Improved methods of providing safe drinking water are essential in an era in which demand for water is increasing but surface water supplies remain scarce. Desalination of brackish groundwater via membrane filtration with nanofiltration and reverse osmosis (NF/RO) offers a solution to this problem. As such, the overall motivation of this study was to improve mechanistic understanding of NF/RO. The first main aim was to evaluate the performance of a renewable energy membrane system previously tested with real groundwater and varying energy conditions. Given sufficient solar availability, the system reliably removed salts and inorganic contaminants, although solute retention varied with energy (and consequently pressure and flow) and pH, depending on dominant retention mechanisms. The second main aim was to assess the specific impact of pH on inorganic contaminant removal in a bench-scale filtration system. The speciation of boron, fluoride and nitrate was linked with ion retention as a function of pH, with results suggesting that there may be important mechanisms such as ion dehydration controlling transport in NF/RO, which would explain the high retention of fluoride when compared to nitrate. The third main aim was to determine the importance of ion hydration in determining transport using molecular dynamics simulations of monovalent anions transporting through an idealized pore. Simulations demonstrated that energy barriers of transport were strongly dependent on ion properties and pore size and were directly attributable to dehydration. The final aim was to experimentally verify molecular dynamics simulations by quantifying energy barriers for ion transport in NF membranes. Experimentally-determined energy barriers were also solute and membrane-specific, with fluoride having a higher barrier than other solutes. Comparison of results with expected dehydration trends and molecular dynamics corroborated that energy barriers in nanofiltration may be due to dehydration. The results obtained in this thesis provide new insight into NF/RO transport mechanisms, which may contribute to improvements in current technologies and predictive models.

This thesis presents a detailed investigation of the technical feasibility, challenges and performance issues associated with the direct-connection of a wind turbine to a membrane (wind-membrane) system for treating brackish water in remote communities. The direct-connection of these two technologies negates the reliance on energy storage in batteries, which are traditionally used, but result in reduced system efficiency and increased life-cycle costs. Furthermore, the lack of knowledge of the safe operating window in which transient operation of membrane systems is beneficial or tolerable can be addressed. The impact of wind speed fluctuations on the performance of the wind-membrane system (using a BW30-4040 membrane and feed waters of 2750 and 5500 mg/L NaCl) showed that the performance deteriorated most under fluctuations at low average wind speeds with high turbulence intensity and long periods of oscillation. Therefore, the main challenge of operating with renewable energy is not the size of the fluctuations, but the effect of the power switching off. Further examination of the impact of wind intermittency (over one hour intervals with intermittent periods from 0.5 – 3 min) showed that the increase in permeate concentration was highest at off-times < 60 s, highlighting the potential for improved performance using short-term energy buffering. The safe operating window and the key constraints to safe operation were determined for several membranes and feed water concentrations to establish the optimum operating strategy for the wind-membrane system. Supercapacitors were used to expand the safe operating window by providing energy during periods of intermittency and enhancing the power quality delivered to the membrane system by absorbing wind fluctuations. When tested over 24 hours using real wind speed data (average 6 m/s), the wind-membrane system produced 0.78 m3 of water with an average permeate concentration of 240 mg/L NaCl and average specific energy consumption (SEC) of 5.2 kWh/m3. With the addition of supercapacitor storage, the system performance improved significantly with 0.93 m3 of water produced with an average permeate concentration of 170 mg/L NaCl and SEC of 3.2 kWh/m3.

