Activated sludge process, aerated lagoon, rotating biological contractors, and aerobic and anaerobic digesters are all biological unit processes used in wastewater treatment. However, only the activated sludge process, aerated lagoon, and aerobic and anaerobic digesters are based on a suspended growth system.

1. Activated Sludge Process:
- The activated sludge process is a widely used biological treatment method for wastewater. It involves the use of a suspended growth system, where microorganisms are suspended in the wastewater and form a sludge mixture.
- In this process, wastewater is mixed with a culture of microorganisms in an aeration tank. The microorganisms consume organic matter in the wastewater as their food source and convert it into biomass and carbon dioxide.
- The mixture of wastewater and microorganisms is called activated sludge, which is then separated from the treated wastewater in a settling tank. The clarified effluent is discharged, while a portion of the activated sludge is recycled back to the aeration tank to maintain the microbial population.

2. Aerated Lagoon:
- An aerated lagoon is another suspended growth system used in wastewater treatment. It consists of shallow basins or ponds where wastewater is treated by the action of aerated microorganisms.
- The lagoon is equipped with mechanical or diffused aeration systems to provide oxygen to the microorganisms. The microorganisms metabolize and break down organic matter in the wastewater through aerobic processes.
- The organic matter is converted into biomass, carbon dioxide, and water. The treated effluent is then discharged or further treated before disposal.

3. Rotating Biological Contractors (RBC):
- Rotating Biological Contractors are a type of fixed-film biological treatment system. They consist of a series of cylindrical discs or media that rotate slowly in wastewater.
- Microorganisms attach to the media surfaces and form a biofilm. As the media rotates, the biofilm comes into contact with wastewater, where the microorganisms metabolize organic matter through aerobic processes.
- The treated wastewater is separated from the biofilm by settling or filtration, and the biofilm is continuously exposed to wastewater as it rotates.

4. Aerobic and Anaerobic Digesters:
- Both aerobic and anaerobic digesters are used for the treatment of sludge generated in wastewater treatment plants.
- In aerobic digestion, sludge is treated in the presence of oxygen. This process helps in reducing the organic content of sludge and stabilizing it.
- Anaerobic digestion, on the other hand, is a biological process that occurs in the absence of oxygen. It involves the breakdown of organic matter by microorganisms to produce biogas (mainly methane) and stabilized sludge.

In summary, the suspended growth systems based on a suspended growth system are the activated sludge process, aerated lagoon, and aerobic and anaerobic digesters. These processes involve the suspension of microorganisms in the wastewater, either in the form of activated sludge or attached to media surfaces. They play a crucial role in the biological treatment of wastewater and sludge stabilization.