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The extensive use of nanoparticles (NPs) has started receiving increased attention because of the knowledge gaps regarding their fate in the environment and the possible impact on the environment and human health. The production of silver nanoparticles (AgNPs) and titanium dioxide nanoparticles (TiO2-NPs) is increasing and it is expected that, due to their great number of applications, their concentration in waste streams will increase in the future. The presence of NPs in waste streams may affect the treatment process (e.g., composting) and, if they are not successfully removed from the waste streams, their presence in the treated waste (e.g., compost) may present an environmental risk. Composting of the biodegradable fractions of municipal solid waste (MSW) is a widely used waste management practice, mainly because it is a cost-effective treatment technology and the final product (i.e., compost) presents several benefits to the environment, particularly as a soil conditioner. The overall aim of this thesis is to assess the effect of Ag-TiO2NPs and AgNPs that may be present in the biodegradable fractions of municipal solid waste on composting and subsequent soil application of compost. For that purpose in-vessel composting of artificial municipal solid waste contaminated with commercial nanoparticles was investigated at laboratory scale, simulating a range of relevant concentration levels. Subsequently, the fate of NPs present in mature compost use as a top-layer soil conditioner was investigated using a column approach at laboratory scale. The toxicity effect of NPs present mature compost on plant growth was further investigated. The impact of NPs during composting was assessed by monitoring the temporal dynamics of organic matter (OM) using Excitation Emission Matrix (EEM) fluorescence spectroscopy. The fate of NPs following application of contaminated mature compost as a top-soil conditioner and potential release to groundwater was investigated using a column leaching experiment while the phytotoxicity of mature compost contaminated with NPs was assessed using a seed germination bioassay. Finally, to investigate further possible environmental impacts due to the application of mature compost contaminated with NPs to soils, a Life Cycle Assessment (LCA) was conducted. The impact of commercial Ag-TiO2 NPs and AgNPs on the in-vessel composting of biodegradable municipal solid waste was investigated over 21 days, using initial concentrations of 0, 5, 10, 20 and 50 mg Ag / kg of OM. Microbial activity was inhibited in the biodegradable waste reactors using 2% NaN3 to evaluate abiotic losses. Physicochemical parameters such as pH, ash content, weight loss, and the formation of humic substances (HS) were determined after 0, 4, 7, 14 and 21 days of composting and after a maturation phase. The results indicated that the presence of 2% NaN3 in biodegradable MSW inhibited effectively the microbial activity during the first week of composting. The microbial population was activated during the second week of composting but the decomposition rate was so low that did not result in the formation of humic substances (HS) following 21 days of composting when 2% NaN3 was used. Both treatments, using Ag-TiO2-NPs and AgNPs, did not show any inhibition of the decomposition process for all the tested concentrations and EEM peaks shifted towards the HS region during in-vessel composting. Higher inorganic carbon removal resulted from NP-contaminated compost with higher NP concentrations. This may indicate that the formation of humins was higher for non-contaminated compost and decreased as the NP concentration in waste increased. The shift of the peaks towards the HS region during composting for all the treatments suggested that NPs did not have an effect on humification and therefore on compost stability. The leaching properties of the NP-contaminated compost were investigated using a column leaching test. Five samples of leachate, of 50 mL each, were collected. The highest concentrations of HS were observed in the first two leaching samples. The leaching results suggested that only a low percentage of the total NPs (in weight) in compost, up to ca. 5% for Ag and up to ca. 15% for Ti, leached out from the columns, which was assumed the amount that potentially could leach to the environment. These results suggested that NPs will mainly accumulate in soils’ top layers following application of compost contaminated with NP. The phytotoxicity of NP-contaminated compost was assessed using a seed germination bioassay and the germination index was then calculated. The results indicated that the NP-contaminated compost did not present any toxic effects to cress germination. The possible environmental impacts due to the NP-contaminated compost application to soils were investigated by conducting a comparative LCA study. The LCA study indicated that the effects of NP-contaminated compost to human health and ecosystems endpoint categories increased due to the presence of NPs. The risks are associated with terrestrial ecotoxicity and human toxicity midpoint categories and are mainly attributed to the accumulation of Ag to soils.

