Removal of heavy metals and arsenic from a co-contaminated soil by sieving combined with washing process

Batch experiments were conducted with a heavy metals and arsenic co-contaminated soil from an abandoned mine to evaluate the feasibility of a remediation technology that combines sieving with soil washing.Leaching of the arsenic and heavy metals from the different particle size fractions was found to decrease in the order: 0.1,2–0.1,and 2 mm.With increased contact time,the concentration of heavy metals in the leachate was significantly decreased for small particles,probably because of adsorption by the clay soil component.For the different particle sizes,the removal efficiencies for Pb and Cd were75%–87%,and 61%–77% for Zn and Cu,although the extent of removal was decreased for As and Cr at 45%.The highest efficiency by washing for Pb,Cd,Zn,and As was from the soil particles 2 mm,although good metal removal efficiencies were also achieved in the small particle size fractions.Through SEM-EDS observations and correlation analysis,the leaching regularity of the heavy metals and arsenic was found to be closely related to Fe,Mn,and Ca contents of the soil fractions.The remediation of heavy metal-contaminated soil by sieving combined with soil washing was proven to be efficient,and practical remediation parameters were also recommended.     

Deficit irrigation: An option to mitigate arsenic load of rice grain in West Bengal, India

Farmers in arsenic (As) contaminated areas of West Bengal, India grow rice during dry months (January to April) and use underground water for irrigation with As concentration above WHO defined critical (0.01 mg l⁻¹) limit. In each season they add 50-150 mg As per m² soil area. Thus growing rice under deficit irrigation in these areas will reduce As load in soil-root-shoot-leaf-grain continuum of rice ecosystem. Suitable deficit irrigation system has to be screened so that As load will decrease with insignificant reduction in grain yield. With this objective, rice grown under four irrigation regimes (i) continuous ponding (CP), (ii) intermittent ponding (IP), (iii) saturation (SAT) and (iv) aerobic (AER) was tested to assess the arsenic load in soil and various parts of rice on 45 and 80 days after transplanting (DAT). Conditions described in treatments ii, iii and iv were imposed during 15-45 DAT. Highest value (18.18 and 18.74 mg kg⁻¹) of soil arsenic was attained under CP followed by IP, SAT and AER. Root arsenic content under AER at 45 and 80 DAT was at the lowest level (6.14 and 20.54 mg kg⁻¹) and this was 31 and 7.0% lower as compared to CP. As content in leaf and grain attained the lowest values under IP. Grain yield insignificantly differed under IP (4.33 Mg ha⁻¹) over CP (4.69 Mg ha⁻¹). Compared to soil As, As added through irrigation showed stronger relationship with As status of various plant parts. Imposition of IP only during vegetative stage was found to be optimum in terms of reduction of As content in straw and grain respectively by 23 and 33% over farmers irrigation practice with insignificant decrease in grain yield.     

Arsenic release from microbial reduction of scorodite in the presence of electron shuttle in flooded soil

Scorodite (FeAsO₄·H₂O) is a common arsenic-bearing (As-bearing) iron mineral in nearsurface environments that could immobilize or store As in a bound state.In flooded soils,microbe induced Fe(Ⅲ) or As(Ⅴ) reduction can increase the mobility and bioavailability of As.Additionally,humic substances can act as electron shuttles to promote this process.The dynamics of As release and diversity of putative As(Ⅴ)-reducing bacteria during scorodite reduction have yet to be investigat...     

Mobilization of arsenic from contaminated sediment by anionic and nonionic surfactants

The increasing manufacture of surfactants and their wide application in industry,agriculture and household detergents have resulted in large amounts of surfactant residuals being discharged into water and distributed into sediment. Surfactants have the potential to enhance arsenic mobility, leading to risks to the environment and even human beings. In this study, batch and column experiments were conducted to investigate arsenic mobilization from contaminated sediment by the commercial anionic surfactants sodium dodecylbenzenesulfonate(SDBS), sodium dodecyl sulfate(SDS), sodium laureth sulfate(AES)and nonionic surfactants phenyl-polyethylene glycol(Triton X-100) and polyethylene glycol sorbitan monooleate(Tween-80). The ability of surfactants to mobilize arsenic followed the order AES SDBS SDS ≈ Triton X-100 Tween 80. Arsenic mobilization by AES and Triton X-100 increased greatly with the increase of surfactant concentration and p H, while arsenic release by SDBS, SDS and Tween-80 slightly increased. The divalent ion Ca~(2+) caused greater reduction of arsenic mobilization than Na~+. Sequential extraction experiments showed that the main fraction of arsenic mobilized was the specifically adsorbed fraction. Solid phase extraction showed that arsenate(As(V)) was the main species mobilized by surfactants,accounting for 65.05%–77.68% of the total mobilized arsenic. The mobilization of arsenic was positively correlated with the mobilization of iron species. The main fraction of mobilized arsenic was the dissolved fraction, accounting for 70% of total mobilized arsenic.     

