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- Biogas reforming as a sustainable solution for hydrogen production: Comparative environmental metrics with steam-methane reforming and water electrolysis in the Portuguese contextPublication . Bento, Cláudia; Lopes, Tiago; Rodrigues, Pedro; Gírio, Francisco; Silva, CarlaABSTRACT: This study delves into the dynamics of hydrogen production, with a specific focus on biogas reforming (BGSMR) for hydrogen generation. It compares the environmental impact of this solution with hydrogen production from natural gas-steam reforming (NGSMR) and commercial electrolysis in the Portuguese context. Various metrics, including carbon footprint, water depletion, energy utilization, and waste valorization are employed for a comprehensive comparison. The assessment explores the impact of operational parameters and different off-gas combustion scenarios, incorporating water recycling practices. Due to challenges in obtaining detailed data on the actual reforming process, the study relies on process simulation techniques, primarily using DWSIM. Commercially available data for water electrolysers were used for comparison. In the context of decarbonizing power systems, hydrogen from water electrolysis emerges as a competitive option only in a scenario where the power system is 100% reliant on renewable sources, particularly with respect to the carbon footprint metric. Biogas systems, characterized by near-zero carbon emissions, stand out as a favourable option from the near future to the long run. This research contributes valuable insights into the dynamics of hydrogen production, shedding light on environmentally viable alternatives across a range of power system scenarios.
- A biorefinery approach for the simultaneous production of biofuels and bioplastics [Poster]Publication . Ortigueira, Joana; Leite, T.; Pereira, J.; Serafim, L.S.; Silva, Carla; Moura, Patrícia; Lemos, Paulo Costa
- The role of heterotrophic microalgae in waste conversion to biofuels and bioproductsPublication . Silva, Teresa Lopes da; Moniz, Patricia; Silva, Carla; Reis, AlbertoABSTRACT: In the last few decades, microalgae have attracted attention from the scientific community worldwide, being considered a promising feedstock for renewable energy production, as well as for a wide range of high value-added products such as pigments and poly-unsaturated fatty acids for pharmaceutical, nutraceutical, food, and cosmetic markets. Despite the investments in microalgae biotechnology to date, the major obstacle to its wide commercialization is the high cost of microalgal biomass production and expensive product extraction steps. One way to reduce the microalgae production costs is the use of low-cost feedstock for microalgae production. Some wastes contain organic and inorganic components that may serve as nutrients for algal growth, decreasing the culture media cost and, thus, the overall process costs. Most of the research studies on microalgae waste treatment use autotrophic and mixotrophic microalgae growth. Research on heterotrophic microalgae to treat wastes is still scarce, although this cultivation mode shows several benefits over the others, such as higher organic carbon load tolerance, intracellular products production, and stability in production all year round, regardless of the location and climate. In this review article, the use of heterotrophic microalgae to simultaneously treat wastes and produce high value-added bioproducts and biofuels will be discussed, critically analyzing the most recent research done in this area so far and envisioning the use of this approach to a commercial scale in the near future.
- Carbon footprint assessment of microalgal biomass production, hydrothermal liquefaction and refining to sustainable aviation fuel (SAF) in mainland PortugalPublication . Pires, Renata; Silva, Tiago; Ribeiro, Cláudia; Costa, Luis; Matos, Cristina T.; Costa, Paula; Lopes, Tiago; Gírio, Francisco; Silva, CarlaABSTRACT: Industrial liquid effluents (e.g., from fertilizer industry) and flue gas streams (e.g., CO2-rich, from cement industry) arise as an opportunity for waste valorization. Microalgae are suitable biomass for assimilating both effluents at the cultivation stage. Under a biorefinery concept, given the urge for energy transition in the aviation sector, this research explores the transformation of a microalgae consortium grown at an industrial site in Portugal and its subsequent harvesting, hydrothermal liquefaction (HTL), and bio-oil refining. A life cycle assessment (LCA) approach is undertaken with two functional units (FU): 1 kg of microalgae dry-cell weight (dw) and 1 MJ of bio-jet fuel. The latter follows an attributional approach with energy allocation for comparison with the Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA) guidelines. HTL is based on data from bench-scale experiments and literature, whereby the Petroleum Refinery Life Cycle Inventory Model (PRELIM) is used to mimic bio-oil refining. Following this approach, achieving Sustainable Aviation Fuel (SAF) compliance requires net-zero electricity (0 gCO2eq/kWh), with an HTL bio-oil yield of 55.6 % dw (the maximum observed), a minimum refining bio-jet fuel yield of at least 16 %. Alternatively, an HTL bio-oil yield of 36.9 % dw (the median observed) with a refining efficiency of at least 24.3 %.
