Application of agro-waste rice husk ash for the removal of phosphate from the wastewater

Abstract

Discharge of phosphate into aquatic environment by various human activities such as agricultural runoff, animal waste, sewage, industry and detergents, leads to the deterioration of water quality. Hence, the effective removal of phosphate from wastewater is essentially required. Considering this, the efficiency of locally available agro-waste rice husk was examined in batch mode for the removal of phosphate using synthetic wastewater. Characterization of adsorbent was done using Fourier transform infrared, X-ray fluorescence and X-ray diffraction spectrophotometeric analysis, which indicates the crystalline silica nature and presence of Si–O–Si group. The effect of various parameters i.e. contact time, adsorbent dose, pH and temperature were studied. Up to 89% phosphate removal was achieved at pH 6 using 2 g/L dose in 120 min of contact time. The equilibrium adsorption data shows best fit for the Langmuir isotherm model (R2 = 0.991) and pseudo-second order kinetic model (R2 = 0.978). Thermodynamic parameters (ΔG, ΔH and ΔS) were also calculated and they indicate that adsorption process is exothermic. Scanning electron microscopy reveals the rough surface of absorbent, which may increases the adsorption capacity. Based on the current study, activated rice husk ash offers efficient and cost-effective removal of phosphate from wastewater.