Interaction between sewage sludge components lignin (phenol) and proteins (alanine) in supercritical water gasification

The interaction between lignin and proteins was investigated to improve understanding of supercritical water gasification (SCWG) of sewage sludge from water treatment. Phenol and alanine were used as model compounds, and mixed in proportions from 0 to 100%. The mixtures were gasified at 400 °C and 22-26 MPa in a batch reactor with a residence time of 30 min. SCWG of the mixtures enhanced total gas, H2, and CO2 yields compared with weighted average values. The maximum increase of H2 yield was at 60 wt% alanine, and the H2 yield was about twice the weighted average value. Co-gasification of the compounds in supercritical water facilitated the removal of total organic carbon and total nitrogen from the aqueous phase, and the generation of oil phase products, mainly phenol compounds and organic compounds containing nitrogen. The increase of gas and oil phase products may be caused by phenol promoting the decomposition of alanine, while alanine promotes the condensation of phenol.