Development of a citrus peel waste biorefinery for the production of high added-value commodities and biofuels

Citrus fruits constitute one of the most highly utilized food products worldwide. The production of citrus fruits reaches over 124×106 t per year, while citrus juice manufacturing generates 25×106 t. During the processing of the fruit, half of its mass is converted into citrus peel waste (CPW) consisting of peels, seeds and segment membranes. Current management practices include the use of CPW as animal feed or disposal in landfills. However, CPW is composed of pectin, cellulose, hemicellulose, soluble sugars and essential oils, components that constitute CPW as a promising feedstock for extraction and production of addedvalue products and biofuels through the biorefinery platform. The proposed biorefinery of this work combines physicochemical and biological treatments for extraction of essential oils and pectin as well as for production of succinic acid (platform chemical), ethanol and methane (biofuels) and a fertilizer. The first step employed distillation for extraction and collection of essential oils where the yield reached 0.43% and 0.24% (v/w) for “Mandora” and household citrus waste respectively. The next step of the proposed biorefinery included acid hydrolysis, where the optimized conditions comprised 116 oC for 10 min using 5% (w/v) of dry raw material for both materials. Afterwards, the extraction of pectin, which reached 30.5% (w/w), was separated from the hydrolyzate generated through addition of ethanol. Subsequently, following ethanol removal, the hydrolyzate was microbially fermented to succinic acid or ethanol. Succinic acid production was enhanced with the addition of corn steep liquor in fermentations, while the addition of vitamins increased the production rate. A fed-batch experiment was also conducted and resulted in slight increase of both the final concentration of succinic acid as well as the product yield. Moreover, ethanol production was studied using P. kudriavzevii KVMP10, a newly thermotolerant yeast which was compared against two major industrial yeasts (S. cerevisiae and K. marxianus) and found to be a more efficient ethanol producer through use of CPW hydrolyzates. Finally, solid biorefinery residues were tested in anaerobic digestion for the production of biomethane and in agricultural applications as fertilizer targeting the development of a zero-waste process.Vasilleios Fotopoulos, Emeritus Emmanuel M. PapamichaelComplete

Bioprocess development for the production of succinic acid from orange peel waste

A preliminary study has been conducted for the development of a bioprocess targeting the valorization of orange peel waste (OPW). Essential oils and pectin were recovered from OPW through distillation, acid hydrolysis and precipitation with ethanol. Optimal conditions for dilute-acid hydrolysis were investigated via estimation of the sugars released and fermentation. Hydrolysis conditions of 109 o C for 20 min and 116 o C for 10 min using 5 % of dry raw material produced the highest sugar yields at 0.76 and 0.77 (gtotal sugars gdry raw material-1) respectively. In order to test the efficiency of enzyme hydrolysis as a pretreatment method for OPW valorization, cellulase production from T. reesei was investigated, which was maximized following 5 days of cultivation. Furthermore, elemental analysis in hydrolyzates from dilute-acid hydrolysis and a combination of acid and enzyme hydrolysis was performed. The results indicate that during acid/enzyme hydrolysis, high concentrations of Mg2+ and Ca2+ ions are liberated in contrast to dilute-acid hydrolysis. A. succinogenes fermentations of glucose and fructose were performed and the succinic acid yields achieved were 0.66 (gsuccinic acid gglucose-1) and 0.33 (gsuccinic acid gfructose-1) respectively, while galactose was not fermented. Overall, OPW may serve as a promising raw material for simultaneous production of essential oils, pectin and succinic acid

A Citrus Peel Waste Biorefinery for Ethanol and Methane Production

This paper deals with the development of a citrus peel waste (CPW) biorefinery that employs low environmental impact technologies for production of ethanol and methane. Three major yeasts were compared for ethanol production in batch fermentations using CPW pretreated through acid hydrolysis and a combination of acid and enzyme hydrolysis. The most efficient conditions for production of CPW-based hydrolyzates included processing at 116 °C for 10 min. Pichia kudriavzevii KVMP10 achieved the highest ethanol production that reached 30.7 g L-1 in fermentations conducted at elevated temperatures (42 °C). A zero-waste biorefinery was introduced by using solid biorefinery residues in repeated batch anaerobic digestion fermentations achieving methane formation of 342 mL gVS-1 (volatile solids). Methane production applying untreated and dried CPW reached a similar level (339-356 mL gVS-1) to the use of the side stream, demonstrating that the developed bioprocess constitutes an advanced alternative to energy intensive methods for biofuel production

Enhancing bioproduction and thermotolerance in Saccharomyces cerevisiae via cell immobilization on biochar: Application in a citrus peel waste biorefinery

