In this study, porous ceramsite was modified using a magnetic material. The modified porous ceramsite was applied to the treatment of coking wastewater in a biofilm reactor. The results showed that the COD and NH3-N removal efficiencies in the modified porous ceramsite biofilm reactor were 25-30% higher than in an activated sludge reactor, and 15-20% higher than in a biofilm reactor without a magnetic carrier. Under conditions with an aeration flow of 1.5 mL/h, aeration duration of 10 h/d, and a temperature of 25-30 degrees C, the removal efficiencies for COD and NH3-N in the porous ceramsite biofilm reactor were similar to 90%. (C) 2014 Elsevier B.V. All rights reserved.