Wastewater aeration is critical to biological treatment systems. These include aerobic activated sludge systems, Sequencing Batch Reactors (SBR), nitrification-denitrification in a single basin, and Membrane Bioreactors (MBR).
Treatment plants inject pressurized air into a liquor of sludge and wastewater. Promoting the growth of microorganisms that consume organic matter and supply the air for diffused aeration systems.
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In this phase, biological processes, like aerobic treatment, decompose organic compounds, and pollutants in the wastewater. Chemical oxidation is used to remove persistent organic pollutants, bacteria, and microbial pathogens.
Typically, the secondary phase removes chemicals and toxic compounds. It is not uncommon to repeat this phase several times or apply tertiary treatment to the water.
A well-designed aeration system directly impacts the level of wastewater treatment achieved. The key to rapid, economic, safe, and effective wastewater treatment is an aeration system that evenly distributes oxygen supply.
Aeration is an activated sludge process. It pumps air into a tank, promoting microbial growth in wastewater. Bacteria that forms the activated sludge, after settling in a separate settling tank, recirculates back to the aeration basin. Recirculating back to the aeration basin increases the decomposition rate.
High volumes of wastewater will require more complex systems compared to simple batch processes used by smaller-scale facilities. The plant design below shows how a system impacts the level of wastewater treatment achieved.
The aeration phase removes organic matter, fine particles, and potentially toxic and harmful chemicals from the influent that enters the system. Read on to learn more about wastewater treatment aeration locations.
An aerated lagoon or aerated basin is a holding treatment pond that supplies artificial aeration. Artificial aeration promotes the biological oxidation of wastewater.
Aeration basins are large, open earthen lagoons or ponds. The large surface areas involved cause more drastic temperature variations than those found in aerobic digesters. Thus, causing variations in sludge retention times. If solids return to the aeration basin process, then there is no difference between an aeration basin and the activated sludge process.
Aerobic digesters are tanks constructed of concrete and are rectangular. This is so multiple tanks can share common walls. Large tanks would have fewer diffusers where most plants have at least two digesters. The aerobic digestion process can be continuous or batch.
Suspension mixed lagoons convert the soluble, biodegradable organics in the influent into biomass that can settle as sludge. The effluent goes to a second pond where the sludge can settle. Then, it is removed from the top with a low chemical oxygen demand (COD), while the sludge accumulates on the floor and undergoes anaerobic stabilization.
Two functions are provided in a surface aerated system:
(1) Transfer air into the basins to facilitate biological oxidation reactions.
(2) They provide the mixing required for dispersing the air and for contacting the reactants (that is, oxygen, wastewater, and microbes).
The floating surface aerators deliver oxygen for aeration. However, surface aerators do not provide mixing that is equivalent to what is achieved in activated sludge systems.
Submerged diffused air is a form of a diffuser grid inside a lagoon. The two main types of submerged diffused aeration systems for lagoon applications are floating and submerged lateral. Both systems utilize fine or medium bubble diffusers to provide aeration and mixing of the process water. The diffusers can be suspended slightly above the lagoon floor or may rest on the bottom.
Channels that distribute wastewater to the primary sedimentation tanks are aerated to keep the solids in suspension, and independent of the water flow rate. The amount of air required ranges and mixed liquor turns to activated sludge settling tanks that are aerated.
Requirements for effluent demand high dissolved oxygen levels. The regulation intends to ensure that low dissolved oxygen level effluent does not mix with a receiving stream.
One method is cascade aeration, where the effluent is aerated by the turbulence of a series of waterfalls. However, the temperature of the water greatly affects the water’s ability to absorb oxygen.
Diffuser aeration is used in larger treatment plants. Diffusers are dependent on the oxygen transfer rate required by the effluent.
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