Which type of material do bacteria in activated sludge primarily feed on?

Bacteria in activated sludge primarily feed on organic material, which serves as their main energy and nutrient source. In wastewater treatment, activated sludge systems utilize these microorganisms to break down organic pollutants present in the water. The organic material typically includes a variety of substances such as carbohydrates, proteins, and fats.

The process of these bacteria metabolizing organic material leads to the production of biomass (new bacterial cells) and other byproducts, ultimately helping to improve the quality of the effluent being treated. This biological activity is essential for reducing the biochemical oxygen demand (BOD) of the wastewater, making it cleaner before it is released into the environment or further treated.

In contrast, while the other materials listed can be involved in various treatment processes, they do not serve as primary food sources for the bacteria. Aluminum sulfate is often used as a coagulant in water treatment, salts may play roles in various chemical reactions, and polyelectrolytes can help in the flocculation process, but none of these substances meet the nutritional and energy needs of the bacteria in the same manner that organic material does.