Biodegradation of bioplastics in natural environments

Digital PCR as an Emerging Tool for Monitoring of Microbial Biodegradation

Biodegradation of contaminants is extremely complicated due to unpredictable microbial behaviors. Monitoring of microbial biodegradation drives us to determine (1) the amounts of specific degrading microbes, (2) the abundance, and (3) expression level of relevant functional genes. To this endeavor, the cultivation independent polymerase chain reaction (PCR)-based monitoring technique develops from endpoint PCR, real-time quantitative PCR, and then into novel digital PCR. In this review, we introduce these three categories of PCR techniques and summarize the timely applications of digital PCR and its superiorities than qPCR for biodegradation monitoring. Digital PCR technique, emerging as the most accurately absolute quantification method, can serve as the most promising and robust tool for monitoring of microbial biodegradation.

Recycling strategies for polyhydroxyalkanoate-based waste materials: An overview

The plastics market is dominated by fossil-based polymers, but their gradual replacement by bioplastics (e.g., polyhydroxyalkanoates) is occurring. However, recycling strategies need to be developed to truly unveil the impact of bioplastics on waste accumulation. This review provides a state of the art of recycling strategies investigated for polyhydroxyalkanoate-based polymers and proposes future research avenues. Research on mechanical and chemical recycling is dominated by the use of extrusion and pyrolysis, respectively, while that on biodegradation of polyhydroxyalkanoates is related to soil and aquatic samples, and to anaerobic digestion towards biogas production. Research gaps exist in the relationships between polymer composition and ease of use of all recycling strategies investigated. This is of utmost importance since it will influence the need for separation at the source. Therefore, research emphasis needs to be given to the area to follow the continuous improvement of the process economics towards widespread commercial production of polyhydroxyalkanoates.

Fungal community dynamics during degradation of poly(butylene succinate-co-adipate) film in two cultivated soils in Japan

Fungi play an important role in the degradation of biodegradable plastics (BPs) in soil. However, little is known about their dynamics in the soil during the degradation of BPs. We studied the community dynamics of BP-degrading fungi during poly(butylene succinate-co-adipate) (PBSA) film degradation in two different types of soils using culture-dependent and culture-independent methods. The Fluvisol and the Andosol soils degrade embedded PBSA films at high and low speeds, respectively. The number of PBSA emulsion-degrading fungi that increased in the Fluvisol soil was higher than that in the Andosol soil after embedding with PBSA films. We succeeded in detecting internal transcribed spacer 1 (ITS1) regions those matched that of the fungi by polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) in both soils. Our results suggest that fungal community analyses using PCR-DGGE in combination with BP degraders isolation techniques enables the monitoring of BP films-degrading fungi.

Challenges with Verifying Microbial Degradation of Polyethylene

Polyethylene (PE) is the most abundant synthetic, petroleum-based plastic materials produced globally, and one of the most resistant to biodegradation, resulting in massive accumulation in the environment. Although the microbial degradation of polyethylene has been reported, complete biodegradation of polyethylene has not been achieved, and rapid degradation of polyethylene under ambient conditions in the environment is still not feasible. Experiments reported in the literature suffer from a number of limitations, and conclusive evidence for the complete biodegradation of polyethylene by microorganisms has been elusive. These limitations include the lack of a working definition for the biodegradation of polyethylene that can lead to testable hypotheses, a non-uniform description of experimental conditions used, and variations in the type(s) of polyethylene used, leading to a profound limitation in our understanding of the processes and mechanisms involved in the microbial degradation of polyethylene. The objective of this review is to outline the challenges in polyethylene degradation experiments and clarify the parameters required to achieve polyethylene biodegradation. This review emphasizes the necessity of developing a biochemically-based definition for the biodegradation of polyethylene (and other synthetic plastics) to simplify the comparison of results of experiments focused for the microbial degradation of polyethylene.

