Release of Chromium from Soils with Persulfate Chemical Oxidation

An important part of the evaluation of the effectiveness of persulfate in situ chemical oxidation (ISCO) for treating organic contaminants is to identify and understand its potential impact on metal co‐contaminants in the subsurface. Chromium is a redox‐sensitive and toxic metal the release of which poses considerable risk to human health. The objective of this study was to investigate the impact of persulfate chemical oxidation on the release of chromium from three soils varying in physical‐chemical properties. Soils were treated with unactivated and activated persulfate [activated with Fe(II), Fe(II)‐EDTA, and alkaline pH] at two different concentrations (i.e., 41 mM and 2.1 mM persulfate) for 48 h and 6 months and were analyzed for release of chromium. Results show that release of chromium with persulfate chemical oxidation depends on the soil type and the activation method. Sandy soil with low oxidant demand released more chromium compared to soils with high oxidant demand. More chromium was released with alkaline pH activation. Alkaline pH and high Eh conditions favor oxidation of Cr(III) to Cr(VI), which is the main mechanism of release of chromium with persulfate chemical oxidation. Unactivated and Fe(II)‐activated persulfate decreased pH and at low pH in absence of EDTA chromium release is not a concern. These results indicate that chromium release can be anticipated based on the given site and treatment conditions, and ISCO system can be designed to minimize potential chromium release when treating soils and groundwater contaminated with both organic and metal contaminants.     

Microbial Dynamics During and After In Situ Chemical Oxidation of Chlorinated Solvents

In situ chemical oxidation (ISCO) followed by a bioremediation step is increasingly being considered as an effective biphasic technology. Information on the impact of chemical oxidants on organohalide respiring bacteria (OHRB), however, is largely lacking. Therefore, we used quantitative PCR (qPCR) to monitor the abundance of OHRB (Dehalococcoides mccartyi, Dehalobacter, Geobacter, and Desulfitobacterium) and reductive dehalogenase genes (rdh; tceA, vcrA, and bvcA) at a field location contaminated with chlorinated solvents prior to and following treatment with sodium persulfate. Natural attenuation of the contaminants tetrachloroethene (PCE) and trichloroethene (TCE) observed prior to ISCO was confirmed by the distribution of OHRB and rdh genes. In wells impacted by persulfate treatment, a 1 to 3 order of magnitude reduction in the abundances of OHRB and complete absence of rdh genes was observed 21 days after ISCO. Groundwater acidification (pH<3) and increase in the oxidation reduction potential (>500 mV) due to persulfate treatment were significant and contributed to disruption of the microbial community. In wells only mildly impacted by persulfate, a slight stimulation of the microbial community was observed, with more than 1 order of magnitude increase in the abundance of Geobacter and Desulfitobacterium 36 days after ISCO. After six months, regeneration of the OHRB community occurred, however, neither D. mccartyi nor any rdh genes were observed, indicating extended disruption of biological natural attenuation (NA) capacity following persulfate treatment. For full restoration of biological NA activity, additional time may prove sufficient; otherwise addition electron donor amendment or bioaugmentation may be required.     

Kinetics of Methyldiethanolamine Mineralization by Using UV/H2O2 Process

The UV/H₂O₂ is one of the popular techniques in the advanced oxidation processes (AOPs) and has been applied in the wastewater treatment during recent two decades. UV exposure on the H₂O₂ generate highly reactive hydroxyl radicals (OH^?), which are used to degrade organic contaminants through oxidation processes in wastewater. This present study involves the estimation of hydroxyl radical rate constants of methyldiethanolamine (MDEA) mineralization at different temperatures by using UV/H₂O₂ in aqueous solution. Laboratory experiments have been conducted and the profile of MDEA mineralization has been established. The hydroxyl radical rate constants and the activation energy of mineralization process have been calculated. The estimated hydroxyl rate constants and the activation energy are in good agreement with those reported in the literature.     

