Detoxification of sugarcane-derived hemicellulosic hydrolysate using a lactic acid producing strain

Integration of lactic acid biorefinery with treatment of red mud from alumina refinery: win-win paradigm for waste valorization

The cost of detoxification and neutralization poses certain challenges to the development of an economically viable lactic acid biorefinery with lignocellulosic biomass as feedstock. Herein, red mud, an alkaline waste, was explored as both a detoxifying agent and a neutralizer. Red mud treatment of lignocellulosic hydrolysate effectively removed the inhibitors generated in dilute acid pretreatment, improving the lactic acid productivity from 1.0 g/L·h-1 to 1.9 g/L·h-1 in later fermentation. In addition, red mud could replace CaCO3 as a neutralizer in lactic acid fermentation, which in turn enabled simultaneous bioleaching of valuable metals (Sc, Y, Nd, and Al) from red mud. The neutralization of alkali in red mud by acids retained in lignocellulosic hydrolysate and lactic acid produced from fermentation led to effective dealkalization, rendering a maximum alkali removal efficiency of 92.2 %. Overall, this study offered a win-win strategy for the valorization of both lignocellulosic biomass and red mud.

First- and second-generation integrated process for bioethanol production: Fermentation of molasses diluted with hemicellulose hydrolysate by recombinant Saccharomyces cerevisiae

The integration of first- (1G) and second-generation (2G) ethanol production by adding sugarcane juice or molasses to lignocellulosic hydrolysates offers the possibility to overcome the problem of inhibitors (acetic acid, furfural, hydroxymethylfurfural and phenolic compounds), and add nutrients (such as salts, sugars and nitrogen sources) to the fermentation medium, allowing the production of higher ethanol titers. In this work, an 1G2G production process was developed with hemicellulosic hydrolysate (HH) from a diluted sulfuric acid pretreatment of sugarcane bagasse and sugarcane molasses. The industrial Saccharomyces cerevisiae CAT-1 was genetically modified for xylose consumption and used for co-fermentation of sucrose, fructose, glucose, and xylose. The fed-batch fermentation with high cell density that mimics an industrial fermentation was performed at bench scale fermenter, achieved high volumetric ethanol productivity of 1.59 g L-1 h-1, 0.39 g g-1 of ethanol yield, and 44.5 g L-1 ethanol titer, and shown that the yeast was able to consume all the sugars present in must simultaneously. With the results, it was possible to establish a mass balance for the global process: from pretreatment to the co-fermentation of molasses and HH, and it was possible to establish an effective integrated process (1G2G) with sugarcane molasses and HH co-fermentation employing a recombinant yeast.

Overcoming extended lag phase on optically pure lactic acid production from pretreated softwood solids

Optically pure lactic acid (LA) is needed in PLA (poly-lactic acid) production to build a crystalline structure with a higher melting point of the biopolymer than that of the racemic mixture. Lignocellulosic biomass can be used as raw material for LA production, in a non-food biorefinery concept. In the present study, genetically engineered P. acidilactici ZP26 was cultivated in a simultaneous saccharification and fermentation (SSF) process using steam pretreated softwood solids as a carbon source to produce optically pure D-LA. Given the low concentrations of identifiable inhibitory compounds from sugar and lignin degradation, the fermentation rate was expected to follow the rate of enzymatic hydrolysis. However, added pretreated solids (7% on weight (w/w) of water-insoluble solids [WIS]) significantly and immediately affected the process performance, which resulted in a long lag phase (more than 40 h) before the onset of the exponential phase of the fermentation. This unexpected delay was also observed without the addition of enzymes in the SSF and in a model fermentation with glucose and pretreated solids without added enzymes. Experiments showed that it was possible to overcome the extended lag phase in the presence of pretreated softwood solids by allowing the microorganism to initiate its exponential phase in synthetic medium, and subsequently adding the softwood solids and enzymatic blend to proceed to an SSF with D-LA production.

Fermentative Lactic Acid Production From Lignocellulosic Feedstocks: From Source to Purified Product

The second (lignocellulosic biomass and industrial wastes) and third (algal biomass) generation feedstocks gained substantial interest as a source of various value-added chemicals, produced by fermentation. Lactic acid is a valuable platform chemical with both traditional and newer applications in many industries. The successful fractionation, separation, and hydrolysis of lignocellulosic biomass result in sugars’ rich raw material for lactic acid fermentation. This review paper aims to summarize the investigations and progress in the last 5 years in lactic acid production from inexpensive and renewable resources. Different aspects are discussed—the type of raw materials, pretreatment and detoxification methods, lactic acid-producers (bacteria, fungi, and yeasts), use of genetically manipulated microorganisms, separation techniques, different approaches of process organization, as well as main challenges, and possible solutions for process optimization.

