Definition of Goal and Scope

The goal is to describe the life cycle environmental and energy performance of the PHBV production pathway developed by the team from glucose in the pot ale. The functional unit considered is one kg of dry PHBV granule. The system boundary defined in this study overlooks the whisky production and considers efforts and environmental burden from whisky production to be delinked from pot ale, thus viewing pot ale to be burden free (Gandy & Hinton 2018). We focused on cradle-to-gate life cycle thus only unit operations within the red dotted line boundary are considered. Usage and end-of-life scenarios are not considered in this study either, again due to the boundary. Consequential LCA is performed for this scenario.

Figure 1. The Proposed Boundary for Life Cycle Assessment of PHBV Production in Scenario 1

Inventory Analysis

Data were collected based on the scope specified previously. Most of the datasets applied in this study were acquired from the Ecoinvent v2.0 database and GaBi Professional Database which are largely based on European sites. The rest of data was obtained from literature and simulation using SuperPro Designer.

Impact Assessment

From the available assessment methods in GaBi, the CML method was selected after careful consideration. Four areas of protection are covered, namely (i) natural resources, (ii) natural environment, (iii) man-made environment, and (iv) human health. The base line impact categories considered in this study are eutrophication and climate change. Characterisation in CML is based on European and global average values, making it reasonable considering the study is based in the United Kingdom. Normalisation was performed so that the baseline global normalisation factors presented were for the years 1990 and 1995 as cumulative yearly world interventions, whereas weighting was not performed in this method.

Interpretation

Life Cycle Impact Assessment

Consequential LCA focuses on the prospective future environmental impact caused by alteration in demand of the product. In this case, the demand of pot ale was predicted to increase due to PHBV production which can be supplied from other distilleries or the current distillery by increasing whisky production.

The first impact category was eutrophication potential with 0.322 kg phosphate equivalent per 1 kg PHBV where 99.38% of it comes from wastewater treatment. The rest of it is contributed by process water, ammonia, ethanol, and sodium hydroxide production. This category falls under natural environment area. When wastewater treatment is omitted from the life cycle, the eutrophication potential is 2080 kg phosphate equivalent per 1 kg PHBV potentially due to the presence of untreated wastewater produced from unit operations involved. Wastewater treatment is not originally within the system boundary; however, this step is necessary and highly recommended as a way to reduce eutrophication potential as shown in this study.

In the second impact category, climate change (specifically global warming potential or GWP) which belongs to human health area, the system is calculated to produce 5.84 kg CO2 equivalent per 1 kg PHBV in 100 year time. The major contributor is again process water production at 36.47% followed by ethanol, ammonia, and sodium hydroxide production, respectively. On the other hand, focusing on land usage change only in this category, the total GWP is 4500 kg CO2 equivalent per 1 kg PHBV in 100 year time whereas the highest contributor is also process water at 80% of the total kg CO2 equivalent followed by sodium hydroxide and ethanol production, respectively. When wastewater treatment is omitted, the total GWP and GWP on land use change only are 5.79 kg and 4410 kg CO2 equivalent, respectively.

Figure 2 Life Cycle Assessment Result for Eutrophication Potential and Global Warming Potential of Scenario 1

In addition, the result from impact assessment above does not show which PHBV unit operations have the highest environmental impact likely due to lack of data available. The major contributors in the categories involved are process water, sodium hydroxide, ammonia, and ethanol production which are indirectly linked to the overall PHBV production (off-sites processes). SuperPro Designer was able to show the power consumption for each unit operation involved as shown in Table 1. The total energy used for 1 kg PHBV was 50.10 kWh with highest power consumption was pre-treatment stage due to its long process.

Table 1 Power consumption of unit operations involved in PHBV production in Scenario 1

As the consequences of using pot ale in PHBV production, other feedstock alternatives must be considered for animal feed production. Plant-based feedstock has been considered as an alternative such as barley and oats, however, a number of factors must be considered as well prior to selecting the feedstock to replace pot ale. Firstly, barley and oats are currently used in food and beverage industry. Their demand is predicted to increase if they are also used in animal feed industry, this definitely requires higher barley and oats production to ensure demands from both industries to be met. Secondly, the alternative feedstock should be able to provide similar nutritional value as pot ale to maintain the livestock quality. Thirdly, pot ale has been regarded as burden free in LCA, thus minimising the entire environmental load of animal feed production. Careful consideration must be made before selecting the appropriate feedstock here to prevent build-up in environmental burden of animal feed production. 