Evaluation of Extensive Secondary Maximum Contaminant Level Exceedances Following Remediation by In Situ Chemical Oxidation

In situ chemical oxidation (ISCO) with activated persulfate is commonly used for the remediation of petroleum impacted soil and groundwater because of its proven efficiency and the perception that reaction end products are completely innocuous. While the reaction products are less hazardous compared to the contaminants being treated, they may inadvertently prolong site closure in areas that have adopted the U.S. Environmental Protection Agency (EPA) Secondary Maximum Contaminant Levels (SMCLs) as enforceable standards. This study examines the occurrence and persistence of iron, manganese, sulfate, sodium, and total dissolved solids (TDS) in groundwater following persulfate ISCO. The concentrations of these chemicals were observed remaining above their respective regulatory criteria almost 3 years following the chemical application. Background concentrations and mobilization due to the petroleum contamination and ISCO application are also evaluated. Baseline sampling revealed substantially higher iron and manganese concentrations inside the plume area compared to the upgradient and downgradient wells suggesting mobilization due to redox reactions occurring inside of the plume. Iron was not a component in the applied chemical formula, yet the iron concentration spiked by 366% in the key monitoring well during the first post-remediation monitoring event. Ionic interactions between the ISCO amendment and native soils are believed to be responsible for displacing significant quantities of iron from the soil. Sulfate, sodium, and TDS exceedances are primarily associated with decomposition products of the ISCO amendments. The iron, manganese, sulfate, sodium, and TDS concentrations are trending downward over time, but still exceed regulatory criteria or pre-ISCO concentrations.     

ISCO for Groundwater Remediation: Analysis of Field Applications and Performance

A critical analysis of in situ chemical oxidation (ISCO) projects was performed to characterize situations in which ISCO is being implemented, how design and operating parameters are typically employed, and to determine the performance results being achieved. This research involved design of a database, acquisition and review of ISCO project information, population of the database, and analyses of the database using statistical methods. Based on 242 ISCO projects included in the database, ISCO has been used to treat a variety of contaminants; however, chlorinated solvents are by far the most common. ISCO has been implemented at sites with varied subsurface conditions with vertical injection wells and direct push probes being the most common delivery methods. ISCO has met and maintained concentrations below maximum contaminant levels (MCLs), although not at any sites where dense nonaqueous phase liquids (DNAPL) were presumed to be present. Alternative cleanup levels and mass reduction goals have also been attempted, and these less stringent goals are met with greater frequency than MCLs. The use of pilot testing is beneficial in heterogeneous geologic media, but not so in homogeneous media. ISCO projects cost $220,000 on average, and cost on average $94/yd³ of target treatment zone. ISCO costs vary widely based on the size of the treatment zone, the presence of DNAPL, and the oxidant delivery method. No case studies were encountered in which ISCO resulted in permanent reductions to microbial populations or sustained increases in metal concentrations in groundwater at the ISCO-treated site.     

Concentration rebound following in situ chemical oxidation in fractured clay

A two-dimensional, transient-flow, and transport numerical model was developed to simulate in situ chemical oxidation (ISCO) of trichloroethylene and tetrachloroethylene by potassium permanganate in fractured clay. This computer model incorporates dense, nonaqueous phase liquid dissolution, reactive aquifer material, multispecies matrix diffusion, and kinetic formulations for the oxidation reactions. A sensitivity analysis for two types of parameters, hydrogeological and engineering, including matrix porosity, matrix organic carbon, fracture aperture, potassium permanganate dosage, and hydraulic gradient, was conducted. Remediation metrics investigated were the relative rebound concentrations arising from back diffusion and percent mass destroyed. No well-defined correlation was found between the magnitude of rebound concentrations during postremedy monitoring and the amount of contaminant mass destroyed during the application. Results indicate that all investigated parameters affect ISCO remediation in some form. Results indicate that when advective transport through the fracture is dominant relative to diffusive transport into the clay matrix (large System Peclet Number), permanganate is more likely to be flushed out of the system and treatment is not optimal. If the System Peclet Number is too small, indicating that diffusion into the matrix is dominant relative to advection through the fracture, permanganate does not traverse the entire fracture, leading to postremediation concentration rebound. Optimal application of ISCO requires balancing advective transport through the fracture with diffusive transport into the clay matrix.     

