A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering in Environmental Engineering and Management

Thesis (M. Eng.) - Asian Institute of Technology, 2026

Indoor air pollution caused by volatile organic compounds (VOCs) is an increasing concern due to its adverse effects on human health, particularly in enclosed indoor environments. This study investigated the potential of pelletized rice straw{u2013}derived biochar as a sustainable adsorbent for indoor total volatile organic compounds (TVOCs), with toluene selected as a representative main pollutant. Rice straw, an abundant agricultural residue in Thailand, was utilized as a low{u2011}cost and renewable biomass resource to reduce open{u2011}field burning activities. Pelletized biochar was produced using slow pyrolysis at temperatures of 350, 450, 550, and 650 °C, and the influence of pyrolysis temperature on biochar yield, physicochemical characteristics, and adsorption performance was systematically evaluated. The results showed that increasing pyrolysis temperature led to a decrease in biochar yield, while fixed carbon content, surface area, and pore development increased significantly. Biochar produced at 650 °C (RSB{u2011}650) exhibited the most favorable properties, including the highest BET surface area (156.67 m²/g) and a well{u2011}developed porous structure. Adsorption experiments conducted under controlled chamber conditions demonstrated that RSB{u2011}650 achieved high toluene removal efficiencies ranging from 86.65% to 88.20% at indoor TVOC concentrations of 0.5{u2013}2.0 ppm. The adsorption kinetic model showed that the pseudo{u2011}second{u2011}order model best described the adsorption behavior, indicating that chemisorption was the dominant mechanism. In addition, Freundlich isotherm analysis provided a better fit than the Langmuir model, confirming heterogeneous surface adsorption. When compared with commercial activated carbon, RSB{u2011}650 exhibited comparable equilibrium adsorption capacity at higher toluene concentrations despite having a lower specific surface area. Cost effectiveness analysis further revealed that RSB{u2011}650 achieved a lower cost per unit surface area, highlighting its economic competitiveness. Overall, the findings suggest that pelletized rice straw-derived biochar produced at high pyrolysis temperatures is a technically effective, economically viable, and environmentally sustainable material for controlling indoor air pollution.