Biomass waste as low-cost adsorbents for methylene blue removal studies

Abstract

Textile, leather, food and paper industries are major contributors to wastewater containing dye pollutants—causing serious human, aquatic and ecological problems. This study focuses on the removal of methylene blue (MB) dye using agricultural waste materials—tamarind seeds and rice husk. Among various dye removal methods, adsorption is found to be simple and effective. Activated carbon (AC) derived from tamarind seeds and rice husk was utilized as an economical adsorbent. The activated carbon from tamarind seeds was produced with a 500°C activation temperature and a 1:1 KOH:tamarind seed charcoal ratio, while the rice husk-based activated carbon was produced at 700°C with a 4:1 KOH:rice husk charcoal ratio. X-ray diffraction (XRD) analysis of tamarind seed-based activated carbon (ATSP) showed a peak at a 2θ value of 32.20°, confirming its crystalline structure. Batch adsorption experiments indicated that the adsorption capacities were 97.05% for activated tamarind seed powder (ATSP) and 89.11% for activated rice husk powder (ARHP). The mixed adsorbent of ATSP and ARHP achieved the highest dye removal efficiency of 95.27%. The adsorption behaviour and kinetics were analyzed using models such as the Langmuir, Freundlich, first-order kinetic model and second-order kinetic model. The Langmuir model exhibited the best alignment with the adsorption data, whereas the second-order kinetic model provided the most accurate description of the adsorption process. These results underscore the strong adsorption capabilities of tamarind seeds and rice husk, indicating their potential use in dye removal for wastewater treatment. Future studies should investigate their efficiency in capturing other industrial dyes.