Which treatment stage primarily focuses on the biological process in wastewater treatment?

The primary focus on biological processes in wastewater treatment is found in secondary treatment. During this stage, biological organisms, such as bacteria, are utilized to break down organic matter found in the wastewater. This process is essential for the reduction of pollutants, particularly biodegradable organic material, which contributes to the overall improvement in water quality.

Secondary treatment typically employs methods like aeration, where oxygen is introduced to support the growth of aerobic bacteria. These microorganisms will metabolize the organic substances present in the wastewater, leading to the conversion of harmful materials into less toxic forms and facilitating their removal from the water. This biological activity is critical for achieving significant reductions in biochemical oxygen demand (BOD) and total suspended solids (TSS).

In contrast, other treatment stages serve different purposes. Primary treatment involves the physical removal of large solids and sediments from the wastewater, while tertiary treatment focuses on further polishing or advanced treatment to remove nutrients, pathogens, and residual contaminants that remain after secondary treatment. Pre-treatment is typically the initial phase aimed at conditioning wastewater before it undergoes primary treatment, often involving the removal of grit and larger debris. Thus, secondary treatment plays a vital role in utilizing biological processes to achieve effective wastewater purification.