Recent progress in electrodes for microbial fuel cells

The performance and cost of electrodes are the most important aspects in the design of microbial fuel cell (MFC) reactors. A wide range of electrode materials and configurations have been tested and developed in recent years to improve MFC performance and lower material cost. As well, anodic electrode surface modifications have been widely used to improve bacterial adhesion and electron transfer from bacteria to the electrode surface. In this paper, a review of recent advances in electrode material and a configuration of both the anode and cathode in MFCs are provided. The advantages and drawbacks of these electrodes, in terms of their conductivity, surface properties, biocompatibility, and cost are analyzed, and the modification methods for the anodic electrode are summarized. Finally, to achieve improvements and the commercial use of MFCs, the challenges and prospects of future electrode development are briefly discussed.     

重金属污染区土壤酶活性变化

从福建龙岩新罗区特钢厂污灌区农田采集土壤,测定土壤基本理化性质及脲酶、纤维素酶、碱性磷酸酶、多酚氧化酶、过氧化氢酶活性和Cu、Cd、Pb、Zn含量,探讨重金属污染和土壤性质对土壤酶活性的影响.结果表明： 4种全量或有效态重金属与土壤脲酶、纤维素酶、碱性磷酸酶和多酚氧化酶活性呈显著正相关,与过氧化氢酶活性呈显著或极显著负相关;土壤pH与碱性磷酸酶活性呈极显著正相关,粉粒含量与过氧化氢酶活性呈显著负相关.经通径分析,重金属污染刺激了脲酶、多酚氧化酶和纤维素酶活性,但对碱性磷酸酶活性的影响较小.有效态Cu、Cd、Pb、Zn对过氧化氢酶活性的直接影响并不大,但通过间接途径抑制了过氧化氢酶活性.土壤理化性质对5种土壤酶活性的影响较大,碱解氮直接抑制了脲酶活性;全磷直接刺激了碱性磷酸酶和过氧化氢酶活性,并通过有效磷刺激了纤维素酶活性;有效磷直接刺激了纤维素酶活性,直接抑制了碱性磷酸酶和过氧化氢酶活性;全钾直接抑制了碱性磷酸酶和多酚氧化酶活性;速效钾通过有效磷刺激了纤维素酶活性;土壤颗粒组成明显影响多酚氧化酶和过氧化氢酶活性.5种酶活性与土壤Cu、Cd、Pb、Zn含量之间的关系不明确,因此其活性不是指示土壤Cu、Cd、Pb、Zn污染的良好指标.     

重金属污染区土壤酶活性变化——以福建龙岩新罗区特钢厂污水灌溉区为例

从福建龙岩新罗区特钢厂污灌区农田采集土壤,测定土壤基本理化性质及脲酶、纤维素酶、碱性磷酸酶、多酚氧化酶、过氧化氢酶活性和Cu、Cd、Pb、Zn含量,探讨重金属污染和土壤性质对土壤酶活性的影响.结果表明:4种全量或有效态重金属与土壤脲酶、纤维素酶、碱性磷酸酶和多酚氧化酶活性呈显著正相关,与过氧化氢酶活性呈显著或极显著负相关;土壤pH与碱性磷酸酶活性呈极显著正相关,粉粒含量与过氧化氢酶活性呈显著负相关.经通径分析,重金属污染刺激了脲酶、多酚氧化酶和纤维素酶活性,但对碱性磷酸酶活性的影响较小.有效态Cu、Cd、Pb、zn对过氧化氢酶活性的直接影响并不大,但通过间接途径抑制了过氧化氢酶活性.土壤理化性质对5种土壤酶活性的影响较大,碱解氮直接抑制了脲酶活性;全磷直接刺激了碱性磷酸酶和过氧化氢酶活性,并通过有效磷刺激了纤维素酶活性;有效磷直接刺激了纤维素酶活性,直接抑制了碱性磷酸酶和过氧化氢酶活性;全钾直接抑制了碱性磷酸酶和多酚氧化酶活性;速效钾通过有效磷刺激了纤维素酶活性;土壤颗粒组成明显影响多酚氧化酶和过氧化氢酶活性.5种酶活性与土壤Cu、Cd、Pb、Zn含量之间的关系不明确,因此其活性不是指示土壤Cu、Cd、Pb、Zn污染的良好指标.     

