Spectroscopic and Microscopic Analysis of Humic Acid Isolated from Stabilized Leachate HSs Fractionation

Abstract

Refractory humic substances (HSs), which include humic and fulvic acid as well as hydrophilic portion, are the prime pollutants of stabilized landfill leachate with a concentrated color and chemical oxygen demand (COD). Spectroscopic and microscopic analysis of humic acid remaining in stabilized leachate as a pollutant contributor were conducted in this study. Microfiltration and centrifugation processes were applied to fractionate the humic acid from the HSs of stabilized leachate. The three-stage isolation process recovered a maximum of 1412 ± 2.5 mg/L (Pulau Burung leachate), 1510 ± 1.5 mg/L (Alor Pongsu leachate) at pH 1.5 and 1371 ± 2.5 mg/L (PBLS), and 1451 ± 1.5 mg/L (APLS) of humic acid (about 42% of the total COD concentration) at pH 2.5, which eventually indicates the efficiency of the process. The spectroscopic analysis of isolated humic acid through scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR) significantly indicates the existence of identical elements in the recovered humic acid. The subsequent reduction (around 37%, 36%, and 39%) in ultra-violet absorbance values (UV254, UV280), COD, and color in the humic acid isolated leachate indicates the acid’s significant contribution as a toxic pollutant through aromaticity and conjugated double-bond compounds.