Recycling of Date Pits Into a Green Adsorbent for Removal of Heavy Metals: A Fractional Factorial Design-Based Approach

Date pits (DPs) have been recycled into a low-cost adsorbent for removing of selected heavy metals (HMs) from artificially contaminated aqueous solutions. Adsorption of targeted HMs, both by raw date pits (RDP) and burnt date pits (BDP) was tested. Results showed that BDP is more efficient as an adsorbent and mostly adsorbing Cu(II). A novel approach; fractional factorial design (2k−p – FrFD) was used to build the experimental pattern of this study. The effects of four factors on the maximum percentage (%) of removal (Y) were considered; pH, adsorbent dose (AD), heavy metal concentration (HMC), and contact time (CT). Statistically significant variables were detected using Pareto chart of standardized effects, normal and half-normal plots together with analysis of variance (ANOVA) at 95.0 confidence intervals (CI). Optimizing (maximizing) the percentage (%) removal of Cu(II) by BDP, was performed using optimization plots. Results showed that the factors: pH and adsorbent dose (AD) affect the response positively. Scanning electron microscopy (SEM) was used to study the surface morphology of both adsorbents while fourier-transform infrared spectroscopy (FTIR) was employed to get an idea on the functional groups on the surface and hence the adsorption mechanism. Raman spectroscopy was used to characterize the prepared adsorbents before and after adsorption of Cu(II). Equilibrium studies show that the adsorption behavior differs according to the equilibrium concentration. In general, it follows Langmuir isotherm up to 155 ppm, then Freundlich isotherm. Free energy of adsorption (ΔGad) is −28.07 kJ/mole, when equilibrium concentration is below 155 ppm, so the adsorption process is spontaneous, while (ΔGad) equals +17.89 kJ/mole above 155 ppm, implying that the process is non-spontaneous. Furthermore, the adsorption process is a mixture of physisorption and chemisorption processes, which could be endothermic or exothermic reactions. The adsorption kinetics were described using a second order model.Funding. This work was made possible by UREP award [UREP 20-116-1-020] from the Qatar National Research Fund (a member of The Qatar Foundation). The statements made herein are solely the responsibility of the authors

Antibiotics in hospital effluent and domestic wastewater treatment plants in Doha, Qatar

Wastewater samples were collected from the main hospital’s effluent (HWW), influents and effluents of the old wastewater treatment plant (OWWTP) built in 1990 and the new one (NWWTP) built in 2010 located in Doha, Qatar. Analytical methods were optimized to determine the concentrations of eight selected antibiotics (ABs): penicillin, amoxicillin, gentamicin, ciprofloxacin, tetracycline, erythromycin, metronidazole, and clavulanic acid. Samples were prepared through automated solid phase extraction (SPE) before analysis using liquid chromatography - mass spectrometry (LC–MS) with positive ion electrospray. Among the eight target compounds tested, recoveries were obtained in the range of 47.5–98%. The highest concentration of metronidazole and ciprofloxacin were detected in the HWW at levels of 5.46 μg/L and 1.99 μg/L, respectively. In effluents samples collected from both WWTPs, clavulanic acid was the most prominent compound at concentration of 84.74 μg/L. The highest concentration of erythromycin (7.20 μg/L) was detected in the influent sample collected from OWWTP. Amoxicillin, penicillin, and erythromycin were below the detection limit (0.1 μg/L). There was a significant statistical correlation between the concentrations of most of the studied antibiotics. Ciprofloxacin was highly correlated with erythromycin, clavulanic acid, and metronidazole in all influent samples, whereas the concentration of erythromycin was highly correlated with those of amoxicillin, ciprofloxacin, tetracycline and penicillin in all effluent samples. No significant difference (P ≥ 0.05) was found between concentrations of the targeted antibiotics in the NWWTP and OWWTP. Generally, both treatment plants showed effective removal rates (99.44%) of penicillin and metronidazole. However, clavulanic acid and ciprofloxacin were not removed from the effluent of either plant, even though the effluent passed through the ultrafiltration stage in the new WWTP. The findings reveal that HWW is not the only source of ABs in wastewater but direct disposal onto the sewer system could be the major source. The study calls for further investigation of additional pharmaceuticals and other emerging contaminants in the wastewater of Qatar as well as their metabolites and biodegradation products as well as application of advanced treatment technologies for highest removal rate and safe water reuse options.We thank Dr. Muhammad Al-Sayrafi, Thomas Michael, Haira Binti Mokhtar, Noor Al-Motawa, Dr. Hany Hussein, Dr. Mohammad Al-Ghouti, Munshi Masudul Haq, and Dr. Mohammed Abu-Dieyeh for various assistances on the project. This study was made possible by a grant from Qatar University Office of Academic Research ( QUST-CAS-FALL-14/15-30 ).Scopu