Comparative Synthesis of H₂SO₄-Activated Rice Straw and KOH-Activated Rice Husk Carbons: Evidence from Selected Wastewater Studies

Abstract

Rice straw and rice husk are promising agricultural residues for producing activated carbon, but reported adsorption performance cannot be compared directly when precursor, activation chemistry, target contaminant, wastewater matrix, and operating conditions differ. This study qualitatively compares three selected experimental studies: H₂SO₄-activated rice straw carbon for Cr(VI) adsorption, KOH-activated rice husk carbon for tofu wastewater, and KOH-activated rice husk carbon for laundry and tofu wastewater. The synthesis compares precursor characteristics, activation conditions, adsorption or treatment conditions, reported performance, isotherm evidence, and potential treatment implications. The H₂SO₄-activated rice straw study reported an adsorption capacity (qₘ) of 5.42 mg/g for Cr(VI) under its reported optimum conditions of pH 7, 100-mesh particle size, and 60 min contact time. The KOH-activated rice husk study for tofu wastewater reported reductions of 27% in Total Dissolved Solids (TDS) and 97% in Total Suspended Solids (TSS), while the comparative laundry/tofu study reported reductions of 82% COD, 27% TDS, and 97% TSS in laundry wastewater and 92% COD, 51% TDS, and 90% TSS in tofu wastewater. These findings are reported within their respective experimental contexts and are not treated as directly comparable performance scores. The synthesis indicates that adsorption behavior is associated with the combined effects of precursor, activation chemistry, pollutant or wastewater characteristics, and operating conditions. The study therefore provides a preliminary comparative framework and identifies the need for standardized experiments to evaluate precursor and activation effects independently.