The presence of >1ppm concentrations of hydrogen sulfide (H2S) in biogas can pose a challenge for the implementation of off-grid biogas-SOFC energy systems in rural Uganda. This study investigated the potential of biochars made from cow dung (CB), jackfruit tree leaves (LB) and jackfruit tree branches (TB) to remove H2S from biogas to below the 1 ppm threshold and compared the findings to the use of commercially available activated carbon (AC). The surface area, pore structure, particle size, trace-metal content, pH and alkalinity were characterized and their influence on the H2S adsorption capacity was qualitatively evaluated. Furthermore, a Central Composite Design (CCD) was used to determine the influence of the gas hourly space velocity (GHSV) and inlet H2S concentration on the H2S adsorption capacity. AC was observed to exhibit the highest H2S adsorption capacity, followed by CB, LB and TB, in that order. The specific surface area (SSA) and micropore volume were argued to be the determining factors to explain the differences in H2S adsorption capacity. Furthermore, the GHSV and inlet H2S concentration were both found to be negatively correlated to the H2S adsorption capacity. The interaction effect between both parameters was observed to be insignificant and no optimum was found by the response surface analysis. The comparison of the research findings with similar studies highlighted the complexity involved in comparing the H2S adsorption capacities of biochars between studies. It is therefore suggested that a reference benchmark breakthrough test should be created and used by future studies. Ultimately, the insights of this study may contribute to the implementation of cost-effective biogas-SOFC systems in rural Uganda. ... Read more

With global water scarcity and demand continuing to rise, alternative water sources are being explored for agricultural irrigation. The brewery industry, among the largest industrial water consumers, generates wastewater typically characterized by high biological oxygen demand (BOD) and chemical oxygen demand (COD) due to organic compounds, as well as total suspended solids (TSS) and nutrients such as phosphorous and nitrogen species. It can also have high sodium concentrations and microbial contaminants such as E. coli that serves as an indicator of fecal contamination. This thesis evaluates the application of nanofiltration (NF) as a tertiary treatment for brewery to assess its potential for agricultural reuse in accordance with Dutch and EU water reuse regulations, Regulation 2020/741.
The relevant reuse standards were first identified to establish target water quality limits. Then six brewery wastewater samples were collected at different time points to characterize influent variability. Physical, chemical and biological parameters were analyzed, including particle size distribution (PSD), TSS, ion concentrations, alkalinity, total organic carbon (TOC), and E. coli as an indicator pathogen of fecal contamination. The results found maximum particle sizes that could cause pore blocking of polymeric membrane fibers and particle load to be a risk for fouling propensity, leading to the investigation of sand filtration as a pretreatment. Comparison of the measured results to the reuse standards identified sodium, sulfate, nitrate, ammonium, and E. coli concentrations were found to exceed their respective thresholds, 120 mg/L, 100 mg/L, 10 mg/L, 1.5 mg/L and 10 CFU/ 100mL, confirming the need for tertiary treatment before being reused for irrigation.
Two nanofiltration membranes, a 0.9 nm ceramic Inopor membrane and a polymeric NX Filtration dNF80 membrane, were experimentally assessed. Experiments were performed at 2 and 4 bars, using both direct and sand filtered influents, including a prolonged fouling test, to evaluate permeability, flux stability, and removal efficiency.
The polymeric membrane achieved higher removal efficiencies of TOC (81% ± 3%) removal and 7 – 55% higher removal efficiency of multivalent ions (phosphate, sulfate, Ca2+ and Mg2+). The ceramic membrane showed more consistent biological removal efficiencies, with all but one fouling test qualifying for class A reuse and 6 – 60% higher removal efficiency for most monovalent ions (Cl-, NO-2, Br-, NO3-, Na+, NH+4, and K-). During the fouling tests, the polymeric membrane recovered 93 - 96% of 5 L over four hours, while the ceramic membrane achieved 15 – 16% recovery of 2 L over 24 hours. The polymeric membrane showed higher fouling sensitivity, while the ceramic membrane had higher stability. Sand filtration pretreatment improved flux stability for both membranes, and higher pressure increased polymeric permeability but did not affect the ceramic membrane.
While the complexity of differences in membrane composition, material, and geometry prevented definitive identification of individual exclusion mechanisms, the findings provide valuable insight into how these factors collectively influence nanofiltration performance. Overall, NF effectively bridges the gap between brewery wastewater and agricultural reuse regulations. The polymeric membrane offers higher organic and multivalent ion removal and higher flux but greater fouling propensity. Whereas the ceramic membrane has a higher resistance to fouling and lower but stable flux. Sodium, nitrate, and ammonium, remain the key limitations for reuse. ... Read more