- Biodesulfurization biorefinery using Gordonia alkanivorans strain 1B: life cycle inventory of the integrated processPublication . Silva, Tiago; Silva, Carla; Paixão, Susana M.; Alves, LuísABSTRACT: High sulfur concentrations are a problem common to fossil fuels and derivatives (such as oil and coal), as well as many new generation fuels and biofuels (such as pyrolysis oils, syngas, biogas or even biodiesel). If the sulfur present in these fuels is released into the atmosphere it can result in SO2/SOx emissions, leading to environmental damage, and health issues. Transportation fuels have sulfur limits that go below 5000 ppm in ships, 3000 ppm in airplanes and 10 ppm in cars, and without treatment fuels can have several thousand ppm of sulfur. As such, they must be submitted to desulfurization, typically through a thermochemical process known as hydrodesulfurization, in which H2 is combined with the fuel at high temperatures and pressures, in the presence of metal catalysts. However, this process has significant environmental impacts. Usually, it depends on hydrogen and heat/steam produced from natural gas, totalizing 4.17 kg natural gas per 2.89 kg sulfur removed. It also involves high electricity and water consumption (approximately 2.9 kWh and 86.9 kg, respectively, per 2.89 kg sulfur removed). Furthermore, these impacts are greater for lower sulfur demands (Burgess & Brennan, 2001). Thus, there has been a search for alternative/complementary processes, one of which is biodesulfurization (BDS). It consists of the use of microorganism that consume the sulfur present in the fuels, at ambient temperature and pressure, without the need for metal catalysts. BDS still presents several bottlenecks, common to many microbial processes, such as low conversion rates and high production costs for the microbial biocatalyst. To surpass these limitations researchers have pursued different strategies: minimization/optimization of culture medium and culture conditions; employment of cheaper alternative nutrient sources; exploitation of added value products. Gordonia alkanivorans strain 1B is a bacterium known for its biodesulfurization properties. It has demonstrated several characteristics which make it interesting: it can perform BDS of different compounds, several of which extremely recalcitrant for the thermochemical process; it has very low nutritional needs; it can be cultivated on several alternative carbon sources; it has been shown to produce two different types of added value products: carotenoids and biosurfactants (Alves et al., 2015; Silva et al., 2020, 2022). Therefore, G. alkanivorans strain 1B is the ideal candidate for a biodesulfurization biorefinery, that simultaneously removes sulfur from fuels and produces carotenoids and biosurfactants.
- Lignin syngas bioconversion by Butyribacterium methylotrophicum: advancing towards an integrated biorefineryPublication . Pacheco, Marta; Pinto, Filomena; Ortigueira, Joana; Silva, Carla; Gírio, FranciscoABSTRACT: Hybrid bio-thermochemical based technologies have the potential to ensure greater feedstock flexibility for the production of bioenergy and bioproducts. This study focused on the bioconversion of syngas produced from low grade technical lignin to C-2-/C-4-carboxylic acids by Butyribacterium methylotrophicum. The effects of pH, medium supplementation and the use of crude syngas were analyzed. At pH 6.0, B. methylotrophicum consumed CO, CO2 and H-2 simultaneously up to 87 mol% of carbon fixation, and the supplementation of the medium with acetate increased the production of butyrate by 6.3 times. In long-term bioreactor experiments, B. methylotrophicum produced 38.3 and 51.1 mM acetic acid and 0.7 and 2.0 mM butyric acid from synthetic and lignin syngas, respectively. Carbon fixation reached 83 and 88 mol%, respectively. The lignin syngas conversion rate decreased from 13.3 to 0.9 NmL/h throughout the assay. The appearance of a grayish pellet and cell aggregates after approximately 220 h was indicative of tar deposition. Nevertheless, the stressed cells remained metabolically active and maintained acetate and butyrate production from lignin syngas. The challenge that impurities represent in the bioconversion of crude syngas has a direct impact on syngas cleaning requirements and operation costs, supporting the pursuit for more robust and versatile acetogens.
- Oleaginous Yeast Biorefinery: Feedstocks, Processes, Techniques, BioproductsPublication . Silva, Teresa Lopes da; Fontes, Afonso; Reis, Alberto; Silva, Carla; Gírio, FranciscoABSTRACT: The world climate crisis has triggered the search for renewable energy sources. Oleaginous yeasts are a potential renewable source of biofuels. However, the yeast-derived biofuels cost is still non-competitive with the fossil fuel prices. To improve the sustainability of yeast-derived biofuels, it is necessary to valorize all yeast biomass fractions, an approach based on the biorefinery concept. This review describes the present situation of the oleaginous yeast biorefinery research, emphasizing the feedstock, processes and techniques involved in this concept, as well as on potential bioproducts that can be obtained from oleaginous yeast biomass.