Looking beyond the banning of lightweight bags: analysing the role of plastic (and fuel) impacts in waste collection at a Portuguese city

The purpose of this work is to assess the environmental impacts of the collection of mixed municipal solid waste (MSW) in a selected neighbourhood of the Portuguese city of Aveiro. To this purpose, the main elements necessary for the collection process (carrier bags, dustbins, street containers and vehicles) were analysed applying the life cycle assessment methodology, making use of locally gathered data. The main impacts associated with this activity are mostly related to the use of polyethylene plastic bags to carry the waste from the household to the waste container, and to the fuel consumption of collection vehicle that picks MSW from street containers and transports it to the treatment facility. The impacts associated with the plastic bags were primarily due to their disposal in a sanitary landfill after use and secondarily to the consumption of fossil raw materials required for their production. Given the relative high impact of the plastic bags, alternative scenarios were tested: using bags entirely produced with recycled polyethylene and bags produced with bio-based plastics derived from starch (TPS) and from wastewater (PHA). PHA bio-based bags were found to perform slightly better than conventional high-density polyethylene (HDPE) bags, but HDPE bags with 100% recycled content remained as the environmentally best option. A sensitivity analysis was performed to check the influence of bag size. Regarding the fuel consumption by collection vehicles, a comparison was performed to check how site-specific conditions can influence the impact of this activity, resulting in remarkably higher consumptions when local data were used instead of reference databases.

Comparison of two mechanical pre-treatment systems for impurities reduction of source-separated biowaste

The treatment of source-separated biowaste is still a challenge due to its high proportion of impurities. Biowaste bins are intended exclusively for the collection of biodegradable matter, such as food, kitchen and garden waste. However, plastics, metals, glass and textiles are also found in biowaste bins. If not properly removed, these impurities cause problems to the treatment facility and depreciate the quality of the final product, when the biowaste is converted to compost. There is ongoing discussion whether the existing treatment systems are able to remove impurities, especially plastics, from biowaste thoroughly enough to ensure that the produced compost complies with state regulations. In this work, two wet mechanical pre-treatment systems were tested for their efficiency to remove impurities. The first system consisted of a screw mill, a star screen, and a food unpacking machine (process I). The second system consisted of a shredder, followed by a piston press with 12 mm pore size (process II). Both processes produced a dry output, which contained the concentrated impurities, and a wet output, which could be used as substrate for anaerobic digestion. Results showed that, although 99% of the incoming plastics were efficiently removed in process I, the impurities concentration was still too high to meet the legal standards of plastics concentration in the final product, according to the German Federal Compost Quality Association (Bundesgütegemeinschaft Kompost e.V.). The removal efficiency of glass particles was low for both processes: at least 80% of the incoming particles were transferred to the wet output.

Bacillus pumilus B12 Degrades Polylactic Acid and Degradation Is Affected by Changing Nutrient Conditions

Poly-lactic acid (PLA) is increasingly used as a biodegradable alternative to traditional petroleum-based plastics. In this study, we identify a novel agricultural soil isolate of Bacillus pumilus (B12) that is capable of degrading high molecular weight PLA films. This degradation can be detected on a short timescale, with significant degradation detected within 48-h by the release of L-lactate monomers, allowing for a rapid identification ideal for experimental variation. The validity of using L-lactate as a proxy for degradation of PLA films is corroborated by loss of rigidity and appearance of fractures in PLA films, as measured by atomic force microscopy and scanning electron microscopy (SEM), respectively. Furthermore, we have observed a dose-dependent decrease in PLA degradation in response to an amino acid/nucleotide supplement mix that is driven mainly by the nucleotide base adenine. In addition, amendments of the media with specific carbon sources increase the rate of PLA degradation, while phosphate and potassium additions decrease the rate of PLA degradation by B. pumilus B12. These results suggest B. pumilus B12 is adapting its enzymatic expression based on environmental conditions and that these conditions can be used to study the regulation of this process. Together, this work lays a foundation for studying the bacterial degradation of biodegradable plastics.

