From agricultural waste to water purification: a critical review from traditional to sustainable and scalable solutions for wastewater treatment

Rapid population growth, urbanization, industrialization, and poor wastewater treatments are increasing heavy metal pollution and worsening global water scarcity. These problems posing serious threat to environmental sustainability, food safety, and human health. Globally, about 359 billion cubic meters of wastewater are generated annually, yet nearly 80% is discharged into ecosystems without proper treatment, lead to the accumulation of toxic metals in ecosystems and the food chain. Prolonged exposure to these metals can cause severe neurological, cardiovascular, and carcinogenic disorders. Although conventional wastewater treatment technologies are effective, but their large-scale application remains constrained by operational costs, energy demand, chemical consumption, complex processes, secondary pollution, and hazardous sludge generation. These limitations highlight the urgent need for sustainable, low-cost, and eco-friendly remediation approaches, particularly in resource-limited regions of world. This review critically examines the agro-waste derived bioadsorbents as green, sustainable, regenerable and cost-effective alternative for wastewater treatment within the framework of waste valorization and circular economy. Unlike previous studies that mainly focused on removal efficiency only, this review provide a comprehensive evaluation of agro-waste based biosorbent, including their preparation, characterization techniques, adsorption mechanisms, isotherm and kinetic models, influencing factors, and comparative assessment with conventional and emerging wastewater treatment technologies. A critical synthesis of studies published between 2001 and 2025 reported that raw biosorbents achieved 60–90% contaminant removal efficiency, whereas chemically modified and thermally activated biosorbent showed significantly higher removal efficiency of 90–97% and up to 99%, respectively. These findings confirm the strong practical potential of agro-waste-derived bioadsorbents for large-scale wastewater treatment. The novelty of this review lies in its holistic perspective of their scientific performance along with sustainability, feasibility, and environmental benefits in line with waste-to-wealth paradigm and sustainable development goals (SDGs). Overall, agro-waste based bioadsorbent offer a promising and greener solution for wastewater treatment that can reduce environmental footprint and support global water security. Therefore, future research should be focused on hybrid treatment system, improved biosorbent modification, standardized testing protocols, techno-economic assessment and pilot-scale validation to support real-world implementation.