The remediation of industrial wastewater is highly challenging, difficult task, and demands highly efficient technologies. Electrochemical and ozonation technologies are among the most efficient methods in treating the industrial wastewater. The electrochemical generation of ozone can provide very high concentrations of the reagent in both the gas phase and solution. The aim of the research reported in this thesis was to develop durable and highly efficient Ni/Sb – SnO2 anodes to generate ozone and to investigate their efficiency in treating industrial wastewater. Different anode sizes were studied: 0.64 cm2, 6.25 cm2 and 24 cm2 using Ti mesh as substrate. With respect to the 0.64 cm2 anodes, replacing Sb and Ni chlorides with their respective oxides and adding Au or Pb had little or no effect upon the anodes electrochemical properties. The research showed that all 0.64 cm2 anodes were porous with dimensionalities < 2. However, the presence of the Au in the precursors reduced the ozone current efficiency. The 0.64 cm2 anodes achieved ozone current efficiencies of ca. 30% at cell voltages of 2.7 V routinely. Using 6.25 cm2 anodes prepared with the Sb and Ni oxides in the precursor solution and annealed at 550 oC gave electrodes which were durable for more than 200 h operation at a current density of 100 mA cm-2 (corresponding to cell voltages of ca. 3 V) in 1 M HClO4. These current densities and service life are the highest reported for Ni/Sb – SnO2 anodes. A service life of more than 600 h was achieved in a later investigation. The 6.25 cm2 anodes achieved current efficiencies up to 38%, with 25 -30% routinely achievable. The presence of Ni is crucial for ozone generation with optimum Ni content (in the precursor solution) of ca. 1.04 at % Ni. The optimum annealing temperature was 460 oC. In terms of the 24 cm2 anodes, they were employed to prepare membrane electrode assemblies (MEA’s) for ozone generation from deionised (Millipore) water. MEA’s with air breathing cathodes suffered from flooding of the cathode pores, resulting in limited current densities. MEA’s with hydrogen – evolving cathodes did not suffer from flooding or low current densities. Overall, current efficiency of ca. 36 % at cell voltage of 1.6 V (40 mA cm-2) with Millipore water as anolyte was obtained using MEA’s with air breathing Preface vii cathodes; corresponding to a power consumption of 16.7 kWh (kg O3)-1 which is the lowest reported for electrochemical ozone generation of any description, MEA’s with H2 cathodes achieved a current efficiency of 33% at ca. 25 mA cm-2 and a cell voltage of 2.5 V, corresponding to ca. 25 kWh (kg O3)-1. The 0.64 cm2 anodes were used to decolourise solutions containing : Reactive Blue 50 (RB50), Naphthol Green B (NGB) and Congo Red (CR) dyes. The operational conditions of the decolourisation process were investigated and the optimum conditions were: 3 g dm-3 Na2CO3 as electrolyte, 50 mA cm-2 and 200 mg dm-3 dye in Millipore water. RB50 solutions could be decolourised completely within 20 min, with 90% of the COD removal after 60 min, NGB and CR proved more refractory. Indirect oxidation mediated by OH radicals was the main decolourisation mechanism at the Ni/Sb – SnO2 anodes. Ozonation, UV254 irradiation and O3/UV were used to decolourise the dye solutions for comparison with electrochemical decolourisation at the Ni/Sb – SnO2 anodes. Ozone was generated by MEA – based electrochemical cells and ozonation occurred in a bubble column reactor (BCR). The O3/UV combination was the most efficient, achieving 100 % decolourisation of RB50 and NGB solutions within 20 and 35 min, respectively, with 33% and 64% COD removal after 60 min.

Increased treatment capability is required on small sewage treatment works to meet ammonium consents that are tightening to effluent concentrations of below 5 mg[Ammonical nitrogen (mg/L)] and in some cases as low as 0.5mg[Ammonical nitrogen (mg/L)] Optimisation of existing assets is preferential over the addition or expansion of the works to minimise associated costs and energy usage. Many small works in the UK currently employ horizontal sub-surface flow constructed wetlands (HSSF CWs) that have restricted capability to nitrify due to limited oxygen transfer and as such artificial aeration has been proposed as a potential upgrade technology. To assess the performance of the technology, full- scale sites were monitored in terms of ammonium and solids removal and hydraulic characterisation over 3 years. Supporting pilot studies were carried out to assess the effect of aeration on the planted vegetation and to determine optimum transfer efficiencies. Cont/d.

