The activated sludge process is a widely used primary biological treatment method for wastewater. It involves the aeration of wastewater to promote the growth of microorganisms that break down organic matter.

In a trickling filter, the wastewater is distributed over a bed of rocks, which provide a surface for the growth of microorganisms that break down organic matter.

Composting is a biological process that involves the decomposition of organic matter by microorganisms under controlled conditions, resulting in the production of a nutrient-rich soil amendment.

Anaerobic digestion is a biological process that converts organic matter into biogas, a mixture of methane and carbon dioxide, through the action of microorganisms in the absence of oxygen.

Biosorption is a biological treatment process that involves the removal of heavy metals from wastewater through the adsorption of metal ions onto the surface of microorganisms or other biological materials.

Bioremediation is the process of using microorganisms to degrade and remove contaminants from soil and groundwater, thereby restoring the natural environment.

Nitrification-denitrification is a biological treatment process that involves the conversion of ammonia and nitrite to nitrate, followed by the reduction of nitrate to nitrogen gas, thereby removing nitrogen from wastewater.

Phytoremediation is the process of using plants to absorb and remove contaminants from soil and water, thereby restoring the natural environment.

Biological phosphorus removal is a biological treatment process that involves the uptake and storage of phosphorus by microorganisms, thereby removing phosphorus from wastewater.

Bioremediation is the process of using microorganisms to degrade and remove organic contaminants from soil and groundwater, thereby restoring the natural environment.

Ozonation is a biological treatment process that involves the use of ozone to oxidize and remove color and odor-causing compounds from wastewater.

Anaerobic digestion is the process of using microorganisms to convert organic matter into methane and carbon dioxide in the absence of oxygen.

Sedimentation is a biological treatment process that involves the settling of suspended solids from wastewater under gravity.

Bioremediation is the process of using microorganisms to degrade and remove hazardous substances from soil and groundwater, thereby restoring the natural environment.

Disinfection is a biological treatment process that involves the use of chemicals or physical agents to kill or inactivate pathogens in wastewater.