Rhodospirillum rubrum is a metabolically versatile phototrophic bacterium with potential applications in sustainable hydrogen and bioplastic production. However, large-scale implementation remains limited by insufficient understanding of its growth dynamics under varying environmental conditions and the high energy costs of cultivation. This study presents a simplified, general mathematical model describing R. rubrum growth under anaerobic dark and light conditions, incorporating metabolic state transitions driven by substrate and carbon monoxide availability. The model, parameterized using literature data, captures key physiological features such as substrate inhibition and lag-phase behavior. Experimental validation under anaerobic light conditions demonstrated reasonable agreement with model predictions, while discrepancies were observed under dark conditions, that were attributed to experimental limitations rather than model deficiencies. The proposed framework provides a foundation for future model refinement and integration with other higher and lower level models. ... Read more

Coffee is a beverage that millions of people around the globe enjoy on a daily basis. Although coffee consumption is becoming increasingly popular, the cultivation of coffee is under threat of: climate change, economic inequality in the coffee value chain, and unsustainable coffee cultivation and processing. Studies predict that all land currently used for the cultivation of Arabica coffee might become unusable by 2080 because of the sensitivity of the crop to changes in temperature, humidity, and the amount of UV irradiation. A shift is needed in the coffee value chain to ensure the livelihood of the current 25 million smallholder coffee farmers responsible for 70 to 80\% of coffee production worldwide. The Climate Smart Coffee Program in the state of Kerala in India focuses on making coffee cultivation and processing more resilient, sustainable, and economical in the future. This is accomplished by conducting research on more sustainable agriculture (such as agroforestry to preserve and nurture valuable land) and reduce carbon emissions and waste generation during the processing of coffee.

The focus of this study is on the use of biomass residues produced during the processing of coffee to meet the energy needs of coffee processing units in the Wayanad district in Kerala. The goal is to make the processing of coffee less carbon-intensive, produce less waste, improve the quality of the coffee, and make coffee processing less energy dependent. This study presents a technoeconomic analysis for a novel approach to the use of these coffee processing mill residues (CPMRs) by using a combination of gasification to produce syngas, a solid-oxide fuel cell (SOFC) to transform the syngas into electricity and heat, and the use of an afterburner to further optimize the energy efficiency of the biomass plant. The biomass plant's goal is to replace the current energy need of the processing units: electricity from the grid and liquefied petroleum gas (LPG).

The results of the technoeconomic model show that the biomass plant produces enough electricity and heat to cover the energy needs of the coffee processing unit that supplies the biomass material. With an hourly feed rate of 1295 kilograms of biomass material the plant produced 2,681 kW of electricity with an electrical efficiency of 41\% and an overall system efficiency of 62\%. The financial analysis of the biomass plant yielded a capital expenditure of \$ 24.1 million, or 8,984 \$ per kWh of electricity generated. The levelized cost of electricity (LCOE) of the plant was 0.45 \$/kWh. A sensitivity analysis revealed that by optimizing the operating conditions of the biomass conversion plant, the LCOE could be decreased to 0.35 \$/kWh. Improving the capacity factor would have the most substantial effect on the costs of the system, increasing the days of operation from 90 in the base model to 300 could result in an LCOE as low as 0.12 \$/kWh. ... Read more

This PhD thesis advances resource recovery from wastewater by focusing on two key technologies: Purple Phototrophic Bacteria (PPB) raceway reactors and anaerobic digesters (ADs). To address challenges such as process variability, monitoring limitations, and operational inefficiencies, this research employs three complementary approaches: mechanistic modeling, hybrid system identification, and adaptive predictive control. Mechanistic models offer detailed insights into microbial interactions and process dynamics; hybrid system identification develops low-order models for practical data reconciliation and forecasting; and adaptive model predictive control dynamically optimizes operations to enhance performance. Key contributions include a novel mechanistic model for PPB cultivation in raceway reactors, a temperature-dependent extension for the anaerobic digestion model no.1, a hybrid system identification method to approximate complex mechanistic models, and an adaptive hierarchical process-oriented MPC framework for PPB reactors and ADs to manage variable operations and unknown disturbances. These approaches advance wastewater resource recovery in their intended perspectives, providing efficient solutions for both case studies. ... Read more