On-site sanitation solutions are an economically feasible method of improving sanitation, and for reducing the burden of diarrhoeal diseases, in low- and middle-income countries. However, suitable faecal sludge management (FSM) solutions are severely lacking in these countries. Black solider fly larvae (BSFL) efficiently reduce food-waste and animal manure, and produce valuable prepupae, high in protein and fat, supporting investigation into a novel BSFL FSM method. The aim of this study was to determine the feasibility of using BSFL as a FSM method, by evaluating their faecal matter reduction (FMR), and prepupal production capacity, when reared on FS under different conditions. Black soldier fly larvae were found to develop successfully on fresh human faeces, effectively reducing waste and converting it to prepupal biomass. A survey of pit latrines in South Africa found physical and chemical characteristics of faecal sludge (FS) similar to previous studies in countries requiring novel FSM methods, with characteristics falling within a range suitable for BSFL development. Key rearing parameters, moisture content, feeding rate, and larval density, significantly influence FMR and prepupal production of BSFL reared on “top layer” homogenised FS. Black soldier fly larvae were found to effectively reduce FS from a variety of depths, each with a range of physical and chemical characteristics, and produce prepupae with nutritious values comparable to previous research, excepting crude fats. The study also demonstrated that reported cleaning chemicals in FS do not affect BSFL mortality at manufacturer recommended, or user reported concentrations. It is proposed that the use of a novel BSFL FSM method is an economically feasible method of improving sanitation in low- and middle-income countries, and may help reduce the burden of diarrhoeal diseases.

Water pollution is a major global issue which poses a serious threat to human health as well as the aquatic environment. In particular, dissolved heavy metal species and persistent organic pollutants (POPs) have been regarded as major problems due to their high toxicity and non-biodegradability. Adsorbents and membrane filtration are the most widely used technologies for the treatment of contaminated waste water, however the high cost and environmental implications of these technologies have encouraged a paradigm shift to the use of photocatalytic processes for wastewater treatment. In this work, an innovative photoelectrochemical process for simultaneous removal of heavy metal ions and POPs from wastewater was developed and demonstrated using a photoelectrochemical cell (PEC) with a W03 photoanode under sunlight irradiation. Synthetic wastewater samples containing 0.5 M of NaCI, 10 ppm of methylene blue (MB, organic pollutant), 500 ppm of CuCh or 500 ppm NiCh were tested as the first examples for demonstration of the principle, device and process. The results showed that upon irradiation of simulated sunlight on the photoanode, metal ions (Cu2+ and Ni2+) can be recovered as metals at the cathode. MB was simultaneously decomposed at the photoanode without using any additional chemicals. The cell voltage required for this dual purpose process was as much as 71 % or 57 % lower than that required for conventional electrodeposition of Cu or Ni respectively with an inert anode. Current efficiency for electrodeposition in the PEC could be adjusted close to 100 % depending on applied cell voltage, minimising charge loss for H2 evolution. Meanwhile, as a potential photocatalyst, CNTs/W03 hybrids were successfully synthesised by a surfactant aided sol-gel method and tested for their photocatalytic performance. It was found that the addition of CNTs to W03 by either hybridisation or mechanical mixing caused a significant drop of both photocurrent and photovoltage of W03, presumably due to the interfacial electronic structure between W03 and CNTs.

To improve our understanding into the key parameters controlling and regulating the microbial groups involved in the anaerobic digestion (AD) process, particularly over multiple changes in operational conditions, triplicate lab-scale digesters fed with sewage sludge were exposed to single and multiple changes in organic loading rate (OLR) using either glycerol waste (a by-product of biodiesel manufacture), or Fats oils and greace (FOG waste) collected from a restaurant grease trap. For the multiple changes in OLR, digesters were either exposed to repeated addition of glycerol waste or repeated addition of both glycerol waste and FOG waste. In all conditions tested, physicochemical variables including volatile fatty acids (VFA), alkalinity, pH, biogas production and composition were analysed. Molecular fingerprint techniques including lipid and ether lipid analysis and 454-pyrosequencing of 16S rRNA genes were used to characterise the microbial communities. These techniques were chosen as they complement each other providing information on the microbial biomass and in-depth phylogenetic analysis of the microbial community, respectively. The key question addressed here was how feedstock composition and variation in OLR would affect the microbial community structure and dynamics and relate this to the performance of the digesters in terms of methane production over a long-term period (> 120 days). Multiple changes in OLR with the same feedstock resulted in faster recovery of methane production (8-10 days faster) compared to digesters exposed to single changes in OLR. This finding was associated specifically with a higher proportion of Clostridia Incertae Sedis XV (closely related to Cloacibacillus genus (83% similarity), family Synergistaceae) in the pre- exposed digesters. It is speculated that members related to Clostridia Incertae Sedis XV play an important role in the syntrophic interactions with the methanogens. Analysis of the VFA profiles supported this by showing that the higher relative abundance of Cloacibacillus was related to higher acetic acid concentrations. The pyrosequencing analysis further showed that community evenness was correlated with the best biogas methane content and shifts in specific bacterial groups was clearly correlated with digester performance. Overall the findings of this PhD provide new insights into the relationships between microbial community structure and digester performance. It also provides new-evidence based knowledge on how molecular microbiological tools can be used in the future to optimise and manage AD plants.