Arsenic speciation in fish from Greek coastal areas

Arsenic speciation analysis was conducted on fish samples(sardine and anchovy) collected from six areas along the Greek coastline, i.e. Artemisium Straits, Thermaikos Gulf, Amvrakikos Gulf,Strymonian Gulf, Thracian Sea, and Elefsina Gulf. Total arsenic levels ranging from 11.8 to62.6 mg As/kg dry weight were determined. Arsenobetaine, a non-toxic form of arsenic, was found to be the main arsenic species, present at 8.6 to 58.8 mg As/kg dry weight, accounting for67–95% of the total arsenic. Also detected in all fish samples was dimethylarsinic acid, although at considerably lower concentrations, ranging from 0.072–0.956 mg As/kg dry weight.Monomethylarsonic acid was detected at low levels in all anchovy samples, and only in sardines from one area. Finally, inorganic arsenic in the form of arsenate was detected only in fish at one area, indicating the possible effect of an environmental parameter on its presence at detectable amounts. Statistical analysis revealed the environmental variables, such as salinity,total organic carbon and nitrogen, ammonium, phosphate, total phosphorus, dissolved oxygen and pressure index, are potentially correlated to As species concentrations. Furthermore, based on factor analysis, the biological parameters, such as fish weight, lipids, protein and ash content,that are correlated to As species concentrations of fish were also identified. The interrelationship of arsenobetaine and dimethylarsinic acid concentrations within each fish species was evaluated.     

Comparison between background concentrations of arsenic in urban and non-urban areas of Florida

Arsenic contamination is of great environmental concern due to its toxic effects as a carcinogen. Knowledge of arsenic background concentrations is important for land application of wastes and for making remediation decisions. The soil clean-up target level for arsenic in Florida (0.8 and 3.7 mg kg⁻¹ for residential and commercial areas, respectively) lies within the range of both background and analytical quantification limits. The objective of this study was to compare arsenic distribution in urban and non-urban areas of Florida. Approximately 440 urban and 448 non-urban Florida soil samples were compared. For urban areas, soil samples were collected from three land-use classes (residential, commercial and public land) in two cities, Gainesville and Miami. For the non-urban areas, samples were collected from relatively undisturbed non-inhabited areas. Arsenic concentrations varied greatly in Gainesville, ranging from 0.21 to approximately 660 mg kg⁻¹ with a geometric mean (GM) of 0.40 mg kg⁻¹, which were lower than Miami samples (ranging from 0.32 to 112 mg kg⁻¹; GM=2.81 mg kg⁻¹). Arsenic background concentrations in urban soils were significantly greater and showed greater variation than those from relatively undisturbed non-urban soils (GM=0.27 mg kg⁻¹) in general.     

三江平原水田灌溉-排水过程中铁形态变化及输出贡献

采集三江平原农田灌溉地下水、稻田积水、渠系排水、土壤侧渗水,并采用切向超滤技术分离水体中不同形态铁,分析在灌溉排水及地下侧渗水中铁的迁移特征,并估算水田排水中铁的输出贡献.结果表明,在灌溉排水过程中,铁主要以低分子量形态和酸性不稳定形态迁移,地下水中Fe2+含量占可溶态铁的80.45%;地下水抽取到稻田后Fe2+含量显著降低,络合态铁含量升高,稻田积水中络合态铁占可溶态铁的75.50%;稻田积水排入渠系后,络合态铁中不稳定弱配位铁含量降低13.58%,其他铁形态变化不大.稻田积水通过地下侧渗进入渠系,随侧渗水体深度加深,Fe2+含量升高,络合态和胶体态铁含量降低,地下侧渗水向渠系水主要提供络合态和胶体态铁.三江平原湿地水田化改变了水体中铁的输出形态,同时,排水过程中铁的输出也对河流形成补给,水田灌溉排水过程可溶态铁的输出通量约为390kg.a-.1km-2,输出系数为0.186,灌溉-排水过程中残留在稻田土壤中铁的量约为1460kg.a-.1km-2,残留在排水渠系土壤中铁的量约为250kg.a-.1km-2,这对三江平原水土环境产生了深远影响.     

