The strong environmental impact caused by plastic pollution has led research to address studies from different perspectives. The mathematical modeling of the biodegradation kinetics of solid materials is a major challenge since there are many influential variables in the process and there is interdependence of microorganisms with internal and external factors. In addition, as solid substrates that are highly hydrophobic, mass transfer limitations condition degradation rates. Some mathematical models have been postulated in order to understand the biodegradation of plastics in natural environments such as oceans. However, if tangible and optimizable solutions are to be found, it is necessary to study the biodegradation process under controlled conditions, such as using bioreactors and composting systems. This review summarizes the biochemical fundamentals of the main plastics (both petrochemical and biological origins) involved in biodegradation processes and combines them with the main mathematical equations and models proposed to date. The different biodegradation studies of plastics under controlled conditions are addressed, analyzing the influencing factors, assumptions, model developments, and correlations with laboratory-scale results. It is hoped that this review will provide a comprehensive overview of the process and will serve as a reference for future studies, combining practical experimental work and bioprocess modeling systems.

Polyhydroxyalkanoates (PHA) are bacterial polyesters that have been described as one of the most promising sustainable alternatives to petroleum-based plastics. A major challenge for PHA to become market-competitive, is to decrease the associated production costs. According to several studies, about 20-50% of the total production costs is attributed to the raw materials and therefore, the use of different types of organic residues have been evaluated as substrates for the microorganisms. In this study, the strain Bacillus cereus ATCC 14579 was cultivated in shake flasks using a defined medium and pretreated grape peel as sole carbon source. The pretreatment of the grape peels was performed by a hydrolysis step with diluted sulfuric acid yielding up to 52.9% (w/w) of total sugars from the dry residue. PHB extraction using dry and wet biomass was performed and evaluated showing up to 3.7-higher yields when using the latter. PHB accumulation of 18.79% (w/w), corresponding to 0.53 g PHB /L, was achieved using the grape peel hydrolyzate at 72 h of cultivation. Eventually, the possibility of producing PHB by the use of non-treated lignocellulosic biomass (LCB) with high contents of fermentable sugars is presented as an interesting alternative to be optimized and projected for sustainable bioplastic production processes.

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