The rising concentration of heavy metals and microplastics in marine environments poses a serious threat to public health and ecosystem stability. This study introduces an eco-friendly method that combines coagulation and filtration to effectively remove Cu2+ and microplastics from seawater using bamboo-based biochar materials. Three types of coagulants were tested at different temperatures (30–40 °C) and flow rates, along with composite adsorbents (B1, B2, B3) made from chitosan, PVA, and cellulose. The efficacy of pollution removal was evaluated using UV-vis spectrophotometry and FTIR spectroscopy, clarifying functional group interactions. Especially at 40 °C and high flow conditions, results indicated that B2 (biochar + chitosan slurry) displayed the best removal performance. The study also found clear signs of non-Stokesian behavior, which is different from traditional sedimentation models due to the irregular shapes of flocs, the way they stretch and flow, and the way polymers interact with pollutants. These results imply that in modeling pollution transfer in hybrid natural systems, conventional Stokes-based models should be reinterpreted. This work shows the possibilities of bio-based materials for effective, environmentally friendly removal of challenging marine contaminants.