Heavy metals are a growing environmental concern as they are unable to be metabolized in the environment, leading to bioaccumulation in the food chain and impacting human health. Treating heavy metals is difficult and expensive. Current methods include precipitation (which generates sludge that is costly to dispose of) or requires the use of a membrane, which fouls and requires regeneration. Microbial electrolysis cells (MECs) represent an alternative for treating heavy metal contaminated wastewater. Reactor components are cheap, and operation requires only a small amount of electricity. The electrically active biofilm oxidizes organics in the wastewater while transferring electrons first to the anode, then to the cathode, where aqueous metals are reduced to a solid deposit, a mechanism called electrodeposition. Few studies have been conducted to investigate the best operational conditions for heavy metal removal in MECs. In this study, the effects of hydrodynamics, applied voltage, and initial metal concentration on heavy metal removal mechanisms are investigated, and the best operational practices are determined on a high level. Mixing in the cathode chamber increased electrodeposition by 15%, decreased the cathode potential by -0.06 V, and increased current generation between 10-30%. Increasing the applied voltage from 0.6 V to 1.2 V increased electrodeposition by 22%. With both mixing and higher voltage applied, 93.35% of cadmium was removed from the catholyte in 24 hours. Although high voltage application maximized electrodeposition for short-term treatment, long-term treatment indicated lower applied voltage resulted in healthier MEC reactors, better overall metal recoveries, along with a more stable cathode potential. / Thesis / Master of Applied Science (MASc)

Activated sludge microorganisms can remove many hazardous substances from wastewater by adsorbing and concentrating them on their surfaces. Biosorption of these substances onto activated sludge surfaces are influenced by the chemical properties of the substance in question as well as the surface properties of the microorganisms. The purpose of this study is to identify the biosorption mechanisms of heavy metals and the effect of extracellular polymer (ECP) composition of activated sludge on the biosorption of Pb(II), Cd(II), Cu(II), Zn(II) and Ni(II). Microorganisms cultured under different growth conditions are expected to have different compositions of ECPs and hence, different biosorption capacities. For this purpose, three sets of reactors with C/N ratios of 9, representing a carbonlimited case / 21, representing conventional municipal wastewater treatment plant activated sludge and 43, representing nitrogen-limited condition, were set up. The semi continuous reactors were fed synthetically and operated at a sludge age of 8 days. Isotherm and kinetic experiments that were held with three different C/N ratios was indicated that the biosorptive capacity of activated sludge was highly dependent on metal species and the C/N ratio. Although, the dependence of biosorptive capacity on C/N ratio was different for each metal, biosorption properties of activated sludge were found to be directly related with ECP composition. Among the heavy metals tested, Pb(II) was the one that was adsorbed at the highest capacity at all C/N ratios. Also, with the purpose of understanding the mechanism of the process, Ca(II) and Mg(II) ions and carbohydrates released into the solution were also monitored and it was indicated that an ion exchange process is involved in the biosorption of heavy metals especially at high metal concentrations but the whole metal removal can not be explained by ion exchange.

Heavy metal contamination in water is a serious environmental and human health issue. Lead (Pb2+) and cadmium (Cd2+) are strictly regulated in wastewater effluent due to their high toxicity at low concentrations. Heavy metals are difficult to remove in conventional biological wastewater treatment because they are water soluble and non-biodegradable. Advanced treatment, such as tight membrane filtration and ion exchange, can be applied but they often require a high electrical energy input and a large amount of chemicals for pre- or post-treatment. Microbial electrolysis cells (MECs) can be used to treat wastewater while simultaneously recovering energy in the form of hydrogen gas. Additionally, MECs were proven to be effective for heavy metal removal. The commonly investigated removal mechanism for heavy metals in MECs is reduction at the cathode where heavy metal ions are reduced to metallic solids. The research presented in this thesis examined the effectiveness of cathodic reduction and other heavy metal removal mechanisms in MECs over a wide range of metal concentrations (10 μg/L-12 mg/L). Lab-scale MEC operation demonstrated successful removal of both Pb2+ and Cd2+ under different electric conditions, operation times, and initial metal concentrations. In addition to cathodic reduction, heavy metal removal in MECs was demonstrated through chemical precipitation at the cathode and electrochemical reduction and biosorption at the bioanode. The results of this research also confirmed the importance of microbial activity at the bioanode to efficiently drive the removal mechanisms in MECs. / Thesis / Master of Applied Science (MASc)

