Table 3.

Comparison of the results obtained during this work with other research works in the literature.

Material	Pretreatment	Type of digestion	Yield of untreated	Yield of treated	% improvement	Reference
			(mL CH4/gVS)
Spruce	Alkali	Thermophilic	30	50	74	Mirahmadi et al., 2010
Birch	Alkali	Thermophilic	250	460	83	Mirahmadi et al., 2010
Spruce	Ionic liquids	Thermophilic	66	245	271	Teghammar et al., 2012
Spruce	NaOH/thiourea	Thermophilic	30	210	600	Mohsenzadeh et al., 2012
Birch	NaOH/thiourea	Thermophilic	230	360	57	Mohsenzadeh et al., 2012
Pine	Alkali	Mesophilic	65	178	181	Salehian et al., 2013
Mixture of spruce and pine	Ionic liquids	Thermophilic	70	150	114	Kabir et al., 2014
Mixture of spruce and pine	Organosolv	Thermophilic	50	340	580	Kabir et al., 2015
Spruce	Hydrothermal	Thermophilic	10	276	2660	Present work
Pine	Hydrothermal	Thermophilic	5	180	3500	Present work
Birch	Hydrothermal	Thermophilic	18	305	1594	Present work