Phosphorous removal from human urine using lateritic soil

Phosphorous (P) in human urine is among the macronutrients in municipal wastewater that has exacerbated eutrophication of water bodies. Adsorption of P from wastewater using cost effective, environmentally friendly, and efficient adsorbents is considered as an attractive method that can both mitigate the eutrophication problem and augment the already strained P reserves. In the present study the adsorption capacity and structural properties of lateritic soil (LS), the adsorbent for removal of P from human urine, was investigated using XRF, SEM, TGA and FTIR techniques. Batch adsorption experiments were conducted to determine various adsorption parameters such as the sorption rates, the concentration, and the amount of adsorbed P at equilibrium. The experimental equilibrium data were fitted to the Langmuir, Freundlich and Dubinin-Radushkevich (D-R) adsorption isotherms. Also, factors influencing adsorption such as the contact time, agitation speed, and adsorbent loading were optimized using response surface methodology (RSM). Based on the D-R model, mean surface adsorption energy of 1.313 × 10-2 kJ/mol was obtained suggesting that the adsorption occurred through weak forces of interaction. The amount of adsorbed P on LS at equilibrium (qe) and pH = 7.5 increased with the initial concentration of P in urine as well as with the contact time. The Langmuir maximum adsorption of P on LS was found to be 15.5 mg/g. The RSM demonstrated that contact time 60 min, agitation speed 80 rpm, and adsorbent loading 0.1 g in 25 mL of urine were optimum for the highest adsorption of P, and a desirability of 0.919. The results presented here show that LS is a promising inexpensive adsorbent for effective removal of P from human urine.