Enhanced lactic acid production from P2O5-pretreated biomass by domesticated Pediococcus pentosaceus without detoxification

Expensive cellulase and complex detoxification procedures increase the cost of biomass lactic acid fermentation. Therefore, it is of great significance to develop a robust method to ferment lactic acid using biomass by avoiding cellulase and detoxification. This study demonstrates the advantage of combining mechanocatalytic P₂O₅ pre-treatment and strain domestication. We show that an enzyme-free mechanocatalytic saccharification process by combining mix-milling of P₂O₅ with biomass and successive hydrolysis produces a fermentable hydrolysate with much less inhibitory compounds than the hydrolysates obtained by conventional methods; only 5-HMF, furfural and acetic acid were detected in the biomass hydrolysate, and no phenolic inhibitors were detected. Pretreatment of biomass with P₂O₅ not only avoided cellulase, but also obtained less toxic hydrolysate. Furthermore, the Pediococcus pentosaceus strain gained superior inhibitor tolerance through domestication. It could tolerate 17.1 g/L acetic acid, 12.5 g/L 5-HMF, 11.9 g/L guaiacol and 11.5 g/L furfural and showed activity in decomposing furfural and 5-HMF for self-detoxification, allowing efficient lactic acid fermentation from biomass hydrolysate without detoxification. The lactic acid concentration and conversion rate fermented by domesticated bacteria were increased by 113.5% and 22.4%, respectively. In addition, the domesticated bacteria could utilize glucose and xylose simultaneously to produce lactic acid selectively. The combination of P₂O₅ pre-treatment and strain domestication to ferment lactic acid is applied to several biomass feedstocks, including corn stalk, corn stalk residue and rice husk residue. Lactic acid concentrations of 29.8 g/L, 31.1 g/L, and 46.2 g/L were produced from the hydrolysates of corn stalk, corn stalk residue and rice husk residue, respectively.

Assessment of different Bacillus coagulans strains for l-lactic acid production from defined media and gardening hydrolysates: Effect of lignocellulosic inhibitors

Cellulose valorisation has been successfully addressed for years. However, the use of hemicellulosic hydrolysates is limited due to the presence of C5-sugars and inhibitors formed during pretreatment. Bacillus coagulans is one of the few bacteria able to utilize both C6- and C5-sugars to produce l-lactic acid, but its susceptibility to the lignocellulosic inhibitors needs further investigation. For such a purpose, the tolerance of different B. coagulans strains to increasing concentrations of inhibitors is studied. The isolated A162 strain reached the highest l-lactic acid productivity in all cases (up to 2.4 g L^-1  h^-1), even in presence of 5 g L^-1 of furans and phenols. Remarkably, most of furans and phenolic aldehydes were removed from defined media and hemicellulosic gardening hydrolysate after fermentation with A162. Considering the high productivities and the biodetoxifying effect attained, A162 could be pointed out as a great candidate for valorisation of mixed sugars from hemicellulosic hydrolysates with high inhibitors concentration, promoting the implementation of lignocellulosic biorefineries.

Production and Purification of l-lactic Acid in Lab and Pilot Scales Using Sweet Sorghum Juice

Sweet sorghum juice (SSJ) was evaluated as fermentation substrate for the production of l-lactic acid. A thermophilic Bacillus coagulans isolate was selected for batch fermentations without the use of additional nutrients. The first batch of SSJ (Batch A) resulted on higher lactic acid concentration, yield and productivity with values of 78.75 g∙L−1, 0.78 g∙g−1 and 1.77 g∙L−1 h−1, respectively. Similar results were obtained when the process was transferred into the pilot scale (50 L), with corresponding values of 73 g∙L−1, 0.70 g∙g−1 and 1.47 g∙L−1 h−1. A complete downstream process scheme was developed in order to separate lactic acid from the fermentation components. Coarse and ultra-filtration were employed as preliminary separation steps. Mono- and bipolar electrodialysis, followed by chromatography and vacuum evaporation were subsequently carried out leading to a solution containing 905.8 g∙L−1 lactic acid, with an optical purity of 98.9%. The results of this study highlight the importance of the downstream process with respect to using SSJ for lactic acid production. The proposed downstream process constitutes a more environmentally benign approach to conventional precipitation methods.