2) CO
2
-absorption Unit (Unit B): Different amounts of biogas is generated during the AD
process based on the content of the reactors (blank, positive control, negative control,
and samples). Biogas is mainly made of methane (CH
4
) and carbon dioxide (CO
2
). The
unit B is where the CO
2
and traces of hydrogen sulphide are removed through a
chemical reaction with a 3 mol/L NaOH solution (Figure 5). The absorption efficiency
is higher than 98% even at high flow rates.
Figure 5. Bottler holder designed for 9 glass bottles (250 mL). AMPTS III is equipped with two bottle
holders.
Carbon dioxide reacts with sodium hydroxide in an acid-base reaction to generate
sodium carbonate and sodium bicarbonate:
In this case, only methane will reach the detection unit (single gas measurements). If
the test aims to measure biogas, the Unit B is not needed, where the setup should
present the following configuration (Figure 6).
Figure 6. Setup for total gas (e.g., biogas) measurements.
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