Regulations and investments in new technologies for biofuel production as an alternative to fossil fuels have boosted in the last years due to concerns about climate change and anthropogenic CO2 emissions. A valuable supply chain of biomass for biofuel production is one the most significant factors, in order to support the market’s demand. A promising feedstock that is widely available and considered a residue can be Namibia’s encroacher bush (EB). Namibia is facing an environmental crisis with bush encroachment, where EB takes over grasslands, reducing biodiversity and groundwater availability. A thermochemical process that can take advantage of EB can be Hydrothermal Liquefaction (HTL). With HTL, biomass feedstocks are liquefied under hot compressed water, producing bio-oil (BO), biochar (BC), an aqueous phase (AP) and gases. Catalytic HTL is a more attractive pathway, due to the increased BO yield and quality. To this day, there has not been a study investigating the potential of catalytic HTL with EB, thus the present MSc Thesis will attempt to close that knowledge gap and provide state-of-theart insight. To achieve that, Acacia Mellifera from Namibia was tested in sub-critical HTL conditions. In particular two campaigns were formulated with two different goals. The first one, focused on the selection of a suitable catalyst among 4 different categories of catalysts (zeolites, alkaline earth metals, lanthanides and transition metals). The catalysts performance was evaluated by comparing the Energy Recovery (ER) under same operational conditions. Then, the catalyst with the highest ER was used in the second experimental campaign using a Desing of Experiments approach. This approach had the goal to optimize HTL reaction conditions -temperature, residence time and catalyst loading- for maximizing BO yield and energy content. Central Composite Design (CCD) of experiments was used, with the parameters ranges being 250-340oC, 5-60mins and 0-10wt%, respectively. Selected BO and BC samples from both campaigns were then characterized using various methods. The HTL experiments with EB revealed that BO from EB could be produced. The highest ER obtained from the catalyst screening campaign was 41.1% . Main organic compounds found in all the BOs were phenolic derivatives, alicyclic ketones and fatty carboxylic acids. Using the best performing catalyst based one ER, the CCD model indicated that the optimum conditions for maximizing BO yield were 340oC, 60 minutes and 5wt%, which yielded 27.0wt% BO. However, the 330oC - 60 minutes - 7.5wt% point gave both the highest yield and highest ER, 28.5wt% and 46.2% respectively. The CCD also reduced the O content in the BO samples by 54%. Finally, BC samples showed fuel characteristics similar to lignite and low concentration of heavy metals, making them legitimate alternatives for solid fuels or soil amendment.

The current approach in the shipping industry by the use of highly toxic coating systems is harmful for our inland waterways and oceans, does not benefit the public health and is very undesirable for all aquatic organisms on our planet. Almost every vessel today uses a toxic coating system which releases toxic compounds continually into our waterways and oceans. In this thesis a research is done to give an answer to the main question: ‘Is there an environmentally friendly and economically attractive coating for the shipping industry that deals with biofouling’. The best approach examined by multiple criteria, is the use of a Hard, Inert Coating. Toxic compounds, like zinc anodes and copper, won’t be released into our waterways anymore. Therefore, the sediments of rivers and ports are better protected from pollution. Which will benefit the water quality and the public health. The Hard, Inert Coating is the solution to prevent the NIS (non-indigenous species) problem. Because the vessel will be cleaned before leaving the port, no more marine organisms will be transported from their own ecosystem to another. Governments and port authorities will save a lot of money by preventing this problem. Clean hulls will give less resistance and will save a lot of fuel consumption and improve its speed. Worldwide, the Hard, Inert Coating system could save $70.000.000.000 worldwide in one year. The sixteen largest ships in this world provide just as much pollution as 800 million cars. If you save 30 percent on fuel, it’s like you’re taking 240 million cars off the road. As Hard, Inert Coatings are clean and do not emit harmful substances, more jobs in North- West Europe will be created. Currently, most ships go for repairs to dry docks in southern Europe and the Persian Gulf. Ruling on the use of toxic compounds are less observed here. By introducing a Hard, Inert Coating repainting is no longer required, and ships can be dry docked without any negative effects on the environment. In other words they can dry dock ”clean”. This will substantially increase the amount of work for ship repair yards in North- West Europe as owners do prefer these yards for technical and availability of service reasons. The use of a 100% non-toxic coating to tackle the age-old problem of biofouling, will benefit the ecosystems all over the world. Different from the current situation, no more marine organisms will be polluted and killed. No more toxic chemicals will be released into the sediments of our ports, rivers and oceans. No more toxic substances will be absorbed by organisms and end up in our food chain. Our public health is continuously in danger by the fact that the toxic chemicals are released continuously day in day out.

