Green Biorefinery Upper Austria – Pilot Plant operation

Escherichia coli-based biorefining process yields optically pure lactic acid from fermented second-generation feedstocks

Within the circular bioeconomy the production of optically pure LA from 2nd generation feedstocks would be ideal but it is very challenging. In this paper genetically engineered Escherichia coli strains were created to resolve racemic LA solutions synthesised and produced from the fermentation of organic waste or ensiled grass. Refining LA racemic mixtures into either a D- or L-LA was achieved by cells being able to consume one LA isomer as a sole carbon and energy source while not being able to consume the other. A D-LA refining strain JSP0005 was grown on fermented source-sorted organic household waste and different grass silage leachates, which are 2nd generation feedstocks containing up to 33 g/L lactic acid racemate. In all growth experiments, L-LA was completely removed leaving D-LA as the only LA stereoisomer, i.e. resulting in optically pure D-LA, which also increased by as much as 248.6 % from its starting concentration, corresponding to 38 g/L. The strains resulting from this study are a promising first step towards a microbial based LA biorefining process.

A Novel Bio-Purification Process Employing an Engineered E. coli Strain for Downstream Processing of Lactic Acid Solutions from the Fermentation of Agro-Industrial by-Products

This study aims to integrate a novel bio-purification process employing an engineered E. coli strain in the downstream processing of lactic acid (LA) fermentation broths from low-cost renewable biological feedstocks. Fermentation broth of candy waste and digestate mixture was used as a real biological feedstock. An engineered E. coli strain that selectively catabolize impurities without catabolizing LA was initially adapted on the biological feedstock, followed by shake flask experiments to prove the bio-purification concept. Scale-up and validation in a bench-scale bioreactor followed, before developing a semi-continuous membrane bioreactor (MBR) bio-purification process. The MBR bio-purification was assessed with biological feedstocks which simulated ultrafiltration or nanofiltration permeates. Incomplete removal of impurities and increased fouling was observed in the case of the ultrafiltration permeate. Contrarily, the nanofiltration permeate was successfully treated with MBR bio-purification, since low membrane fouling, 100% maltose and acetic acid removal, and no LA catabolism was achieved. MBR bio-purification as a post-treatment step in the downstream processing of LA was demonstrated as a promising technology for increasing the purity of LA solutions.

Development of a hybrid bio-purification process of lactic acid solutions employing an engineered E. coli strain in a membrane bioreactor

BACKGROUND

A potential alternative to lactic acid production through sugar fermentation is its recovery from grass silage leachate. The separation and purification of lactic acid from fermentation broths remain a key issue, as it amounts to up to 80% of its industrial production cost. In this study, a genetically engineered E. coli strain (A1:ldhA), that cannot catabolize lactic acid, has been used to selectively remove impurities from a synthetic medium comprising typical components (i.e., glucose and acetic acid) of green grass silage leachate. A systematic approach has been followed to provide a proof-of-concept for a bio-purification process of lactic acid solutions in a membrane bioreactor operating in semi-continuous mode.

RESULTS

The synthetic medium composition was initially optimized in shake-flasks experiments, followed by scale-up in bench-scale bioreactor. Complete (i.e., 100%) and 60.4% removal for glucose and acetic acid, respectively, has been achieved in batch bioreactor experiments with a synthetic medium comprising 0.5 g/L glucose and 0.5 g/L acetic acid as carbon sources, and 10 g/L lactic acid; no lactic acid catabolism was observed in all batch fermentation tests. Afterwards, a hybrid biotechnological process combining semi-continuous bioreactor fermentation and ultrafiltration membrane separation (membrane bioreactor) was applied to in-situ separate purified medium from the active cells. The process was assessed under different semi-continuous operating conditions, resulting in a bacteria-free effluent and 100% glucose and acetic acid depletion, with no lactic acid catabolism, thus increasing the purity of the synthetic lactic acid solution.

CONCLUSIONS

The study clearly demonstrated that a bio-purification process for lactic acid employing the engineered E. coli strain cultivated in a membrane bioreactor is a technically feasible concept, paving the way for further technological advancement.