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Two secondary metabolites, geosmin (GSM) and 2-methylisoborneol (MIB) cause the majority of taste and odour (T/O) problems in surface waters. This research focused primarily on identifying biological sources, and both abiotic and biotic factors associated with the production and release of these compounds in three Wessex Water (WW) drinking water reservoirs. Historical water quality data, collected by WW over 9 - 10 years was interrogated. Planktonic filamentous cyanobacteria in Durleigh and Sutton Bingham reservoirs and benthic cyanobacteria in Nutscale were identified as the most likely key producers of GSM. Corroborating evidence in support of this came from the isolation of a dominant GSM-producing strain of the planktonic cyanobacterium Aphanizomenon gracile (Aph-ll01) from Durleigh reservoir and two GSM-producing cyanobacterial strains, tentatively identified as members of the genus Phormidium were isolated from benthic mats. Geosmin and/or MIB producing actinobacteria were also isolated from each site. Concentrations of MIB in all reservoirs typically fell below the human odour threshold concentration (OTC) of 15 ng L-1, however, GSM concentrations frequently exceeded the human OTC of 3.8 ng L-1. Regression tree analysis revealed that all three reservoirs were typically characterised by elevated GSM concentrations, during periods of low DIN:SRP (typically < 10 by mass). Hydrological conditions were also highlighted as important, particularly at Nutscale reservoir where increased reservoir capacity, coupled with longer residence times since 2007, may have promoted the development of benthic mats, potentially explaining the significant increase in GSM concentrations observed over the study period. Understanding the relative proportions of intra- and extracellular GSM can have implications for the removal of these compounds by water companies, as extracellular GSM is more difficult to remove. An evaluation was made of the solid-phase extraction (SPE) method coupled with gas chromatography-mass spectrometry (the protocol commonly used in the UK water industry) and an additional step was introduced enabling the quantification of intra- and extracellular GSM concentrations in microbial cultures. A full method validation confirmed that SPE offered a viable high throughput alternative to the solid-phase microextraction (SPME) method for measuring GSM, which is typically reported in the scientific literature. Investigations revealed that in vitro, Aph-ll01 produced GSM throughout its growth period in batch culture and retained the majority (64-95%) of its GSM intracellularly. The keystone grazer Daphnia pulex consumed Aph-ll01, releasing intracellular GSM from the filaments into the medium. Grazing was identified as an important route for elevating the ratio of intracellular: extracellular GSM in reservoirs. Although no empirical evidence was gained in support of virus-mediated GSM release, the potential role of both lytic and temperate cyanophage was discussed in relation to T/0 outbreaks.

The study presented in this thesis focuses on the critical evaluation of the on-going maintenance strategies of seawater desalination plants in the Sultanate of Oman. The unexpected failures of critical desalination plant equipment consequently escalate annual plant maintenance costs. Reverse Osmosis (RO) and Multistage Flash (MSF) seawater desalination plants are considered in this study. A comprehensive Failure Mode and Effect Analysis (FMEA) is conducted to identify the critical components/partsljunctions and the causes that contribute significantly to equipment failures of both RO and MSF plants. Failure in most cases leads to undesirable outcomes such as production losses and other catastrophic incidents. Through the FMEA analysis, common failure modes of differing severity for equipment in both RO and MSF desalination plants were examined Among other failure modes assessed in this study, scaling and fouling are very common in seawater desalination plants. Scaling and fouling are mainly caused by the accumulation of solid particles and algal blooms on the internal surfaces of critical plant equipment. The effects of scaling and fouling are explored by modelling the plant breakdown following these failure mode events. Historical failures and maintenance data are collected from both RO and MSF plants respectively. An exploratory statistical data analysis is conducted and the results are compared against the competing failure modes identified A graphical display of the RO and the MSF plant failures' inter-arrival times and maintenance data, as well as the sequence of downtime events are presented to give a better insight of the failures pattern. The inter-arrival times between failures tend to be shorter at some points on the graphs presented.