Maintaining a constant supply of clean drinking water is among the most pressing global challenges in our time. About one-third of the population is affected by the water scarcity and it can only get worse with climate change, rapid industrialization, and the population growth. Even though nearly 70 percent of the planet is covered by water, the consumable freshwater content is only 2.5 percent of it. Unfortunately, the accessible portion of it is only 1 percent. Even so, most of the freshwater bodies are choked with pollution. Considering the vast availability of saline water on the planet and the increasing wastewater generation, seawater desalination, and wastewater treatment and recycling seem to have the potential to address current water-related issues. Therefore, it is necessary to find efficient techniques for seawater desalination and wastewater treatment. The use of nanostructured materials for these applications is becoming a popular approach due to the unique chemical and physical properties they possess compared to bulk materials Solar energy is the cleanest and most abundant renewable natural resource available. Materials for solar photothermal energy conversion are highly sought after for their cost savings, clean environment, and broad utility in providing water heating and/or steam for many applications including domestic water heating and solar-driven desalination. Extensive research efforts have been made to develop efficient solar absorbers with characteristics such as low weight, low thermal conductivity, broad solar absorption and porosity to be able to float on water to provide more efficient and cost-effective solar steam generation systems. Metal NPs have been proposed to take advantage of the high efficiency of the photothermal energy conversion associated with surface plasmon resonance absorption. Nanostructured carbon-based materials such as graphene oxide, carbon nanotubes, carbonized biomass are also in use due to their excellent photothermal energy conversion ability over the range of the visible and near infra-red region of the electromagnetic spectrum. In this dissertation, five projects based on the utility of nanostructured materials for desalination, photocatalysis and water treatment will be discussed. The first three projects involve the fabrication and design of plasmonic and carbon-based photothermal materials for applications in solar steam generation, water desalination, and wastewater treatment. In the fourth project, a unique shape of ZnO nanostructure was synthesized for photodegradation of organic dyes in industrial wastewater. The final project demonstrates the shape-controlled synthesis of iron carbide nanostructures and composite materials of aminated graphene oxide for the removal of Cr(VI) from wastewater.

>Magister Scientiae - MSc / Environmental pollution is a major threat to all life, which needs to be addressed. Heavy metals are well-known environmental pollutants due to their toxicity and, persistence in the environment toxicity for living organisms and having a bioaccumulative nature. Environmentally, the most common hazardous heavy metals are: Cr, Ni, Cu, Zn, Cd, Pb, Hg, and As. Remediation using conventional physical and chemical methods is uneconomical and generates waste chemicals in large quantities. This study focuses on the extraction and determination of heavy metals (Nickel, Copper and Cobalt) by chelating Schiff base ligands of the type [O,N,N,O] with these metal ions. Two Schiff base ligands [N,N’-ethylenebis(salicylimine)] (Salen) and ligand [1,3-bis(salicylideneamino)-2-propanol] (Sal-DAP) were synthesized and characterised using FTIR, 1H and 13C NMR spectrometry and GC-MS techniques. Electrochemical detection of heavy metal ions in this work was achieved via ligand-metal complexation via two approaches. The in-situ method in which the metal and ligands were added to the electrochemical cell and stirred to allow complexation to occur and monitored by square wave voltammetry. While the ex-situ approach involved modifying the electrode surface by depositing a thin film of Schiff base on the electrode surface and immersed into a heavy metal solution to allow the complexation. Three modified GCE were used viz. Salen coated GCE, reduced graphene oxide-Salen coated GCE and a nafion-Salen coated GCE. The two approaches used for the electrochemical detection were successful and effective. The ex-situ approach was selected for the modification of the electrode surface since it demonstrated a higher capacity for heavy metal ion extraction.

