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A combined hydrothermal gasification -solid oxide fuel cell system for sustainable production of algal biomass and energy
Abstract
Hydrothermal gasification (HTG) is a promising technology that allows the recovery of nutrients from wet biomass with simultaneous production of an energy-rich gas. In this work, wastewater effluent (leachate) obtained from a composter sanitary system operating without external connection to sewer pipes was used as a feedstock for HTG process. The leachate effluent was characterized by its high moisture and inorganic content. Mainly H 2 rich gas was obtained from the HTG of the leachate at 600 °C, 28 MPa with almost full recovery of nitrogen and phosphorus; up to 74.4% and 92% respectively. For an efficient power-generation system with low emissions, experimental results combining solid oxide fuel cells (SOFC) with the obtained gas from the HTG were performed. Thermodynamic calculations were performed on the gas compositions to evaluate the performance and the risk of solid carbon formation at a typical SOFC operation temperature 750 °C. Furthermore, for nutrient recycling purposes, the obtained nutrient rich effluent from the gasification was used as a growth medium for microalgae Chlorella vulgaris. Finally, a complete valorization chain based on both experimental study and model prediction that combine, energy conversion and microalgae valorization was investigated.
... Wastewater is a rich source of various valuable resources, with each gram of chemical oxygen demand (COD) containing approximately 17.8-28.7 kJ of energy [4]. Among these resources, nutrients, energy, and water (NEW) are critical and can be recovered through various wastewater treatment technologies [5], including microbial fuel cells (MFCs) [6], hydrothermal gasification (HTG) [7], and aqueous phase reforming (APR) [8] for the recovery of energy from high-energy wastewater, membrane times, with an average citation frequency of 33.39 per paper and an h-index of 33. Figure 1 illustrated the annual volume of published papers, showing a notable upward trend prior to 2017, and peaking with 13 publications in that year. Following a minor dip, papers published on the topic surged to 11 in 2022. ...
Osmotic microbial fuel cells (OsMFCs) with the abilities to simultaneously treat wastewater, produce clean water, and electricity provided a novel approach for the application of microbial fuel cell (MFC) and forward osmosis (FO). This synergistic merging of functions significantly improved the performances of OsMFCs. Nonetheless, despite their promising potential, OsMFCs currently receive inadequate attention in wastewater treatment, water reclamation, and energy recovery. In this review, we delved into the cooperation mechanisms between the MFC and the FO. MFC facilitates the FO process by promoting water flux, reducing reverse solute flux (RSF), and degrading contaminants in the feed solution (FS). Moreover, the water flux based on the FO principle contributed to MFC’s electricity generation capability. Furthermore, we summarized the potential roles of OsMFCs in resource recovery, including nutrient, energy, and water recovery, and identified the key factors, such as configurations, FO membranes, and draw solutions (DS). We prospected the practical applications of OsMFCs in the future, including their capabilities to remove emerging pollutants. Finally, we also highlighted the existing challenges in membrane fouling, system expansion, and RSF. We hope this review serves as a useful guide for the practical implementation of OsMFCs.
... The simulation of catalytic hydrothermal gasification was implemented in the ASPEN Plus process flowsheeting software by applying a yield-type reactor combined with the outputs of the LM-10-17-17-6-6 artificial neural network model. The effects of HTG process parameters on the gas yield and carbon conversion ratio are illustrated in Fig. 6. Damergi et al. (2019) reported that high HTG temperature levels (up to 600 • C) are required in the absence of catalysts to achieve adequate biomass conversion with a carbon conversion efficiency of 41-43%. Our study shows that the carbon conversion ratio and the total gas yield can be increased above 50% and 39 mol kg − 1 by elevating the temperature from 550 • C to 700 • C (Fig. 6a) at ideal pressure levels (Fig. 6c). ...
Global warming and climate change urge the deployment of close carbon-neutral technologies via the synthesis of low-carbon emission fuels and materials. An efficient intermediate product of such technologies is the biomethanol produced from biomass. Microalgae based technologies offer scalable solutions for the biofixation of CO2, where the produced biomass can be transformed into value-added fuel gas mixtures by applying thermochemical processes. In this study, the environmental and economic performances of biomethanol production are examined using artificial neural networks (ANNs) for the modelling of catalytic and noncatalytic hydrothermal gasification (HTG). Levenberg-Marquardt and Bayesian Regularisation algorithms are applied to describe the thermocatalytic transformation involving various types of feedstocks (biomass and wastes) in the training process. The relationship between the elemental composition of the feedstock, HTG reaction conditions (380 °C–717 °C, 22.5 MPa–34.4 MPa, 1–30 wt% biomass-to-water ratio, 0.3 min–60.0 min residence time, up to 5.5 wt% NaOH catalyst load) and fuel gas yield & composition are determined for Chlorella vulgaris strain. The ideal ANN topology is characterised by high training performance (MSE = 5.680E-01) and accuracies (R² ≥ 0.965) using 2 hidden layers with 17-17 neurons. The process flowsheeting of biomass-to-methanol valorisation is performed using ASPEN Plus software involving the ANN-based HTG fuel gas profiles. Cradle-to-gate life cycle assessment (LCA) is carried out to evaluate the climate change potential of biomethanol production alternatives. It is obtained that high greenhouse gas (GHG) emission reduction (−725 kg CO2,eq (t CH3OH)⁻¹) can be achieved by enriching the HTG syngas composition with H2 using variable renewable electricity sources. The utilisation of hydrothermal gasification for the synthesis of biomethanol is found to be a favourable process alternative due to the (i) variable synthesis gas composition, (ii) heat integration-, and (iii) GHG emission mitigation possibilities.