The Degradative Capabilities of New Amycolatopsis Isolates on Polylactic Acid

Polylactic acid (PLA), a bioplastic synthesized from lactic acid, has a broad range of applications owing to its excellent proprieties such as a high melting point, good mechanical strength, transparency, and ease of fabrication. However, the safe disposal of PLA is an emerging environmental problem: it resists microbial attack in environmental conditions, and the frequency of PLA-degrading microorganisms in soil is very low. To date, a limited number of PLA-degrading bacteria have been isolated, and most are actinomycetes. In this work, a method for the selection of rare actinomycetes with extracellular proteolytic activity was established, and the technique was used to isolate four mesophilic actinomycetes with the ability to degrade emulsified PLA in agar plates. All four strains—designated SO1.1, SO1.2, SNC, and SST—belong to the genus Amycolatopsis. The PLA-degrading capability of the four strains was investigated by testing their ability to assimilate lactic acid, fragment PLA polymers, and deteriorate PLA films. The strain SNC was the best PLA degrader—it was able to assimilate lactic acid, constitutively cleave PLA, and form a thick and widespread biofilm on PLA film. The activity of this strain extensively eroded the polymer, leading to a weight loss of 36% in one month in mesophilic conditions.

Analysis of the Possibility of Environmental Pollution by Composted Biodegradable and Oxo-Biodegradable Plastics

Composting the municipal organic fraction of waste results in a valuable product in the form of compost, which could be used instead of other forms of fertilisation. The organic waste stream may contain oxo-biodegradable and biodegradable plastics used for waste collection. Their components and decomposition residues may contaminate the compost chemically and physically. In this paper, the results of studies on the content of selected macro- and microelements in new and composted plastics have been analysed. Statistical analyses were carried out in order to determine the most characteristic components of plastics and to determine the character of chemical composition changes. The analysis of the test results showed that multidirectional changes in the content of macro- and microelements occur during composting, and they may be the source of contamination of the fertiliser produced. Contaminants in the form of microplastics may also be released into the environment, which may pose a threat to many elements of the environment, including animals and humans.

Disintegration behaviour of bio-based plastics in coastal zone marine environments: A field experiment under natural conditions

The accumulation of plastic wastes in the marine environment represents a steadily increasing global environmental threat. The replacement of conventional plastics with bio-based biodegradable materials may contribute to alleviating the problem in the long run. This work studies the disintegration behaviour of three bio-based plastic materials, namely Polyhydroxybutyrate (PHB), Polybutylene sebacate (PBSe), Polybutylene sebacate-co-terephthalate (PBSeT), in three different coastal zone marine environments under natural conditions. The three studied environments were: 1) the seashore zone which is periodically covered by the seawater due to waves or tide, called eulittoral or intertidal zone; 2) the water column zone of small depth (about 10 m), called pelagic zone; and 3) the interface zone between the water column and the seabed sediment at small depth (about 20 m), called sublittoral or benthic zone. The experiments took place in the Aegean Sea at the SW coast of Salamis Island. The results showed that disintegration, as an indicative measure of biodegradation, occurs in all three tested environments, even though the rate depends on the material, the habitat, and the prevailing during the testing period environmental conditions. The degrees of disintegration of all materials in the three environments exhibited significant differences: Benthic > Intertidal > Pelagic. The observed disintegration can be attributed to biodegradation since the negative reference Low-density Polyethylene (LLDPE) material did not disintegrate.

Bacterial Candidates for Colonization and Degradation of Marine Plastic Debris

With the rising plastic pollution in the oceans, research on the plastisphere-the microorganisms interacting with marine plastic debris-has emerged. Microbial communities colonizing plastic have been characterized from several ocean regions and they are distinct from the communities of the surrounding waters, and a few plastic-degrading microorganisms have been isolated from other environments. Therefore, we propose that marine microorganisms have adapted to plastic as a surface for colonization and potentially degradation. When comparing the taxonomic patterns of plastic-associated, marine bacteria, recurring groups and families such as the families Erythrobacteraceae and Rhodobacteraceae (Alphaproteobacteria), Flavobacteriaceae (Bacteriodetes), and the phylum of cyanobacteria (such as the Phormidium genus) can be identified. Thereby, we provide a perspective on which bacterial candidates could play a role in the colonization and possible degradation of plastic in the oceans due to their occurrence on marine plastic debris. We emphasize the need for extended and reproducible collection of data to assess the existence of a core microbiome or core functionalities of the plastisphere and confirm the capability of these bacterial candidates for biodegradation of plastic. Furthermore, we suggest the next steps in research to elucidate the level of natural bioremediation and the exploitation of bacterial degradative mechanisms of plastic.

