Arsenic in groundwater is a serious problem. This paper investigates the role of biochar derived from agricultural waste byproducts to remediate arsenic from water. Composites were synthesized by thermal and chemical modifications in biomass. The biochar composites were characterized for their BET surface area and porosity. XPS, SEM, TEM, XRD, FT-IR, PPMS, ICP-MS were studied to analyze their magnetic moment, surface chemistry, mineralogy, crystallinity, elemental composition and functional group identification. Batch sorption studies, sorption equilibrium and kinetic studies were conducted using various mathematical equations and isotherm models to find sorption efficiency. As(III) removal occurred in pH 7.5–9.0. High adsorption capacities were reported for rice husk and wheat husk composites. Therefore, it can be considered to replace commercial adsorbents. Plausible mechanism and chemistry of As(III) adsorption was thus established.