Achieving the EU 2030 vision of a 15% minimum amount of biofuels utilized in the road transportation require more research on biofuel production from biomass feedstock. To this end, this review study examines the use of green, deep eutectic solvents and direct transesterification approaches for biomass conversion to biofuels. Next, biogas production from anaerobic co-digestion of microalgae biomass is presented. Lastly, the effect of operating conditions, as well as advantages and limitations of several biomass conversion techniques are outlined. Of note, this study presents promising microalgae conversion processes which could be progressed are the use of bio-based solvents and supercritical fluids for biodiesel production, hydrothermal liquefaction for biogas production, microwave-induced pyrolysis for syngas production, and ultrasound/microwave enhanced extraction for bio-oil production. These are based on the possibility of high yield and process economics. We have also enumerated knowledge gaps needed to propel future studies.
Steam generation of the industrial steam networks through an internal process driven by a renewable energy can be extremely demanding. Conventionally, fossil fuels are used for this aim since a high-temperature heat source is needed to reliability drive a steam network. To address this demand and decrease environmental penalty associate with the conventional methods, an innovative and high-efficient biomass-driven cogeneration system is proposed for the real need of the utility systems by considering a suitable total-site heat recovery and distribution mechanism. The proposed cogeneration system consists of a biomass gasifier, a gas turbine cycle, a solid oxide fuel cell, and a steam network unit. In comparison with the previous cogeneration systems, the steam required for the gasification process in the gasifier is supplied by some portion of the steam generated at the last stage of the steam network unit. Also, natural gas is used as an auxiliary fuel to satisfy the surplus fuel required for the steam generation. A new methodology is introduced to use a biomass-driven cogeneration system as a primary steam generator of the steam network unit instead of using a conventional boiler or gas turbine with heat recovery steam generator. The proposed system produces additional heating load of 235.26 MW in comparison with the topping system (i.e., combined solid oxide fuel cell/gas turbine system). Integrating the steam network unit also increased the energy efficiency of the basic system from 20.05% to 54.35% and the net power from 47.55 MW to 72.3 MW. The proposed integrated system can be regarded as a promising futuristic layout for simultaneous steam and power generation of the petrochemical industries.
This study targets the research gap in co-hydrothermal gasification (HTG) process conditions and composition of sewage sludge and microalgae biomass on hydrogen enriched gas production. This study also focuses on zero emission concept for waste disposal and value addition of these wastes for green energy production. The effect of solid catalyst synthesized from carbon-zinc battery waste on higher amount of hydrogen gas production was studied. Response surface methodology (RSM) was used for modelling and optimizing the hydrogen yield from HTG process. Uppermost hydrogen composition was 38.27 wt% in gaseous product (40.7 wt%) at catalyst dose of 4 wt% for 2: 1 ratio at a temperature of 440 °C. HTG mechanism involves water-gas shift, steam reforming and methanation reactions for hydrogen production. Optimisation studies showed catalyst load of 2.3 wt%, temperature of 426.36 °C and time of 70.22 min will result in 40 wt% of hydrogen gas yield.
Energy consumption and sludge production minimization represent rising challenges for wastewater treatment plants (WWTPs). The goal of this study is to investigate howenergy is consumed throughout the whole plant and how operating conditions affect this energy demand. A WWTP based on the activated sludge process was selected as a case study. Simulations were performed using a pre-compiled model implemented in GPS-X simulation software.Model validationwas carried out by comparing experimental and modeling data of the dynamic behavior of the mixed liquor suspended solids (MLSS) concentration and nitrogen compounds concentration, energy consumption for aeration, mixing and sludge treatment and annual sludge production over a three year exercise. In this plant, the energy required for bioreactor aeration was calculated at approximately 44% of the total energy demand. A cost optimization strategy was appliedby varying theMLSS concentrations (from1 to 8 gTSS/L)while recordingenergy consumption, sludge production and effluent quality. An increase ofMLSS led to an increase of the oxygen requirement for biomass aeration, but it also reduced total sludge production. Results permit identification of a key MLSS concentration allowing identification of the best compromise between levels of treatment required, biological energy demand and sludge production while minimizing the overall costs.
This study evaluated the use of mixed indigenous microalgae (MIMA) as a treatment process for wastewaters and CO2 capturing technology at different temperatures. The study follows the growth rate of MIMA, CO2 Capturing from flue gas, removals of organic matter and nutrients from three types of wastewater (primary effluent, secondary effluent and septic effluent). A noticeable difference between the growth patterns of MIMA was observed at different CO2 and different operational temperatures. MIMA showed the highest growth grate when injected with CO2 dosage of 10% compared to the growth for the systems injected with 5% and 15 % of CO2. Ammonia and phosphorus removals for Spirulina were 69%, 75%, and 83%, and 20%, 45% and 75 % for the media injected with 0, 5 and 10% CO2. The results of this study show that simple and cost-effective microalgae-based wastewater treatment systems can be successfully employed at different temperatures as a successful CO2 capturing technology even with the small probability of inhibition at high temperatures.
