Explain the function of bar screens in a wastewater treatment plant.

Solve this crossword puzzle:

Across
3. Liquid waste products.
4. Solid waste extracted in sewage treatment.
6. A word related to hygiene.
8. Waste matter discharged from the human body.
Down
1. Used water.
2. A pipe carrying sewage.
5. Microorganisms which causes cholera.
7. A chemical to disinfect water.

Study the following statements about ozone:

(a) It is essential for the breathing of living organisms.

(b) It is used to disinfect water.

(c) It absorbs ultraviolet rays.

(d) Its proportion of the air is about $3\%$.

Which of these statements is correct?