Erik Gydesen Søgaard

Influence of chloride and carbonates on the reactivity of activated persulfate

Chloride and carbonates have the potential to impact pathway, kinetics, and efficiency of oxidation reactions, both as radical scavengers and as metal complexing agents. Traditionally, it is assumed that they have an overall negative impact on the activated persulfate performance. This study investigated the influence of carbonates and chloride on the reactivity of persulfate for three different activation techniques to produce reactive free sulfate radicals; heat, alkaline and iron activation. By using p-nitrosodimethylaniline as model target compound, it was demonstrated that iron activation at neutral pH was not affected by Cl(-) or HCO(3)(-), alkaline activation was enhanced by Cl(-) and even more by CO(3)(2-), and heat activation was enhanced by Cl(-), and no effect from HCO(3)(-) was observed. At pH 2 destruction of perchloroethylene by iron activated persulfate was significantly affected by chloride. Reaction rates decreased, but the overall oxidation efficiency was unaffected up to 28 mM Cl(-). The effect of chloride and carbonates is caused by direct attack of produced reactive chlorine, or carbonate species or by catalysis of the propagation reactions resulting in more sulfate radicals. These results show that carbonate and chloride might play an important role in activated persulfate applications and should not strictly be considered as scavengers.

Conditions for biological precipitation of iron by Gallionella ferruginea in a slightly polluted ground water

Abstract A sand filter has been built as a pilot plant with the purpose of biological precipitation of Fe from ground water polluted with mainly chlorinated aliphatics. The ground water is pumped directly from a well in a polluted ground water aquifer in Esbjerg, Denmark. The pollution includes trichlorethylene and tetrachlorethylene together with smaller amounts of pesticides. Furthermore the best conditions for Fe precipitating bacteria were not expected to be present because of a relatively high O 2 content, up to 6.7 mg/l, a low Fe content, 0.2 mg/l and a pH of ∼5 in the ground water. Added FeSO 4 increased the Fe content of the ground water to about 4 mg/l. These rather extreme conditions for precipitating Fe were observed over a period of 3 months. The goal of the research was to observe the mechanism of Fe precipitation in a sand filter in the above-mentioned conditions comparative to normal conditions for biotic as well as abiotic Fe mineralization in sand filters of fresh water treatment plants. The Fe precipitating bacterium Gallionella ferrugenia was found to dominate the biotic Fe oxidation/precipitation process despite the extreme conditions. A huge amount of exopolymer from Gallionella was present. The precipitated Fe oxide was determined to be ferrihydrate. The rate of the Fe oxidation/precipitation was found to be about 1000 times faster than formerly found for abiotic physico-chemical oxidation/precipitation processes. The hydrophobic pesticides and some of their degradation products were not adsorbed in the filter. An added hydrophilic pesticide was adsorbed up to 40%. Trichlorethylene was not adsorbed in the filter. The reason for the poor adsorption of the hydrophobic compounds and trichlorethylene is due to the pronounced hydrophilic property of the exopolymers of Gallionella and the precipitated ferrihydrite.

Conditions and Rates of Biotic and Abiotic Iron Precipitation in Selected Danish Freshwater Plants and Microscopic Analysis of Precipitate Morphology

Abstract This study compares the biotic precipitation of iron in the sand filters of a new freshwater plant, Astrup, with the abiotic precipitation of iron in the sand filters of a traditional freshwater plant, Forum, in the same area of Denmark. We have observed that a third freshwater plant, Grindsted, which was planned to precipitate iron in the traditional abiotic way is in fact precipitating iron biotically because of poor aeration and very low oxygen content of the raw water. The dominant iron-precipitating bacteria was Gallionella ferruginea in both Astrup and Grindsted. The morphology of the iron precipitates were investigated using light, X-ray, scanning electron and transmission electron microscopy. The physicochemical conditions governing precipitation and the precipitated iron sludge were also investigated. The biotically precipitated iron was shown to be oxidised and precipitated with a rate about 60 times faster than the traditional abiotic process in spite of the much poorer physicochemical conditions for the process. The faster kinetics indicate a catalytic activity due to the presence of exopolymers from Gallionella ferruginea . A model is proposed for the relationship between the differences in characteristics of the iron precipitate and the kinetics of the precipitation.

