A two-step process for sewage sludge treatment: Hydrothermal treatment of sludge and catalytic hydrothermal gasification of its derived liquid

• Published in: Fuel processing technology 2018-11, Vol.180, p.67-74
• Main Authors: Zhang, Xiao-Pei, Zhang, Cheng, Li, Xin, Yu, Sheng-Hui, Tan, Peng, Fang, Qing-Yan, Chen, Gang
• Format: Article
• Language: English
• Subjects: Carbon dioxide; Catalysis; Catalysts; Catalytic hydrothermal gasification; Catalytic oxidation; Derived liquid; Flow velocity; Fluid dynamics; Fuel cells; Gasification; Hydrothermal treatment; Liquid flow; Methane; Sewage sludge; Sludge; Sludge disposal; Water treatment plants
• ISSN: 0378-3820; 1873-7188
• DOI: 10.1016/j.fuproc.2018.08.012

The worldwide increase in amount of sewage sludge has recently attracted considerable interest in developing an efficient and economical sludge disposal method. A sewage sludge treatment process combining the hydrothermal treatment (HT) of sludge and the catalytic hydrothermal gasification (CHTG) of its derived liquid (HT&CHTG-Process) is proposed in this paper. Liquid hourly space velocity (LHSV) value of 25–100 h−1 and liquid flow rate of 10–40 mL/min were employed with a self-designed CHTG experimental setup. During the first stage of the HT-Process, approximately 56% of the carbon in the sludge was transferred into the derived liquid at 300 °C. During the second stage of the CHTG-Process, the derived liquid was gasified into CH4, H2, and CO2 using a Ni/carbon catalyst, and the carbon conversion reached 88% at 350 °C and 20 MPa with a LHSV of 25 h−1. Using the integrated HT&CHGT-Process, approximately 0.78 Nm3 of CH4, 0.62 Nm3 of H2 and 0.31 Nm3 of CO2 were generated from 1 kg of carbon in the sewage sludge. The combined process was expected to be an efficient method for sewage sludge treatment due to its mild conditions (≤350 °C and ≤20 MPa) and high yield of fuel gases. [Display omitted] •A novel two-step process for treatment of sludge and its derived liquid is proposed.•Catalytic hydrothermal gasification was conducted in a self-designed experimental setup.•The integrated process was carried out under mild conditions.•0.78 Nm3 of CH4, 0.62 Nm3 of H2 and 0.31 Nm3 of CO2 were generated from 1 kg of carbon in sludge.