Constant Initial Concentration Research Articles

Phosphorus Removal from Wastewater Using Oven-Dried Alum Sludge

The present study deals with the removal of phosphorus from wastewater by using oven-dried alum sludge (ODS) as adsorbent that was collected from Al-Qadisiya treatment plant (Iraq); it was heated in an oven at 105∘C for 24 h and then cooled at room temperature. The sludge particles were then crushed to produce a particle size of 0.5–4.75 mm. Two modes of operation are used, batch mode and fixed bed mode, in batch experiment the effect of oven-dried alum sludge doses 10–50 g/L, pH of solution 5–8 with constant initial phosphorus concentration of 5 mg/L, and constant particle size of 0.5 mm were studied. The results showed that the percent removal of phosphorus increases with the increase of oven-dried alum sludge dose, but pH of solution has insignificant effect. Batch kinetics experiments showed that equilibrium time was about 6 days. Adsorption capacity was plotted against equilibrium concentration, and isotherm models (Freundlich, Langmuir, and Freundlich-Langmuir) were used to correlate these results. In the fixed bed isothermal adsorption column, the effect of initial phosphorus concentration (𝐶𝑜) 5 and 10 mg/L, particle size 2.36 and 4.75 mm, influent flow rate (Q) 6 and 10 L/hr, and bed depth (H) 0.15–0.415 m were studied. The results showed that the oven-dried alum sludge was effective in adsorbing phosphorus, and percent removal of phosphorus reaches 85% with increasing of contact time and adsorbent surface area (i.e., mass of adsorbent 50 g/L with different pH).