Driven by the increasing demand for waste reduction and green energy production, an integrated system which combines an anaerobic membrane bioreactor (AnMBR) and a solid oxide fuel cell (SOFC) was proposed in this research project for blackwater treatment and energy production. The potentials of using an AnMBR for wastewater treatment and biogas production, and the feasibilities of producing energy from biogas with a SOFC have been investigated by many researchers. Although, combining the two equipment might raise new challenges and opportunities. The AnMBR pH has direct impacts on the biogas composition, which would subsequently affect the SOFC operational strategy. Therefore, this research project focused on the influence of the AnMBR pH on the SOFC operational strategy, which would provide insights for connecting AnMBR and SOFC. The AnMBR pH was controlled around 8 initially, and then reduced to 7. The composition of the biogas produced under each pH condition was analyzed before the biogas was conditioned for the SOFC operation. Biochar adsorption and CO2 addition were applied for biogas conditioning. pH 8 was favorable for biochar adsorption, whereas pH 7 was favorable for CO2 addition. The aim of biochar adsorption was to ensure that the H2S concentration remaining in the biogas after adsorption was less than 0.5 ppm, so that sulfur poisoning could be avoided at the anode of SOFC. A biochar column (BC) was attached to the AnMBR for the adsorption of sulfur compounds in the biogas. The BC was packed with biochar made of cow manure. The adsorption capacity of the biochar was measured to determine the amount of biochar required in the BC. After biochar adsorption, the ratio between CH4 and CO2 was balanced by adding CO2 to the biogas, to reduce the risk of carbon deposition at the anode of SOFC. The exhaust gas discharged by the SOFC could also be recycled as an alternative to CO2 addition. The performance of the SOFC system using the conditioned biogas as the fuel was assessed based on electric power output and fuel utilization efficiency. Based on the results of biogas production, conditioning, and utilization, the influence of the AnMBR pH on the SOFC operational strategy was analyzed. Furthermore, the potentials and the limitations of connecting AnMBR and SOFC were discussed. ... Read more

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.
... Read more

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. ... Read more

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.
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The global temperature rise has pushed governments more into finding ways to reduce CO2 emissions, by increasing the use of renewable fuels. Lignocellulosic biomass (wood, forest residues, agricultural residues) is a renewable fuel that has still not been utilized to its full potential. That is because it lacks properties such as homogeneity, high volumetric energy density and low moisture that its main fossil fuel competitor -coal- has. Therefore, a type of pre-treatment is needed for these disadvantages. Torrefaction, a process of heating biomass (200-300 oC) in an inert environment (no combustion), provides a product with improved physicochemical properties: reduced hydrophobicity, easier grindability, homogeneity, reduced microbial activity and increased calorific value. However, it is not enough to torrefy the biomass, as it needs to be densified in order to be utilized. With the process of pelletizing, a type of densification, torrefied biomass becomes compact and can be considered as bio-coal. While pelletizing is influenced by many parameters (moisture content, die pressure, torrefaction temperature etc), herbaceous types of biomass such as wheat straw, hay, reeds and grass, still cannot produce quality pellets without the addition of a binder. Typical organic binders such as starch, lignin and sawdust can either be expensive or biologically degrade in storage conditions. That is why addition of plastic binder should be considered. The aim of this report was to investigate how quality torrefied pellets from herbaceous biomass can be produced with the addition of plastic binder in a commercial capacity. Wheat straw and woodchips were used as feedstock, while polyethylene resin was the plastic binder. The biomasses were torrefied at 240 oC and 270 oC on the Torrgreen facilities, via a pilot-scale packed bed reactor, which recycles the volatiles from torrefaction for inertization and pelletized with a 100 kg/h pellet mill. For the torrefied wheat straw, a design of experiments was formed, to investigate how 4 parameters for pelletizing (torrefaction temperature, moisture content, plastic binder addition and pellet diameter) improved mechanical durability. Results indicated that 5% of plastic improved durability and pellet formation in total, while higher torrefaction temperature weakens the pellets and aggravates pellet formation. The highest durability achieved was 90.3%. Torrefied wood chips were pelletized for reference and showed low durability, mostly due to inability of the pelletizer. Water immersion tests on the straw pellets showed that higher torrefaction temperature increased hydrophobicity a lot, while plastics also had a positive effect. Comparison of the straw pellets produced with conventional wood pellets revealed that the former lack in mechanical durability and are high in ash content, making them incompliant with current standards. Overall, inclusion of plastics in pelletizing of torrefied herbaceous biomass, demonstrated very positive results and improved their quality, while making the operation smoother, but for scaling up and keeping the whole process sustainable a polyethylene (or other plastic) waste stream should be utilized. ... Read more

