In this study, switchgrass was used as the feedstock to develop bio-adsorbent via hydrothermal pre-treatment with and without using potassium hydroxide and subsequent mild chemical activation. The hydrothermal carbonization was modified to study the effects of pH (5.92 and 10), temperature (200° and 240°C), and residence time (0.5 and 1 hour). The best-treated hydrochar were activated at 700°C for 1 hour to obtain superior mesoporous and microporous bio-adsorbents with a specific surface area of 339.92 m2/g. The bio-adsorbents were filled in a lab-scale fixed bed adsorber to test the adsorption of carbon-dioxide from 60% methane and 40% carbon-dioxide configured biogas. It was found that alkaline-based bio-adsorbent adsorbed 10.92% of CO2 after 60 s test at 1 bar. The physicochemical properties of the hydrochar and bio-adsorbent were studied using proximate and elemental analysis, Thermo-Gravimetric Analysis (TGA), Fourier-Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscope (SEM) images, and Brunauer–Emmett–Teller (BET) analysis to distinguish the specific impact of the parameters and study the surface morphology.