Chelating agents for diluted geothermal brine reinjection.

"Blue energy" could be produced by exploiting the large salinity gradient between geothermal fluids and freshwater through a SaltPower system. This study is an attempt to select the most favorable chemicals to avoid injectivity issues when a diluted geothermal fluid resulting from the SaltPower system is returned to the reservoir. Three synthetic chelating agents (oxalic acid, EDTA, and EDDS) and one natural (humic acid) were evaluated through speciation simulations and isothermal titration calorimetry (ITC) experiments. The speciation simulation results indicate that the degree of complexing is highly dependent on pH and chelating agent type. The ITC experiments show that the total heat for the formation of soluble metal-ligand complexes in the rock + geothermal brine system follows: EDTA > EDDS > oxalic acid > humic acid. The simulations and calorimetry results suggest that EDTA could be used to avoid the precipitation of Fe(III) oxides and other minerals (e.g., calcite and dolomite) inside the porous media upon the reinjection of diluted geothermal brine coming from SaltPower electricity production.

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.

Comparison of methods for evaluation of activity of photocatalytic films.

OBJECTIVE: This work aims to investigate the correlation between the photocatalytic activity determined by methylene blue bleaching (DIN 52980), stearic acid degradation, and degradation of acetone in gas phase. METHOD: The photocatalytic TiO(2) coatings included in this investigation ranged from thin commercially available coatings (Activ(TM) and BioClean(TM)) and ready to use suspensions (Nano-X PK1245) to lab-produced PVD and sol-gel coatings. XRD analysis of the photocatalytic coatings showed that all the coatings consisted of nanocrystalline anatase, although the thickness and porosity varied considerably. RESULTS: The study showed that the reproducibility of the activity measurements was good. However, more importantly, the investigation showed that there is a good correlation between the activities determined by the different methods even though the characteristics of the photocatalytic coatings and the organic probe molecules varied considerably. CONCLUSION: The overall findings of this work suggest that there is a good correlation between the investigated methods. These results are promising for the future work concerning standardization of methods for determination of the activity of photocatalytic films.

Use of ESI-MS to determine reaction pathway for hydrogen sulphide scavenging with 1,3,5-tri-(2-hydroxyethyl)-hexahydro-s-triazine.

To study the reaction between hydrogen sulphide and 1,3,5-tri-(2-hydroxyethyl)-hexahydro-s-triazine, which is an often used hydrogen sulphide scavenger, electro spray ionisation mass spectrometry (ESI-MS) was used. The investigation was carried out in positive mode, and tandem mass spectrometry was used to investigate the nature of unknown peaks in the mass spectra. The reaction was found to proceed as expected from theory with the triazine reacting with hydrogen sulphide to form the corresponding thiadiazine. This species subsequently reacted with a second hydrogen sulphide molecule to form the dithiazine species, hereby confirming previously obtained results and showing the ability of the ESI-MS method for studying the scavenging reaction. The final theoretical product s-trithiane was not detected. Furthermore, fragmentation products of thiadiazine and dithiazine were detected in the solution, and possible pathways and structures were suggested to describe the observed fragments. In these, thiadiazine fragmented to 2-(methylidene amino)-ethanol and 2-(1,3-thiazetidin-3-yl)-ethanol and N-(2-hydroxyethyl)-N-(sulfanylmethyl)-ethaniminium, which underwent a further fragmentation to N-methyl-N-(2-oxoethyl)-methaniminium. Dithiazine fragmented to N-methyl-N-(2-oxoethyl)-methaniminium as well. The by-product from this reaction is methanedithiol, which was not detected due to its low polarity.

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.

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 Fenton's 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.

Identification and fate of halogenated PAHs formed during electrochemical treatment of saline aqueous solutions.

Halogenations of polycyclic aromatic hydrocarbons (PAHs) comprise a serious problem, when electrochemical oxidation (EO) is applied for treatment of chloride and bromide containing polluted sea water. In this study, the possible non-polar halogenated byproducts formed were identified in a series of chemical hypochlorination experiments using GC-MS, and the analytical information from these experiments was used in the primary EO treatment tests. An electrochemical cell equipped with a Ti/Pt(90)-Ir(10) anode was used in a batch recirculation setup with naphthalene, pyrene, and fluoranthene as the parent PAHs. Contrary to the chemical hypochlorination experiments, naphthalene as the most soluble compound was the only one to be halogenated in detectable amounts during EO. In a single sodium chloride electrolyte, up to 13% of the initial naphthalene was chlorinated at the peak concentration during treatment before it was subsequently removed. Even small concentrations of added bromide in a mixed electrolyte completely dominated the byproduct pattern with formation of primarily mono brominated naphthalene in peak concentrations up to 30-39% of the initial naphthalene. All of the considered byproducts were despite a more recalcitrant behavior degraded at prolonged treatment times, which need to be applied to ensure a safe discharge of the treated water.