The TS and VS of the substrate were determined before and after
AD. The total carbon and total nitrogen of the substrate were
analyzed with an element analyzer (VarioEl III). The pH value
was detected by a pH meter (Mettler Toledo FE20, Switzerland).
The ammonia nitrogen (AN) was measured according to the
standard method [23]. The contents of lignin, cellulose and
hemicellulose were tested according to the Van Soest method
[24]. The trace elements were tested using ICP-AES (VISTA-MPX,
USA). The compositions of biogas were determined using an
Agilent gas chromatography (Agilent Micro3000-GC)