3,285 research outputs found

    Sewage sludge minimisation by OSA-MBR: A pilot plant experiment

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    This study presents the excess sludge minimisation in a Membrane Bioreactor (MBR) system by an Oxic Settling Anaerobic (OSA) process. The pilot plant was fed with real wastewater and OSA was operated with two different hydraulic retention times (HRT), respectively 4 (Period II) and 6 h (Period III) and compared to an MBR (Period I). Multiple parameters/variables were monitored: sludge minimisation, nitrogen and carbon removal, membrane fouling, and biokinetic behaviour through respirometry. With respect to the current literature, greenhouse gas emissions were also here monitored, often neglected. Results demonstrated that combining MBR and OSA systems can significantly reduce excess sludge production (89.7%, in Period III and 59.7% in Period II, compared to Period I). However, Period III presented better PO4-P removal efficiencies but worse performances in the other parameters (COD, NH4 and Total Nitrogen). No substantial variation in membrane fouling was obtained over the experimental periods. Finally, the HRT increase in the anaerobic reactor promoted a N2O-N increase inside the unaerated reactors, highlighting the need for a trade-off between sludge minimisation and GHG emission

    From Photosynthesis to Detoxification: Microbial Metabolisms Shape Earth’s Surface Chemistry

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    Earth’s chemistry, through geologic time and in the present, is inextricably linked with biologically mediated reactions. All major elemental cycles on Earth’s surface have arisen from two competing processes – life shaping its chemical environment through the evolution of key biochemical pathways, and the environment constraining metabolism by dictating which reactions will occur. Understanding this complicated interplay motivates the research presented in this thesis, which studies this phenomenon over two major elemental cycles – the modern Nitrogen (N) and ancient Carbon (C) cycle. Chapters One and Two focus on the evolution of ribulose-1,5-bisphosphate carboxylase/oxygenase (rubisco), the enzyme that catalyzes the key carbon fixation step in modern oxygenic photosynthesis. This reaction also imparts a large kinetic isotope effect (KIE) that causes the fixed carbon to be relatively depleted in natural abundance ¹³C compared to its substrate; this isotopic fingerprint can be seen in both the modern C cycle and in rock records recording the ancient C cycle. Therefore, this KIE has been used both in vitro (outside the cell) by biochemical models to rationalize rubisco’s reaction mechanism, and in vivo (in the cell) as a proxy for environmental CO₂ concentrations in the past and present. However, both the in vitro and in vivo measurements are calibrated using modern organisms even though rubisco and oxygenic photosynthesis have undergone profound evolution over geologic time. Therefore, we measured the KIE in vitro and in vivo of a reconstructed ancestral Form IB rubisco dating to &gt;&gt; 1 Ga, and the KIE in vitro of a recently discovered Form I’ rubisco that presents a modern analogue to ancestral Form I rubiscos prior to the evolution of the small subunit. Overall, we find that the KIEs of both rubiscos are smaller than their modern counterparts, which is surprising given that the rock record indicates overall carbon isotope fractionations in vivo are larger in the past. In addition, we find that models strictly based on modern organisms may not apply to the past, questioning the basic assumption that uniformitarianism can be readily applied to biological processes. However, these models can be rescued by accounting for other aspects of cell physiology. Chapter Three focuses on disentangling the source of key metabolites, like nitrous oxide (N₂O) in the modern N cycle. Like Chapters 1 and 2, an isotopic fingerprint that measures the ‘preference’ of ¹⁵N for the central or outer nitrogen site in N₂O (“Site Preference” or “SP”) has primarily been calibrated using dissimilatory, or energy-generating, nitric oxide (NO) reductases (NORs). However, there exists a much larger and phylogenetically widespread class of NO-detoxifying enzymes; in particular, flavohemoglobin proteins (Fhp/Hmp) produce N₂O as a strategy to neutralize damaging NO-radicals in anoxic conditions. This enzyme, which generates N₂O in non-growing and anoxic conditions, may be more relevant to natural environments where N₂O production has been detected. Surprisingly, we found that Fhp imparts a distinct SP on N₂O that differs from both bacterial and eukaryotic NORs, and that this value better aligns with existing in situ measurements of N₂O from soils. In addition, we find that in strains with both Fhp and NOR, the Fhp signal dominates when cells are first exposed to high concentrations of NO in oxic conditions while growing before being shifted to an anoxic, non-growing state. Therefore, in addition to telling us ‘Who’s there,’ the SP fingerprint may also be able to tell us something about cell physiology in vivo. We propose a new framework for interpreting the source of N₂O based on SP values.</p

    Optimisation of small-scale aquaponics systems using artificial intelligence and the IoT: Current status, challenges, and opportunities