蛋白核小球藻对Pb(Ⅱ)和Cd(Ⅱ)的生物吸附及其影响因素

藻类吸附作用影响重金属在水生生态系统中的迁移过程及其环境行为。同时,利用藻类吸附能力是修复重金属污染水体和重金属废水处理的一项清洁、廉价和高效的技术。测定了蛋白核小球藻对Pb²⁺和Cd²⁺的吸附和脱附动力学,表明吸附是快速表面过程,吸附4 h后基本达到平衡,不易脱附。研究了蛋白核小球藻对Pb²⁺和Cd²⁺的吸附热力学,绘制了吸附等温线,并用Langmuir模型进行拟合,相关系数<em>R</em>²分别为0.9906和0.9827,计算得到最大吸附量分别为0.373 mmol Pb/g和0.249 mmol Cd/g。考察了pH值、离子强度和温度等环境因素对蛋白核小球藻吸附Pb²⁺和Cd²⁺的影响。结果表明,蛋白核小球藻对Pb²⁺和Cd²⁺的吸附量在pH值5.0-6.0之间达到最大值,并随着溶液离子强度的增加而降低,随着溶液温度的升高而增加。温度的影响还表明,蛋白核小球藻对Pb²⁺和Cd²⁺的吸附是吸热过程。实验还考察了水体环境中普遍存在的溶解性有机质主要成分-富里酸的影响,表明富里酸会抑制蛋白核小球藻对Pb²⁺和Cd²⁺的吸附,重金属离子浓度较低时的抑制效果更明显,最大抑制率分别达到了34.2%和34.9%。由于其对重金属的较高吸附量和吸附本身快速完成的特性,蛋白核小球藻有望成为较理想的生物吸附剂,在重金属污染水体的生物修复及废水处理中发挥重要作用。;The remains of aquatic algae are widespread and constitute an important organic fraction in natural freshwater environments. Accordingly, their adsorption of heavy metals may influence or determine the environmental processes and behavior of the metals. Conversely, they may be developed into low cost biosorbents for the removal of heavy metals from water, thus serving as green adsorbents for industrial heavy metal wastewater treatment and remediation of metal polluted natural water bodies. This study investigated the adsorption of two toxic heavy metals that are of great concern, Pb(Ⅱ) and Cd(Ⅱ), from water by the freshwater alga <em>Chlorella pyrenoidsa</em>. In addition, the factors that influence the adsorption were evaluated. To accomplish this, the alga was cultured for self-reproduction, after which the cells were collected and freeze-dried to obtain the biosorbent. Initial kinetic measurements showed that both Pb and Cd were rapidly adsorbed by the alga with equilibria acquired within 5 minutes to 4 hours, and that these metals resisted desorption. Accordingly, the adsorption of Pb and Cd was conducted using a range of solution concentrations by mixing for 4 hours while maintaining the pH at 5.0. After attaining equilibrium, both the solution phase and algal phase were analyzed for metal concentrations. The adsorption isotherms obtained for both Pb and Cd followed a Langmuir shape, with the adsorption initially increasing rapidly and then approaching saturation with further increasing metal concentration. The alga significantly adsorbed both metals, apparently in response to an abundance of acidic functional groups such as -COOH and -OH on the algal cell walls that formed complexes with the metal ions. While both metals are divalent, Pb was comparatively more effectively adsorbed than Cd. This may have resulted from the difference in the metal radius caused by Pb being less hydrated and thus more strongly bound to the adsorption sites of the alga. By fitting adsorption data to the Langmuir equation, the obtained maximal adsorptions were 0.373 and 0.249 mmol/g for Pb and Cd, respectively. When 400 mg/L of dissolved fulvic acid was present in solution, the adsorption of both metals by the alga was inhibited by up to 34%. This was clearly caused by the competitive binding of metals with fulvic acid. The overall smaller inhibition by fulvic acid that was observed at higher metal concentrations likely resulted from the full occupation of fulvic acid binding sites by the metal ions. The effects of pH, ionic strength and temperature on the adsorption were determined by using a constant initial metal concentration while varying these factors. The adsorption of both metals increased as the pH increased from 2.0 to 5.0, reached the maximum value at pH 5.0-6.0, and then decreased as the pH increased further. This was due to the progressively increased dissociation of acidic functional groups of the alga with increasing pH in acidic solutions that facilitated the metal complexation but reduced the availability of metal ions via binding with increased -OH in neutral to weakly basic solutions. As the concentration of NaNO₃ (ionic strength) increased to 0.15 mol/L, the adsorption of both metals decreased by up to 15% due to increasingly compressed double electric layers leading to charge neutralization and enhanced aggregation of algal particles. By increasing the temperature from 277 K to 323 K, the adsorption of both Pb and Cd by the alga increased, with the extent of the increase for the former metal being much higher than that for the latter. This enhancement of adsorption with temperature may have resulted from the surfacing of existing adsorption sites that were initially concealed and/or the creation of new adsorption sites by elevated temperature. The enhancement also indicated that the adsorption was endothermic. According to the Clausius\\Clapeyron equation, the heat of adsorption was calculated to be in the range of 12194-21706 J/mol and 3398-9520 J/molfor Pb and Cd, respectively. In view of its high self-reproduction and thus wide availability, the alga <em>Chlorella pyrenoidsa</em> characterized by strong adsorption of heavy metals as well as resistance to desorption may be applied as an effective biosorbent for the remediation of metal-polluted natural water bodies and the treatment of metal-containing waters under proper manipulation of water pH and temperature.

Hydrogen gas production from cheese whey powder (CWP) solution by thermophilic dark fermentation

Hydrogen gas production from cheese whey powder (CWP) solution by thermophilic dark fermentation was investigated at 55 °C. Experiments were performed at different initial total sugar concentrations varying between 5.2 and 28.5 g L −1 with a constant initial bacteria concentration of 1 g L −1. The highest cumulative hydrogen evolution (257 mL) was obtained with 20 g L −1 total sugar (substrate) concentration within 360 h while the highest H 2 formation rate (2.55 mL h −1) and yield (1.03 mol H 2 mol −1 glucose) were obtained at 5.2 and 9.5 g L −1 substrate concentrations, respectively. The specific H 2 production rate (SHPR = 4.5 mL h −1 g −1cells) reached the highest level at 20 g L −1 total sugar concentration. Total volatile fatty acid (TVFA) concentration increased with increasing initial total sugar content and reached the highest level (14.15 g L −1) at 28.5 g L −1 initial substrate concentration. The experimental data was correlated with the Gompertz equation and the constants were determined. The optimum initial total sugar concentration was 20 g L −1 above which substrate and product (VFA) inhibitions were observed.