Groundwater arsenic removal by coagulation using ferric(III) sulfate and polyferric sulfate: A comparative and mechanistic study

Elevated arsenic (As) in groundwater poses a great threat to human health. Coagulation using mono- and poly-Fe salts is becoming one of the most cost-effective processes for groundwater As removal. However, a limitation comes from insufficient understanding of the As removal mechanism from groundwater matrices in the coagulation process, which is critical for groundwater treatment and residual solid disposal. Here, we overcame this hurdle by utilizing microscopic techniques to explore molecular As surface complexes on the freshly formed Fe flocs and compared ferric(III) sulfate (FS) and polyferric sulfate (PFS) performance, and finally provided a practical solution in As-geogenic areas. FS and PFS exhibited a similar As removal efficiency in coagulation and coagulation/filtration in a two-bucket system using 5 mg/L Ca(ClO)₂. By using the two-bucket system combining coagulation and sand filtration, 500 L of As-safe water (< 10 μg/L) was achieved during five treatment cycles by washing the sand layer after each cycle. Fe k-edge X-ray absorption near-edge structure (XANES) and As k-edge extended X-ray absorption fine structure (EXAFS) analysis of the solid residue indicated that As formed a bidentate binuclear complex on ferrihydrite, with no observation of scorodite or poorly-crystalline ferric arsenate. Such a stable surface complex is beneficial for As immobilization in the solid residue, as confirmed by the achievement of much lower leachate As (0.9 μg/L–0.487 mg/L) than the US EPA regulatory limit (5 mg/L). Finally, PFS is superior to FS because of its lower dose, much lower solid residue, and lower cost for As-safe drinking water.     

砷的发生、形态、污染源及地球化学循环

文章首先总结了砷在地表水、地下水、土壤、沉积物、岩石、大气中的含量和分布;归纳了砷的地球化学循环过程;分析了砷在水和土壤/沉积物固相中的形态;并重点阐述了砷在土壤和沉积物中的迁移转化机理。砷通常与Fe、Al、Mn的氧化物和氢氧化物、粘土矿物、硫化物、磷酸盐和碳酸盐矿物结合,砷的生物可用性和迁移性与其在土壤和沉积物中的形态有密切关系。文章最后定量阐述了砷的污染源,包括金属开采与冶炼,化学燃料的燃烧和含砷化学品使用。     

半壁山金矿矿业活动区砷赋存的矿物特征及其对农田土壤砷累积的影响

为探索青龙满族自治县半壁山金矿矿业活动地区砷赋存的矿物特征及其对农田土壤砷的污染特征,应用矿物学和化学分析方法对矿业周边的矿石、废石、底泥、河流及土壤样品进行分析.在偏光显微镜下发现半壁山金矿周边的土壤与矿石、废石中均存在含砷矿物——毒砂,且废石中的毒砂已出现风化氧化现象,氧化的毒砂容易在土壤中迁移释放砷,存在较大的潜在危害.由于矿业运输活动以及土法冶炼的影响,砷主要分布在道路两旁或村民聚集地的农田耕层土壤0～20 cm,但在小巫岚村中也发现个别点位深层土壤砷含量高的现象.小巫岚村和高杖子村土壤砷的含量范围在7. 2～196. 2 mg·kg~(-1)之间,砷的超标率分别为45. 9%和82. 1%.根据RAC法评估,小巫岚村和高杖子村农田土壤主要处于低-中等风险,其中小巫岚村部分土壤点位已处于高风险.总体上,半壁山矿业活动周边含砷矿物毒砂部分已出现氧化现象且农田土壤砷的累积明显,可能会对当地的农作物以及长期居住在矿区周边的居民产生危害.建议对土壤-农作物-大气-人体系统开展砷的风险评估,并进一步对含砷矿物毒砂风化过程中的转换规律和机制进行研究,为耕地环境保护提供科学指导.     