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    Environment changes, water scarcity, soil depletion, and urbanisation are making it harder to produce food using traditional methods in various regions and countries. Aquaponics is emerging as a sustainable food production system that produces fish and plants in a closed-loop system. Aquaponics is not dependent on soil or external environmental factors. It uses fish waste to fertilise plants and can save up to 90–95% water. Aquaponics is an innovative system for growing food and is expected to be very promising, but it has its challenges. It is a complex ecosystem that requires multidisciplinary knowledge, proper monitoring of all crucial parameters, and high maintenance and initial investment costs to build the system. Artificial intelligence (AI) and the Internet of Things (IoT) are key technologies that can overcome these challenges. Numerous recent studies focus on the use of AI and the IoT to automate the process, improve efficiency and reliability, provide better management, and reduce operating costs. However, these studies often focus on limited aspects of the system, each considering different domains and parameters of the aquaponics system. This paper aims to consolidate the existing work, identify the state-of-the-art use of the IoT and AI, explore the key parameters affecting growth, analyse the sensing and communication technologies employed, highlight the research gaps in this field, and suggest future research directions. Based on the reviewed research, energy efficiency and economic viability were found to be a major bottleneck of current systems. Moreover, inconsistencies in sensor selection, lack of publicly available data, and the reproducibility of existing work were common issues among the studies

    Ecology of methanotrophs in a landfill methane biofilter

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    Decomposing landfill waste is a significant anthropogenic source of the potent climate-active gas methane (CH₄). To mitigate fugitive methane emissions Norfolk County Council are trialling a landfill biofilter, designed to harness the methane oxidizing potential of methanotrophic bacteria. These methanotrophs can convert CH₄ to CO₂ or biomass and act as CH₄ sinks. The most active CH₄ oxidising regions of the Strumpshaw biofilter were identified from in-situ temperature, CH₄, O₂ and CO₂ profiles. While soil CH₄ oxidation potential was estimated and used to confirm methanotroph activity and determine optimal soil moisture conditions for CH₄ oxidation. It was observed that most CH₄ oxidation occurs in the top 60cm of the biofilter (up to 50% of CH4 input) at temperatures around 50ºC, optimal soil moisture was 10-27.5%. A decrease in in-situ temperature following CH₄ supply interruption suggested the high biofilter temperatures were driven by CH₄ oxidation. The biofilter soil bacterial community was profiled by 16S rRNA gene analysis, with methanotrophs accounting for ~5-10% of bacteria. Active methanotrophs at a range of different incubation temperatures were identified by ¹³CH₄ DNA stable-isotope probing coupled with 16S rRNA gene amplicon and metagenome analysis. These methods identified Methylocella, Methylobacter, Methylocystis and Crenothrix as potential CH₄ oxidisers at the lower temperatures (30ºC/37ºC) observed following system start-up or gas-feed interruption. At higher temperatures typical of established biofilter operation (45ºC/50ºC), Methylocaldum and an unassigned Methylococcaceae species were the dominant active methanotrophs. Finally, novel methanotrophs Methylococcus capsulatus (Norfolk) and Methylocaldum szegediense (Norfolk) were isolated from biofilter soil enrichments. Methylocaldum szegediense (Norfolk) may be very closely related to or the same species as one of the most abundant active methanotrophs in a metagenome from a 50ºC biofilter soil incubation, based on genome-to-MAG similarity. This isolate was capable of growth over a broad temperature range (37-62ºC) including the higher (in-situ) biofilter temperatures (>50ºC)

