In STP, solid and large sized wastes are removed by .................. while organic wastes are subjected to microbial decomposition by ..................

Explanation

**Step-by-Step Solution:**

1. **Understanding STP**: The question refers to a Sewage Treatment Plant (STP), which is designed to treat wastewater and sewage.

2. **Primary Treatment**: In the first stage of sewage treatment, known as primary treatment, solid and large-sized wastes are removed. This is typically done through a process called filtration, where larger particles are separated from the liquid waste.

3. **Identifying the First Blank**: Based on the explanation of primary treatment, the first blank in the question can be filled with "primary treatment".

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