In drinking water treatment, there is growing interest in the application of natural cationic polymers that provide an alternate means to achieve enhanced coagulation. A review of the relevant literature concerning the coagulation mechanisms and action of polymer is presented with particular reference to the polymer character, such as polymer type, charge density and molecular weight. In addition, basic knowledge of a novel coagulant, a tannin-based modified polymer, is described. A full characterization of the tannin-based polymer (TBP) has been undertaken to provide an unambiguous description of the polymer, or monomer, structure. Some specialised newer analytical techniques in combination with several old classical techniques for polymer examination have been used to determine the chemical nature of the TBP, including its dissociation and precipitation behaviour, molecular weight, charge density, charge variability with pH, elemental content, functional group and chemical bonding, etc. The overall assessment of TBP indicated that it can be classified as a medium molecular weight polymer with a non-quaternized amine group and a charge density that varies with pH and time. The fundamental coagulation mechanisms and stoichiometry of suspended solid/dissolved organic matter with TBP have been investigated through laboratory experiments. Suspensions of kaolin clay and humic acid have been flocculated in a Gator jar using TBP as a sole primary coagulant. Using online analysis by Photometric Dispersion Analyzer (PDA), the relative floc size was indicated by a Flocculation Index (FI) during the coagulation process and the optimal concentration of coagulants was determined in overall terms by NPDOC, turbidity, colour, UV/Vis absorbance and Floc volume. Under given conditions the optimum dose of TBP corresponded to that required for maximum a 3 Flocculation Index (FI). The optimum dose of TBP was found to depend on the charge density of TBP and hence on the pH values of the solution. At neutral and acid condition, quantitative evidence of a stoichiometric relationship between TBP dosages with the concentrations of model impurity was illustrated. Complicating effects were present at higher pH values. The coagulation behaviour of TBP was generally in agreement with the coagulation mechanisms widely observed, and typical, of cationic polymers. It was evident that the coagulation performance and kinetics of TBP was also influenced by other factors, such as the velocity gradient, ageing of polyelectrolyte and reactor design. For comparative purposes, alum and a commonly used synthetic cationic polymer (polyDADMAC) were also assessed in this study as coagulants. The potential benefits to improving coagulation performance through the combination of TBP with alum as a dual primary coagulant have been investigated. Coagulation experiments using different model waters were carried out under conditions designed to optimize the maximization of flocculation. A full matrix of coagulation tests demonstrated that a unique optimal dosage of combined alum and cationic TBP exists at a given pH and component concentration. In this case, a significant reduction of alum with an improvement of coagulation efficiency was achieved. An approach to minimize the residual soluble TBP in treated waters and increase the floc settling by attaching the TBP to an inert solid (fine sand) has been attempted. The coagulation performance using this particle suspension (‘solid bound TBP’) as coagulant was found to be inferior with a high shear rate in accordance with the floc strength interpretations of TBP. Additional tests with raw waters were carried out to confirm the validity of the findings from the model water experiments using TBP and the alum/TBP combinations as primary coagulants. In the light of these studies, the relative importance of TBP’s chemical properties, especially molecular weight, charge density and solubility, as crucial 4 parameters of coagulation mechanism is discussed. Furthermore, approaches to improve flocculation performance with either partial replacement of inorganic coagulant or the combination with microsand are suggested and analysed.

