Xiaohui Lei

Simultaneous reduction of nitrate and oxidation of by-products using electrochemical method

Electrochemical denitrification was studied with an objective to enhance the selectivity of nitrate to nitrogen gas and to remove the by-products in an undivided electrochemical cell, in which Cu-Zn cathode and Ti/IrO(2)-Pt anode were assembled. In the presence of 0.50 g/L NaCl as supporting electrolyte, the NO(3)(-)-N decreased from 100.0 to 9.7 mg/L after 300 min electrolysis; no ammonia and nitrite were detected in the treated solution. The surface of the cathode was appeared to be rougher than unused after electrolysis at initial pH 6.5 and 12.0. After electrolysis of 5h at the initial pH 3.0, passivation of the Cu-Zn cathode was observed. The reduction rate slightly increased with increasing current density in the range of 10-60 mA/cm(2) and temperatures had little effect on nitrate reduction. Nitrate could be completely removed by the simultaneous reduction and oxidation developed in this study, which is suitable for deep treatment of nitrate polluted water.

Electrochemical regeneration of zeolites and the removal of ammonia.

The electrochemical regeneration of zeolites was investigated with the objective of removing ammonia from water harmlessly and reusing the regeneration solution in an undivided electrochemical cell assembled with a Ti/IrO(2)-Pt anode and a Cu/Zn cathode. Zeolites could be completely regenerated through the electrochemical method in this study. With NaCl as a supporting electrolyte, the conversion rate of ammonia adsorbed by the zeolites into nitrogen gas was more that 96%, while the conversion rate to nitrate was less than 4%; no ammonia or nitrite was detected in the solution after electrolysis. The surface of the cathode appeared to be rougher after electrolysis than before. More nitrate was produced when the amount of NaCl was raised or when the current density was increased to the range of 20-60 mA/cm(2). The regeneration solution can be repeatedly reused over a long period of time with the proper amount of NaCl added to the solution. Even after the solution was reused for five times, it could still completely regenerate the zeolites, saving both water resources and the chemical reagent.

Flood simulation using parallel genetic algorithm integrated wavelet neural networks

The conventional means of flood simulation and prediction using conceptual hydrological model or artificial neural network (ANN) has provided promising results in recent years. However, it is usually difficult to obtain ideal flood reproducing due to the structure of hydrological model. Back propagation (BP) algorithm of ANN may also reach local optimum when training nodal weights. To improve the mapping capability of neural networks, wavelet function was adopted (WANN) to strengthen the non-linear simulation accuracy and generality. In addition, genetic algorithm is integrated with WANN (GAWANN) to avoid reaching local optimum. Meanwhile, Message Passing Interface (MPI) subroutines are introduced for distributed implement considering the time consumption during nodal weights training. The GAWANN was applied in the flood simulation and prediction in arid area. The test results of 4 independent cases were compared to reveal the relations between historical rainfall and runoff under different time lags. The simulation was also carried out with Xinanjiang model to demonstrate the capability of GAWANN. The numerical experiments in this paper indicated that the parallel GAWANN has strong capability of rain-runoff mapping as well as computational efficiency and is suitable for applications of flood simulation in arid areas.

Development of efficient and cost-effective distributed hydrological modeling tool MWEasyDHM based on open-source MapWindow GIS