Distribution of extractable heavy metals in different soil fractions

Abstract

Due to the difficulties of precisely characterizing environmentally contaminated soil, the effects of heavy metals on plants are studied using uncontaminated soil spiked with known quantities of heavy metals. One problem in using spiked soils is how accurately the distribution of metals mimics stabilized natural soils. We studied the distribution of cadmium, chromium, copper, lead, nickel, and zinc in soil fractions after application in soluble form. The soil samples included a control (an uncontaminated Typic Argiudoll) and two samples spiked with either a moderate or high heavy metal concentration). After application of the salts the soils were subjected to wet/dry cycles over the course of three months. The soils were fractionated using a sequential chemical extraction procedure employing: (1) CaCl₂,(2) NaOH, (3) Na₂EDTA and (4) HNO₃, HCl, and HF. Soil physical separation was carried out by ultrasonic dispersion. The heavy metal levels were determined using ICP-AES. Each heavy metal displayed a unique behavior when added to soil in the form of soluble salts. Cadmium and zinc remained in the soluble fraction, indicating that no equilibrium was attained, while nickel primarily appeared in the insoluble fraction. Chromium, copper and lead were distributed among various soil chemical fractions. The highest levels of all metals appeared in the clay fraction except lead which was mainly present in the silt fraction.     

长期重金属胁迫对农田土壤微生物生物量、活性和种群的影响

调查了沈阳张士灌区长期污水灌溉造成的原位农田土壤重金属污染状况,从土壤微生物生物量、微生物活性和微生物种群数量的角度评价了长期重金属污染对农田土壤生态系统的影响.结果表明,张士灌区土壤存在严重的Cd污染,土壤Cd含量达1.75～3.89 mg·kg ^-1,部分区域还伴有Cu、Zn复合污染.在目前污染程度下,土壤微生物生物量碳(C_mic)、微生物商(qM)、土壤脱氢酶活性以及自生固氮菌数量随土壤重金属含量增加呈下降趋势,代谢商(qCO₂)随土壤重金属含量增加显著升高,而底物诱导呼吸强度(SIR)、纤维素酶活性以及细菌、放线菌和真菌数量无明显变化.相关性分析表明,土壤Cd含量变化是影响微生物参数变化的主要因素,在微生物参数中微生物商和代谢商对重金属污染最敏感.     

攀钢冶炼渣堆土壤与优势植物的重金属含量

采用原子吸收分光光度法测定攀钢西渣场冶炼渣堆土壤和6科12种优势植物中Mn、Pb、 Ni、 Cu、Cd等5种重金属含量,并计算优势植物对重金属的富积系数和转移系数.结果表明:渣堆土壤中重金属含量Mn最高(3869.14 mg/kg),次后顺序为Pb>Ni>Cu>Cd;植物与土壤的重金属分布基本一致;所测优势植物中,多数植物对重金属的富积系数较低,而转移系数却较高,如天名精对Cu的转移系数为5.1,羽芒菊对Pb转移系数为3.3,五月艾对Cd的转移系数为6.0,其中8种植物(天名精、羽芒菊等)对Mn的转移系数均大于1.该结果为重金属污染土壤的植物修复提供了参考物种,同时也为植物重金属耐受机制的研究提供了筛选对象.     

The performance of vetivers (Chrysopogon zizaniodes and Chrysopogon nemoralis) on heavy metals phytoremediation: laboratory investigation

Abstract

Phytoremediation with vetiver was investigated in relation to heavy metal contaminated soil in Thailand. The work compared the performance of two species of vetiver named Songkhla 3 (Chrysopogon zizaniodes) and Prachuap Khiri Khan (Chrysopogon nemoralis) in absorbing lead, zinc, and cadmium in contaminated soils. Toxicity Characteristic Leaching Procedure (TCLP), and Allium tests were conducted to determine toxicity of treated soil. Ethylenediaminetetraacetic acid (EDTA) was also used to increase heavy metals concentration in solution in soil, which led to an increase in translocation and bioaccumulation factors. In general, results showed that concentration of heavy metals decreased in soil and increased in both the shoots and roots of vetivers during a 4-month treatment period. TCLP results indicated that the concentration of zinc and cadmium in contaminated soil was reduced over treatment time, and significantly increased after EDTA was applied. To confirm vetiver performance in phytoremediation, Allium testing showed that remained heavy metals in treated soils had no effect on nucleus aberration. Songkhla 3 and Prachuap Khiri Khan showed similar trends in their ability to remediate lead, zinc, and cadmium from contaminated soil. Both species could accumulate higher concentrations of heavy metals in their shoots and roots over time, and with EDTA application.     

Uptake by corn and chemical extractability of heavy metals from a four year compost treated soil

This paper gives the results from four-year field experiments on compost application, added at the maximum rate allowed by Italian legislation (30 t/ha/y). The purpose of the experiment was to evaluate any eventual heavy metal accumulation in soil and corn plants. Cadmium in corn plants increased particularly in the roots from 0.22 mg kg⁻¹ to 1.31 mg kg⁻¹, concentration of Zn and Cu increased in grains, from 26.8 to 35.8 and from 2.4 to 4.2 mg kg⁻¹ respectively. Relevant increase in the roots was detected for Zn from 34.6 to 146.8 mg kg⁻¹. Only in the 4th year Ni concentration increases in the root portion while the content of Pb and Cr in corn was generally unaffected by the compost application. Heavy metals in the soil determined by a sequential chemical extraction, indicated that extractability changed with time. A certain increase was found from the beginning to the end of the experiment particularly for Zn, from 23.3 mg kg⁻¹ to 45.1 mg kg⁻¹ in extractable forms. Nevertheless the extractable amounts are rather small in respect to the total heavy metal content of compost.     

