Aeration In Wastewater Treatment Plants

HOFFMAN & LAMSON blowers are the most well-known brand in the wastewater treatment industry. Our blowers provide oxygen to microorganisms that consume organic matter and supply airflow for diffused aeration systems. Due to quiet operation, constant pressure systems with varying flows, our blowers are the preferred technology and uphold a strong reputation for longevity and service.

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Plant Layout

HOFFMAN & LAMSON blowers for aeration

Aeration Basins & Aerobic Digesters 

An aerated lagoon or aerated basin is a holding treatment pond that supplies artificial aeration. Artificial aeration promotes the biological oxidation of wastewaters. These aeration basins use oxygen (or air) and microbial action to biotreat the pollutants in wastewater.

Aerobic digesters and aeration basins are very similar. Aeration basins are considered to be a large, open earthen lagoon or pond. The large surface areas involved cause more drastic temperature variations than found in aerobic digesters. Thus, causing variations in sludge retention times. If solids are returned to the aeration basin process, there is no difference between an aeration basin and the activated sludge process.

Aerobic digesters are better described as a tank than as a pond. These aerobic digesters are generally constructed of concrete and are rectangular so multiple tanks can share common walls. Large tanks would have two diffusers where most plants have at least two digesters. The aerobic digestion process can be continuous or batch.

Aeration in Wastewater Treatment

Suspension Mixed Lagoons

Suspension mixed lagoons convert the soluble, biodegradable organics in the influent into biomass that can settle as sludge. Usually, the effluent is sent 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.

Floating Surface Aerators 

In a surface aerated system, the aerators provide two functions: they transfer air into the basins to facilitate the biological oxidation reactions, and they provide the mixing required for dispersing the air and for contacting the reactants (that is, oxygen, wastewater, and microbes). Typically, the floating surface aerators deliver sufficient oxygen or air for aeration. However, surface aerators do not provide mixing equivalent to the mixing that normally is achieved in activated sludge systems.

Biological oxidation processes are sensitive to temperatures between 32°F and 104°F (0°C and 40°C). The rate of bio-reactions increases with temperature. Most surface aerated vessels operate between 39°F and 90°F (4°C and 32°C).

Submerged Diffused Aeration

Submerged diffused air is essentially a form of a diffuser grid inside a lagoon. The two main types of submerged diffused aeration systems for lagoon applications are floating lateral 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.

Channel Aeration 

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 from 2-5 cfm per linear foot of the channel (0.2-0.5 m3/linear meter/minute). The mixed liquor to activated sludge settling tanks are aerated.

Post Aeration 

Recent requirements for effluent demand high dissolved oxygen levels (4 to 8 MG/L). 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.  

In larger treatment plants, non-porous (coarse bubble) and porous (fine bubble), diffuser aeration is used.  The choice of a diffuser is dependent on the oxygen transfer rate required by the effluent.

Aeration in Wastewater Treatment

Trusted Experts

Equipment is tested before reaching the customer or end-user. Thus ensuring top quality and avoids unforeseeable issues or operational downtime. Therefore, upholding Hoffman & Lamson’s strong reputation as the worldwide leader of engineered solutions and producing premier quality products efficiently and economically. There are over 100,000 HOFFMAN & LAMSON multistage centrifugal blowers/exhausters in operation worldwide.