406 / 2018-07-01 17:28:25

Hydrothermal conversion of sewage sludge: focusing on the characterization of wastewater and their methane yields

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The conversion of sewage sludge into bio-oil and hydro-char by hydrothermal conversion (HTC) has been well studied. However, there are huge amount of wastewater (HTCWW) generated during the HTC, which is often overlooked. The present study aimed to investigate the organic compositions of HTCWW obtained under different temperatures and residence time (170 °C-320 °C, 0.5–6 h) and their potential use for methane production through anaerobic digestion (AD). Results showed that the methane yield achieved 286 mL CH4/g COD when hydrothermal temperature was 170 °C while it was decreased to only 136 mL CH4/g COD when temperature was increased to 320 °C. The methane yields of HTCWW were also decreased with the increase of hydrothermal residence time. Further study showed that proteins and volatile fatty acids (VFAs) were the main products of HTCWW. Although high amount of easily degradable compounds of VFAs were produced, more recalcitrant degradable compounds have also been detected in HTCWW when hydrothermal temperature was increased. 3D-EEM analysis showed that more humic acid-like and melanoidins refractory organics were produced, which might result in the lower methane yield of HTCWW obtained at increased temperatures