In this work, the hydrothermal gasification of microalgae, Scenedesmus obliquus, under supercritical water conditions was studied. The gasification experiments were conducted at a laboratory unit in KIT. The algal biomass used was cultivated by Strategic Science Consult (SSC) GmbH in Hamburg using a novel configuration of a flat-plate photobioreactor (BIQ-House) which utilizes sunlight for the growth of microalgae. The ultimate target being researched is the integration between the algal biomass production and hydrothermal gasification. This can be realized by increasing the energetic efficiencies of the two processes and by using byproducts from the hydrothermal gasification as a feed input to algal cultivation. For this purpose, the algal biomass was gasified in a tubular reactor under a temperature of 600-650 °C and a pressure of 28 MPa. The biomass concentration (Dry matter, DM) ranged from 2.5 to 5 % and a catalyst consisting of potassium carbonate (K 2 CO 3) with a [K + ] concentration of 1500 ppm was applied. The mean residence time at these conditions was 3-3.5 minutes and the product consisted mainly of (H 2 , CO 2 and CH 4) with small amounts of lighter hydrocarbons. Our experimental results show high carbon gasification efficiencies (> 90%). A continuous operation up to 50 hours has been achieved. The composition of the gas mixture at steady state operation was measured to be (Vol. %; 46% H 2 , 19% CH 4 , 29% CO 2 , 4.5% C 2 H 6), having a lower heating value (LHV) of ~ 18.5 MJ/Kg DM. In addition, the experiments for algal cultivation were conducted by SSC GmbH using the byproducts (residual water and nutrients) of hydrothermal gasification and the results provide an indication that the integration between the two processes might be possible.
Food security for all is a global political goal and an outstanding moral concern. The common response to this concern is agricultural intensification, which includes among other things increasing inputs of fertilisers. The paper addresses the fact that phosphorus (P) is essential for agricultural production but large and increasing amounts of P fertilisers stem from depletable mines. This raises sustainability concerns and the possibility of long-term food insecurity. The paper analyses three scenarios for global phosphorus extraction and recycling under discounted utilitarianism. First, for a benchmark scenario without recycling, food security will inevitably be violated in the long run. Second, if we introduce P recycling, food security can be maintained but food production falls over time and approaches a minimum level just sufficient to feed the global population. Third, a sustainable (i.e. non-declining) path of food production is feasible. Compared to just maintaining a minimum level of food production the sustainable path requires greater recycling efforts. Recycling efforts are increasing over time but the total discounted costs are finite and, hence, sustainable food production seems feasible even if it depends on depletable phosphate mines.
In this study, for the first time, a microalga was grown on non-diluted human urine. The essential growth requirements for the species Chlorella sorokiniana were determined for different types of human urine (fresh, hydrolysed, male and female). Batch experimental results using microtiter plates showed that both fresh and synthetic urine supported rapid growth of this species, provided additional trace elements (Cu, Fe, Mn, and Zn) were added. When using hydrolysed urine instead of fresh urine, additional magnesium had to be added as it precipitates during hydrolysis of urea. C. sorokiniana was able to grow on non-diluted urine with a specific growth rate as high as 0.104 h−1 under light-limited conditions (105 μmol photons m−2 s−1), and the growth was not inhibited by ammonium up to a concentration of 1,400 mg NH4+-N L−1. The highest growth rate on human urine was as high as 0.158 h−1. Because it was demonstrated that concentrated urine is a rich and good nutrient source for the production of microalgae, its application for a large-scale economical and sustainable microalgae production for biochemicals, biofuels and biofertilizers becomes feasible.
Micro-algae have received considerable interest as a potential feedstock for producing sustainable transport fuels (biofuels). The perceived benefits provide the underpinning rationale for much of the public support directed towards micro-algae research. Here we examine three aspects of micro-algae production that will ultimately determine the future economic viability and environmental sustainability: the energy and carbon balance, environmental impacts and production cost. This analysis combines systematic review and meta-analysis with insights gained from expert workshops.We find that achieving a positive energy balance will require technological advances and highly optimised production systems. Aspects that will need to be addressed in a viable commercial system include: energy required for pumping, the embodied energy required for construction, the embodied energy in fertilizer, and the energy required for drying and de-watering. The conceptual and often incomplete nature of algae production systems investigated within the existing literature, together with limited sources of primary data for process and scale-up assumptions, highlights future uncertainties around micro-algae biofuel production. Environmental impacts from water management, carbon dioxide handling, and nutrient supply could constrain system design and implementation options. Cost estimates need to be improved and this will require empirical data on the performance of systems designed specifically to produce biofuels. Significant (>50%) cost reductions may be achieved if CO2, nutrients and water can be obtained at low cost. This is a very demanding requirement, however, and it could dramatically restrict the number of production locations available.
This paper presents a process model for the polygeneration of Synthetic Natural Gas (SNG), power and heat by catalytic hydrothermal gasification of biomass and biomass wastes in supercritical water. Following a systematic process design methodology, thermodynamic property models and thermo-economic process models for hydrolysis, salt separation, gasification and the separation of CH4, CO2, H2 and H2O at high pressure are developed and validated with experimental data. Different strategies for an integrated separation of the crude product, heat supply and energy recovery are elaborated and assembled in a general superstructure. The influence of the process design on the performance is discussed for some representative scenarios that highlight the key aspects of the design. Based on this work, a thermo-economic optimisation will allow for determining the most promising options for the polygeneration of fuel and power depending on the available technology, catalyst lifetime, substrate type and plant scale.