Studying the effects of different land uses on evaporation and stream flow is a hot and frontier topic in global hydrological research. The occurrence and development of flood disasters are restricted and affected by many factors such as meteorology, hydrology, underlying surfaces and human activities. In recent decades, the changes of evaporation and stream flow caused by land use in the river basin have been more and more important. By calculating the long-term average proportion of all land use types in each catchment during the study period, the effects of six main land use types are evaluated one by one, including forest, grassland, pasture land, cropland, shrub land and wetland. This thesis mainly uses Budyko framework to analyze large-sample catchments with different land uses in the United States. Totally 200 small catchments (<1000 km2) located almost evenly in the continental United States are selected as the research samples. Budyko framework is established with long-term mean precipitation, potential evaporation and actual evaporation from 1981 to 2013. The difference between evaporation index estimated from data and theoretical evaporation index calculated from theoretical Budyko equation is regarded as the best indicator to evaluate the impacts of different land uses qualitatively. Then, the Budyko framework is divided into five bins according to the dryness index and these watersheds are studied in each bin. Besides, the effects of each land use are quantitatively evaluated by making multiple linear regressions. It also discusses two other methods, Fu's equation and Zhang's equation. The best-fit values of parameter w of the main land types are calculated by nonlinear regression. The best-fit w values in this thesis are compared with previous researches to find out some possible reasons causing the differences.  From the results in this thesis, forest and shrub land coverage evaporate less and lead to more runoff. However, cropland, grassland and pasture land coverage evaporate more and lead to less runoff. It needs to be emphasized that the results show forest land evaporates more than grassland, which is contradictory with what others found. Some physical and hydrometeorological characteristics of the catchments are the possible reasons to explain the results, including mean slopes, precipitation, root systems and so on. Lastly, the evaluation of the impacts of land use in small watersheds on evaporation and stream flow also provides strategic guidance for future land use planning.

Improving circularity and reducing greenhouse gas emissions can be achieved by utilizing secondary streams like Fischer-Tropsch biosludge, which is typically disposed of in landfills. Biochar, which has accumulated increased interest recently, has significant potential for decreasing carbon emissions and can be created from biosludge. This master thesis was set up as an opportunity-based research project to understand the utilization of Fischer-Tropsch biosludge by the hydrothermal carbonisation process and characterise its product phases; biochar, aqueous phase and gaseous phase. A central composite surface response design was used to conduct experiments to analyse the impact of temperature and time on the characteristics of the phases. Three different levels of the factors have been used. The high ash content and low surface area of the biochar made it difficult to determine a specific use case for the biochar. Yet, the aqueous phase has low ash and possible potential for biogas creation by anaerobic digestion. The gas phase is quantitatively not of significance. Stockpiling the biochar could sequestrate carbon credits and more research can be conducted to find a post- or pre-treatment to improve the biochar for a social-economically benefiting application.

In the context of steering product formation in anaerobic digestion systems, the present thesis work elaborates on the potential role of elevated CO2 partial pressures as an environmental driver that may influence end-product selectivity from methane towards compounds from the carboxylic platform. As an emerging field of research, organic acid production via mixed culture fermentation is currently in an exploratory phase and the understanding of basic functional principles driving each of the biochemical conversions of interest is of vital importance.The present investigation forms part of a series of studies conjunctively aimed at elucidating the effect of elevated CO2 partial pressures on glucose fermentation, which consists of a complex network of several metabolic routes. Specifically, this thesis work focuses on the effects of CO2 partial pressure on the degradation of two key metabolites that are central and/or highly relevant to the glucose conversion pathways, namely pyruvate and butyrate.