- Raw Glycerol Based Medium for DHA and Lipids Production, Using the Marine Heterotrophic Microalga Crypthecodinium cohniiPublication . Moniz, Patricia; Silva, Carla; Oliveira, Ana Cristina; Reis, Alberto; Silva, Teresa Lopes daABSTRACT: Crude glycerol, a biodiesel industry byproduct, and corn steep liquor (CSL) derived from a starch industry, were used as carbon and nitrogen sources, respectively, for lipid production, using the heterotrophic microalga C. cohnii grown in a bench bioreactor, in a batch culture. The maximum biomass concentration, lipid content and lipid productivity attained were 5.34 g/L, 24.6% (w/w Dry Cell Weight-DCW) and 0.016 g L−1 h−1, respectively. Flow cytometry analysis was used to evaluate the impact of these substrates on the microalgae cells. A high proportion of intact cells with enzymatic (esterases) activity (>50%) was present throughout the cultivation time course. These results indicate that crude glycerol and CSL can be used in the medium formulation for DHA and lipid production using this microalga, which reduce the process costs in an expected maximum of 84%.
- A Systematic Review of Syngas Bioconversion to Value-Added Products from 2012 to 2022Publication . Pacheco, Marta; Moura, Patrícia; Silva, CarlaABSTRACT: Synthesis gas (syngas) fermentation is a biological carbon fixation process through which carboxydotrophic acetogenic bacteria convert CO, CO2, and H-2 into platform chemicals. To obtain an accurate overview of the syngas fermentation research and innovation from 2012 to 2022, a systematic search was performed on Web of Science and The Lens, focusing on academic publications and patents that were published or granted during this period. Overall, the research focus was centered on process optimization, the genetic manipulation of microorganisms, and bioreactor design, in order to increase the plethora of fermentation products and expand their possible applications. Most of the published research was initially funded and developed in the United States of America. However, over the years, European countries have become the major contributors to syngas fermentation research, followed by China. Syngas fermentation seems to be developing at "two-speeds", with a small number of companies controlling the technology that is needed for large-scale applications, while academia still focuses on low technology readiness level (TRL) research. This systematic review also showed that the fermentation of raw syngas, the effects of syngas impurities on acetogen viability and product distribution, and the process integration of gasification and fermentation are currently underdeveloped research topics, in which an investment is needed to achieve technological breakthroughs.
- Cascading Crypthecodinium cohnii biorefinery: global warming potential and techno-economic assessmentPublication . Silva, Carla; Moniz, Patricia; Oliveira, Ana Cristina; Vercelli, Samuela; Reis, Alberto; Silva, Teresa Lopes daABSTRACT: Prior to the commissioning of a new industrial biorefinery it is deemed necessary to evaluate if the new project will be beneficial or detrimental to climate change, one of the main drivers for the sustainable development goals (SDG) of the United Nations. In particular, how SDG 7, Clean and Efficient Energy, SDG 3, Good Health and Well Being, SDG 9, Industry Innovation and Infrastructure, and SDG 12, Responsible Production and Consumption, would engage in a new biorefinery design, beneficial to climate change, i.e., fostering SDG 13, Climate Action. This study uses life cycle assessment methodology (LCA) to delve in detail into the Global Warming Impact category, project scenario GHG savings, using a conventional and a dynamic emission flux approach until 2060 (30-year lifetime). Water, heat and electricity circularity are in place by using a water recirculation process and a combined heat and power unit (CHP). A new historical approach to derive low and higher-end commodity prices (chemicals, electricity, heat, jet/maritime fuel, DHA, N-fertilizer) is used for the calculation of the economic indicators: Return of investment (ROI) and inflation-adjusted return (IAR), based upon the consumer price index (CPI). Main conclusions are: supercritical fluid extraction is the hotspot of energy consumption; C. cohnii bio-oil without DHA has higher sulfur concentration than crude oil based jet fuel requiring desulfurization, however the sulfur levels are compatible with maritime fuels; starting its operation in 2030, by 2100 an overall GHG savings of 73% (conventional LCA approach) or 85% (dynamic LCA approach) is projected; economic feasibility for oil productivity and content of 0.14 g/L/h and 27% (w/w) oil content, respectively (of which 31% is DHA), occurs for DHA-cost 100 times higher than reference fish oil based DHA; however future genetic engineering achieving 0.4 g/L/h and 70% (w/w) oil content (of which 31% is DHA), reduces the threshold to 20 times higher cost than reference fish oil based DHA; N-fertilizer, district heating and jet fuel may have similar values then their fossil counterparts.