Production of low phenolic naphtha-rich biocrude through co-hydrothermal liquefaction of fecal sludge and organic solid waste using water-ethanol co-solvent

Abstract

Biocrude production from wet waste through hydrothermal liquefaction (HTL) has become a hotspot for researchers that serves as an alternative to fossil fuel, reducing greenhouse gas emissions and promoting waste to energy approach. However, higher phenolic compounds in hydrothermal liquefaction-derived biocrude have raised concerns about its quality. This study focuses on the production of low phenolic naphtha-rich biocrude through co-liquefaction (320 °C and 60 min) of fecal sludge (FS) and organic solid waste (OSW), two major wet streams by optimizing feedstock (1:0, 1:1, 0:1) and water-ethanol co-solvent (1:0, 3:1, 1:1, 1:3, 0:1). The results revealed that the highest biocrude yield of 55.7 % was achieved at 1:1 (FS: OSW) feedstock and 1:1 (water: ethanol) co-solvent with a heating value of 37.5 MJ/kg, indicating its potentiality to replace petrocrude (42–49 MJ/kg). Notably, produced biocrude is enriched with a lighter fraction (C < 20) of 90 % (85 % naphtha and 5 % jet fuel). The composition of the biocrude comprises 58 % ester, 25 % hydrocarbon, 15 % organic acid, and <1 % phenol, which ensures the least amount of phenolic compounds due to the replacement of the –OH group by the more stable ethoxy group, leading to increased naphtha yield and the absence of phenolic toxicity. Furthermore, the highest API value was recorded at 23.3, which emphasizes its similarity to conventional petroleum API gravity (medium-lighter crude). This energy-positive system (energy recovery 88 % and energy consumption ratio 0.38) could generate revenue of US$ 550 per metric ton of feedstock, suggesting the potentiality of commercialization and contributing to sustainable green energy production.