Energy sustainability analysis and durability of Microbial Fuel Cells (MFCs) as energy source are necessary in order to move from the laboratory scale to full-scale application. This paper focus on ...these two aspects by considering the energy performances of an original experimental test with MFC conducted for six months under an external load of 1000 Ω. Energy sustainability is quantified using Energy Payback Time, the time necessary to produce the energy already spent to construct the MFC device. The results of experiment reveal that the energy sustainability of this specific MFC is never reached due to energy expenditure (i.e. for pumping) and to the low amount of energy produced. Hence, different MFC materials and architectures were analysed to find guidelines for future MFC development. Among these, only sedimentary fuel cells (Benthic MFCs) seem sustainable from an energetic point of view, with a minimum duration of 2.7 years. An energy balance approach highlights the importance of energy calculation. However, this is very often not taken into account in literature. This study outlines promising methodology for the design of an alternative layout of energy sustainable MFC and wastewater management systems.
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•Energy sustainability analysis of experimental results of lab-scale MFC.•Net energy balance results negative due to energy expenditure to feed the system.•Other configurations have been taken into account to reach positive energy balance.•The time to recover the initial energy cost has been evaluated in all configurations.•Sedimentary FC and down-flow MFC represent good perspective for scaled-up system.
In contemporary society we observe an everlasting permeation of electron devices, smartphones, portable computing tools. The tiniest living organisms on Earth could become the key to address this ...challenge: energy generation by bacterial processes from renewable stocks/waste through devices such as microbial fuel cells (MFCs). However, the application of this solution was limited by a moderately low efficiency. We explored the limits, if any, of additive manufacturing (AM) technology to fabricate a fully AM-based powering device, exploiting low density, open porosities able to host the microbes, systems easy to fuel continuously and to run safely. We obtained an optimal energy recovery close to 3 kWh m(-3) per day that can power sensors and low-power appliances, allowing data processing and transmission from remote/harsh environments.
Rice is one of the most important crops throughout the world, as it contributes toward satisfying the food demand of much of the global population. It is well known that rice production generates a ...considerable number of by-products, among which rice bran deserves particular attention. This by-product is exceptionally rich in nutrients, since it contains a wide spectrum of macronutrients (proteins, fats, carbohydrates) as well as dietary fibers and bioactive compounds. However, rice bran is usually wasted or just used for the production of low-cost products. The lipidic fraction of rice bran contains an unsaponifiable fraction that is rich in such functional components as tocopherols, γ-oryzanol, tocotrienols, and phytosterols. This lipidic fraction can be extracted to obtain rice bran oil (RBO), a high value-added product with unique health properties as a result of its high concentration in γ-oryzanol, a powerful antioxidant mixture of bioactive molecules. Conventional extraction methods employ hexane as the solvent, but these methods suffer from some drawbacks linked to the toxicity of hexane for humans and the environment. The aim of the review presented herein is to point out the new green technologies currently applied for the extraction of RBO, by highlighting reliable alternatives to conventional solvent extraction methods that are in line with the twelve principles of green chemistry and a circular economy.
For the development of long lasting portable microbial fuel cells (MFCs) new strategies are necessary to overcome critical issues such as hydraulic pump system and the biochemical substrate retrieval ...overtime to sustain bacteria metabolism. The present work proposes the use of a synthetic solid anolyte (SSA), constituted by agar, carbonaceous and nitrogen sources dissolved into diluted seawater. Results of a month-test showed the potential of the new SSA-MFC as a long lasting low energy consuming system.
A process aimed at producing energy needs to produce more energy than the energy necessary to run the process itself in order to be energetically sustainable. In this paper, an energy balance of a ...batch anaerobic bioreactor has been defined and calculated, both for different operative conditions and for different reactor scales, in order to analyze the sustainability of hydrogen production through dark anaerobic fermentation. Energy production in the form of hydrogen and methane, energy to warm up the fermentation broth, energy loss during fermentation and energy for mixing and pumping have been considered in the energy balance. Experimental data and literature data for mesophilic microorganism consortia have been used to calculate the energy balance. The energy production of a mesophilic microorganism consortium in a batch reactor has been studied in the 16–50 °C temperature range. The hydrogen batch dark fermentation resulted to only have a positive net production of energy over a minimal reactor dimension in summer conditions with an energy recovery strategy. The best working temperature resulted to be 20 °C with 20% of available energy. Hydrogen batch dark fermentation may be coupled with other processes to obtain a positive net energy by recovering energy from the end products of hydrogen dark fermentation. As an example, methane fermentation has been considered to energetically valorize the end products of hydrogen fermentation. The combined process resulted in a positive net energy over the whole range of tested reactor dimension with 45–90% of available energy.