On the 14th of July 2013, a methane peak was observed in the Gale crater. This methane peak has been investigated in a non-biological context before. This study applies exoplanet research strategies and knowledge about biological methane production on Earth to investigate the biological context. Bayes formula is the foundation of the Bayesian framework approach as proposed by Walker et al. [53]. This Bayesian framework allows for separate investigation of biotic and abiotic methane production pathways to assess the likelihood that one of these pathways is responsible for the methane observation. Before probability is investigated, the viability of biotic methane production is gauged by Thermodynamic calculations. These calculations use the Gibbs free energy and show methanogenesis and sulfate reduction as viable catabolic reactions under Martian temperature and chemical soil and atmosphere compositions. Mars analogue Experiments were conducted into the kinetics of methane and hydrogen sulfide gas production under the influence of Martian Regolith analogue and Martian atmospheric analogue. The seed organisms were gathered from the Belgian Boom clay layer in the HADES lab because the Boom clay layer has strong mineralogical similarities to the Martian regolith. The experiments show that both methane and hydrogen sulfide gas production is not significantly affected by the introduction of modified Phylosilicate Martian Regolith Analog (P-MRA) and Martian Atmosphere Analog (MAA). Comparison with the ADM1 kinetic model shows that only methane gas production is comparable within one standard deviation between all experiments and the model. Biomass growth and sulfur gas production are inconsistent between experiments and the kinetic model. To quantify the probability of biotic methane production, a modified ADM1 model was used for Monte Carlo (MC) analysis of the correlation between the Martian observed methane peak and the kinetic model output for varying initial chemical conditions and virtual reactor volumes. Based on this, 78% of the simulations showed a significant correlation. Using Bayes formula, the posterior probability of the methane peak being biological in origin is higher than the prior probability of an anaerobic community being active around the Gale crater. However, this misses the crucial information on the chance of this methane peak occurring in abiotic conditions. ... Read more

Coffee farmers and producers in Kerala (India) face a serious obstacle in their pursuit of a self-sustaining coffee processing technology and fuel deficiency. Research indicates that coffee, as one of the largest industries, generates a huge amount of waste, namely Spent Coffee Grounds (SCGs). This study aims to evaluate the feasibility and efficiency of converting SCG into biochar using a solar-assisted biomass torrefying technique, while keeping frugal or "jugaad" innovation in mind. To torrefy the feedstock, it was intended to use the available SK14 solar cooker in conjunction with a prototype reactor unit. Based on previous research on torrefying coffee waste, this study asks: Can the biomass torrefied using the SK 14 cooker be utilized as fuel? In this context: Solar biomass torrefaction is an endothermic process of converting the feedstock in an inert environment at low temperatures of 200-300 °C provided by concentrated solar energy in order to produce a high yield of solid biochar.

Based on the literature research, it was important to characterize the SK14 cooker, the feedstock, and to understand the operating principles of the chosen reactor, namely Evacuated Tube Vacuum Collectors (EVCs). Since the design of the reactor and cooker were interdependent, COMSOL was used to simulate the heat distribution profile and temperature profile of the reactor model. Literature and simulation results were used to construct a prototype reactor, and torrefaction tests were conducted in Hyderabad (India). SCG was effectively torrefied to generate biochar at 240 °C and 260 °C, as evidenced by high heating values of 26 MJ/kg (21% increase) and 26.3 MJ/kg (22.50% increase), respectively compared to the raw material. The results show that the current system can be utilized as a small-scale solar biomass torrefier, creating biochar that can be used as a fuel. However, the reactor's non-homogeneous heating rate and poor heat retention severely hampered its applicability. Further study is required to find other features and aspects that might not only improve the design and efficacy of the torrefier, but also facilitate its implementation for coffee producers in Kerala.
... Read more

