Secondary treatment

Definition

Secondary treatment is a crucial stage in wastewater treatment that involves the biological processes designed to remove dissolved and suspended organic matter from wastewater. This step typically follows primary treatment, where solids are settled out, and is essential for reducing biochemical oxygen demand (BOD) and ensuring that the effluent is safe for discharge or further processing. It can utilize natural or engineered systems to break down pollutants, highlighting the importance of microorganisms in maintaining water quality.

5 Must Know Facts For Your Next Test

1. Secondary treatment significantly reduces BOD levels in wastewater, often achieving reductions of 85% or more.
2. This process can occur in various forms, including activated sludge systems, trickling filters, and oxidation ponds.
3. Microorganisms play a vital role in secondary treatment, breaking down organic matter and transforming it into less harmful substances.
4. Aeration is a key component in many secondary treatment processes, providing the necessary oxygen for microorganisms to thrive.
5. The success of secondary treatment is usually monitored through testing for residual BOD and total suspended solids in the treated effluent.

Review Questions

• How does secondary treatment differ from primary treatment in wastewater management?
  • Secondary treatment differs from primary treatment primarily in its focus on biological processes to remove dissolved and suspended organic materials. While primary treatment involves physical methods like sedimentation to separate solids from wastewater, secondary treatment utilizes microorganisms to decompose organic matter. This not only reduces biochemical oxygen demand (BOD) significantly but also helps prepare the effluent for either discharge into water bodies or for further purification processes.
• Evaluate the importance of microorganisms in the secondary treatment process and their impact on water quality.
  • Microorganisms are essential in secondary treatment as they play a critical role in breaking down organic pollutants present in wastewater. These organisms metabolize organic matter, significantly reducing biochemical oxygen demand (BOD) and transforming harmful substances into less toxic forms. The effectiveness of this biological process directly impacts water quality, ensuring that treated effluent meets environmental standards before being released back into natural water bodies.
• Assess how different methods of secondary treatment can influence the overall efficiency of wastewater management systems.
  • Different methods of secondary treatment, such as activated sludge processes or trickling filters, can greatly influence the overall efficiency of wastewater management systems by affecting pollutant removal rates and energy consumption. For instance, activated sludge systems typically provide higher BOD reduction but may require more energy for aeration compared to trickling filters, which are more passive but can be less effective under certain conditions. Choosing the appropriate method based on specific environmental and operational needs is crucial for optimizing treatment efficiency and ensuring compliance with regulatory standards.

Related terms

biochemical oxygen demand (BOD): A measure of the amount of oxygen that microorganisms will consume while decomposing organic matter in water, indicating the level of pollution.

activated sludge process:

A commonly used method in secondary treatment where aeration tanks promote the growth of microorganisms that digest organic pollutants.

trickling filter: A type of biological treatment system where wastewater is passed over a bed of media covered with microorganisms that break down contaminants.