Three conventional coalescence filters including walnut shells (WS), polystyrene resin particles (PR), and quartz sand (QS) were compared with bamboo charcoal (BC) to treat oily wastewater in a coalescence system process. The results showed the order of oil removal efficiency was QS>BC>WS>PR. To improve the oil removal efficiency of BC further, six types of modified BC were prepared. The results showed that the modified BC using silane coupling agent (SCA) significantly increased oil removal efficiency, but the other types (including the use of NaOH, HNO3, H2O2, FeCl3 and ultrasound) of modified BC exhibited nearly the same level of efficiency as that of pure BC. Infra-red, X-ray diffraction, scanning electron microscopy, and the contact angle for modified BC were measured to reveal the modified mechanism. It was found that the higher oil removal efficiency of the SCA-modified BC occurred due to the changed crystal structure of the BC and the increase in its surface hydrophobicity, which resulted in higher oil removal efficiency. Therefore, modified bamboo charcoal is an attractive filter candidate for oil removal in a coalescence system process.