article · Sustainability
Treating heavy metal contamination in water presents major remediation difficulties. This study investigated biochar and nanobiochar derived from locally collected water hyacinth and black tea waste as low-cost sorbents to remove cadmium, chromium, and nickel from aqueous solutions. Laboratory batch experiments evaluated both single-metal and competitive multi-metal adsorption systems, with results fitting best to the Freundlich isotherm model. Nanobiochars demonstrated superior removal efficiency compared to standard biochars across all evaluations. Nanobiochar from water hyacinth and black tea waste achieved cadmium removal efficiencies of 99.8 percent or higher in single-metal solutions, notably at lower concentrations. In both single and competitive systems, black tea nanobiochar eliminated more than 98.8 percent of chromium. While nickel was removed less efficiently than cadmium and chromium, its removal rates remained very high. Findings showed cadmium was the most readily removed metal, though multi-metal presence fully occupied binding sites.
Heavy metal contamination poses serious risks to aquatic ecosystems and human health. Converting nuisance plants like water hyacinth and common municipal residues like spent tea into high-performing nanobiochars offers a dual environmental benefit. It creates an affordable, sustainable approach for decontaminating polluted waters while providing a constructive waste management pathway for abundant organic biomass.
The findings could inform water purification products and industrial wastewater treatment processes managed by environmental remediation contractors or municipal utilities. However, the study relies strictly on laboratory-scale batch experiments using synthetic aqueous solutions, placing the technology at an early stage of development. Moving towards practical application will require testing in complex real-world effluents, continuous-flow column studies, and assessments of material durability and regeneration costs.
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The treatment of heavy metal-contaminated water is challenging. The use of nanomaterials from many environmental wastes is promising for removing metals and contaminants from aqueous solutions. This study is novel in using nanobiochar of water hyacinth (WH) and black tea waste (TW) as a promising approach to water decontamination owing to its unique properties that play an effective role in metal adsorption. The mono- and multi-adsorption systems of cadmium (Cd), chromium (Cr), and nickel (Ni) on biochar and nanobiochar of water hyacinths (BWH and NBWH) and black tea waste (BTW and NBTW) were investigated in this study as potential low-cost and environmentally friendly absorbents for the removal of previously mentioned heavy metals (HMs) from aqueous solutions. The WH and TW were collected from the locality, prepared, and kept until used in the experiment. Nanobiochar was prepared by grinding, characterizing, and storing in airtight containers until used. A batch experiment was designed in mono- and competitive systems to study the adsorption equilibrium behavior of HMs on biochar and nanobiochars. The Freundlich and Langmuir isotherm models were fitted to the mono- and competitive-adsorption equilibrium results. The Freundlich isotherm model provided a better fit. Furthermore, it was noticed that NBWH and NBWT efficiently removed the Cd in the mono-system by ≥99.8, especially in the smaller concentration, while NBWT and BTW removed ≥99.8 and 99.7% in the competitive system, respectively. In the mono- and competitive systems, the nanobiochars of NBTW removed more than 98.8 of Cr. The sorbents were less efficient in Ni removal compared to Cd and Cr. However, their effectiveness was very high also. The results revealed that Cd was the highest metal removed by sorbents, nanobiochars were better than biochars to remove the HMs, and the results also indicated that co-occurrence of multi-metals might fully occupy the adsorption sites on biochars and nanobiochars.
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DOI: 10.3390/su141610118
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