Seawater inundation mapping plays a crucial role in climate change adaptation and flooding risk reduction for coastal low-lying areas. This study presents a new elevation model called the digital impermeable surface model (DISM) based on the topographical data acquired by unmanned aerial vehicle (UAVs) for improving seawater inundation mapping. The proposed DISM model, along with the bathtub model, was used to assess coastal vulnerability to flooding in significant tropical cyclone events in a low-lying region of Victoria Harbor in Hong Kong. The inundation simulations were evaluated based on the typhoon news and reports which indicated the actual storm surge flooding conditions. Our findings revealed that the proposed DISM obtains a higher accuracy than the existing digital elevation model (DEM) and the digital surface model (DSM) with a RMSE of 0.035 m. The DISM demonstrated a higher skill than the DEM and the DSM by better accounting for the water-repellent functionality of each geospatial feature and the water inflow under real-life conditions. The inundation simulations affirmed that at least 88.3% of the inundated areas could be recognized successfully in this newly-designed model. Our findings also revealed that accelerating sea level rise in Victoria Harbor may pose a flooding threat comparable to those induced by super typhoons by the end of the 21st century under two representative emission scenarios (RCP4.5 and RCP8.5). The seawater may overtop the existing protective measures and facilities, making it susceptible to flood-related hazards.
Moving bed biofilm reactor (MBBR) technique is a useful technology for the treatment of mature landfill leachate. The reactor start-up and acclimation processes illustrated that many factors, such as biomass, C/N ratio, and influent volumetric loading rates, could affect the ammonium-nitrogen (NH4 + -N) and COD removal. The factorial experiments were carried out to determine the optimal reactor operational conditions, and the results demonstrated that when DO 2-4 mg/L, pH 7.5, and hydraulic retention time (HRT) 16 h, the high removal efficiencies of NH4 + -N and COD would be achieved at 0.2-0.25 kgNH4 + -N/m 3 •d of influent NH4 + -N volumetric loading rate and 0.6-0.8 kgCOD/m 3 •d of influent COD volumetric loading rate, respectively. To achieve the effective removal of NH4 + -N or COD at optimal conditions, the effluent reflux ratio would be controlled to obtain proper influent NH4 + -N or COD volumetric loading rates; to simultaneously achieve the effective removal of NH4 + -N and COD at optimal conditions, influent volumetric loading rates and C/N ratios would be properly taken; moreover, proper amounts of extra nutrients would be added to promote the growth and activity of microorganisms in the treatment processes. Stable short-cut nitrification with high nitrosation rate and low nitrate-nitrogen concentration could be achieved at the conditions of low DO concentration, moderate pH value, and low C/N ratio. Moreover, controlling different operational conditions could achieve the accumulation of different concentrations of nitrite, and then different subsequent biological processes would be applied for the effective removal of NH4 + -N.
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