Why is Aeration Important for Wastewater Treatment?


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Wastewater Aeration is the process of water treatment where air and water commingle in order to remove dissolved gases from the water. Aeration is an essential part of the wastewater treatment process because it assists in removing constituents from the water in preparation for the next phase of water treatment. Additionally, the methodology by which aeration uses is organic, cost-effective, and environmentally friendly. 

Most municipal and industrial water treatment plants use aeration as part of an overall process to purify the water and rid it of its pollutants. Aeration is a simple tool and speeds up the natural elements towards keeping a healthy ecosystem balance. When the balance is offset, the evidence is seen in sludge-filled waterways, algae-laden lakes and rivers, and polluted oceans. In very serious instances of failed water treatment, contaminated waterways contribute to illness even death in all species connected to the water source – humans included. 

What is Aeration in Water Treatment? 

There are three major parts of water treatment. The first is sort of a screening process. This is where they basically remove all the big stuff out of the water. This may be branches, tires, last year’s taxes, Jimmy Hoffa…(What a find that would be!)

Once the larger particles are removed, sediment is allowed to float to the surface and forms a sludgy compound that is then further filtered out and shifted into another holding tank. They commonly used sand as a filter method because it is very effective at absorbing greasy compounds from the surface This is when the concept of aeration is introduced. 

During the process of aeration, oxygen is evenly distributed and circulates throughout the water. This encourages a natural biodegradation of the organic contaminants contained in the wastewater. The dissolved gases escape into the air leaving the remaining sewage behind. Sewage harbors millions of microorganisms that create harmful volatile organic compounds or VOCs that left untreated can pollute the air and infiltrate the freshwater supply to nearby communities. 

Volatile Organic Compounds Can Include:

  • Benzene
  • Trichloroethylene
  • Dichloroethylene
  • Perchloroethylene

Aeration accelerates the sludge process and promotes microbial growth using the naturally occurring elements already in the wastewater. The bacteria actively feed on the material in the water and naturally separates itself into pockets of collected material referred to as flock. Through continual recirculation within the water basin furthering the decomposition process. By way of this aeration process, soluble iron and manganese are oxidized into insoluble components. It also helps to reduce hydrogen sulfide and ammonia levels. 

Types of Aerators Used in Water Treatment 

Some aeration devices are simple schematics where open holding tanks allow dissolved gases to escape into the open surrounding air. Other aeration devices have a more complex design featuring a column or tower filled with packing material. When the water passes through the packing material, the gases are released. There are three main types of aerators used in waste treatment facilities:

Packed Tower Aerator

Image Credit: Alley © 1998; reprinted by permission of McGraw-Hill, Inc.). Copyright© 1998

This system uses a cylindrical-shaped tower that is very tall (8-12ft) and it is filled with packing material. This packing material can range from ¼ inch to 3 inches in size and maybe pieces of ceramic or plastic. The purpose of the packing is to encourage close contact between the molecules of target pollutants and the liquid absorbent. The liquid absorbent is sprayed evenly over the top of the packing material which flows downward. Volatile gases and contaminants stream upwards dissolving into the liquid absorbent at the top of the tower and then venting to the outside.

Diffused Bubble Aerator

A diffused bubble aerator has several chambers paired with a diffuser that produces tiny bubbles that flow throughout the chamber. These bubbles carry the harmful gases and other constituents through a specialized vent leading to an outdoor chamber. Larger systems come equipped with a high-float switch that triggers an alarm in case of rising waters resulting in a flooded chamber. 

The benefits associated with using a diffusing type of aerating system are:

  • They offer complete mixing from bottom to top.
  • They are suitable for deeper tanks schematics.
  • They are highly efficient and have capabilities for diverse applications. 
  • The designs are flexible.
  • They are environmentally friendly.
  • They offer supreme reliability in extreme weather. 
  • They are low maintenance.
  • They are economical and because of their durability, they save money over the long term. 
  • They are considered to be safe systems.

The downsides of using a diffused aeration system are that they can be complex to manage in certain ways. For example, you have to tailor your diffuser to the size of the wastewater tank. Also, you have to provide the correct amount of air and the number of diffusers to make it efficient. The big deterrent to this system is the up-front costs. (No problem right? Money grows on trees last time we checked.) All kidding aside, it is an investment and eventually, the cost makes sense but not initially. 

Spray Aerator

This is a common type of aeration method used in industrial settings. Water moves through the pipe under pressure and a fine spray disperses through the nozzle and falls through the surrounding air. (Picture the fountain-type sprays seen in local ponds.) Spray aeration is successful in oxidizing iron and manganese, removing CO2, VOCs (volatile organic compounds), and also increases the dissolved oxygen in the water. Foul odors that are common to wastewater are also removed. The newly treated aerated water then spills over and is collected in a special collection tank. Waste air from the aerator needs to be vented to the outside as it contains volatile contaminants.

The benefits of spray aerators are: 

  • They are easy to install.
  • They are aesthetically pleasing to the eye and often serve as focal points for local parks and such, but they can be easily fitted to wastewater applications as well.

One of the main disadvantages associated with spray aerator systems is that they are notoriously difficult to install. Plus, the nozzles can be a little tricky. They also aren’t suitable for freezing temperatures.

