Abstract: Excess sludge from sewage treatment plant is utilized in this work to modify the substrate of a bioretention system to cope with the problems of urban non-point source pollution control and disposal of excess sludge. We determine the optimal content range of excess sludge added to the substrate based on its physical and chemical properties, and examine the effect of rainwater runoff reduction by the sludge-improved bioretention system. The results show that adding the sludge up to a content of 44.8% in the upper substrate layer of 15 cm thick could effectively enhance the system’s capability of runoff regulation. A higher content leads to a better effect of this system in controlling the total stormwater runoff, but a slightly upward trend the concentration of pollutants in effluent. Compared with sandy-soil substrate, a bioretention system with 40% sludge substrate increases the total runoff reduction rate by 16.9%. The average effluent concentration of COD, TN, NH4+-N and TP are 29.10, 3.25, 1.66 and 0.093 mg/L respectively, meeting the standards of Class ΙⅤ, Class Ⅴ, Class Ⅴ and Class Ⅱ of the Environmental Quality Standard for Surface Water (GB 3838-2002).

Key words: bioretention system, excess sludge substrate, physical and chemical properties, total runoff reduction, source pollution control