Use of Moringa Oleifera (Moringa) seed pods and sclerocarya birrea (Morula) nutshells for metal removal from wastewater and borehole water

Abstract

A study to investigate the possible use of non-edible seed pods of Moringa Oleifera (moringa) and Sclerocarya birrea (morula) nutshells for removal of metal ions from wastewater and borehole water samples was carried out. One variable at a time method was used to optimize parameters that affect sorption capacity of both sorbents. Contact time, pH, temperature, particle size, sorbent dose and initial metal concentration were the parameters investigated. Removal of seven selected metal ions were studied including lead (Pb), cadmium (Cd), copper (Cu), manganese (Mn), iron (Fe), zinc (Zn) and magnesium (Mg). Determination of residual metal ions after employing sorbent was done using flame atomic absorption spectroscopy (FAAS). Using 200 ng metal ion mixture in 50 mL of water sample, the optimized parameters for Moringa seed pods were 60 min contact time, 1 g of sorbent dose, pH 8, 100 μm sorbent particle size and extraction temp 35°C. While using Morula nutshells, the optimized conditions were 120 min contact time, 2 g sorbent dose, pH 8, 100 μm sorbent particle size and extraction temp 35°C. The percentage removal of Fe, Zn, Cu, Cd, Mg, Mn and Pb from water samples using treated MNS was 79.6, 52.9, 78.2, 58.6, 90.3, 100.0 and 93.4 while using treated MSP was 80.9, 57.6, 89.0, 65.5, 88.2, 100.0 and 94.7 respectively. Moringa seed pods was found to be a better sorbent in comparison to morula nut shells since the percentage removal of metals was higher while using Moringa seed pods. The developed methods were validated and the % removal was found to range between 86.49 ± 4.33 to 99.63 ± 3.36%. The method indicated good linearity (R2 > 0.99) for all selected metals and also proved to be sensitive as low LODs were achieved ranging from 0.010 ± 0.003 to 0.067 ± 0.02 mgL-1. Determination of the functional groups in the sorbents was done using Fourier Transform Infrared spectroscopy (FTIR). The experiments were done for sorbents before and after metal removal by sorbents. Shift in transmittance (%) and intensity of the peaks of the different functional groups in the sorbents was attributed to the metal binding to these functional groups and hence responsible for removal of metal from water samples. SEM-EDX was used to determine the morphology and the elemental analysis of the sorbents. Presence of irregular surface and pores showed that the sorbent has different sites that can act as adsorbing sites. The removal efficiency of acid treated sorbents was compared to that of untreated sorbents and it was found to be higher for acid treated sorbents for both Morula nutshells and Moringa Oleifera seed pods. These non-edible plant parts for Morula and Moringa Oleifera plants are proposed as a cheap, simple and an effective alternative for purification of water contaminated with heavy metals.