The eradication of global poverty is central to the concept of sustainable development. In developing nations the lack of essential infrastructure and technologies, which are necessary to provide people with their basic human rights, offer a central role for the engineer. These needs are increasing as new global threats, such as the pressures caused by population growth, the harmful effects of climate change or the increasing frequency and intensity of disasters, have only heightened the difficulties which threaten the world’s poorest nations. Decades of development practice has allowed the profession of engineering to engage with many of these global issues. Over this period the engineering approaches, particularly in Sub-Saharan Africa, have gradually moved from high impact and short-term disasters relief interventions to long-term endogenous solutions. This change in overall aims has raised awareness of the sustainability of current engineering interventions. Many of the results are not entirely positive. For example, in water supply engineering, certain national estimates of sustainability of hand-pump wells for countries in Sub-Saharan Africa can range from 30- 80%. The role that the engineer could provide in addressing the concerns of poorer nations has not yet been fully realised. This thesis evaluates the current engineering models of service delivery that are used by Non-Governmental Organisations (NGOs) in developing nations. These models of technology transfer are supposed to provide communities in developing nations with a sustainable access to technologies that can provide for their basic rights. It is from within these models that engineers, who in many cases are foreign to the socio-cultural systems of the host nation, perform their engineering function and activities. The field research focuses on a case study of water supply engineering projects that have been carried out within the rural District of Tonkolili in Sierra Leone. To address the complex socio-cultural and socio-technical systems in Sierra Leone this field research adopted a combination of qualitative and quantitative assessment methods. This involved investigating both the technical and social sustainability issues found in Sierra Leone. The research visits were both inductive and deductive. They covered 150 spatially distributed villages in the rural district of Tonkolili. The methodologies used as part of this study involved; interviews, focus group discussions, community mapping, transect walks and technical observations, to provide a broad understanding of the sustainability issues affecting engineering projects. A total of 309 hand-pump wells, pulley systems and borehole water points were evaluated as part of the research. The study investigated the technical, socio-technical and socio-cultural consequences of these technology transfers - as well as the current condition of the social support mechanisms that are designed to sustain the water schemes. The results of the technical observations demonstrated that there are a diverse range of failures, from extreme to moderate, that have occurred at many of the water points. During the field visits observations of water supply solutions found to have urgent technical problems were frequent occurrences. The majority of the water points (96%) were found to have at least one technical failing that required immediate maintenance or further engineering assistance. The social research also indicated that, of the 4,700 individual categories monitored, a significant proportion (49%) were technical problems that were within the capacities of village members to address locally. These technical problems found to be ignored by the host communities. The NGO trained support mechanisms, which were designed to provide sustainability to the systems, for innumerable reasons, were unable to operate effectively. The breakdown in function of these supporting systems highlighted the serious weakness of current service delivery models in their ability to achieve sustainable engineering solutions. Investigating the relationship between the households and the water points suggests that the communities are not acting rationally towards their water sources. The majority of households were found to have unsafe water practices regardless of the provision of their improved sources. For example, many households that had access to improved water sources were found to still use their unimproved sources (30%). Many more (53%) complemented, and mixed, their unimproved water with water from their improved wells. This attitude towards safe water suggested that there were fundamentally flawed assumptions about how communities would receive and interact with their technologies. These household decisions, and the associated technical concerns, are directly attributable to the actions of the engineers from the project implementing development agencies. The results of these misinterpretations have undermined the long term sustainability of water supplies in Sierra Leone. The research indicated that to address sustainability the engineering profession is at a crossroads in determining its future in international development. Engineers have the capacity to acknowledge that the complexities of development limit their efficacy and therefore seek support from other professions. This would narrow the scope of their interventions. They are also capable of actively seeking the opposite; to broaden the scope as well as the responsibilities, expectations and skills of the engineers. It is this decision that will define the role of the engineer in international development.