Hydrothermal (HT) conversion is a promising and suitable technology for the generation of biofuels from microalgae. Besides the fact that water is used as a “green” reactant and solvent and that no biomass drying is required, the technology offers a potential nutrient source for microalgae culture using an aqueous effluent very rich in essential inorganic nutrients. However, upon continuous and multiple recycling of this HT effluent, the recalcitrant organic fraction is likely to increase and may potentially attain toxic thresholds for microalgae use. In this work, we show the presence of recalcitrant N-containing organic compounds (NOC's) in the HT effluent. The most prominent NOC's in the extracts were carefully examined for their effect on microalgae, namely 2-pyrrolidinone and β-phenylethylamine (β-PEA). The first set of experiments consisted in testing these two substances at three different concentrations (10, 50 and 150 ppm) using three different microalgae strains: Phaeodactylum tricornutum, Chlorella sorokiniana and Scenedesmus vacuolatus. The confirmed half maximal inhibitory concentration (IC50) was approximately 75 ppm for all tested species. In the second set of experiments, P. tricornutum was grown using diluted HT effluent. Experimental conditions were set by adjusting the nitrogen concentration in the HT effluent to be equal to a known commercial medium. The concentrations of specific NOC's were lowered to concentrations of 8.5 mg/L 2-pyrrolidinone and 0.5 mg/L β-PEA after dilution. The growth of P. tricornutum using the diluted HT solution was kept constant with no evidence of inhibition or consumption of NOC's, as the concentration of the specific compounds remains the same before and after growth. Therefore, in order to avoid effects of accumulation of NOC's upon continuous recycling, the HT effluent was pumped through the existing hydrothermal gasification unit as a water clean-up step. The conversion of NOC's to ammonium was successfully achieved.
A combined process for carotenoids extraction and efficient bioenergy recovery from the wet microalgae biomass is proposed. High added-value products could thus be extracted prior a hydrothermal gasification of the algal biomass into synthetic natural gas. The economic sustainability of biofuel production from algal biomass as well as the large energy demands of microalgae cultivation and harvesting is addressed in this paper. Two green solvents, ethanol and 2-methyltetrahydrofuran (MTHF), were used to achieve the maximum extractability of selected carotenoids. Pure MTHF was tested for the first time as an alternative renewable solvent for carotenoid extraction from wet biomass and promising results were obtained (30 min at 110 °C), with 45% of total carotenoids being extracted. The energy content of the residual biomass corresponds to a High Heating Value (HHV) of 18.1 MJ/kg. With a 1:1 mixture of both MTHF and ethanol, more carotenoids were extracted from wet biomass (66%) and the remaining HHV of the residual biomass was 15.7 MJ/kg. The perspectives of combined carotenoid extraction and energy recovery for a better microalgae valorization are discussed.
Fuel cell and hydrogen technologies are re-gaining momentum in a number of sectors including industrial, tertiary and residential ones. Integrated biogas fuel cell plants in wastewater treatment plants and other bioenergy recovery plants are nowadays on the verge of becoming a clear opportunity for the market entry of high-temperature fuel cells in distributed generation (power production from a few kW to the MW scale). High-temperature fuel cell technologies like molten carbonate fuel cells (MCFCs) and solid oxide fuel cells (SOFCs) are especially fit to operate with carbon fuels due to their (direct or indirect) internal reforming capability. Especially, systems based on SOFC technology show the highest conversion efficiency of gaseous carbon fuels (e.g., natural gas, digester gas, and biomass-derived syngas) into electricity when compared to engines or gas turbines. Also, lower CO2 emissions and ultra-low emissions of atmospheric contaminants (SOX, CO, VOC, especially NOX) are generated per unit of electricity output. Nonetheless, stringent requirements apply regarding fuel purity. The presence of contaminants within the anode fuel stream, even at trace levels (sometimes ppb levels) can reduce the lifetime of key components like the fuel cell stack and reformer. In this work, we review the complex matrix (typology and amount) of different contaminants that is found in different biogas types (anaerobic digestion gas and landfill gas). We analyze the impact of contaminants on the fuel reformer and the SOFC stack to identify the threshold limits of the fuel cell system towards specific contaminants. Finally, technological solutions and related adsorbent materials to remove contaminants in a dedicated clean-up unit upstream of the fuel cell plant are also reviewed.
