Experimental study on the hydrological performance of green roofs in the application of novel biochar

Abstract

Biochar has the potential to be a soil amendment in green roofs owing to its water retention, nutrient supply, and carbon sequestration application. The combined effects of biochar and vegetated soil on hydraulic performance (e.g., saturated hydraulic conductivity, retention and detention, and runoff delay) are the crucial factor for the application of the novel biochar in green roofs. Recent studies investigated soil water potential (i.e., suction) either on vegetated soil or on biochar-amended soil but rarely focused on their integrated application. With the purpose of investigating the hydraulic performance of green roofs in the application of biochar, the combined effect of biochar and vegetated soil on hydrological processes was explored. Artificial rainfall experiments were conducted on the four types of experimental soil columns, including natural soil, biochar-amended soil, vegetated natural soil, and vegetated biocharamended soil. The surface ponding, bottom drainage and the volumetric water content were measured during the rainfall test. Simulation method by using HYDRUS-1D was adopted for estimating hydraulic parameters and developing modelling analysis. The results indicated that the saturated hydraulic conductivity of vegetated soil columns were higher than bare soil columns. The addition of biochar decreased the saturated hydraulic conductivity, and the magnitude of decrease was much significant in the case of vegetated soil. The influence of vegetation on permeability is more prominent than biochar. The vegetated biochar-amended soil has the highest retention and detention capacity, and shows a preferable runoff delay effect under heavy rain among the four soil columns. The results from the present study help to understand the hydrological processes in the green roof in the application of biochar, and imply that biochar can be an alternative soil amendment to improve the hydraulic performance.

Improvement in pollutant controlling performance by modified aggregate structure in extensive green roof substrate layer

“…This is consistent with the result of Huang's research. 34 Meanwhile, the EMC and load of NH 4 + –N in the outflow of the EGR experimental devices with modified AS were more unstable compared with that of CN.…”

“…Given that the removal of NH 4 + -N by EGRs mainly depends on nitrification, substrate ion exchange and adsorption, 33 the decrease in the NH 4 + -N removal capacity may be due to the water-air conducting channels formed in the modified AS. 34 These channels can provide oxic conditions for nitrification, while significantly reducing the contact area and time between the rainwater and substrate, therefore depressing the NH 4 + -N removal performance of the EGRs with modified AS in their substrate layers. The average load of NH 4 + -N in the B-0.5 and B-1.0 outflows was lower than that of CN, which was 0.920 mg and 0.893 mg, respectively.…”

Nutrient leaching in extensive green roof substrate layers with different configurations

“…The substrate layer modifier comprises biochar and polyacrylamide (PAM). The addition of biochar in the EGR substrate layer can effectively reduce the bulk density, increase the porosity of the substrate layer and improve the environmental adaptability of vegetation to substrate (Ouyang et al 2016;Huang et al 2020;Chen et al 2018). PAM has strong cohesiveness.…”

The rainwater retention mechanisms in extensive green roofs with ten different structural configurations

“…Instead, each soil column container was approximately 100 mm higher than the substrate surface to allow surface water retention. Similar modules have been used in previous studies (Poë et al 2015;Sims et al 2016;Liu et al 2019b;Huang et al 2020). Although the vertical flow might be affected by scale effects and the module walls, the focus of this study was to compare the differences in RRCs among various structural configurations.…”

“…Although the vertical flow might be affected by scale effects and the module walls, the focus of this study was to compare the differences in RRCs among various structural configurations. Before soil filling, a thin layer of Vaseline was applied on the inner wall of each module to minimize preferential flow (Huang et al 2020). Each module was divided into two parts using a porous acrylic sheet.…”