Palm oil is a popular ingredient in domestic products. The palm oil industry has been growing rapidly over the past decades, so that the amount of palm oil mill effluent (POME) generated from the palm oil production has been increasing as well. The anaerobic membrane bioreactor (AnMBR) is a treatment solution that can remove organic pollutants from POME while generating methane as an energy source. In comparison to conventional anaerobic digestors, the AnMBR technology has an additional membrane unit that can produce effluent with higher water quality. More specifically, if ultrafiltration is applied, the AnMBR will be able to effectively remove bacteria from the effluent, making it suitable for direct fertigation (Uman et al., 2021; Bray et al., 2021). However, in cases where infectious viruses are also present, further disinfection method might be required. In this experiment, a lab-scale AnMBR system was used for POME treatment. In order to evaluate how well the system can perform in terms of pollutant removal and methane production, under the controlled experimental conditions, several criteria were monitored: (1) chemical oxygen demand (COD) removal, (2) biomass growth, (3) biogas production, (4) digestion efficiency, and (5) volatile fatty acids (VFA) accumulation. A Long chain fatty acids (LCFA) analysis method was developed using the liquid chromatography/mass spectrometry (LC/MS), to elaborate on underlying conversion mechanisms. A COD balance analysis was also conducted. Factors that would potentially contribute to the COD gaps in the COD balance analysis were quantified and discussed in this paper as well to validate the experimental results. The solid retention time (SRT) was controlled at 140 days, and the organic loading rate (OLR) at 3 gCOD·L-1·d-1 during the first phase of the experiment, when synthetic POME and VFAs were added to the bioreactor. During the second phase, the SRT and the OLR of POME remained the same, whereas the VFAs were replaced by starch and the OLR of starch was increased, in order to simulate the real POME composition, because in addition to lipid, carbohydrate and protein are also found in POME. During Phase I, the AnMBR system could remove 98%-99% of the incoming COD, and produce about 5 L of methane each day. During Phase II, the microbes did not have enough time to adapt to the new experimental condition, but the stability of the AnMBR system could be achieved overtime, when the mixing is improved and the buffer solution is adjusted properly according to the pH variation. Although, based on the positive biomass net growth and the increased methane production, it could be predicted that adding carbohydrates to the feed for a more representative POME composition would promote biomass growth and methane production, suggesting that the AnMBR system would have higher potential when the real POME is used for energy recovery. ... Read more

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. ... Read more

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. ... Read more

Palm oil mill effluent (POME) is a high organic pollution produced during the palm oil mill process, with a brownish color and stingy odor at high temperatures. Given the popularity in palm oil output over the years, the massive amount of POME causes growing concern. The enforcement of wastewater discharge standards and laws, as well as energy recycling of sustainability goals have facilitated the development of POME treatment processes. Several lab-scale studies have looked into the treatment of industrial wastewater using anaerobic membrane bioreactor (AnMBR) which has received considerable research interest due to its demonstrated potential for POME treatment. In this study, the synthetic POME was treated by a lab-scale crossflow anaerobic membrane bioreactor system. This study tested the feasibility of thermophilic PVDF-AnMBR systems for synthetic POME treatment, and meanwhile evaluated the biological and filtration performance of AnMBR treating lipid-rich wastewater at different sludge retention times (SRTs = 60 days, 90 days, and 140 days). AnMBR showed an adequate biological performance during the stabilizing state. The synthetic POME could be treated with over 98% of COD removal efficiency in all operational conditions. Plus, better digestion efficiency could be achieved at higher SRT (140 days). However, this study stresses that even though the membrane ensures biomass retention, the AnMBR process is still dodged by long-chain fatty acid (LCFA) accumulation and inhibition problems, especially at short SRT (60 days). The continuous reduction of biomass concentration during the stabilizing process of SRT at 60 days eventually resulted in the decreased methane production and system instability. Under all operational conditions, sufficient filtration performance and net permeate fluxes between 8 and 11 LMH were achieved. The trans-membrane pressure (TMP) was under 200 mbar throughout operating process. No membrane cleaning was needed. The results showed that better sludge filterability could be achieved at SRT of 90 days. The sludge filterability was compared as per the standard methods, including specific resistance to filtration and capillary suction time, which did not show a linear relationship with SRTs. Meanwhile, the physical-chemical characteristics of the sludge during the operational phases, including TSS concentrations and SMP, have a close correlation with sludge filterability parameters, such as capillary suction time and supernatant filterability. ... Read more

