# DBT JRF 2020 — Question 104

Exam: DBT JRF 2020 · Section: B · Topic: Bioprocess Engineering · Difficulty: Hard

## Question

Which of the following is not a suitable material for a depth filter used in air sterilization?

## Options

- **A.** muslin cloth (pore size = 40 - 50 μm)
- **B.** glass wool (pore size < 10 μm)
- **C.** norite (pore size = 0.1 - 4 μm)
- **D.** glass fiber (pore size = 2 – 8 μm)

## Answer

Option A

## Explanation

Air sterilisation depth filters remove microorganisms by interception, impaction, and diffusion mechanisms (NOT by sieving/pore exclusion). Effective pore sizes for sterilisation: Bacteria average 1–2 μm diameter → filter must have effective pore size <10 μm to retain bacteria by interception. Evaluation of options: Glass wool (pore size <10 μm) ✔ suitable; Norite (activated carbon, pore 0.1–4 μm) ✔ suitable; Glass fibre (2–8 μm) ✔ suitable; Muslin cloth (pore size 40–50 μm) ✘ NOT suitable — the 40–50 μm pores are far too large to retain bacterial cells (1 μm) by interception. Air would pass through muslin carrying bacteria along with it. Therefore muslin cloth is NOT a suitable depth filter for air sterilisation.

Source: https://mypyqbuddy.com/questions/which-of-the-following-is-not-a-suitable-6a05a8a02adafec470293280