Name two groups of organisms which constitute 'flocs'. Write their influence on the level on BOD during biological treatment of sewage.

Explanation

**Step-by-Step Solution:**

1. **Identify the Groups of Organisms in Flocs:**
- The two groups of organisms that constitute 'flocs' are:
- **Aerobic Bacteria:** These bacteria thrive in the presence of oxygen and play a crucial role in breaking down organic matter in sewage.
- **Fungal Filaments (Hyphae):** These are part of fungi that form a network (mycelium) and are associated with the aerobic bacteria in the flocs.

2. **Understand the Role of Flocs in Biological Treatment of Sewage:**
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