Generally, biofilm-supporting carriers in biological contact oxidation processes are made from thermoplastic polymers, which cause potential ecological damage because of the low biodegradation and high accumulation in organisms. Thus, four bamboo-based fibers, bamboo primitive fiber, bamboo fiber, bamboo charcoal fiber (BBF) and bamboo charcoal–cotton blending fiber (BCBF), were used as carriers and compared with two commercial carriers (vinylon (VY) and polypropylene (PP)) in a biological contact oxidation process system with the goal to develop a biodegradable and sustainable biofilm medium. Under steady state conditions, pollutants (chemical oxygen demand and NH4+-N) in stage 1 (days 1–29, hydraulic retention time (HRT) = 12 h) were efficiently removed with a removal efficiency ranging from 85 to 95%. In stage 2 (days 30–53, HRT = 4–12 h), the pollutant-removal efficiency of four reactors (BBF, BCBF, VY and PP) were nearly indistinguishable and were higher than the two other reactors, especially when the HRT was set at 4 h (days 46–53). Consequently, two optimized bamboo-based fibers (BBF and BCBF) can be developed as biofilm carriers for wastewater treatment in the future. Furthermore, studies demonstrated that the biofilm development difference showed good correlation with their specific area and relative oxygen content but not with their tenacity and antimicrobial activity.