Physical Properties and Extraction Measurements for the Athabasca Bitumen + Light Hydrocarbon System: Evaluation of the Pressure Effect, Solvent-to-Bitumen Ratio, and Solvent Type

Phase behavior study and solvent-saturated phase properties are of crucial importance for heavy oil in situ recovery methods as well as pipeline transportation, surface upgrading, and refining. In this study, the extraction of light components and liquid–liquid equilibrium (LLE) for Athabasca bitumen/ethane systems were studied at ambient temperature over a wide range of pressure. The impact of the ethane-to-bitumen ratio on the physical properties of the saturated phases as well as the partitioning of solvent in each liquid phase was evaluated. The experiments were conducted using a designed pressure–volume–temperature (PVT) apparatus to obtain LLE properties as well as the extraction yield for bitumen/solvent systems. The experimental results indicated the extraction yield increased with increasing initial solvent concentration at all operating conditions. Comparatively, higher bitumen fractions were extracted at higher pressures, considering a constant initial solvent concentration. Increasing either t...

One-Pot Synthesis of Poly(methacrylic acid-co-poly(ethylene oxide) methyl ether methacrylate)-b-polystyrene Amphiphilic Block Copolymers and Their Self-Assemblies in Water via RAFT-Mediated Radical Emulsion Polymerization. A Kinetic Study

The RAFT-mediated emulsion polymerization of styrene was carried out in a one-pot, two-step procedure using two poly(methacrylic acid-co-poly(ethylene oxide) methyl ether methacrylate) macroRAFT agents of different compositions carrying a reactive trithiocarbonate end-group. The latter were prepared in situ, directly in aqueous solution at acid pH. In all cases, the synthesis was fast and efficient, leading to very high conversions and very good control over the polymer features. It was moreover particularly reproducible, which is an important outcome for the robustness of the method. Then, styrene was added and directly polymerized in the formed emulsion system until very high conversion in short reaction time. The method led to amphiphilic block copolymers, self-assembled into stable spherical particles. The diameter of the latter was directly governed by the initial concentration of macroRAFT agent, which also controlled the molar mass of the polystyrene block at constant styrene initial concentration....

Concordant 210Pb and 137Cs ages of black sea anoxic unconsolidated sediments

Two independent geochronologic radiometric methods: 137Cs and 210Pb were used to determine the sedimentation rate and subsequently to date the oldest sediments of a 50 cm core containing unconsolidated sediments collected at a depth of 600 m below sea surface in the anoxic zone of the Western Black Sea, off the Romanian town of Constanta. Both methods gave coincident value within experimental uncertainties of 0.42±0.20 mm·y−1 for 137Cs and 0.49±0.03 mm·y−1 in the case of 210Pb, within the Constant Initial Concentration model, which gave for the lower most sediments an age of 1.00±0.01 ka. The constant sedimentation model as well as the possible causes of observed discrepancy between experimental uncertainties are discussed.

210Pb-dating of a lake sediment core from Lough Carra (Co. Mayo, western Ireland): use of paleolimnological data for chronology validation below the 210Pb dating horizon

The chronologies and sediment accumulation rates for a lake sediment sequence from Lough Carra (Co. Mayo, western Ireland) were established by applying the constant initial concentration (CIC) and constant rate of supply (CRS) hypotheses to the measured 210Pb excess profile. The resulting chronologies were validated using the artificial fallout radionuclides 137Cs and 241Am, which provide independent chronostratigraphic markers for the second half of the 20th century. The validity of extrapolating the derived CIC and CRS dates below the 210Pb dating horizon using average sedimentation rates was investigated using supplementary paleolimnological information and historical data. Our data confirm that such an extrapolation is well justified at sites characterised by relatively stable sedimentation conditions.

