How to Reduce Biological Oxygen Demand (BOD) in Wastewater

Compliance with environmental discharge limits depends on effectively reducing the organic pollution load in wastewater. The two primary indicators of this load are Biological Oxygen Demand (BOD) and Chemical Oxygen Demand (COD).

High levels of BOD and COD indicate a significant presence of organic matter, which, if discharged untreated, can consume essential oxygen in receiving water bodies, thereby harming aquatic life. Fortunately, modern aeration wastewater treatment systems and biological processes provide highly efficient solutions.

Here’s an overview of the core strategies and key technologies for achieving maximum organic load reduction:

1. The Role of Aerobic Treatment: Activated Sludge

The most common and effective method for rapidly reducing biological oxygen demand is through aerobic treatment, primarily the activated sludge treatment process. This method involves cultivating a dense, healthy population of aerobic bacteria and microorganisms in an aeration tank. These microbes consume soluble organic matter in wastewater as their food source, converting it into harmless byproducts such as carbon dioxide and water, along with new biomass.

Enhancing Aeration Efficiency: The KEE Triton

The efficiency of activated sludge treatment is directly related to the amount of Dissolved Oxygen (DO) supplied to the bacteria. High-efficiency aeration technology plays a crucial role here:

• The KEE Triton: This dual-function surface and submerged aerator and mixer maximises oxygen transfer while simultaneously providing the necessary mixing to keep the activated sludge in suspension and in constant contact with the pollutants. Its ability to rapidly achieve high DO levels results in faster BOD and COD reductions and lower energy costs.

2. Utilising Anaerobic Treatment for High-Strength Waste

For industrial facilities dealing with high-strength wastewater, typically characterised by very high COD concentrations, such as those from food processing, brewing, or chemicals, anaerobic reactor technology offers a powerful and energy-efficient solution.

In an anaerobic reactor, organic matter is broken down without the presence of oxygen. The primary advantages include:

• Biogas Production: This process converts up to 90% of the organic load into biogas (methane), which can be captured and used to power the facility, providing substantial energy recovery benefits.
• Reduced Sludge: Anaerobic digestion generates significantly less sludge than aerobic methods, lowering disposal costs.

Using an anaerobic reactor as a pretreatment step enables efficient removal of the bulk of the high COD load, significantly reducing the load on the subsequent aerobic polishing stage.

3. Integrated Solutions for Enhanced Stability (IFAS)

Specific wastewater streams may be susceptible to shock loads or lack sufficient capacity for expansion. In such cases, an Integrated Fixed-Film Activated Sludge (IFAS) system presents a viable solution.

IFAS enhances traditional activated sludge treatment by introducing high-surface-area plastic carriers (media) into the aeration tank. These carriers provide a stable environment for a secondary population of microorganisms (a fixed biofilm) that complements the suspended bacteria. This dual-growth system offers:

• Stability: The attached biofilm demonstrates high resistance to shock loading and pH fluctuations.
• Capacity: It increases the concentration of active biomass in the tank without requiring additional space, resulting in higher BOD removal rates.

4. Essential Pre-Treatment and Physical/Chemical Steps

Before the biological treatment stages, several preliminary steps can significantly reduce the initial organic load:

• Solids Removal: Eliminating Total Suspended Solids (TSS) through screening, sedimentation, or Dispersed Air Flotation (DAF) is the priority, as a substantial portion of the biological oxygen demand is associated with these solids.
• Chemical Treatment: For pollutants that are difficult for microbes to digest (non-biodegradable COD), chemical treatment processes such as coagulation and flocculation can be employed. These processes group fine organic particles, facilitating easier separation and removal.
• pH Control: Maintaining the wastewater stream at the optimal pH is critical because biological processes are sensitive to acidity and alkalinity.

By selecting the appropriate combination of high-efficiency wastewater aeration systems, such as the Triton, which integrates an anaerobic reactor, and fine-tuning your overall activated sludge treatment strategy, you can consistently achieve the low BOD and COD levels required for compliance and environmental sustainability.