Corrosion and fouling are considered major factors affecting the performance of water-steam cycles (WSC). Flow-accelerated corrosion (FAC), present in feed and condensate systems, is a well known corrosion mechanism, eroding and dissolving the protective magnetite layers. Fouling of the boiler, by suspended magnetite particles, is partly controlled by forces arising due to surface charging. Film forming amines (FFA) are gaining acceptance as means to control FAC. However, its performance in low pH regions is unknown. In addition, despite FFA being a surfactant, its effect on the colloidal magnetite surface charge and point of zero charge (pzc) are unknown. This research set out to determine the effect of FFAs on the formation of a protective magnetite layer and its resistance against acidic FAC, and to determine the effect of FFAs on the surface charge of colloidal magnetite. This study focused on two FFAs, Octadecylamine (ODA) and Oleyl Propylenediamine (OLDA). In 48h 230-250 ºC immersion corrosion tests magnetite layers were formed on C1010 coupons, inside a high pressure high temperature autoclave under different treatments: untreated (blank), 2ppm ODA and 2ppm Ammonia, 2ppm OLDA and 2ppm Ammonia, and only 2ppm Ammonia. 48h 150 ºC re-immersion corrosion tests were performed to test the magnetite layer performance under acidic (acetate 0.08ppm) FAC. After the corrosion tests, the layers were verified using XRD, EDS + SEM and Weigh-loss measurements. Potentiometric titrations were employed to measure the proton induced surface charge of magnetite particles (10g/L) at an ionic strength of 0.01, and 0.1 mol/kg (KNO3) in the presence or absence of ODA, or OLDA (2ppm) over a wide pH range, at 25, and 150 ºC. This gave the magnetite surface charge density curves. The pzc was determined using the inflection point of titrations (pHinfl) and common intersection point (pHcip). XRD confirmed the presence of magnetite layers on all coupons after the immersion and re-immersion tests. The SEM measured magnetite layer decrease after the re-immersion tests was: 19.1%, 14.5%, 8.6%, and 23.3% for blank, ODA, OLDA, and ammonia treatment respectively. Weight loss determined corrosion rates taken over both immersion and re-immersion tests were: 0.070, 0.057, 0.060, and 0.073 mm/y for blank, ODA, OLDA, and ammonia treatment respectively. All magnetite surface charge density curves were unaffected by the presence of ODA, and OLDA, except for ODA at 0.1 mol/kg KNO3 and 25 ºC, which resulted in a raised/neutralized surface charge density curve in the alkaline pH region. Magnetite layers formed under ODA, and OLDA additions were smoother, thinner, and more uniform compared to layers formed under an ammonia only chemistry, and blank chemistry. Layers formed under the ODA, and OLDA chemistries were better resistant against acidic FAC and offered better protection, in terms of corrosion rate. At the applied concentration ratio, and ionic strength of 0.01M, ODA, and OLDA did not affect the magnetite colloid surface charge over pH. However, both caused magnetite particles to agglomerate. At higher ionic strengths of 0.1M, ODA neutralized the magnetite surface charge in the alkaline region.

This thesis constitutes a part of the "IMPRESS" project which is aiming at the production of bio-plastics by utilizing hemicellulosic hydrolysates. The hydrolysate stream, after following the steps of acid hydrolysis and neutralization, consists of monosaccharides (C5/C6 sugars), salt and sugar degradation products. The C5/C6 sugars need to be concentrated by a factor of 10 to be purified afterwards in downstream processes. Evaporation has been the most dominant technology in the sugar treatment sector, however the current study aimed to investigate tubular nanofiltration (NF) and vacuum membrane distillation (VMD) units for concentrating the C5/C6 sugars, as more sustainable alternatives. Synthetic solutions with C5/C6 sugars and salt were used to assess the performance of the NF and MD membranes in terms of sugar and salt rejection before the experiments with the real hydrolysate solution. Among the different NF and MD membranes, the one that met the C5/C6 sugar rejection requirements (>90 %) during the synthetic solution experiments was tested for concentrating the C5/C6 sugars. The most suitable technology for concentrating the C5/C6 sugars was also assessed for its energy consumption. Additionally, single filtration tests were conducted to characterize the NF membranes, while surface tension and contact angle measurements were performed to predict the membrane wetting phenomena during the VMD operation. Based on the C5/C6 sugar rejection values (range of 22-81 %) obtained with ceramic and polymeric NF membranes, it was deduced that the tubular NF membranes were not capable of meeting the C5/C6 sugar concentration goals. The polymeric membranes performed better than the ceramic ones in terms of C5/C6 sugar rejection, with a maximum sugar rejection of 81 %. However, the polymeric membranes were found to be more prone to fouling, showing a maximum decrease of 34 % in the water permeability after 4 hours of operation with the hydrolysate solution. Additionally, the characterization of the NF membranes based on the Donnan Steric Pore Model (DSPM) revealed membrane pore sizes larger than those provided by the manufacturer. On the contrary, the 0.2 μm MD membrane showed >99 % of C5/C6 sugar rejection and was used for the sugar concentration tests. The maximum C5/C6 sugar concentration factor (CF) achieved with the VMD was 8 with a negligible sugar loss (<1 %) in the permeate, indicating that concentrating the C5/C6 sugars by a factor of 10 is feasible with this technology. Surface tension and contact angle measurements disclosed inconsistencies in the hydrophobicity of the MD membrane, which can be linked to the membrane wetting phenomena occurred during the VMD operation. The fouling of the MD membrane (50 % of flux decrease after 39 hours of operation) was found to be reversible with complete flux recovery after chemical cleaning and drying of the membrane. The energy assessment of the VMD technology showed that the main energy consumer was the cooler, contributing to 96 % of the total consumed energy. Based on the cooler's efficiency, the energy consumption of the VMD unit was calculated to be in the range of 207-736 KWh/m3 of distillate. When compared with multi-effect evaporators with up to three effects, the VMD was found to be more energy efficient. Investigating less energy-intensive alternatives for concentrating the C5/C6 sugars, experiments with electrodialysis (ED) showed 90 % removal of both acid and salt from the raw and neutralized hydrolysate water, respectively, making it feasible for reverse osmosis (RO) membranes to be further tested for concentrating the C5/C6 sugars. Therefore, a treatment scheme of ED and tubular RO membranes is proposed for further research on concentrating the C5/C6 sugars. Overall, a pre-treatment step with the most permeable ceramic NF membrane is suggested, as evinced by the high color removal achieved (elimination of big foulants) and the high permeation of the C5/C6 sugars and salt.