Effects of Microplastics in Soil Ecosystems: Above and Below Ground

Environmental contamination by microplastics is now considered an emerging threat to biodiversity and ecosystem functioning. Soil ecosystems, particularly agricultural land, have been recognized as a major sink of microplastics, but the impacts of microplastics on soil ecosystems (e.g., above and below ground) remain largely unknown. In this study, different types of microplastics [biodegradable polylactic acid (PLA)], conventional high-density polyethylene (HDPE), and microplastic clothing fibers were added to soil containing the endogeic Aporrectodea rosea (rosy-tipped earthworm) and planted with Lolium perenne (perennial ryegrass) to assess the biophysical soil response in a mesocosm experiment. When exposed to fibers or PLA microplastics, fewer seeds germinated. There was also a reduction in shoot height with PLA. The biomass of A. rosea exposed to HDPE was significantly reduced compared to control samples. Furthermore, with HDPE present there was a decrease in soil pH. The size distribution of water-stable soil aggregates was altered when microplastics were present, suggesting potential alterations of soil stability. This study provides evidence that microplastics manufactured of HDPE and PLA, and synthetic fibers can affect the development of L. perenne, health of A. rosea and basic, but crucial soil properties, with potential further impacts on soil ecosystem functioning.

Methodologies to assess biodegradation of bioplastics during aerobic composting and anaerobic digestion: A review

Bioplastics are emerging on the market as sustainable materials which rise to the challenge to improve the lifecycle of plastics from the perspective of the circular economy. The article aims at providing a critical insight of research studies carried out in the last 20 years on the degradation of bioplastics under aerobic composting and anaerobic digestion conditions. It mainly focuses on the various and different methodologies which have been proposed and developed to monitor the process of biodegradation of several bioplastic materials: CO₂ and CH₄ measurements, mass loss and disintegration degree, spectroscopy, visual analysis and scanning electron microscopy. Moreover, across the wide range of studies, the process conditions of the experimental setup, such as temperature, test duration and waste composition, often vary from author to author and in accordance with the international standard followed for the test. The different approaches, in terms of process conditions and monitoring methodologies, are pointed out in the review and highlighted to find significant correlations between the results obtained and the experimental procedures. These observed correlations allow critical considerations to be reached about the efficiency of the methodologies and the influence of the main abiotic factors on the process of biodegradation of bioplastics.

Photo-Oxidative and Soil Burial Degradation of Irrigation Tubes Based on Biodegradable Polymer Blends

Irrigation tubes based on biodegradable polymers were prepared via an extrusion-drawing process by Irritec and compared to conventional pipes made of high-density polyethylene (HDPE). A commercial polylactide/poly (butyleneadipate-co-butyleneterephthalate) (PLA/PBAT) blend (Bio-Flex^®) and Mater-Bi^® were used. The polymers were characterized from rheological and mechanical points of view. Irrigation pipes were subjected to photoaging with continued exposure to UV radiation up to 22 days. The degradability in the soil of irrigation tube samples was studied. The influence of temperature and UV irradiation on soil burial degradation was investigated. A soil burial degradation test was carried out at 30 °C and 50 °C for up to 70 days. The degree of degradation was evaluated from the weight loss percentage. The degradation rate of irrigation tube samples based on Mater-Bi^® was higher at 30 °C and was stimulated after 14 days of UV irradiation. Higher temperatures or UV aging encouraged the disintegration in soil of Bio-Flex^®-based irrigation tubes. Furthermore, tube samples, before and after UV and soil burial degradation, were analyzed by Attenuated Total Reflection-Fourier Transform Infra-Red (ATR-FTIR) spectroscopy.

