What is the main role of microbial activity in a septic system?

The main role of microbial activity in a septic system is to decompose waste materials into simpler compounds. This process is essential for breaking down solid waste and organic materials that enter the septic tank. The bacteria present in the system perform anaerobic digestion, which allows them to consume and break down these materials, converting them into liquid effluent and gases.

This microbial decomposition is critical because it reduces the volume of waste and helps to convert potentially harmful substances into less harmful byproducts, which can safely flow into the drainage field and be further treated by the soil. Through this breakdown of waste, the bacteria play a vital role in maintaining the efficiency and effectiveness of the septic system, ensuring that it operates properly and minimizes environmental impact.

In contrast to other options, filtering water is a secondary function of septic systems where soil plays a significant role, maintaining water levels is not a primary function of microbial activity, and extracting nutrients for plant growth is a function associated with the effluent's interaction with the soil rather than the microbial activity within the septic tank itself.