Oceanic CO2 capture technology can be used as a negative emission technology, or pre-treatment to reduce inorganic fouling (i.e., scaling) potential when further processing seawater. In this work CO2 from (synthetic) seawater was captured electrochemically via bipolar membrane electrodialysis. Although previous studies showed promising results regarding energy consumption (kJ/mole CaCO3), inorganic fouling is a drawback, which is why an inorganic fouling control and removal study was done. The effect of applied current density and flowrate on inorganic fouling build-up and dissolved organic carbon removal was investigated for 2 cell pair configurations. For inorganic fouling removal 5 methods were investigated. This research was a proof of concept.

Galdieria sulphuraria (G. sulphuraria ) is a eukaryotic, extremophilic, spherical and unicellular species of red algae. G. sulphuraria can grow at very low pH-values (pH 0.05 – 5.0) and high temperatures (35 – 56 °C). The growth conditions of G. sulphuraria make it suitable for axenic cultivation because the low pH and high temperature minimalize the risk of microbial contamination. Next to its ability to remove nutrients in wastewater treatment, G. sulphuraria is a prospective producer of a valuable product, Phycocyanin (PC), a thermostable blue pigment-protein complex, which is used as, among others food additive and food colorant. These characteristics of G. sulphuraria lead its selection by Evides Industriewater for the uptake of the ammonium present in the reverse osmosis (RO) concentrate of New Energy and REsources from Urban Sanitation (NEREUS). NEREUS focuses on the re-use of nutrients present in wastewater, among others ammonium. One of the goals of NEREUS is to re-use the ammonium present in the RO concentrate with the use of algae. In order to recover ammonium from the RO concentrate of NEREUS, it is necessary to test whether G. sulphuraria is capable of growing on such medium. The possibility of cultivating of G. sulphuraria on the RO concentrate from water and resource recovery pilot plant of NEREUS was investigated in this thesis. The objectives of this thesis were to find the optimal growing conditions and assess the biomass growth and nutrients consumption. Screening experiments with synthetic Allen medium, which is usually used for the cultivation of the G. sulphuraria, were conducted to obtain the best growing conditions of G. sulphuraria. In order to understand the best growing conditions for the cultivation of G. sulphuraria, the effects of several factors were investigated, which are: 1) different metabolism, 2) different nitrogen sources and concentrations (ammonium: 100 – 1000 mgNH4+-N/L and nitrate: 247 mgNO3--N/L), 3) different carbon sources (glucose, bicarbonate and CO2) and different glucose concentrations (C:N = 5:1 and 10:1), 4) different phosphate concentrations (N:P = 37:1 and 7.2:1), 5) culture densities. Ammonium with mixotrophic metabolism turned out to be the best nitrogen source. Biomass concentration on ammonium was four times higher than on nitrate. Increasing the ammonium concentration from 200 mgNH4+-N/L to 1000 mgNH4+-N/L resulted in around 25% more biomass and no firm conclusions could be drawn from the experiment performed with different phosphate concentrations. No significant increase in the growth of G. sulphuraria was observed between Carbon:Nitrogen (C:N) ratio = 5:1 and 10:1. Furthermore, culture densities higher than 0.7 g/L of biomass resulted to a slower growth of G. sulphuraria. Experiment with synthetic RO concentrate shows that there was light limitation involved during the cultivation. Highest and fastest growth (µmax = 0.78 day-1) was observed in the mix of 40% real RO concentrate and 60% synthetic RO concentrate medium culture. Growth inhibition was observed in cultures containing RO concentrate of NEREUS. Still, G. sulphuraria did grow on RO concentrate of NEREUS. This work is contributing to the scientific and engineering community in the field of microalgae.