Pyrene and Phenanthrene Sorption to Model and Natural Geosorbents in Single- and Binary-Solute Systems

Sorption of pyrene and phenanthrene to model (illite and charcoal) and natural (Yangtze sediment) geosorbents were investigated by batch techniques using fluorescence spectroscopy. A higher adsorption of phenanthrene was observed with all sorbents, which is related to the better accessibility of smaller molecules to micropores in the molecular sieve sorbents. In addition, pyrene sorption in binary-solute systems with a constant initial concentration of phenanthrene (0.1 μmol L(-1) or 2 μmol L(-1)) was studied. A 0.1 μmol L(-1) concentration of phenanthrene causes no competitive effect on the pyrene sorption. A 2 μmol L(-1) concentration of phenanthrene significantly suppresses the sorption of pyrene, especially in the low concentration range; nonlinearity of the pyrene sorption isotherms thus decreases. The competitive effect of 2 μmol L(-1) phenanthrene on the pyrene sorption is overestimated by the ideal adsorbed solution theory (IAST) using the fitted single sorption results of both solutes. An adjustment of the IAST application by taking into account the molecular sieve effect is proposed, which notably improves the IAST prediction for the competitive effect.

REMOVAL OF COPPER IONS FROM WASTE WATER BY ADSORPTION WITH MODIFIED AND UNMODIFIED SUNFLOWER STALKS

Unmodified and modified sunflower stalks were examined for adsorption as a replacement of expensive activated carbon which has been recognized as a highly effective adsorbent for the removal of heavy metal-ion.Two modes of operation were used, batch mode and fixed bed mode. In batch experiment the effect of sunflower stalk doses (2,3,4,5 and 6g/L) with constant initial copper concentration of 100 mg/L and constant particle size less than1.18 mm was studied.Batch kinetics experiments showed that the adsorption rate of copper ion by sunflower stalks was rapid and reached equilibrium within 60 min. Adsorption models Freundlich, Langmuir and Freundlich-Langmuir were fitted to experimental data and the goodness of their fit for adsorption was compared. In the fixed bed isothermal adsorption column, the effect of particle size (1.18-2.36, 2.36-4.75 and 4.75-9.00) mm, influent flow rate (2,4and 6) L/hr, bed depth (25, 30 and 35) cm and initial metal concentration (100 and 150) mg/L was studied. In addition, the modification of sunflower stalks could enhance their natural capacity. Sunflower stalks were modified by activation with nitric acid. The results of this study show that sunflower stalk, both modified and unmodified, is an efficient adsorbent for the removal of copper from waste water. Percent removal of copper reaches 100% when particle size (2.36-4.75)mm ,bed depth 35 cm and influent flow rate 4 L/hr.

Sedimentation rates in Atibaia River basin, São Paulo State, Brazil, using 210Pb as geochronometer

The constant initial concentration (CIC) of unsupported/excess (210)Pb model was successfully used to assess (210)Pb data of nine sediment cores from Atibaia River basin, São Paulo State, Brazil. The (210)Pb-based apparent sediment mass accumulation rates ranged from 47.7 to 782.4 mg/cm(2)yr, whereas the average linear sedimentation rates between 0.16 and 1.32 cm/yr, which are compatible with the calculated sediment mass fluxes, i.e. a higher sediment mass accumulation rate yielded a higher linear sedimentation rate. The higher long-term based accumulation rate tended to be found in topographically softer regions. This occurs because the sediments are preferentially transported in topographically steeper regions instead of being deposited. Anthropic activities like deforestation possibly interfered with the natural/normal sedimentation processes, which increased in accordance with modifications on the channel drainage. The radionuclide geochronology as described in this paper allows determination of sedimentation rates that are compatible with values estimated elsewhere. The adoption of an appropriate factor generated from previous laboratory experiments resulted in a successful correction for the (222)Rn-loss from the sediments, bringing the estimate of the parent-supported (in-situ produced) (210)Pb to reliable values required by the CIC model.

Poly(N-isopropylacrylamide) Microgels at the Oil−Water Interface: Interfacial Properties as a Function of Temperature