Implementation of zero-valent iron (ZVI) into drinking water supply: Role of the ZVI and biological processes

Arsenic in drinking water is concerning millions of people around the world, even though many solutions to the problem have come up in recent years. One of the promising solutions for removing arsenic from water is by implementation of a zero-valent iron (ZVI) in the drinking water production. The purpose of this work was to study a treatment of As pollution based on the ZVI, aeration and sand filtration that was monitored for period of 45 months. In applied configuration and conditions ZVI was not able to remove arsenic alone, but it worked as a source of ferrous ions that during its oxidation enabled to co-precipitate arsenic compounds in the sand filter. The results show that after a lag phase of about 6 months, it was possible to achieve water production with an As content from 20 μg L(-1) to below 5 μg L(-1). The treatment also enabled to remove phosphates that were present in groundwater and affected As uptake by hindering its co-precipitation with Fe compounds. Determination of colony forming units on As amended agar helped to find arsenic resistant bacteria at each stage of treatment and also in the sand filter backwash sludge. Bacterial communities found in groundwater, containing low concentration of As, were found to have high As resistance. The results also indicate that the lag phase might have been also needed to initiate Fe ions release by corrosion from elemental Fe by help of microbial activity.

Aggregation kinetics of sol-gel process based on titanium tetraisopropoxide

The kinetics of hydrolysis and condensation of titanium tetraisopropoxide (TTIP) under neutral conditions has been investigated by a light scattering method for different TTIP and water concentrations. The evaluation of kinetics data confirmed the complex nature of the process, which includes hydrolysis, condensation and aggregation of primary particles. Instead of commonly used inverse value of induction time, the rate of an individual particle mass growth for the adequate description of kinetics during induction period was used. Taking into account the initial water consumption allowed a unified description of kinetic data in different ranges of reagent concentrations to be obtained.

Mobilization of metals during treatment of contaminated soils by modified Fenton's reagent using different chelating agents

Changes in pH and redox conditions and the application of chelating agents when applying in situ chemical oxidation (ISCO) for remediation of contaminated sites can cause mobilization of metals to the groundwater above threshold limit values. The mechanisms causing the mobilization are not fully understood and have only been investigated in few studies. The present work investigated the mobilization of 9 metals from two very different contaminated soils in bench and pilot tests during treatment with modified Fentons reagent (MFR) and found significant mobilization of Cu and Pb to the water in mg/l levels. Also Fe, As, Mn, Ni, Zn, Mg, and Ca mobilization was observed. These findings were confirmed in a pilot test where concentrations of Cu and Pb up to 52.2 and 33.7 mg/l were observed, respectively. Overall, the chelating agents tested (EDTA, citrate and pyrophosphate) did not seem to increase mobilization of metals compared to treatment with only hydrogen peroxide and iron. The results strongly indicate that the mobilization is caused by hydrogen peroxide and reactive species including oxidants and reductants formed with MFR. Based on these results, the use of chelating agents for ISCO will not cause an increase in metal mobilization.

Study of degradation intermediates formed during electrochemical oxidation of pesticide residue 2,6-dichlorobenzamide (BAM) at boron doped diamond (BDD) and platinum-iridium anodes

Electrochemical oxidation is a promising technique for degradation of otherwise recalcitrant organic micropollutants in waters. In this study, the applicability of electrochemical oxidation was investigated concerning the degradation of the groundwater pollutant 2,6-dichlorobenzamide (BAM) through the electrochemical oxygen transfer process with two anode materials: Ti/Pt90-Ir10 and boron doped diamond (Si/BDD). Besides the efficiency of the degradation of the main pollutant, it is also of outmost importance to control the formation and fate of stable degradation intermediates. These were investigated quantitatively with HPLC-MS and TOC measurements and qualitatively with a combined HPLC-UV and HPLC-MS protocol. 2,6-Dichlorobenzamide was found to be degraded most efficiently by the BDD cell, which also resulted in significantly lower amounts of intermediates formed during the process. The anodic degradation pathway was found to occur via substitution of hydroxyl groups until ring cleavage leading to carboxylic acids. For the BDD cell, there was a parallel cathodic degradation pathway that occurred via dechlorination. The combination of TOC with the combined HPLC-UV/MS was found to be a powerful method for determining the amount and nature of degradation intermediates.