Use of Chrysotile Fibres in the Degradation of Cationic and Nonionic Surfactants in Aqueous Solutions

It was previously observed that sodium dodecylbenzenesulfonate (SDBS) is degraded in the presence of chrysotile fibres. A higher catalytic efficiency was obtained than the reported values for TiO₂ under the same conditions. Chrysotile, a clay mineral fibre of low cost and relatively abundant, probably acts as a catalyst through an Advanced Oxidative Process (AOP) involving free radical formation. In this work, experiments with non‐ionic – Triton X‐45 (octil‐phenoxy polyethoxy ethanol) – and cationic – Herquat 3500 (alkyl dimethyl benzyl ammonium chloride) – surfactants were carried out. Diluted aqueous solutions (50 ppm) of these surfactants were kept in contact with chrysotile (4.0 g) in the dark at room temperature. The aromatic ring disappearance was followed through the absorbance peaks at 224 nm (Triton X‐45) and 208 nm (Herquat 3500) in the UV spectra. After 4 h, reductions in the surfactant solution concentration of 65.0% and 35.0% were observed for the Triton X‐45 and the Herquat 3500 surfactants, respectively. In both cases, reactions carried out without aeration showed a lower reduction of the aromatic ring concentration (30.0% less) when compared to the values obtained for the systems with airflow. The system containing the non‐ionic surfactant seems to achieve equilibrium after 2 h, what is not observed for the cationic surfactant system.     

Effects of In Situ Remediation Using Oxidants or Surfactants on Subsurface Organic Matter and Sorption of Trichloroethene

In situ remediation technologies have the potential to alter subsurface properties such as natural organic matter (NOM) content or character, which could affect the organic carbon‐water partitioning behavior of chlorinated organic solvents, including dense nonaqueous phase liquids (DNAPLs). Laboratory experiments were completed to determine the nature and extent of changes in the partitioning behavior of trichloroethene (TCE) caused by in situ chemical oxidation or in situ surfactant flushing. Sandy porous media were obtained from the subsurface at a site in Orlando, Florida. Experiments were run using soil slurries in zero‐headspace reactors (ZHRs) following a factorial design to study the effects of porous media properties (sand vs. loamy sand with different total organic carbon [TOC] contents), TCE concentration (DNAPL presence or absence), and remediation agent type (potassium permanganate vs. activated sodium persulfate, Dowfax 8390 vs. Tween 80). Results revealed that the fraction of organic carbon (f_oc) of porous media after treatment by oxidants or surfactants was higher or lower relative to that in the untreated media controls. Isotherm experiments were run using the treated and control media to measure the distribution coefficient (K_d) of TCE. Organic carbon‐water partitioning coefficient values (K_oc) calculated from the experimental data revealed that K_oc values for TCE in the porous media were altered via treatment using oxidants and surfactants. This alteration can affect the validity of estimates of contaminant mass remaining after remediation. Thus, potential changes in partitioning behavior should be considered to help avoid decision errors when judging the effectiveness of an in situ remediation technology.     

Optimal Field Approaches for Electrokinetic In Situ Oxidation Remediation

Numerical simulations were used to identify and evaluate optimum electrode configurations and approaches for electrokinetic in situ chemical oxidation (EK‐ISCO) remediation of low‐permeability sediments. A newly developed groundwater and EK flow and reactive transport numerical model was used to conduct two‐dimensional scenario simulations of the coverage of an injected oxidant, permanganate, and the oxidation of a typical organic contaminant (tetrachloroethene, PCE). For linear configurations of vertical electrodes, the spacing of same‐polarity electrodes is recommended to be about one‐third to one‐quarter of the anode–cathode spacing. Greater coverage could also be achieved by locating additional oxidant injection wells at the divergence of the electric field in linear electrode configurations. Horizontal electrodes allowed greater contact between the injected permanganate and PCE and resulted in faster degradation of PCE compared to vertical electrodes. Pulsed oxidant injection, closer electrode spacing, and electric field reversal also resulted in faster EK‐ISCO remediation.     