Haloacetic acids (HAAs) are a group of disinfection by-products (DBPs) found in drinking water which are regulated in the USA but not yet in the EU. Epidemiology tests have shown that they may have carcinogenic and mutagenic effects on human beings. HAAs are produced during the disinfection process from the use of chlorination and they may persist during water distribution and finally reach the customers’ tap at concentrations of concern. The formation of HAAs arises from the reaction between precursor material – principally natural organic matter (NOM) – and chlorine, and the species and amount of HAAs produced depends on the nature of the NOM and the reaction conditions, such as the temperature, chlorine dose, pH, and the presence of bromide. NOM is a heterogeneous mixture of numerous organic molecules originating from aquagenic and pedogenic sources, and its content changes significantly with water source, and temporarily for a given water source. Due to the complex properties of NOM, no conclusive connections have been established between the properties of precursor materials and HAA formation (compound yield or individual species distribution). The thesis provides details of a new-developed fractionation method that has been used to characterise NOM obtained from natural waters. This method can effectively reveal the effect of seasonal variation and traditional treatment on NOM properties. The reactivity of each organic fraction in terms of HAA formation, seasonal variation and treatment efficiency has also been studied and is discussed in the thesis. Algae represent an important component of NOM, and as such algae species can also be responsible for the formation of HAAs. The thesis describes an extensive study of two prominent algae species in terms of their role in producing trihalomethane (THM) and HAA compounds, and their productivity in comparison with other organic precursors. Finally, the presence of bromide ion in source water leads to formation of brominated HAA species during chlorination which are believed to be of greater toxicological significance than non-brominated species. This thesis summarises an experimental investigation of the fundamental role of bromide in HAA formation and the relationship with initial NOM concentration and chlorine dose.

No description available.

This thesis focuses on the decay of chlorine in pipes of drinking water distribution networks due to wall and bulk demand. Accurate prediction of chlorine decay is important, as both chlorine concentrations which are too low and too high pose serious health risks, the former due to pathogen formation and the latter due to the formation of disinfection by-products. Water quality models used for the prediction of chlorine decay make use of parameterisations for the wall demand in the form of Sherwood number Sh correlations, which couple the wall mass flux to a Reynolds number Re, Schmidt number Sc and wall roughness. These correlations are subject to significant uncertainty, particularly for turbulent flows. A combined analytical and numerical approach is taken to study in detail the interaction between flow, turbulence and mass transport, with the aim of improving the understanding and accuracy of wall demand parameterisations for chlorine. Simulations of the chlorine decay in an axisymmetric pipe with hydraulically smooth walls were performed for Re = 104 to 106 and Sc = 1000 using Reynolds averaged conservation equations. These values are typical for chlorine transport in distribution networks. The simulations confirmed that the assumptions made in water quality models for chlorine wall demand are valid. Asymptotic solutions for high Sc solutes were developed which are applicable both to linear and nonlinear wall reactions. Results showed that the Sh correlation is independent of the reaction type. For rough walls, the two main wall demand parameterisations are mutually inconsistent: one is valid for low and the other for high wall demand coefficients only. Numerical simulation of flow and high Sc mass transport over a dtype rough surface at Re = 2.5×105 showed that the inconsistency between the two parameterisations was caused by the geometry. For low wall demand coefficients, the existence of roughness elements causes higher wall demand than for a smooth wall. However, at high wall demand coefficients the maximum wall demand achievable in the cavities was much smaller than for the crests. Hence, the effective surface area and therefore the wall demand became lower than for a smooth wall. A parameterisation was developed which reproduced the solute mass decay over the entire range of wall demand coefficients. Most of the solutions and parameterisations developed in this thesis are on the same level of description as water quality models. The findings of this thesis can be used as supportive evidence for the validity of assumptions made for water quality models, and to inform how processes should be modelled when these assumptions are violated.

Coal-fired utility plants are the largest anthropogenic source of mercury emiSSIOns. Mercury abatement legislation for these plants is in place in Canada and U.S.A. Several facilities are achieving mercury emission reductions by using commercial activated carbons. However, these carbons are expensive. The present project aimed to determine mercury capture efficiencies of some fly ashes and sorbents produced from scrap tyre rubber and sewage sludge, compared to the effectiveness of commercial active carbons. E.U. legislation limits the methods available for disposing of waste materials, using them to manufacture sorbents provides a cost-effective disposal solution. A novel bench scale fixed-bed sorbent test system was designed and built for evaluating mercury capture efficiencies of sorbents by exposing the samples to different gaseous atmospheres. Pre-treating selected sorbents with a gas stream containing either NOx or HCl gave information on the effect of acid gases. Thermal desorption experiments completed on spent sorbents provided indications regarding the adsorption process.