植物修复──重金属污染土壤整治有效途径

系统论述了重金属污染土壤植物修复的概念、原理、方法与研究动态,列举了污染土壤植物修复的一些实例。探讨了土壤重金属超富集植物的类型、特点、应用潜力以及基因工程等现代生物技术的应用、效果与最新展望,为土壤污染的综合整治及生态修复提出了新的思路。     

Cadmium regulation by Lasius niger: A contribution to understanding high metal levels in ants

Ants (Formicinae, Hymenoptera) are considered efficient accumulators of Zn and Cd. In this study the relationship between Cd concentrations in soil and in Lasius niger workers was assessed for 20 colonies located along a gradient of Cd pollution. As soil Cd concentration increased from 1 to 8 mg/kg, ant body Cd concentration increased rapidly to about 40 mg/kg, and remained stable at this level, through a progressive increase of soil Cd concentration from 8 to 21 mg/kg. The phase of rapid increase confirms the high ability of L. niger for Cd accumulation, while the stabilization of Cd body concentration indicates either increasing elimination rate or decreasing rate of uptake. Therefore it can be concluded that Lasius niger has a high ability to accumulate Cd, but simultaneously an ability for Cd regulation was detected.     

高生物量经济植物修复重金属污染土壤研究进展

植物修复是重金属污染土壤修复的重要方法之一。利用高生物量经济植物修复重金属污染土壤,能够兼顾生态和经济效益,具有很大的应用前景。本文系统分析了植物修复现状及存在的问题,提出利用高生物量经济植物修复重金属污染土壤的优势,总结了近年来利用高生物量经济植物吸收重金属的研究进展,探讨了改善高生物量经济植物修复重金属污染土壤效率的方法,以期为提高植物修复经济效益、促进植物修复广泛应用提供参考。     

PHYTOREMEDIATION OF INORGANICS: REALISM AND SYNERGIES

There are very few practical demonstrations of the phytoextraction of metals and metalloids from soils and sediments beyond small-scale and short-term trials. The two approaches used have been based on using 1) hyperaccumulator species, such as Thlaspi caerulescens (Pb, Zn, Cd, Ni), Alyssum spp. (Ni, Co), and Pteris vittata (As) or 2) fast-growing plants, such as Salix and Populus spp. that accumulate above-average concentrations of only a smaller number of the more mobile trace elements (Cd, Zn, B). Until we have advanced much more along the pathway of genetic isolation and transfer of hyperaccumulator traits into productive plants, there is a high risk in marketing either approach as a technology or stand-alone solution to clean up contaminated land. There are particular uncertainties over the longer-term effectiveness of phytoextraction and associated environmental issues. Marginally contaminated agricultural soils provide the most likely land use where phytoextraction can be used as a polishing technology. An alternative and more useful practical approach in many situations currently would be to give more attention to crops selected for phytoexclusion: selecting crops that do not translocate high concentrations of metals to edible parts. Soils of brownfield, urban, and industrial areas provide a large-scale opportunity to use phytoremediation, but the focus here should be on the more realistic possibilities of risk-managed phytostabilization and monitored natural attenuation. We argue that the wider practical applications of phytoremediation are too often overlooked. There is huge scope for cross-cutting other environmental agenda, with synergies that involve the recovery and provision of services from degraded landscapes and contaminated soils. An additional focus on biomass energy, improved biodiversity, watershed management, soil protection, carbon sequestration, and improved soil health is required for the justification and advancement of phytotechnologies.     

Multianalysis of trace elements in mosses with inductively coupled plasma-mass spectrometry

As a part of an air-pollution biomonitoring survey, a procedure using inductively coupled plasma-mass spectrometry (ICP-MS) and microwave digestion was developed to achieve a high sample throughput and guarantee the accuracy of the results. This article presents an analytical method to measure 22 trace elements. As, Ba, Cd, Ce, Co, Cr, Cs, Cu, Fe, Hg, La, Mo, Ni, Pb, Rb, Sb, Sr, Th, Tl, U, V, W were analyzed in 563 mosses collected in France. The digestion was performed in polytetrafluoroethylene (PTFE) vessel using the mixture HNO₃-H₂O₂-HF. The data were reprocessed taking into account the drift curve calculated for each element. The detection limits (DL) calculation was based on the standard deviations of the reagent blanks concentrations. The DL varied from one batch to another, because of the heterogeneity of the mosses’ elemental contents. The DL ranged between 0.001 μg/g (Cs, Tl) and 70 μg/g (Fe) and were mainly around 0.01 μg/g (As, Cd, Ce, Co, Hg, La, Mo, Sb, Sr, U, V, W). The detection limits obtained were in agreement with the concentrations observed in the samples, except for Hg and Ni. The reproducibility between duplicates and the analytical precision were near 10%. The procedure was tested with the mosses’ reference materials.     