Hydrothermal liquefaction of biomass

Biomass is one of the most abundant sources of renewable energy, and will be an important part of a more sustainable future energy system. In addition to direct combustion, there is growing attention on conversion of biomass into liquid energy carriers. These conversion methods are divided into biochemical/biotechnical methods and thermochemical methods, such as direct combustion, pyrolysis, gasification, liquefaction, etc. This chapter focuses on hydrothermal liquefaction, where high pressures and intermediate temperatures together with the presence of water are used to convert biomass into liquid biofuels, with the aim of describing the current status and development challenges of the technology. During the hydrothermal liquefaction process, the biomass macromolecules are first hydrolyzed and/or degraded into smaller molecules. Many of the produced molecules are unstable and reactive and can recombine into larger ones. During this process, a substantial part of the oxygen in the biomass is removed by dehydration or decarboxylation. The chemical properties of the product are mostly dependent of the biomass substrate composition. Biomass consists of various components such as carbohydrates, lignin, protein, and fat, and each of them produce distinct groups of compounds when processed individually. When processed together in different ratios, they will most likely cross-influence each other and thus the composition of the product. Processing conditions including temperature, pressure, residence time, catalyst, and type of solvent are important for the bio-oil yield and product quality.

Electrochemical degradation of PAH compounds in process water: a kinetic study on model solutions and a proof of concept study on runoff water from harbour sediment purification

The present study has investigated the possibility to apply electrochemical oxidation in the treatment of polycyclic aromatic hydrocarbon (PAHs) pollutants in water. The reaction kinetics of naphthalene, fluoranthene, and pyrene oxidation have been studied in a batch recirculation experimental setup applying a commercial one-compartment cell of tubular design with Ti/Pt(90)-Ir(10) anode. The rate of oxidation has been evaluated upon variations in current density, electrolyte composition and concentration. All three PAHs were degraded by direct anodic oxidation in 0.10 M Na(2)SO(4) electrolyte, and the removal rates were significantly enhanced by a factor of two to six in 0.10 M NaCl due to contribution from the indirect hypochlorite oxidation. Second order reaction kinetics was observed for the degradation of naphthalene in all electrolytes whereas fluoranthene and pyrene followed first order kinetics. Decreased current densities from 200 to 15 mA cm(-2) in the NaCl electrolyte also decreased the removal rates, but significantly enhanced the current efficiencies of the PAH oxidation, based on a defined current efficiency constant, k(q). This observation is believed to be due to the suppression of the water oxidation side reaction at lower applied voltages. A proof of concept study in real polluted water demonstrated the applicability of the electrochemical oxidation technique for larger scale use, where especially the indirect chloride mediated oxidation approach was a promising technique. However, the risk and extent of by-product formation needs to be studied in greater detail.

Study of degradation intermediates formed during electrochemical oxidation of pesticide residue 2,6-dichlorobenzamide (BAM) in chloride medium at boron doped diamond (BDD) and platinum anodes

For electrochemical oxidation to become applicable in water treatment outside of laboratories, a number of challenges must be elucidated. One is the formation and fate of degradation intermediates of targeted organics. In this study the degradation of the pesticide residue 2,6-dichlorobenzamide, an important groundwater pollutant, was investigated in a chloride rich solution with the purpose of studying the effect of active chlorine on the degradation pathway. To study the relative importance of the anodic oxidation and active chlorine oxidation in the bulk solution, a non-active BDD and an active Pt anode were compared. Also, the effect of the active chlorine oxidation on the total amount of degradation intermediates was investigated. We found that for 2,6-dichlorobenzamide, active chlorine oxidation was determining for the initial step of the degradation, and therefore yielded a completely different set of degradation intermediates compared to an inert electrolyte. For the Pt anode, the further degradation of the intermediates was also largely dependent on active chlorine oxidation, while for the BDD anode anodic oxidation was most important. It was also found that the presence of active chlorine led to fewer degradation intermediates compared to treatment in an inert electrolyte.