The effectiveness of vitis vinifera (grape) leaf litter to remove U.S. EPA priority phenols from simulated and industrial wastewaters

Abstract

This study sought to prepare and characterise activated carbons from Vitis vinifera (grape) leaf litter, and assess the efficiency and potential application of the adsorbent for the removal of four phenolic compounds (phenol (P), 2-nitrophenol (2-NP), 4-nitrophenol (4-NP) and 2-chlorophenol (2-CP)) from synthetic and industrial wastewaters.

Vitis vinifera (grape) leaf litter (GL) was obtained locally, and washed, dried and pulvirized. Chemically activated carbons were prepared using H3PO4 (GLA) and NaOH (GLB). The adsorbents were characterized with SEM, FTIR, EDX and proximate analysis was also carried out. Phenols were extracted from water samples with SPE and analysed with HPLC. The prepared adsorbents were used in sorption of phenols from simulated phenolic wastewaters for optimization of adsorption. Optimal adsorption conditions were then applied for removal of phenols from wastewater samples collected from influents of treatment plants. Column and desorption studies were also carried out.

The surface texture and morphology micrographs (using SEM) of the prepared materials/adsorbents showed that the prepared activated carbons possess improved pore structure, cavities and heterogeneous irregular surfaces capable of providing enhanced adsorption. EDX spectroscopy was used for elemental microanalysis and showed that the major constituent of the adsorbent is carbon. FTIR analysis revealed changes and absorption waveband drifts of surface functional groups after activation and adsorption. The proximate analysis of the prepared precursors demonstrated good quality of the active carbons. They had low moisture content (< 12%) and their inorganic matter content (ash) was less than 9% for the three sorbents. Iodine number value of the adsorbents was 342, 1065, and 571 mg/g for GL, GLA and GLB respectively.

Excellent recoveries (92.60 – 102.85%) were obtained for the phenolic compounds (P, 2-NP, 4-NP and 2-CP) using polymeric SPE cartridges.

Phosphoric acid activation yielded the most efficient activated carbon material relative to the non-treated biomass and those chemically activated with NaOH. Percentage removal was 92.70%, 99.92%, 99.98% and 99.90% for P, 2-NP, 4-NP and 2-CP respectively using GLA. Optimal pH for adsorption was 8, 4 and 7 for GLA, GLB and GL respectively at an equilibration time of 240 min.

The evaluation of adsorption kinetics showed the adsorption process of GLA and GLB followed a pseudo-second order kinetic model while adsorption using GL was best described by intraparticle diffusion model. Adsorption equilibrium data were well fitted with Freundlich isotherm model for all three adsorbents.

Adsorption capacity of GLA (for removal of phenols) was found to decrease with increase in temperature. In contrast, the sorption efficiency of GL and GLB increased when temperature was increased. Thermodynamic parameters of adsorption (ΔGo, ΔHo & ΔSo) were evaluated. Results revealed favourability and exothermic nature of adsorption of the phenols using GLA. Adsorption processes using GLB and GL were spontaneous and endothermic.

Vitis vinifera leaf litter yielded good activated carbons and was effective in remediation of P, 2-NP, 4-NP and 2-CP from contaminated wastewaters.