Experimental evaluation of the rainfall retention and inorganic pollutant mitigation effect by dual-layer and polyacrylamide-modified green roofs.

Abstract

Research on substrate layer modification and filler configuration is an important direction for improving the retention and interception efficiency of green roofs. In this study, four green roof modules were established using peat soil, vermiculite, and zeolite as the main substrate layer. In addition, a polyacrylamide (PAM) modifier was added and mixed with these substrates. By simulating seven rainfall events, this study calculated and analyzed the outflow of each green roof as well as the average event mean concentration (EMC) and cumulative outflow quantity (COQ) of turbidity, ammonia nitrogen ([Formula: see text]), nitrate nitrogen ([Formula: see text]), total nitrogen (TN), and total phosphorus (TP). At the same time, the nitrogen mass balance of each green roof was analyzed. The experimental results showed that the interception capacity of the LP module was higher than the unmodified green roofs under heavy rain conditions. The modules also showed an improved capacity to inhibit the leaching of [Formula: see text]; therefore, TN was effectively suppressed. However, suppression of [Formula: see text] did not significantly improve. The outflow turbidity from the MP and LP modules was low and stable, and the TP concentration showed no apparent change. After the simulated rainfall experiment with the rainfall of 426.3 mm, the proportion of TN leaching out of the LP module was at its lowest (0.85%), and the residual proportion of TN reached 80.7%. Overall, the addition of PAM to the dual-substrate layer can better form the soil aggregate structure, to improve the retention and purification effect of the extensive green roofs.