Extensive Green Roof Substrate Composition Based on Sludge Recycling

Abstract

The experiment was carried out to study the reasonable composition of stable anaerobic sludge in the extensive green roof growth substrate by a total of 650 mm artificial rainfall event. Combined with the N, P leaching problem of the sludge resources utilization, the quality of the effluent and the change of the nutrient content of the substrate in the process of application were investigated. The results showed that the anaerobic sludge could significantly increase the plant biomass and the average weight gain was 808%. Stable anaerobic sludge caused a large amount of leaching of TP and water treatment residual could effectively control TP leaching and did not affect the absorption of P to the plant. During the experiment, the TP of the effluent was reduced by 68.66%.After stabilization, the effluent TP reached the surface water Ⅴ standard. The main form of leached TN was NO3--N and the leaching of NO3--N could be reduced by rice husk charcoal. In the experiment, the NO3- -N leaching mass was reduced by 28.86% totally. Increasing the amount of rice husk charcoal helped to control NO3--N leaching. SS and COD could be quickly decreased and stabilized. The COD of effluent after stabilization was about 30 mg·L-1, which was better than the standard of surface water Ⅴ. Under the condition of actual precipitation with medium and small rainfall, the anaerobic sludge nutrient retention time should be more than 1 year, which meets the growing needs of plants for a long time.