Flocs in STP (Sewage Treatment Plants) refer to the clumps or aggregates of microorganisms that form during the treatment process. These flocs play a crucial role in wastewater treatment as they help in the removal of organic matter and pollutants from the sewage.

The correct answer is option 'C', which states that flocs in STP include filaments of fungi and aerobic bacteria. This means that the flocs are composed of both fungi and aerobic bacteria.

Here is a detailed explanation of why option 'C' is the correct answer:

1. Fungi in Flocs:
- Fungi are a group of microorganisms that play an important role in the decomposition of organic matter.
- In sewage treatment, fungi are responsible for breaking down complex organic compounds into simpler forms.
- They help in the degradation of cellulose, lignin, and other complex polymers present in the wastewater.
- Fungal filaments or hyphae can form part of the flocs, contributing to the overall structure and function of the aggregates.

2. Aerobic Bacteria in Flocs:
- Aerobic bacteria are bacteria that require oxygen for their metabolism and growth.
- In sewage treatment plants, aerobic bacteria are responsible for the breakdown of organic matter through the process of aerobic respiration.
- These bacteria utilize oxygen to break down complex organic compounds into carbon dioxide and water.
- They play a crucial role in the removal of organic pollutants and help in the clarification of the wastewater.
- Aerobic bacteria form filaments within the flocs, contributing to their structure and functioning.

3. Importance of Flocs in STP:
- Flocs provide a surface area for the attachment of microorganisms involved in the treatment process.
- They facilitate the removal of suspended solids, organic matter, and pollutants from the wastewater.
- The flocs act as a medium for the growth of microorganisms, providing them with the necessary conditions for their metabolic activities.
- The microorganisms present in the flocs help in the breakdown of organic matter, nutrient removal, and reduction of pollutants.
- Flocs also aid in the settling process, as they increase the weight and size of the particles, allowing them to settle down more easily.

In conclusion, flocs in STP include filaments of fungi and aerobic bacteria. These aggregates of microorganisms play a crucial role in wastewater treatment by facilitating the removal of organic matter and pollutants from the sewage.

Filaments of fungi and aerobic bacteria.