饱和多孔介质中水流停滞对胶体吸附与解吸的影响

地下水水流停滞区域是胶体污染物吸附的重要场所.为研究水流停滞时间对胶体在饱和多孔介质中再迁移的影响,在石英砂柱与胶体达到稳定吸附后中断水流,分别设置水流停滞时间0、15、32、64、87、120 h,比较胶体的再迁移能力.结果表明:①水流停滞时间在32 h以内时,通入去离子水可使5.2%~5.3%的胶体被解吸出来再次随水流迁移,解吸量介于0.54~0.56 mg之间,对胶体再迁移能力的影响不明显;水流停滞时间为32~120 h时,水流停滞时间增加会导致胶体再迁移能力降低;水流停滞时间达到120 h,胶体主要楔在石英砂颗粒间,难以被解吸出来,此时仅有1.8%的胶体再次随水流迁移.②水流停滞时,以自上而下的流通方式吸附在土柱中的胶体受重力作用可能跨过能垒吸附在初级势阱中,使再迁移能力降低;然而在自下而上的流通方式下吸附在土柱中的胶体受重力影响难以跨过能垒吸附在初级势阱中,胶体再迁移能力较强.③当以≤ 30.2 m/d的流速通入背景液时,流速对胶体解吸的影响不如通入去离子水时显著.研究显示,水流停滞时间对吸附在饱和含水介质上胶体的再迁移能力有明显影响,重力作用在不同的流通方式下不同.      

新疆奎屯地区高砷地下水DOM三维荧光特征

新疆奎屯地区是中国大陆第一个地方性砷（As）中毒病区,为了解析该地区高As地下水中溶解性有机物（DOM）的组分和来源,探索其在As迁移转化过程中的作用,利用三维荧光光谱结合平行因子分析法对奎屯地区水样进行研究.结果表明：该地区地下水As含量范围在1.30~400.68μg/L,平均值为61.18μg/L,有68.99%的地下水为高As地下水.地下水中DOM含有3种组分：类腐殖质C1（260（325） nm/425nm）,占2.78%;类色氨酸C2（275nm/350nm）,占18.74%;微生物源的还原性醌类C3（260（375） nm/475nm）,占54.12%.研究区水体DOM的荧光指数在1.2~1.52之间,均值为1.36,水中DOM以陆源为主.该地区地下水整体呈现还原-弱碱性环境,地下水中As的释放过程主要有铁氧化物矿物还原和脱硫酸作用,水中的DOM参与了铁、硫酸盐的还原反应过程,类色氨酸C2主要在微生物呼吸过程中充当电子供体角色,还原性醌类C3担任了电子飞行过程中的电子穿梭体,增强了As从含水层沉积物中释放到地下水的迁移性能.     

新疆奎屯地区高砷地下水DOM三维荧光特征

新疆奎屯地区是中国大陆第一个地方性砷（As）中毒病区,为了解析该地区高As地下水中溶解性有机物（DOM）的组分和来源,探索其在As迁移转化过程中的作用,利用三维荧光光谱结合平行因子分析法对奎屯地区水样进行研究.结果表明：该地区地下水As含量范围在1.30~400.68μg/L,平均值为61.18μg/L,有68.99%的地下水为高As地下水.地下水中DOM含有3种组分：类腐殖质C1（260（325） nm/425nm）,占2.78%;类色氨酸C2（275nm/350nm）,占18.74%;微生物源的还原性醌类C3（260（375） nm/475nm）,占54.12%.研究区水体DOM的荧光指数在1.2~1.52之间,均值为1.36,水中DOM以陆源为主.该地区地下水整体呈现还原-弱碱性环境,地下水中As的释放过程主要有铁氧化物矿物还原和脱硫酸作用,水中的DOM参与了铁、硫酸盐的还原反应过程,类色氨酸C2主要在微生物呼吸过程中充当电子供体角色,还原性醌类C3担任了电子飞行过程中的电子穿梭体,增强了As从含水层沉积物中释放到地下水的迁移性能.     