Microbial degradation of four biodegradable polymers in soil and compost demonstrating polycaprolactone as an ideal compostable plastic

Plastics are an indispensable material but also a major environmental pollutant. In contrast, biodegradable polymers have the potential to be compostable. The biodegradation of four polymers as discs, polycaprolactone (PCL), polyhydroxybutyrate (PHB), polylactic acid (PLA) and poly(1,4 butylene) succinate (PBS) was compared in soil and compost over a period of more than 10 months at 25 °C, 37 °C and 50 °C. Degradation rates varied between the polymers and incubation temperatures but PCL showed the fastest degradation rate under all conditions and was completely degraded when buried in compost and incubated at 50 °C after 91 days. Furthermore, PCL strips showed a significant reduction in tensile strength in just 2 weeks when incubated in compost >45 °C. Various fungal strains growing on the polymer surfaces were identified by sequence analysis. Aspergillus fumigatus was most commonly found at 25 °C and 37 °C, while Thermomyces lanuginosus, which was abundant at 50 °C, was associated with PCL degradation.

Constructing Slow-Release Fungicide Formulations Based on Poly(3-hydroxybutyrate) and Natural Materials as a Degradable Matrix

Slow-release fungicide formulations (azoxystrobin, epoxiconazole, and tebuconazole) shaped as pellets and granules in a matrix of biodegradable poly(3-hydroxybutyrate) and natural fillers (clay, wood flour, and peat) were constructed. Infrared spectroscopy showed no formation of chemical bonds between components in the experimental formulations. The formulations of pesticides had antifungal activity against Fusarium verticillioides in vitro. A study of biodegradation of the experimental fungicide formulations in the soil showed that the degradation process was mainly influenced by the type of formulation without significant influence of the type of filler. More active destruction of the granules led to a more rapid accumulation of fungicides in the soil. The content of fungicides present in the soil as a result of degradation of the formulations and fungicide release was determined by their solubility. Thus, all formulations are able to function in the soil for a long time, ensuring gradual and sustained delivery of fungicides.

Biodegradation of oil-based plastics in the environment: Existing knowledge and needs of research and innovation

The production of synthetic oil-based plastics has led to the accumulation of huge amounts of the plastic waste in the environment, especially in the marine system, very often the final sink for many types of conventional wasted plastics. In particular, (micro)plastics account for the majority of litter items in the marine environment and a high percentage of such litter is originating from land sources. Attempts to mitigate the harmful effects of conventional plastics such as the development of novel management strategies together with the gradual substitution of them with biodegradable (bio)plastics are representing future solutions. However, high amounts of conventional plastics have been accumulating in the environment since several years. Although many studies reported on their potential biodegradation by microbes in and from terrestrial environments, very little is known about the biodegradability of these plastics in freshwater systems and only recently more reports on their biodegradation by marine microorganisms/in marine environment were made available. In this review, we first provide a summary of the approaches applied for monitoring and assessing conventional plastics biodegradation under defined conditions. Then, we reviewed historical and recent findings related to biodegradation of four major plastics produced in European Union (EU), i.e. Polyethylene, Polyvinyl Chloride, Polypropylene and Polystyrene, in terrestrial and aquatic environments and by pure and mixed microbial cultures obtained from them.

Engineering biosynthesis of polyhydroxyalkanoates (PHA) for diversity and cost reduction

PHA, a family of natural biopolymers aiming to replace non-degradable plastics for short-term usages, has been developed to include various structures such as short-chain-length (scl) and medium-chain-length (mcl) monomers as well as their copolymers. However, PHA market has been grown slowly since 1980s due to limited variety with good mechanical properties and the high production cost. Here, we review most updated strategies or approaches including metabolic engineering, synthetic biology and morphology engineering on expanding PHA diversity, reducing production cost and enhancing PHA production. The extremophilic Halomonas spp. are taken as examples to show the feasibility and challenges to develop next generation industrial biotechnology (NGIB) for producing PHA more competitively.

