Chromium exists largely in two oxidation states, namely hexavalent chromium (Cr(VI)) which is carcinogenic, mutagenic to living organisms including humans and trivalent chromium (Cr(III)) which is known to be 1000 times less toxic than Cr(VI). It is therefore desirable in most cases to reduce Cr(VI) to Cr(III). Various studies have been conducted on the Cr(VI) reduction process either in situ or ex situ. However in situ bioremediation using permeable reactive barrier system appears as a potential and attractive technology compared to other in situ technologies. This study was conducted to evaluate the reduction of Cr(VI) to Cr(III) in the short term and regeneration of the biological reactive barrier to achieve continuous long term operation. It was observed from the study that the chromium hydroxide Cr(OH)3(s) precipitated and thus affected the porosity and hydraulic conductivity of the barrier system. It was therefore proposed to implement a regeneration process involving remobilization of precipitated Cr(OH)3 using a dilute acid (0.1% HCl) and recover Cr(III) by electrokinetics. Lowering the pH in the reactor introduced harsh conditions which necessitated the evaluation of a possible culture shift during the regeneration phase. Microbial culture composition during bioremediation and after soil washing was evaluated using a 16S rRNA finger printing method. The microbial barrier was initially inoculated with indigenous bacterial species from dried sludge. The results presented in the phylogenic tree diagrams confirm that, after microbial barrier system operation, the well-known Cr(VI) reducers Bacillus mycoides, Lysinibacillus fusiformis and Micrococcus lylae were the predominant species in the microbial community of the barrier. The microbial barrier system successfully achieved near complete removal of Cr(VI), whereby approximately 75% Cr(VI) removal was achieved within 63 days of operation. The formation of Cr(OH)3(s) was observed in the second week of operation. After 4 weeks of operating the mesocosm under soil washing with 0.1% HCl and electrokinetics remediation with a DC voltage of 50-150 V an increase in total chromium (73%) was observed suggesting that the trapped chromium species in the mesocosm was effectively remobilized with the assumption that Cr(III) had attached to the cathode forming a white-yellow precipitate layer around the cathode. Additionally more than 95% Cr(VI) was transformed to lower toxicity Cr(III) during electrokinetics and soil washing remediation. However, one of the limitations of electrokinetics is near anode focusing effect whereby a layer of precipitate is formed around the anode that lead to the reduction of efficiency of the technology. / Dissertation (MSc)--University of Pretoria, 2014. / lk2014 / Chemical Engineering / MSc / Unrestricted

Volatile organic compound (VOC) contamination of low permeability geologic deposits due to Dense Non-Aqueous Phase Liquid (DNAPL) penetration through fractures is exceptionally difficult to remediate using in-situ methods as the low permeability of the sediments limits the delivery of reagents proximal to contaminant mass. This thesis examines in detail the extent of organic contaminant treatment away from hydraulically-induced fractures injected with particulate Zero Valent Iron as (1) ZVI and glycol (G-ZVI) and (2) an emulsified ZVI (EZVI) mixture within a contaminated glaciolacustrine clayey deposit. Continuous vertical cores were collected through the treatment zone at 2 and 2.5 years after substrate injections and soil sub-sample spacing was scaled to show the extent of the treatment zone adjacent to the ZVI in the fractures, expecting the treatment would be controlled by diffusion limited transport to the reaction zone. Analytical results show evidence of treatment in both the EZVI and the G-ZVI containing fractures with the presence of degradation by-products and reduced VOC concentrations in the fracture and surrounding clay matrix. / Natural Sciences and Engineering Research Council of Canada, University Consortium for Field-Focused Groundwater Contamination Research

Thesis (Ph.D.) -- Mississippi State University. Dave C. Swalm School of Chemical Engineering. / Title from title screen. Includes bibliographical references.