Biomass is an attractive renewable and stored energy that can be converted to transportation fuels, chemicals and electricity using bio-chemical and thermo-chemical conversion routes. Notably, biofuels have relatively lower greenhouse gas emissions compared to the fossil fuels. A biomass gasifier can convert lignocellulosic biomass such as wood into syngas, which can be used in Solid Oxide Fuel Cell (SOFC) to produce heat and electricity. SOFC has very good thermodynamic conversion efficiency for converting methane or hydrogen into electricity, and integration of SOFC with gasifier gives heat integration opportunities that allow one to design systems with electricity production efficiencies as high as 70%. Generally, process design and operational optimization problems have conflicting performance objectives, and Multi-Objective Optimization (MOO) methods are applied to quantify the trade-offs among the objectives and to obtain the optimal values of design and operating parameters. This study optimizes biomass gasifier and SOFC plant for annual profit and annualized capital cost, simultaneously. A Pareto front has been obtained by solving MOO problem, and then net flow method is used to identify some optimal solutions from the Pareto front for the implementation into next phase. The constructed composite curves, which notify maximum amount of possible heat recovery, and first law efficiency also indicate better performance of the integrated plant. Uncertainty of market and operating parameters has been added to the optimization problem, and robust MOO of the integrated plant has been performed, which retains less sensitive Pareto solutions during the optimization. Finally, Pareto solutions obtained via normal and robust MOO approaches are considered for uncertainty analysis, and Pareto solutions obtained via robust MOO found to be less sensitive.
Human urine contains significant amounts of N (nitrogen) and P (phosphorus); therefore it has been successfully used as fertilizer in different crops. But the use of urine as fertilizer has several constraints, such as, the high cost of transportation, an unpleasant smell, the risk of pathogens, and pharmaceutical residue. A combined and improved N stripping and P precipitation technique is used in this study. In this technique, Ca(OH)2 is used to increase the pH of urine which converts ammonium into ammonia gas and precipitate P as Ca-P compound. The ammonia gas is stripped and passed into the sulfuric acid where ammonium sulfate and hydrogen triammonium disulfate is formed. The experiment was performed using 700 ml of urine and the pH of the urine was increased above 12. Our results showed that 85-99% of N and 99% of P (w/w) can be harvested from urine in 28 h at 40 oC and in 32 h at 30 oC. The harvested N (13% N w/w) and P (1.5% P w/w) can be used as mineral fertilizer. The economic assessment of the technique showed that the extraction of N and P from 1 m3 of pure urine can make a profit of €2.25.
The toxic effects of phenol on four marine microalgae (Dunaliella salina, Platymonas subcordiformis, Phaeodactylum tricornutum Bohlin, and Skeletonema costatum) were evaluated. The 96 h EC50 values were 72.29, 92.97, 27.32, and 27.32 mg L⁻¹, respectively, which were lower than those values of freshwater microalgae reported in the literature. During a 96-h exposure to a sub-lethal concentration of phenol (1/2 96 h EC50) with green alga (D. salina) and diatom (S. costatum), reactive oxygen species (ROS) accumulation, and chlorophyll a (Chl a) content decrease were simultaneously observed in diatom cells after 48 h treatment. On the contrary, other chlorophylls in both algae were unaffected. Under transmission electron microscopy (TEM), the phenol-induced ultrastructure alterations included disappearance, or shrinkage, of nucleolus and enlargement of vacuoles, which may result in programmed cell death (PCD). The increase in number of lipid droplets may be related to phenol detoxification. These results indicate that the sensitivity of marine microalgae to phenol was dependent on some biotic factors such as cell size, ROS production, and phenol degradation ability in algal cells.
This book reports on the most recent applications of processes with a particular focus on the source and the properties of biogas and on the characteristics of the fuel cells (FCs). It describes adsorbing materials of potential interest are reviewed and the preparation methods and treatments employed to improve the adsorption properties as well as the stability and regenerability. The characterization of the chemical and physical properties involved in these processes is examined in particular detail. The book also covers aspects that concern the development of the adsorption apparatus with particular attention on the target of low residual concentration and high selectivity.
High temperature FCs, such as molten carbonates (MCFCs) or solid oxides (SOFCs), are efficient, with a low environmental impact, and they can use a wide variety of fuels, such as biogas. The presence of some poisonous compounds such as sulphides, halides, and siloxanes can react with electrode catalysts and electrolyte, leading to the degradation and short lifetime of the cell. The treatment of raw biogas to obtain a FC-compatible fuel is mainly based on adsorption processes on suitable materials.
A paradigm shift to waste reuse has started in the wastewater sector with many experts calling for greater resource recovery, often facilitated by alternative solutions such as source separation. Source separation has been shown to be advantageous for improving treatment capacity, food security, and efficiency; yet these systems are still immature, considered risky by professionals and scarcely implemented. This study attempts to answer the question of why source separation is still marginalized by examining the Swedish experience with source separated wastewater from the perspective of Technology Innovation Systems (TIS) in order to identify obstacles and policy recommendations. Considering that source-separation is still in a development phase, the study found that source separation works moderately well within the on-site niche and that blackwater systems in general perform better than urine diversion. Knowledge development is found to be the weakest function. A major blocking mechanism is the weakness of interchange between knowledge development and entrepreneurial activity. Policy recommendations include: increased R&D; building networks and communication platforms; and establishing guidelines for technologies, legislation interpretation and organizational models.
