Abstract:
Wastewater contains P (Phosphorus) from human excreta, household detergents and some industrial
and trade effluents in the form of orthophosphates, organic compounds and polyphosphates. Out of
these, phosphate is the most available form of P. Thus, the need for the removal of excess phosphate
is a necessity. Since P is a nutrient, release of wastewater containing excess P could lead to create
problems of eutrophication. Apart from that, P is a finite resource, therefore, recovery of P from
wastewater is also of interest. Sorption has been given importance in this regard mainly by using
Activated Carbon (AC). However, use of kinetics and adsorption isotherm models to describe this P
sorption process on to AC is limited in the literature. Therefore, this study is sought at describing
adsorption kinetics and equilibrium adsorption isotherms of P on to AC and the desorption process
to enhance the recovery of phosphate. Different reaction parameter impacts on the adsorption
process were tested. Experiments were conducted with synthetic solutions having an initial P
concentration of 25 ppm prepared by using KH2PO4. Results of the kinetic study done in triplicate
showed that the phosphate removal reached its maximum value (38.37%) after four hours and thirty
minutes. The Elovich model fit well with the kinetic study experimental data explaining that the rate
of adsorption of P on to AC gets decreased exponentially as the amount of adsorbed P on to AC
increases. Equilibrium isotherm study results suggested that this adsorption process could be well
explained by the Langmuir model with the maximum adsorption capacity of -0.5488 mg g-1. The
results also revealed that the pH of the solution significantly influences the adsorption process as P
removal efficiency is considerably decreased from lower pH to higher pH. Desorption study w
results showed that the phosphate adsorbed by AC could be successfully desorbed using 1 M NaOH
solution up to 84.17% after 1.6 hrs.
Keywords: Phosphorus; Adsorption; Elovich model; Langmuir model; Desorption