Definition of Goal and Scope

The goal for this scenario is to conduct an attributional LCA to study the environmental impacts of PHBV production starting from draff and pot ale. A secondary goal was to identify the ecological “hot spots” of the modelled process, as well as to quantify the green-house gases (GHG) emissions and the energy consumption of the processes. The functional unit is one kg of dry and granulated PHBV. The system boundaries of the study include the following processes: 1. draff and pot ale preparation, 2. seed culture, 3. fed batch culture, 4. PHBV extraction, 5. chemicals recovery, 6. liquid waste management, 7. solid waste management, 8. PHBV physical recycling scenario, and 9. PHBV chemical recycling scenario.

Figure 3 The Proposed Boundary for Life Cycle Assessment of PHBV Production in Scenario 2

The system boundary of this study omits production of plastic products (bottles, films, etc.), collection, transport, use and sorting and classification of recyclables as these are assumed to be identical to a typical plastic, and will occur regardless of the origin of the plastic. Other assumptions and simplifications made throughout the modelling include;

• The draff and pot ale are by-products of the whisky industry and will be produced regardless of their later use as feedstock. Therefore, its production would be supposed as carbon neutral for calculation and timesaving. However, as has been explained previously (Ellen MacArthur Foundation 2016) the carbon cycle of the agriculture and whisky process has to be take into account for a better understanding of the model.
• The properties and applications of PHBV are similar to petroleum-based plastics. For that reason, the PHBV produced from whisky by-products and other plastics are comparable. Formerly, the product manufacturing and use phases can be supposed to have the same environmental impact for both cases and does not have repercussions in the life cycle. In short, the manufacturing and use stages are not considered as part of the present LCA.
• Only the operational phases of the process were considered, the equipment installation, maintenance of the equipment used are excluded from the model.
• The wastewater resulting from each process is treated in a water plant and is reincorporated into the system.
• For the disposal scenarios, the collection of the plastic and separation of residual activities are assumed equal operations compared with petroleum-based plastics, and for that reason are not included the system boundaries and the model of the waste scenario.

Attributional LCA was performed on this scenario.

Inventory Analysis

The inventory of the input and output flows of mass and energy for each step of the PHBV production and physical recycling was derived from the mass and energy balances obtained in SPD. Meanwhile, the estimated data for the chemical recycling operation was an adjustment from Fernandez-Dacosta et al., 2016 report. The database used for the model of the production of electricity, heat and water consumption is the Ecoinvent 3.01. British electricity mix, heat and water sources are assumed.

Impact Assessment

The environmental impact categories of interest for this LCA are:  Climate change, abiotic depletion, ecotoxicity, eutrophication and human toxicity. For that reason, the Life Cycle Impact Assessment was done with CML-IA baseline impact method.

Interpretation

Life Cycle Assessment Analysis

The thickness of red lines shown in Figure 4 indicates the severity of the negative impact of each assembly to the LCA. On the other hand, the green lines indicate environmental benefit impacts which can be seen from recycling scenario section. According to Figure 4, recycling process has positive impact to the whole life cycle at -36.8% whereas the downstream or extraction process is the top negative contributor to the life cycle at 106%. Meanwhile in the waste scenario, the assembly of the physical treatment of the PHBV is the number one positive contributors at -70.1%.

Figure 4. PHBV production model visualisation at 35.6% in SimaPro

Life Cycle Impact Assessment Analysis

The analysis of an LCIA can be divided into two levels; the full life cycle and the assembly level. The full life cycle allows the practitioner to make comparisons between the production and the recycling scenario. Conversely, the assembly level grants more opportunity to examine the necessary detail to produce recommendations for the design of the process.

According to the results of the full life cycle of PHBV production, the major environmental impacts are demonstrated by the eutrophication and marine aquatic ecotoxicity categories subsequent to normalisation which shown in the following figure. The production assembly carries the biggest load, whereas the only category that shows positive impacts is eutrophication. Nevertheless, this statement is not sufficient to emit any recommendation of how to manage a decrease.

Figure 5. Normalised impact categories for the full life cycle of PHBV for Scenario 2

The PHBV assembly is composed of the pre-treatment, fermentation and downstream. The characterised results for the PHBV assembly are shown in Figure 6.  Furthermore, the individual impact categories were analysed using the same type of results. The PHBV assembly stages are the most significant thus the comparison of the impacts of each process are reported.

                          
 Figure 6 Impact categories of the PHBV assembly in Scenario 2

Global Warming Potential and Energy Demand

The first category is climate change as implied by Global Warming Potential (GWP) which is related to the emissions of greenhouse gases to air. Having a process where the CO₂ emissions are bigger than the CO₂ sequestration and removal is a major challenge (Narayan 2011). Having a bioplastic production with a bio-renewable feedstock offers the possibility for a neutral carbon footprint; which would leave the bottleneck to be the design of a process with the lowest greenhouse gas emissions. Figure 7 shows that the downstream processing is contributing a major charge of GWP of the PHBV assembly and to the whole life cycle, as has been previously stated. This is correlated to the high usage of fossil fuel for energy production and thus resulting to the increase in the greenhouse gases generation. It is virtually impossible to achieve carbon neutral PHBV production with the continuous and dependent usage of fossil fuels for energy. Thus, the goal of decoupling plastic production from petroleum can only be attained by the shift to the usage of renewable energy sources throughout the production.