Sustainable treatment and disposal of mine waste is a serious environmental issue faced by the mining industry worldwide. Conventional methods of mine waste management predominantly involve indefinite retention in engineered tailings dams. The cost and liability of such surface storage facilities have increased significantly in recent years as an outcome of stringent environmental legislation and mine closure requirements gradually transforming the economics of mine waste disposal. Backfill methods, particularly cemented paste backfill, are increasingly perceived as sustainable, environmentally friendly and cost-effective alternatives as they put waste material to practical use. Controlled low-strength materials (CLSM) offer an effective and practical alternative to similar analogues - requiring minimal compaction, being self-levelling and excavatable in the future if necessary. The aim of this research was to develop and evaluate CLSM, previously un-tested at mines, in which novel utilisation of bioleach waste is maximised and Portland cement content minimised while satisfying performance requirements for classification as CLSM. Leachability of toxic substances was minimised through encapsulating CLSM within a coating of relatively inert CLSM. Formulation and optimisation of CLSM using statistical mixture design and response surface analysis has ensured proper understanding of component interactions and influence on mechanical strength with a minimum amount of experiments. Optimised CLSM formulations were tested for their mechanical, physical, micro-structural, mineralogical and chemical properties. Effects of encapsulation were determined by assessing chemical leaching. The work indicated that bioleach waste could be beneficially reformed as CLSM of appropriate compressive strength for application in groundwork as loadbearing materials. Porosity and hydraulic conductivity were correspondingly high. Leachability of arsenic, barium, chromium, lead and zinc was significant (levels varied depending on waste type). Encapsulation significantly reduced leachability indicating promising potential for implementation of this technology in the mining industry. The research presented in this thesis substantiated the need for, and potential of, sustainable novel alternative technologies such as CLSM to augment future waste management strategies in the mining industry via safe emplacement of solid bioleach waste in the sub-surface.

Polymer pipes have been used in water distribution networks in the UK since the 1950’s. Prior to this, the water system implemented in the Victorian era had served the country for over 100 years. In more recent times, the Victorian pipe system has undergone extensive renovation. Much of this has required the replacement of the old network using polymer pipes, which are expected to have a working life of 50-100 years. The value of using polymer water pipes has been studied for many decades. Specifically, research has used set conditions to determine overall pipe in-service lifetime. However, these set conditions often do not mirror reality; in-service pipes experience and must cope with, different loads, varying soil types and changeable chemical composition of water additives. As a result, water companies currently have no methodology to accurately determine the remaining in-service life of their polymer pipes. Currently, a water pipe is only replaced when it has failed, or is deemed to have reached the end of its in-service life. The ability to do small scale tests to obtain accurate service life information would greatly benefit the planning of works and the locating of sites where pipes are no longer fit for service. This in turn would improve cost effectiveness of pipe replacement works and importantly, maintain good customer-relations. This thesis aimed to review how different techniques could be utilised to predict the overall lifetime of polymer pipes under various, more realistic conditions, and to critically assess each for suitability and accuracy. To thoroughly investigate each of these techniques, tests were carried out on polyethylene pipes. Two different polyethylene grades currently used by Thames Water were tested: PE100 used mostly as the central main pipeline and PE80 used to connect the mains to the customer. Accelerated ageing was employed to artificially age pipe material for varying periods of time and under different stresses and temperatures. In order to quantify the incurred effects upon the polymer pipe, specific markers pertaining to polymer carbonyl content, crystallinity, density and susceptibility to thermal oxidation were subsequently investigated. Extrapolation methods were then used to identify suitable markers for determining remaining in-service lifetime of polymer pipe. The results presented in this thesis are of numerous chemical evaluations carried out on various aged polyethylene samples. The identification and subsequent use of appropriate chemical evaluation techniques allowed the generation of a method that ranked pipes in terms of replacement priority. Furthermore, these results indicate that polyethylene degrades via a different mechanism in Arkopal as compared with water; it appears that Arkopal promotes polymer chain disentanglement, not oxidation-related embrittlement.