Green Biorefinery systems for the production of climate-smart sustainable products from grasses, legumes and green crop residues

Grasses, legumes and green plant wastes represent a ubiquitous feedstock for developing a bioeconomy in regions across Europe. These feedstocks are often an important source of ruminant feed, although much remains unused or underutilised. In addition to proteins, these materials are rich in fibres, sugars, minerals and other components that could also be used as inputs for bio-based product development. Green Biorefinery processes and initiatives are being developed to better capitalise on the potential of these feedstocks to produce sustainable food, feed, materials and energy in an integrated way. Such systems may support a more sustainable primary production sector, enable the valorisation of green waste streams, and provide new business models for farmers. This review presents the current developments in Green Biorefining, focusing on a broad feedstock and product base to include different models of Green Biorefinery. It demonstrates the potential and wide applicability of Green Biorefinery systems, the range of bio-based product opportunities and highlights the way forward for their broader implementation. While the potential for new products is extensive, quality control approval will be required prior to market entry.

Fibrolytic enzyme treatment prior to ensiling increased press-juice and crude protein yield from grass silage

Grass is a versatile raw material for green biorefineries and preserving it as silage provides a year-round feedstock. The objective of the current study was to evaluate the effect of fibrolytic enzyme application on silage as a feedstock for a biorefinery. Two batches of grass (mixture of timothy and meadow fescue) silages were ensiled in pilot scale after fibrolytic enzyme was applied to them at four levels. Enzyme application increased fibre degradation linearly during ensiling and increased lactic and acetic acid concentrations in the silage. Simultaneously, silage fermentation quality improved as indicated by decreasing pH and ammonia values. Press-juice and crude protein yields increased in response to the fibrolytic enzyme application, which is beneficial in a biorefinery concept for retrieving valuable nutrients from grass matrix. Optimized ensiling methodology can be considered as a pretreatment for a biorefinery process.

Biosynthesis of poly-3-hydroxybutyrate from grass silage by a two-stage fermentation process based on an integrated biorefinery concept

Grass silage as a renewable feedstock for an integrated biorefinery includes nutrients and carbon sources directly available in the press juice (PJ) and in lignocellulosic saccharides from the plant framework. Here, a novel two-stage fed-batch fermentation process for biosynthesis of poly-3-hydroxybutyrate (PHB) by Cupriavidus necator DSM 531 is presented. For bacterial growth, nutrient-rich PJ was employed as a fermentation medium, without any supplements. Saccharides derived from the mechano-enzymatic hydrolysis of the press cake (PC) were subjected to a lactic acid fermentation process, before the fermentation products were fed into the polymer accumulation phase. By combination of pH-stat feeding and cell recycling, the PHB content in 22 g L^-1 total-dry cells reached 39% after 32 h of cultivation. Using mimicked hydrolyzate of diluted PJ artificially supplemented with glucose and xylose, the resulting cell dry weight of 21 g L^-1 contained 42% PHB.

Techno-environmental assessment of the green biorefinery concept: Combining process simulation and life cycle assessment at an early design stage

The Green biorefinery (GBR) is a biorefinery concept that converts fresh biomass into value-added products. The present study combines a Process Flowsheet Simulation (PFS) and Life Cycle Assessment (LCA) to evaluate the technical and environmental performance of different GBR configurations and the cascading utilization of the GBR output. The GBR configurations considered in this study, test alternatives in the three main steps of green-biorefining: fractionation, precipitation, and protein separation. The different cascade utilization alternatives analyse different options for press-pulp utilization, and the LCA results show that the environmental profile of the GBR is highly affected by the utilization of the press-pulp and thus by the choice of conventional product replaced by the press-pulp. Furthermore, scenario analysis of different GBR configurations shows that higher benefits can be achieved by increasing product yields rather than lowering energy consumption. Green biorefining is shown to be an interesting biorefining concept, especially in a Danish context. Biorefining of green biomass is technically feasible and can bring environmental savings, when compared to conventional production methods. However, the savings will be determined by the processing involved in each conversion stage and on the cascade utilization of the different platform products.

Deacidification of grass silage press juice by continuous production of acetoin from its lactate via an immobilized enzymatic reaction cascade

An immobilized enzymatic reaction cascade was designed and optimized for the deacidification of grass silage press juice (SPJ), thus facilitating the production of bio-based chemicals. The cascade involves a three-step process using four enzymes immobilized in a Ca-alginate gel and uses lactic acid to form acetoin, a value-added product. The reaction is performed with a continuous, pH-dependent substrate feed under oxygenation. With titrated lactic acid yields of up to 91% and reaction times of ca. 6h was achieved. Using SPJ as titrant yields of 49% were obtained within 6h. In this deacidification process, with acetoin one value-added bio-based chemical is produced while simultaneously the remaining press juice can be used in applications that require a higher pH. Such, this system can be applied in a multi-product biorefinery concept to take full advantage of nutrient-rich SPJ, which is a widely available and easily storable renewable resource.

