When is it necessary to add microorganisms to a wastewater treatment system?

In today’s wastewater treatment systems, microorganisms play a central role in decomposing and removing organic pollutants. However, during operation, the microbial population may decline due to various causes such as shock loading, toxic chemicals, or unstable environmental conditions. At that point, microbial supplementation becomes a necessary solution to restore treatment efficiency and ensure that the effluent quality meets the required standards.

1. Overview of microorganisms in wastewater treatment

Microorganisms are extremely small living organisms that cannot be seen with the naked eye and require a microscope for observation. They include various groups such as bacteria, fungi, algae, and protozoa. In the natural environment, microorganisms exist everywhere, especially in water, soil, and air. Thanks to their ability to decompose and convert organic substances, they play an important role in many biological processes.

In wastewater treatment systems, microorganisms play a core role in breaking down organic pollutants. They use compounds such as BOD and COD as nutrient sources for growth and development. Through this process, harmful substances are converted into simpler and less hazardous forms. As a result, the quality of treated water is significantly improved before being discharged into the environment.

Common types of microorganisms (aerobic, anaerobic, anoxic)

• Aerobic microorganisms: This group requires dissolved oxygen (DO) to grow and decompose organic matter. They typically operate in aeration tanks or aerobic biological treatment tanks.
• Anaerobic microorganisms: This group functions in an oxygen-free environment. They break down complex organic matter into gases such as CH₄ and CO₂.
• Anoxic microorganisms: This group operates under conditions with little to no free oxygen but can still utilize oxygen from compounds such as NO₃⁻.

In wastewater treatment systems, microorganisms play a key role in decomposing organic pollutants.

2. Signs indicating the need for microbial supplementation

When a wastewater treatment system is not operating effectively, this is often a sign that the microbial population is experiencing issues. Early identification of abnormal signs helps ensure timely microbial supplementation and prevents impacts on effluent quality.

• Wastewater has an unusual foul odor: The presence of foul odor indicates that the decomposition of organic matter is incomplete or interrupted. This is often caused by weakened or insufficient microorganisms. If not treated promptly, the odor problem will become increasingly severe.
• High COD and BOD levels: When pollution indicators such as COD and BOD exceed allowable limits, it indicates that the microorganisms cannot handle the pollutant load in time. This is a clear sign of insufficient microbial density or reduced microbial activity. Supplementation is required to restore treatment capacity.
• Weak sludge with poor settling ability: Activated sludge becomes loose, fails to form flocs, or settles poorly, indicating an unstable microbial system. This directly affects sludge-water separation efficiency. The cause is usually microbial death or nutrient deficiency.
• Excessive foam or scum formation: An abnormal layer of foam or scum on the tank surface indicates microbial imbalance. Certain filamentous bacteria may proliferate when the microbial system weakens. This is a sign that requires close monitoring and early corrective action.
• Unstable system operation: Fluctuating treatment efficiency, effluent not meeting standards, or inconsistent performance are clear warning signs. This is often related to microbial decline or imbalance. Microbial supplementation will help stabilize the system again.

3. Appropriate timing for microbial supplementation

Supplementing microorganisms at the right time helps the wastewater treatment system quickly achieve optimal performance. If carried out promptly, many operational risks and additional costs can be minimized.

Supplementing microorganisms at the right time helps the wastewater treatment system quickly achieve optimal performance.

3.1 During initial system startup

At the initial stage of operation, the microbial population has not yet been established or is still very weak. Microbial supplementation helps shorten the acclimation period and quickly establish a stable microbial community. As a result, the system can achieve the desired treatment efficiency sooner.

3.2 After system cleaning or maintenance

The cleaning or maintenance process may significantly reduce the microbial population in the tank. This causes the system to lose balance and operate less effectively for a short period. Supplementing microorganisms helps rapidly restore the biological system and stabilize the treatment process.

3.3 When microbial die-off occurs

“Microbial die-off” occurs when most microorganisms are destroyed due to shock loading or toxic chemicals. At that point, the treatment capacity is almost completely lost and needs to be rebuilt from the beginning. Microbial supplementation is the necessary solution to restore system performance.

3.4 After environmental incidents (heavy rain, abnormal discharge)

Factors such as heavy rain or sudden wastewater discharge may alter pH, temperature, and pollutant loading. This directly affects the survival and activity of microorganisms. Supplementing microorganisms after such incidents helps the system quickly regain balance and return to stable operation.

4. How to supplement microorganisms effectively

Proper microbial supplementation plays an important role in ensuring wastewater treatment efficiency. If carried out correctly, the system will quickly stabilize and achieve high treatment performance.

• Selecting the appropriate microbial strains: It is necessary to choose the correct type of microorganisms according to the wastewater characteristics, such as aerobic, anaerobic, or anoxic strains. Specialized microorganisms help improve pollutant degradation efficiency and shorten the acclimation period. In addition, products with clear origin and stable quality should be prioritized.
• Dosage and application method: The use of microorganisms must follow the manufacturer’s recommended dosage to ensure effectiveness. Too little supplementation will result in insufficient microbial density, while too much may cause system imbalance. It is recommended to dissolve or activate the microorganisms before introducing them into the tank to enhance their activity.
• Optimal environmental conditions (pH, DO, temperature): Operating conditions directly affect microbial activity. In general, a suitable pH range is 6.5–8.5, sufficient DO for aerobic systems, and stable temperature conditions will support healthy microbial growth. If these parameters exceed acceptable limits, treatment efficiency will decrease significantly.
• Combined nutrient supplementation: Microorganisms require nutrients such as nitrogen (N) and phosphorus (P) for growth and organic matter degradation. When wastewater lacks nutrients, microorganisms will perform poorly or weaken. Balanced nutrient supplementation helps maintain a healthy and stable microbial system over the long term.

Proper microbial supplementation plays an important role in ensuring wastewater treatment efficiency.

Supplementing microorganisms at the right time and in the correct manner not only helps the wastewater treatment system operate stably but also improves treatment efficiency and reduces operating costs. At the same time, maintaining suitable environmental conditions and conducting regular monitoring will help the microbial population develop sustainably. Therefore, understanding when microbial supplementation is required is a key factor in ensuring the long-term efficiency of the entire system.