This study focuses on the interaction between geological heterogeneity and the reservoir processes which govern fluid flow in porous media. We have developed and tested a measure of heterogeneity which uses the coefficient of variation of the vorticity of the flow field to quantify the impact of geological uncertainty on oil recovery. We go on to explore the vorticity formulation of the equations of motion in porous media as a basis for understanding reservoir dynamics, particularly in the presence of heterogeneity and density differences. We derive dimensionless numbers to quantify the relative importance of viscosity and density differences, molecular diffusion, dispersion, and permeability heterogeneity on reservoir flow behaviour. This approach is used to develop an objective measure of the impact of permeability heterogeneity on reservoir performance, which we have compared with traditional heterogeneity indices and shown how it may be used for realistic 2D and 3D geological models. We have used our heterogeneity index, and the dimensionless numbers to analyse the impact of heterogeneity, buoyancy effects, mobility ratio and dispersion on breakthrough time and recovery for first contact miscible gas injection processes using geologically realistic reservoir models. We find that the new heterogeneity number, in conjunction with these dimensionless numbers, provides meaningful results for real non-linear reservoir flows. We present phase diagrams which show how reservoir performance depends on mobility ratio, viscous-gravity ratio, and heterogeneity. We have proposed that the phase diagram, and a comparison of these dimensionless numbers can be used to identify the key factors which control recovery, thus assisting the engineer in determining appropriate enhanced oil recovery (EOR) techniques, without resort to detailed flow simulation. This will enable a quick, and more robust, evaluation of the impact of geological uncertainty in the field.

In order to minimize the health risks to agricultural workers, and consumers of wastewater irrigated produce, the World Health Organisation has developed guidelines for the safe use of wastewater in agriculture. This study sought to test the appropriateness of the current Quantitative Microbial Risk Assessment model and the multiple-barrier approach advocated by the WHO guidelines. Over a one year period, over 500 produce and ready-to-eat salad samples were collected from fields, markets, and kitchens in Accra, Ghana, and over 300 soil and irrigation water samples were collected. All samples were analysed for E. coli, human adenovirus and norovirus using standard microbiological procedures. In addition, almost 700 participants including farmers, food vendors, and consumers were interviewed and observed to assess critical exposures associated with the transmission of faecal pathogens. The results showed that irrigation water was significantly more contaminated than farm soil, though exposure to soil was found to pose the key risk to farmers due to hand-to-mouth events. Over 80% of produce samples were found contaminated with E. coli, with street food salad being the most contaminated (4.23 Log E. coli/g), and that consumption of salads did not meet health standards. Risk factors identified for produce contamination included farm soil contamination, wastewater use for irrigation, poor hygiene, and operating with a hygiene permit. Awareness of the source of irrigation water was low, but despite the high awareness of health risk, consumers did not prioritize health indicators when buying produce from vendors. Similarly, farmers’ awareness of health risk did not influence their adoption of safer farm practices. The study recommends the promotion of interventions that would result in more direct benefits to producers and vendors, together with hygiene education and inspection, hygiene certification and enforcement of food safety byelaws in order to increase the uptake of the multi-barrier approach.

This study of the root-zone method of wastewater treatment describes the relationships between the type of substrate, i.e. soil or gravel, and the presence/absence of the common reed Phragmites australis, the removal of pollutants, i.e. pathogenic microorganisms, organic matter and the microbial community present within the system. Information concerning BOD (biochemical oxygen demand) and bacteria removal kinetics suggest that the root-zone method is more of a physico-chemical process than a biological process. Organic matter, suspended solids, and bacteria accumulate near the inlet section of the system. The concentration of ciliated protozoa is also higher near the inlet section. Results of this study tend to confirm that reed do not provide enough oxygen for nutrient removal. Removal rates of ammonia were poor in the full-scale systems and very poor in the microcosms. The ciliated protozoan community of various designs of the root-zone method of wastewater treatment is described. Data show that there is a significant difference between gravel beds and soil beds communities, and between planted soil bed and unplanted soil bed communities. The bacterivory of dominant ciliates is estimated by grazing experiments using hydroethidine-labelled Escherishia coli. These experiments confirm that ciliates remove E. coli from the wastewater, and may play an important role in bacteria removal. Comparison of data gathered from full-scale systems and microcosms were limited by the use of synthetic sewage instead of settled sewage, the potential immaturity of microcosm, and the microcosm design. However the full-scale systems the microcosms show the same trends regarding the release of free-living amoebae, and the BOD and bacteria removal kinetics. Gravel systems provide the best removal of suspended solids and free-living amoebae, whilst the planted soil systems provide the best BOD removal. The unplanted soil systems showed a poor removal of bacteria, free-living amoebae, BOD, and suspended solids. A hybrid system, i.e. a soil system followed by a gravel system, might be the optimal design.

