Valorization of Lignocellulose by Producing Polyhydroxyalkanoates under Circular Bioeconomy Premises: Facts and Challenges

Abstract

In light of the current concerns about environmental issues caused by the excessive use of fossil resources, more emphasis has been paid to the transition to a sustainable and circular economy. Bioplastics as eco-friendly products originating from biomass wastes have gained much attention to solve the problem of plastic pollution. Among them, polyhydroxyalkanoates (PHAs) are microbial polyesters produced using various feedstocks�renewable or recycled waste materials�contributing to a more sustainable commercial plastic life cycle by being a part of a circular bioeconomy. However, the scale-up of the PHA process cost effectively and sustainably remains challenging for large-scale industrial applications. This perspective provides a comprehensive overview of the current insights into lignocellulosic biomass's role in achieving a circular bioeconomy. Emerging greener biomass conversion technologies are discussed to characterize energy demand, cost, and sustainability within biorefinery PHA production. In addition, recent advances in synthetic biology and fermentation processes for PHA production are discussed. Technological challenges, i.e., bioreactor setup, downstream operation, and inconsistent properties to improve the sustainable production of PHAs and to help transfer this technology to real-world applications, are also addressed.

Integrated Biorefinery Design with Techno‐Economic and Life Cycle Assessment Tools in Polyhydroxyalkanoates Processing

“…Lignocellulosic biomass represents the nonedible, abundant, carbon-neutral, and inexpensive raw material, [136] thus it has inspired various studies, aiming for the efficient utilization of it for PHAs production. [37,43,137,138] Lignocellulosic biorefinery processes biomass for PHAs production and is a highly promising and sustainable platform, however lignocellulosic biorefinery still faces some challenges such as costly biomass conversion process and low volume of PHAs production. [139] Advances in biorefinery technologies have greatly contributed to the development of a new manufacturing concept for converting sustainable biomass into multiple products such as PHAs, biofuels, amino acids, proteins, and other fine chemicals, generally referred to as integrated lignocellulosic biorefinery.…”

“…PHAs' bioplastics are perfectly fit in this model since they are contributing to a more sustainable commercial life cycle by being part of a circular economy. [ 37 ] The progress of the lignocellulose‐based PHAs production toward the circular economy is illustrated in Figure . The design of integrated processes for PHAs production within biorefinery is the paving pathway toward a sustainable circular economy.…”

“…[35,36] The utilization of cellulose, hemicellulose, and lignin feedstock for the production of other value-added chemicals along with PHAs is very important for the implementation of the circular economy approach in PHAs production. [37] In this context, conventional pretreatments are not suitable to advance biorefineries for economic and environmental sustainability reasons. Additionally, the limited raw materials and technologies are the major disadvantages of the conventional biorefinery processes that restrict to use of a single feedstock, thus minimizing the opportunity to produce multiple products.…”

“…[23,37,43,[45][46][47][48] The current paradigm for the biological valorization of lignocellulose to PHAs has involved four operational units: i) biomass pretreatment, ii) saccharification, iii) fermentation, and iv) downstream processing to recover and purify PHAs polyesters from microbial biomass. [37] These processes are segmented into different combinations, over time efforts have focused on the design of integrated strategies to reduce the overall process costs and improve sustainability in lignocellulose-based PHAs production. Currently, most of the pilot-scale and industrial-scale processes are proceeding through separate saccharification and bioconversions.…”

“…[ 28 ] Metabolic engineering and synthetic biology can be defined as the use of genetic engineering to modify the metabolism and redesign of microorganisms to achieve specified objectives. [ 37 ] These objectives include improving the yield of desired products (PHAs), and the co‐production of bio‐based fine chemicals along with PHAs that wild strains could not produce due to a lack of metabolic capability to synthesize multiple products. Metabolic engineering and synthetic biology can be performed to allow the microorganisms to utilize seasonal variable biomass feedstocks.…”