Aerating Raises pH During Wastewater Treatments

Because aeration can raise the pH during wastewater treatment, it is a good idea to monitor it carefully. Microorganism colonies tend to thrive best in pH ranges between 6.5 and 8.5. Monitoring and adjusting pH is considered a best practice and serves to keep healthy levels of microorganisms needed during wastewater treatment. Industrial pH probes are ideal for monitoring activated sludge treatments. They are designed specifically to resist breakage and damage.

Aeration Plays a Role in the Nutrient Tests for Wastewater Treatment

There are many contributors to what is known as wastewater contaminants. Agriculture, animal feeding, and stormwater runoff are some of the many contributors to excessive algae bloom. This occurs because of too many nutrients in the wastewater.  Those nutrients are in the form of nitrogen (from ammonia, nitrite, nitrate, and organic nitrogen) and phosphorus. In most cases, there is even the presence of heavy metals. Testing for these nutrients is vital because it indicates important co-factors involved in the process of organic waste breakdown. 

One of the most important factors being how each element may trickle down in such a way thus negatively impacting aquatic life. The idea of treating wastewater is to return the water process to a biological natural state where it can continue its role as an essential ecosystem platform. Aeration affects how wastewater chemicals and nutrients interact together. Together these systems work to purify the water. The following measurements are vital tools in wastewater treatment: 

Dissolved Oxygen Readings can indicate quite a few things about what is going on in the water. We know that aeration raises both the pH and oxygen levels. Testing water samples for dissolved oxygen is advised because when DO levels are insufficient, microorganisms will not be present in the mixed liquid, and effluent turbidity increases. 

BOD Measurements or Biochemical Oxygen Demand is a common tool to measure the amount of biodegradable in the wastewater or sewage. It tells the amount of oxygen used in the process to break large molecules into smaller molecules. This is important because wastewater high in BOD can deplete the amount of oxygen in receiving waters creating great disturbances in the ecosystem. Waters that are too low in BOD can affect the number of anaerobic bacteria in the leaching field commonly referred to as the biomat. We want the biomat to be high functioning in order to properly filter the water before it is absorbed into soil.  Aeration plays an important role in BOD levels and water sample testing is an essential wastewater measurement. 

Nitrogen Levels tend to be high in wastewater. This is simply because of the type of components that make up the waste constituents i.e. human waste. These compounds contribute to the nitrogen levels and then further broken down completely to ammonia, NH3, by microorganisms naturally inhabiting the wastewater. Effluents in the wastewater containing nutrients such as nitrogen and phosphorus can lead to excessive algae growth in lakes, streams, rivers, wetlands, or other waterways. 

Ammonia Levels are released in the sludge accumulation during the nitrification process of bacteria. Nitrifying bacteria in the aeration tank convert the incoming ammonia nitrogen to nitrogen called nitrate (NO3). If the sludge mixing process isn’t sufficient, ammonia levels can exceed desired amounts. This is an unwanted situation because ammonia levels that are higher than the effluent actually break down the water clarifier resulting in a stalled purification process. The ideal ammonia level for effluent is 15mg/l or less of ammonia. Testing the wastewater for ammonia during the treatment process is advised. ORP readings can provide a comprehensive value of nutrient levels overall and indicate treatment efficiency. 

Phosphorous Levels that are very high are known to be mainly caused by soil erosion. However, excessive aeration can interrupt the process of biological phosphorus removal from wastewater or BPR. Testing is needed to ensure an adequate balance because in many treatment applications coarse bubble aeration is used to produce large air releases which encourage bacteria to grow and consume dissolved nitrogen and phosphorous. Too much phosphorus in wastewater can lead to a reduction in dissolved oxygen as well. Therefore, it can be a tough balancing act, but using DO water test results can provide a lot of insight into what is happening during the aeration process. 

The process of aeration influences all the above water variables and is an organic method of treating wastewater. The overall picture of what happens during the water following the process of aeration is multifaceted. Here is a glimpse of the changed water chemistry of wastewater conditions following the aeration tank: 

  • The CBOD is reduced to low levels by aerobic and facultative bacteria as a carbon food source.
  • High ammonia levels are reduced and oxidation occurs. New compounds are formed (Nitrates, Nitrites)
  • Dissolved oxygen demand has decreased, residual dissolved oxygen has increased.
  • Total alkalinity (as calcium carbonate) has decreased.
  • pH has decreased.
  • Several pounds of oxygen have been consumed by aerobic and anaerobic bacteria to oxidize CBOD and ammonia levels from the water.
  • Significant bacterial pockets have been formed, trapping suspended and colloidal solids, including particulate organic nitrogen.

Atlas Scientific for Wastewater Testing Tools and Resources

We know that wastewater isn’t something most people want to visualize. However, all communities want to be able to view clean and safe waterways. Water is something most people probably take for granted and don’t pay attention to the processes that make it possible for both humans and aquatic life to have viable, pure water sources.

Atlas Scientific understands the need for reliable testing equipment. Our knowledgeable staff is available to help treatment managers select the measurement tools that will function best in wastewater environments. Contact us for more information. 

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