Pomegranate Peels as Versatile Adsorbents for Water Purification: Application of Box–Behnken Design as a Methodological Optimization Approach Marwa El-Azazy , a Razan N. Kalla, a Ahmed A. Issa, a Maetha Al-Sulaiti, a Ahmed S. El-Shafie, a Basem Shomar, b and Khalid Al-Saad a a Department of Chemistry and Earth Sciences, College of Arts and Sciences, Qatar University, Doha, 2713, Qatar; marwasaid@qu. edu.qa (for correspondence) b Qatar Environment and Energy Research Institute (QEERI), Hamad Bin Khalifa University, Doha, Qatar Published online 00 Month 2019 in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/ep.13223 Pomegranate peels (PGP) were tested as a green adsorbent for the removal of Ni(II) from contaminated water samples. Both raw (RPG), and char/burnt peels (BPG) were tested. A multivari- ate analysis approach, Box–Behnken (BB) design was executed to augment the efficiency of BPG as adsorbent. Three factors were considered thereof; contact time (CT), adsorbent dose (AD), and heavy metal concentration (HMC). The percentage of heavy metal removal was the designated response (Y). Main effects plot together with analysis of variance (ANOVA) were used to decide on the substantial factors. Obtained results showed that AD was the most significant linear factor, while the interaction between AD*HMC was the most influential two-way interaction. Contour and response surface plots were used to study the factorial inter- actions and optimize the response. Desirability function was used to find the best factorial combination for maximum removal of Ni(II). Efficacies of both adsorbents were compared and BPG was more effectual achieving 99.99% removal of Ni(II). Surface morphology was characterized using FTIR, BET, SEM, and EDX analyses. Results indicated that functional groups such as hydroxyl, amino, carboxylic acid are available on sur- face of PGP and might be responsible for the adsorption process. © 2019 American Institute of Chemical Engineers Environ Prog, 2019 Keywords: agricultural wastes, Chemometrics, Box–Behnken design, ICP-OES and AAS, surface characterization INTRODUCTION With the progress of human life, innumerable contaminants are intimidating the aquatic system. These threats include, but not limited to mechanization, intensive use of chemicals, and the increased population. Consequently, water pollution is becoming a critical health and environmental concern [1–3]. Heavy metals (HMs), in specific, are widely released from many industrial, domestic, and agricultural applications. Being nondegradable, HMs represent a potential influence on public health and the eco- system in general [4–6]. Ni(II), is naturally existent in water and is beneficial at the ultratrace level. Being extensively released through industrial processes, Ni(II) beyond the tolerable limits can lead to several acute and chronic disorders, for example, gastrointestinal distress, renal edema, skin dermatitis, and severe damage to lungs, embolism, birth defects, and chronic bronchi- tis [7–9]. Treatment of wastewater from HMs is becoming a concern of an increasing prominence. Trace amounts of toxic metal- loids and HMs would contaminate large volumes of water, an issue that makes the removal of these ultra-trace pollutants from wastewater a “challenge.” Several technologies are being used for wastewater treatment. Yet, many of these procedures, though being widely used, are of limited application either due to high cost or limited efficiency. Others are tedious and require pre, and/or post treatments [6,10,11]. Being simple, cost-effective, and of reasonable efficacy, adsorption is one of the techniques that is commonly used for removal of HMs. However, it is always challenging to develop a “good” adsorbent. Typically, a “model” adsorbent is one that has high surface area, of low cost with sound adsorption properties; capability, reuse, availability, sustainability, selectivity, and stabil- ity. Based on these properties, a novel class of adsorbents—green adsorbents—is becoming a target for extensive research. Green adsorbents, obtained from natural sources (fruits, vegetables, nat- ural wastes, etc.), have the previously mentioned ideal properties, an issue that makes them competitive for the complicated adsor- bents though might be “subordinate” in their adsorption capacity [1,12–15]. Pomegranates (Punica granatum) are commonly consumed “raw” as fruits or “processed” as juices, wines and jams. With their bright red color, pomegranates are widely used by tanners. Pomegranate peels (PGP), then represent a burden on the envi- ronment if not properly reutilized. Few studies have been reported on the application of PGP for removal of different HMs from water samples. Peels were used as such (untreated) or after modification (chemically or thermally) [16–23]. A common feature among all these methods is the investiga- tion of the influence of four main factors; dose of adsorbent, pH, contact time, heavy metal concentration, and temperature on the efficiency of the adsorption process using the one variable at time (OVAT) approach as a maneuver, where one predictor is changed while the rest are kept constant. This methodology, although being widely used by researchers, is time, effort, and resources consuming, and therefore negatively impacts the method greenness. Nonetheless, the resultant portrayal of “ideal © 2019 American Institute of Chemical Engineers Environmental Progress & Sustainable Energy DOI 10.1002/ep 1