Improving Biomethane Production and Mass Bioconversion of Corn Stover Anaerobic Digestion by Adding NaOH Pretreatment and Trace Elements

Table 2

Factors and levels of coding table.

Factor	Level
	1; mg·L^−1·d^−1	2; mg·L^−1·d^−1	3; mg·L^−1·d^−1	Compounds
A (Fe)	1.00	5.00	10.00	FeCl2·4H2O
B (Co)	0.05	0.20	0.40	CoCl2·6H2O
C (Ni)	0.20	0.40	0.60	NiCl2·6H2O