Assessment of leaching properties of solid residue from subcritical water extraction of

\nLandfilling is known as a popular way to get rid of municipal waste because it is easy to use and reasonably priced, but it also leads to environmental issues like leachate pollution. Thus, solid residues from Zingiber zerumbet rhizome subcritical water extraction (SWE) were assessed in this study to see if they met the criteria for municipal waste that could be disposed of safely in a landfill. The assessment comprises of four crucial properties; ignitability, corrosivity, reactivity, and toxicity and was conducted on a sample taken during a 15-minute SWE following the United States Environmental Protection Agency (USEPA) and Malaysian Department of Environment (DOE) criteria. The residue was found to be non-ignitable (flash point above 200°C), non-corrosive (pH of 6.65 ± 0.02), and non-reactive (no visible toxic gases, vapors, or fumes) in normal environmental settings. Meanwhile, in accordance with the Toxicity Characteristics Leaching Procedure (TCLP), the toxicity analysis results were considered at their maximum limits. Heavy metals such as barium showed the highest detectable concentration at < 0.8 mg/L, while cadmium followed at < 0.6 mg/mL, but both remained below the limits of ≤ 100.0 mg/L and ≤ 1.0 mg/L, respectively. The volatile organic compounds (VOCs), semi-volatile organic compounds (SVOCs) and herbicides detected in the sample were at remarkably low concentrations below the legal limit. Overall, these results provide convincing evidence that the solid residues of the rhizome of Z. zerumbet from the SWE can be categorised as municipal solid waste. Pre-treatment prior to landfill is therefore unnecessary. SWE promotes ecological waste management practises thus contributing to a safer and more sustainable future for all.\n