Direct numerical simulation of matrix diffusion across fracture/matrix interface

Accurate descriptions of matrix diffusion across the fracture/matrix interface are critical to assessing contaminant migration in fractured media. The classical transfer probability method is only applicable for relatively large diffusion coefficients and small fracture spacings, due to an intrinsic assumption of an equilibrium concentration profile in the matrix blocks. Motivated and required by practical applications, we propose a direct numerical simulation （DNS） approach without any empirical assumptions. A three-step Lagrangian algorithm was developed and validated to directly track the particle dynamics across the fracture/matrix interface, where particle＇s diffusive displacement across the discontinuity is controlled by an analytical, one-side reflection probability. Numerical experiments show that the DNS approach is especially efficient for small diffusion coefficients and large fracture spacings, alleviating limitations of the classical modeling approach.

Drinking Water from Hand-Pumps in Mali, Niger, and Ghana, West Africa: Review of Health Effects

The purpose of this study was to evaluate parameters of drinking water quality from hand-pumps in Ghana, Mali, and Niger, evaluate possible sources of parameters, and provide an overview of potential health effects in the population. Concentrations of 22 parameters in 3337 groundwater samples were analyzed and compared with World Health Organization drinking water guidelines. In general, F, Mn, and Al had relatively larger and more common rates of occurrence, though there was by country. For F, there were reports of skeletal fluorosis in Niger and dental fluorosis in Ghana. For Mn and Al it was difficult to assess health effects due to scarce information.

多目标优化下平原河网引调水改善水环境效果评估

引调水是改善平原河网地区水环境的重要方法之一,通过构建太湖流域走马塘东南片平原河网区一维水动力水质数学模型,研究不同引调水方案对区域水环境改善效果,确定引调水过程中的异质性因子.从决策目标、水质指标、空间指标3个层面综合考虑,构建环境效益与经济效益结合的多目标函数及评价体系,对引调水方案进行评估优选.结果表明:引调水流量较大时,能够在一定程度上改善区域水环境状况,规划方案下引调水5 d后,高锰酸盐指数、氨氮、总磷的平均改善率分别为30.7%、22.2%、26.4%;引调水时,区域河网中不同空间点位、不同水质指标之间的水质改善过程与效果都存在一定异质性;引调水水量、调度模式及污染源分布都会对调水后的河网区水质产生差异性影响;本研究建立的多目标评价体系较现有方法能够有效涵盖引调水中存在的异质性因子,从多个目标层面优选引调水方案,实现水量水质综合优化调控,为平原河网地区水环境长效管理与科学决策提供理论参考.

Developing an Approach for a Three-Dimensional Hydrogeologic Framework to Find Water in Northern Ghana

The purpose of this study was to develop an approach for constructing a three-dimensional hydrogeologic framework using borehole driller logs. The ultimate goal is to increase drilling success rates via a better understanding of the regional hydrogeologic framework in northern Ghana. Groundwater development has increased in northern Ghana, but drilling successful boreholes is difficult due to complex geology and limited aquifer characteristic information. An approach was developed to construct a three-dimensional hydrogeologic framework of the basin using 900 borehole logs from World Vision International’s Ghana Integrated Water, Sanitation, and Hygiene Project, located in northern Ghana. The study’s approach consists of: evaluating potential software programs;collecting borehole drilling logs;data QA/QC;data standardization and normalization;analysis for trends and correlations;and creation of a three-dimensional hydrogeologic framework and two-dimensional cross sections. This approach can be used and adapted by others working to provide groundwater in developing countries.

Detention basins as best management practices for water quality control in an arid region

Flood control detention basins （DBs） can act as water quality control structures or best management practices （BMPs）. A key pollutant that DBs serve to settle out is particulate phosphorus, which adsorbs onto sediment. This study examines the sediment phosphorus concentration and its relationship with the particle size of sediment microcosms from pre- and post-rain event samples obtained from six DBs located in Clark County, Nevada. DBs were allotted a land use classification to determine if there was a correlation between the sediment phosphorus concentration and surrounding land use. The curve number method was used to calculate the runoff and subsequent phosphorus carried into the DB by the runoff. Our data show sediment phosphorus concentrations to he highest in soils from undeveloped areas. Runoff amount also plays a substantial role in determining the amount of phosphorus brought into the DB by sediment. This research has implications for improvement of water quality in arid regions.

