Phosphate Adsorption from Aqueous Solution Using Different Mass of Raw Waste Marsh Clam Shells as an Alternative Novel Adsorber

Eutrophication occurs when excess phosphate is released from domestic wastewater, deteriorating the receiving water body. Phosphate pollutants are effectively removed by using chemical treatment in the tertiary wastewater treatment process; however, this method bears a high cost. Hence, this study used waste raw marsh clam shells as an adsorbent to remove phosphate from a synthetic phosphate solution (10 mg/L). The phosphate solution was mixed with the different adsorbent masses (2, 4, 6, 8, and 10 g) with particle sizes ranging from 1.18 to 2.36 mm. The batch experiment data were fitted to kinetic and isotherm adsorption models. The physicochemical properties of the shells were also analyzed to determine the adsorbent characteristics by using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray fluorescence (EDXRF), and Fourier transform infrared spectroscopy (FTIR). In this study, the highest phosphate removal efficiency from solution was 51.67% in 10 g of raw adsorbent, where the high amount of adsorbent increased phosphate removal efficiency from the solution due to the high number of active sites on the adsorbent surface. The data fitted well with a pseudo-second-order kinetic model where the R2 value was 0.9989, demonstrating that the adsorption process is a chemisorption. Meanwhile, the analysis of the isotherm model shows that the Freundlich model (R2 = 0.7322) is the best model to represent phosphate adsorption onto marsh clam shell, showing that the adsorbent surface is heterogeneous. In a nutshell, raw marsh clam shell has been proven to be an excellent adsorbent material for removing phosphate from wastewater.