Dry matter yield, chemical composition and estimated extractable protein of legume and grass species during the spring growth

BACKGROUND

Knowledge of the variation of extractable protein amount in legumes and grasses as affected by harvest time is important for identifying optimal combinations to enable a high protein production in a biorefinery. The extractability of protein was estimated using the Cornell Net Carbohydrate and Protein System across six harvests during the spring growth.

RESULTS

The estimated extractable protein [g kg^-1 dry matter (DM)] defined as the easily available fractions B₁ +B₂ was significantly higher in white clover and lucerne at all harvests while, if the more cell wall attached fraction B₃ can be extracted, white clover had the highest extractable protein amongst all species. Total yield of B₁ +B₂ per ha was higher in white clover and red clover at the early growth while B₁ +B₂ +B₃ was by far the highest for red clover through all harvests.

CONCLUSION

White clover could be a good candidate for protein production purpose in a biorefinery due to its high extractable protein content per kg DM. In order to maximise the protein production capacity, harvest should take place during early growth due to a decline in protein extractability with maturity. The final economy of the concept will depend on the value of the fibre after extraction of the protein. © 2017 Society of Chemical Industry.

Integrated biorefinery concept for grass silage using a combination of adapted pulping methods for advanced saccharification and extraction of lignin

An integrated refining and pulping process for ensiled biomass from permanent grassland was established on laboratory scale. The liquid phase, containing the majority of water-soluble components, including 24% of the initial dry matter (DM), was first separated by mechanical pressing. The fiber fraction was subjected to high solid load saccharification (25% DM) to enhance the lignin content in the feed for subsequent organosolvation. The saccharification enzymes were pre-selected applying experimental design approaches. Cellulose convertibility was improved by a secondary pressing step during liquefaction. Combined saccharification and organosolvation showed high degree of saccharide solubilization with recovery of 98% of the glucan and 73% of the xylan from the fiber fraction in the hydrolysates, and enabled the recovery of 41% of the grass silage lignin. The effects of the treatment were confirmed by XRD and SEM tracking of cellulose crystallinity and fiber morphology throughout the pulping procedure.

Uses of miscanthus press juice within a green biorefinery platform

This study assesses some uses of nutrient-rich juice mechanically extracted from freshly harvested Miscanthus x giganteus (MxG) as part of a green biorefinery system. The juice was used for culturing Saccharomyces cerevisiae and lactic acid bacteria. MxG juice was further used as substrate for fermentation to produce lactic acid using Lactobacillus brevis and Lactobacillus plantarum. The results show that MxG juice was a highly nutritious source for the cultivation of bacteria. Higher concentrations of MxG juice used as culture media, resulted in higher cell growth both aerobically and anaerobically. The highest ethanol yield of 70% theoretical and concentration of 0.75g/100ml were obtained from S. cerevisiae cultivated with 90% (v/v) MxG juice media and used for miscanthus solid fraction fermentation. 11.91g/L of lactic acid was also successfully produced from MxG juice through SSF.

Soluble phenolic compounds in fresh and ensiled orchard grass (Dactylis glomerata L.), a common species in permanent pastures with potential as a biomass feedstock

High-value coproducts can greatly improve the feasibility of utilizing plant feedstocks for biorefining and biofuel production. Plant polyphenolics have potential application in the pharmaceutical and cosmetic industries. Orchard grass varieties have been noted for accumulation of polyphenolic compounds, and the current study determined the soluble phenol profile and content in the orchard grass variety 'Abertop'. Hydroxycinnamates and flavonoids were monitored during the transition from vegetative to flowering stage at maximum crop yield. Caffeic acid derivatives, related to bioactives in the Asian medicinal herb Salvia miltiorrhiza , and novel hydroxycinnamate-flavone conjugates were also identified in extracts. Harvest yields of hydroxycinnamates and flavonoids ranged from 2.6 to 4.0 kg/ha and from 2.1 to 5.1 kg/ha, respectively. Abundant compounds showed high levels of antioxidant activity comparable with that of trolox. Minimal changes in soluble phenol content and composition were observed after ensiling with the exception of increases in caffeic acid, a caffeic acid derivative, and a caffeic acid breakdown product, dihydroxystyrene.