Enhanced biological wastewater treatment using sodium alginate-immobilized microorganisms in a fluidized bed reactor

In this study,a microbial consortium isolated from an activated sludge tank of a conventional wastewater treatment plant was immobilized using sodium alginate(SA)as a support material for contaminant biodegradation in wastewater.A volume of 500 mL of activated sludge was immobilized in the SA beads(with a mass concentration of 25 g/L).The resulting SA beads were characterized,introduced into a fluidized bed reactor,fed with 1000 mL of the sample,and characterized again after the treatment process.The SA-immobilized microorganisms were tested first for degradation of organic matter(expressed as chemical oxygen demand)and total phosphorous in domestic wastewater,achieving removal efficiencies of 71%and 93%,respectively,after 12 h.Subsequently,the SA-immobilized microorganisms were tested for degradation of a basic blue 9(BB9)textile dye in a condition that simulated textile wastewater.The efficiency of the BB9 degradation was found to be as high as 99.5%after 2 h.According to these results,SA-immobilized microorganisms were found to be an environmentally friendly and cost-effective alternative for treatment of municipal and industrial wastewater effluents.

Peroxymonosulfate decomposition by homogeneous and heterogeneous Co: Kinetics and application for the degradation of acetaminophen

Peroxymonosulfate(PMS)decomposition,hydroxyl radical(·OH)generation,and acetaminophen(ACT)degradation by the Co/PMS system using homogeneous(dissolved cobalt)and heterogeneous(suspended Co3O4)cobalt were assessed.For the homogeneous process,>99%PMS decomposition was observed and 10 mmol/L of·OH generation was produced using 5 mmol/L of PMS and different dissolved cobalt concentrations after 30 min.A dissolved cobalt concentration of 0.2 mmol/L was used to achieve>99%ACT degradation using the homogeneous process.For the heterogeneous process,60%PMS decomposition and negligible·OH generation were observed for 5 mmol/L of the initial PMS concentration using 0.1 and 0.2 g/L of Co3O4.Degradation of ACT greater than 80%was achieved for all experimental runs using 5 mmol/L of the initial PMS concentration independently of the initial Co3O4 load used.For the heterogeneous process,the best experimental conditions for ACT degradation were found to be 3 mmol/L of PMS and 0.2 g/L of Co3O4,for which>99%ACT degradation was achieved after 10 min.Because negligible·OH was produced by the Co3O4/PMS process,a second-order kinetic model was proposed for sulfur-based free radical production to allow fair comparison between homogeneous and heterogeneous processes.Using the kinetic data and the reaction by-products identified,a mechanistic pathway for ACT degradation is suggested.

美国迈卡伦湿地河流主槽-洪泛区水力连通特征

基于先进的Ad H水动力学计算模型,以美国内华达州塔基河迈卡伦研究域为例,从主槽-洪泛区系统的流场特性、不同河道形态下的跨界流量分布以及粒子在系统内运动传输规律三个方面,详尽地分析洪水过程下主槽与洪泛区之间的水力交互连通关系。研究结果表明,在洪峰流量期间,有接近60%的洪峰流量从洪泛区经过,约为主槽流量的1.52倍;主槽-洪泛区之间的跨界流量交换方向和量级受到河流形态和洪峰流量的共同影响;粒子示踪统计结果表明绝大数(>85%)粒子能够至少一次穿过河流边界,揭示出主槽和洪泛区之间存在较强的水体交换,此外,粒子运动轨迹和停留时间分布特点反映主槽-洪泛区系统水力交互关系具有较强的时空分异特性。