Growing concerns regarding the impact of fossil fuel use upon the environment and the cost of production have led to a growth in the interest of obtaining energy from biomass. 1st and 2nd generation biomass types, however, are often criticised for their high energy requirements and environmental impacts. Algal biomass is considered a 3rd generation biomass which does not require arable land for cultivation, typically has a high productivity and can be converted to a wide variety of energy carriers. Despite research on the concept of producing energy from algal biomass dating back to the 1960s there has been limited commercial development and the environmental advantages are still in doubt. This thesis investigated the potential of algal biomass as a source of bioenergy feedstock by considering the cultivation and processing of localised species of algae and applying life cycle assessment (LCA) methodology to algal biofuel production systems. Experiments were conducted to examine the productivity of a wild algal species in wastewater and the potential recoverable bioenergy yields. The LCA studies drew together data from external studies, commercial databases, industrial reports and experimental work to assess the environmental impacts and the energy balance for each system considered. The thesis investigated the generation of biofuel from both freshwater algal biomass and marine algal biomass. For both cases, the current state of research was examined and the gaps determined. Existing studies suggest the high intensity of microalgal biomass production (fertiliser requirements, high energy harvesting) greatly reduces the overall sustainability. Part of this thesis therefore investigated the possibility of a low input system of microalgal cultivation. A recommended approach was suggested using local species cultivated in wastewater as the nutrient source and a conversion strategy based on the characteristics of the dominant species. The practicality and effectiveness of cultivating and processing locally grown algal biomass under low input conditions was determined by experiments that were conducted in the laboratory. Algal biomass was collected locally and cultivated in the laboratory using agricultural effluent as the nutrient source. The productivity of the algae was monitored alongside the uptake of nutrients. The effluent provided a good media for the cultivation of the wild algae and the nitrogen and phosphorous loading of the effluent was reduced by as much as 98% for NH4+ and 90% for PO4³-. The algal biomass was also tested for its potential as a feedstock for bioethanol production as well as biochar alongside pyrolysis oils and gases. Compared to alternative biomass types tested, the algal biomass appeared to be a good candidate for bioethanol production providing a 38% recovery of bioethanol. The biomass appeared a less favourable substrate for energy recovery from pyrolysis but this process could be considered for carbon biofixation. The sustainability of incorporating microalgal cultivation in wastewater treatment was tested by conducting a life cycle assessment of a large scale system. The life cycle assessment used Haifa wastewater treatment plant in Israel as a case study. The study compared algal cultivation with energy recovery to conventional nutrient removal (A2O process) for enhanced nutrient removal within the wastewater treatment plant. It was found that the use of algal ponds for nutrient removal compared favourably to conventional treatment under specific conditions. These conditions were: the algal biomass is converted to both biodiesel and biogas and the algal biomass is converted to biodiesel, bioethanol and biogas. In these cases the energy balance was greater and the global warming potential and eutrophication potential were less. The conventional nutrient removal was, however, found to be the better method in terms of the acidification potential. Despite being the favourable method of nutrient removal the cultivation and processing of algae relies upon several key assumptions: high year round growth of algae, no contamination and access to a high land area for the cultivation ponds. The sustainability of recovering bioenergy from the cultivation of macroalgae was also tested. A life cycle assessment was conducted investigating the energy return on investment and six environmental impacts for three cultivation methods and three process streams to convert the biomass to bioenergy. Cultivation and processing in Chile was used as a case study due to the depth of knowledge and availability of data. The cultivation scenarios were: bottom cultivation of Gracilaria chilensis, the long line cultivation of Gracilaria chilensis and the long line cultivation of Macrocystis pyrifera. The processing streams were: bioethanol, biogas and both bioethanol and biogas. Most of the data used in the life cycle assessment was obtained from studies conducted in Chile and from communication with local fisherman. It was found that the bottom cultivation of Gracilaria chilensis and conversion to bioethanol and biogas produced the best energy return on investment (2.95) and was most beneficial in terms of the environmental impacts considered. Alternative circumstances were also considered which included new research (untested on a large scale) related to the value used for productivity and conversion of the biomass. This analysis indicated that an EROI of 10.3 could be achieved for the long-line cultivation of Macrocystis pyrifera and conversion to bioethanol and biogas alongside very limited environmental impacts. This result relies, however, upon favourable assumptions that have not yet been proven on a large scale. The work conducted in this thesis highlights the potential of recovering energy from algal biomass. The experimental work and life cycle analysis of freshwater algal cultivation demonstrates the importance of using wastewater treatment as added value to the system. Maximising energy recovery by using a combination of conversion techniques was also shown to be key in providing the most sustainable solution. The sustainability of energy produced from macroalgae was established as being preferable to several conventional energy sources. Innovative methods to improve the system were also shown to greatly enhance the concept.

