Life cycle assessment (LCA) has the capacity of pinpointing the hotspots in a system to allow its improvement with a more sustainable outlook which will definitely benefit the environment as well as the current and future generations. This year, the University of Edinburgh Overgraduate iGEM team engineered PHA production pathway in E. coli. And in this project, LCA analysis was conducted to analyses sustainability of industrial scale PHA production, helping to understand the implication of using a whisky by-product as the feedstock in the production as well as its impact upon the environment.
Since five decades ago, computer simulation models have been extensively used in order to investigate economical and physical implications from experimental alterations, to facilitate in both plant design and business plan. From numerous simulation software available, SuperPro Designer v9.5(Academic Site Edition) (Intelligen Inc.) was chosen to be used here as it is a comprehensive process simulator that supports modelling, evaluation, and optimisation of various pharmaceutical, chemical, food and related processes. Process simulator is a crucial tool and has been used widely especially in the Bioprocess Engineering field. Considering there is limited information regarding industrial scale PHBV production available, we decided to simulate PHBV production that incorporate PHA synthesis pathway that we personally engineered in this project.
We aim to analyse sustainability of industrial scale PHBV production by simulating the process in SuperPro Designer. The result obtained from this was fed into our Life Cycle Assessment.
PHBV production was simulated from the pre-treatment stage of the whisky by-product (pot ale) to the recovery stage using SuperPro Designer v9.5 (Academic Site Edition). Prior to any simulation, batch process operating mode was selected with default annual operating time of 7920.0 h. All components used were registered under Pure Components (such as sodium chloride and carbon dioxide) or Stock Mixture (such as ethanol (10% (v/v)). Unit operations and its respective parameters involved were added and connected with one another to construct the complete simulation setup. The selected unit operations are adapted from various literatures as listed in Table 1.
Table 1 List of unit operations utilised in the PHBV production simulation using Superpro Designer
Unit Operations
References
Pre-treatment Stage
Sterilisation
Rodriguez-Perez et al. (2018)
Enzymatic hydrolysis
Tokuda et al. (1998)
Centrifugation
Fermentation Stage
Fermentation
Srirangan et al. (2016), Bothfeld et al. (2017), Shehata and Marr (1971)
Recovery Stage
NaOH treatment
Choi and Lee (1999), Anis et al. (2013)
Washing using ethanol
Drum Drying
Van Wegen, Ling and Middelberg (1998)
Results and Discussion
PHBV production was simulated at a smaller scale (1 L or lab scale) and then upscaled gradually through pilot to an industrial scale. And in this study, the adjustments considered were substrate feeding substrate feeding style, time, and the recovery method.
Figure 1 1,000 L scale PHBV production simulation and mass balance
The complete the mass balance of each unit operation is shown in Table 2. One batch of PHBV production using 1,000 L working volume resulted in 42.06 kg PHBV with 94.93% purity and 91.48% recovery yield. The entire system required 8.79 days to complete.
Table 2 Mass Balance of PHBV production in 1,000 L working volume scale
Input
Output
Detail
Amount
Pre-treatment (includes sterilisation and enzymatic hydrolysis)
Untreated pot ale
28,223.30 kg
Treated pot ale
28,504.07 kg
Enzyme
280.52 kg
Steam
598.78 kg
Water – CIP
5,412.19 kg
Waste water
50,382.74 kg
Steam – sterilisation
Cooling water – heat transfer agent
44,970.55 kg
Glucose Recovery (centrifugation)
Concentrated pot ale
624.93 kg
4,476.17 kg
32,355.31 kg
Seed culture (fermentation)
Media
2.56 kg
Biomass
3.49 kg
Inoculum
0.99 kg
Gas emission
5.34 kg
Ammonia
1 kg
Waste Water
219.34 kg
Air
4.26 kg
Steam – SIP
0.22 kg
201.97 kg
Chilled water – heat transfer agent
17.37 kg
PHBV production (fermentation)
Media – pot ale
454.55 kg
PHBV slurry
1,000.33 kg
Fed media – concentrated pot ale
1,779.25 kg
21,378.61 kg
25.00 kg
1670.16 kg
1,328.12 kg
20,050.49 kg
PHBV recovery (NaOH treatment)
PHBV treated slurry
3,444.81 kg
NaOH
9.78 kg
1,492.06 kg
Water – NaOH dissolvent
2,434.70 kg
PHBV recovery (centrifugation)
Solid stream – PHBV
273.58 kg
4,663.29 kg
Washing (ethanol treatment)
Washed PHBV
271.29 kg
Ethanol
37.78 kg
1,683.25 kg
Water – ethanol mixture
151.12 kg
Drum drying
PHBV
42.06 kg
458.45 kg
229.22 kg
Future work
The simulation had provided insights into the efficiency of the proposed process. This will certainly need to be further optimized before being implemented in large scale.
