Ultrasound-assisted dilute acid hydrolysis for production of essential oils, pectin and bacterial cellulose via a citrus processing waste biorefinery.

An orange peel waste biorefinery was developed employing a design of experiments approach to optimize the ultrasound-assisted dilute acid hydrolysis process applied for production of useful commodities. Central composite design-based response surface methodology was used to approximate the combined effects of process parameters in simultaneous production of essential oils, pectin and a sugar-rich hydrolyzate. Application of a desirability function determined the optimal conditions required for maximal production efficiency of essential oils, pectin and sugars as 5.75% solid loading, 1.21% acid concentration and 34.2 min duration. Maximum production yields of 0.12% w/w essential oils, 45% w/w pectin and 40% w/w sugars were achieved under optimized conditions in lab- and pilot-scale facilities. The hydrolyzate formed was applied in bacterial cellulose fermentations producing 5.82 g biopolymer per 100 g waste. Design of experiments was efficient for process analysis and optimization providing a systems platform for the study of biomass-based biorefineries.

A biorefinery for conversion of citrus peel waste into essential oils, pectin, fertilizer and succinic acid via different fermentation strategies.

A process for the valorization of citrus peel waste (CPW) has been developed aiming to produce succinic acid and a series of added-value products through the biorefinery platform. CPW was subject to physicochemical and biological treatment to isolate essential oils (0.43%) and pectin (30.53%) as extractable products, pretreating the material for subsequent production of succinic acid that enabled application of remaining biorefinery residues (BR) as fertilizer substitute. Cellulose, hemicellulose and lignin contents of CPW accounted for 22.45%, 8.05% and 0.66% respectively, while acid hydrolysis reduced hemicellulose by 3.42% in BR. Moreover, essential oils extracted from CPW included 17 compounds, among which D-limonene reached 96.7%. The hydrolyzate generated was fermented for succinic acid production using Actinobacillus succinogenes. Different batch experiments demonstrated that the combined use of corn steep liquor (CSL) and vitamins in a lab-scale bioreactor resulted in product concentration and yield that reached 18.5 g L-1 and 0.62 g g-1 respectively. Although simultaneous saccharification and fermentation (SSF) could not enhance succinic acid production, a fed-batch fermentation strategy increased succinic acid concentration and yield generating 22.4 g L-1 and 0.73 g g-1 respectively, while the mass of the platform chemical formed was enhanced by 27% as compared to the batch process. BR was explored as fertilizer substitute aiming to close the loop in the management of CPW towards development of a zero-waste process demonstrating that although the material imposed stress on plant growth, the content of potassium, phosphorus and nitrogen in the mixture increased.