Solutions and Integrated Strategies for the Control and Mitigation of Plastic and Microplastic Pollution

Plastic pollution is generated by the unsustainable use and disposal of plastic products in modern society, threatening economies, ecosystems, and human health. Current clean-up strategies have attempted to mitigate the negative effects of plastic pollution but are unable to compete with increasing quantities of plastic entering the environment. Thus, reducing inputs of plastic to the environment must be prioritized through a global multidisciplinary approach. Mismanaged waste is a major land-based source of plastic pollution that can be reduced through improvements in the life-cycle of plastics, especially in production, consumption, and disposal, through an Integrated Waste Management System. In this review paper, we discuss current practices to improve life cycle and waste management of plastics that can be implemented to reduce health and environmental impacts of plastics and reduce plastics pollution. Ten recommendations for stakeholders to reduce plastic pollution include (1) regulation of production and consumption; (2) eco-design; (3) increasing the demand for recycled plastics; (4) reducing the use of plastics; (5) use of renewable energy for recycling; (6) extended producer responsibility over waste; (7) improvements in waste collection systems; (8) prioritization of recycling; (9) use of bio-based and biodegradable plastics; and (10) improvement in recyclability of e-waste.

Degradation of brominated polymeric flame retardants and effects of generated decomposition products

Brominated flame retardants are often associated with adverse environmental effects. Nevertheless, these chemicals are required in order to comply with fire safety standards. Therefore, a better environmental profile is desirable. A "new" class of flame retardants is claimed to fulfil this request while still being feasible for established industrial processes. Different to previous brominated flame retardants, this new group is based on a polymeric structure that could indeed lead to a better environmental profile. However, not much is known about the long-term behaviour of such flame retardants. This short review summarizes what has already been published. With an annual production volume of 26,000 metric tons, "Polymeric FR" is currently the only industrially produced representative of this group. It has been shown to degrade under specific circumstances (following UV and heat exposure). Detected degradation products cause almost no acute toxicity, whereas chronic toxicity might be relevant. Nevertheless, as long as polymeric flame retardants are only used in building insulation, the actual risk seems to be rather limited.

Corn and Rice Starch-Based Bio-Plastics as Alternative Packaging Materials

Due to the negative environmental impacts of synthetic plastics, the development of biodegradable plastics for both industrial and commercial applications is essential today. Researchers have developed various starch-based composites for different applications. The present work investigates the corn and rice starch-based bioplastics for packaging applications. Various samples of bioplastics are produced, with different compositions of corn and rice starch, glycerol, citric acid, and gelatin. The tensile properties were improved after adding rice starch. However, water absorption and water solubility were reduced. On the basis of these results, the best sample was analyzed for thickness testing, biodegradability properties, SEM, hydrophilicity, thermogravimetric analysis, and sealing properties of bioplastic. The results show the suitability of rice and corn-based thermoplastic starch for packaging applications.

Commercial plastics claiming biodegradable status: Is this also accurate for marine environments?

Concerns about plastic pollution and global public policies have encouraged consumers to acquire environmentally friendly products. Thus, products made of biodegradable plastics have been preferred by the public, despite their costs. However, greenwashing practices, promising more environmental benefits than the products actually offer, has become frequent. Nevertheless, no studies assessing the occurrence of greenwashing in commercial plastic products sold in large world economies have been performed. The present study aimed to experimentally evaluate alterations in structure and chemical composition of selected plastic products marketed in Canada, USA and Brazil. The aging experiments carried out by seawater immersion for 180 days showed no evidence of degradation in 4 out of the 6 studied samples, despite product claims of biodegradability or 100% degradability status. This finding denotes unequivocal greenwashing practices, even including bags made of polyethylene, an ordinary non-biodegradable polymer. Thus, the inadequate adoption of green marketing is deceiving to consumers and may lead to improper disposal of these materials. These practices are highly counterproductive in view of the global public policies recently adopted to control plastic pollution. Therefore, considering the technologies currently available for identification of polymers, a strict control should be exercised over products that claim biodegradable status.

Green Bioplastics as Part of a Circular Bioeconomy

The rapid accumulation of plastic waste is driving international demand for renewable plastics with superior qualities (e.g., full biodegradability to CO₂ without harmful byproducts), as part of an expanding circular bioeconomy. Higher plants, microalgae, and cyanobacteria can drive solar-driven processes for the production of feedstocks that can be used to produce a wide variety of biodegradable plastics, as well as bioplastic-based infrastructure that can act as a long-term carbon sink. The plastic types produced, their chemical synthesis, scaled-up biorefinery concepts (e.g., plant-based methane-to-bioplastic production and co-product streams), bioplastic properties, and uses are summarized, together with the current regulatory framework and the key barriers and opportunities.

