The feasibility of producing biochar and its steam-activated counterpart in a large scale (1000 kg) from spent mushroom substrate (SMS) and their usage as effective environmental remediation tools to augment current SMS management strategies were explored. Steam-activated SMS biochar exhibited enhanced surface area (332 m(2)/g), pore volume (0.29 cm(3)/g), and porosity (77.1%). The effectiveness of activation was higher on the cationic dye, crystal violet (CV) by 4.1 times increase from 255 mg/g to 1057 mg/g. The biochar and its steam-activated counterpart, respectively exhibited high COD and color removal efficiencies of 49.6% and 40.1%, and 67.7 and 99.6% for CV-spiked real wastewater. Reusability studies confirmed the dominant role of chemisorption in the adsorption process. The lower production cost coupled with the superior physicochemical properties and adsorption performances rendered the biochar with/without steam activation, as a promising alternative adsorbent to serve as a green, viable and effective environmental remediation tool.