Spectroscopic Assessment of Dissolved Organic Matter Removal in Adsorbent-Based Water Filtration Assisted by Comsol Multiphysics

Abstract

This study sought to characterise and evaluate the Dissolved Organic Matter adsorption capacity of granular activated carbon, using X-ray diffraction, Fourier transform infrared spectroscopy, absorbance, transmittance, fluorescence, and polarized light microscopy. The impact of the activating agents, adsorbent mass, and retention times on the adsorbent's performance was assessed. Twelve adsorbents were prepared, six CaCl2 activated and six NaCl activated. The adsorbents were derived from a furnace or conventional carbonisation of coconut shells, cassia siamea tree, and shea nut tree branches. The adsorbents were tested using a surface water sample at different retention times (5 minutes, 10 minutes, and 15 minutes) and adsorbent masses (10 g, 20 g, and 30 g). Analysis of the X-ray diffraction spectra revealed the presence of three phases of silicon dioxide (SiO2). This indicates the amorphous nature of the adsorbents and confirms the presence of carbon and graphite, which are essential for effective adsorption. The Fourier transform infrared spectra exhibited C–O and Si–O stretching, attributed to the presence of silicon- containing minerals. Absorbance, transmission, and fluorescence results demonstrated a high efficiency in DOM removal, particularly for the CaCl2- activated adsorbents (75%). These findings were further validated through multivariate analysis. The polarized light imaging technique proved effective in distinguishing between the efficiency of the adsorbent at a polarization angle of 90 o. Each technique provided valuable insights into the adsorbents' performance in DOM removal from surface water. The study was assisted by COMSOL Multiphysics simulation, which mimicked the behaviour of the adsorbents under specific filtration conditions.