A critical review of low-cost biosorbents derived from animal dung for effective adsorption of dye pollutants

Valorization of biomass waste into adsorbents that can remove pollutants remains one of the key synergetic strategies to promote environmental sustainability. This study aimed to review the adsorptive removal of dyes from aqueous media using animal dung-based biosorbents (ADBBs) as a low-cost material. Notably, findings from this study showed that modified animal dung-based biochar and activated carbon were the most effective ADBB classes for dye removal. Specifically, the highest adsorption capacity (q_m = 1241 mg/g) was recorded for rhodamine B using activated cow-dung biochar. Also, findings revealed that H-bonding, electrostatic interactions, and π–π interactions are the main mechanisms of dye uptake by the ADBBs. Furthermore, in most studies, dye adsorption followed the Langmuir isotherm and pseudo-second-order kinetics, indicating monolayer adsorption governed by pore availability on the ADBBs surface. This study also established that ADBBs have good reusability potential, with over 70 % of the original efficiency maintained after 3–10 cycles. The implications of these findings highlight that ADBBs provide a sustainable and cost-effective route for wastewater treatment while simultaneously promoting the waste-to-wealth initiative. Additionally, the demonstrated efficiency and reusability suggest ADBBs' suitability for industrial-scale applications.