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Question 20N.3.SL.TZ0.11

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Date November 2020 Marks available [Maximum mark: 4] Reference code 20N.3.SL.TZ0.11
Level SL Paper 3 Time zone TZ0
Command term Explain Question number 11 Adapted from N/A
11.
[Maximum mark: 4]
20N.3.SL.TZ0.11

Trickle filter beds are used to treat sewage.

[Source: © International Baccalaureate Organization 2020.]

Explain the role of biofilms in sewage treatment.

[4]

Markscheme

a. biofilms are formed by bacteria;

b. bacteria in the biofilm secrete a matrix/EPS;

c. (matrix of biofilm) attaches (firmly) to the trickle bed/rocks/gravel/plastic/other media;

d. the biofilm breaks down organic material / feed on sewage
OR
the bacteria in the biofilm are saprophytic;

e. aerobic conditions are maintained through the bed / by aerating sprinklers;

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