Highly monodisperse poly(N-isopropylacrylamide), PNiPAM, microgels were prepared by the conventional radical polymerization of NiPAM in the presence of dimethylamino ethyl methacrylate (DMAEMA) monomers at various concentrations. The effect of DMAEMA on the polymerization of PNiPAM microgels was examined at constant initiator (V50) and cross-linker (MBA) concentrations. The presence of DMAEMA in the synthesis batch allows for the preparation of PNiPAM microgels with controlled size and a narrow size distribution. The oil(dodecane)/water interfacial properties of the model PNiPAM microgels were then investigated. The pendant drop technique was used to measure the interfacial tensions as a function of temperature. Over the whole range of temperature (20-45 degrees C), the interfacial tension remains low (on the order of 17 mN/m) and goes through a minimum (12 mN/m) at a temperature of about 34 degrees C, which well matches the volume phase transition temperature (VPTT) of PNiPAM microgels. Below the VPTT, the decrease in the interfacial tension with temperature is likely to be due to the adsorption of dense layers because of the decrease of the excluded volume interactions. Above the VPTT, we suggest that the increase in the interfacial tension with temperature comes from the adsorption of loosely packed PNiPAM microgels. We also studied the effect of temperature on the stability of emulsions. Dodecane in water emulsions, which form at ambient temperature, are destabilized as the temperature exceeds the VPTT. In light of the interfacial tension results, we suggest that emulsion destabilization arises from the adsorption of aggregates above the VPTT and not from an important desorption of microgels. Aggregate adsorption would bring a sufficiently high number of dodecane molecules into contact with water to induce coalescence without changing the interfacial tension very much.

Dynamic studies of nitrophenols adsorption on perfil in a fixed-bed column: application of single and two resistance model

The mechanism of 4-nitrophenol (4-NP) and 2,4-dinitrophenol (2,4-DNP) adsorption on perfil-natural mineral taken from Bulgarian deposits, in a fixed-bed column was investigated. The single component experiments were conducted at constant initial sorbate concentration, volumetric flow rate, temperature and pH. The effect of adsorbent bed depth (Z 1, 2, 3, 6 cm) and sorbate nature on the adsorption capacity, mass transfer parameters and mechanisms was studied. The equilibrium behaviour of the system 4-NP-perfil was described by Langmuir, Freundlich and Redlich-Peterson models. The single resistance Thomas model, including Reynolds-Richards and Walter solutions, and the two-resistance Arnold model were applied for mathematical modeling of the experimental data. The comparative analyses indicated that external mass transfer was the rate limiting mechanism during the initial adsorption stages, while intraparticle diffusion was dominant in the middle and high concentration ranges. The effect of axial dispersion on the dynamics of adsorption was evaluated.

REMOVAL OF DYES FROM TEXTILE EFFLUENT BY ADSORPTION ONTO OVEN DRIED ALUM SLUDGE

The present study deals with the removal of dyes from the effluent of the state company for cotton textile industries located at Al-Khadmya by using oven dried alum sludge (ODS) as adsorbent. Two different dyes; Direct black and solar brown are studied. Alum sludge was collected from Al-Qadisiya water treatment plant; it was heated in an oven at 105°C for 24 hours, then cooled at room temperature and crushed to produce particle sizes of 1.18-2.36 and 4-4.75 mm. Batch and fixed bed mode were used. In batch experiments the effect of oven dried alum sludge weight on adsorption process and equilibrium isotherm were studied by using 15-125 g/l of oven dried alum sludge for direct black and 15-175 g/l for solar brown, with constant initial dyes concentration of 10 mg/l and constant particle size of 4-4.75 mm. Batch kinetics experiments showed that equilibrium time was about 12-14 days. The three models Freundlich, Langmuir and Freundlich-Langmuir gave good fitting for the adsorption capacity. In the fixed bed isothermal adsorption column, the effect of initial dye concentration (Co), particle size, influent flow rate (Q) and bed depth (H) were studied. The results showed that the oven dried alum sludge was effective in adsorbing dyes with removal efficiency ranged between 90% to 92%.

Distribution of radionuclides in the guano sediments of Xisha Islands, South China Sea and its implication

Several natural and anthropogenic radionuclides ( 210Pb, 226Ra and 137Cs) in guano-phosphatic coral sediments and pure guano particles collected from Ganquan, Guangjin, Jinqing and Jinyin Islands of the Xisha archipelago, South China Sea, were analyzed. The Constant Initial Concentration (CIC) model and the Constant Rate of Supply (CRS) model were applied for age calculation. The average supply rate of 210Pb was 126 Bq m −2 a −1, very close to the flux of northern hemisphere average (125 Bq m −2 a −1). The activities of anthropogenic radionuclides in the sediments were very low, indicating that human nuclear tests did not notably impact this region. The main source of radionuclides in the sediments was from atmospheric precipitation, and the organic matter derived from plant and produced by nutrient-rich guano could further enhance them.

