dimensions and operating conditions.Corners and tank ends are trouble spots that may need special attention as they are prone to developing dead zones. It is important for operators to watch how the carriers are distributed within the reactor during start-up. When the carriers tend to accumulate in some spots, minor modifications in layout or air flow can help to enhance circulation. The air piping system also should be designed such that an equal amount of air flow is provided to each set of diffusers in a row. If a row of diffusers receives too much air in proportion to other rows, unequal air distribution will result. Balanced flow and a proper pipe sizing arrangement including balancing valves, where appropriate will result in more efficient operation of the entire system.For instance, the operator of a wastewater plant in an industrial complex noticed an excess accumulation of a carrier on one side of an MBBR. Although the diffusers themselves were functional and functioning normally, the piping did not seem to distribute air flow evenly among rows. A system adjustment by balancing air flow through the piping and some small adjustments to diffuser placement greatly improved carrier movement uniformity.Just as critical as proper installation and design is regular post-installation monitoring. Visual inspection of carrier action and movement patterns, do monitoring, and air flow patterns monitoring can detect minor issues before they develop into more serious operational problems.