Removal of phosphates from eutrophic water by utilizing Sylhet sand and rice hull ASH as low-cost adsorbent

Abstract

Phosphorous is an important nutrient moreover discharge of phosphate into aquatic environment by various human activities causes the deterioration of water quality and causes as threat to the environment by facilitated algal bloom.Hence, the effective removal of phosphate from wastewater is essentially required.Various methods or techniques have been applied for the removal of phosphate from wastewater. Among the various techniques applied, adsorption has been found to be most attractive phosphate removal method, due to its high efficiency, simplicity and economic validity. In this study, we exploited the strong selective interaction of phosphate withFe containing Rice hull ash(RHA) and Sylhet sand. Sylhet sand didn’t need any modification & used directly for the adsorption process. On the contrary, RHA was modified by FeCl3 for this study for adsorbing phosphates. The efficiency of locally available RHA and Sylhet sand examined in batch and column mode for the removal of phosphate using synthetic wastewater. Characterization of adsorbents was done by using Fourier transform infrared (FTIR), X-ray diffraction spectrophotometric analysis (XRD). Adsorption studies shows the optimal conditions for phosphate removal were pH 5 and a 3-hour contact time. Fe-treated rice hull ash removed 78.5% of the phosphate from a 5-ppm test solution. The Sylhet sand achieved a 49.6% reduction. When an actual sample of runoff from the Tangua hoar was subjected to the sorbents, the rice hull ash removed 83.8% and the Sylhet sand removed 83% for same test solution. Both materials were found to be re-usable for several cycles of phosphate removal. Phosphate removal study shows that, 42.9% &71.6% recovery of adsorbed phosphorous from Rice hull ash and Sylhet Sand respectively. Among the desorbed phosphorous 74% could be recovered by precipitating as FePO4. The overall removal capacities of the two sorbent materials were 2.37 μg/g rice hull ash (RHA) and 0.475 μg/g Sylhet sand. This ratio of about 5 to 1 is reflected in the quantities of sorbents that were used in this series of experiments. This data shows that Sylhet Sand is an effective adsorbent to remove excess phosphate from waste water.