Can Polyhydroxyalkanoates Be Produced Efficiently From Waste Plant and Animal Oils?

Abstract

Polyhydroxyalkanoates (PHAs) are a potential replacement for some petrochemical-based plastics. PHAs are polyesters synthesized and stored by various bacteria and archaea in their cytoplasm as water-insoluble inclusions. PHAs are usually produced when the microbes are cultured with nutrient-limiting concentrations of nitrogen, phosphorus, sulfur, or oxygen and excess carbon sources. Such fermentation conditions have been optimized by industry to reduce the cost of PHAs produced commercially. Industrially, these biodegradable polyesters are derived from microbial fermentation processes utilizing various carbon sources. One of the major constraints in scaling-up PHA production is the cost of the carbon source metabolized by the microorganisms. Hence, cheap and renewable carbon substrates are currently being investigated around the globe. Plant and animal oils have been demonstrated to be excellent carbon sources for high yield production of PHAs. Waste streams from oil mills or the used oils, which are even cheaper, are also used. This approach not only reduces the production cost for PHAs, but also makes a significant contribution toward the reduction of environmental pollution caused by the used oil. Advancements in the genetic and metabolic engineering of bacterial strains have enabled a more efficient utilization of various carbon sources, in achieving high PHA yields with specified monomer compositions. This review discusses recent developments in the biosynthesis and classification of various forms of PHAs produced using crude and waste oils from the oil palm and fish industries. The biodegradability of the PHAs produced from these oils will also be discussed.

Microbial Production of Biodegradable Lactate-Based Polymers and Oligomeric Building Blocks From Renewable and Waste Resources

“…Polyhydroxybutyrate (PHB) was the first to be discovered and is the most studied PHA member ( Anjum et al, 2016 ). More than 150 hydroxyalkanoic acid monomer structures have been reported in PHAs ( Raza et al, 2018 ; Sagong et al, 2018 ; Surendran et al, 2020 ). The diversity of monomeric structures gives flexible properties of PHAs such as brittleness, elasticity, and stickiness ( Raza et al, 2018 ).…”

Biosynthesis of Random-Homo Block Copolymer Poly[Glycolate-ran-3-Hydroxybutyrate (3HB)]-b-Poly(3HB) Using Sequence-Regulating Chimeric Polyhydroxyalkanoate Synthase in Escherichia coli

“…Polyhydroxyalkanoates (PHAs) are bacterial storage polyesters, which are currently used as a biobased replacement for some petroleum-derived plastics ( Surendran et al, 2020 ; Zheng et al, 2020 ). PHAs have attracted considerable interest in recent years for their potential as a biodegradable material ( Morohoshi et al, 2018 , 2020 ), since the polymers degrade well in the environment by the action of PHA depolymerases ( Juengert et al, 2018 ).…”

Integrated and Consolidated Review of Plastic Waste Management and Bio-Based Biodegradable Plastics: Challenges and Opportunities

“…Israni and Shivakumar [94] report that the production costs for PHAs are 5 to 10 times higher than those of petroleum-based plastics, thus hampering their large scale production. Israni and Shivakumar [94] attributed 50% of the cost to the feedstock, thus highlighting the need for alternative feedstocks [95]. Ivanov et al [90] attributed the high costs currently associated with PHA production to the use of pure cultures (aseptic cultures) where sterile conditions are required, expensive carbon sources, and the use of organic solvents [90].…”

“…The density of P3HB ranges from 1.18 to 1.26 g/cm 3 , and its melting point varies from as low as 40 • C [96] to 180 • C, while thermal degradation temperature is 185 • C; therefore, it cannot be used in high temperature applications. Although its mechanical properties are almost equivalent to polypropylene (PP) [98], P3HB is stiff and is less ductile, with its elongation to break at 5% compared to PP, which is approximately 400% [91,95]. However, the flexibility and impact strength of this polymer can be improved by increasing valeric acid content during production to form a copolymer of hydroxybutyrate and hydoxyvalerate [91,99].…”