Interest in biogas has increased due to natural gas shortages and the energy transition. Most digesters in the EU have internal heating for process stability. Unheated reactors could potentially lower costs, but have decreased kinetics due to low operational temperatures, especially in winter. This raises the question how seasonal temperature fluctuations effect biogas production. If this effect could be incorporated in current models such as the Anaerobic Digestion Model no.1 (ADM1), scenarios could be compared to investigate when heating is worthwile. In this thesis, an extension is created to the ADM1 in Python to predict the operational temperature and its effects on the anaerobic digestion process. To lower the stiffness of the ADM1, different pH calculation methods were compared. These methods and the used Python version of the model were validated by digestion of the Benchmark Simulation Model 2 (BSM2) ADM1 influent. It was found that the combination of the Differential Algebraic Equation (DAE) with the Radau numerical solving method produced the smallest errors with the lowest computational burden. A heat-transfer model was included, which calculates bulk liquid temperature as a function of weather data, digester design and some operational factors. A One-At-a-Time (OAT) sensitivity analysis showed the dependence of yearly temperature fluctuations on several design and operational parameters. The calculated operational temperature is coupled to the ADM1 through several temperature inhibition functions for biochemical processes. Furthermore, the dependency of the liquid-gas transfer coefficient was investigated. It was found that this last step in biogas production could potentially become rate-limiting at temperatures lower than 30 °C, but this result was not validated. The coupled heat transfer - ADM1 model is used to study the case of an unheated fixed-dome reactor for the co-digestion of spent wort and Waste Activated Sludge (WAS) of the La Trappe brewery in the Netherlands. The influent substrate concentrations were determined by a biochemical fractionation procedure, and the model was able to simulate methane production curves found in Biochemical Methane Potential (BMP) experiments. Simulations of digestion for the La Trappe case showed seasonality in biogas production, increasing in summer and decreasing in winter. The extent of the effect was found to be dependent on substrate composition, with lipid-rich substrates being affected more than carbohydrate- or protein-rich substrates. Furthermore, the simulation showed seasonality in rate limiting step, with hydrolysis in summer and methanogenesis in winter. This caused the pH to lower with winter, and it was found that higher base dosage is needed in colder winters to prevent acidification. Higher influent temperatures improved process stability, lowered amounts of base needed and increased biogas production. Furthermore, the relation between temperature and volume showed that washout of methanogens and consequent VFA accumulation is dependent on the absolute temperature inhibition function for acetoclastic methanogens. Simulation of the digestion of BSM2 influent showed that the maximum Organic Loading Rate (OLR) increased with temperature till 30 °C, but decreased above this point as free ammonia inhibition starts to limit methanogenic metabolism. For La Trappe, OLR determines the needed base dosage, allowing smaller volumes if more base is added. Lastly, internal heating with the produced biogas was investigated, and optimal heating for biogas production was found. The found results from the model were used to asses the costs and benefits of several design and operational options for the digester at La Trappe. This digester will be used in future research for validation of the model.

