even more. After these conditions were maintained for 6 batches
(254 d), methane production suddenly increased to 3.5 l kg− 1 CM
(25 ml g− 1 VS) at the end of the 7th batch. This continued despite
high production of ammonia at 14 g-N kg− 1 CM, which remained high
for 2 more batches, at 4 l kg− 1 CM (28 ml g− 1 VS) in the 8th batch
(duration for 55 d) and at 4.4 l kg− 1 (31 ml g− 1 VS) in the 9th batch
(duration for 55 d) (Fig. 2).