Manure Application and Cannabis Cultivation Influence on Speciation of Lead and Cadmium by Selective Sequential Extraction

The contamination of agricultural soils by heavy metals is a worldwide problem. Degradation of organic matter (OM) from organic amendments used in the remediation of metal-contaminated soils leads to changes in soil chemical properties shortly after their addition, which may affect the soil metal distribution. The effects of four differing organic amendments on chemical forms of Pb and Cd in a contaminated soil were investigated in a pot experiment of control unamended soil and soils amended with dry cow and poultry manures (20 g CM or PM kg^?1 soil), and cow and poultry manure extracts (2 g CME or PME kg^?1 soil) cultured with cannabis sativa. After eight weeks, a sequential extraction scheme was used to fractionate soil Pb and Cd into soluble-exchangeable (Sol-Exch), organic matter associated (AOM), and carbonates associated (ACar) forms. The addition of animal manures and their extracts increased the DTPA-extractable Pb and Cd in soil significantly. Soil Pb and Cd in Sol-Exch fraction were increased by manure applications. Both Pb and Cd in AOM fraction were increased by application of manures and their extracts. This increase was more obvious for Pb in application of cow and poultry manure extracts. The ACar chemical forms of Pb and Cd were also increased by application of manures and their extracts. The increases of Pb and Cd in Acar fraction was noticeable in soils treated with cow manure. Soil cultivation with cannabis sativa increased available, Sol-Exch, and AOM chemical forms of Pb in soil significantly compared to control soil. However, soil Pb and Cd in ACar fraction were decreased significantly by cannabis cultivation. The effect of cannabis cultivation on all of the Cd chemical forms (except on Sol-Exch) was similar to the results of Pb chemical forms. Plant cultivation had no significant effect on Cd in Sol-Exch chemical form.     

In-Situ Remediation of Lead–Zinc Polymetallic Mine Contaminated Soils by MnFe2O4 Microparticles

In-situ remediation is a practical approach to remediate soils contaminated with heavy metals. The MnFe₂O₄ microparticles (MM) were prepared for the in-situ remediation of contaminated soils from a lead–zinc polymetallic mine in Inner Mongolia province, China. The effects of MM dosage, pH on remediation efficiency, were determined with static vibration leaching experiment, and the release risk of heavy metals of treated soil was studied by column leaching experiment. The results showed that the leached Cu, Pb, Zn, and As concentration decreased drastically with increasing MM dosage, when the dosage was lower than 10 g/kg. Moreover, the decrease of pH caused increase of leached concentration of Cu, Pb, Zn, but slight decrease of leached As concentration. For the amended soil, concentrations of leached heavy metals were lower than Grade III limit of Chinese Environmental Quality Standards for Ground and Surface water (GB3838-2002) under simulated acid rain leaching condition. In comparison with non-amended soils, the total amount of Cu, Pb, Zn, and As release from amended soils was reduced by 93.6%, 69.2%, 57.0%, and 99.7%, respectively. The MM is a kind of promising amendment for heavy metals contaminated soil.     

Metal contents and fractionation in contaminated soil after column leaching using [S,S]-EDDS

Abstract

Column leaching using [S, S]-ethylene diamine disuccinate ([S, S]-EDDS) on copper tailing soils was carried out to investigate metal content and fractionation after leaching. The soil column was divided into four layers after leaching. Fractionation of Cu, Pb, Zn, and Mn in soil was analyzed using a modified BCR sequential extraction method. Metal contents (Cu, Pb, Ca, Mn) in soil layers increased with the depth of the soil column after leaching in the [S, S]-EDDS treatment. The cumulative extraction efficiency was approximately 43.1% for Cu, 26.8% for Zn, 19.5% for Pb, 10.5% for Ca, 2.07% for Mg, 58.5% for Mn, and 7.92% for Fe. The removal of the reducible fractions of Cu and Mn and the exchangeable fraction of Zn was the most significant in the treatment with [S, S]-EDDS. The exchangeable fraction of Pb was the main fraction that was affected by leaching using [S, S]-EDDS. Distribution of Cu and Mn were severely modified by leaching with [S, S]-EDDS. Percentages of residual fractions of the tested heavy metals in the treatment with [S, S]-EDDS after leaching were much higher than that in the control. Although column leaching using [S, S]-EDDS could remove target metals effectively and impaired their availability, it also dissolved large amounts of major elements and modified the distribution of Mn appreciably.