Effectiveness of cactus biomass and its combusted products in removal of colour, turbidity and selected metal ions from contaminated water
Mbugua, M. M.
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Provision of clean and safe drinking water to low income earners living in remote and dry regions remains a major challenge in many developing countries. Exploring simple ways of developing cheap adsorbent materials from resources that can be easily found in dry and semi-arid regions for use in water purification at household level is crucial. Cactus is an excellent compromise as it is not only known to naturally and readily grow in very dry regions but its mucilage is associated with water coagulant and traditional medicinal herbs. The current work reports the capacity and efficacy of the biomass and its combusted products derived from Opuntia vulgaris plant to remove, Pb2+, Cd2+, colour and turbidity from contaminated water. The biomass was prepared by drying strips of 1 cm width in an oven at 60° C for 24 hours and grinding to powder to prepare biomass. Ash was obtained by heating the dry leaves in a furnace while the residue was obtained by dissolving the ash in distilled water to remove the soluble alkali. The charcoal was prepared by heating the dry cactus in a furnace in absence of oxygen. Batch experiments were carried out to determine the effect of metal ion concentration, initial pH, contact time (t), temperature (T), and adsorbent dose on percentage removal of Pb2+, Cd2+, colour and turbidity by the adsorbents. The results showed that the percentage removal of turbidity by ash and ash residue increased with increase in amount of bio-solid used. The maximum turbidity removal by ash and ash residue was 98.90%, biomass 78.10% and charcoal 82.80%. The data obtained for adsorption of Pb2+ on ash residue, Cd2+ on biomass, ash, ash residue and MB on ash and charcoal best fitted the Langmuir isotherm model while adsorption of Pb2+ on biomass, charcoal, ash, Cd2+ on charcoal and ash and MB on ash residue and charcoal best fitted the Freundlich model. Adsorption capacities for Pb2+ ions on ash residue, ash, charcoal and biomass adsorbents were 1000.00, 173.62, 13.34 and 3.17 mg/g, respectively, while that of Cd2+ ions were 416.84, 299.90, 21.74 and 8.61 mg/g and methylene blue was 5.81, 4.65, 23.99 and 8.27 mg/g, respectively. The findings showed that Opuntia vulgaris species of cactus is a potential biosorbent for Pb2+, Cd2+, turbidity and colour from contaminated water.