Evaluation of an Ultrafiltration Method for Surfactant Recovery and Reuse During In Situ Washing of Contaminated Sites: Laboratory and Field Studies

Feasibility studies were conducted on the use of ultrafillration to recover surfactant from aqueous waste streams generated from the in situ surfactant washing of a site contaminated with poly-chlorinated biphenyls (PCBs) and oils. A Romicon Model HF-Lab-5 ultrafiltration unit and three types of ultrafillration membranes (PM500, XM50, and CM50) were evaluated for their permeability to a nonionic surfactant previously selected for the in situ washing. Results from laboratory studies using the XM50 membrane cartridge showed that 78 percent of the surfactant passed through the membrane surface (permeate) and was recovered.
Two field-pilot tests of the ultrafiltralion system were conducted using leachate containing a mixture of water, oils, PCBs, and surfactant that was collected from an in situ surfactant-washing demonstration test. Forty-six percent of the surfactant (mass) was recovered during the first field test using the XM50 membrane. The membrane retained 94 percent of the PCBs and 89 percent of the oils. The second field test showed that the PM500 membrane recovered 67 percent of the surfactant in the permeate and retained more than 90 percent and 83 percent of the PCBs and oils, respectively. This study indicates that a significant volume of a nonionic surfactant can be recovered from leachatc mixture containing PCBs and oils by ultrafillration. The recovered surfactant could be reused to improve the economic viability of in situ surfactant washing of contaminated sites.     

Evaluation of the presence of major anionic surfactants in marine sediments

The contamination of aquatic environments has become the focus of increasing regulation and public concern due to their potential and unknown negative effects on the ecosystems. The present work develops a monitoring and statistical study, based on the analysis of variance test (ANOVA) and the multivariable analysis, both for insoluble soap and LAS in order to compare the behavior of different anionic surfactants in this environmental compartment. First, a novel and successfully validated methodology to analyze insoluble soap in these samples is developed. The matrix effect and the comparison of different extraction techniques were also performed. The optimized analytical methodologies were applied to 48 representative samples collected from the Almeria Coast (Spain) and then a statistical analysis to correlate anionic surfactant concentration and several variables associated with marine sediment samples was also developed. The results obtained showed relevant conclusions related to the environmental behavior of anionic surfactants in marine sediments.     

Surfactant effects on the water‐stable aggregation of wettable soils from the continental USA

Surfactants may affect soil structure differently depending upon the soil or the quality of rainfall or irrigation water. This study examined whether the water‐stable aggregation of 11 wettable soils was affected by surfactants and the water in which the soils were sieved. The study also examined whether the wettable soils' water drop penetration time (WDPT) was affected by surfactants, water drop quality, and elapsed time since the surfactants were applied. Two nonionic surfactants and a surfactant‐free water control were sprayed (by misting) upon air‐dry soil, then WDPT was measured 1 and 72 h thereafter. Subsequently, this treated soil was slowly wetted with an aerosol to its water content at a matric potential of ?3 kPa, then immediately sieved for 600 s in water that contained either appreciable or few electrolytes. Water‐stable aggregation, quantified as mean weight diameter (MWD), varied widely among soils, ranging from 0.10 to 1.36 mm. The MWDs were affected (at p = 0.06) by surfactant treatments, depending upon the soil but not sieving water quality. Surfactants affected the MWD of an Adkins loamy sand and Feltham sand, two of the three coarsest‐textured soils. Although WDPTs never exceeded 5 s, depending upon the soil WDPTs were affected by surfactant treatments but not by water drop quality. After surfactant application, WDPTs generally decreased with time for three soils but increased with time for one soil. Findings suggested that surfactants interacted (1) with clay mineralogy to affect MWD and (2) with soluble calcium to affect WDPT for certain soils. Surfactant treatments but not water quality affected both MWD and WDPT for some but not all of 11 wettable, US soils. Published 2012. This article is a US Government work and is in the public domain in the USA.     

