Abstract:
Phosphorous discharged into the water bodies stimulates the growth of aquatic micro and macro
organisms in nuisance quantities, which in excess can cause eutrophication in stagnant water
bodies. Phosphorous removal from water and wastewater has been achieved by methods such as
coagulation, chemical precipitation, biological treatment, ion exchange and adsorption.
Adsorption by volcanic rocks is investigated as a possible alternative to conventional method of
pollutant removal from aqueous solutions. In this work adsorption of P(V) on to Scoria (VSco)
and Pumice (VPum) has been studied by using a batch method at room temperature. The effect
of various design parameters, i.e. contact time, initial pH, adsorbent dose, agitation speed,
adsorbent particle size, and initial P(V) ion concentration using the VPum and VSco, has been
studied. The sorption process was relatively fast and equilibrium has been reached at 60 min
contact time and the maximum adsorption yield, 92.50% for VSco and 94.70% for VPum , was
obtained at an adsorbent loading weight of 15 g/L for VSco and 10 g/L for VPum. Kinetic data of
P(V) adsorption followed well the pseudo-second order equation (R2>0.99) suggested the
chemisorptions mechanism of P(V) adsorption on VPum and VSco. The overall uptake for the
VPum and VSco were maximum at pH 6 and 7 respectively. The sorption data were better
represented by the Freundlich isotherm (R2 = 99, 98: SSE ≈ 0.0034, 0.0084) than by the
Langmuir, giving a coefficient of adsorption 0.50 and 0.34 L/g respectively. The coexistence of
other anions in solutions has a significant effect on P(V) adsorption; a decrease in adsorption
capacity followed the order of anions: Mixture > SO42- > HCO3- > NO3- > Cl- > CO3-. In
addition, the adsorbed P(V) could be desorbed by 0.1 and 0.2 M NaOH solutions. The optimized
method was applied for P(V) removal from real wastewater. The achieved P(V) removal
efficiency was 91.48% and 95.23% using VSco and VPum respectively. Results indicate that the
freely abundant, locally available, low-cost adsorbent, VSco and VPum can be treated as
economically viable for the removal of P(V) from wastewater.
