Removal of Heavy Metal Ions from Household Drinking Water Using Acacia Galpinii Seeds and Seed Pods

BACKGROUND. Contamination of drinking water with heavy metals poses a human health threat, particularly in low-income countries where point-of-use water purification systems are beyond the reach of a majority of households. OBJECTIVES. The study was undertaken to evaluate the efficacy of Acacia galpinii (monkey thorn tree) biomass in removing lead (Pb (ll)), cadmium (Cd (ll)), calcium (Ca (ll)), and magnesium (Mg (ll)) ions from drinking water. METHODS. A. Galpinii biomass from seed and seed pods was processed by pulverizing, Soxhlet oil extraction and particle size grading. The material was analyzed by X-ray fluorescence (XRF) and Fourier transform infrared (FTIR) spectrophotometry. Influence of the physiochemical parameters (contact time, initial concentration, adsorbent dosage, pH) on the effectiveness of the biomass in removing Pb (ll), Cd (ll), Ca (ll) and Mg (ll) ions was evaluated and the best fit adsorption isotherm model (Langmuir vs. Freundlich) was also determined. RESULTS. Particle size, dose, contact time and pH all played significant roles in the effectiveness of metal removal for both seed and seed pod biomass. At biomass particle size <90 microns, 98% removal rates of Pb (II) ions were achieved for powdered seed pods compared with 65% for powdered seeds. The same trend was observed for Cd, Ca and Mg. Contact time for effective removal of metal ions by pod powder and seed powder was 90 minutes and 120 minutes, respectively. Maximum adsorption was achieved at solution pH 6-8 for all metals. Lead adsorption followed a Langmuir isotherm model with maximum adsorption capacities of 10.8932 for pod powder and 3.4412 for seed powder. Adsorption of Ca and Mg followed a Freundlich model, with adsorption capacity of 1.1789 for Ca and 1.4521 for Mg. CONCLUSIONS. Acacia galpinii seeds and seed pods are inexpensive, readily available and may serve as a cost effective means for treatment of drinking water for domestic users in low and middle income countries.