Evaluating a nonionic surfactant as a tool to improve water availability in irrigated cotton

Nonionic surfactants have been well researched in turf grass environments as a tool to ameliorate water‐repellant conditions. However, few studies have evaluated the risks and benefits of nonionic surfactant applications in row‐crop agricultural systems. The objective of this study was to evaluate the impact of a nonionic surfactant on cotton (Gossypium hirsutum L.) production on a Faceville loamy sand (fine, kaolinitic thermic Typic Kandiudult) in the coastal plain region of Georgia. The experiment consisted of two components: (1) on‐site rainfall simulation and (2) agronomic cotton field trials. Treatments were designed to test the impact of rate and frequency of surfactant applications using six combinations of application rates and timings. For the rainfall simulation component, only the control (0·0 L ha^?1) and high rate (0·51 L ha^?1) of surfactant applications were evaluated. During the field trial, soil water content, cotton stand counts, and yield were measured. Rainfall simulations showed that the addition of surfactant increased runoff, decreased infiltration, and promoted surface sealing. Despite the demonstrated potential for water loss, agronomic field trials showed that crop yields were not significantly different between surfactant‐treated and untreated plots. No differences in soil water content were observed between treatments at 5 and 15 cm depths; however, soil water content was significantly higher in untreated control plots at the 30 cm depth. Data demonstrate the need for clarification of soil physical/chemical properties and surfactant interactions that may lend themselves to the creation of surface seals and how these seals impact soil/water conservation and crop yield. Published in 2009 by John Wiley & Sons, Ltd.     

In Situ Chemical Oxidation of RDX-Contaminated Groundwater with Permanganate at the Nebraska Ordnance Plant

Groundwater beneath the former Nebraska Ordnance Plant (NOP) is contaminated with the explosive hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX). The current pump and treat facility is preventing offsite migration but does not offer a short-term solution. Our objective was to quantify the effectiveness of permanganate to degrade RDX in situ. This was accomplished by performing laboratory treatability experiments, aquifer characterization, and a pilot-scale in situ chemical oxidation (ISCO) demonstration. Treatability experiments confirmed that permanganate could mineralize RDX in the presence of NOP aquifer solids. The pilot-scale ISCO demonstration was performed using an extraction-injection well configuration to create a curtain of permanganate between two injection wells. RDX destruction was then quantified as the RDX-permanganate plume migrated downgradient through a monitoring well field. Electrical resistivity imaging (ERI) was used to identify the subsurface distribution of permanganate after injection. Results showed that RDX concentrations temporally decreased in wells closest to the injection wells by 70% to 80%. Observed degradation rates (0.12 and 0.087/d) were lower than those observed under laboratory batch conditions at 11.5 °C (0.20/d) and resulted from lower than projected permanganate concentrations. Both ERI and spatial electrical conductivity measurements verified that permanganate distribution was not uniform throughout the 6.1-m (20 feet) well screens and that groundwater sampling captured both treated and nontreated groundwater during pumping. Although heterogeneous flow paths precluded a uniform permanganate distribution, pilot-scale results provided proof-of-concept that permanganate can degrade RDX in situ and support permanganate as a possible remedial treatment for RDX-contaminated groundwater.     

