This is
lower than that for manure from other farm animals, food waste,
and waste active sludge (Bujoczek et al., 2000; Niu et al., 2013)
and can lead to operational difficulties through inhibition of the
methanogenic microflora as a result of free ammonia accumulation
in the digester (Sun et al., 2015a; Yenigun and Demirel, 2013).