Environmental Aspects of Biotechnology

A key motivation behind the development and adoption of industrial biotechnology is the reduction of negative environmental impacts. However, accurately assessing these impacts remains a formidable task. Environmental impacts of industrial biotechnology may be significant across a number of categories that include, but may not be limited to, nonrenewable resource depletion, water withdrawals and consumption, climate change, and natural land transformation/occupation. In this chapter, we highlight some key environmental issues across two broad areas: (a) processes that use biobased feedstocks and (b) industrial activity that is supported by biological processes. We also address further issues in accounting for related environmental impacts such as geographic and temporal scope, co-product management, and uncertainty and variability in impacts. Case studies relating to (a) lignocellulosic ethanol, (b) biobased plastics, and (c) enzyme use in the detergent industry are then presented, which illustrate more specific applications. Finally, emerging trends in the area of environmental impacts of biotechnology are discussed.

Plastic waste as a significant threat to environment - a systematic literature review

Context Materials which exceed the balance of their production and destruction lead to the deterioration in the environment. Plastic is one such material which poses a big threat to the environment. A huge amount of plastic is produced and dumped into the environment which does not readily degrade naturally. In this paper, we address the organization of a large body of literature published on the management of waste plastics being the most challenging issue of the modern world. Objectives To address the issue of the management of waste plastics, there is a dire need to organize the literature published in this field. This paper presents a systematic literature review on plastic waste, its fate and biodegradation in the environment. The objective is to make conclusions on possible practical techniques to lessen the effects of plastic waste on the environment. Method A systematic literature review protocol was followed for conducting the present study [Kitchenham B, Brereton OP, Budgen D, Turner M, Bailey J, Linkman S. Systematic literature reviews in software engineering - A systematic literature review. Inf Softw Technol 2009;51(1):7-15.]. A predefined set of book sections, conference proceedings and high-quality journal publications during the years 1999 to September 2017 were used for data collection. Results One hundred and fifty-three primary studies are selected, based on predefined exclusion, inclusion and quality criteria. These studies will help to identify the fate of different waste plastics, their impact and management and the disposal techniques frequently used. The study also identifies a number of significant techniques and measures for the conversion of waste plastic materials into useful products. Conclusion Five fundamental strategies are used for the handling of plastic waste. These strategies include: recycling, depositing in landfill, incineration, microbial degradation and conversion into useful materials. All of these methods have their own limitations, due to which there is need to explore the studies for optimum solutions of the management of plastics waste.

The Positive Fate of Biochar Addition to Soil in the Degradation of PHBV-Silver Nanoparticle Composites

The environmental contamination of soils by polymeric and nanomaterials is an increasing global concern. Polymeric composites containing silver nanoparticles (AgNP) are collectively one of the most important products of nanotechnology due to their remarkable antimicrobial activity. Biochars are a promising resource for environmental technologies for remediation of soils considering their high inorganic and organic pollutant adsorption capacity and microbial soil consortium stimulation. In this work we report, for the first time, the use of biochar material as a tool to accelerate the degradation of polyhydroxybutyrate- co-valerate (PHBV) and PHBV composites containing AgNP in a tropical soil system, under laboratory conditions. This positive effect is associated with microbial community improvement, which increased the degradation rate of the polymeric materials, as confirmed by integrated techniques for advanced materials characterization. The addition of 5-10% of sugarcane bagasse biochar into soil has increased the degradation of these polymeric materials 2 to 3 times after 30 days of soil incubation. However, the presence of silver nanoparticles in the PHBV significantly reduced the degradability potential of this nanocomposite by the soil microbial community. These results provide evidence that AgNP or Ag⁺ ions caused a decline in the total number of bacteria and fungi, which diminished the polymer degradation rate in soil. Finally, this work highlights the great potential of biochar resources for application in soil remediation technologies, such as polymeric (nano)material biodegradation.

