SS-AD of lignocellulosic biomass has recently been studied by
several researchers, but methane yields and total solids (TS) degradation
were generally low and potential instability (Liew et al.,
2012; Yan et al., 2015; Yang et al., 2015). Low methane yield could
be caused by the recalcitrance of lignocellulosic biomass or
retarded mass transfer in SS-AD, while the imbalance of nutrients
and accumulation of digestion intermediates, such as ammonia
and volatile fatty acids (VFAs), may lead to system instability.