The risk of a worldwide phosphorus (P) crisis has been predicted in the past ten years by many researchers and organizations who sought alternative resources of P. Source-separation of urine is being widely considered as a suitable waste stream for P recovery to mitigate the shortage of P while also preventing the eutrophication of receiving waters. In dense cities, urine separation and P recovery as struvite can be efficiently implemented in every building. In order to evaluate the impact of the urine separation and P recovery system in buildings, this study determines the potential amounts of P recovered, freshwater saved, and the environmental impacts of the large-scale production of struvite from source-separated human urine in both typical residential and office buildings in dense cities. The results show that the net struvite production amounts in a typical dense city can cover the diammonium phosphate (DAP) fertilizer consumptions in many countries and the net freshwater saving amounts can be up to 47–87 L/(person·d). These benefits can be achieved with less than 0.3% additional energy consumption and 1% additional environmental emissions compared with conventional buildings. Moreover, the use of environmental friendly materials can further reduce the environmental emissions to a significant extent. Therefore, based on the results obtained in this study, the urine separation and P recovery system is strongly recommended to be implemented in buildings of dense cities.
The poisoning effect by hydrogen chloride (HCl) on state-of-the-art Ni anode-supported solid oxide fuel cells (SOFCs) at 750 °C is evaluated in either hydrogen or syngas fuel. Experiments are performed on single cells and short stacks and HCl concentration in the fuel gas is increased from 1 ppm(v) up to 1000 ppm(v) at different current densities. Characterization methods such as cell voltage monitoring vs. time and electrochemical impedance response analysis (distribution of relaxation times (DRT), equivalent electrical circuit) are used to identify the prevailing degradation mechanism. Single cell experiments revealed that the poisoning is more severe when feeding with hydrogen than with syngas. Performance loss is attributed to the effects of HCl adsorption onto nickel surfaces, which lowered the catalyst activity. Interestingly, in syngas HCl does not affect stack performance even at concentrations up to 500 ppm(v), even when causing severe corrosion of the anode exhaust pipe. Furthermore, post-test analysis suggests that chlorine is present on the nickel particles in the form of adsorbed chlorine, rather than forming a secondary phase of nickel chlorine.
This study experimentally analyzes the performance and degradation issues of an anode-supported (AS) Ni-YSZ solid oxide fuel cell exposed to thiophene (C4H4S). The impact of this organic sulfur compound on the performance of SOFC Ni-YSZ anodes is reported as a function of temperature and the impurity concentration. There are extensive investigations on the effect of hydrogen sulfide as inorganic sulfur compound on the performance of SOFC but much less of complex sulfur-containing molecules like thiophene. The main objective of this study is to evaluate the impact of thiophene at constant (5 ppmv) and variable (1–15 ppmv) concentrations in the fuel stream on the SOFC performance and regeneration. With the help of the observed results on polarization with time and impedance spectroscopy, including the use of a new equivalent gas composition of reformed bio-syngas, the degradation mechanism is explained. Post-test characterization (SEM-EDX) helps to clarify carbon formation and degradation due to the sulfur impurity.
The gasification of microalgae in supercritical water was investigated in this work. The product gas contained mainly H2, CO2, CH4, and C2H6. Operation at high temperatures and lower biomass concentrations resulted in the highest carbon gasification efficiency and the lowest total organic carbon levels in the residual water. Due to its content of inorganic nutrients, the residual water was applied as cultivation medium for microalgae. However, algal growth in the untreated residual water was inhibited by the existence of potentially toxic substances evolved from gasification. Upon treatment by activated carbon filtration and ultraviolet light degradation, these substances were eliminated and cultivation in the residual water was possible. The major fraction of inorganic residues from gasification was recovered by means of water purging, increasing the potential of nutrient recycling for cultivation.
This work presents the poisoning effect of organic oxo-silicon compounds (siloxanes) which are generally found in sewage biogas. Lifetime and durability associated with solid oxide fuel cell (SOFC) technology is strongly related to the amount of contaminants that reach the stack. Several experiments on Ni anode-supported (AS) single cells are performed in order to clarify the mechanism of degradation and also the possibility of cell performance recovery. Three experiments focus on the degradation and recovery of AS Ni-YSZ fed with H2, co-feeding 5 ppm D4-siloxane (octamethylcyclotetrasiloxane, C8H24O4Si4) as representative compound for the organic silicon species, at 800 °C. A fourth experiment focuses on the durability of the AS Ni-YSZ cell with variable concentrations of the impurity (0–5 ppm), during steady state polarization (0.25 A cm−2) for 250 h, using simulated biogas-reformate fuel H2/CO/CO2/H2O: irreversible degradation was observed with the D4-impurity feed in the anode gas. Post-test scanning electron microscopy (SEM) results indicate formation of SiO2(s) deposits, which block pores and reduce the TPB length.
Within the context of sustainable energy supply and CO2 emissions reduction a Solid Oxide Fuel Cell (SOFC) - gas turbine hybrid system, fuelled with gasified woody biomass is studied in detail for small and medium scale applications (100 kWth,BM and 8 MWth,BM of dry biomass input). The system consists of an air dryer unit, a gasifier, a hot cleaning section made of a particulate removal unit (cyclone and candle filter) and a two-stage tar removal unit, a SOFC and a gas turbine with optional CO2 capture. This modern technology has the advantage of using a renewable and CO2-neutral source and to be economically competitive at medium scales. The competitiveness of different process options is systematically compared by applying a coherent approach combining flowsheeting, energy integration and economic evaluation in a multi-objective optimization framework. This analysis reveals the importance of process integration maximizing the heat recovery and valorizing the waste heat, by cogeneration for example. The studied process options include direct and indirect circulating fluidized bed gasifier (using respectively oxygen or steam as gasification agent) and Viking gasifier, atmospheric or pressurized systems and optional pre-reforming in the hot gas cleaning. To close the thermal energy balance, a fraction of the produced syngas can be burnt. The energy integration results reveal that the steam production for the gasification and reforming are key parameters (S/B and S/C ratio) defining the process performance. A multi-objective optimization maximizing the efficiency and minimizing the capital investment costs is performed with respect to the operating conditions and the process configuration in order to assess the trade-offs and identify optimal process designs. The analysis shows the potential of the system converting woody biomass into electricity with an energy efficiency greater than 70%.
