Optimization of Heavy Metals Removal Through Pecan Shell-Based Modified Activated Carbon from Pharmaceutical Wastewater and Evaluation of the Treated Effluent for Irrigating Pisum sativum

The simultaneous presence of pharmaceuticals and heavy metals (HMs) in wastewater generated by the pharmaceutical industries may result in a variety of environmental concerns. For that reason, it is necessary to remove HMs and pharmaceuticals before releasing industrial effluent in the environment. The aim of this work was to develop an improved and optimized adsorption process employing modified activated carbon (MAC) to remove HMs from pharmaceutical wastewater and evaluate the suitability of the treated effluent for irrigation purposes. Pecan shells were used to produce the activated carbon (AC), which was then modified with FeCl₂ and FeCl₃. The modified activated carbon (MAC) was characterized using various analytical techniques including Scanning Electron Microscopy (SEM), Energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FT-IR), Vibrating Sample Magnetometry (VSM) and Brunauer–Emmett–Teller (BET). The response surface method (RSM) with central composite design (CCD) was used to optimize the conditions of the adsorption process for the removal of HMs from pharmaceutical wastewater (PWW). To test its impact on plant growth parameters and germination, two distinct pea plant (Pisum sativum) varieties (Climax and P-2009) were irrigated with treated effluent. The results revealed that the MAC performed excellently under the optimized condition of a MAC dose of 0.6 g/L, pH 11, contact time of 65 min, and temperature of 35 °C, removing more than 90% of the selected HMs (Pb, Cd, and Cu) from PWW. The elimination of HMs from pharmaceutical effluent reduces its toxicity, as evidenced by the greater germination percentage and germination index for P. sativum irrigated with treated wastewater as opposed to untreated wastewater. In addition, the P. sativum irrigated with treated wastewater exhibited significantly improved outcomes from the untreated wastewater in terms of plant growth indicators such as biomass, number of leaves, leaf area, number of branches, and length of roots and shoots.