    Evaluating the sustainability and resiliency of local food systems

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    With an ever-rising global population and looming environmental challenges such as climate change and soil degradation, it is imperative to increase the sustainability of food production. The drastic rise in food insecurity during the COVID-19 pandemic has further shown a pressing need to increase the resiliency of food systems. One strategy to reduce the dependence on complex, vulnerable global supply chains is to strengthen local food systems, such as by producing more food in cities. This thesis uses an interdisciplinary, food systems approach to explore aspects of sustainability and resiliency within local food systems. Lifecycle assessment (LCA) was used to evaluate how farm scale, distance to consumer, and management practices influence environmental impacts for different local agriculture models in two case study locations: Georgia, USA and England, UK. Farms were grouped based on urbanisation level and management practices, including: urban organic, peri-urban organic, rural organic, and rural conventional. A total of 25 farms and 40 crop lifecycles were evaluated, focusing on two crops (kale and tomatoes) and including impacts from seedling production through final distribution to the point of sale. Results were extremely sensitive to the allocation of composting burdens (decomposition emissions), with impact variation between organic farms driven mainly by levels of compost use. When composting burdens were attributed to compost inputs, the rural conventional category in the U.S. and the rural organic category in the UK had the lowest average impacts per kg sellable crop produced, including the lowest global warming potential (GWP). However, when subtracting avoided burdens from the municipal waste stream from compost inputs, trends reversed entirely, with urban or peri-urban farm categories having the lowest impacts (often negative) for GWP and marine eutrophication. Overall, farm management practices were the most important factor driving environmental impacts from local food supply chains. A soil health assessment was then performed on a subset of the UK farms to provide insight to ecosystem services that are not captured within LCA frameworks. Better soil health was observed in organically-farmed and uncultivated soils compared to conventionally farmed soils, suggesting higher ecosystem service provisioning as related to improved soil structure, flood mitigation, erosion control, and carbon storage. However, relatively high heavy metal concentrations were seen on urban and peri-urban farms, as well as those located in areas with previous mining activity. This implies that there are important services and disservices on farms that are not captured by LCAs. Zooming out from a focus on food production, a qualitative methodology was used to explore experiences of food insecurity and related health and social challenges during the COVID-19 pandemic. Fourteen individuals receiving emergency food parcels from a community food project in Sheffield, UK were interviewed. Results showed that maintaining food security in times of crisis requires a diverse set of individual, household, social, and place-based resources, which were largely diminished or strained during the pandemic. Drawing upon social capital and community support was essential to cope with a multiplicity of hardship, highlighting a need to develop community food infrastructure that supports ideals of mutual aid and builds connections throughout the food supply chain. Overall, this thesis shows that a range of context-specific solutions are required to build sustainable and resilient food systems. This can be supported by increasing local control of food systems and designing strategies to meet specific community needs, whilst still acknowledging a shared global responsibility to protect ecosystem, human, and planetary health

    Reuse of Sludge as Organic Soil Amendment: Insights into the Current Situation and Potential Challenges

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    Sludge generation as an organic by-product of wastewater treatment has seen a consistent increase worldwide due to population growth and industrial activities. This poses a chronic challenge regarding management options and environmental concerns. The agricultural valorization of unconventional organic materials has become inevitable, especially in semi-arid and arid countries that suffer from depleted soils and shortages in farm manure supply. High-income countries have also been interested in this recycling practice to mitigate landfilling or incineration issues. Sewage and some industrial sludges contain a complex mixture of beneficial and harmful substances, which varies with the origin of effluents. Therefore, sludge land application should be well managed in order to achieve sustainable agro-environmental goals. This review paper focuses on different aspects related to sludge reuse in agriculture, starting by investigating the diversity of sludge types and composition. In addition to the preponderant urban sewage sludge, the less-studied industrial sludges, such as those generated from pulp and paper mills or gas-to-liquid industries, are hereby addressed as well. Then, post-land application effects are discussed in relation to sludge quality, dose, and reuse conditions. The present paper also examines the disparities between guidelines that determine sludge conformity for land application in various countries or regions. Accordingly, special attention is given to increasing risks related to emerging pollutants in sludge such as pharmaceuticals, which have been overused since the outbreak of COVID-19 pandemic. This exhaustive investigation will assist the establishment of sustainable strategies for the safe agricultural reuse of biosolids.This review paper is an outcome of the research project M-QJRC-2020-9 funded in the framework of collaboration between Qatar University and Marubeni Corporation.Scopu

    Reuse of Water and Nutrients in Soilless Plant Culture

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    This dissertation proposes two approaches to mitigating the dependency of soilless culture on scarce mineral fertilisers. The first approach aims to increase the lifetime of the NS used in recirculating hydroponic systems, while the second approach presents a holistic method for the treatment and use of aquacultural sludge as NS for soilless growth systems. This method includes two steps: nutrient mobilisation using aerobic digestion (AD), followed by solids precipitation using the biopolymer chitosan as the flocculant. The recovered NS was used to grow lettuce in a recirculating hydroponic system. The outcome of the first approach showed that NS can be used for several weeks before discharge, even though many growers discard recycling NS at weekly intervals. In this study, NS was reused for 6 weeks, corresponding to a production of 1 kg lettuce per 10 litres tank volume of NS, in a closed hydroponic system without compromising the yield and apparent quality of lettuce. The results from the second approach indicated that AD is an efficient method to mobilise nutrients in aquacultural waste to concentrations close to or exceeding the mineral levels recommended for soilless growth systems. In addition, the biopolymer chitosan proved to be an efficient and safe alternative for solids removal from aerobically digested aquacultural waste. The recovered NS was successfully used for lettuce production in a closed hydroponic system, with yield and quality comparable to those of lettuce grown with conventional NS. The results obtained clearly show the possibility of substituting synthetic fertilisers with recovered NS from aquaculture waste, which can be considered an alternative and resource-efficient fertilisation strategy for soilless culture systems. Both approaches are described in this dissertation, while detailed explanations of the materials and methods used, as well as the obtained results, can be found in the appended papers.publishedVersio

