Catalytic hydrothermal liquefaction of contaminated construction wood waste for biocrude production and investigation of fate of heavy metals

Abstract

Heavy metals (HMs) are undoubtedly an unavoidable nuisance in today's era, and their appropriate handling and disposal carry the utmost significance. Construction wood (CW), specifically hazardous and non-hazardous wood is contaminated due to a mixture of different materials like paints, coatings, and copper layers, etc. that need proper attention for safe disposal. Wood waste from building and urban waste streams is abundantly available, which essentials to manage appropriately for energy recovery. In that respect, this study focused on the disposal option of contaminated wood waste via hydrothermal liquefaction (HTL) by turning waste into biocrude. CW is categorized into four types named Untreated wood (UNW), Non-hazardous wood (NHZW), Hazardous wood (HZW), and Mixed wood (MXW). Maximum biocrude yield was obtained by the liquefaction of UNW followed by NHZW, HZW, and MXW in the range between 24.86 and 36.35 wt%. Additionally, the fate of selected heavy metals (chromium, copper, nickel, zinc) was investigated in HTL products. It was concluded that, by the liquefaction of CW, the majority of HMs shifted to the solid residue. The negligible amount of HMs merged into the biocrude and aqueous phase. This study suggests HTL as a promising and sustainable route for the disposal of contaminated wood waste by turning into higher added value (or high quality) products especially biocrude with less HMs concentration as a fruitful product at large scale.