147
is associated with the feedstock. From an economic perspective, agricultural feedstocks may make up around 25% of the total production cost. In comparison, use of
industrial wastewater allows offset of treatment costs or trade waste tariffs, which
can result in 25% cost reductions (Dacosta et al. 2015, Gurieff and Lant 2007).
From an environmental perspective, most life cycle analysis studies show polyhydroxyalkanoates to be more environmentally friendly than petrochemical plastics
(Leong et al. 2016) or at least similar (Hottle et al. 2013). However, a few studies
have demonstrated that pure culture polyhydroxyalkanoates production from agricultural feedstock may be worse than petrochemical plastics, primarily due to the
impacts associated with crop production and sterilization (Gerngross 1999; Kim
and Dale 2005). Combined industrial wastewater treatment and polyhydroxyalkanoates production avoids issues with both crop production and sterilization.
However, while Dacosta et al. (Dacosta et al. 2015) showed that GHG emissions
were slightly lower than pure culture agricultural feedstock polyhydroxyalkanoates
or petrochemical PET, nonrenewable energy use was significantly higher than both
alternatives. High energy use was similarly reported by Gurieff and Lant (2007) and
Gerngross (1999). However, replacement of energy sources with renewables provides a means to significantly reduce these impacts (Kim and Dale 2005). Moreover,
microbial-based polyhydroxyalkanoates production has been shown to be significantly more environmentally friendly than plant-based polyhydroxyalkanoates production, mostly due to the high steam requirements in processing plant material
(Zhong et al. 2009).
Areas of improvement in the process could lead to significantly reduced environmental footprint of polyhydroxyalkanoates production. One area of potential focus
is the solvent extraction, which is a major contributor of overall impacts in an industrial wastewater treatment polyhydroxyalkanoates production facility (Dacosta
et al. 2015). The use of alternative solvents is one approach. For instance, a comparison of various implementations of dimethyl carbonate as solvent has shown
benefits across all assessed impact categories in comparison to a more traditional
1,2-dichloroethane solvent followed by methanol precipitation (Righi et al. 2017).
Koller and Braunegg (Martin and Gerhart 2018) also highlight the need for fully
integrated plant design and the benefits achieved when making use of harvested cell
debris for biogas production and the subsequent supernatant as a nutrient source to
the process. Fermentation nutrient addition (notably nitrogen) and aeration are two
significant factors leading to environmental burdens from microbial mixed culture–
based polyhydroxyalkanoates (Gerngross 1999), and the ability to reduce these
through smart process design has potential for reduced impacts.
While a number of studies exist for assessing environmental impacts of polyhydroxyalkanoates, only a handful of these are related to microbial mixed cultures and
integration with wastewater treatment. These studies have focused on similar process layouts consisting of three-stage fermentation and hypochlorite/chlorine-based
cell digestion for extraction (Gurieff and Lant 2007; Dacosta et al. 2015). Therefore,
there is a need for further studies in this area, particularly exploring different fermentation and extraction techniques due to the significantly lower biomass concentrations that may impact assessment results in comparison to pure culture systems.
5 Integration of Polyhydroxyalkanoates Production with Industrial Wastewater…
is associated with the feedstock. From an economic perspective, agricultural feedstocks may make up around 25% of the total production cost. In comparison, use of
industrial wastewater allows offset of treatment costs or trade waste tariffs, which
can result in 25% cost reductions (Dacosta et al. 2015, Gurieff and Lant 2007).
From an environmental perspective, most life cycle analysis studies show polyhydroxyalkanoates to be more environmentally friendly than petrochemical plastics
(Leong et al. 2016) or at least similar (Hottle et al. 2013). However, a few studies
have demonstrated that pure culture polyhydroxyalkanoates production from agricultural feedstock may be worse than petrochemical plastics, primarily due to the
impacts associated with crop production and sterilization (Gerngross 1999; Kim
and Dale 2005). Combined industrial wastewater treatment and polyhydroxyalkanoates production avoids issues with both crop production and sterilization.
However, while Dacosta et al. (Dacosta et al. 2015) showed that GHG emissions
were slightly lower than pure culture agricultural feedstock polyhydroxyalkanoates
or petrochemical PET, nonrenewable energy use was significantly higher than both
alternatives. High energy use was similarly reported by Gurieff and Lant (2007) and
Gerngross (1999). However, replacement of energy sources with renewables provides a means to significantly reduce these impacts (Kim and Dale 2005). Moreover,
microbial-based polyhydroxyalkanoates production has been shown to be significantly more environmentally friendly than plant-based polyhydroxyalkanoates production, mostly due to the high steam requirements in processing plant material
(Zhong et al. 2009).
Areas of improvement in the process could lead to significantly reduced environmental footprint of polyhydroxyalkanoates production. One area of potential focus
is the solvent extraction, which is a major contributor of overall impacts in an industrial wastewater treatment polyhydroxyalkanoates production facility (Dacosta
et al. 2015). The use of alternative solvents is one approach. For instance, a comparison of various implementations of dimethyl carbonate as solvent has shown
benefits across all assessed impact categories in comparison to a more traditional
1,2-dichloroethane solvent followed by methanol precipitation (Righi et al. 2017).
Koller and Braunegg (Martin and Gerhart 2018) also highlight the need for fully
integrated plant design and the benefits achieved when making use of harvested cell
debris for biogas production and the subsequent supernatant as a nutrient source to
the process. Fermentation nutrient addition (notably nitrogen) and aeration are two
significant factors leading to environmental burdens from microbial mixed culture–
based polyhydroxyalkanoates (Gerngross 1999), and the ability to reduce these
through smart process design has potential for reduced impacts.
While a number of studies exist for assessing environmental impacts of polyhydroxyalkanoates, only a handful of these are related to microbial mixed cultures and
integration with wastewater treatment. These studies have focused on similar process layouts consisting of three-stage fermentation and hypochlorite/chlorine-based
cell digestion for extraction (Gurieff and Lant 2007; Dacosta et al. 2015). Therefore,
there is a need for further studies in this area, particularly exploring different fermentation and extraction techniques due to the significantly lower biomass concentrations that may impact assessment results in comparison to pure culture systems.
5 Integration of Polyhydroxyalkanoates Production with Industrial Wastewater…