No 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.

In this study, an immobilized algae and bacteria symbiotic biofilm reactor (ABSBR) with pink luminescent filler (PLF) was constructed. The effects of PLF addition in the construction of an algae and bacteria symbiotic biofilm system on the nitrogen and phosphorus removal efficiencies and algae viability were evaluated. Our results showed that for influent TN and TP concentrations of 40 ± 5 and 5 ± 0.8 mg/L, respectively, the pollutant removal rates (PRRs) of TN and TP by the ABSBR can reach up to 74.74 and 88.36%, respectively. The chlorophyll-a (chl-a) concentration on the PLF reaches approximately 5,500 μg/L with a specific oxygen generation rate (SOGR) of 65.48 μmolO2 mg−1Chl-a h−1. These results indicate that the adding PLF into algae and bacteria symbiosis systems can effectively improve the nitrogen and phosphorus removal efficiencies of the sewage as well as increase biomass and viability of the algae in the system.

Multiple adsorption substrates have a synergistic effect on the adsorption and interception of pollutants. Layered substrate layer have significant NH 4 + -N interception capacity due to the unique lower adsorption layer. The addition of polyacrylamide in EGR substrate layer is likely to cause additional nitrogen pollution. Biochar can be used as an excellent modifier to enhance the rainfall runoff pollution interception capacity of EGRs. DeclarationsEthics approval and consent to participate: Not applicable Consent for publication: Not applicable Availability of data and materials: The datasets used and analyzed during the current study are available from the corresponding author on reasonable request

Due to substrate layers with different substrate configurations, extensive green roofs (EGRs) exhibit different rainfall runoff retention and pollution interception effects. In the rainfall runoff scouring process, nutrient leaching often occurs in the substrate layer, which becomes a pollution source for rainwater runoff. In this study, six EGR devices with different substrate layer configurations were fabricated. Then, the cumulative leaching quantity (CLQ) and total leaching rate (TLR) of NH4+, TN and TP in the outflow of nine different depth simulated rainfall events under local rainfall characteristics were evaluated and recorded. Furthermore, the impact of different substrate configurations on the pollution interception effects of EGRs for rainfall runoff was studied. Results show that a mixed adsorption substrate in the EGR substrate layer has a more significant rainfall runoff pollution interception capacity than a single adsorption substrate. PVL and PVGL, as EGRs with layered configuration substrate layers, exhibited good NH4+-N interception capacity. The CLQ and TLR of NH4+-N for PVL and PVGL were -114.613 mg and -63.43%, -121.364 mg and -67.16%, respectively. Further, the addition of biochar as a modifier significantly slowed down the substrate layer TP leaching effect and improved the interception effect of NH4+-N and TN. Moreover, although polyacrylamide addition in the substrate layer aggravated the nitrogen leaching phenomenon in the EGRs outflow, but the granular structure substrate layer constructed by it exhibited a significantly inhibited TP leaching effect.