Effect of current density on groundwater arsenite removal performance using air cathode electrocoagulation

• With the same charge, current density had little effect on As(III) removal in ACEC. • ACEC had the lowest energy consumption compared with EC/O₂ or EC/N₂. • There was a trade-off relationship between energy consumption and removal time. • The ·OH concentration in ACEC was 1.5 times of that in the EC/O₂ system. Naturally occurring arsenic enrichment in groundwater poses a huge threat to human health. Air cathode electrocoagulation (ACEC) has recently been proposed to enhance As(III) oxidation and lower energy consumption. In this study, ACEC, EC/O₂ and EC/N₂ were evaluated with different current densities from 1 to 8 mA/cm² to investigate the effect on As(III) removal in different redox environments. Current density had no appreciable effect on arsenic removal efficiency given the same charge in ACEC because the concentration ratio of Fe/H₂O₂ under different current densities remained stable. However, in EC/O₂ and EC/N₂, As(III) removal was inhibited at higher current densities (4–8 mA/cm²), likely because more Fe(II) competed with As(III) for the oxidant, leading to less effective oxidation of As(III). In all EC systems, the ·OH units generated per power consumption reached the highest value at the lowest current density. Compared with other EC systems, the ACEC system showed lower energy consumption at all current densities due to the low energy consumption of the electrode reaction and more free radical generation. A lower current density saved more energy at the expense of time, showing the trade-off relationship between energy consumption and removal time. The operation costs for As(III) removal under optimal conditions were calculated as 0.028 $/m³ for ACEC, 0.030 $/m³ for EC/O₂, and 0.085 $/m³ for EC/N₂     

The implications of planting mode on cadmium uptake and remobilization in rice: Field experiments across growth stages

•Direct seeding (DS) method led to more distributed Cd in aerial parts of rice. •The Cd content was significantly higher in brown rice with planting mode of DS. •Using DS lessened the Fe plaque covering the root surface in all growth stages. •Transplantation mode should be considered as a priority in Cd-contaminated areas. Global rice production practices have gradually changed from a reliance on transplanting to direct seeding. Yet how this shift may alter cadmium (Cd) accumulation in rice is poorly known. Here we conducted field experiments with two rice genotypes cultivars that were planted using three methods: via direct seeding (DS), seedling throwing (ST), and manual transplanting (MT). Rice samples were collected during four growth stages. The formation and distribution of iron plaque were analyzed using DCB (dithionite-citrate-bicarbonate) extractions and observed under micro-XRF (micro X-ray fluorescence). The results revealed that, in each growth stage, DS rice was more apt to harbor Cd distributed in the plant’s aerial parts, and the Cd concentration of brown rice from DS was 21.8%–43.3% significantly higher than those from ST and MT at maturity stage (p<0.05). During the vegetative stages, the Cd uptake percentage was higher in DS than MT rice, and those plants arising from the DS method were capable of absorbing more Cd earlier in their growth and development. Conversely, using DS decreased the amount of iron plaque covering the root surface in every growth stage, especially in the critical period of Cd accumulation, such that the roots’ middle areas were distinguished by a near-complete absence of iron plaque, thus weakening its role as an effective barrier to Cd uptake from soil. Collectively, this study demonstrated that implementing the DS mode of planting will increase Cd’s distribution in the aboveground parts of rice, and heightening the risk of Cd contamination in grain.     

一起换流变阀侧套管升高座重瓦斯动作原因分析

在已经投入运行的换流站中,换流变压器的非电气量保护在换流变压器保护中占有重要地位。通过介绍某±660 kV换流站换流变压器阀侧套管升高座重瓦斯保护动作的经过,利用现场收集的换流变非电量保护及保护暂态故障录波对故障进行分析,同时对一、二次设备进行事故后的检查和试验,得出此次故障的主因是瓦斯继电器行程较小引起的误动,并提出了相应的预防和改善措施。     

Influence of human activity and monsoon dynamics on spatial and temporal hydrochemistry in tropical coastal waters (Sanya Bay,South China Sea)

Human activities and oceanic influences like mixing and/or upwelling define the hydrochemical and biological characteristics of coastal regions. In Sanya Bay, northern South China Sea, the balance between these two influences on spatial and temporal scales is poorly understood. The influence from human activities was due to discharge from Sanya River, whereas the most important marine influence was related to seasonal changes in hydrodynamics. Spatial differences (p<0.05) in total nitrogen (TN) and chlorophyll-a (Chl-a) were observed. Seasonal differences were observed for temperature and nutrients. Human activities are the dominant factor influemcing hydrochemistry in the inner bay. This region exhibited the maximum influence of discharge from Saya River as estimated by higher nutrient levels. Oceanic influences like upwelling and mixing caused by monsoons are the dominant factors influencing hydrochemistry in the central and outer bay. Both human activities and oceanic influences play important roles in coastal ecosystems in Sanya Bay. This study has defined these characteristics so that better management policies can be enacted.     