Biochar for horticultural and agricultural applications using high temperature torrefaction technology Pradeep Ravi Supervisors: Prof Dr. D.J.E.M Roekaerts, ir.Bart de Vries, Dr. Luis Cutz, Dr.Lorenzo Botto & Dr.Ralph Lindeboom Biomass currently accounts for less than 10 percentage of the world’s renewable energy production. Currently the major global sustainability issue stems from the sourcing of virgin wood chips from dense forests for pellet production. An alternative is to use residual biomass from agriculture or forestry, which is produced in large volumes, to produce different products that range from biofuels to chemicals via thermochemical conversion technologies. Among thermochemical technologies, torrefaction is a promising route to produce solid biofuel known as biochar. With an increasing potential for biomass production coupled with an increased scrutiny on the use of biomass as a green fuel, the need for alternative clean applications for the biochar is critical. The aim of this study is to investigate new and novel agricultural residues or other waste streams to produce biochar using high temperature (350 °C) torrefaction technology. The obtained biochar is evaluated experimentally to determine the best feedstocks out of the ones that are selected from a performance and cost point of view for horticultural applications. . This research aims to provide a clear and useful analytical tool which will benefit the scientific community to select suitable biomass materials based on material properties and end applications. The efficacy for the various torrefied biomass feedstocks on the soil and its stability are tested. Overall, about 50 different biomass feedstocks were identified and evaluated based on past performances from literature. The top 10 best performing feedstocks were sourced and subjected to various physical and chemical characterization tests with a specific focus on soil remediation. The selected materials were torrefied in a fixed bed pilot reactor Scanning Electron Microscopy with Energy Dispersive X-Ray Spectroscopy (SEM-EDS), Brunauer–Emmett–Teller (BET) and pH measurements. Ultimately the feedstocks were scored and ranked from best to worst performing biochar for soil remediation and sequestration-based applications. The results of this project indicate potential for biochar production from woody, grassy and other processed materials that could help to remove the dependence on evergreen forests and wood chips. The system proposed in this work could also yield negative emissions since the feedstocks are residual flows and the biochar is going to be used in the soil.

This study explored the interactions between alkaline hydrothermal pretreatment (AHPT) operational conditions temperature (°C), NaOH concentration (M) and residence time (min) on the compositional characteristics of the solid (SH) and liquid hydrolysate (LH) obtained from AHPT of sugarcane bagasse (SCB), empty fruit bunch (EFB) and agave bagasse (AB). The experimental design was carried out with a three factors five levels (−훼, −1, 0, 1, and +훼) central composite rotatable design. Response variables for the liquid hydrolysate included glucose, xylose and arabinose content. Whereas the effects on the solid hydrolysate were evaluated with delignification and solids recovery (%). Biogas production and in situ biogas upgrading by co digestion of SH and NaOH rich LH was evaluated against mono digestion of raw and treated fibers. Therefore, methane production and methane content in the biogas were also considered response variables. Compositional characteristics were fiber dependent. Glucose, xylose and arabinose were found in SCB and AB LHs whereas for EFB LH cellobiose was also detected. A significant (p-value <0.05) linear interaction between treatment temperature and glucose release was found for SCB and AB. EFB showed significant (p-value <0.05) a quadratic interaction between temperature and retention time with glucose release. Arabinose presented a significant (p-value <0.05) linear positive interaction with temperature and NaOH concentration in all fibers. Delignification of SCB had a significant (p-value <0.05) negative correlation with the coupled effect of temperature and NaOH concentration. Solids recovery showed a significant (p-value <0.05) negative interaction with temperature and NaOH concentration for all fibers. Methane production from SCB hydrolysates co digestion presented significant (p-value <0.05) interaction with NaOH concentration and retention time. EFB hydrolysates co digestion presented a significant (p-value <0.05) interaction with temperature and NaOH concentration. Methane content in biogas presented a significant (p-value <0.05) linear interaction with temperature and NaOH concentration. No energy gain from pretreated SCB was observed. A maximum energy gain of 3.5MJ Kg-1 for pretreated empty fruit bunch. Agave bagasse presented a maximum net energy gain of 4.8 MJ Kg-1.Keywords: Empty fruit bunch; sugarcane bagasse; agave bagasse; hexoses; pentoses; lignin degradation.

