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Aeration of Wastewater by means of a blower & air diffusors What Wastewater Aeration Does By adding air to wastewater in a treatment plant it assists the aerobic microorganisms in the consumption of pollutants. Wastewater aeration is a vital part of most every biological treatment system. A well designed and operated wastewater aeration system will accomplish two main jobs: • Adds air to the wastewater thus increasing the dissolved oxygen (DO) levels • Mixes the wastewater Adding Air to Wastewater The first job of wastewater aeration is adding air to the wastewater. In a secondary biological treatment process, aerobic microorganisms consume the organic pollutants in the wastewater. These microorganisms require adequate dissolved oxygen or “DO” to thrive. Without sufficient oxygen, microorganisms are not able to consume the incoming organic pollutants in a reasonable time. In order to maintain DO levels, an aeration system is a must. Mixing the Wastewater The second job of wastewater aeration is mixing the wastewater. Proper mixing keeps solids in suspension thus avoiding a build-up of sludge. Mixing also ensures that there are no anaerobic (without air) zones in the wastewater. A common problem, especially with lagoons, is that there is less oxygen present on the bottom. Mixing makes sure all the water and microorganisms come into contact with oxygen. How does Wastewater Aeration Work? Sub-Surface Aeration A sub-surface aeration system provides oxygen to microorganisms by injecting air into the wastewater. Blowers (side channel blowers or Roots / rotary lobe type blowers) or low-pressure screw compressors or turbo blowers for the larger installations) the air which is delivered through airlines to diffusers installed on the
bottom of the tank or lagoon. The diffusers are installed in a pattern on the bottom of the tank or lagoon for uniform coverage. The diffusers have tiny holes that create bubbles that come into contact with the water. Diffusers come in two basic types: fine bubble and course bubble. Fine Bubble Diffusers Fine bubble diffusers typically have thousands of tiny holes and produce the smallest bubbles. The smaller bubbles provide the maximum surface area for contact with the wastewater. They also rise to the surface at a slower rate which provides for a longer contact time. These two factors make fine bubble diffusers the best choice for what is called “Oxygen Transfer Efficiency”. Oxygen transfer efficiency is the amount of air absorbed by the wastewater as a percentage of the amount of air produced by the aeration system. Course Bubble Diffusers Course bubble diffusers typically have a few larger holes that produce larger bubbles. These larger bubbles travel faster to the surface than the fine bubbles. This aspect creates more turbulence and mixing in the wastewater. Course bubble diffusers are an excellent choice in situations where mixing is most important. It should be noted that course bubble diffusers can require twice as much air to operate as fine bubble diffusers. Wastewater Aeration as Part of a Treatment Process Wastewater aeration is typically used during the secondary treatment process. This process is most often an activated sludge process. Aeration in an activated sludge process is accomplished by pumping air into the tank or lagoon. Proper aeration promotes the growth of microorganisms or microbes in the wastewater. The microbes feed on the organic pollutants and form flocs which can easily settle out. The flocs are allowed to settle out in a separate settling tank or lagoon. The flocs of bacteria that settle and accumulate on the bottom of the tank or lagoon form activated sludge. The activated sludge can then be recirculated back to the aeration basin or lagoon to increase the rate of consumption of pollutants. Wastewater aeration is also used in tanks and lagoons used for storage. Examples of these storage tanks and lagoons would be ones used as sludge holding and flow equalization. In these portions of a wastewater treatment system (tank or lagoon) it is important to maintain the living microorganisms. If the microorganisms begin to die, the wastewater will become septic, and odour will start to be an issue. Air & Vacuum Technologies (Pty) Ltd can assist you with all your needs when it comes to most of the equipment required on a wastewater treatment plant. We are the direct importer of the full Robuschi range of Rotary lobe, screw compressors, turbo blowers & centrifugal pumps, all commonly found on said plants. We offer peristaltic pumps, doing pumps & side channel blowers. We are the SOLE distributor for the WTE range of air diffusers.
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Pipes, Pumps and Valves Africa - Jan/Feb 2022
