Effluent quality of extensive green roofs with different substrates

Effluent qualities of pilot-scale green roof facilities with different substrate compositions were evaluated and compared with runoff qualities of an asphalt roofing, the blank control roof and rain water for total 20 rainfall events. The results show that the concentration of TP, NH4+-N and COD in effluent of the facility using commercial green roof medium are 0.95, 1.66 and 115 mg·L-1, respectively, which are higher than those of runoff from asphalt roofing and control facility effluent. The effluent quality of the experiment facility using light inorganic medium and the cheap medium made of brick scrap and sand are better than the effluent of control facility. Considering runoff volume reduction effect, the pollution loads of different green roof facilities are not pollution source for every monitored pollutant compared with the load of asphalt roof and control facility, for NH4+-N load the green roof facilities can even reduce the load of rain water. The aboveground biomass of green roof is positively related to the effluent quality, and the facility using commercial green roof medium presents a better growth status than those using media emphasizing effluent water quality. Application of water treatment residual as component of the medium, the leaching of P from commercial green roof medium is significantly reduced and the growth of vegetation is not affected. © 2015, Science Press. All right reserved.