3.2. Biogas production after hydrothermal pretreatment
The above results show that there was no significant difference in the accumulative biogas and methane yields when increasing the HTPT temperature at 120–160 °C and pretreatment time within 0–30 min. Thus, the hydrothermal condition of 120 °C, 20 min was chosen for studying the biogas production characteristics of hydrothermally pretreated CPCAR, considering that HTPT at a higher temperature means better equipment requirements and more operation problems and meanwhile HTPT at a longer duration accords means a lower operation efficiency. Here, it must be pointed out that the temperature and duration (actually 30 min for 115–122 °C due to difficulty in temperature control) enable thorough degradation of residual cephalosporin C (Zhang et al., 2014) and are necessary for material sterilization for anaerobic digestion. After HTPT under the chosen condition, the obtained suspension had a pH value of 5.2 and an View the MathML source-N concentration of 2600 mg L−1 for its supernatant liquor.