Pharmaceuticals, personal care products and their metabolites are contiuously entering the environment through many route, especially from the effluent of sewage treatment plants. The aim of this work was to examine the fate and removal of pharmaceuticals during sewage treatment, and establish ways in which current sewage treatment technologies could be optimised to improve removal. Based on an analysis of pharmaceutical usage and environmental effects, four compounds were selected for further study (triclosan, tetracycline, carbamazepine, and caffeine). Reliable analytical methods were developed, using HPLC-UV, to detect these compounds in sewage samples. The amounts of removal of the four compounds were quantified using laboratory sorption and biodegradation tests. Both tetracycline and triclosan were shown to be readily biodegradable, and to sorb strongly to biomass, although sorption occurred at different rates. Caffeine degraded rapidly, but did not sorb to biomass, whilst carbamazepine did not sorb or biodegrade. Grab samples were taken before and after every major process unit at four sewage treatment plants (STPs). Although tetracycline was not detected in any samples, triclosan was measured at concentrations up to 5115 ng 1-1, caffeine was measured at concentrations up to 82,300 ng1-1, and carbamazepine was measured at concentrations up to 1461 ng 1-1. This is the first time carbamazepine and caffeine concentrations have been reported in UK sewage. The grab samples showed that a wide range of pharmaceutical effluent concentrations can be enough to cause immediate harm (i.e. death) to aquatic organisms. However, there is insufficient infomation to determine whether exposure to these low concentrations, typically around PNEC levels, may have an effect over a long period of time. Further composite sampling conducted at one STP generated data, modelled using Toxchem+, which demonstrated how variations in a wide range of parameters were correlated with the removal of pharmaceuticals. These showed that whilst sludge age may be the most important parameter, pH, temperature, hydraulic retention time, and chemical oxygen demand could have a critical effect on the removal of pharmaceuticals. Several ways of optimising sewage treatment plants have been proposed, including pH adjustments and longer HRTs to enhance sorption, as well as a novel adaptation to activated sludge tanks incorporating two IFAS type bioreactors to enhance biodegradation. The effects of plant operating events, such as aeration failures, were also investigated. These showed that a typical length of aeration loss (four hours) could result in reduced pharmaceutical removal (through decreases in both sorption and biodegradation) for up to twelve hours. Overall, this work has shown that it may be possible to adapt current sewage treatment technology to improve removal of pharmaceuticals which sorb or biodegrade readily. With further research, these adaptations could become a viable alternatice to tertiary treatment technologies such as ozonation, granular activated carbon, or chlorine dioxide.

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The most significant operational cost in a treatment plant is related to the dewatering and disposal of sludge. Coagulation is the most common process in water and wastewater treatment plants and produces sludge as a by-product. The influence of different important coagulation factors has been investigated in this study to assess corresponding impacts on sludge dewaterability. The CST (Capillary Suction Time) apparatus was used as the main tool to measure sludge dewaterability, followed by the turbidimeter, the particle size analyzer, and the SRF (Specific Resistance to Filtration) as a comparison and also for verification. The CST results indicate that the magnetic stirrer produces the lowest CST values, while the other four shapes of mixers produced similar but higher trends. Rapid mixing velocity and rapid mixing time have varying degrees of influence on the CST value and hence on sludge dewaterability. Rapid mixing velocity seems to have a more significant impact on the CST value than rapid mixing time. The coagulants aluminium sulphate and ferric chloride have similar effects on CST values. The performance of aluminium sulphate and Moringa oleifera are affected by temperature, but the performance of coagulant ferric chloride was hardly impacted. Different synthetic water samples do not significantly affect the CST value. The turbidity result correlates well with the CST value. Observations using the particle size analyzer indicate that, in general, the floc size has a direct correlation with the CST value. The larger the floc size, the lower the CST value. Floc size distribution results show that synthetic raw water has a narrow particle size distribution; synthetic domestic wastewater produced a wider distribution than synthetic raw water. The comparison between the CST and SRF results indicates that the CST and SRF are well correlated if different methods (rapid mixing velocity and rapid mixing time) are used, but uncorrelated if different materials (mixers, coagulants, temperature and water samples) are used. Based on the results of this investigation, the working of the magnetic stirrer should be investigated further in order to implement this mixer in the treatment process. The magnetic stirrer does not only produce the lowest CST value but is also the only mixer that produces different CST values significantly. This is because it produces the optimum G value for sludge formation. The implementation of rapid mixing velocity is more important than rapid mixing time in the operation of a treatment plant. Due to its correlation with temperature, ferric chloride is the most appropriate coagulant among the three types of coagulants used in the treatment plant to reduce sludge dewaterability. Based on the results using different water samples, all of these factors can be used for both inorganic and organic water and wastewater to produce lower sludge dewaterability.

No description available.