Removal of Phenanthrene from wastewater with low-cost adsorbents

The potential to remove Phenanthrene (PHE) from water matrices through adsorption onto natural organic substances (NOSs) and natural inorganic compounds (NICs) was studied. Coffee waste (CW) and activated carbon (AC) produced from CW, and chemically pre-treated with NaOH or H3PO4 were chosen as NOS, and diatomaceous earth (DE) and DE pre-treated with NaOH or H3PO4 was chosen as NIC. Comparative analysis showed that the AC produced from CW pre-treated with NaOH and pyrolyzed at 800 °C (CWAC-NaOH-800) was the most efficient adsorbent, and used for parametric analysis with respect to the initial pH of the solution, the contact time, and initial PHE concentration. The pore structure parameters of adsorbents were determined from nitrogen sorption isotherms. The pseudo-second-order kinetic model was fitted better to the experimental data, showing that chemisorption is the rate-controlling step in the adsorption process. Sips isotherm gave the best fit to the experimental isotherm data indicating that adsorption occurs on a heterogenous system, and adsorption capacity was found qmax = 143.85 mg/g. The results show that CWAC-NaOH-800 with the highest specific surface area (SSA=910 m2/g) is very efficient toward the adsorption of PHE which makes it a well-promising material for the removal of PAHs from waters.