Plastic is one of the most widely used materials in the world and has become a necessity in everyday life. Over the last 60 years, plastic has provided economic, environmental, and societal benefits. The use of plastics has increased dramatically since the 1950s due to numerous advantages such as their versatility and resistance [1]; [2]. In 2015, the annual plastic production was nearly equal to the combined weight of the human population [3]. China is the world's largest producer of plastic, with over 370 million tons being produced in 2019, accounting for 31% of the global output. Additionally, approximately 62 million tons of plastic were produced in Europe [4]. As a result of the rapidly increasing production of disposable plastic products and their widespread use, plastic pollution has emerged as one of the most serious environmental issues [4]. It was expected that the amount of plastic flowing in the ocean would be 150 MMT by 2016, and the weight of plastics would exceed that of sea fish by 2050 [5].
The negative effects of plastics on humans and the environment are becoming universally recognizable.
The Group of Seven Summit acknowledged in 2015 that marine pollution is a global issue that affects both marine and coastal environments, as well as human health. In 2018, the Ocean Plastics Charter was implemented, with pledges being made for concrete efforts to be taken to eliminate plastics from the marine environment [6]. The Group of Twenty also agreed to the 2017 Marine Litter Action Plan [1]. As a result, many countries are taking action to address plastic pollution on a regional, national, and global level [7]. Bioplastics are environmental-friendly materials for replacing petroleum-derived plastic since they are biodegradable and/or produced from various renewable resources [8]. Biodegradable bioplastics could be well degraded by following the waste treatment pathway and could reduce the amount of plastic trash that ends up in our environment. In addition, bio-derived bioplastics could dramatically decrease carbon emissions associated with resource extraction [9]. Because raw materials absorb carbon dioxide throughout their growth, and to reduce the economy's reliance on fossil fuels [10], numerous bioplastics have been marketed over the last few decades, including polylactic acid [11], polyhydroxyalkanoates (PHAs) [12], polybutylene succinate [12], and thermoplastic starch [13], as well as bio-polyethylene terephthalate (bioPET) and bio-polyethylene (bioPET), which resemble non-renewable substances [14]. Although bioplastics have been studied for almost a century, their commercialization still does not show promising growth[6]. However, the global market for bioplastics is growing at the moment. According to the European Bioplastics Association's 2019 study, the global production of bioplastics was 2.11 million ton in 2018, accounting for 0.6 percent of the total plastic production [6], and is predicted to reach 289 million ton by 2025. However, the market cap for bioplastics is still limited as a result of their higher production costs and generally lower mechanical properties compared to those of conventional plastics [6]. However, based on the global trend of replacing oil-based plastics with bridgeable plastics to mitigate environmental issues, the market for bioplastics over petrochemical plastics is expected to rise significantly in the years ahead [15]. PHAs have the potential to become a promising bioplastic on a global scale. PHAs can be biologically synthesized by accumulating within the cells of the specific microorganisms. Additionally, PHAs exhibit similar properties to polymers derived from fossil fuels; however, they are more environmentally friendly because of their high biodegradability [16]. In recent years, PHAs have been highlighted for their various benefits including, but not limited to, their simple synthesization, UV resistance, and durability [17, 18]. Thus, PHA is a potential bioplastic that can be used for replacing petroleum-based polymers such as polyethylene (PE), polyethylene terephthalate (PET), and polypropylene (PP) [19]. Typically, the PHA production process is divided into three stages: acidification, PHA production, and downstream processing. The acidification process is the initial step in the production of PHA. Firstly, significant carbon sources are biologically converted to VFA in a fermentation process. Secondly, the mixed microbial cultures (MMC) produce and accumulate PHA in their cells following the acidification process by utilizing VFA generated from the first step; thus, the PHA-rich biomass is obtained. However, the accumulated PHA cannot be used inside the cell. The downstream process (DSP) is the final stage for extracting the produced PHA from the microbial cells. Following these three techniques, PHA can be synthesized as bioplastic pellets [20]. A method for producing PHA using various engineered microbial communities has been proposed as a potential technique for overcoming the high production cost and environmental impact. However, majority of research has been done on the production of PHAs using pure cultures or pure substrates such as acetate and glucose[16]. As a result, PHA has become a prohibitively expensive material with respect to the high production cost. Due to their natural origin, biodegradability, and functionality, PHAs have attracted extensive interest as a viable alternative to traditional plastics. But PHAs have high production costs, which are projected to be 20–80% more than those associated with petrochemical-based plastics [20]. Typically, the price of PHAs polymer is between 2.2 and 5.0 Euros per kilogram while traditional oil-based plastic price is always less than 1 Euro per kilogram. Thus, the price of PHA is approximately three times higher, which could potentially hinder the utilization of this bioplastic [17, 18]. The objective of this research is to perform the technoeconomic analysis of the PHA production to form high-strength waste (i.e., molasses) using MMC as the microbial sources.