Activated sludge systems are commonly used for robust and efficient treatment of municipal wastewater. However, these systems cannot achieve their maximum potential to recover valuable resources from wastewater. This study demonstrates a procedure to design a feasible novel configuration for maximizing energy and nutrient recovery. A simulation model was developed based on literature data and recent experimental research using steady-state energy and mass balances with conversions. The analysis showed that in the Netherlands, proposed configuration consists of four technologies: bioflocculation, cold partial nitritation/Anammox, P recovery, and anaerobic digestion. Results indicate the possibility to increase net energy yield up to 0.24 kWh/m3 of wastewater, while reducing carbon emissions by 35%. Moreover, sensitivity analysis points out the dominant influence of wastewater organic matter on energy production and consumption. This study provides a good starting point for the design of promising layouts that will improve sustainability of municipal wastewater management in the future.
Hydrothermal liquefaction (HTL) of microalgae is a promising technology offering production of biofuels in a sustainable way. Thanks to the supercritical conditions applied, the recycling of water and nutrients including carbon capture becomes feasible1–2. Through HTL, the target bio-oil is generated together with process water containing valuable nutrients. In this study we have provided an environmentally friendly and resource efficient strategy to produce renewable microalgae biomass. Feasibility test on microalgae cultivation, using the nutrient-rich effluent from the HTL of same algal biomass, was performed in a 5 L, flat panel airlift (FPA)–photobioreactor (PBR). 1 g(DW) L− 1 d− 1 of microalgae was the productivity average achieved with the diluted aqueous solution (25-fold). This is comparable to the productivity obtained with the standard growth medium even if an adaptation time of four days was necessary. Our results show that the nutrient rich HTL aqueous product of microalgal biomass conversion can replace to a great extent mineral salts of the culture medium. Together with an efficient water management, the nutrient recovery applied here promotes the recycling and prevents the release of waste materials and therefore shows the potential for driving the system towards a nutrient neutral production of biomass for biofuels.
Lifetime and durability issues connected with Solid Oxide Fuel Cell (SOFC) technology are strongly related to the amount of contaminants that reach the stack. In this study the focus is on organic silicon compounds (siloxanes) and their highly detrimental effects on the performance of SOFC Ni-YSZ anodes. The involved mechanism of degradation is clarified and quantified through several test runs and subsequent post-mortem analysis on tested samples. In particular, experiments on both Ni anode-supported single cells and 11-cell- stacks are performed, co-feeding D4-siloxane (octamethylcyclotetrasiloxane, C8H24O4Si4) as model compound for the organic silicon species which are generally found in sewage biogas. High degradation rates are observed already at ppb(v) level of contaminant in the fuel stream. Post-test analysis revealed that Si (as silica) is mostly deposited at the inlet of the fuel channel on both the interconnect and the anode side of the cell suggesting a relatively fast condensation-type process. Deposition of the Si was found on the interconnect and on the anode contact layer, throughout the anode support and the three phase boundary in the anode, correlating with the observed increase of polarization losses from the EIS analysis of tested cells.
Internal steam reforming (IR) of methane was investigated on Ni-YSZ anode supported cells, looking in particular at the effect of the steam to carbon (S/C) ratio on the degradation rate. The cells were fed with different H2O/CH4 mixtures during 100 hours sequences, alternating with sequences of dry H-2 feeding. V-I characterization was performed before and after each sequence, and EIS measurements were performed regularly. A marked degradation was observed during the IR sequences while it was negligible under dry H-2 feed. The observed degradation, attributed to carbon deposition on the anode active sites, was partially reversible for S/C >1.5, whereas it became irreversible at lower S/C.
The potential of microalgae as a source of renewable energy based on wastewater has received increasing interest worldwide in recent decades. A freshwater microalga Chlorella sp. was investigated for its ability to remove both nitrogen and phosphorus from influent and effluent wastewaters which were diluted in four different proportions (namely, 100%, 75%, 50% and 25%). Chlorella sp. grew fastest under 50% influent and effluent wastewaters culture conditions, and showed an maximum cell density (4.25 x 10(9) ind 1(-1) for influent wastewater and 3.54 x 109 ind l(-1) for effluent wastewater), indicating the levels of nitrogen and phosphorus greatly influenced algal growth. High removal efficiency for total nitrogen (17.04-58.85%) and total phosphorus (62.43-97.08%) was achieved. Further, more than 83% NH4-N in 75%, 50%, 25% influent wastewater, 88% NOx-N in effluent wastewater and 90% PO4-P in all treatments were eliminated after 24 days of incubation. Chlorella sp. grew well when PO4-P concentration was very low, indicating that this might be not the limiting factor to algal growth. Our results suggest the potential importance of integrating nutrient removal from wastewater by microalgae cultivation as biofuel production feedstock.
