Experimental study on the selection of common adsorption substrates for extensive green roofs (EGRs)

Abstract

Adsorption substrate in the substrate layer of an extensive green roof (EGR) is one of the most important factors affecting rainwater retention and pollution interception capacity. However, the contact time between runoff and adsorption substrate is extremely short in actual rainfall, and adsorption substrate cannot show fully rainwater retention and pollution interception capacity. So, selection of adsorption substrate based on its physical properties and theoretical adsorption capacity is unreliable. In this study, eight commonly-used adsorption substrate experimental devices are constructed with the same configuration. The delayed outflow time and runoff reduction rate of each device, along with event measurement concentration (EMC), average EMC, and cumulative pollutant quantity of SS, ammonium (NH4+), nitrate (NO3−), total nitrogen (TN), and total phosphorus (TP) in each device outflow under nine simulated rainfall events are measured and evaluated. The results indicate that vermiculite has a significant interception effect on NH4+ and TP with the advantages of low bulk density, high porosity, low cost, and a good rainfall runoff retention capacity under torrential rain and downpour events. In future practical engineering and related studies of EGR, attention should be paid to ameliorating the deficiencies of the adsorption substrates and optimizing their synergistic effects when combined with nutrient substrates.

Comparison of rainwater management performance of modified extensive green roof substrate layer with different additives in rainstorm events

“…Substrate adsorption is a fast-acting process 38 and vermiculite has high cation exchange and NH 4 + –N adsorption capacity. 22 Thus, the NH 4 + –N interception performance of SL was not significantly affected by rainfall depth even in rainstorm events. However, the addition of additives instead amplified the negative impact of rainfall depth on NH 4 + –N interception of the substrate layer.…”

Nutrient leaching in extensive green roof substrate layers with different configurations

“…Furthermore, the total CLQ of TN in the PVG outflow was lower than that of PV, indicating that the combination of vermiculite and green zeolite configures in the substrate layer with direct mixing or layered configuration had better nitrogen interception capacity than single vermiculite. Xu et al (2021) found that single vermiculite, as the substrate layer, has better rainfall runoff interception efficiency than single green zeolite. Therefore, the selection of a mixed adsorption substrates instead of a single adsorption substrate in the substrate layer can effectively improve the EGR ability to intercept nitrogen in rainfall runoff.…”

“…The total CLQ of TN in the PVGL outflow during the entire simulated rainfall process was the lowest (199.397 mg). Furthermore, the total CLQ of TN in the PVG outflow was lower than that of PV, indicating that the combination of vermiculite and green zeolite configures in the substrate layer with direct mixing or layered configuration had better nitrogen interception capacity than single vermiculite Xu et al (2021). found that single vermiculite, as the substrate layer, has better rainfall runoff interception efficiency than single green zeolite.…”

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

“…24 Vermiculite is a silicate mineral with strong ion exchange capacity and has been proven in numerous works in literature to be an excellent adsorption substrate. 12,30…”

“…24 Vermiculite is a silicate mineral with strong ion exchange capacity and has been proven in numerous works in literature to be an excellent adsorption substrate. 12,30 PAC and bentonite were used as the modifiers in this study. Both PAC and bentonite have a certain degree of cohesiveness in the wet state, which is conducive to the formation of AS in the substrate layer.…”