This thesis deals with a contaminated area in the municipality of Östersund where a gas plant has previously been operating from 1914 to 1951. Operations at the property where the gas plant has been located currently consist of a workshop and commercial premises with associated car parking. In order to be able to build on the gas plant area, the municipality intends to implement post-treatment measures in the area. The substances found in the contaminated area (hotspot area E) are polycyclic aromatic hydrocarbons (PAH), aromatics, arsenic, nickel, lead and benzene. Measurement data indicate that these substances have been found at high levels, above the Swedish Environmental Protection Agency's guideline values for contaminated soil. Many areas today are polluted to the level that they pose great risks to the environment and people, and this thought requires the treatment of contaminated soil. A risk assessment for hotspot area E determined that PAH, aromatics, arsenic, nickel, lead and benzene pose an unacceptable risk, and the area is therefore deemed to need remediation. Based on nearby buildings, in-situ soil remediation is a suitable approach that fits. This study summarizes the progress made in remediation research and shows that soil remediation methods have different advantages and disadvantages, and different strains on human health and the environment. Based on this study, it may be more appropriate to wait for more efficient or cheaper remediation techniques to be developed, but with the idea that these substances are volatile, toxic, and dangerous to us humans and the environment. This means that they pose a potential risk to society and a tendency to spread easily. Conclusions that can be drawn are that all in-situ methods included in this work can be applied in Sweden based on the geological conditions. In order to achieve optimum in-situ soil remediation, site-specific conditions, such as large groundwater flow or heterogeneous soil, control the choice of remediation method.

No description available.

Groundwater arsenic contamination is currently a global problem, and also a concern at numerous former industrial sites, agricultural sites, landfill sites and mining operations in the U.S. This dissertation aims to develop improved strategies of remediating these arsenic contaminated aquifers. It focuses on two distinct approaches of remediation: (1) mobilizing arsenic from contaminated aquifer sediments to decrease the quantity of arsenic at the source of contamination; and (2) immobilizing arsenic in situ, to decrease the mobility and bioavailability of this arsenic. Optimal remediation may well involve combinations of these two approaches. Arsenic mobilization using oxalic acid is effective because oxalic acid dissolves arsenic host minerals and competes for sorption sites on those minerals. In this dissertation, oxalic acid treatment was tested using sediments with contrasting iron mineralogies and arsenic contents from the Dover Municipal Landfill and the Vineland Chemical Company Superfund sites. Oxalic acid mobilized arsenic from both sites and the residual sediment arsenic was less vulnerable to microbial reduction than before the treatment. Oxalic acid thus could improve the efficiency of widely used pump-and-treat remediation. Oxalic acid did not remove all of the reactive iron(III) minerals in Vineland sediment samples, and thus released significant quantities of arsenic into solution under reducing conditions than the Dover samples. Therefore, the efficacy of pump-and-treat must consider iron mineralogy when evaluating its overall potential for remediating groundwater arsenic. Arsenic immobilization occurs by changing the chemical state, or speciation, of arsenic and other elements in the system. Arsenic is often assumed to be immobile in sulfidic environments. In this dissertation, sulfate reduction was stimulated in sediments from the Vineland Superfund site and the Coeur d'Alene mining district. Sulfate reduction in the Coeur d'Alene sediments was more effective at removing arsenic from solution than the Vineland sediments. The Vineland sediments initially contained abundant reactive ferrihydrite, and underwent extensive sulfur cycling during incubation. As a result, arsenic in the Vineland sediments could not be effectively converted to immobile arsenic-bearing sulfides, but instead a part of the arsenic was probably converted to soluble thioarsenates. Therefore, coupling between the iron and sulfur redox cycles must be fully understood for arsenic immobilization by sulfate reduction to be successful. Arsenic can also be immobilized by retention on magnetite (Fe3O4). Magnetite is stable under a wide range of aquifer conditions including both oxic and iron(III)-reducing environments. In this dissertation, a series of experiments were performed with sediments from the Dover and Vineland Superfund sites, to examine the potential of magnetite for use in arsenic immobilization. Our data suggest that the formation of magnetite can be achieved by the microbial oxidation of ferrous iron with nitrate. Magnetite can incorporate arsenic into its structure during formation, forming a stable arsenic sink. Magnetite, once formed, can also immobilize arsenic by surface adsorption, and thus serve as a reactive filter when contaminated groundwater migrates through the treatment zone. Reactive transport modeling is used for investigating the magnetite based arsenic immobilization strategy and for scaling laboratory results to field environments. Such modeling suggests that the ratio between iron(II) and nitrate in the injectant regulates the formations of magnetite and ferrihydrite, and thus regulates the long-term evolution of the effectiveness of the strategy. The results from field-scale models favor scenarios that rely on the chromatographic mixing of iron(II) and nitrate after injection. The studies in this dissertation demonstrate that the environmental fate of arsenic depends on the biogeochemical cycling of arsenic, iron, and to a lesser extent, sulfur. The development of effective groundwater arsenic remediation strategies depends on a good understanding of each of the involved processes, and their combinations.

