Take HRT ¼ 7 days, the COD removal efficiencies of steel slag, limestone, maifanite and bamboo charcoal are 79.7%, 73.6%, 81.3% and 67.6%, respectively; the average COD concentrations in the final effluent are 51.2 mg/L, 61.3 mg/L, 53.2 mg/L and 93.4 mg/L, respectively. Among these four substrates, maifanite and steel slag have larger specific surface areas and maifanite is relatively softer; consequently, the efficiency of the interception, adsorption and absorption of pollutants is better, and provide a more advantageous growing environment of microorganisms