This thesis reports the development of novel electrochemical methods applied for the quantification of important analytes in the field of water quality. Chapter 1 of this thesis focuses on the analytical methodologies used and the current requirements for low cost, environmental friendly and portable analytical tools into the field of water quality. In this chapter it is described how the analytical methodologies based on the use of screen-printed electrochemical sensors meets these requirements and why the development of such methodologies is the main purpose of this thesis. Chapter 2 overviews the relevant fundamental electrochemical concepts with which this thesis is concerned. Chapter 3 gives a synopsis of the electrode materials as well as screen-printing upon which this thesis is based upon with a detailed overview not only of the screen-printing process, but also its current applications within the field of electrochemistry with particular attention paid towards the development of novel screen-printed electrode sensors applied into the field of water quality. Chapter 4 describes the generic experimental methods used in this thesis. It gives details of the electrode materials, chemicals and real samples used in this thesis. Additionally it describes the screen-printing process on which the production of the in-door carbon based screen-printed sensors was based. Chapter 5 reports the first examples of using electrochemical sensors for the target analytes selenium (IV), antimony (III) phenol and chlorophenols within drinking water; simplification of these analytical protocols is demonstrated through the production of screen-printed sensors. Chapter 6 describes the development of screen-printed graphite sensors for the novel detection of dissolved phosphorus within environmental samples through the electrochemical adaption of a colorimetric protocol. The electroanalytical protocol for the detection of dissolved phosphorus, a key parameter of eutrophication, was independently verified with ion chromatography and inductively coupled - plasma atomic emission spectroscopy. Finally, Chapter 7 reports the first example of sensing cyclohexylamine and morpholine commonly used in industrial water as corrosion inhibitors for steam condensate treatment via indirect electrochemical protocol using screen-printed sensors. This is the first time that screen-printed sensors are applied into the detection of water treatment chemicals.

The impacts of climate change are of increasing interest to water resources managers since the changes in water resources affect many fields such as agriculture, ecosystem, water quality and quantity etc. The typical framework of climate change impact studies on water resources is based on the utilisation of climate models and hydrological models. This thesis aims to explore and fill in the knowledge gaps in this framework. The Thorverton catchment (606 sq. km) in Southwest England is chosen as the case study catchment. The studies are composed of two main parts: bias correction of regional climate model (RCM) and hydrological modelling under climate change. Firstly, I propose four new bias correction schemes. The first two studies are related to grouping criteria and the other two are related to the data uncertainty: 1) an improved bias correction scheme based on comparative precipitation characteristics; 2) the Optimal number of bias correction groups; 3) bias correction methods for RCM simulations considering the distributional parametric uncertainty underlying the observations; and 4) precipitation ensembles conforming to natural variations derived from Regional Climate Model using a new bias correction scheme. Secondly, a new parameterisation scheme for the nonstationary hydrological system is explored. The calibration is based on changing the model parameter with time by adapting the parameter. Only one parameter is selected for optimisation while the other parameters are fixed. It is concluded that the performance of the proposed method is better than the conventional method whose parameters are stationary. In addition, calibration of non-continuous time series has been explored. Currently there is no consensus method on how to calibrate this non-continuous time period. I have explored two sub-annual calibration schemes (serial and parallel) and recommended that the right choice is dependent on the purpose (e.g. interested in soil moisture or flow) of the model usage.