What is Aerobic Wastewater Treatment?
This technical guide explains the process known as aerobic wastewater treatment, and how it is used to improve the quality of industrial wastewater streams. The guide looks at what the process involves, and how it works. It also considers each of the most popular types of aerobic system used by businesses including activated sludge, fixed bed bioreactors, moving bed bioreactors, membrane bioreactors and biological trickling filters.
Aerobic wastewater treatment systems
Aerobic digestion is usually employed as a second stage wastewater treatment process, and kicks in after larger contaminants have been removed from the waste stream using filtration or sedimentation techniques.
Aerobic treatments are popular because they offer a cheap and efficient way of removing contamination in situations where there is lots of organic material in the wastewater.
It’s particularly effective in food and drink, chemical and petrochemical industries.
How does aerobic wastewater treatment work?
The aerobic treatment of wastewater uses oxygen, bacteria and other tiny microorganisms which feed on oxygen to clean up wastewater streams, helping to breakdown organic material and other pollutants such as phosphorous and nitrogen.
This is the opposite of an anaerobic treatment system, which depends on bacteria which do not need oxygen to function.
The anaerobic bacteria speed up the natural process of decomposition, and break down contamination in the water by converting it into carbon dioxide and biomass to make it easier to remove.
What is biological oxygen demand?
Organic contamination in waste streams is usually measured as what is called Biological Oxygen Demand, or BOD.
It gives an indication of the amount of dissolved oxygen in the wastewater and can be used to determine the levels of microorganisms needed to treat the waste.
High BOD levels indicate that there is a lot of bio-material contained in the wastewater.
This bio-material can come from external pollution including sources such as industrial discharge, domestic sewage or agricultural contamination.
Why is oxygen important in an aerobic treatment system?
All aerobic digestion treatment systems need oxygen to work effectively, so there must be some way of getting oxygen into the biomass.
The injection of oxygen is often achieved by using large wastewater treatment ponds or lagoons where the liquid surface comes into contact with the air, or by using a mechanical device to pump air or oxygen directly into the wastewater.
There may be several different stages to the aerobic digestion process depending on the type of effluent, all using different types of microorganisms.
As the growth in the biomass has to be kept at the right levels for the microbes which are present, there is often a need for constant monitoring of the oxygen levels and adjustment to keep the bacteria multiplying at the right rate to treat the wastewater to ensure it meets the right discharge standards.
Operators of aerobic treatment systems also have to balance their systems for temperature, pH, flow, nutrients and overall load.
Keeping all of these different parameters in perfect balance is often not an easy job and requires skilled staff to keep everything under control.
What are the main types of aerobic digestion system?
The main types of aerobic digestion systems used to treat wastewater include:
Here we’ll review each of these systems in more detail.
Activated sludge
The use of activated sludge is typically employed in aerobic digestion systems which you’d find in your local sewage treatment plant.
Wastewater flows out of the primary treatment phase and then into a large settling tank.
The aerobic microorganisms float freely in the water, and consume the unwanted organic material in the wastewater.
This process forms biological solids which form clumps known as flocs… the process itself is called flocculation.
The solid flocs sink to the bottom of the tank, and can then be easily removed.
Levels of suspended solids can be controlled by recycling settled solids through the system.
The downsides to activated sludge systems are that they need a lot of space, and the levels of sludge created can be considerable.
However, they are cheap to build and compared with other options, ongoing maintenance costs are also typically low.
Fixed bed bioreactors (FBBRs)
Fixed bed bioreactors use a series of tanks, all of which contain multiple chambers.
These chambers are filled with porous material, most often made from plastic, foam or ceramics.
As the wastewater stream passes through these beds, the high surface area created inside the chambers ensures that a biofilm forms readily.
This type of fixed bed bioreactor creates less sludge, and therefore reduces waste disposal and handling costs.
Good bioreactors allow the wastewater to flow without plugging.
Additional biological and other processes can be added into the system too, such as specialist filtration, nitrification or denitrification.
Different tanks can also be set up with various types of material, and configured separately to account for any process specific waste.
Moving bed bioreactors (MBBRs)
Moving bed bioreactors use a series of aeration tanks typically containing polyethylene biofilm carriers which are constructed so they are free to move.
There are different types of plastic biofilm carriers available in varying shapes and sizes, but most tend to be formed as cylinders or cubes.
One of the main advantages of moving bed bioreactors is that they allow for the treatment of wastewater with a high BOD in a smaller area when compared with other wastewater treatment options.
No sludge is recycled through this type of system as it tends to settle into a slurry which is easily removed using a vacuum truck.
Alternatively, settled solids can be pressed to remove moisture and turned into a solid waste for more convenient disposal.
Membrane bioreactors (MBRs)
Membrane bioreactors offer an advanced wastewater treatment option which takes the best aspects of both activated sludge and membrane filtration to separate out suspended solids and recycle them.
Membrane bioreactors can work well with much higher levels of suspended solids, and can produce effluent of a much higher quality than traditional activated sludge processes.
MBR systems are designed to take into account both the chemistry of the water, and the effluent consent standards which need to be achieved prior to discharge into the sewerage system.
Most membrane bioreactors comprise treatment tanks for aerobic and anaerobic digestion, a tank with a specialist membrane, a clean in place system and a special membrane for filtration or ultrafiltration.
The downside to this type of wastewater treatment system, incorporating lots of different components and cleaning processes in that it can expensive to build, operate and maintain.
Biological trickling filters
Biological trickling filters are designed to create a biofilm which forms on a specific media by passing either air or water over it.
The biofilm is usually composed of both aerobic and anaerobic bacteria and this is used to help break down the organic particles in either the air or the water that pass over it.
Trickling filters can be made from foam, sand, gravel or ceramics.
This style of filter is commonplace at sewage treatment plants, but is also a good option for any industrial process or location where controlling odours is an important consideration.
Wastewater treatment training
The industrial and process water treatment specialists at Water Treatment Services have developed a series of professional water and wastewater treatment training courses including WTS 0070 “Industrial Wastewater”.
This specialist wastewater treatment training course comprises an intensive one day session designed for plant operators, environmental process engineers, maintenance and engineering contractors, and those with responsibility for the operation and management of industrial wastewater treatment systems.
Wastewater treatment solutions for business
Water Treatment Services offer a comprehensive range of industrial wastewater treatment solutions, including aerobic treatment systems for businesses across all sectors.
Find out how we can help reduce your costs, achieve regulatory compliance and improve environmental performance.
Our industrial wastewater experts can provide advice and full support to help you identify the most appropriate strategies for managing your wastewater and effluent streams.
With offices in London serving the South and South East England, Manchester (North West), Birmingham (Midlands), Bristol (South East England and Wales), Leeds (North and North East) and Glasgow (Scotland), supported by regional teams of specially trained engineers, wastewater specialists and technicians we offer cost effective environmental support solutions across the whole of the UK and Ireland.
Contact us today to learn how our wastewater management solutions can help improve environmental performance, reduce costs and achieve cost effective compliance with trade effluent consents.
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