Instructions for Effective Microbial Cultivation in Wastewater Treatment

1. What is microbial seeding?

Microbial seeding is the process of introducing microorganisms into the biological treatment system to develop a microbial community capable of decomposing pollutants in wastewater. In the initial stage, microorganisms need time to adapt to environmental conditions and available nutrients. The goal of seeding is to build a strong, high-density microbial population suitable for the type of wastewater being treated. This ensures stable biological performance and long-term system operation.
Microorganisms play a core role in biological treatment, especially in stages such as activated sludge, aerobic, or anoxic processes. They can degrade organic pollutants like COD and BOD and convert nitrogen compounds (ammonia, nitrate) and phosphorus through nitrification, denitrification, and biological phosphorus removal. A well-developed microbial system not only improves treatment efficiency but also maintains system stability, minimizes shock loading, and adapts to fluctuations in flow and wastewater composition.

2. Factors affecting microbial seeding efficiency

2.1 Microbial sources

• Pure cultures are taken from activated sludge or from systems that are already stably operating, as they are already acclimated to similar wastewater environments. Choosing the right microbial source increases treatment efficiency and long-term stability.
• Commercial microorganisms are available in dry or liquid form and contain specialized strains for treating industrial, domestic, or specific pollutant-rich wastewater. Their advantages include easy storage, convenient use, and quick effectiveness during the system startup phase.

2.2 Environmental conditions

• pH: The ideal pH range is 6.5–8.5, which is optimal for most aerobic bacteria and ensures stable activity for some anaerobic microbes. A pH that is too high or too low can reduce biological productivity and cause microbial shock.
• Temperature: Keeping the temperature between 25–35 °C supports microbial activity, especially for nitrifying bacteria. If the temperature falls below 15 °C or exceeds 40 °C, biological reaction rates will significantly drop.
• DO (dissolved oxygen): Maintain >2 mg/L to ensure aerobic conditions, allowing microorganisms to efficiently degrade COD and BOD, and avoid oxygen-deficient conditions that can directly harm microbial communities.

2.3 Supporting nutrients

• A BOD:N:P ratio of approximately 100:5:1 (can vary between 100:10:1 and 100:5:1) is considered the standard to ensure that microbes have sufficient energy and nutrients for degrading organic matter, cell synthesis, and enzyme activity.
• If nitrogen or phosphorus is lacking, BOD removal efficiency may drop, causing sludge bulking or unstable floc formation.

3. What is the effective microbial seeding process?

3.1 Startup phase

In the startup phase, microbes are introduced into the biological tank along with a small amount of wastewater with low COD, allowing them to gradually acclimate. At the same time, the system must maintain gentle mixing and continuous aeration to evenly distribute microorganisms and provide enough oxygen for their activity and growth.

3.2 Adaptation phase

3.3 Stabilization phase

When the microbial community becomes stable, MLSS (mixed liquor suspended solids) should reach around 2,500–3,500 mg/L, indicating an appropriate biomass density. Microbes will also form strong flocs, settle well, and avoid sludge floating — ideal conditions for long-term operation and for minimizing biological issues such as pin-floc or sludge bulking.

4. Important notes when seeding microorganisms

• Avoid excessive COD input at once: Prevent shock loading by not adding a large amount of organic matter to the biological tank all at once, as it may stress or kill off microorganisms.
• Avoid toxic chemicals: Eliminate or minimize the introduction of oils, heavy metals, solvents, and detergents into the tank since these can inhibit microbial enzymes, disrupting nitrification, floc formation, and sludge settling.
• Daily monitoring: Monitor key indicators such as pH, DO, MLSS, SV30/SVI, along with visual observations of odor and water color to detect early changes in the environment, sludge flotation, or microbial imbalance and make timely adjustments.