Purpose
This work studies the immobilization of two enzymes, the alcohol dehydrogenase (ADH) and the aldehyde dehydrogenase (AldDH) both from
Saccharomyces cerevisiae
, which could be used to produce ...high value-added molecules from carboxylic acids embedded in anaerobic digestate.
Methods
In particular, three mesoporous siliceous materials, with different specific surface areas and pore sizes, (MSU-H, MSU-F and MCF
0.75
) were used as supports for covalent immobilization. The support materials were characterized by complementary techniques. Then, after a functionalization, creating a covalent bond between the enzyme and the support was performed. The specific activity and immobilization yield of the biocatalysts were then evaluated.
Results
The best results were obtained with MSU-H and MSU-F, resulting in an immobilization yield greater than 50% in all cases, a specific activity of 0.13 IU/g
supp
with the AldDH/MSU-H, 0.10 IU/g
supp
with AldDH/MSU-F, 48.6 IU/g
supp
with ADH/MSU-H and 12.6 IU/g
supp
with ADH/MSU-H. These biocatalysts were then characterized by optimal pH and temperature and the stability factor was evaluated. With ADH/MSU-F no decrease in activity was observed after 120 h incubated at 50 °C. Finally, the biocatalysts AldDH/MSU-H and ADH/MSU-H were used to perform the reduction reaction and it was seen that after five reaction cycles the residual activity was greater than 20% in both cases.
Conclusion
The ADH and AldDH enzymes have been successfully immobilized on mesoporous siliceous supports, considerably increasing their thermal stability and being able to reuse them for several reaction cycles. The use of this immobilization and these supports is adaptable to a wide variety of enzymes.
Graphical Abstract
Global warming due to the increased atmospheric carbon dioxide concentration is the driving force for developing strategies that exploit CO2 as raw material to produce interesting compounds for ...industry. According to this approach, Acetobacterium woodii was modified to convert CO2 and H2 into acetone. Gas fermentation was performed at high pressure to debottleneck the issue of the low availability of gaseous substrates in the liquid medium. This work aimed to investigate the catalytic performance of a modified A. woodii strain for acetone synthesis at 10 bar providing an H2-CO2 blend. First, tests were performed to assess the ability of the biocatalyst to survive heterotrophically at high pressure. Moreover, a reference test was set up in autotrophy at atmospheric pressure to confirm that it produced both acetate and acetone. Feeding the strain at 10 bar with the H2-CO2 mix resulted in growth inhibition and formic acid production. This outcome suggested a metabolism impairment due to bicarbonate build-up in the reactor at high CO2 partial pressure. Thus, bacteria were grown at atmospheric pressure in a medium with an augmented exogenous salt concentration. Results confirmed that formic acid production and growth inhibition could be due to HCO3–. Furthermore, the modified A. woodii grown at atmospheric pressure in a sterile medium pressurized before inoculation showed the same outcomes. Finally, tests at 10 bar lowering the CO2 partial pressure indicated that this gas was responsible for formic acid production but was not the only inhibitory factor for autotrophic cell growth at high pressure.
•Modified Acetobacterium woodii resistance at 11 bar pressure.•Modified Acetobacterium woodii H2-CO2 fermentation at 10 bar pressure.•Influence of CO2 partial pressure on modified A.woodii metabolism.