Η ρύπανση του εδάφους από βιομηχανικά και αστικά απόβλητα αποτελεί παγκοσμίως ένα από τα σημαντικότερα περιβαλλοντικά προβλήματα. Ανάμεσα στους πιο επικίνδυνους ρύπους συγκαταλέγονται και οι υδρογονάνθρακες πετρελαιοειδών. Αναπόφευκτη συνέπεια της διαφυγής των υγρών ρύπων στο έδαφος είναι η μεταφορά τους προς στην ακόρεστη ζώνη του εδάφους μέσω μιας σειράς διεργασιών (ροή, διαλυτοποίηση, εξάτμιση, διασπορά, ρόφηση, κτλ) και η ρύπανση των υποκείμενων ταμιευτήρων υπογείων υδάτων. Οι πλέον κλασσικές μέθοδοι απομακρυσμένης (ex situ) απορρύπανσης εδαφών περιλαμβάνουν εκσκαφή και μεταφορά του εδάφους σε κατάλληλους χώρους (π.χ. αποτεφρωτήρες, βιο-σωροί, κλπ). Τα τελευταία χρόνια έχει αναπτυχθεί έντονο ενδιαφέρον για την ανάπτυξη και εφαρμογή τεχνολογιών επιτόπιας απορρύπανσης των εδαφών (in situ soil remediation) με χαμηλό κόστος και ελάχιστο περιβαλλοντικό αποτύπωμα. Στην παρούσα εργασία μελετώνται δύο σχετικά νέες μέθοδοι επιτόπιας απορρύπανσης: α) ο βιοαερισμός και, β) η έγχυση ατμού. Και στις δύο περιπτώσεις, για να αυξηθεί η ακτίνα δράσης της απορρύπανσης, το έδαφος διεγέρθηκε με την δημιουργία οριζόντιων υδραυλικών ρωγμών που λειτουργούν ως οριζόντια φρεάτια διαβίβασης και εξαγωγής ρευστών. Το πεδίο μελέτης είναι ένα πρώην στρατιωτικό αεροδρόμιο της Βόρειο-Δυτικής Πολωνίας, το Kluczewo, το οποίο έχει ρυπανθεί εκτεταμένα με κηροζίνη για μεγάλο χρονικό διάστημα (1935-1992). Το έδαφος της περιοχής αυτής παρουσιάζει ρωγμές ενώ η πορώδης μήτρα έχει σχετικά χαμηλή διαπερατότητα. Οι ίδιες γεωλογικές συνθήκες επικρατούν σε μεγάλο μέρος του υπεδάφους της Βόρειας Ευρώπης. Λόγω της ισχυρά ετερογενούς φύσης αυτών των εδαφών από την κλίμακα των πόρων στην κλίμακα του πεδίου και της δημιουργίας προτιμητέων μονοπατιών ροής, είναι αρκετά δύσκολο να σχεδιαστούν αποδοτικές μέθοδοι απορρύπανσης. Κύριος στόχος της εργασίας είναι η αξιολόγηση της απόδοσης των δύο μεθόδων απορρύπανσης μετά την εφαρμογή τους στην ακόρεστη ζώνη ετερογενούς εδάφους που έχει ρυπανθεί εκτενώς με υδρογονάνθρακες πετρελαιοειδών (κηροζίνη). Για να προσδιοριστεί η απόδοση κάθε μεθόδου, συλλέχθηκαν δείγματα εδάφους από ένα μεγάλο αριθμό σημείων και πραγματοποιήθηκαν χημικές αναλύσεις μέτρησης της συγκέντρωσης και της σύστασης των υδρογονανθράκων με GC-MS και GC-FID. Προκειμένου να διευκρινιστoύν καλύτερα οι κύριοι μηχανισμοί απομάκρυνσης του ρύπου και να εκτιμηθεί η αποδοτικότητα της έγχυσης ατμού και του βιοαερισμού, διεξήχθησαν πειράματα έγχυσης ατμού και βιοαερισμού και σε εργαστηριακή κλίμακα (oρθογώνιο κελί από PMMA με διαστάσεις 55 cm x 50 cm x 12 cm και υπό ακόρεστες συνθήκες). Λόγω των ετερογενειών της πορώδους δομής, στον βιοαερισμό ο κύριος μηχανισμός απομάκρυνσης ρύπου ήταν η εξάτμιση των υδρογονανθράκων και η σχετικά γρήγορη μεταφορά των ατμών μέσω διάχυσης και λόγω της μεγάλης βαθμίδας συγκέντρωσης από την μικροπορώδη μήτρα προς μονοπάτια προτιμητέας ροής (preferential flow paths) αέρα (αερισμός). Αντιστοίχως, λόγω της χαμηλής διαπερατότητας του εδάφους, στην περίπτωση της έγχυσης ατμού ο κύριος μηχανισμός απομάκρυνσης των ημι-πτητικών και μη πτητικών συστατικών ήταν η απόσταξη ατμού (δηλαδή η μείωση του σημείου ζέσεως των υδρογονανθράκων λόγω της παρουσίας μη αναμίξιμης υδατικής φάσης). Η σύγκριση των δύο μεθόδων απορρύπανσης με διάνοιξη οριζόντιων υδραυλικών ρωγμών έδειξε ότι και οι δύο μέθοδοι είναι αρκετά αποδοτικές όσον αφορά στη μείωση της μάζας του ρύπου (~72%) σε ισχυρά ετερογενή εδάφη με ρωγμές. Η έγχυση ατμού όμως είναι πολύ πιο γρήγορη (3 μήνες) από το βιοαερισμό (12 μήνες) αλλά ταυτόχρονα και αρκετά πιο ακριβή από αυτόν (14-25%). Όσον αφορά το ποσοστό μείωσης επικινδυνότητας του υπολειπόμενου ρύπου, ο βιοαερισμός δίνει με μεγάλη διαφορά καλύτερα αποτελέσματα (93%) από ότι η έγχυση ατμού (8-68%) όπου παρατηρείται και μεγάλη διακύμανση τιμών. / Soil contamination by industrial and urban wastes is nowadays one of the most important pollution problems worldwide. The petroleum hydrocarbons are included