Detecting Operational Inactivation of Horseradish Peroxidase using an Isoconversional Method

AbstractKinetic parameters of operational inactivation of horseradish peroxidase during the enzymatic oxidation of 2‐aminophenol with hydrogen peroxide were estimated using an isoconversional method. This method only requires the progress kinetic curves obtained at constant initial concentrations of the substrates. In order to investigate the possible pathways of low‐reactive species compound III formation, a kinetic model was proposed and several rate constants were calculated using an optimization computing program. Generation of an oxygen reactive species in the reaction system was also considered in the reaction scheme. Sensitivity analysis, corroborated with the overall inactivation kinetics observed with the isoconversional method, allows the conclusion that the inactivation of the enzyme occurs mainly via the reaction of compound II with hydrogen peroxide.

The use of the 210Pb method for preliminary evaluating the sedimentation rate in Amazon river mouth

The use of the 210Pb method for preliminary evaluating the sedimentation rate in Amazon river mouth This investigation reports the preliminary results for determining the sedimentation rate at the Amazonas River mouth, Brazil, by the 210Pb method. The CIC (constant initial concentration) of unsupported/excess 210Pb model was successfully applied to one sediments core. The measurements were made in a sediments core comprising ten samples 10 cm - thick each. The year of the sampling (2006) was used as reference for the establishment of the rate of sedimentation from the beginning of the top of the testimony. However, the atmospheric conditions and climate in Amapá State, Brazil, claimed for optimization of the results. Because the Channel North is opened into the Atlantic Ocean, it exhibits a huge water volume, causing a permanent motion of sediments and water. So, heavy waves are formed at the water surface, stirring the upper sand strata. Only at a depth of 40-50 cm the profile tends to be more homogeneous, where it is mostly composed by fine sand and very fine sand. Thus, it is reasonable utilize the CIC model from 210Pb data, which allows estimate a sedimentation rate corresponding to 0.61 g/cm2yr and a mean linear rate of 0.8 cm/yr. The 238U and 210Pb activities in the sediments allowed the reconstruction of the sedimentation processes over a period of about 130 years.

Physical State Study of (Sugar Mixture)-Polymer Model Systems

The physical state of components in the unfrozen solute phase of frozen solutions was determined by using differential scanning calorimetry (DSC) for mixtures of lactose, sucrose, and trehalose with albumin, gelatine, or cornstarch. An equal weight ratio (1:1) of lactose-sucrose, lactose-trehalose and sucrose-trehalose mixtures with polymer systems (sugar mixture-albumen (1:1:1), gelatine (1:1:1), and cornstarch (1:1:1), as well as cornstarch-gelatine (1:1:1:1) was used. Mixed sugar mixture (lactose/sucrose)-polymer systems were further studied for maximum freeze-concentration in complex systems. A comparative thermal study between sugar-polymer and mixed sugar-polymer systems was conducted. The sugar-polymer and mixed sugar-polymer systems showed similarities and differences in thermal behaviour. The similarities included maximum freeze-concentration of a frozen system at an annealing temperature (Tm´-1) °C, constant initial concentration independent onset of glass transition Tg´, and onset of ice melting temperature Tm´, and increased in temperature difference between Tg´ and Tm´ or increase in broadness of transition with the addition of polymeric compound.

Modelling of batch kefir fermentation kinetics for ethanol production by mixed natural microflora

Non-structured kinetic models are proposed for the mathematical description of principal kinetics involved in ethanol production during kefir fermentation in a batch reactor system. Experimental data collected from a series of batch fermentations, which were performed at constant temperature ( ϑ = 21 °C) and initial kefir grains mass concentration ( γ KG,0 = 42 g L −1) over different fermentation periods in the interval from (0–89) h, were used to estimate parameters and also to validate the proposed models. The optimal values of the kinetic parameters were approximated by minimizing the discrepancy between the model predictions and corresponding experimental data. The growth of kefir grains could be expressed by a logistic function model, which describes the growth as a function of initial kefir grains concentration, time, specific growth rate, and final kefir grains concentration. The modified Gompertz model, which gives the lag time, the specific production rate and the maximum ethanol mass concentration, was able to describe the formation of ethanol as the fermentation proceeded. In both cases, the model simulation matches well with the experimental observations, which made it possible to elucidate the fermentation characteristics of kefir grains during efficient ethanol production. These models thus can be employed for the development and optimization of bio-based ethanol production processes.