Abstract Many regions are still threatened with frequent floods and water resource shortage problems in China. Consequently, the task of reproducing and predicting the hydrological process in watersheds is hard and unavoidable for reducing the risks of damage and loss. Thus, it is necessary to develop an efficient and cost-effective hydrological tool in China as many areas should be modeled. Currently, developed hydrological tools such as Mike SHE and ArcSWAT (soil and water assessment tool based on ArcGIS) show significant power in improving the precision of hydrological modeling in China by considering spatial variability both in land cover and in soil type. However, adopting developed commercial tools in such a large developing country comes at a high cost. Commercial modeling tools usually contain large numbers of formulas, complicated data formats, and many preprocessing or postprocessing steps that may make it difficult for the user to carry out simulation, thus lowering the efficiency of the modeling process. Besides, commercial hydrological models usually cannot be modified or improved to be suitable for some special hydrological conditions in China. Some other hydrological models are open source, but integrated into commercial GIS systems. Therefore, by integrating hydrological simulation code EasyDHM, a hydrological simulation tool named MWEasyDHM was developed based on open-source MapWindow GIS, the purpose of which is to establish the first open-source GIS-based distributed hydrological model tool in China by integrating modules of preprocessing, model computation, parameter estimation, result display, and analysis. MWEasyDHM provides users with a friendly manipulating MapWindow GIS interface, selectable multifunctional hydrological processing modules, and, more importantly, an efficient and cost-effective hydrological simulation tool. The general construction of MWEasyDHM consists of four major parts: (1) a general GIS module for hydrological analysis, (2) a preprocessing module for modeling inputs, (3) a model calibration module, and (4) a postprocessing module. The general GIS module for hydrological analysis is developed on the basis of totally open-source GIS software, MapWindow, which contains basic GIS functions. The preprocessing module is made up of three submodules including a DEM-based submodule for hydrological analysis, a submodule for default parameter calculation, and a submodule for the spatial interpolation of meteorological data. The calibration module contains parallel computation, real-time computation, and visualization. The postprocessing module includes model calibration and model results spatial visualization using tabular form and spatial grids. MWEasyDHM makes it possible for efficient modeling and calibration of EasyDHM, and promises further development of cost-effective applications in various watersheds.

Hydrological and associated pollution load simulation and estimation for the Three Gorges Reservoir of China

This study demonstrates an integrated study by coupling a NPS pollution load estimation sub-model with a distributed hydrological model to simulate the hydrological processes and associated pollution load processes in the Three Gorges (TG) Reservoir which is the largest water conservancy project in China, and further estimates the pollution loads and their responses to rainfall changes. The distributed hydrological model Easy Distributed Hydrological Model (EasyDHM) is featured as containing easy rain-runoff generation processes, comprehensive pre-process and post-process modules. Based on EasyDHM, this study develops a NPS pollution load estimation sub-model Easy Distributed Non-Point source evaluation sub-model taking both point source (PS) and NPS pollution into consideration. Through the application of the models in the TG area, this study clarifies the mechanism and characteristics of NPS pollution and estimates the pollution loads in the region. This study could provide technical support for the establishment of Best Management Practices for NPS pollution in the region, and references for the government during the processes of formulating and implementing decision-makings on pollution control and comprehensive management in the TG area.

Future changes in Yuan River ecohydrology: Individual and cumulative impacts of climates change and cascade hydropower development on runoff and aquatic habitat quality

The eco-hydrological system in southwestern China is undergoing great changes in recent decades owing to climate change and extensive cascading hydropower exploitation. With a growing recognition that multiple drivers often interact in complex and nonadditive ways, the purpose of this study is to predict the potential future changes in streamflow and fish habitat quality in the Yuan River and quantify the individual and cumulative effect of cascade damming and climate change. The bias corrected and spatial downscaled Coupled Model Intercomparison Project Phase 5 (CMIP5) General Circulation Model (GCM) projections are employed to drive the Soil and Water Assessment Tool (SWAT) hydrological model and to simulate and predict runoff responses under diverse scenarios. Physical habitat simulation model is established to quantify the relationship between river hydrology and fish habitat, and the relative change rate is used to assess the individual and combined effects of cascade damming and climate change. Mean annual temperature, precipitation and runoff in 2015-2100 show an increasing trend compared with that in 1951-2010, with a particularly pronounced difference between dry and wet years. The ecological habitat quality is improved under cascade hydropower development since that ecological requirement has been incorporated in the reservoir operation policy. As for middle reach, the runoff change from January to August is determined mainly by damming, and climate change influence becomes more pronounced in dry seasons from September to December. Cascade development has an effect on runoff of lower reach only in dry seasons due to the limited regulation capacity of reservoirs, and climate changes have an effect on runoff in wet seasons. Climate changes have a less significant effect on fish habitat quality in middle reach than damming, but a more significant effect in lower reach. In addition, the effect of climate changes on fish habitat quality in lower reach is high in dry seasons but low in flood seasons.

