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With water scarcity as a pressing issue in Saudi Arabia and other Middle Eastern countries, the treatment and reuse of municipal wastewater is increasingly being used as an alternative water source to supplement country water needs. Standards are in place to ensure a safe treated wastewater quality, however they do not regulate pathogenic bacteria and emerging contaminants. Information is lacking on the levels of risk to public health associated with these factors, the efficiency of conventional treatment strategies in removing them, and on wastewater treatment in Saudi Arabia in general. In this study, a municipal wastewater treatment plant in Saudi Arabia is investigated to assess the efficiency of conventional treatment in meeting regulations and removing pathogens and emerging contaminants. The study found pathogenic bacterial genera, antibiotic resistance genes and antibiotic resistant bacteria, many of which were multi-resistant in plant discharges. It was found that although the treatments are able to meet traditional quality guidelines, there remains a risk from the discussed contaminants with wastewater reuse. A deeper understanding of this risk, and suggestions for more thorough guidelines and monitoring are needed.

Plants possess integrated signalling networks that mediate the responses to various environmental conditions. Mitogen-activated protein kinases (MAPKs) constitute a highly conserved family of enzymes in eukaryotes, and in plants MAPK-based signal transduction modules regulate a large number of physiological processes, including responses to environmental stresses and phytohormones. Regulated dephosphorylation of active MAPKs is a key component of the control of MAPK signalling cascades, and in mammals, members of the MAPK phosphatase (MKP) sub-class of dual-specificity tyrosine phosphatases have been recognized as key players for inactivating MAPKs. Five MKP homologues are found in Arabidopsis thaliana, but only limited information is available concerning their properties and biological roles. Based on initial data derived from my reverse genetics and protein interaction studies of these five potential MKPs, as well as gene function information in the literature, I chose to focus on two putative Arabidopsis MKPs, AtMKP2 and Indole-3-Butyric Acid-response 5 (IBR5). By using a combination of genetic and biochemical studies, I established that the previously uncharacterized MKP designated AtMKP2, participates in the regulation of cellular homeostasis in ozone-challenged tissue, and can influence the activation state of two MAPKs, MPK3 and MPK6. AtMKP2-suppressed plants displayed significantly prolonged MPK3 and MPK6 activation during ozone treatment, and recombinant AtMKP2 was able to dephosphorylate both phospho-MPK3 and phospho-MPK6 in vitro, providing direct evidence that AtMKP2 may target these oxidant-activated MAPKs. A mutation in IBR5, one of the five potential AtMKPs, was previously reported to confer reduced sensitivity to auxin and ABA in Arabidopsis. My protein interaction studies demonstrated that IBR5 and MPK12 are physically coupled and that the C-terminus of MPK12 is essential for its interaction with IBR5. In vitro dephosphorylation assays indicated that recombinant phosphoMPK12 is efficiently dephosphorylated by IBR5. In transgenic plants with reduced expression of the MPK12 gene, root growth is hypersensitive to exogenous auxins, consistent with the lower auxin sensitivity reported for ibr5 mutants. Taken together, my data demonstrate for the first time that both AtMKP2 and IBR5 are bona fide Arabidopsis MAPK phosphatases and that they serve as important regulators of oxidative stress and auxin signalling, respectively, in Arabidopsis.

Pretreatment of waste activated sludge (WAS) and the subsequent near-critical water gasification (NCWG) is a potential avenue to convert WAS into value added products. Part one of the research investigated thermal and thermochemical pretreatments. No difference was observed in the percentage of sludge liquefied beyond 10min between 200°C to 300°C. It was found that pretreated activated sludge supernatant (PASS) doubled the gas yield compared to untreated sludge when gasified. The order of effectiveness for sludge treatment was thermo-alkali > thermal > thermo-acid for hydrogen production in NCWG. Part two investigated NCWG parameters to identify optimal conditions. High gasification yields were obtained using a commercial catalyst (Raney nickel), with hydrogen content of 65-75% of the gas phase products. Thermo-alkali treated PASS was found to perform well at subcritical temperatures with 25% higher yields than thermally treated PASS. Increased catalyst loading had little additional effect on gas yields above 0.075g.