The Next Generation of Sustainable Food Packaging to Preserve Our Environment in a Circular Economy Context

Packaging is an essential element of response to address key challenges of sustainable food consumption on the international scene, which is clearly about minimizing the environmental footprint of packed food. An innovative sustainable packaging aims to address food waste and loss reduction by preserving food quality, as well as food safety issues by preventing food-borne diseases and food chemical contamination. Moreover, it must address the long-term crucial issue of environmentally persistent plastic waste accumulation as well as the saving of oil and food material resources. This paper reviews the major challenges that food packaging must tackle in the near future in order to enter the virtuous loop of circular bio-economy. Some solutions are proposed to address pressing international stakes in terms of food and plastic waste reduction and end-of-life issues of persistent materials. Among potential solutions, production of microbial biodegradable polymers from agro-food waste residues seems a promising route to create an innovative, more resilient, and productive waste-based food packaging economy by decoupling the food packaging industry from fossil feed stocks and permitting nutrients to return to the soil. To respond to the lack of tools and approach to properly design and adapt food packaging to food needs, mathematical simulation, based on modeling of mass transfer and reactions into food/packaging systems are promising tools. The next generation of such modeling and tools should help the food packaging sector to validate usage benefit of new packaging solutions and chose, in a fair and transparent way, the best packaging solution to contribute to the overall decrease of food losses and persistent plastic accumulation.

Biodegradable Plastic Blends Create New Possibilities for End-of-Life Management of Plastics but They Are Not a Panacea for Plastic Pollution

Plastic waste pollution is a global environmental problem which could be addressed by biodegradable plastics. The latter are blended together to achieve commercially functional properties, but the environmental fate of these blends is unknown. We have tested neat polymers, polylactic acid (PLA), polyhydroxybutyrate, polyhydroxyoctanoate, poly(butylene succinate), thermoplastic starch, polycaprolactone (PCL), and blends thereof for biodegradation across seven managed and unmanaged environments. PLA is one of the world's best-selling biodegradable plastics, but it is not home compostable. We show here that PLA when blended with PCL becomes home compostable. We also demonstrate that the majority of the tested bioplastics and their blends degrade by thermophilic anaerobic digestion with high biogas output, but degradation times are 3-6 times longer than the retention times in commercial plants. While some polymers and their blends showed good biodegradation in soil and water, the majority of polymers and their blends tested in this study failed to achieve ISO and ASTM biodegradation standards, and some failed to show any biodegradation. Thus, biodegradable plastic blends need careful postconsumer management, and further design to allow more rapid biodegradation in multiple environments is needed as their release into the environment can cause plastic pollution.

The Microbial Production of Polyhydroxyalkanoates from Waste Polystyrene Fragments Attained Using Oxidative Degradation

Excessive levels of plastic waste in our oceans and landfills indicate that there is an abundance of potential carbon sources with huge economic value being neglected. These waste plastics, through biological fermentation, could offer alternatives to traditional petrol-based plastics. Polyhydroxyalkanoates (PHAs) are a group of plastics produced by some strains of bacteria that could be part of a new generation of polyester materials that are biodegradable, biocompatible, and, most importantly, non-toxic if discarded. This study introduces the use of prodegraded high impact and general polystyrene (PS0). Polystyrene is commonly used in disposable cutlery, CD cases, trays, and packaging. Despite these applications, some forms of polystyrene PS remain financially and environmentally expensive to send to landfills. The prodegraded PS0 waste plastics used were broken down at varied high temperatures while exposed to ozone. These variables produced PS flakes (PS1⁻3) and a powder (PS4) with individual acid numbers. Consequently, after fermentation, different PHAs and amounts of biomass were produced. The bacterial strain, Cupriavidus necator H16, was selected for this study due to its well-documented genetic profile, stability, robustness, and ability to produce PHAs at relatively low temperatures. The accumulation of PHAs varied from 39% for prodegraded PS0 in nitrogen rich media to 48% (w/w) of dry biomass with the treated PS. The polymers extracted from biomass were analyzed using nuclear magnetic resonance (NMR) and electrospray ionization tandem mass spectrometry (ESI-MS/MS) to assess their molecular structure and properties. In conclusion, the PS0⁻3 specimens were shown to be the most promising carbon sources for PHA biosynthesis; with 3-hydroxybutyrate and up to 12 mol % of 3-hydroxyvalerate and 3-hydroxyhexanoate co-monomeric units generated.