With increasing pressure on natural water resources, wastewater is gradually being considered as a potential source for potable water. Current WWTPs are designed for the removal of parameters like solids, nutrients, organic matter, and pathogens. For achieving a high-quality effluent, that enables reuse, it is important to also address the removal of micropollutants, particularly antibiotics, from the wastewater. Due to these antibiotics, antibiotic resistance spreads among the microorganisms and increases through various mechanisms. Antibiotics of sulfamethoxazole (SMX), trimethoprim (TMP), ciprofloxacin (CIP), and ampicillin (AMP) are known to be found abundantly in natural waters all across the globe. The abilities of an anaerobic membrane bioreactor (AnMBR) of maintaining high SRTs with low biomass losses help in treating wastewater containing antibiotics. A recently developed technique of adding limited aeration to AnMBR has the potential of removing recalcitrant antibiotics by improving the performance of the reactor. Hence, this research aims to study the removal mechanisms of the antibiotics (SMX, TMP) and the persistence of corresponding antibiotic resistance in AnMBR, followed by the effect of the antibiotics on the performance of the AnMBR. In addition, antibiotics CIP and AMP were tested via anaerobic batch tests to investigate the effect of the limited aeration on their removal.
After adding the antibiotics SMX and TMP to the reactor, no significant difference in COD and nutrients removal was observed. The biogas production was reduced slightly after the addition of SMX 150 µg/L initially, however, it increased back to the original state after few days. Total removal of SMX and TMP was 86% and 97% respectively in the reactor. Results showed that 85% of SMX and 94% of TMP were removed through biodegradation/biotransformation and 14% of SMX and only 3% of TMP were discharged through the effluent. From the adsorption batch tests conducted, it was observed that the linear adsorption isotherm fits well for TMP. With the increase in temperature, the adsorption potential of TMP was reduced with a Kd value of 1.234 L/g at 10˚C and 0.513 L/g at 37˚C. The removal of SMX was low through adsorption and high due to degradation and follows the first-order rate kinetics with a half-life of 1.71 days. After two weeks of SMX addition to the reactor, almost all the bacteria present in the effluent gained resistance either to TMP or SMX or both. Of all the ARGs measured in this study, the genes responsible for the resistance development were sul1 and sul2. The addition of antibiotics increased the presence of ARGs in the system. The correlation between the presence of sul1 and TMP resistant bacteria, and sul1 and SMX resistant bacteria was 0.91-0.93, indicating that the gene sul1 might be involved in multidrug resistance. ARGs sul1, sul2, and dfrA1 were removed respectively by 3.2 log, 3.6 log, and 7.3 log units by the membrane. In addition, the class 1 integrons and 16s rRNA were removed by 3 log and 3.2 log units respectively. Removal of CIP and AMP was found to be high with values of 82% and 84% respectively in limited aeration assisted anaerobic batch tests. The removal efficiencies of all antibiotics were more than 80% and independent of their initial concentrations in the selected range. The increase in the removal of CIP and AMP in comparison to literature points to a relation with the added limited aeration. Nevertheless, more studies need to be performed to establish this.
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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. ... Read more

