4+1 wastewater treatment technologies explained

4+1 wastewater treatment technologies explained

Did you know that the ancient Greek civilization of Crete, called the Minoan civilization, was the first to use underground clay pipes for sanitation purposes? Planning and constructing sewer systems, as well as the treatment and purification of wastewater have come a long way since then. It has evolved a lot and is still being modernized. Nowadays, wastewater treatment is an increasing challenge for professionals and operators working at wastewater treatment plants.

In the following article, we introduce 4 + 1 classic and innovative wastewater treatment techniques and their advantages. If you are interested in the topic, you will certainly find it useful.

1. Conventional Activated Sludge (CAS)

A Conventional Activated Sludge (CAS) system in wastewater treatment plants typically includes two tanks: an aeration tank for biological degradation and a sedimentation tank for separating the sludge from the treated wastewater. In a CAS system, the treatment starts at the aeration tank, where wastewater gets combined with air to activate microorganisms. As the organisms digest the wastewater, they collide and create bigger particles called flocs, which have more potential to destroy the biological components of the wastewater. A secondary clarifier or settling tank follows the aeration basin. Microorganisms with adsorbed organic material sink at this stage. Wastewater from the secondary clarifier is delivered to disinfection and final discharge facilities, or other tertiary treatments for additional purification.

What are the main advantages of CAS?

  • Self-sustaining wastewater treatment plant system
  • Small area requirement
  • Cost-effective
  • Good quality effluent
  • Loss of head is small
  • Easy to maintain

2. Membrane bioreactor (MBR)

The term ‘Membrane Bioreactor’ (MBR) refers to wastewater treatment plant systems in which a perm-selective membrane, such as ultrafiltration or microfiltration, is combined with a biological process, typically a suspended growth bioreactor. MBRs are distinct from ‘polishing’ methods in which the membrane is used as a separate tertiary treatment step with no return of active biomass to the biological process. A membrane bioreactor is basically a modified activated sludge (CAS) system. For solid and liquid separation CAS method employs a secondary clarifier or settling tank, whereas MBR uses a membrane.

3. Moving Bed Biofilm Reactor (MBBR)

If the “bulk” of the pollutant load must be disposed of (as a cost-cutting measure) or if relevant discharge requirements are not as stringent, the Moving Bed Bioreactor (MBBR) provides an economically viable method for wastewater treatment plants. This technique is used to remove organic contaminants, as well as nitrification and denitrification. MBBR allows high disposal efficiency while consuming low energy.

What are the main advantages of MBBR?

  • Small and compact units
  • No filter channeling is needed in the wastewater treatment plant
  • Low head loss
  • Expanded treatment capacity
  • Enhanced settling characteristics
  • Improved process stability
  • Complete solids removal
  • Operation at higher suspended biomass
  • Less sludge production and no issues with sludge bulking
  • Doesn’t require periodic backwashing

4. Integrated Fixed Film Activated Sludge (IFAS)

Integrated Fixed Film Activated Sludge (IFAS) is one of the newest technologies in wastewater treatment plants. It refers to any suspended growth system that includes an attached growth media within the suspended growth reactor. Biofilm carriers are classified as either ‘fixed media’ or ‘dispersed media’. This technology, which is typically used in highly developed wastewater treatment plants, may be employed to enhance existing facilities or can be built newly. Expert knowledge is required for the design, and the system must be operated by skilled laborers.

Water recycling in large sewage treatment plant.

Main advantages of IFAS

  • Enhanced process stability
  • Lower sludge production
  • Extended capacity of activated sludge systems within the same tank volume
  • Improved denitrification processes
  • Resistance to organic and hydraulic shock loads
  • High levels of efficiency for a large scope of wastewater
  • Additional biomass to help non-nitrifying plants nitrify
  • Potential improvements and reduced variation in the Sludge Volume Index (SVI)

+1. Sequencing Batch Reactor (SBR)

Sequencing Batch Reactors (SBR) are also referred to as Sequential Batch Reactors or fill-and-draw systems. SBRs are industrial tanks in wastewater treatment plants, where wastewater treatment happens in batches. The system is made up of at least two similarly fitted tanks with a shared intake that may be swapped between them. The tanks are designed with a “flow-through” system, with raw wastewater (influent) entering one end and treated water (effluent) exiting the other. While one tank is settling and decanting, the other is aerating and filling.

A typical SBR system sequence is as follows:

  1. Fill:  the tank is loaded with fresh wastewater
  2. React: aeration and mixing techniques are used to promote microbial removal of waste components
  3. Settle: aeration and mixing devices are turned off to let suspended solids sink
  4. Draw:  clear effluent is drawn from the reactor.

Waste solids can be removed from the reactor either after the Draw stage or during the React stage when the wastewater is fully mixed.


Clean water is a vital resource for all living creatures all throughout planet Earth. Those that supply wastewater treatment solutions play a critical role in restoring clean, safe water to its source. In wastewater treatment plant facilities, operational efficiency is always one of the biggest importance, and this has long pushed innovation in the sector. Great strides have recently been achieved in the development of efficient technologies, but with increasing pollution of the environment, challenges seem to always remain.