Zur selektiven Entfernung von Schwermetallen aus industriellen Abwässern und Prozesslösungen der metallverarbeitenden Industrie werden synthetische metallkomplexierende funktionelle Polymere – mit Iminodiessigsäure (IDE) als aktive Spezies – seit Jahren erfolgreich zur Eliminierung störender Kationen eingesetzt. Ständig steigende Anforderungen an die Qualität der aufzubereitenden Wässer verlangen nach leistungsfähigen Selektivaustauschern, die den Erhalt der Eigenschaften von Prozesslösungen (z. B. pH-Wert, Salzgehalt) ermöglichen. Ziel der Untersuchungen war es, die strukturellen Matrixeinflüsse auf Beladung, Kapazität, Selektivität und Kinetik durch Variation der Matrix und der experimentellen Bedingungen näher zu untersuchen. Auf Basis einer monodispersen Erstsubstitution eines Styren-Divinylbenzen-Copolymerisates wurde durch gezielten Einbau funktioneller Gruppen – Synthese mit differenziertem Substitutionsgrad (TK/N 1-2) – versucht, systematisch den Einfluss des Substitutionsgrades der Matrix auf die Eigenschaften der Ionenaustauscher zu analysieren. Methodisch geordnet wurden zunächst die Versuche nach dem Batch- und anschließend nach dem Säulenverfahren durchgeführt und parallel dazu die Matrix charakterisiert. Das Verhalten der funktionellen Ankergruppen in Abhängigkeit vom pH-Wert der Lösung (pH-Bereich 2 - 5) wurde untersucht, der optimale Anreicherungs-pH-Wert, die maximale Beladung (Kapazität) und Selektivität der unterschiedlich substituierten Proben für die Schwermetall-Ionen Cu, Zn, Ni, Cd, Pb und Co ermittelt. Den statischen Versuchen folgten dynamische Untersuchungen im Säulenverfahren. Ziel war die Ermittlung des Durchbruchverhaltens und der Durchbruchkapazität bei optimalem pH-Wert in Abhängigkeit vom Substitutionsgrad gegenüber den Einzelmetallionen (Cu, Ni, Zn) und ausgewählten Paaren (Cu/Ni, Cu/Zn, Ni/Zn). Alle Ionenaustauscher wurden ausschließlich in der Ca-Form eingesetzt. / Selective ion exchange offers a good solution for cleaning many waste streams. The aim of this study was to develop selective ion exchange materials for effective and economical applications in waste water treatment. The investigation of chelate resins is based on iminodiacetate with different secondary substitution (degree of substitution TK/N 1 - 2, from aminoacetic acid to iminodiacetate as functional group). As comparison the weak acid resin Lewatit TP 207 was used. The research focused on the application of selective ion exchange resins for waste effluents to ascertain the feasibility of a selective ion exchange process employing chelating cation exchangers for heavy metal removal. The metals of interest were copper (Cu), zinc (Zn), nickel (Ni), cobalt (Co), lead (Pb) and cadmium (Cd) and the resins appointed in the Ca-form. The batch operation was conducted to determine the equilibrium data and the operating resin capacity, one of the most important properties. The main equilibrium parameter affecting the ion exchange was the pH value (array 2-5). The best accumulation pH value was obtained using pH 5 for all metals. The only exception was lead with pH 3. After determining the viability of the different resins with batch systems, this study has focused on the column mode experiments. They were generated for the selected resins in the continuous ion exchange process which are essentially reserved for industrial applications. A practical application of the breakthrough curves is the determination of the breakthrough time which helps to find the best operating conditions.