in the list of toxic pollutants that have contaminated extensive areas all over the world. An inevitable consequence of liquid pollutants release on the ground is their transport by a variety of mechanisms (e.g. gravity flow, dissolution, volatilization, dispersion, sorption, etc) in the unsaturated zone of soil, and subsequent pollution of the underlying aquifers. Conventional methods of ex-situ soil remediation are the soil excavation and its transportation in appropriate places (e.g. incinerator, bio-piles, etc). During the last years, there is a growing interest for the development and application of low-cost and sustainable (low environmental impact) in-situ soil remediation technologies. In the present work, two relatively new in-situ remediation technologies, bioventing and steam injection, were tested on the vadose zone of a low permeability and fractured glacial till sediment that was contaminated by jet fuel. The experimental site is situated in an abandoned military airport (Kluczewo) in North-Western Poland. The area was polluted extensively by jet fuel over a long period (1935-1992). The geological characterization revealed the existence of vertical desiccation fractures at the upper layers and horizontal/sub-horizontal tectonic fractures at the deeper ones, and a relatively low permeability and heterogeneous micro-porous matrix. The same geologic conditions dominate in a major part of the subsurface in Northern and Central Europe. Due to the multi-scale heterogeneities, ranging from the pore-scale to the field-scale, and the creation of preferential flow paths in such soils, it is very difficult to design successful remediation strategies based on vertical wells. For this reason, in both field experiments (bioventing and steam injection), the soil was stimulated by opening hydraulic fractures which acted as horizontal wells of fluid injection/extraction, and enhanced the influence radius of remediation. The main goal of the work is to evaluate, under field conditions, steam injection and bioventing as sustainable and efficient technologies for the removal of petroleum hydrocarbons from highly heterogeneous soils. In order to determine the efficiency of each remediation method, soil samples were collected from twelve wells and seven depths, and placed inside specific flasks pre-filled with dichloromethane (DCM). After the accelerated extraction of non-aqueous phase liquid (NAPL) from the soil and its dissolution in DCM, the composition and concentration of hydrocarbons (NAPL) was performed by using GC-MS and GC-FID. In order to clarify the main NAPL removal mechanisms and evaluate the effectiveness of steam injection and bioventing, lab-scale experiments were also conducted in soil tanks by using synthetic NAPL (PMMA cell with 55 cm x 50 cm x 12 cm dimensions) and keep the conditions comparable to the field ones. Due to pore structure heterogeneities, the main NAPL removal mechanism in bioventing was the volatilization of hydrocarbons and the fast vapour transfer through diffusion (due to the high concentration gradient) from the porous matrix to the high hydraulic conductivity preferential flow paths of injected air (ventilation). Respectively, due to the low soil permeability, in steam injection the main removal mechanism of semi- and non-volatile substances was steam distillation (namely the reduction of NAPL compounds bubble point because of the coexistence of immiscible water). The comparison of the two remediation technologies, steam injection and bioventing, indicate that both methods are efficient with respect to the reduction of the pollutant mass (~72%) in highly heterogeneous and fractured soils. With respect to cost issues, steam injection albeit faster, is 14-25% more expensive than bioventing. Finally, concerning the risks associated with the reduction of residual NAPL in groundwater, bioventing was more effective (~93%) than steam injection (8-68%).

