APPLICATION OF MICROBIAL ELECTROCHEMICAL SYSTEMS FOR VALORISATION OF CHEESE WHEY IN BIOREFINERY FRAMEWORK

In the last decades, the current unsustainable fossil-based economic model has been worldwide disputed by policies and public opinion. As consequence, the exploitation of biomasses has arisen as pivotal towards a green and circular economy. In this context, waste biorefineries would represent the optimal technical solution. Firstly, the integration of feasible bioprocess can generate a mix of biofuels and bioproducts, according to the cascade principle, thus making possible to hit the market with products characterised by either significant market size or high market value, guaranteeing economic sustainability. In addition, the use of organic wastes as alternative to dedicated biomasses would significantly tackle costs of waste management and related environmental impacts. Due to their qualitative homogeneity and volumes of production, agro-industrial residues are currently pointed out as suitable for multi-step valorisation in biorefinery. However, their valorisation is currently aimed to few products, like biogas and compost, characterised by low market value. Therefore, the full achievement of waste biorefineries potential has to be achieved yet, since it would greatly impact the economic and environmental resilience of the whole agro-industrial sector, in particular for smaller supply chains. Sheep milk supply chain is a notable example in this respect: even though it represents a small portion of European milk market, it is a fundamental source of income in few southern regions like Sardinia, and it cyclically experiences economic difficulties. This research aims to evaluate the integration of Microbial Electrochemical Systems (MESs) in a biorefinery framework for the valorisation of cheese whey, as the main by-product of dairy industry. It started by assessing the state of art of available bioprocesses for feedstock valorisation. The literature review highlighted the current weakness of MESs treating this substrate, but also found how their integration as downstream process of Dark Fermentation (DF) can significantly enhance the power output generation in comparison to standalone processes. Consequently, a general overview on DF and MESs was provided, to also stress out how MESs can also expand material outputs generated during DF. The experimental work focused then on the application of Electro fermentation of lactate rich effluents from DF to propionate and acetate, which are seldom reported as main metabolites in DF broths. Then, a novel Microbial Fuel Cell for electricity generation is presented and characterised by mathematical modelling, aiming to a deeper understanding of reactor design to favour future systems scale up. Last experimental work gives a proof of concept of hydrogen production by Microbial Electrochemical Cells, underlining the further energy recovery and carbon removal achievable by their implementation. Finally, two biorefinery schemes are presented and analysed, pointing out their novelty and potential benefits to cheese making plants

Modelling Miniature Microbial Fuel Cells with Three-dimensional Anodes

Microbial fuel cells (MFCs) exploit the metabolic activity of electroactive microorganisms for oxidation of organic compounds and extracellular electron transfer to an external electrode. the technology is associate with very slowreaction rates, resulting in low current densities. Anodes with high specific surface should be used to increase the overall electricity generation. Carbon-based 3D materials, with high surface per unit of volume, are largely used anode materials in MFCs, although may show significant lack in efficiency due to mass transfer limitations, concentration gradients, velocity distribution and resistivity of the material. Consequently, the concomitant effect of several parameters should be assessed and quantified to design highly performing MFCs implementing 3D anode materials. In this work, miniature MFCs with 3D anodes are mathematically modelled to quantify the effect of operative parameters on performance. The model combines equations of charge conservation, mass transport phenomena, hydrodynamics, and kinetics of the involved processes under transient conditions, and provides 3D profiles with time of velocity, biofilm thickness, substrate concentration, current density and potential. The solution predicts a laminar flow, as it was expected with the low flow rates used. The concentration profiles show the consumption of substrate in the anode, with low values of local concentrations depending on organic load in the feed stream. The model also provides a versatile tool to optimise the operative conditions of the system, managing the flow arrangements to maximise either substrate removal or electricity generation

Dark Fermentation of Sheep Cheese Whey: Biochemicals and Biofuels Production as a Function of Fermentation Time and pH

Cheese whey (CW) is the main by-product of the cheese making process and is composed mainly by lactose, proteins, lipids and mineral salts. The environmental impacts and other potential negative effects linked to the traditional management strategies of CW are no longer considered sustainable, therefore alternatives need to be explored. Dark fermentation (DF) may be a promising approach for CW valorization. Though the issue has been already addressed by several studies with particular emphasis on biohydrogen production, less attention has been paid to the possibility of recovering also other valuable products. Optimizing the effects of operating pH and fermentation time is a strategy worth to be studied in order to obtain specific biochemicals and/or biofuels from CW. In this framework, batch DF tests were performed under mesophilic conditions on sheep CW, without inoculum addition, adopting different operating pHs, and relating type and production yields of the observed gaseous and liquid byproducts to the duration of the process. CW fermentation evolved over time according to two steps; the first phase was characterised by lactose conversion to lactic acid, whilst during the second one lactic acid was degraded to soluble and gaseous products such as short chain fatty acids (mainly acetate, butyrate and propionate) and hydrogen. The adopted operating pHs affected the production kinetics and yields, as well as metabolic pathways. In particular, setting the operating pH to 6 proved to be optimal in terms of both lactic acid or hydrogen production yields