Effect of ionic strength on the efficiency of heavy metal removal and recovery from aqueous solutions via continuous mode polymer enhanced ultrafiltration (PEUF) method was examined. Application of PEUF to divalent ions of cadmium, nickel and zinc after their prior linking with polyethylenimine (PEI) results in complete removal of metal ions from single component aqueous solutions at high pHs. Binding ability and hence the extent of metal retention in high ionic strength medium exhibits differences between solutions containing single and multicomponent metal mixtures. In single component metal solutions, extent of retention decreases but binding order of metals remains unaffected both in low and high ionic strength medium. But, in binary component metal mixtures, with increase in ionic strength the binding order of metals changes. Fractional separation of Cd, Ni and Zn ions from equimolar binary and ternary mixtures of these metals and effect of ionic strength on fractional separation efficiency were investigated. Depending on pH and salt concentration and metal pairs present in the solution fractional separation can be achieved.Dynamic and static light scattering experiments were performed in order to gain insight about the conformational changes in PEI structure due to the pH and ionic strength alternations in solution. It was found that, the increase in ionic strength reduces the size of the macromolecules. A chemical equilibrium model was developed in order to estimate the apparent binding constants of metal-PEI complexes. Based on the data obtained from continuous and batch mode PEUF experiments apparent binding constants were estimated and compared to reveal the performance differences between these operational modes.

Utilizing biomass such as lignin, bamboo, soybean, corn stalk, rice husk, etc., as a carbon source to produce graphene-based nanomaterials has been reported recently. However, the potential of using such nanomaterials for engineering and environmental applications has not been realized. This dissertation investigates the use of graphene-based nanomaterials synthesized from using biomass as a carbon source for water remediation and cement-based composites’ (CBCs) property enhancement. The first chapter introduces graphene and graphene-based nanomaterials, as well as the synthesis and application of graphene-based nanomaterials for removing heavy metals in an aqueous solution and for property enhancement in CBCs. The experimental investigation on the pyrolytic synthesis of graphene-encapsulated iron nanoparticles from biochar (BC) as the carbon source (BC-G@Fe0) was covered in the second chapter. Two synthetic routes for producing BC-G@Fe0, i.e., impregnation-carbonization (route-I) and pyrolysis-impregnation-carbonization (route-II) processes, were investigated experimentally using different characterization techniques and heavy metal removal methods. The third chapter reports the experimental performances of the heavy metal removal of Pb2+, Cu2+, and Ag+ from an aqueous solution using BC-G@Fe0. The effectivenesses of various adsorption benchmarks, such as pH, kinetics, and isotherms were assessed. Additionally, the removal efficiency of BC-G@Fe0 was evaluated. BC-G@Fe0 sample made from route II, in particular, FeCl2-impregnated-BC with 15% wt% iron loading carbonized at 1000 ℃ for 1h showed promising Pb2+, Cu2+, and Ag+ removal capacities of 0.30, 1.58, and 1.91 mmol/g, respectively. The fourth chapter experimentally investigated the reinforcement effect of commercially sourced, industrial graphene nanoplates (IG) on the mechanical properties of CBCs. This investigation was based on a hypothesis that the uniform dispersion of IG would significantly enhance the compressive strength of CBC. The main outcome of this research was that, while the wet dispersion mixing process of IG into CBC did not consistently yield significant increases in the composite compressive strength, but the newly proposed dry dispersion process demonstrated significant increases (22%) in the composite compressive strength. Chapter Five investigated the synthesis of lignin-based graphene nanoplatelets (LG) and their application in CBC reinforcement. The main findings were that LG did not show impressive increases compared to IG, even when dry dispersion was introduced. This was attributed to LG's lack of effective surface area compared to IG. Finally, a general conclusion and outlook for the future of research into biomass-based graphene nanomaterials were discussed in chapter six.