Pretreatment of waste activated sludge (WAS) and the subsequent near-critical water gasification (NCWG) is a potential avenue to convert WAS into value added products. Part one of the research investigated thermal and thermochemical pretreatments. No difference was observed in the percentage of sludge liquefied beyond 10min between 200°C to 300°C. It was found that pretreated activated sludge supernatant (PASS) doubled the gas yield compared to untreated sludge when gasified. The order of effectiveness for sludge treatment was thermo-alkali > thermal > thermo-acid for hydrogen production in NCWG. Part two investigated NCWG parameters to identify optimal conditions. High gasification yields were obtained using a commercial catalyst (Raney nickel), with hydrogen content of 65-75% of the gas phase products. Thermo-alkali treated PASS was found to perform well at subcritical temperatures with 25% higher yields than thermally treated PASS. Increased catalyst loading had little additional effect on gas yields above 0.075g.

Granular Activated Carbon (GAC) is used in packed beds to treat trace quantities of icropollutants. Many years of research and industrial use has ensured that it is highly effective as a water treatment process. However, GAC is expensive and economic considerations mean it has to be recovered and re-used Powdered Activated Carbon (PAC; is a cheaper alternative but the particle size range means it is unsuitable for packed bed applications. This thesis describes a novel method for utilising PAC to treat micropollutants. By contacting carbon paracles with air bubbles, under conditions o.lrotational shear and a binding agent, oleyl alcohol, carbon-coated air bubbles form which remain stable while agitated byflowing water. A stabilised air bubble can be visualised as a phere with an impervious core (the air bubble), surrounded by a thin layer of porous matehal (PAC). Theory dictates that all these stabilised air bubbles can be moved counter-currently to a contaminated stream, higher throughputs than conventional packed beds are possible. Several aspects of this process are investigated. Bubble generation is critical and so the literature was reviewed to explain the mechanisms involved Practical use was made of this knowledge in designing a larger bubble generator. Transferring the coated-bubbles to a contacting column was difficult. Problems associated with the various methods employed are described and recommendations are made for improvement. The contacting column was used to assess the stability and adsorptive capacity of the bubbles. The possibility of counter-current flow using stabilised air bubbles was also evaluated and found to be incompatible with the current column design. The stabilised bubbles collected in the column resembled an inverted fluidised bed. Experiments were performed to test Richardson and Zaki's hydrodynamic laws for conventional fluidised beds were applicable to inverted beds. The adsorptive capacity of the bubbles was assessed by dosing the water with trace levels of phenol and p-chlorophenol. Samples taken from before and after the fluidised bed were analysed and compared. The results were inconclusive, although the concentration profile produced indicated that flow through the bubble bed was piston-flow.

Iodine number, BET surface area, taste and odour compound isotherms, and trace capacity number tests were used to rank five different granular activated carbons according to thermodynamic adsorption performance. These tests were compared to expected activated carbon service life and loading results of rapid small-scale column tests (RSSCTs) run with water from two lake sources spiked with geosmin and 2-methylisoborneol (MIB). Trace capacity number, used to specifically identify high adsorption energy sites on activated carbon, was hypothesized to be correlated to geosmin/MIB breakthrough and loading performance of different activated carbons. This study found no such clear correlation. However, when only bituminous coal activated carbons were considered, correlations to MIB breakthrough were strengthened. Natural organic matter (NOM) adversely affected adsorption, resulting in decreased RSSCT throughput to breakthrough in surface water with higher total organic carbon (TOC). Methods for improving characterization tests and RSSCTs when NOM is present are discussed.

Biogas, produced from anaerobic digestion of cattle manure, is an attractive alternative energy source as it is rich in methane. However, it is necessary to remove hydrogen sulfide from the biogas before it can be used in engines for electricity generation. Currently, large scale biogas systems employ physical adsorbing solvents to upgrade and purify biogas which is not economically feasible for small scale biogas systems. Activated carbon made from anaerobic digestate proves to be an effective adsorbent of hydrogen sulfide because it has minimal operating costs and essentially zero raw material cost. A model is developed to predict the adsorption capacity, carbon bed life span, and breakthrough time for this carbon material. By analyzing the reaction constant, adsorption constant, and degradation constant, adsorption behavior under different operating conditions were studied. The model can be scaled-up to model adsorption for biogas loading rates for small to large scale cattle farms.