Fill in the following blank with suitable words:
Vermi-processing toilets use…………..to treat human waste.

Answer

**Step-by-Step Solution:**

1. **Identify the Type of Toilet**: The question refers to "Vermi-processing toilets," which are a specific type of toilet designed to treat human waste.

2. **Understand the Treatment Process**: In vermi-processing toilets, human waste is treated using a natural process involving living organisms.

3. **Identify the Organism Used**: The key organism used in this process is earthworms. They play a crucial role in breaking down the human waste.

4. **Complete the Sentence**: Based on the information gathered, we can fill in the blank in the sentence: "Vermi-processing toilets use **earthworms** to treat human waste."

5. **Explain the Outcome**: The process not only treats the waste but also converts it into a useful product known as vermicakes, which can be used as manure and fertilizer.

**Final Answer**: Vermi-processing toilets use **earthworms** to treat human waste.

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