Nanofiltration (NF) membranes have been applied successfully for the removal of inorganic and organic pollutants, including micropollutants, from drinking water for the past two decades. However, a complete and quantitative understanding of NF removal mechanisms has yet to be achieved. Quantifying the factors governing solute transport and retention by NF is necessary in order to achieve higher treatment efficiency at a lower cost. The aim of this research was to contribute to the current state of the knowledge of the mechanisms of solute retention and transport by NF membranes. The focus was on evaluating the contribution of solute-solute interactions and solute-membrane interactions on solute removal and transport mechanisms. To the knowledge of the author, at the start of this research there was a lack of understanding of the simultaneous impacts of both interactions on the performance of NF membranes, which renders this research novel. To highlight challenges faced by modern membrane plants and identify inorganic and organic pollutants of interest, a study of water quality in Scotland was carried out. Experiments were performed in dead-end stirred cells using two commercial NF membranes, TFC-SR2 and TFC-SR3 provided by Koch, which were extensively characterized. Radiolabeled Endosulfan (ES, 10 μg/L), manganese (5-1,500 mg/L) and Humic Acids (HA, 5-250 mgC/L) were spiked in synthetic water with background electrolyte (1 mM NaHCO3 and 20 mM NaCl). Calcium (Ca, 2.5 mM) was employed in fouling experiments. The influence of the complexation of solutes with HA on solute retention by NF was for the first time quantified for the solute concentrations employed in this study. It was found that manganese retention was influenced by membrane pore size and charge (solute-membrane interactions) and solute speciation (solute-solute interactions). Complexation of manganese and HA (solute-solute interactions) occurred at alkaline conditions but did not enhance manganese retention. At high pH manganese precipitated as solid MnCO3 and these precipitates achieved high retention (99%), even without the presence of HA. ES retention by NF membrane was controlled by size exclusion (solute-membrane interactions). For the tighter TFC-SR3, whose pore size are smaller than the size of ES, ES retention increased in the presence of HA, while for the looser TFC-SR2, whose pores are bigger than ES diameter, ES retention decreased in the presence of HA. For TFC-SR3 increase of ES retention in the presence of HA was due to size exclusion (solute-membrane interactions) and formation of ES-HA complexes (solute-solute interactions). For TFC-SR2 HA-membrane interactions were dominant with respect to solute-solute interactions, increasing membrane molecular weight cut-off (MWCO) and in turn passage of ES. The influence of pressure (5-15 bar) on ES retention in the presence of HA was systematically investigated. Results showed that ES transport through TFC-SR2 and TFC-SR3 was dominated by convection. For the tighter TFC-SR3 lower permeate flux was responsible for the increase of retention with pressure, while for the looser TFC-SR2 higher permeate flux increased concentration polarisation, decreasing retention with pressure. The presence of HA lowered the permeate flux, resulting in a less pronounced variation of retention with pressure for TFC-SR2 and in constant retention for TFC-SR3. The impact of manganese scaling on the performance of NF membranes was investigated at neutral pH. The effects of inorganic precipitates on flux and solute retention by NF have been so far scarcely studied and the impact of inorganic scaling on micropollutant retention by NF is unknown. Findings from this research indicated that manganese deposits did not foul the membranes but on the contrary enhanced their flux and prevented fouling by HA and Ca. The retention of ES, manganese and HA by membranes through which manganese was previously filtered was found to decrease with respect to solute retention by virgin membranes. Manganese filtration was shown to increase membrane MWCO and hydrophilicity. It was proposed that manganese-membrane interactions caused swelling of the membrane active layer by increasing the membrane free volume. The findings of this research indicated the importance of investigating simultaneously the impacts of solute-solute interactions and solute-membrane interactions to understand and explain transport and removal mechanisms of organic and inorganic contaminants by NF.