A novel method for enhancement of ethanol production and temperature tolerance of S. cerevisiae through the development of biochar-based biocatalysts (BBBs) is reported. Immobilized BBBs were applied in alcoholic fermentations of hydrolyzates generated via a citrus peel waste (CPW) biorefinery, which allowed extraction of high-purity pectin that reached 30.5% (w/w). Pistachio-nut shells, peanut shells and corks were employed for biochar generation via pyrolysis to produce the cell carriers required. All materials were highly carbonaceous with mesopore size structures (1–50 μm), while peanut shells biochar was crystalline incorporating calcite and sylvite. S. cerevisiae immobilized on pistachio-nuts biochar grown on a synthetic CPW hydrolysate, exhibited 63 g L−1 ethanol concentration and 7.9 g L−1 h−1 productivity improving substantially biosystem performance as compared to unsupported cultures. Alcoholic fermentations conducted at different elevated temperatures (37–41 °C) exhibited stable performance of the immobilized system for six repeated batch experiments. Fermentations of the CPW-hydrolyzate formed through the biorefinery at 41 °C using BBB produced 30.8 g L−1 of ethanol, while free cells achieved significantly lower concentration (13.4 g L−1). The proposed technology confers thermotolerance on S. cerevisiae, which buffers the negative impact of high temperatures on cells leading in increased bioethanol production and lower energy demand

Development of a citrus peel-based biorefinery strategy for the production of succinic acid

A preliminary study has been performed for the valorization of citrus peel waste (CPW) through the biorefinery platform aiming to produce succinic acid. Following extraction of essential oils and pectin, different conditions of dilute acid hydrolysis were evaluated based on estimation of the sugars liberated and subsequent fermentation of hydrolyzates for production of succinic acid by Actinobacillus succinogenes. The most suitable pretreatment conditions involved 116 degrees C for 10 min using 5% (w/v) of dry raw material (drm). Thus, a total sugar (ts) yield of 0.21 g(ts) g(drm)(-1) and a succinic acid (sa) yield via microbial fermentations of 0.77 g(sa) g(tsc)(-1) was achieved, while the use of lower solid contents resulted in higher sugar yields. The residues from dilute acid hydrolysis were applied for subsequent enzyme hydrolysis using commercial enzymes and the most suitable combination of enzyme units included 30 IU cellulases and 25 BGL beta-glucosidases achieving a yield of 0.58 g(ts) g(drm)(-1). Moreover, elemental analysis in hydrolyzates obtained from dilute acid hydrolysis and a combination of acid and enzyme hydrolysis indicated that during the combined treatment, high concentrations of Mg2+ and Ca2+ ions are liberated as compared to dilute acid hydrolysis, while the concentration of hydroxymethylfurfural was 0.038 g L-1 demonstrating low formation of inhibitors. The hydrolyzate generated through the combined pretreatment proposed was applied as feedstock for the production of succinic acid achieving a yield of 0.70 g(sa) g(tsc)(-1). However, although the combined hydrolysis approach could approximately double the sugars released in the hydrolyzate, the economic analysis performed confirmed that the use of the enzymatic treatment could not be competitive. The developed bioprocess constitutes a valuable alternative to the application of energy intensive chemical technologies for succinic acid production

Biotechnological production of fumaric acid: The effect of morphology of Rhizopus arrhizus NRRL 2582

Fumaric acid is a platform chemical with many applications in bio-based chemical and polymer production. Fungal cell morphology is an important factor that affects fumaric acid production via fermentation. In the present study, pellet and dispersed mycelia morphology of Rhizopus arrhizus NRRL 2582 was analysed using image analysis software and the impact on fumaric acid production was evaluated. Batch experiments were carried out in shake flasks using glucose as carbon source. The highest fumaric acid yield of 0.84 g/g total sugars was achieved in the case of dispersed mycelia with a final fumaric acid concentration of 19.7 g/L. The fumaric acid production was also evaluated using a nutrient rich feedstock obtained from soybean cake, as substitute of the commercial nitrogen sources. Solid state fermentation was performed in order to produce proteolytic enzymes, which were utilised for soybean cake hydrolysis. Batch fermentations were conducted using 50 g/L glucose and soybean cake hydrolysate achieving up to 33 g/L fumaric acid concentration. To the best of our knowledge the influence of R. arrhizus morphology on fumaric acid production has not been reported previously. The results indicated that dispersed clumps were more effective in fumaric acid production than pellets and renewable resources could be alternatively valorised for the biotechnological production of platform chemicals