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.

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