The demand for clean water is on the increase as rapid industrialization is still contributing to pollution. Nowadays, as water is the basic need for mankind, efforts have gathered momentum to decontaminate it in order to address the acute shortage of clean and pure water. Maize tassel was used as the precursor for making activated carbon for the adsorption of Pb(II) ions. The product obtained was characterized and utilized for the removal of Pb(II) from aqueous solutions over a wide range of initial metal ion concentration (10–50 mg/L), contact time (5–300 min), adsorbent dose (0.1–2.5 g), and pH (2–12). The optimum set of conditions for biosorption of Pb(II) ion were found to be initial concentration 10 mg/L, dosage 1.2 g, and pH 5.4. The adsorption data conformed to both the Langmuir and the Freundlich isotherms but fitted best into the Langmuir model. TheR2for Langmuir equation was 0.9997 and that for Freundlich was 0.9515. The Langmuir monolayer adsorption capacity of the activated carbon was calculated to be 37.31 mg/g. The results indicate that activated carbon might be used to effectively adsorb Pb(II) ions from wastewater treatment plants.

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Coagulation-flocculation processes play an important role in the treatment of water using inorganic and synthetic materials. Presently, cactus Opuntia ficus indica is explored as a cheap, abundant and eco-friendly bioflocculant of Pb(II) ions from aqueous solutions. The cactus powder was characterized by Fourier transform infrared spectrometer (FTIR), and the coagulation-flocculation process was optimized for pH, initial concentration of Pb(II) ions, particle size, dosage, ionic strength, contact time and temperature before its application to Mukuvisi River water. FTIR confirmed the involvement of -C-O-C-, -OH, -C=O, -N-H and -C-H groups of the polysaccharides, carboxylic acids and amino acids in the removal of Pb(II) ions. The variation of percentage removal and zeta potential with pH and flocculant dosage suggested the involvement of adsorption-charge neutralization and adsorption-bridging mechanisms in the coagulationflocculation process. The process was optimum at pH 5, natural ionic strength, dosage of 8 mg/L, corresponding to zero zeta potential, with particle size \75 lm, at 35°C for a floc settling time of 180 min. The coagulation-flocculation process was spontaneous and endothermic with a positive change in entropy of the system. Total heavy metal removal of 100 % (Pb), 85.74 % (Zn), 84.16 % (Cd) and 93.02 % (Cu) were achieved, under optimum conditions, when Opuntia ficus indica powder was used to remove metals from water sampled from Mukuvisi River, Harare, Zimbabwe. The cactus Opuntia ficus indica powder was found to be an efficient, eco-friendly flocculant that can effectively remediate Pb(II) ions from wastewaters.

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