Groundwater is an essential source of drinking water, and it often contains contaminants in the form of dissolved metal ions that pose health risks and affect its suitability for consumption. Removal of these contaminants by conventional treatment methods, such as oxidation and filtration, results in additional treatment steps for managing sludge. New techniques are needed to prevent the formation of low-value sludge and provide better control over the drinking water treatment process. This study focused on understanding the mechanistics of electrochemical reduction for its utility as a groundwater treatment method. It was done by passing artificial groundwater containing dissolved metal ions Fe2+, Mn2+, and Al3+ through a stainless steel cathode in an electrochemical cell. It resulted in the removal of these ions through electrochemical reduction and the recovery of metals as deposits. The experiments were performed with very high metal ion concentrations (0.72 mmol/L) to obtain clear and noticeable results from their electrochemical reduction. It was observed that while Fe2+ and Mn2+ were removed from the water and deposited on the cathode, Al3+ did not get electrochemically reduced. It was due to the system settings adopted for the study being unsuitable for Al3+ removal. It highlights the potential of electrochemical reduction as a selective treatment process that offers control by manipulating the system settings. Upto 51.4% removal was observed in Fe experiments, while for Mn experiments, up to 22.22% removal was observed. As the deposits grew with the volume of water treated during an experiment, the electrochemical reduction declined. The removal of metal ions from water became negligible when the volume of water treated reached 6.3 L. The decrease in the effective surface area of the cathode because of deposits and the changing water composition near the cathode, as the volume of the water treated was increasing, was detrimental to the transfer of electrons from the cathode to the dissolved metal ions. It was also observed that the voltage rises continuously as the water is treated due to increasing cell resistance. Another observation was that the pH of the water matrix is an essential factor in the electrochemical reduction of the species, with cathodic depositions increasing as the pH increases. Fe depositions increased 5.8 times from 0.109 μm at pH 4 to 0.630 μm at pH 7, while Mn at pH 4 had negligible deposits, which rose to 0.213 μm at pH 7. As the pH decreases, the entropic barrier of H+ ions decreases, leading to H2 production and a decline in FE. Further, it was observed that the electrochemical reduction performs better when a water matrix has only one type of metal ion (individual) instead of a water matrix with all three types of metal ions simultaneously (combined). The FE of Fe2+ ions in the individual case is 35.05% while it is 11.5% in combined, at pH 7. It is 14.90% for Mn2+ in individual and 1.75% in combined. This could be from the decreased availability of the free metal ions in the combined case - due to the formation of bonds between the ionic species and changes in the thermodynamic feasibility of electrochemical reduction resulting from changes in the water matrix composition. Further investigations are required to check performance with natural groundwater samples, optimize the system settings and find cathode material that best fits the desired contaminant removal.

In a WWTP operating with full scale mesophilic digestion, a thermophilic digestion pilot and a digestate ammonia stripping pilot were installed. Benefits of the aforementioned sludge treatment processes, such as energy and nutrient recovery, are extensively recognized. However, drawbacks, such as deficient sludge dewatering, are amply disregarded despite their substantial influence on the treatment scheme and treatment cost. Consequently, the installations research resolved to determining the causality of the unsatisfactory dewaterability. The digester feed, mesophilic digestate, thermophilic digestate and ammonia stripped thermophilic digestate were compared. Harsher sludge treatments led to a severe deterioration in dewaterability. An increase in presence of colloids resulted in a worsening of dewaterability, to an extent originating from size and surface charge of colloids; unlike variations in presence and size of supracolloids, which were inconsequential. Moreover, inferior dewaterability was strongly associated with the increased concentrations of carbohydrates, proteins and humics in the bulk and loosely bound phases, and with the decreased presence of proteins in the tightly bound phase. Furthermore, the decreased calcium and increased iron presences in the bulk and tightly bound phases were correlated to a degradation in dewaterability; whilst sodium, potassium, ammonium and magnesium in all phases were found of no or insignificant influence. Recognizing the dewatering determinant factors enables the search for digestate specific conditioning and dewatering methods.

Ghana as a developing country has some challenges for the future. These challenges include an energy crisis, a high dependence on firewood and high levels of poverty. Biogas technology has the potential to make a contribution in solving these challenges, but is not yet widely implemented in Ghana. For this reason, the aim of this thesis was to find ways to increase the use of biogas technology in Ghana. To do this, a business model for community based biogas enterprises was created which was based on Ghanaian cultural values and by that included the most appropriate complexity and scale of biogas technology. To arrive at a representation of Ghanaian culture, a field study was done in which thirteen SMEs were visited. Data were collected by in-depth interviews and participatory observation. For the cultural analysis, a model was made based on cultural dimensions by Hofstede and Trompenaars. The model consisted of six dimensions which were given a score between one to five. Based on these scores, the degree in which a civil society and innovative entrepreneurship are present in Ghana were determined. A multi criteria analysis was done to find the most appropriate form of biogas technology in a Ghanaian business setting. The feedstock availability of an average Ghanaian community was assessed to find the most feasible alternative and determine the size of the digester. Various value propositions were compared on their economic viability by calculating their NPV, IRR and DPB. The major findings of this research were that the garage-type digester was the most appropriate digester design, fed with only crop residues available from the community. For an average community size of 491 people, a digester size of 67 m3 would be needed. The best value proposition was concluded to be collecting all the available crop residues from within the community with a cargo tricycle, digesting the crop residues in a garage-type digester, using the produced biogas to generate electricity, selling it to the grid, and drying the digestate and selling it as organic fertilizer. The cultural analysis and discussion showed that additional training for the workforce would be required in cooperation, dialogue, proper work ethic, due planning and precision in labor.

