No abstract

Injecting H 2 O 2 into aquifers is a widely used in situ chemical oxidation (ISCO) technology for groundwater remediation. Dissolved silicate has been reported to decrease the reactivity of iron (III)-bearing minerals toward H 2 O 2 . In this study, the effect of naturally occurring levels of dissolved silicate (≤1 mM) on the catalyzing hydrogen peroxide (CHP) with Fe(II) minerals is revaluated, and new observations that contradict previous studies are reported. Specifically, dissolved silicate enhances the CHP process with Fe(II) minerals. In the presence of Fe(II) minerals, siderite and ferrous oxide (FeO), which had a stronger dissolution tendency than Fe(III) minerals, dissolved silicate could prevent the dissolved iron species from precipitation through a coordinating effect, therefore reinforcing the homogeneous CHP process and the degradation of 2,4-dichlorophenol. The solution pH decreased due to the generation of degradation intermediates, and the solution acidification in turn promoted further dissolution of Fe(II) minerals. FeO particles exhibited the strongest silicate adsorption among the minerals; therefore, a higher initial silicate concentration of 1 mM was needed to observe the enhancing effect. This study redefines the role of dissolved silicate in the CHP process and provides clues to the design of an efficient H 2 O 2 -based ISCO system for the remediation of groundwater.

Change of the environment, namely climate change and human activities, is influencing hydrological cycles globally. Nonstationary changes have been widely detected in precipitation series, which has significantly increased the flood risk in various areas. Taking Taihu Basin as the typical study area, the nonstationary characteristics of precipitation are analyzed through the Mann-Kendall trend test, Pettitt abrupt change test, Sen’s slope estimator and Seasonality Index in this study. Spatial distributed daily precipitation data during 1979–2017 is used. An 1D-2D coupling hydrodynamic model is built by MIKE Zero to simulate the change of flood risk under the nonstationarity of precipitation. According to the results of statistical analysis, the precipitation of Taihu Basin shows increasing trends in various temporal and spatial scales. Especially, the torrential rain and extreme precipitation, which are the main cause of flood disasters of the basin, are increasing significantly especially in highly urbanized areas such as Shanghai city. According to simulation results, the increase of flood risk shows high correlation with the nonstationary change of precipitation. The results indicate a great impact of climate change and urbanization on the regional flood risk, which must be well solved during social and economic sustainable development.

Jiangyin is a typical plain river network city in the Yangtze River Delta. The water ecological environment in urban area faces a range of environmental challenges, including poor water quality, black and odorous water bodies, serious isolation of river network, degradation of water ecological environment and low efficiency in urban wastewater treatment. This study proposed a systematic treatment plan which includes source sewage control, river regulation, water cycle enhancement, water environment restoration and waterscape improvement. Such an approach was informed by four principles, which is prioritizing pollutant control, introducing flowing water, co-management of river and bank, and combination of construction and management. By implementing such measures, the water environment carrying capacity and water ecological restoration capacity of the urban area have been greatly improved, and the overall water ecological environment quality has been significantly improved. The urban water system has realized a new picture of smooth river, clear water, green bank and beautiful scenery.

Panggong District, surrounded by the Han River on three sides, is close to Xiangyang Ancient City. It is the key area of strategic layout of Xiangyang’s urbanization development. The low-lying topography and high-level underground water with a lack of drainage channel and rainwater storage area cause a serious problem of drainage and waterlogging prevention in this region. A river system connection project was planned to solve this problem, in which new river systems were excavated and necessary gates and pumping stations were constructed to improve the capacity of drainage and waterlogging prevention of the region. Furthermore, the operation schemes of the connection project were determined in flood season and dry season, the project benefit was analysed, and related problems were discussed.