Adsorption of BTEX on Surfactant Modified Granulated Natural Zeolite Nanoparticles: Parameters Optimizing by Applying Taguchi Experimental Design Method

In this paper, a novel adsorbent developed by means of granulating of natural zeolite nanoparticles (i.e., clinoptilolite) was evaluated for possible removal of the petroleum monoaromatics (i.e., benzene, toluene, ethylbenzene, and xylene, BTEX). To do this, the natural zeolite was ground to produce nanosized particulate, then modified by two cationic surfactants and granulated. The effect of various parameters including temperature, initial pH of the solution, total dissolved solids (TDS), and concentration of a competitive substance (i.e., methyl tert‐butyl ether, MTBE) were studied and optimized using a Taguchi statistical approach. The results ascertained that initial pH of the solution was the most effective parameter. However, the low pH (acidic) was favorable for BTEX adsorption onto the developed adsorbents. In this study, the experimental parameters were optimized and the best adsorption condition by determination of effective factors was chosen. Based on the S/N ratio, the optimized conditions for BTEX removal were temperature of 40°C, initial pH of 3, TDS of 0 mg/L, and MTBE concentration of 100 µg/L. At the optimized conditions, the uptake of each BTEX compounds reached to more than 1.5 mg/g of adsorbents.     

Homogeneous Catalytic Ozonation of Lipids Involving Fe2+ and Mn2+: An Experimental and Modeling Study

Given the issue of lipids in effluent treatment systems and their negative impact on the environment, this study aimed to examine lipid degradation by homogenous catalytic ozonation with the aid of iron and manganese ions. This technology presents the possibility of completely mineralizing pollutants using hydroxyl radicals. Milk is chosen as the lipid source because of the high concentration of triglycerides in its matrix, this kind of lipid being the one found most frequently in food and, consequently, in effluent treatment systems. The milk pH value is controlled, and acidic, neutral, and basic conditions are evaluated. The rates of pseudo‐first‐order reactions and the effective value are estimated. It is shown that under acidic conditions low catalyst dosages are enough to cause the complete degradation of lipids. Under neutral conditions, a similar behavior is observed. Under basic conditions, higher catalyst dosages give higher reaction rates. The order of effectiveness of the catalysts under acidic and basic conditions is Fe²⁺ > Mn²⁺, with Mn²⁺ > Fe²⁺ under neutral conditions. Homogeneous catalytic ozonation is therefore efficient at lipid degradation. This technique is viable economically, since the lipid removal occurred at low ozone levels. In addition, the ions used as catalysts are naturally abundant.     

Surfactant‐Enhanced Electroosmotic Flushing in a Trichlorobenzene Contaminated Clayey Soil

Remediation of the sites contaminated with organic contaminants, such as chlorobenzenes, remains a challenging issue. Electroosmotic flushing can be a promising approach which is based on mechanism of electrokinetic remediation for removal of organic contaminants from fluids in low‐permeability soil. To select an optimum surfactant that can effectively enhance electroosmotic flushing, three common surfactants, Triton X‐100 (EK2), Tween 80 (EK3), and a mixture of sodium dodecyl sulfate and Triton X‐100 (EK4) buffered with Na₂HPO₄/NaH₂PO₄ solution, were tested. The efficiency of each kind of surfactant was evaluated using a three‐dimensional box filled with a clayey soil spiked with 1,2,4‐trichlorobenzene, and compared with a test (EK1) without surfactant. The results demonstrated that the buffer solutions efficiently neutralized H⁺ and OH^? produced by electrolysis. EK3 with Tween 80 added in the flushing solution reached the highest electroosmotic permeability of 10^?4 cm²/v/s and achieved a notably high cumulative electroosmotic flow (EOF) of 5067 mL within 6 d, which was 6.3, 3.4, and 4.2 times higher than that in EK1, EK2, and EK4, respectively. There were 420 mL more cumulative EOF obtained after 50 h of electrical application in EK4 than in EK2. The introduction of nonreactive ions can increase the current, thereby benefiting the EOF. Both the higher pH caused by the buffer and the application of nonionic surfactants can make the zeta potential more negative, thereby increasing the EOF. Tween 80 can be recommended as the best flushing solution for removing organic contaminants from sites when electrokinetic remediation is applied.     