Physico-chemical characterization and source tracking of black carbon at a suburban site in Beijing

Particles from ambient air and combustion sources including vehicle emission, coal combustion and biomass burning were collected and chemically pretreated with the purpose of obtaining isolated BC (black carbon) samples. TEM (transmission electron microscopy) results indicate that BC from combustion sources shows various patterns, and airborne BC appears spherical and about 50 nm in diameter with a homogeneous surface and turbostratic structure. The BET (Barrett–Emmett–Teller) results suggest that the surface areas of these BC particles fall in the range of 3–23 m²/g, with a total pore volume of 0.03–0.05 cm³/g and a mean pore diameter of 7–53 nm. The nitrogen adsorption–desorption isotherms are indicative of the accumulation mode and uniform pore size. O₂-TPO (temperature programmed oxidation) profiles suggest that the airborne BC oxidation could be classified as the oxidation of amorphous carbon, which falls in the range of 406–490°C with peaks at 418, 423 and 475°C, respectively. Generally, the BC characteristics and source analysis suggest that airborne BC most likely comes from diesel vehicle emission at this site.     

木质垃圾与废铁泥制备Fe0-BC材料及其对水中Cr(Ⅵ)的去除行为

含铬废水的直接排放会对自然环境造成严重危害.为探究零价铁-生物炭材料(Fe⁰-BC)与Cr(Ⅵ)的反应效能,以木质垃圾与印染行业废铁泥两种亟需处理的固体废物作为原料,在不同温度下通过碳热还原制备Fe⁰-BC,并将其应用于水中Cr(Ⅵ)的去除.材料表征结果表明,1 200℃下制备的Fe⁰-BC材料(Fe⁰-BC-1200)性能最佳,其比表面积为105.6 m³/g,孔径为6.23 nm,物相主要由Fe⁰、Cu0、C以及少量杂质构成,其中Fe⁰以球状的颗粒形式分散附着在碳的孔结构中,且大小均匀,粒度基本达到纳米级.通过静态试验考察了Fe⁰-BC材料对Cr(Ⅵ)的去除过程,发现Fe⁰-BC-1200对Cr(Ⅵ)的去除效果最好,在初始浓度为20 mg/L、初始pH为3.5、投加量为2.5 g/L的条件下,Cr(Ⅵ)的去除率达到95.2%. Cr(Ⅵ)的去除过程符合准二级反应动力学过程和Langmui...     

Unraveling the size distributions of surface properties for purple soil and yellow soil

Soils contain diverse colloidal particles whose properties are pertinent to ecological and human health, whereas few investigations systematically analyze the surface properties of these particles. The objective of this study was to elucidate the surface properties of particles within targeted size ranges (i.e. > 10, 1–10, 0.5–1, 0.2–0.5 and < 0.2 μm) for a purple soil (Entisol) and a yellow soil (Ultisol) using the combined determination method. The mineralogy of corresponding particle-size fractions was determined by X-ray diffraction. We found that up to 80% of the specific surface area and 85% of the surface charge of the entire soil came from colloidal-sized particles (< 1 μm), and almost half of the specific surface area and surface charge came from the smallest particles (< 0.2 μm). Vermiculite, illite, montmorillonite and mica dominated in the colloidal-sized particles, of which the smallest particles had the highest proportion of vermiculite and montmorillonite. For a given size fraction, the purple soil had a larger specific surface area, stronger electrostatic field, and higher surface charge than the yellow soil due to differences in mineralogy. Likewise, the differences in surface properties among the various particle-size fractions can also be ascribed to mineralogy. Our results indicated that soil surface properties were essentially determined by the colloidal-sized particles, and the < 0.2 μm nanoparticles made the largest contribution to soil properties. The composition of clay minerals within the diverse particle-size fractions could fully explain the size distributions of surface properties.     