Rising energy demand, up coming shortage of natural gas and oil and increasing awareness of the effect of global warming are the driving forces behind the development of new, highly efficient processes with integrated carbon capture and storage, using fuels with predicted long term availability. Gasification and especially fluidised bed gasification is seen as a promising near zero emissions route to utilise low value coal, waste and biomass for energy production via the integrated gasification combined cycle process (IGCC). The integration of a carbon capture and storage (CCS) technology into the design of IGCC plants changes the design framework for the gasification process as a pure stream of CO2 at the downstream end of the plant is now available. Therefore a novel oxy-fuel fluidised bed gasification process is proposed in which the gasifier is operated as part of an IGCC plant with pure O2 and recycled CO2. Steam is used to enhance the carbon conversion if necessary. A laboratory scale fluidised bed gasifier capable to operate up to 1000°C and 20 bar was used to study the implications of oxy-fuel firing on flue gas composition and operability of the gasifier. Maintaining a constant feed rate (1 - 6 g/min) a stable fuel gas composition was obtained for up to 30 min. Using a lignite as feedstock, carbon conversions higher than 95% and a fuel gas with a medium heating value were obtained under oxy-fuel conditions. With the addition of steam, the operating temperature could be reduced from 950°C to 850°C while maintaining the gasification performance. The decrease in carbon conversion with increasing pressure was investigated using experimental data from a wire mesh rector and optical char surface analysis. Strategies to optimize the gasification performance were developed for atmospheric and pressurised operations. Besides the lignite, two bituminous coals and different mixtures of biomass and lignite were tested for their use in an oxy-fuel fluidised bed gasifier. Analysis of the tar, H2S and NH3 content of the fuel gas provided information about the influence of operation conditions on the emissions of pollutants. The results show that oxy-fuel firing of a fluidised bed gasifier could be a promising route to avoid N2 dilution of the fuel gas and reduce the costs of integrating CCS technology. In order to assist further research, the results obtained in this study are used to derive design recommendations for large scale testing facilities.

Recovery of metal values from metal-containing wastes and low-grade ores is important in reducing consumption of metals from primary sources. The potential for ionic liquids (ILs) to be used to recover valuable constituents from waste by selectively dissolving target materials and then recovering them from the IL prior to regeneration and use of the IL in further extraction is demonstrated. A literature review shows the different types of ILs, their syntheses and applications as solvents in extraction procedures. The use of rapid synthesis methods (particularly, open- and closed-vessel microwave-assisted methods) to prepare ILs, of suitable purity for extracting value from wastes and low-grade ores, is described, with the benefits of more rapid synthesis, more efficient reagent conversion, higher purity product, reduced loss of starting materials and less use of volatile organic solvents, all of which contribute to a more environmentally-sound synthesis methodology. The solubilities of a range of metals and metal compounds, in the prepared ILs, show selective dissolution of metals can be achieved with the recovery of these metals, from IL solution also being reported. Testing the use of ILs as solvents to recover metals from alkali battery black mass waste and the mineral, malachite, as model systems, was studied, with recovery of zinc and manganese from the battery waste being achieved using HBetNTf2 and recovery of copper, from malachite, using protomimBr and protomimCl. Crystals have been isolated from solutions of Zn, ZnO, ZnS, CuO, CoCl2, Mn and MnO2 in protomimBr and their crystal structures determined, which show that complex formation between components of the IL and the metal ions provides the mechanism for the dissolution of metals from solids into the ILs. The complex formation can, however, involve either the nitrogen atom of the imidazolium-IL cation (for zinc, copper and manganese) or the IL halide anion (for cobalt).

No description available.