Electrical Resistivity Imaging of a Permanganate Injection During In Situ Treatment of RDX‐Contaminated Groundwater

Groundwater beneath the former Nebraska Ordnance Plant (NOP) is contaminated with the explosive hexahydro‐1,3,5‐trinitro‐1,3,5‐triazine (RDX) and trichloroethene (TCE). Previous treatability experiments confirmed that permanganate could mineralize RDX in NOP aquifer material. The objective of this study was to determine the efficacy of permanganate to transform RDX in the field by monitoring a pilot‐scale in situ chemical oxidation (ISCO) demonstration. In this demonstration, electrical resistivity imaging (ERI) was used to create two‐dimensional (2‐D) images of the test site prior to, during, and after injecting sodium permanganate. The ISCO was performed by using an extraction‐injection well configuration to create a curtain of permanganate. Monitoring wells were positioned downgradient of the injection zone with the intent of capturing the permanganate‐RDX plume. Differencing between ERI taken preinjection and postinjection determined the initial distribution of the injected permanganate. ERI also quantitatively corroborated the hydraulic conductivity distribution across the site. Groundwater samples from 12 downgradient wells and 8 direct‐push profiles did not provide enough data to quantify the distribution and flow of the injected permanganate. ERI, however, showed that the permanganate injection flowed against the regional groundwater gradient and migrated below monitoring well screens. ERI combined with monitoring well samples helped explain the permanganate dynamics in downgradient wells and support the use of ERI as a means of monitoring ISCO injections.     

Influence of Surfactants on Degradation of 1‐(2‐Chlorobenzoyl)‐3‐(4‐chlorophenyl) Urea by Nanoscale Zerovalent Iron

Nanoscale zerovalent iron (NZVI) has been proved to be effective in the degradation of environmental pollutants and exhibits advantages in the removal of 1‐(2‐chlorobenzoyl)‐3‐(4‐chlorophenyl) urea (CCU), an analog of diflubenzuron. This present study focused on the influence of surfactants in the degradation procedure with NZVI in order to provide a simple and rapid removal method for CCU. Triton X‐100, Tween 20, Tween 80, sodium dodecyl sulfonate (SDS), and cetyltrimethylammonium bromide (CTAB) were investigated under anaerobic conditions. The experimental results demonstrated that the degradation rate increased sharply with the presence of SD during the first 15 min, up to 99.97% with addition of 0.01 g L^?1 SDS, whereas the presence of Triton X‐100, Tween 80, and Tween 20 resulted in a slight enhancement of the degradation of CCU. The enhancement strength of them was in the order Tween 20, Triton X‐100, and Tween 80. However, addition of the cationic surfactant CTAB resulted in a significant inhibitive effect. In contrast, the mixed surfactants did not result in the expected performance, and the performance was lower than that using some certain single surfactant among the mixed surfactants.     

Biogeochemistry of iron in an acidic lake

In this paper, the fate of iron in Lake Cristallina, an acidic lake in the Alps of Switzerland, is discussed. A simple conceptual model is developed in order to explain the observed diel variation in dissolved iron(II) concentration. Biotite weathering provides reduced iron that is oxidized and subsequently precipitated in the lake. The amorphous Fe(III)hydroxide (FeOOH xH₂O), found in the sediments of Lake Cristallina, is an Fe(II) oxidation product. This oxygenation reaction is most probably catalyzed by bacteria surfaces, as indicated by the relatively high estimated oxidation rate compared to the oxidation rate of the homogeneous oxidation of inorganic Fe(II) species at the ambient pH of Lake Cristallina (pH 5.4 at 4 °C) and by the scanning electron micrograph pictures. Under the influence of light, these amorphous iron(III)hydroxide phases are reductively dissolved. The net concentration of Fe(II) reflects the balance of the reductive dissolution and the oxidation/precipitation reactions and tends to parallel the light intensity, leading to a diurnal variation in the Fe(II) concentration. The rate of the photochemical reductive dissolution of Lake Cristallina iron(III)hydroxides is greatly enhanced in situ and in the laboratory by addition of oxalate to the lake water.