What process primarily follows primary treatment in wastewater treatment operations?

In wastewater treatment operations, primary treatment involves the removal of large solids and settling of sediments from the wastewater. This initial step mainly focuses on physical processes to reduce the load of contaminants in the water, but it does not significantly break down dissolved organic matter or pathogens.

Following primary treatment, the process that primarily continues is secondary treatment. This phase is crucial as it targets the biological degradation of remaining organic matter and the removal of nutrients such as nitrogen and phosphorus. Secondary treatment typically involves microbial processes, where bacteria and other microorganisms break down organic pollutants in aerated tanks (activated sludge process) or ponds. This step significantly enhances the quality of the water before it moves on to the next stages of treatment.

While coagulation, tertiary treatment, and disinfection are all essential components of the broader wastewater treatment process, they either occur simultaneously or after secondary treatment. Tertiary treatment is often used to polish effluent after secondary treatment by removing additional pollutants, and disinfection is generally one of the final stages to ensure that pathogens are eliminated before the treated water is discharged or reused. Thus, secondary treatment is the primary step that follows after primary treatment in the sequence of wastewater treatment operations.