反应气氛对绿色合成纳米铁的组分及其活性的影响

成本低廉和无二次污染的"绿色"合成纳米材料是发展原位纳米环境修复技术的前沿研究课题之一.本文以绿茶提取液为还原剂和稳定剂进行"绿色"合成纳米铁,探讨在不同的气氛下"绿色"合成的纳米铁颗粒的主要成分,以期为调控合成纳米铁系材料提供基础研究.首先,利用扫描电子显微镜(SEM)、X射线能谱(EDS)、X射线光电子能谱分析(XPS)和傅里叶变换红外光谱(FTIR)等表征手段对不同反应气氛下合成的纳米铁颗粒的表面微观形貌、尺寸和价态结构进行分析.结果发现,在通入N2情况下,合成的纳米铁颗粒粒径为(84.7±11.5)nm,其主要成分以纳米零价铁为主;在通入空气情况下,合成的纳米铁粒径为(117.8±26.2)nm,其主要成分是纳米零价铁、氧化铁和四氧化三铁的混合物;通入O2时,合成的纳米铁粒径为(141.2±26.3)nm,其主要成分以四氧化三铁为主.其次,评价在不同气氛条件下合成纳米铁颗粒对去除亚甲基蓝(MB)的反应活性.结果表明,在反应温度313 K下降解初始浓度为50 mg·L-1的MB溶液,反应5 min时已达到平衡,通入N2合成的纳米铁降解MB,去除率高达98.7%,而通入O2合成的纳米铁反应效率低,对MB的去除率仅为65.3%.最后,从以上发现提出不同气氛下可以调控"绿色"合成的铁系纳米材料成分,从而导致不同的纳米修复环境中污染物的能力.     

Fabrication of bimetallic Ag/Fe immobilized on modified biochar for removal of carbon tetrachloride

As an effective conventional absorbent, biochar exhibited limited adsorption ability toward small hydrophobic molecules. To enhance the adsorption capacity, a novel adsorbent was prepared by immobilizing nanoscale zero-valent iron onto modified biochar (MB) and then the elemental silver was attached to the surface of iron (Ag/Fe/MB). It''s noted that spherical Ag/Fe nanoparticles with diameter of 51 nm were highly dispersed on the surface of MB. As the typical hydrophobic contaminant, carbon tetrachloride was selected for examining the removal efficiency of the adsorbent. The removal efficiencies of carbon tetrachloride by original biochar (OB), Ag/Fe, Ag/Fe/OB and Ag/Fe/MB were fully investigated. It''s found that Ag/Fe/MB showed higher carbon tetrachloride removal efficiency, which is about 5.5 times higher than that of the OB sample due to utilizing the merits of high adsorption and reduction. Thermodynamic parameters revealed that the removal of carbon tetrachloride by Ag/Fe/MB was a spontaneous and exothermic process, which was affected by solution pH, initial carbon tetrachloride concentration and temperature. The novel Ag/Fe/MB composites provided a promising material for carbon tetrachloride removal from effluent.     

Influence of zeta potential on the flocculation of cyanobacteria cells using chitosan modified soil

Using chitosan modified soil to flocculate and sediment algal cells has been considered as a promising strategy to combat cyanobacteria blooms in natural waters. However, the flocculation efficiency often varies with algal cells with different zeta potential (ZP) attributed to different growth phases or water conditions. This article investigated the relationship between ZP of Microcystis aeruginosa and its influence to the flocculation efficiency using chitosan modified soil. Results suggested that the optimal removal efficiency was obtained when the ZP was between − 20.7 and − 6.7 mV with a removal efficiency of more than 80% in 30 min and large floc size of > 350 μm. When the algal cells were more negatively charged than − 20.7 mV, the effect of chitosan modified soil was depressed (< 60%) due to the insufficient charge density of chitosan to neutralize and destabilize the algal suspension. When the algal cells were less negative than − 6.7 mV or even positively charged, a small floc size (< 120 μm) was formed, which may be difficult to sink under natural water conditions. Therefore, manipulation of ZP provided a viable tool to improve the flocculation efficiency of chitosan modified soil and an important guidance for practical engineering of cyanobacteria bloom control.     

Zero-valent iron doped carbons readily developed from sewage sludge for lead removal from aqueous solution

Low-cost but high-efficiency composites of iron-containing porous carbons were prepared using sewage sludge and ferric salts as raw materials. Unlike previous time- and energy-consuming manufacturing procedures, this study shows that pyrolyzing a mixture of sludge and ferric salt can produce suitable composites for lead adsorption. The specific surface area, the total pore volume and the average pore width of the optimal composite were 321 m²/g, 0.25 cm³/g, and 3.17 nm, respectively. X-ray diffraction analysis indicated that ferric salt favored the formation of metallic iron, while Fourier transform infrared spectroscopy revealed the formation of hydroxyl and carboxylic groups. The result of batch tests indicated that the adsorption capacity of carbons activated with ferric salt could be as high as 128.9 mg/g, while that of carbons without activation was 79.1 mg/g. The new manufacturing procedure used in this study could save at least 19.5 kJ of energy per gram of activated carbon.