This study is an assessment of hydrothermal pre-treatment of waste activated sludge for enhancement of
biogas production by anaerobic digestion. This assessment was carried out in order to ascertain the
optimal hydrothermal pre-treatment temperature. Anaerobic digestion efficacy was investigated by
biochemical methane potential (BMP) tests and subsequent statistical analyses. Hydrothermal pretreatment
was found to improve solubilization of waste activated sludge and increase the response
surface, resulting in increased biogas production. BMP tests revealed that hydrothermal pre-treatment of
waste activated sludge increased COD solubilization (30e37%) and soluble COD (SCOD) levels; in addition,
it reduced volatile solids (VS), and improved final methane yields. The optimum temperature for
hydrothermal pre-treatment using subcritical water was found to be ~180e210 C. Methane yields of
130.2 (180 C pre-treatment) and 126.6 (210 C pre-treatment) ml CH4/g-VS were measured following
hydrothermal pre-treatment. In pre-treated waste activated sludge samples, methane composition was
found to be 63.4 and 58.8% (180 and 210 C pre-treatment, respectively) and VS removal was measured to
be ~60 and 58% (180 and 210 C pre-treatment, respectively). These findings show that in order to
achieve high conversion efficiency, an accurately designed pre-treatment step must be included in the
overall anaerobic digestion process for wastewater treatment