2. Introduction
Agro-industrial Waste
● 8 megatons of plastic waste and 3,700 megatons of agricultural residue are
produced annually worldwide
● The economic value of agricultural residue is generally less than the cost of recovery
and reuse, so it is discarded and causes unfavorable environmental effects
○ Effective utilization could be valuable if it’s used for the development of novel products, which are
sustainable and cost-effective
● Agricultural residues can be converted into useful compounds through biorefinery
approaches, for example, lactic acid which can be used as a monomer for the
production of bioplastics.
3. Introduction
Poly-lactic Acid
● Poly-lactic acid (PLA) has emerged as one of the most popular biodegradable
plastics
○ PLA is most commonly used as plastic filament in 3D printing
● Its monomer can be found in plant starches such as corn, cassava, sugarcane, or
sugar beets
● Biotechnological production of lactic acid can be produced from different renewable
feedstocks with lower environmental impact and high efficiency in terms of
productivity and purity
Left:
https://en.wikipedia.org/wiki/Polylac
tic_acid
Right: https://felfil.com/pla-filament-
for-3d-printing-learning-about-
plastic-materials/?v=5ea34fa833a1
4. Goal
● The main goal for this project involves the fermentation of raw materials in order
to produce lactic acid products, which will then be used as biodegradable
materials and PLA
● Overall, this method utilizes many characteristics of bioprocessing engineering,
including reducing the environmental impact of harmful man-made products
using organic, renewable, and biocompatible materials
Cottonseed cake PLA
5. Literature Review
Fermentation Strategy - Shaofeng Ding and Tianwei Tan
● This study compared pulse fed-batch, constant feed batch,
and exponential fed-batch for lactic acid production and
compared them based on lactic acid concentration,
productivity, and yield
● The batch culture had the lowest lactic acid concentration,
productivity, and yield
● The exponentially fed-batch had the best outcome in terms of
lactic acid production rate in g/L *hr at more than double the
non-fed batch method
This figure shows the results
from the exponentially fed
batch experiment over the 84
hour run time
Fig 2. Shaofeng Ding, Tianwei Tan, l-lactic acid production by Lactobacillus casei
fermentation using different fed-batch feeding strategies,
6. Literature Review
Substrate Treatment
● The aim of this study was to look at activity of peptides with
defatted cottonseed and with wheat proteins as substrate
● Neutral proteolytic enzyme preparation from Bacillus
amyloliquefaciens
● The data showed that the rate of hydrolysis was fastest
when an acid protease is used due to cotton seeds’ alkaline-
soluble proteins
● Our design does not include enzymatic pretreatment and
assumes the media is treated prior to going into the sterilizer
This image shows a
sample enzymatic
digester typically used in
pretreatment
https://www.energy.gov/sites/prod/files/2017/05/f34
/Pretreatment%20and%20Process%20Hydrolysis.pdf
7. Proposed Process
Pretreatment
● Possible pretreatments for lactic acid production in feedstocks involves the following
processes:
○ Milling: performed in order to reduce particle size in the feedstock, allows
fermentation to be more efficient; pressing out excess oils
○ Hydrolysis: breaks down complex carbohydrates and facilitates biochemical
conversion, brings out most abundant residues
○ Heat sterilization: used to delignify (remove lignocellulosic agricultural residues)
and sterilize the process
● Our proposed pretreatment process will involve heat sterilization
8. Proposed Process
Fed-batch Fermentation
● Traditional batch fermentation operations suffer from low cell mass and product because
a high initial glucose concentration causes substrate and product inhibitions
● Fed-batch process exhibits lower substrate inhibition and a reduced lag phase, which
improves lactic acid production
○ Proves to be more beneficial than traditional batch fermentation operations
● Governing equation:
○ Where F is the feed rate, V is Volume, X is cell concentration, μ is the constant
specific growth rate, Yx/s is the theoretical cell yield, t is culture time, and S is
substrate concentration
9. Proposed Process
Centrifugation + Product Use
● The final step in the process is lactic acid separation by centrifugation
● The output from the fermentation process is centrifuged to produce two different
outputs:
○ Lactic acid
○ Recovered inoculum (cells and excess glucose)
● The lactic acid obtained from this process can then
be used in the production of poly-lactic acid (PLA) or
other biotechnological products
Centrifuge for separation of
materials following fermentation
11. Comparison of Design
● Our design looked at just lactic
acid fermentation rather than the
full process of PLA production
and refinement
● PLA refinement is expensive but
the value of PLA makes up for it
● The price of refined lactic acid is
around $1 per kg while PLA is
around $5+ per kg
This figure shows a PLA production
process using banana peels as the starch
and glucose source rather than cottonseed
residue
Fig 2. A Bello et al 2020 J. Phys.: Conf. Ser. 1655 012078
12. Evaluation of Design
● Using a batch run time of 84 hour and a total facility run
time of 7900 hours annually, our design could process 94
batches of 1000L each per year
● Our main input is cottonseed cake valued at 0.30 $/kg and
our main output is Lactic acid valued at 1 $/kg
● About 40% of cottonseed cake composition will be
fermentable
● A production rate of 2.14 g/L*hr of lactic acid is expected
using the exponential fed batch method, with a target yield
of 90%
● Value of lactic acid produced yearly: $16,900
● Cost of cottonseed cake required yearly: $14,000
This graph shows the increasing market
for PLA and the industries using it
13. Conclusion
● Cottonseed cake will continue to be produced as a byproduct from cottonseed
oil pressing and is a suitable biomass for a PLA production design
● A full PLA production facility with additional ethanol recovery would likely be
required to turn a profit, as lactic acid is too low value to be the sole product
● Exponentially fed batch fermenters have been shown to have higher production
rates and yields of lactic acid from cottonseed residue than traditional batch or
continuously fed batch fermenters
● Energy and water saving efforts must be made, particularly
in the processes following lactic acid fermentation, in order
to produce PLA at a profit
