Photocatalytic Degradation of Plastic

Due to rapid growth and modernization, the consumption of plastic has increased rapidly. However, due to the non-biodegradable nature of plastics, its management and disposal have become an environmental concern. The majority of plastics end up in landfill sites or oceans through rivers which is a threat to the marine ecosystem. Plastic can remain in the environment for thousands of years furthermore due to physical degradation plastics are converted into microplastics. Current techniques of recycling plastic require a significant amount of segregation which is not feasible due to economic constraints. Photocatalyst enhances the rate of degradation using light as a source of energy hence making the process economically feasible. This chapter provides a comprehensive review focusing on plastics, its pollution and type of polymers. Further, the chapter also reviews the various research conducted for the photocatalytic degradation of plastics.

Enzymes Involved in Plastic Degradation

The global increase in production of plastic and accumulation in the environment is becoming a major concern especially to the aquatic life. This is due to the natural resistance of plastic to both physical and chemical degradation. Lack of biodegradability of plastic polymers is linked to, amongst other factors, the mobility of the polymers in the crystalline part of the polyesters as they are responsible for enzyme interaction. There are significantly few catabolic enzymes that are active in breaking down polyesters which are the constituents of plastic. The synthetic polymers widely used in petroleum-based plastics include polyethylene (PE), polypropylene (PP), polyvinylchloride (PVC), polyurethane (PUR), polystyrene (PS), polyamide (PA) and polyethylene terephthalate (PET) being the ones used mostly. Polymers with heteroatomic backbone such as PET and PUR are easier to degrade than the straight carbon-carbon backbone polymers such as PE, PP, PS and PVC.

Introduction, Past and Present Scenarios of Plastic Degradation

The fascinating properties of plastic make its use widely possible in every field for the ease of human life. On the other hand, these properties make plastic non-biodegradable in nature. Hence the increasing accumulation of plastic in the environment is the arising concern for environmentalists and human society. This growing concern has motivated researchers and technologist to promote research activity for finding new degradation methods for plastics, synthesis of new plastic with biodegradable nature or find alternatives to plastics. Considering these facts, this book chapter briefly discusses the management of post-consumer plastic products and all the possible methods for plastic degradation such as photo and thermo-oxidative, catalytic, mechano-chemical and chemical along with the factors affecting these degradation methods.

Recovery of Biodegradable Bioplastics from Different Activated Sludge Processes during Wastewater Treatment

To overcome the environmental hazards of petroleum based plastics, synthesis and use of microbial bioplastics became popular. Polyhydroxyalkanoates (PHAs) are biodegradable biopolymers having plastic like properties mainly used in tissue engineering and packaging. Bacteria can produce bioplastics in carbon abundance. Activated sludge process is a simultaneous process for treating wastewater and producing PHAs. Wastewaters are treated by using mixed sludge, aerobic granular sludge and chemically treated sludge which provided more than 40% PHA yield. This chapter describes the PHA structure, synthesis pathways, types of wastewaters and activated sludge processes used with reactor parameters and environmental factors effecting PHA productions.

Versatile Applications of Degradable Plastic

In the last 50 years, plastics has become a favorite industry for packaging materials for their ease of manufacture and excellent performance. The advancement of food, electronics, automobile, medical and agricultural industries has increased the demand for packaging and casing materials made of large hydrocarbon polymers. Since plastics show resistance to biodegradation, they pose considerable threats to the environment. Degradable plastics and biopolymers offer promising solutions to this problem. Degradable plastics can be easily absorbed in the environment while exhibiting the properties of conventional plastics. There are three types of biopolymers according to their source: biomass extracted polymers, synthesized from microorganisms and produced from bio-derived monomers. Biodegradable plastics are commonly used in one-off packaging such as crockery, food service containers and cutlery. Although biodegradable plastics can replace conventional plastics in a lot of applications, their performance and cost are sometimes problematic. This chapter analyses the growth of the degradable plastic industry and explores their potential applications.

