Development of a citrus peel waste biorefinery for the production of high added-value commodities and biofuels
Date Issued
December 2019
Author(s)
Advisor
Abstract
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.
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.
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