A facial strategy to efficiently improve catalytic performance of CoFe2O4 to peroxymonosulfate

Cobalt iron spinel (CoFe₂O₄) has been considered as a good heterogeneous catalysis to peroxymonosulfate (PMS) in the degradation of persistent organic pollutants due to its magnetic properties and good chemical stability. However, its catalytic activity needs to be further improved. Here, a facial strategy, “in-situ substitution”, was adopted to modify CoFe₂O₄ to improve its catalytic performance just by suitably increasing the Co/Fe ratio in synthesis process. Compared with CoFe₂O₄, the newly synthesized Co_1.5Fe_1.5O₄, could not only significantly improve the degradation efficiency of phenol, from 50.69 to 93.6%, but also exhibited more effective mineralization ability and higher PMS utilization. The activation energy advantage for phenol degradation using Co_1.5Fe_1.5O₄ was only 44.2 kJ/mol, much lower than that with CoFe₂O₄ (127.3 kJ/mol). A series of related representations of CoFe₂O₄ and Co_1.5Fe_1.5O₄ were compared to explore the possible reasons for the outstanding catalytic activity of Co_1.5Fe_1.5O₄. Results showed that Co_1.5Fe_1.5O₄ as well represented spinel crystal as CoFe₂O₄ and the excess cobalt just partially replaced the position of iron without changing the original structure. Co_1.5Fe_1.5O₄ had smaller particle size (8.7 nm), larger specific surface area (126.3 m²/g), which was more favorable for exposure of active sites. Apart from the superior physical properties, more importantly, more reactive centers Co (Ⅱ) and surface hydroxyl compounds generated on Co_1.5Fe_1.5O₄, which might be the major reason. Furthermore, Co_1.5Fe_1.5O₄ behaved good paramagnetism, wide range of pH suitability and strong resistance to salt interference, making it a new prospect in environmental application.     

GROUND WATER DROUGHT MANAGEMENT BY A FEEDFORWARD CONTROL METHOD1

ABSTRACT: Management of a regional ground water system to mitigate drought problems at the multi‐layered aquifer system in Collier County, Florida, is the main topic. This paper developed a feedforward control system that consists of system and control equations. The system equation, which forecasts ground water levels using the current measurements, was built based on the Kalman filter algorithm associated with a stochastic time series model. The role of the control equation is to estimate the pumping reduction rate during an anticipated drought. The control equation was built based on the empirical relationship between the change in ground water levels and the corresponding pumping requirement. The control system starts with forecasting one‐month‐ahead ground water head at each control point. The forecasted head is in turn used to calculate the deviation of ground water heads from the monthly target specified by a 2‐in‐10‐year frequency. When the forecasted water level is lower than the target, the control system computes spatially‐varied pumping reduction rates as a recommendation for ground water users. The proposed control system was tested using hypothetical droughts. The simulation result revealed that the estimated pumping reduction rates are highly variable in space, strongly supporting the idea of spatial forecasting and controlling of ground water levels as opposed to a lumped water use restriction method used previously in the model area.     

DROUGHT INDICATORS AND TRIGGERS: A STOCHASTIC APPROACH TO EVALUATION1

ABSTRACT: Drought management depends on indicators to detect drought conditions, and triggers to activate drought responses. But determining those indicators and triggers presents challenges. Indicators often lack spatial and temporal transferability, comparability among scales, and relevance to critical drought impacts. Triggers often lack statistical integrity, consistency among drought categories, and correspondence with desired management goals. This article presents an approach for developing and evaluating drought indicators and triggers, using a probabilistic framework that offers comparability, consistency, and applicability. From that, a multistate Markov model investigates the stochastic behavior of indicators and triggers, including transitioning, duration, and frequency within drought categories. This model is applied to the analysis of drought in the Apalachicola‐Chattahoochee‐Flint River Basin in the southeastern United States, using indicators of the Standardized Precipitation Index (for 3, 6, 9, and 12 months), the Palmer Drought Severity Index, and the Palmer Hydrologic Drought Index. The analysis revealed differences among the performance of indicators and their trigger thresholds, which can influence drought responses. Results contribute to improved understanding of drought phenomena, statistical methods for indicators and triggers, and insights for drought management.     

高级氧化技术在水处理中的应用

介绍了高级氧化技术的发展及其特点,并综述了化学氧化、光催化氧化、水热氧化以及高压脉冲放电等离子体、超声等高级氧化技术及其在水处理中的应用。随着对高级氧化技术不断深入的研究,其在水处理领域的应用将更加成熟并且越来越广泛。     

基于流域地形地貌特征的分布式汇流方法

以长江三峡区间沿渡河流域为例,采用HEC-HMS水文模型系统为模拟工具,基于流域下垫面特征和水动力条件提出了一种分布式单位线方法,并应用于降雨径流过程模拟。以自然分水线划分子流域,基于DEM数据和GIS工具提取河网水系特征。采用7种模型评估指标,分别从总量平衡,过程拟合,高水流量和低水流量4个角度评判模型的模拟效果及精度,并给出了模型模拟结果的量化统计指标。模拟结果表明:25场洪水中,洪峰流量相对误差小于20%的有80%,径流深相对误差小于20%的有96%,Nash-Sutcliffe效率系数大于0.8的有84%。由此可知,提出的分布式汇流方法可有效利用流域下垫面特征和GIS工具提取模型参数信息,适应于无资料流域的降雨径流过程模拟应用。     

