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Editors, Contents, Cover details
No full textOn The Cover: Bioelectrochemistry is a broad discipline that studies the electrochemistry
of living systems. Some of the most interesting applications of bioelectrochemistry
use externally imposed currents as sources of electrons in microbial redox reactions,
a process termed electro-fermentation. In pages 866–878 of this issue, Schievano
and colleagues discuss the emerging industrial uses for electro-fermentation
technology, including the anaerobic digestion of organic wastes to value-added
chemicals. Cover image and cover design by Deepak Pant and Andrea Schievano
Substituting energy crops with organic wastes and agro-industrial residues for biogas production
No full textIn this study, industrial and agro-industrial by-products and residues (BRs), animal manures (AMs), and
various types of organic wastes (OWs) were analyzed to evaluate their suitability as substitutes
for energy crops (ECs) in biogas production. A comparison between the costs of the volume of
biogas that can be produced from each substrate was presented with respect to the prices of the
substrates in the Italian market. Furthermore, four different feeding mixtures were compared with
a mixture of EC and swine manure (Mixture A) used in a full-scale plant in Italy. Swine manure is always
included as a basic substrate in the feeding mixtures, because many of the Italian biogas plants are
connected to farms. When EC were partially substituted with BR (Mixture B), the cost (0.28 V Nm 3) of
the volume of biogas of Mixture A dropped to 0.18 V Nm 3. Furthermore, when the organic fraction of
municipal solid waste (OFMSW) and olive oil sludge (OS) were used as possible solutions (Mixtures C and
D), the costs of the volume of biogas were 0.20 and 0.11 V Nm 3, respectively. The negative price
signifies that operators earn money for treating the waste. For the fifth mix (Mixture E) of the OFMSW
with a high solid substrate, such as glycerin from biodiesel production, the resulting cost of the volume of
biogas produced was 0.09 V Nm 3. By comparing these figures, it is evident that the biogas plants at
farm level are good candidates for treating organic residues of both municipalities and the agroindustrial
sector in a cost-effective way, and in providing territorially diffused electric and thermal
power. This may represent a potential development for agrarian economy
Supercritical CO2 and Green Extraction methods for Added Value Products : Carotenoids, Chlorophylls and Phycocyanin from Spirulina Microalgae
No full textNowadays, the blue-green microalgae of the genus Arthrospira, commonly known as Spirulina, are commercially grown all around the world for their nutritional properties. The popularity of Spirulina as a food supplement is mainly due to its high protein content (up to about 70% by dry weight) and its richness in minerals, vitamins and provitamins, phytochemicals, essential amino acids, fibres and pigments 1. Among them, carotenoids, chlorophylls and phycocyanins are of high relevance as food and feed dyes. In particular, phycocyanin has been widely considered as a precious protein target because of its rare intense-blue colour, due to the presence of linear tetrapyrrole chromophores, covalently bound to cysteine residues via thioether bonds. Its protein-based structure is arranged in αβ protomers associated into trimers (αβ)3 and hexamers (αβ)6. Its absorption in the visible region (max=620 nm) and its natural fluorescence account for its application as marker in the medical field. The presence of the protein in the algae, carrying specific chromophores, is able to enhance the absorption range in the visible spectrum of light, facilitating the photosynthesis.
Different strategies were developed for the isolation and purification of phycocyanin in the last decade, all of them however discarding the residual pigment fraction 2.
This study suggests an integrated and “green” extraction chain that only leads to phycocyanin at the end. The body of the strategy involves two consecutive steps of extraction of carotenoids and chlorophylls through supercritical-CO2, a well-recognised “green” extraction method, before phycocyanin extraction 3.
The biomass residue, exhausted in terms of carotenoids and chlorophylls, is finally extracted in water to yield phycocyanin. On the basis of recent and past literature on the topic, a strategy to yield the blue pigment with high purity was developed, keeping an eye on the scalability of the overall process in terms of cost and time consumption. Consecutive steps were carried out in order to enhance the phycocyanin purity, including electrocoagulation, dialysis and protein salting-out. These processes yielded 250 mg g−1 of phycocyanin (by dry Spirulina weight). A potentially scalable strategy to obtain the blue pigment with high purity (A620/A280 = 2.2) was set up. The practical application of the extracted blue phycocyanin pigment as a cotton-based tissue colorant was also experimented.
References:
[1] G. Chamorro-Cevallos, Int. J. Food Nutr. Sci., 2016, 3, 1-10.
[2] R. Chaiklahan, N. Chirasuwan, V. Loha, S. Tia, B. Bunnag, Bioresour. Technol., 2011, 102, 7159–7164.
[3] S. Marzorati, A. Schievano, A. Idà, L. Verotta, Green Chemistry, 2020, 22, 187-196
Electro-stimulated microbial factory for value added product synthesis
No full textInterplay of charge between bacteria and electrode has led to emergence of bioelectrochemical systems which leads to applications such as production of electricity, wastewater treatment, bioremediation and production of value added products. Many electroactive bacteria have been identified that have unique external electron transport systems. Coupling of electron transport with carbon metabolism has opened a new approach of carbon dioxide sequestration. The electron transport mechanism involves various cellular and sub cellular molecules. The outer membrane cytochromes, Mtr-complex and Ech-complex are few key molecules involved in electron transport in many electrogenic bacteria. Few cytochrome independent acetogenic electroactive bacteria were also discovered using Rnf complex to transport electrons. For improved productivity, an efficient bioreactor design is mandatory. It should encompass all certain critical issues such as microbial cell retention, charge dissipation, separators and simultaneous product recovery
Evaluation of low cost cathode materials for treatment of industrial and food processing wastewater using microbial electrolysis cells
No full textMicrobial electrolysis cells (MECs) can be used to treat wastewater and produce hydrogen gas, but low cost cathode catalysts are needed to make this approach economical. Molybdenum disulfide (MoS2) and stainless steel (SS) were evaluated as alternative cathode catalysts to platinum (Pt) in terms of treatment efficiency and energy recovery using actual wastewaters. Two different types of wastewaters were examined, a methanol-rich industrial (IN) wastewater and a food processing (FP) wastewater. The use of the MoS2 catalyst generally resulted in better performance than the SS cathodes for both wastewaters, although the use of the Pt catalyst provided the best performance in terms of biogas production, current density, and TCOD removal. Overall, the wastewater composition was more of a factor than catalyst type for accomplishing overall treatment. The IN wastewater had higher biogas production rates (0.8-1.8 m3/m3-d), and COD removal rates (1.8-2.8 kg-COD/m3-d) than the FP wastewater. The overall energy recoveries were positive for the IN wastewater (3.1-3.8 kWh/kg-COD removed), while the FP wastewater required a net energy input of -0.7 - 1.2 kWh/kg-COD using MoS 2 or Pt cathodes, and -3.1 kWh/kg-COD with SS. These results suggest that MoS2 is the most suitable alternative to Pt as a cathode catalyst for wastewater treatment using MECs, but that net energy recovery will be highly dependent on the specific wastewater
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