An analysis of the factors that influence industrial water use in Tianjin, China

Abstract This study identifies the driving forces behind maximizing Tianjin’s industrial water use efficiency in China. For this purpose, a decomposition method is developed to quantify the degree of the impact of each factor. The results show that industrial expansion was responsible for an increase in annual water use of 78 million m³, while technical advances and water efficiency measures contributed annual water savings of about 76 million m³. Further, the results highlight that Tianjin has not considered the rise in water efficiency to be the primary goal of restructuring local industries over the past decade.

Monthly spatial distributed water resources assessment: a case study

Water resource conservation is of utmost importance, especially for agriculture in developing countries. Frequent occurrences of water shortage have driven more social efforts in researching on water resources spatial distribution, as the land cover changes recently have shown positive influences. For the purpose of efficient water resources management, hydrological processes under different types of land covers and soil textures are supposed to be accurately analyzed and evaluated. Recently developed distributed hydrological mode (DHM) has been a strong hydro-cycle simulation tool for inferring variability and heterogeneity of water resources distribution. In this paper, a spatially distributed Water and Energy Transfer between Soil, Plants and Atmosphere under quasi Steady State (WetSpass) model was introduced in the distributed hydro-cycle simulation on upstream Han river basin. The simulation time-step of WetSpass model was modified from originally one season to currently one month. In addition, an experiential non-linear routing algorithm was integrated into WetSpass for discharge confluence. The study area was delineated into 12 upstream to downstream routing related catchments whose land covers and soil textures were investigated and illustrated. Model verification was completed through the calibration of simulated hydrograph against observation using eleven years of continuous precipitation and meteorological data. Moreover, four criteria were used to evaluate the model performance and the calibrated results of routing parameters were discussed. Furthermore, the distribution of surface runoff generation, evapotranspiration and groundwater recharge were illustrated and analyzed considering the spatial heterogeneity of land cover and soil texture. Results showed that water resource spatial distribution and hydrological processes were closely related to land cover and soil texture and the model had achieved a success in hydro-cycle modeling of upstream Han river basin.

Development of an AutoWEP distributed hydrological model and its application to the upstream catchment of the Miyun Reservoir

Based on the physically characterized distributed hydrological modeling scheme - WEP-L - a more generalized and expandable method - AutoWEP - has been developed that is equipped with updated modules for pre-processing and automatic parameter identification. Sub-basin scale classifications of land use and soil are undertaken by incorporating remote sensing data and geographic information system techniques. In the process of developing the AutoWEP modeling scheme, a new concept of parameter partitioning is proposed and an automatic delineation of parameter partitions is achieved through programming. The sensitivity analysis algorithm, LH-OAT, and the parameter optimization algorithm, SCE-UA, are embedded in the model. Its application to the upstream watershed of the Miyun Reservoir shows that AutoWEP features time-savings, improved efficiency and suitable generalizations, that result in a long series of acceptable simulations.

Development and Application of a Distributed Hydrological Model: EasyDHM

AbstractDistributed hydrological models have been commonly used in research involving water management because of their consideration of spatial variability. However, practical applications still encounter technical challenges such as complicated modeling, low computational efficiency, and parameter equifinality. A user-friendly model, EasyDHM, was developed and was shown effective over the years. In this paper, the essential parts of this model, namely, discretization of the spatial units, preparation and initiation of data and parameters, and the main physical processes are briefly introduced. In particular, the roles of the parameter sensitivity analysis and optimization for this model, which have considerably improved the prediction accuracy, are highlighted in this study. From the application to the upstream basin of Han River in China, the simulation and parameter estimation by EasyDHM turned out to be effective and easy to operate. EasyDHM can, therefore, be widely used for practical water manageme...