This study examined the chemical characteristics and the anaerobic degradability of the aqueous product from hydrothermal liquefaction (HTL-ap) from the conversion of mixed-culture algal biomass grown in a wastewater treatment system. The effects of the HTL reaction times from 0 to 1.5 h, and reaction temperatures from 260 degrees C to 320 degrees C on the anaerobic degradability of the HTL-ap were quantified using biomethane potential assays. Comparing chemical oxygen demand data for HTL-ap from different operating conditions, indicated that organic matter may partition from organic phase to aqueous phase at 320 degrees C. Moderate lag phase and the highest cumulative methane production were observed when HTL-ap was obtained at 320 degrees C. The longest lag phase and the smallest production rate were observed in the process fed with HTL-ap obtained at 300 degrees C. Nevertheless, after overcoming adaptation issues, this HTL-ap led to the second highest accumulated specific methane production. Acetogenesis was identified as a possible rate-limiting pathway. (C) 2014 Elsevier Ltd. All rights reserved.