The increasing contamination of aquatic environments with cadmium (Cd²⁺) has become a difficult environmental and public health issue regarding its extraordinary toxicity, non-biodegradable behavior, and the ability to bio-accumulate in living organisms. Cadmium is one of the most toxic heavy metal contaminations in soil and water. Exposure to cadmium-contaminated water was related to severe health impacts like kidney dysfunction, bone damage, and carcinogenic risks, which emphasize the need for efficient and sustainable remediation strategies. However, conventional techniques such as chemical precipitation, membrane filtration, and ion exchange have drawbacks, including high operational costs, sludge production, or decreased efficiency at low metal levels. Thus, the use of bio-based adsorbents as a green and cost-effective alternative for cadmium removal in wastewater has gained momentum. In this review, the main sources, structure characteristics, adsorption mechanisms, and important parameters affecting their performances of recent innovations in bio-based adsorbents for cadmium removal from aqueous solutions are analyzed. It covers perhaps fewer systematic reviews of agricultural waste, plant biomass, microorganisms, fungi, and algae-derived bio-adsorbents with respect to their abundance, renewability, and surface functional groups (–OH, –COOH, –NH₂ or –PO₄³⁻), which participate in binding of Cd²⁺ ions. Other approaches to improve the adsorption capacity, stability, and selectivity of sorbents in sustainable remediation technologies, such as chemical activation, surface modification, and biochar-based composites, are also highlighted. Adsorption processes are often controlled by different mechanisms, such as ion exchange, surface complexation, electrostatic attraction, and precipitation, highly influenced by operational parameters (pH, contact time, initial metal concentration, and competing ions). Furthermore, response surface methodology (RSM) and artificial neural networks (ANN) are new optimization tools that can be used to enhance adsorption efficiency and estimate system behavior with fluctuating factors. While substantial progress has been made, challenges still exist, including differences in experimental methods, few studies on regeneration and reuse, and limited validation with actual wastewater systems. Moreover, post-adsorption processes regarding cadmium recovery and safe disposal of exhausted adsorbents are also still lacking. Bio-based adsorbents are a promising and rapidly evolving bullet point for cadmium remediation with potential large-scale application in wastewater treatment. Hybrid material development, AI-assisted optimization, and circular economy integration are suggested as future research directions to improve efficiency, scalability, and environmental sustainability.
Nwakamma et al. (Fri,) studied this question.