Due to the quick growth in human population and subsequently a high rate of urbanization, fresh water sources are under pressure. Estimated 1.8 billion people drink water from potentially sewage-contaminated sources and also the presence of antibiotic resistant bacteria in sewage has made the improper treatment of wastewater effluent an emerging problem. Iron electrocoagulation (Fe-EC) has shown to be successful in reducing pathogen concentration, although to different extent for types of pathogens. Besides, the water quality was found to be of influence on the effectiveness. This study therefore aimed to determine the removal mechanism for both bacteria and virus as well as assess the effect of wastewater components on the Fe-EC treatment process. EC experiments were conducted in an aerated beaker with a volume of 1L, continuously stirred. pH and current were kept stable at 7.5 and 200mA, respectively. The total charge dosage was 180 C/L. After electrolysis the samples were left to settle. Blank measurements were conducted in a 230 mg/L NaCl solution. Wastewater components were added in concentration of 4.0 mg/L for phosphate, 60 mg/L calcium, and 10 mg/L humic acids. E. coli WR1 and 휙X174 were used as indicator organisms. Contributing disinfection mechanisms for E. coli were inactivation and physical removal. During electrolysis a log removal of 3.8 log units was found, ascribed to inactivation. Further increase in removal to 6.0 log units was observed after settling. In the presence of TEMPOL only 0.3 log units removal were observed during electrolysis, but removal after settling still amounted 5.5 log units. For 휙X174 removal reactive species were not effective. Disinfection after settling equaled 4 log units, when settling was complete. Settling was found to be dependent on mixing conditions, and removal was correlated as well. Extended mixing promoted the formation of larger flocs and thereby enabled sweep flocculation for phage removal. Phosphate decreased attenuation of E. coli either for inactivation, 2.0 log units as for physical removal, 4.7 log units. Phosphate has high affinity for iron and competes with bacteria for iron surface. Calcium as well inhibited abatement of E. coli. Inactivation only amounted for 1.4 log units and removal after settling equaled 2.1 log units. Calcium is expected to complex bacteria surface, increasing repulsive forces between E. coli and iron. The effect of carbonate was only seen during electrolysis, 1.3 log units. The formation of the carbonate radical is suggested as explanation for the decrease in effectiveness. The effect of NOM on E. coli attenuation was unclear. Inactivation was inhibited to only 1.4 log units, but no effect was found on the total removal. Therefore, it can be concluded that NOM does not successfully compete with bacteria for iron surface. 휙X174 attenuation was not effected by addition of phosphate, calcium, or carbonate. On the other hand, the addition of NOM inhibited phage removal, only 0.6 log units in comparison to 4.0 log units for the blank. Adsorption of NOM onto iron surface is expected to negatively change the surface charge, inhibiting association between iron and virus. ... Read more

Purple non-sulphur bacteria (PNSB) are phototrophic bacteria currently under study in the wastewater treatment sector due to their performant nutrient and resource recovery. Until recently, most of researches have focused on closed anaerobic photobioreactors resulting in high selectivity of PNSB and appealing hydrogen, microbial proteins, and carotenoids productivity. Unfortunately, these researches also showed that the implementation of this technology is hampered by its relatively high costs. As is the case for microalgae technology, raceway reactors could possibly overcome this problem thanks to their low investment and maintenance costs. However, a survey of the scientific literature shows that only few researches have investigated the application of PNSB technology with open raceway reactors and that the limited available mechanistic models do not consider the specific conditions which characterize these reactors. Therefore, this study aims to construct a mechanistic mathematical model which includes the mixotrophic metabolism of PNSB and could be used to predict the nutrient removal and recovery and PNSB relative abundance in the raceway reactor. The model was structured mainly considering the photoorganoheterotrophic and respiring chemoorganoheterotrophic growth of PNSB competing with standard (an)aerobic-respiring and fermenting chemoorganoheterophic bacteria under semi-aerobic conditions. The model was tuned with seven batch and sequencing batch reactor (SBR) laboratory experiments. It simulates the reactor performance (COD removal rate 480-780 mgCOD/L/d, yield 0.40– 0.65 mgCODx/mgCODs) and the relative PNSB abundance (10-60%) under different operational conditions (light, dissolved oxygen, surface area) with a relative error around ± 20%. This research proposes an one-at-the-time sensitivity analysis, analysing the impact of those variables (TSS, SRT, COD, light, and biotic competition) which could play an important role in real-case scenarios. From this analysis, it emerged that influent suspended solids (TSS>250 mgTSS/L), hourly variations of the natural light cycle intensity and drops of the available soluble substrate (COD<1000mgCOD/L) could strongly disturb the abundance of PNSB in the system (from 48% to 10%). An extension of the sludge retention time, from 2 to 5 days, was observed to favour the relative abundance of PNSB (from 48% to 60%) and to increase the TSS productivity (from 235 to 400 mgTSS/L/d). The model was intended as a first attempt to simulate the nutrient removal and the PNSB dynamic in a raceway reactor. It has the flexibility to study the impact of the crucial parameters evidenced from the literature review (light, oxygen, carbon source). However, several implementations will be needed in the future, mainly focusing on anoxic chemoheterotrophic growth and hydrolysis. ... Read more