Carboxylic acids production and electrosynthetic microbial community evolution under different CO2 feeding regimes

Microbial electrosynthesis (MES) is a potential technology for CO2 recycling, but insufficient information is available on the microbial interactions underpinning electrochemically-assisted reactions. In this study, a MES reactor was operated for 225 days alternately with bicarbonate or CO2 as carbon source, under batch or continuous feeding regimens, to evaluate the response of the microbial communities, and their productivity, to dynamic operating conditions. A stable acetic acid production rate of 9.68 g m-2 d-1, and coulombic efficiency up to 40%, was achieved with continuous CO2 sparging, higher than the rates obtained with bicarbonate (0.94 g m-2 d-1) and CO2 under fed-batch conditions (2.54 g m-2 d-1). However, the highest butyric acid production rate (0.39 g m-2 d-1) was achieved with intermittent CO2 sparging. The microbial community analyses focused on differential amplicon sequence variants (ASVs), allowing detection of ASVs significantly different across consecutive samples. This analysis, combined with co-occurence network analysis, and cyclic voltammetry, indicated that hydrogen-mediated acetogenesis was carried out by Clostridium, Eubacterium and Acetobacterium, whereas Oscillibacter and Caproiciproducens were involved in butyric acid production. The cathodic community was spatially inhomogeneous, with potential electrotrophs, such as Sulfurospirillum and Desulfovibrio, most prevalent near the current collector. The abundance of Sulfurospirillum positively correlated with that of Acetobacterium, supporting the syntrophic metabolism of both organisms.This publication was supported by the Science Foundation of Ireland (SFI) Research Professorship Programme on Innovative Energy Technologies for Bioenergy, Biofuels and a Sustainable Irish Bioeconomy (IETSBIO3, award 15/RP/2763) and the Research Infrastructure grant Platform for Biofuel Analysis (Award no. 16/RI/3401). MI gratefully acknowledges the Sardinian Regional Government for the financial support of his PhD scholarship (P.O.R. Sardegna F.S.E. - Operational Programme of the Autonomous Region of Sardinia, European Social Fund 2014-2020 - Axis III Education and training, Thematic goal 10, Investment Priority 10ii), specific goal 10.5. UZI is supported by a NERC Independent Research Fellowship (NE/L011956/1). GC and SM were supported by a European Research Council Starting Grant (3C-BIOTECH 261330). GC is supported by the SFI Career Development Award programme (award no. 17/CDA/4658). The authors acknowledge the facilities, and scientific and technical assistance of the Centre for Microscopy & Imaging at the National University of Ireland Galway (www.imaging.nuigalway.ie)

The dairy biorefinery: Integrating treatment processes for cheese whey valorisation

With an estimated worldwide production of 190 billion kg per year, and due to its high organic load, cheese whey represents a huge opportunity for bioenergy and biochemicals production. Several physical, chemical and biological processes have been proposed to valorise cheese whey by producing biofuels (methane, hydrogen, and ethanol), electric energy, and/or chemical commodities (carboxylic acids, proteins, and biopolymers). A biorefinery concept, in which several value-added products are obtained from cheese whey through a cascade of biotechnological processes, is an opportunity for increasing the product spectrum of dairy industries while allowing for sustainable management of the residual streams and reducing disposal costs for the final residues. This review critically analyses the different treatment options available for energy and materials recovery from cheese whey, their combinations and perspectives for implementation. Thus, instead of focusing on a specific valorisation platform, in the present review the most relevant aspects of each strategy are analysed to support the integration of different routes, in order to identify the most appropriate treatment train.This work was supported by the Science Foundation of Ireland (SFI) Research Professorship Programme on Innovative Energy Technologies for Bioenergy, Biofuels and a Sustainable Irish Bioeconomy (IETSBIO3, award 15/RP/2763). It was conducted on the framework of the “Waste Biorefinery” task group of the International Waste Working Group (IWWG). Fabiano Asunis and Marco Isipato gratefully acknowledges Sardinian Regional Government for the financial support of their PhD scholarship (P.O.R. Sardegna F.S.E. - Operational Programme of the Autonomous Region of Sardinia, European Social Fund 2014–2020 - Axis III Education and training, Thematic goal 10, Investment Priority 10ii, Specific goal 10.5)

The dairy biorefinery: Integrating treatment processes for cheese whey valorisation