This master thesis is focused on groundwater remediation of chlorinated ethylenes and methanes in the area of chemical factory Spolchemie in the Czech Republic, Ústí nad Labem city. For these purposes nano zero valent iron particles were used. For the remediation two separate applications of different types of particles together in suspension with tracer (lithium chloride), were carried out. The results from the first application were evaluated by the supervisor of this thesis and are briefly summarized and discussed together with the second application which was evaluated by the author of this thesis. Second application of particles was carried out in October 2015 and observed for 424 days. Observation consisted of monitoring of groundwater level, physical-chemical parameters and collection of water samples for the analysis of concentrations of chlorinated hydrocarbons, their degradation products and several chosen ions. Nanoiron particles had the assumed effect onto the physical-chemical parameters and reduction of contamination. The application of tracer had proven the expected groundwater flow and made a possibility to distinguish between the process of reductive dehalogenation and dilution caused by the injected water, the dilution did not exceeded 5 % in most monitored points. Other...

D. Tech. Chemical Engineering / Aims of this research project was to add value to largely wasted South African sawdust by development of low-cost AC of high efficiency for removal of toxic Cr (VI), phenol and glutaraldehyde from dilute aqueous media. The main objectives of the research project were: a) To develop low-cost AC based on South African P. patula sawdust using economical physical superheated steam activation.Characterization of carbon samples for selection of optimum preparation conditions for development of low-cost AC of effective microporosity mesoporosity and surface functionality for enhanced adsorption capacity of Cr (VI) and/or phenol and/or glutaraldehyde from dilute aqueous solution. Acid-amine surface groups modification of optimally developed AC for further enhancement of adsorption capacity for mixed polarized glutaraldehyde molecules from aqueous solution. b) To evaluate the aqueous phase batch adsorption properties of developed AC for Cr (VI) and phenol and, of acid-amine modified developed AC for glutaraldehyde. Determination of optimum pH for adsorption; accurate adsorption isotherm modelling for determination of maximum adsorption capacity, comparison of maximum adsorption capacities for Cr (VI) and phenol of developed AC with commercial AC and literature ACs, and attempt to establish average micropore size for enhanced capacity for Cr (VI) and phenol from dilute aqueous solution.Kinetics reaction and diffusion modelling for determination of adsorption rate constants and diffusion parameters; and determination of adsorption thermodynamic parameters.Evaluation of equilibrium selectivity of developed AC for Cr (VI) and/or phenol in binary aqueous solutions. c) To evaluate aqueous phase fixed-bed adsorption characteristics of developed AC for single Cr (VI) and mixed solution using Rapid Small Scale column Tests (RSSCTs). Generation of breakthrough curves at optimum adsorption conditions for evaluation of column performance indicators at different process conditions, bed regeneration-reusability potential, and dynamic adsorption selectivity of developed AC for Cr (VI) from solution of base metals. Determination of column diffusion parameters; accurate mass transfer and empirical modelling of breakthrough data; determination of applicable RSSCT scaling equation; and optimization of breakthrough data for accurate RSSCT scale-up.