Since the model plays an important role in diagnosing solid oxide fuel cell (SOFC) system, this paper proposes a review of existing SOFC models for model-based diagnosis of SOFC stack and system. Three categories of modelling based on the white-, the black- and the grey-box approaches are introduced. The white-box model includes two types, i.e. physical model and equivalent circuit model based on EIS technique. The black-box model is based on artificial intelligence and its realisation relies mainly on experimental data. The grey-box model is more flexible: it is a physical representation but with some parts being modelled empirically. Validation of models is discussed and a hierarchical modelling approach involving all of three modelling methods is briefly mentioned, which gives an overview of the design for implementing a generic diagnostic tool on SOFC system.
Hydrothermal technologies are broadly defined as chemical and physical transformations in high-temperature (200–600 °C), high-pressure (5–40 MPa) liquid or supercritical water. This thermochemical means of reforming biomass may have energetic advantages, since, when water is heated at high pressures a phase change to steam is avoided which avoids large enthalpic energy penalties. Biological chemicals undergo a range of reactions, including dehydration and decarboxylation reactions, which are influenced by the temperature, pressure, concentration, and presence of homogeneous or heterogeneous catalysts. Several biomass hydrothermal conversion processes are in development or demonstration. Liquefaction processes are generally lower temperature (200–400 °C) reactions which produce liquid products, often called “bio-oil” or “bio-crude”. Gasification processes generally take place at higher temperatures (400–700 °C) and can produce methane or hydrogen gases in high yields.
Wastewater treatment consumes large amounts of energy and materials to comply with discharge standards. At the same time, wastewater contains resources, which can be recovered for secondary uses if treated properly. Hence, the goal of this paper is to review the available resource recovery methods onsite or offsite of municipal wastewater treatment plants. These methods are categorized into three major resource recovery approaches: onsite energy generation, nutrient recycling and water reuse. Under each approach, the review provides the advantages and disadvantages, recovery potentials and current application status of each method, as well as the synthesized results of the life cycle studies for each approach. From a comprehensive literature review, it was found that, in addition to technology improvements, there is also a need to evaluate the applications of the resource recovery methods in wastewater treatment plants from a life cycle perspective. Future research should investigate the integration of the resource recovery methods to explore the combined benefits and potential tradeoffs of these methods under different scales.
Lignin and cellulose were gasified at 400 °C with gas yields of 30% and 70%, respectively, in supercritical water with a ruthenium catalyst. In both cases, the main gas product was CH4 and no solid product was formed. Without water or catalyst, lignin and cellulose were gasified slightly and a brown solid product was formed. The decomposition of formaldehyde was also demonstrated in supercritical water. Formaldehyde was rapidly decomposed to gases such as CH4, CO2, and H2 with ruthenium, whereas formaldehyde was converted into methanol and CO2 without catalyst. The catalytic conversion of biomass with ruthenium in supercritical water is an efficient method for biomass gasification at temperatures of 400 °C.
This study reports on the combination of solid oxide fuel cell (SOFC) generators fueled with biogas as renewable energy source, recoverable from wastes but at present underexploited. From a mobilisable near-future potential in the European Union (EU-15) of 17 million tonnes oil equivalent (Mtoe), under 15% appears to be converted today into useful heat and power (2 Mtoe).SOFCs could improve and promote the exploitation of biogas on manifold generation sites as small combined heat and power (5–50 kWel), especially for farm and sewage installations, raising the electrical conversion efficiency on such reduced and variable power level. Larger module packs of the high temperature ceramic converter would also be capable of operating on contaminated fuel of low heating value (less than 40% that of natural gas) which can emanate from landfill sites (MW-size). Landfill gas delivers 80% of current world biogas production.This document compiles and estimates biogas data on actual production and future potential and presents the thermodynamics of the biogas reforming and electrochemical conversion processes. A case study is reported of the energy balance of a small SOFC co-generator operated with agricultural biogas, the largest potential source.
The generation of energy by clean, efficient and environmental-friendly means is now one of the major challenges for engineers and scientists. Fuel cells convert chemical energy of a fuel gas directly into electrical work, and are efficient and environmentally clean, since no combustion is required. Moreover, fuel cells have the potential for development to a sufficient size for applications for commercial electricity generation. This paper outlines the acute global population growth and the growing need and use of energy and its consequent environmental impacts. The existing or emerging fuel cells’ technologies are comprehensively discussed in this paper. In particular, attention is given to the design and operation of Solid Oxide Fuel Cells (SOFCs), noting the restrictions based on materials’ requirements and fuel specifications. Moreover, advantages of SOFCs with respect to the other fuel cell technologies are identified. This paper also reviews the limitations and the benefits of SOFCs in relationship with energy, environment and sustainable development. Few potential applications, as long-term potential actions for sustainable development, and the future of such devices are discussed.
vanherle@epfl.ch) Gave technical instructions concerning the SOFC experiments and contributed to the revision of the manuscript
- Jan Van Herle
Jan Van Herle (jan.vanherle@epfl.ch)
Gave technical instructions concerning the SOFC experiments and
contributed to the revision of the manuscript.
- E Damergi
E. Damergi, et al.
Algal Research 41 (2019) 101552