With an estimated worldwide production of 190 billion kg per year, and due to its high organic load, cheese whey represents a huge opportunity for bioenergy and biochemicals production. Several physical, chemical and biological processes have been proposed to valorise cheese whey by producing biofuels (methane, hydrogen, and ethanol), electric energy, and/or chemical commodities (carboxylic acids, proteins, and biopolymers). A biorefinery concept, in which several value-added products are obtained from cheese whey through a cascade of biotechnological processes, is an opportunity for increasing the product spectrum of dairy industries while allowing for sustainable management of the residual streams and reducing disposal costs for the final residues. This review critically analyses the different treatment options available for energy and materials recovery from cheese whey, their combinations and perspectives for implementation. Thus, instead of focusing on a specific valorisation platform, in the present review the most relevant aspects of each strategy are analysed to support the integration of different routes, in order to identify the most appropriate treatment train.This work was supported by the Science Foundation of Ireland (SFI) Research Professorship Programme on Innovative Energy Technologies for Bioenergy, Biofuels and a Sustainable Irish Bioeconomy (IETSBIO3, award 15/RP/2763). It was conducted on the framework of the “Waste Biorefinery” task group of the International Waste Working Group (IWWG). Fabiano Asunis and Marco Isipato gratefully acknowledges Sardinian Regional Government for the financial support of their PhD scholarship (P.O.R. Sardegna F.S.E. - Operational Programme of the Autonomous Region of Sardinia, European Social Fund 2014–2020 - Axis III Education and training, Thematic goal 10, Investment Priority 10ii, Specific goal 10.5).peer-reviewe

The dairy biorefinery: Integrating treatment processes for cheese whey valorisation

With an estimated worldwide production of 190 billion kg per year, and due to its high organic load, cheese whey represents a huge opportunity for bioenergy and biochemicals production. Several physical, chemical and biological processes have been proposed to valorise cheese whey by producing biofuels (methane, hydrogen, and ethanol), electric energy, and/or chemical commodities (carboxylic acids, proteins, and biopolymers). A biorefinery concept, in which several value-added products are obtained from cheese whey through a cascade of biotechnological processes, is an opportunity for increasing the product spectrum of dairy industries while allowing for sustainable management of the residual streams and reducing disposal costs for the final residues. This review critically analyses the different treatment options available for energy and materials recovery from cheese whey, their combinations and perspectives for implementation. Thus, instead of focusing on a specific valorisation platform, in the present review the most relevant aspects of each strategy are analysed to support the integration of different routes, in order to identify the most appropriate treatment train.This work was supported by the Science Foundation of Ireland (SFI) Research Professorship Programme on Innovative Energy Technologies for Bioenergy, Biofuels and a Sustainable Irish Bioeconomy (IETSBIO3, award 15/RP/2763). It was conducted on the framework of the “Waste Biorefinery” task group of the International Waste Working Group (IWWG). Fabiano Asunis and Marco Isipato gratefully acknowledges Sardinian Regional Government for the financial support of their PhD scholarship (P.O.R. Sardegna F.S.E. - Operational Programme of the Autonomous Region of Sardinia, European Social Fund 2014–2020 - Axis III Education and training, Thematic goal 10, Investment Priority 10ii, Specific goal 10.5).peer-reviewe

Propionate production by bioelectrochemically-assisted lactate fermentation and simultaneous CO2 recycling

Production of volatile fatty acids (VFAs), fundamental building blocks for the chemical industry, depends on fossil fuels but organic waste is an emerging alternative substrate. Lactate produced from sugar-containing waste streams can be further processed to VFAs. In this study, electrofermentation (EF) in a two-chamber cell is proposed to enhance propionate production via lactate fermentation. At an initial pH of 5, an applied potential of −1 V vs. Ag/AgCl favored propionate production over butyrate from 20 mM lactate (with respect to non-electrochemical control incubations), due to the pH buffering effect of the cathode electrode, with production rates up to 5.9 mM d–1 (0.44 g L–1 d–1). Microbial community analysis confirmed the enrichment of propionate-producing microorganisms, such as Tyzzerella sp. and Propionibacterium sp. Organisms commonly found in microbial electrosynthesis reactors, such as Desulfovibrio sp. and Acetobacterium sp., were also abundant at the cathode, indicating their involvement in recycling CO2 produced by lactate fermentation into acetate, as confirmed by stoichiometric calculations. Propionate was the main product of lactate fermentation at substrate concentrations up to 150 mM, with a highest production rate of 12.9 mM d–1 (0.96 g L–1 d–1) and a yield of 0.48 mol mol–1 lactate consumed. Furthermore, as high as 81% of the lactate consumed (in terms of carbon) was recovered as soluble product, highlighting the potential for EF application with high-carbon waste streams, such as cheese whey or other food wastes. In summary, EF can be applied to control lactate fermentation toward propionate production and to recycle the resulting CO2 into acetate, increasing the VFA yield and avoiding carbon emissions and addition of chemicals for pH control.This work was funded by the Science Foundation of Ireland (SFI) Research Professorship Programme on Innovative Energy Technologies for Bioenergy, Biofuels and a Sustainable Irish Bioeconomy (IETSBIO3, award 15/RP/2763) and the Research Infrastructure research grant Platform for Biofuel Analysis (Grant Number 16/RI/3401). GC and SM were supported by a European Research Council Starting Grant (3C-BIOTECH 261330). GC was supported by an SFI Career Development Award (17/CDA/4658)