This study presents the immobilization with aldehyde groups (glyoxyl carbon felt) of alcohol dehydrogenase (ADH) and formate dehydrogenase (FDH) on carbon‐felt‐based electrodes. The compatibility of ...the immobilization method with the electrochemical application was studied with the ADH bioelectrode. The electrochemical regeneration process of nicotinamide adenine dinucleotide in its oxidized form (NAD+), on a carbon felt surface, has been deeply studied with tests performed at different electrical potentials. By applying a potential of 0.4 V versus Ag/AgCl electrode, a good compromise between NAD+ regeneration and energy consumption was observed. The effectiveness of the regeneration of NAD+ was confirmed by electrochemical oxidation of ethanol catalyzed by ADH in the presence of NADH, which is the no active form of the cofactor for this reaction. Good reusability was observed by using ADH immobilized on glyoxyl functionalized carbon felt with a residual activity higher than 60 % after 3 batches.
Alcohol dehydrogenase (ADH) and formate dehydrogenase (FDH) were covalently immobilized on CF electrodes using aldehyde groups. The enzymatic electrosynthesis was performed with the prepared bioelectrode and the properties of the bioelectrode were demonstrated by the regeneration of the nicotinamide adenine dinucleotide (NAD) cofactor.
Anaerobic digestates from sewage sludge (SSADs) are a by-product of the wastewater treatment process that still preserves a certain agronomic interest for its richness in plant nutrients and organic ...matter. Fertilizing properties of two liquid and two dewatered SSADs were tested on tomato plants (Solanum lycopersicum L.). Pot experiments were performed on sandy soil and peat substrate under greenhouse conditions with a SSADs application rate of 170 kg N/ha over a period of three months. Beneficial effects of SSADs were reported on different growth parameters, revealing an increase in biomass and height up to 37.5 and 6-folds over untreated control. No phytotoxic effect occurred on SSAD-exposed plants. Chemical analysis of soils treated with SSADs showed enrichment of macro- and micro-nutrients as well as organic matter. In some cases, the chemical characterization of leaves revealed an enhancement of uptaken macronutrients. This study contributed in general to deepen the knowledge on the short-term growing season fertilizing effects of SSAD. Despite the treatment dosage was calculated only on nitrogen requirements, the study highlighted the importance of the other nutrients and organic matter on plant growth.
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•Anaerobic digestates from sewage sludge increased plant biomass up to 37.5-folds.•No phytotoxic effect occurred on plants exposed to anaerobic digestates.•Digestates application induced soil enrichment in nutrients and organic matter.
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•Methanol is firstly produced by CO2 electroreduction with a CuO/ZnO/Al2O3 catalyst.•CO2-to-methanol conversion is scaled-up from lab data process simulation results.•Electrocatalytic ...CO2 conversion is sustainable with 90% of FE and 200 mA/cm2.•CO2-to-Methanol could be economically competitive at productivity >20 kg/hmethanol.•The carbon footprint is 62% lower for both processes using 100% of renewable energy.
Electrocatalytic (EC) and thermocatalytic (TC) conversion of CO2 to methanol are promising carbon capture and utilization technologies. Herein, these CO2-to-methanol conversion processes are analysed in terms of technical, environmental and economic feasibility. To this purpose, the catalytic performance of the same catalyst (CuO/ZnO/Al2O3) was evaluated in both EC and TC processes. Here is showed for the first time that this catalyst is (apart from TC route) also able to generate methanol through CO2 EC reduction. This work presents lab scale tests, scaled-up simulations and evaluates the environmental and economic performance of these processes.
The carbon footprint of the TC and EC processes, scaled-up to the same productivity of ~ 3 kg/h methanol, scored ~ 8 kgCO2 eq/kgCH3OH. Strategies to reduce this impact are presented, such as improving the current density of the EC cell (i.e. 200 mA/cm2 results in a reduction of 68% to 2.72 kgCO2 eq/kgCH3OH) and the availability of 100% renewable electricity (saving up to 62% carbon footprint of both processes). Considering an effective allocation of the methanol productivity on a real market scenario, both the TC and EC processes would start to be economically competitive at methanol productivities > 19.1 kg/h and 3.3 kg/h, respectively. Moreover, if O2 valorisation, a low price of the renewable electricity and a carbon tax are considered, the economic profitability will rise; e.g. the minimum levelised cost of product (LCOP of 1.45 €/kg and 1.67 €/kg, respectively) could be reduced by 53%. Finally, our results pointed out that the CO2 electroreduction process must be optimized (e.g. improving catalysts performance and EC cell design reducing mass transfer limitations) to achieve industrially relevant rates and the maturity of the thermocatalytic technology.
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