数据缺失条件下基于MLP神经网络的水华风险预警方法研究

针对水华风险预警过程中相关监测指标数据缺失的问题,借鉴多元统计和随机分析构建了一种缺失数据插补方法,用于弥补现场调查数据的不足.基于主成分分析,对水华相关影响指标进行降维,确定水体水华风险预警模型的输入层变量.同时,采用多层感知器(MLP)人工神经网络模型对水华表征指标叶绿素a的浓度进行预测,并引入风险概率的概念,提出了水华风险概率计算公式,完善了水华预警的风险表达.最后以三峡库区典型支流大宁河为案例的研究证明了上述方法的可操作性.研究结果显示,插补数据条件下和未插补数据条件下的大宁河水华风险预警模型决定系数分别为0.9711和0.7769,前者的模型准确性更高,叶绿素a浓度预测效果更好;预测时段内大宁河11 d为水华蓝色预警(无警)级别,水华发生的风险概率为1.99%~18.61%;1 d达到水华橙色预警(中警)级别,水华发生概率为90.48%.     

大型再生水厂不同工艺的COD、TN和TP去除效果及其影响因素分析

以北京某大型再生水厂为研究对象,通过统计分析历史数据,系统研究了2008和2013年不同工艺(倒置A2/O工艺、A2/O工艺、A2/OMBR工艺)中主要污染物COD、TN和TP去除效果的年际、年内汛期、寒冷季和温暖季的变化特征,并分析了2013年这3种污染物去除效果变化的影响因素.结果表明,同2008年相比,2013年不仅进水的COD浓度升高,TN浓度和TP浓度降低,导致进水的碳/氮/磷比值从2008年的100∶14.5∶1.4升高到2013年的100∶10.1∶0.9,而且主要污染物去除效果均有明显改善,改善幅度依次为TPCODTN.年内变化特征表现为:汛期进水COD、TN和TP的浓度降低但波动加剧,它们的去除率降低,因此汛期出水COD稳定、TN浓度降低而TP浓度波动;温暖季进水COD、TN和TP的浓度高,它们的去除率有不同程度提高,因此温暖季出水的TN浓度波动较大、COD和TP浓度稳定.冗余分析(RDA)结果表明,一期倒置A2/O工艺的出水TN和TP浓度同步波动,主要受工况变化影响,脱氮除磷的碳源竞争是导致出水TN浓度降低、TP浓度升高的重要原因.二期A2/O工艺的出水COD浓度和TN浓度主要受进水水质波动影响.三期A2/O-MBR工艺的出水水质最稳定,膜运行性能至关重要.     

Improved Weather Generator Algorithm for Multisite Simulation of Precipitation and Temperature

The KnnCAD Version 4 weather generator algorithm for nonparametric, multisite simulations of temperature and precipitation data is presented. The K‐nearest neighbor weather generator essentially reshuffles the historical data, with replacement. In KnnCAD Version 4, a block resampling scheme is introduced to preserve the temporal correlation structure in temperature data. Perturbation of the reshuffled variable data is also added to enhance the generation of extreme values. The Upper Thames River Basin in Ontario, Canada is used as a case study and the model is shown to simulate effectively the historical characteristics at the site. The KnnCAD Version 4 approach is shown to improve on the previous versions of the model and offers a major advantage over many parametric and semiparametric weather generators in that multisite use can be easily achieved without making statistical assumptions dealing with the spatial correlations and probability distributions of each variable.     

青岛大气气溶胶中铁的溶解度及其影响因素

大气气溶胶的干湿沉降带来的铁对海洋初级生产和固碳能力有着重要影响,但这种影响从根本上决定于沉降铁的溶解度.本文利用2012年12月在青岛连续采集的31个总悬浮颗粒物(TSP)样品,分析了其中微量元素Fe的总浓度和溶解态浓度,讨论了颗粒物浓度、气溶胶来源及酸化过程对Fe溶解度的影响.结果表明,气溶胶中Fe的总浓度和溶解态浓度分别为(3248±1683)ng·m-3和(43.3±16.4)ng·m-3,溶解度为0.57%~4.86%,平均为1.63%±1.02%.随着气溶胶中总Fe浓度的增加,Fe溶解度呈现规律性降低.气溶胶中Fe的溶解度与富集因子(EF)无相关关系,而与无机和有机酸性离子存在显著正相关关系.气团后向轨迹的聚类分析显示,观测期间,64.5%的气溶胶样品主要受北方沙尘源(DS)影响,35.5%的样品主要受到华北城市群等人为源(AS)影响.AS样品中Fe的溶解度平均为2.06%,高于DS样品中的1.36%.两组样品中Fe的EF值相当,但AS样品中酸性离子与溶解度的相关关系明显好于DS组,表明酸化过程可能是造成两组样品Fe溶解度差异的主要原因.     

基于离散裂隙网络的烟台水封洞库渗水点分析

建立在致密结晶岩地区的地下水封洞库开挖过程中洞室及水幕巷道的渗水具有不均匀性,而现阶段主要在开挖后根据实际渗水量组织施工排水,若排水不及时容易造成洞室或巷道大面积浸水而形成安全风险。为在洞室开挖前对渗水点分布及渗水量进行一定预测,从而提前且合理安排排水工作,降低施工风险,以烟台地下水封洞库丁烷库区为例,在对该库区裂隙调查结果进行一定的统计分区后,采用Monte-Carlo随机模拟方法建立离散裂隙网络模型,通过多次迭代确定裂隙模拟置信区间,并选取在置信区间范围内的裂隙模拟结果按照立方定律求取渗透系数,按区间进行水封洞库渗水点分布区划分,同时与实测大流量渗水区域进行比对,结果发现两者具有较好的一致性,表明该方法能借助前期裂隙统计结果预测洞室开挖后渗水情况,协助组织施工期洞室排水。