Comparative studies of co-conversion of waste activated sludge and lignocellulosic wastes through hydrothermal liquefaction

The effects of feedstock type on hydrothermal liquefaction were explored through the co-conversion of waste activated sludge and various lignocellulosic biomass sources, including birchwood sawdust, cornstalk, and waste newspaper. This investigation aimed to produce bio-oil under consistent conditions at 310 °C and a 10-min reaction time, with subsequent comparison to results obtained using single feedstocks. The co-feeding of sludge with cornstalk and sawdust demonstrated the highest bio-oil yields at 34.2 % and 33.7 % wt%, respectively. The comprehensive characterization of the bio-oil products revealed that feedstock type influenced elemental composition and, consequently, the higher heating value of the bio-oils. Bio-oils derived from co-feeds exhibited a significant presence of nitrogenous compounds, esters, and fatty acids in contrast to the high percentage of phenolic compounds found in bio-oils from single feedstocks. Furthermore, these co-feed bio-oils displayed lower molecular weights, higher quantities of low boiling point compounds, increased volatile matter content, and reduced fixed carbon content compared to bio-oils produced from single feedstocks. • Co-conversion of wastewater sludge and lignocellulosic biomass was investigated. • A maximum bio-oil yield in the range of 33–34 wt% was obtained using mixed feedstock. • Co-conversion resulted in higher quality bio-oils compared to single feedstock. • By-products of the process can be used for energy generation or as fertilizers.