基于注意力机制的人群计数方法

为准确预测固定场景中的人群计数,在人群分析领域,采用一种融合注意力机制的卷积神经网络(CNN)进行人群计数,该模块结合空间域注意力和通道域注意力,空间域注意力可以编码整个图像的像素级上下文信息,以更准确地表达像素级别的密度图,而通道域注意力可以在不同的通道中提取更多的区分特征使网络显著表达人群的局部区域,并在多个公开数...     

三峡库区消落区水体-沉积物重金属迁移转化特征

结合三峡水库反季节调度模式,对消落区沉积物中Cu、Pb、Cd、Cr这4种重金属的存在形态及迁移转化特征进行研究.结果表明,不同重金属在消落区沉积物中形态分布各异,Cu主要以有机物及硫化物结合态和残渣态形式存在,Pb主要以碳酸盐结合态、Fe-Mn氧化物结合态及残渣态存在,Cd主要以碳酸盐结合态、Fe-Mn氧化物结合态存在,Cr主要以残渣态存在.伴随着消落过程的进行,汛期出露沉积物的有机质及AVS含量下降、ORP升高、pH值降低,沉积物中可提取态重金属的相对含量显著下降,重金属具有向水体迁移趋势, Cu、Pb、Cd、Cr平均迁移率分别为30.50%、 26.10%、 33.50%和11.77%,4种重金属的迁移性大小依次为Cd>Cu>Pb>Cr.可提取态Cu、Pb、Cd、Cr对重金属迁移贡献率分别为77.15%、 86.09%、 94.86%和32.34%,可提取态是重金属发生迁移的主要部分.研究结果表明, 消落区重金属迁移呈"缓释"特征,三峡水库的反季节调度模式有利于缓解消落区重金属迁移诱导的生态风险,库区水体重金属含量处于较低水平.     

农村生活污水土地处理示范项目的可推广性研究——以上海为例

农村生活污水处理示范项目建造的目的就是为了大面积地推广,但是一个适宜推广的示范项目至少应该满足技术可行、成本有效和管理便捷的要求。以上海市汇中村和双津村为例,从技术适用性、成本有效性、管理便捷性三方面对农村生活污水土地处理示范项目的可推广性进行了分析。研究发现,采用土地处理系统的示范项目,技术上可以基本满足农村生活污水处理的要求,管理上非常便捷,可以由农民自行维护,比较有利于推广;但从成本有效性方面来看,现有示范项目还存在较大的成本下降空间。在实现成本有效的条件下,农村生活污水生地处理示范项目将具有很强的推广空间。     

石脑油/脱丁烷塔进料换热器结垢腐蚀原因及对策

对轻烃回收装置石脑油/脱丁烷塔进料换热器E-1202B结垢腐蚀进行了检查、检验,从腐蚀介质来源、垢样分析结果、流速等多方面分析了换热器腐蚀泄漏的原因,提出了相应的对策。     

环境内分泌干扰物前处理方法研究新进展

环境内分泌干扰物因其能够紊乱生物体正常内分泌功能而引起人们的广泛关注,然而内分泌干扰物在水环境中浓度极低,水体中复杂机质的干扰较大,在分析监测前一般要经过样品前处理过程,以起到富集痕量组分、消除基体干扰、提高方法灵敏度的作用。针对不同环境样品中内分泌干扰物的前处理方法不同,分别介绍了液体、固体或类固体环境样品的前处理技术,提出了各前处理方法的优缺点,总结并展望了环境内分泌干扰物样品前处理方法的发展方向。     

Adsorption of isoxaflutole degradates to aluminum and iron hydrous oxides

Isoxaflutole is a preemergence herbicide that has been marketed as a substitute for atrazine. It is rapidly transformed to a more stable and soluble diketonitrile degradate (DKN) after field application and can further degrade to a benzoic acid degradate (BA) within soil. However, no previous research has been conducted to investigate DKN and BA sorption to metal oxide minerals. The primary objective of this research was to elucidate the interactions of DKN and BA with synthetic hydrous aluminum and iron oxides (HAO and HFO, respectively) to understand how variably charged minerals may influence adsorption of these compounds in soil. The herbicide degradates did adsorb to HAO and HFO, and the data were well described by the Freundlich model (R2 > 0.91), with Nvalues ranging from 0.89 to 1.2. Adsorption isotherms and Kd values demonstrate that BA is adsorbed to HFO to a greater extent than other degradate-mineral combinations that were studied. The degree of hysteresis between adsorption/desorption isotherms was characterized as slight (hysteresis index values < 1.7), suggesting weak DKN and BA retention to HFO and HAO oxide surfaces. Degradate adsorption was observed to greatly diminish as suspension pH increased. Attenuated total reflectance-Fourier transform infrared spectra show no evidence that DKN or BA adsorb to mineral surfaces as inner-sphere complexes under hydrated conditions. Instead DKN and BA adsorb to positively charged metal oxide surfaces as outer-sphere or diffuse ion swarm complexes via electrostatic attraction. This research indicates that metal oxides may serve as important retardants for DKN and BA migration through acidic soils enriched with aluminum and iron oxides.