Biodegradable Plastics from Cyanobacteria

High accumulation of generated plastic waste is a growing concern. Alternatively, scientific efforts are underway to drive industrial demand to replace these products with superior quality, adequate biodegradable resources. Cyanobacteria are a versatile group of phototrophic prokaryotes capable of producing polyhydroxyalkanoates (PHAs) using sunlight and carbon dioxide (CO2) as a form of carbon and energy reserve. PHAs are appealing alternatives for traditional chemical plastics because these have to resemble characteristics, biocompatibility, and complete biodegradability. In this sense, this chapter aims to address the potential of cyanobacteria as a biodegradable alternative solution.

Degradable Plastic Recycling

The public demand of plastics for food, drinks, consumable and packaging is increasing enormously all over the world. Due to limited available plastic resources, it is challenging to meet the stipulation of the massive population. The contribution of the synthetic plastic industry is encouraging to cope with these challenges. However, it is not only restricted towards production, but the degradation of its waste is also equally arduous and even more complicated to a large extent. A useful solution to this problem is recycling instead of degradation. In order to optimize the utility of recycling, various techniques are in progress. Plastic recycling is an acceptable technique to keep the economy in circulation. Moreover, it is an effective way to reduce the environmental pollution and to promote green environment.

Plastics Versus Bioplastics

Plastics are polymers of long chain hydrocarbons based on petrochemicals. Due to their physiochemical properties these are almost non-degradable and their complete recycling is impossible. High production rate and less disposal capacities have made plastic environmental pollutant resulting in severe impacts on the health of organisms and destruction of habitats thus effecting the biosphere in different ways. Biodegradation, thermal and catalytic degradation of plastics is widely studied to ensure a sustainable disposal of plastic waste with limited results until the present however, a new field where ecofriendly polymers obtained from natural biomass are used to make materials is flourishing. Bioplastics are polymers derived from biomass such as cellulose, starch, chitin and microbial polyhydroxyalkanoates that have the ability to produce products of daily use that can replace their counter parts made from the synthetic plastics. Bioplastics degrade easily in natural environment and replace the petrochemical based plastic polymers, thus saving the natural environment from plastic pollution and ensuring a sustainable environment.

Plastic Biodegradation

Plastics that are degraded by microbial or enzymatic activity are known as biodegradable plastics. Biodegradable plastics are an alternative to conventional plastics that are chemically synthesized and are responsible for causing environmental pollution due to unwanted accumulation occurring via disposal practices. There was a serious need to introduce biodegradable plastics in the market since the level of plastic pollution in the air, water, and soil has reached its threshold values. The non-biodegradable plastics are increasingly accumulating in the environment, which can be a threat to the planet in the coming future. This chapter provides detailed insight into biodegradables polymers, mostly aliphatic polyesters that are considered as a solution against synthetic plastic. It also gives brief information on the current scenario of plastic biodegradation, recent advancements, opportunities, and future challenges. Also, it comprises precise strategies currently used at a laboratory scale to enhance biodegradation of classical synthetic plastics (e.g., polyethylene, polystyrene, etc.). Moreover, the factors affecting the biodegradation process and the characterization techniques being employed to assess degradation extent are also discussed. The overall work focuses on thrust areas to be improved concerning environmental safety and sustainable vision.

Biodegradable Plastics from Renewable Raw Materials

Fossil oil prices are soaring steeply due to the depleting petroleum raw materials. Extensive research has been carried out around the globe to develop efficient processes that can replace oil-derived polymers (conventional plastic) with bio-based polymers that originate from renewable resources. Fossil-oil based plastic products take decades to degrade, leading to the unwanted accumulation of plastic waste that can be seen all around. Further, greenhouse gases emission occurs during the production and destruction of synthetic plastic. Therefore, plastic waste has become a massive threat to the biosphere and needs to be addressed immediately. To overcome this issue, a new type of plastic can be produced from bio-resources that can fulfill even the energy demand in today's world. This new form of plastic must be accommodated fast in daily life, considering the range of applications of plastics. Biodegradable plastics made from renewable raw materials can retain all the benefits of petroleum-based plastic without having any negative impacts on the environment. Bioplastics are not toxic in nature and can easily decay back into carbon dioxide via degradation. The products made from bioplastics may be commercialized, considering their superior properties over conventional plastic. The discovery and implementation of plastic made from renewable raw material resources could be a giant leap into the sustainable future.