    Development of spectroscopic assays for rapid monitoring of estrogen biodegradation

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    Estrogen hormones are well-established environmental micropollutants which have been linked to endocrine disruption in aquatic organisms in wastewater discharge sites. Biological degradation is the primary wastewater treatment mechanism for estrogen removal. However, treatment efficacy is highly variable and difficult to engineer due to the “black box” nature of biological treatment. Microbial strain selection is a critical impediment towards engineering estrogen biodegradation, since isolating endogenous strains with specific metabolic traits requires lengthy enrichment cultures and is limited to culturable organisms. Furthermore, the highly sensitive and selective chemical trace analysis techniques used to measure estrogen removal are relatively expensive and inefficient. In this thesis, we developed rapid, high-throughput spectroscopic methods designed to monitor estrogen biodegradation. The spectroscopic methods include a fluorometric assay based on the uptake of a fluorescently-labelled estrogen and a colorimetric biosensor using gold nanoparticles (AuNPs) and an aptamer bioreceptor. A synthetic microbial community comprised of characterised estrogen-degrading reference strains was used to evaluate the fitness for purpose of the developed methods. A trace analysis method using conventional chromatography was developed to validate the use of the fluorescent probes with the synthetic microbial community. The biochemical fate and distribution of the BODIPY-estrogen in the estrogen-degrading bacteria – specifically, the biotransformation of BODIPY-estradiol to BODIPY-estrone by Caenibius tardaugens – was used to inform the design of the fluorometric assay. The fluorometric assay utilises a cell impermeable halide quencher to suppress the extracellular fluorescence, and thus, the obtained fluorescence response was attributed to the selective internalisation of BODIPY-estrogen by C. tardaugens. While the fluorometric assay was developed to screen for estrogen-degrading bacteria, the colorimetric aptasensor, which was adapted from published AuNP biosensors and aptamers for this application, was developed to quantify 17β-estradiol (E2) in buffered culture media. The developed aptasensor was evaluated against industry guidelines for ligand-binding assays. While the analytical performance of the aptasensor satisfied the majority of the guidelines’ acceptance criteria, the method suffered from biological interferences by the estrogen-degrading bacteria. The work in this thesis contributes towards expanding the available bioanalytical methods in environmental biotechnology

    Quantifying Aquatic Carbon and Nitrogen Dynamics and Greenhouse Gas Mitigation Potential in Riparian Agroforestry Zones

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    Agricultural intensification in Canada has led to a loss of riparian areas, which has resulted in the degradation of freshwater aquatic ecosystems due to an increasing amount of fertilizer and nutrients being introduced from the upland vegetation. Rehabilitation/restoration of the riparian areas has been shown to minimize these effects. The main objective of my research study is to quantify the carbon (C) and nitrogen (N) dynamics in the aquatic component of the Riparian Agroforestry Systems (RAFS) with varied vegetation located along Washington Creek, Ontario, Canada. The four different treatments studied had the following vegetation types: rehabilitated forest (RH), undisturbed natural forest dominated by deciduous vegetation (UNF-D), herbaceous vegetation (HB), or undisturbed natural forest dominated by coniferous vegetation (UNF-C). No significant spatial differences were found in the Carbon di-oxide concentrations of the RAFS. Among the four riparian treatments, UNF-C recorded significantly lower (p = 0.003) and HB recorded significantly higher (p = 0.002) Methane concentration. Stream DOC concentrations were different among the treatments, with UNF-C reporting significantly lower (p = 0.035) concentrations as compared to the other treatments. Sediment OC was the highest in the RH treatment, and lowest in the HB treatment. Among the four riparian treatments, HB recorded significantly lower (p = 0.024) and UNF-C recorded significantly higher (p = 0.000) Nitrous oxide concentration. Riparian zone averages for TN concentration show that on average UNF-C recorded significantly higher (p = 0.000) values compared to the other treatments, where other N species like ammonium and nitrate were not significantly different amongst treatments. Mean sediment ammonium concentrations were the highest in the RH treatment, along with stream TN. Stream nitrate concentrations were similar among the treatments. Even though the terrestrial morphology of the RH and UNF-D riparian zone were different, including vegetation type and buffer width, but the aquatic component morphology for parameters like discharge, pH, DO, water temperature were similar. Furthermore, the chemical composition of the water in these riparian streams, that is, the GHG concentrations and other C and N species, were insignificantly different. This finding is the highlight of this study. Despite the differences in the terrestrial component, RH, which is a shorter and younger rehabilitated buffer, is just as effective at improving the water quality as is a 100-year-old and much wider forested buffer UNF-D. Therefore, implementing RH buffers at a BMP could potentially lead to water quality improvement in an agricultural landscape
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