Figure 7 Environmental impacts of the PHBV assembly in the Global Warming Potential category

The cumulative energy demand is a valuable parameter to assess the sustainability performance of a process, rather than only focussing on the impacts generated by the use of substances. The downstream processing entails a great number of operations in this scenario, thus it is not surprising that it contributes the highest impact to the overall life cycle. It must be kept in mind that the results above referred to 1 kg of PHBV. Hence, if an optimal condition of highest cell production and energy optimisation of the downstream processing are achieved then the impacts would consequentially be lowered in an ideal scenario and thus making the whole life cycle more feasible. Correspondingly, the first step to improve the overall PHBV production is to enhance the yield of PHBV produced in fermentation stage and to increase the efficiency of the energy use. 

Human Toxicity

The health risks on the human environment derived from the use of toxic substances in a system are incorporated into the human toxicity category (PreConsultants 2014). This category is one of least reported for LCA studies and we believe that without a doubt is in need of improvement. In terms of synthetic biology, one of the major concerns is the use of genetically modified organism (GMO) and the risks that it entails – risk that is not included in the human toxicity or any other toxicity category. Because of this there are several critics stating that LCA studies are not suitable to evaluate processes using synthetic biology in any of its stages (Seager, et al. 2017). Even if the toxicity impact were actually higher due of the use of GMOs, only fermentation assembly would be reflect such result. For our general purposes, the use of toxic chemicals continues to be a matter of importance as indicated by the downstream stage as can be seen in the Figure 21, rather than the use of GMOs.

Figure 8 Human toxicity potential for PHBV assembly in Scenario 2. The results refer to 1,4-dichlorobenzene equivalent kg emission. 

Ecotoxicity

The ecotoxicity potential category indicates the impacts of the release of toxic substances to water and soil (PreConsultants 2014). The downstream processing continues to be the top contributor in the life cycle process that generates most of the environmental impacts. Three sub-categories namely fresh water, marine aquatic and terrestrial are considered here, the normalised results for the complete life cycle showed that the impacts of the marine aquatic ecotoxicity stand out above the rest. Subsequent to further investigation, it was discovered that the contained substances washed in the downstream processing can be identified as the cause of this.

The ecotoxicity category once again failed to include the potential impact of using GMOs in the process. For this reason, the data is presented as an initial point for future work. This limitation is mainly due to the use of pre-existed methods for LCIA. For a better suitability of LCA for SynBio processes, an impact category focusing on the risks of using GMOs (for example, the release of them, the current policies for their use, the problems of reproducibility and mutations in the strains) would be highly recommended to be considered for a more comprehensive analysis.

Figure 9 Ecotoxicity potential for the PHBV assembly. The results are referred to 1,4-dichlorobenzene

Eutrophication

This category includes the potential impacts of disposing of macro-nutrients into the environment (PreConsultants 2014). By consulting the inventory for this impact, it can be said that the substance responsible is the ammonia in the system. Even though ammonia is the mainly utilised in the fermentation stage, it is mostly emitted during the downstream process thus resulting to this stage to be the main contributor to the environmental impact in this life cycle as shown in Figure 10.

Figure 10. Eutrophication potential, the results are expressed as kg PO4 equivalents per kg emission

Comparison with Secretion System

Across all the impact categories described, the downstream processing is perceived to be the biggest contributors to the environmental impacts. This observation corresponds with what has been stated in literature. For this reason a second life cycle assessment was modelled with modified downstream processing which comprise of in-situ secretion system by the E. coli instead of cell disruption method. The LCAs of both processes were compared and the results reported in Figure 11.

Figure 11. Comparison of Life Cycle Assessment of Scenario 2 (Conventional process) and Modified Scenario 2 with in-situ secretion process as part of the downstream stage. The percentage represented in green represents the reductions in the environmental impacts by using the in-situ secretion system.

For all the impact categories in Figure 11, the full life cycle with Scenario 2’s with in-situ secretion process shows a decrease in the environmental impacts through all the categories. This indicates that the use of the in-situ secretion possesses the potential of large beneficial influence in reducing the negative impacts of the downstream processing stage. However, this indication should be taken with a little caution, as further research is still needed. The in-situ secretion system has to be further improved in order to provide a high yield of PHBV outside the cell, as well as the scale-up experiments for this secretion system. However, this path can be addressed using synthetic biology and metabolic engineering tools.