The ammonia formation was initiated by adding 2 kg
of fresh CM with 0.8 kg of the seed sludge and NaOH to adjust
the initial pH. This fermentation was conducted as a single batch
operation for 10 days. During the first 5 days of the experiment
the resulted biogas (used as a stripper gas), was made to pass
through a gas washer solution (2 N sulfuric acid) to remove ammonia,
through the oxygen absorber bottle, containing ferrite powder,
and then returned to the headspace of the reactor. After 6 days the
treated biogas was returned to the bottom of the reactor with a gas
pump to bubble the biogas deeply through the substrate at the
flow rate of 5 L min1 as presented in Fig. 1. Samples were drawn
daily from the reactor and used for measurement of pH, ammonia
and VFAs. Samples from sulfuric acid solutions used for ammonia
removal from the biogas were also drawn at the same time intervals
to check on the absorbed ammonia.