Biogas is the well-known product of Anaerobic Digestion (AD), but nowadays, the intermediate products (volatile fatty acids - VFAs) of anaerobic metabolism have gained increasing attention inside the “carboxylate platform”. However, steering and optimizing the process for selective metabolite production is still an unraveled task inside this field since it relies on the manipulation of operational parameters. The objective is to understand the conversion of glucose and glycerol in the mixed culture of anaerobic digestion to unravel possibilities to steer product formation. Glucose and glycerol are the main components in the waste streams of beverage and biodiesel industries. Regarding the degradation pathways in AD, both glucose and glycerol are oxidized to pyruvate by fermentative bacteria to obtain energy and metabolic intermediates under anaerobic conditions through the same intermediate, glyceraldehyde-3-phosphate. Pyruvate, the key branching-point, allows the process to enter different metabolic pathways which lead to the formation of various metabolites. Under the fermentation conditions, redox balance is necessary to be maintained through terminal electron transfer to internally produced compounds. Since glycerol has a higher degree of reduction than glucose (Glucose: 0.33 NADH/C-Glucose; Glycerol: 0.66 NADH/C-Glycerol), the conversion of glycerol into pyruvate generates a double amount of reducing equivalents. On the one hand, this provides the advantage of higher theoretical product yield of reduced compounds. On the other hand, half of the glucose is lost as CO2 during the fermentation, and this reduces the product yield.1 Therefore, we assume that elevated pCO2 could have a more significant detrimental effect on glucose fermentation. In this research, batch experiments at different pCO2 (0.3, 1, 3, 5, 8 bar) were performed, and different types of measurements and analyses were employed to monitor the pCO2 effect on the metabolism. We designed some of the potential pathways of glucose and glycerol conversion under elevated pCO2. The elevated pCO2 converged the product spectrum of both substrates towards propionate production but affected the degradation and production phase of propionate and acetate. Initial pCO2 of 0.3 bar and 1 bar did not cause visible inhibition on the propionate production of both substrates. However, the propionate degradation was kinetically affected under 0.3 and 1 bar initial pCO2. Although propionate was degradable, its degradation phase at 1 bar initial pCO2 was longer than 0.3 bar. On the contrary, when the pCO2 was elevated to 3, 5, and 8 bar, not only the propionate production phase became longer, but also the maximum concentration became lower on both substrates. Moreover, propionate degradation was ceased. The lower propionate production was suspected to be due to the inhibition of NADH production as a consequence of the elevated pCO2 effect. The undegradable propionate might be attributed to unfavored decarboxylation reactions under elevated pCO2. The enrichment approach was applied to examine the adaptability of the microbial consortium under the CO2-exposing environment. Therefore, not only the more predominant metabolic reaction would be favored during the enrichment, but also changes in the community due to CO2 influence were expected. Propionate degradation was achieved with this inoculum at the only tested condition (5 bar initial pCO2). From the community analysis, Smithella was enriched during the enriched and it was suspected to play a significant role in the propionate conversion. Besides, the difference between the substrates on the fermentation has been observed. Due to the higher available reducing power of glycerol than glucose, glycerol was potentially able to generate more propionate. However, the butyrate formation also needs the reducing power to proceed with the reaction, but it was not detected in the glycerol fermentation. Therefore, reducing power distribution from specific substrates with elevated pCO2 might also be affected. Moreover, the substrate was also hypothesized to influence cell viability, where glycerol fermentation increased the cell viability but glucose not. The degradation of acetate and butyrate in the non-enriched inoculum was observed to be kinetically affected by elevated pCO2, with the later becoming undegradable at 8 bar. The reason for this phenomenon needs further investigation.