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Abstract Plastics have been a revolutionary material in every aspect of human life
since their development, but have also led to one of the leading environmental issues
with regard to their disposal. These petrochemical-derived plastics take up to
2000 years to break down in the environment and accumulate within living organisms. A potential alternative is to replace petroleum-based plastics by biodegradable
ones. Polyhydroxyalkanoates are one of the most promising types of biodegradable
polymers with properties similar to polypropylene and are readily produced by
more than 90 known species of bacteria as intracellular polyester stores. The most
widely employed production technique for polyhdroxyalkanoates is by singleorganism fermentation processes under a feast-famine regime. However, the high
cost of sterilization and substrates typically employed for industrial production
means commercial production is limited for niche polymer applications. Industrial
wastewater provides an alternative low-cost carbon feedstock that can provide benefits of combined organic treatment and polyhydroxyalkanoates production. Such
combination precludes single-organism systems, meaning microbial mixed cultures
must be used.
This chapter explores the limitations and factors essential for successful microbial mixed culture cultivation and polyhydroxyalkanoates production coupled with
industrial wastewater treatment. The specific target operating conditions will differ
depending on the specific wastewater substrate and target microorganisms for
enrichment. A high degree of cellular storage is important for high productivity and
economic processing and can be induced through various redox conditions, specific
feeding regimes, use of nutrient limitation, specific pH control, and, in the case of
photosynthetic cultures, light intensity, all of which influence the specific microorganisms enriched. The specific enriched microorganisms in conjunction with the
substrate are the primary factors defining the monomer compositions of the polyhydroxyalkanoates, which infers its mechanical properties and potential application.
Use of microbial mixed cultures compared with single-organism cultures makes
control of polyhydroxyalkanoates composition more challenging, but provides
greater resilience to wastewater composition and flow fluctuations due to community redundancy and microbial succession. The most significant drawback, however, of microbial mixed culture use with industrial wastewater treatment is the
downstream processing of more dilute cell concentrations than single-organism
processes. Further research into both cell concentrating and polyhydroxyalkanoates
extraction techniques will help improve economics and sustainability of the process. Nevertheless, initial theoretical assessments show that development of commercial polyhydroxyalkanoates production from industrial wastewater using
microbial mixed cultures should be cost competitive and more sustainable than
either petrochemical plastics or polyhydroxyalkanoates produced by singleorganism fermentation.
Keywords Biopolymers · Intracellular storage · Circular economy · Resource
recovery · Mixed microbial culture · Bioplastic · Feast-famine ·
Polyhydroxybutyrate (PHB) · Substrate · Redox
S. Sali and H. R. Mackey
Abstract Plastics have been a revolutionary material in every aspect of human life
since their development, but have also led to one of the leading environmental issues
with regard to their disposal. These petrochemical-derived plastics take up to
2000 years to break down in the environment and accumulate within living organisms. A potential alternative is to replace petroleum-based plastics by biodegradable
ones. Polyhydroxyalkanoates are one of the most promising types of biodegradable
polymers with properties similar to polypropylene and are readily produced by
more than 90 known species of bacteria as intracellular polyester stores. The most
widely employed production technique for polyhdroxyalkanoates is by singleorganism fermentation processes under a feast-famine regime. However, the high
cost of sterilization and substrates typically employed for industrial production
means commercial production is limited for niche polymer applications. Industrial
wastewater provides an alternative low-cost carbon feedstock that can provide benefits of combined organic treatment and polyhydroxyalkanoates production. Such
combination precludes single-organism systems, meaning microbial mixed cultures
must be used.
This chapter explores the limitations and factors essential for successful microbial mixed culture cultivation and polyhydroxyalkanoates production coupled with
industrial wastewater treatment. The specific target operating conditions will differ
depending on the specific wastewater substrate and target microorganisms for
enrichment. A high degree of cellular storage is important for high productivity and
economic processing and can be induced through various redox conditions, specific
feeding regimes, use of nutrient limitation, specific pH control, and, in the case of
photosynthetic cultures, light intensity, all of which influence the specific microorganisms enriched. The specific enriched microorganisms in conjunction with the
substrate are the primary factors defining the monomer compositions of the polyhydroxyalkanoates, which infers its mechanical properties and potential application.
Use of microbial mixed cultures compared with single-organism cultures makes
control of polyhydroxyalkanoates composition more challenging, but provides
greater resilience to wastewater composition and flow fluctuations due to community redundancy and microbial succession. The most significant drawback, however, of microbial mixed culture use with industrial wastewater treatment is the
downstream processing of more dilute cell concentrations than single-organism
processes. Further research into both cell concentrating and polyhydroxyalkanoates
extraction techniques will help improve economics and sustainability of the process. Nevertheless, initial theoretical assessments show that development of commercial polyhydroxyalkanoates production from industrial wastewater using
microbial mixed cultures should be cost competitive and more sustainable than
either petrochemical plastics or polyhydroxyalkanoates produced by singleorganism fermentation.
Keywords Biopolymers · Intracellular storage · Circular economy · Resource
recovery · Mixed microbial culture · Bioplastic · Feast-famine ·
Polyhydroxybutyrate (PHB) · Substrate · Redox
S. Sali and H. R. Mackey