Effect Factors on the Degradation of MTBE with Fenton Reagent

The fundamentals of the Fenton reagent-based degradation methyl tert-butyl ether (MTBE) in batch reactors under initially anaerobic conditions are discussed in this work, and the objective of the study was to elucidate the effect of the FR to MTBE molar ratio, pH, initial MTBE concentration, H 2 O 2 concentration and inorganic anions on MTBE decomposition. The results show that the added amount of FR proved to be an important controlling parameter of the overall MTBE degradation efficiency. Under the conditions investigated in the present study at pH 3.0 and equimolar ratio of Fe 2 + to H 2 O 2 , FR to MTBE molar ratio of 6:1 was the minimum required to achieve complete MTBE degradation. The MTBE decay curves at four different initial MTBE concentrations with a constant initial FR concentration, the decomposition ratio arrived by 90.8%, 82.3%, 71.6% and 41.8%, while the initial MTBE concentration at 10.0, 20.0, 40.0 and 60 mg/L, respectively. The amount of hydrogen peroxide has a positive influence on the degradation rate, at low peroxide levels, increasing the amount of hydrogen peroxide results in the generation of more hydroxyl radicals, and thereby enhances the decay rate of MTBE. Moreover, the Fenton reaction is extremely sensitive to the inorganic anions present in the solution. In the case of the PO 4 3 − ions, oxidation is clearly inhibited, but the addition of SO 4 2 − influences the reaction to a much smaller extent, the anions suppress the decomposition of MTBE in the following sequence: PO 4 3 − >HPO 4 2 − >H 2 PO 4 − >Cl − >SO 4 2 − .

Age modeling of young non-varved lake sediments: methods and limits. Examples from two lakes in Central Chile

High-resolution and highly precise age models for recent lake sediments (last 100–150 years) are essential for quantitative paleoclimate research. These are particularly important for sedimentological and geochemical proxies, where transfer functions cannot be established and calibration must be based upon the relation of sedimentary records to instrumental data. High-precision dating for the calibration period is most critical as it determines directly the quality of the calibration statistics. Here, as an example, we compare radionuclide age models obtained on two high-elevation glacial lakes in the Central Chilean Andes (Laguna Negra: 33°38′S/70°08′W, 2,680 m a.s.l. and Laguna El Ocho: 34°02′S/70°19′W, 3,250 m a.s.l.). We show the different numerical models that produce accurate age-depth chronologies based on 210Pb profiles, and we explain how to obtain reduced age-error bars at the bottom part of the profiles, i.e., typically around the end of the 19th century. In order to constrain the age models, we propose a method with five steps: (i) sampling at irregularly-spaced intervals for 226Ra, 210Pb and 137Cs depending on the stratigraphy and microfacies, (ii) a systematic comparison of numerical models for the calculation of 210Pb-based age models: constant flux constant sedimentation (CFCS), constant initial concentration (CIC), constant rate of supply (CRS) and sediment isotope tomography (SIT), (iii) numerical constraining of the CRS and SIT models with the 137Cs chronomarker of AD 1964 and, (iv) step-wise cross-validation with independent diagnostic environmental stratigraphic markers of known age (e.g., volcanic ash layer, historical flood and earthquakes). In both examples, we also use airborne pollutants such as spheroidal carbonaceous particles (reflecting the history of fossil fuel emissions), excess atmospheric Cu deposition (reflecting the production history of a large local Cu mine), and turbidites related to historical earthquakes. Our results show that the SIT model constrained with the 137Cs AD 1964 peak performs best over the entire chronological profile (last 100–150 years) and yields the smallest standard deviations for the sediment ages. Such precision is critical for the calibration statistics, and ultimately, for the quality of the quantitative paleoclimate reconstruction. The systematic comparison of CRS and SIT models also helps to validate the robustness of the chronologies in different sections of the profile. Although surprisingly poorly known and under-explored in paleolimnological research, the SIT model has a great potential in paleoclimatological reconstructions based on lake sediments.