Biodegradation Of Plastic Waste Using Marine Micro-Organisms

Abstract

Synthetic polymers are the plastic polymers which are mainly formed by chemical means. In this research work we will mainly study about some synthetic polymers like Polyethylene terephthalate (PET) and Polymethyl-methacrylate (PMMA), thermosetting plastics formed by the condensation process of production of polymers. Plastics are the materials which are highly resistive and assist high durability. Microbial biodegradation is a process by which organic matter are mainly broken down by the micro-organisms especially, bacteria or fungi. Biodegradation of these types of synthetic polymers raise a significant attention for environmental protection. Fungi native to agricultural soils that colonized commercially available biodegradable PET strips were isolated from the marine water near Sunderban area and were analyzed for potentiality in degrading plastics. The present work evaluates the effect of different types of fungus growth on different types of media for the biodegradation behavior on the PET (Polyethylene Terephthalate) bottle strips, and also the growth of fungi on the sterile PET films. The biodegraded LDPE (Low Density Polyethylene) strips were characterized by Weight loss study. We will also observe the effect of Methyl Methacrylate (MMA) modified cellulose nano-fibers on the biodegradation behavior of Polymethyl Methacrylate (PMMA)/cellulose composites. The identification and characterization of these types of fungal species degrading these types of various synthetic polymers have been done. Keywords: Synthetic plastics, Biodegradable polymers, PET strips, Nano-fibers.

Introduction

Plastic is the term used for polymeric materials so as to improve performance of substances and reducing costs. Plastics, thermoplastics or thermosetting plastics can be modifically formed by different polymerization techniques like Addition Polymerization and Condensation Polymerization. Degradation is been considered as undesirable attribute as it shortens life span of a product and its durability. Recently, consciousness of the environmental problems by plastic waste as durable material has made biodegradable plastics an attractive alternative to conventional plastic materials. Degradation (defined as structural changes, fragmentation, and reduction in molecular weight, integrity, and strength) occurs via a series of events, including both abiotic processes (thermal stress, photo-oxidation, hydrolysis, erosion and mechanical stress), and biological degradation. Abiotic processes can change the structural changes of a plastic material directly or indirectly. Plastics have different types of advantages of having low cost materials, light weighted and unbreakable bonding.

Plastics have high molecular mass, high yield of specific ability of deforming. Biodegradable studies on plastic polymers are mainly done by using microbial entities. Biological degradation is a process or phenomena which describes the breakdown or cut down of organic compounds by living organisms, bacteria or fungi. Polymers are used in huge amounts in our daily lives as packaging materials, consumer goods, pharmaceutical and personal care products, dyes, lacquers, and in many other fields. Recently experimental studies signifies that awareness for different environmental problems can be harnessed by the plastics and thus the most effective way is by the process of bioremediation which emphasizes on not accumulating the various hazardous chemicals to be replenished as environmental pollutants and to overcome the problems furnished by durable plastic wastes.

Materials & Methods

Preparation process of PMMA

Polymer Polymethyl-methacrylate (PMMA) is formed by suspension polymerization technique involving heterogenous reactions using mechanical agitation technique so as to separate the monomer Methyl-Methacrylate (MMA), which is also the initiator and water was removed by shaking it with 5% NaOH solution in a separating funnel by continous washing with distilled water. Then we repeated this same procedure for atleast 4-5 times for the removal of the inhibitor. Benzoyl peroxide and polyvinyl alcohol (PVOH) along with linseed oil was added. Benzoyl peroxide, sodium chlorite and sodium hydrogen sulphite were used for removing the lignin from the sugarcane bagasse fibres. Cellulose was extracted from raw sugarcane bagasse. Sulphuric acid was used for acid hydrolysis during the production of nanocellulose. Cellulose was broken down into a micro and nano level with the help of freeze drying/lyophilization.

Preparation of cellulose micro/nano fibres from Sugarcane Bagasse

Cellulose yielding amounts of micro as well as nano- fibers of about 20 g was treated with sugarcane bagasse fibres along with 0. 7% sodium chlorite (NaClO2) solution at pH 4, kept for continuous stirring of 2 hrs, treated with 2 % sodium hydrogen sulphite (NaHSO3) for about 15 mins, was filtered, dried and then again treated with 17. 5% NaOH solution for 15 mins, then again filtered, washed and thus subjected to acid hydrolysis, 47% H2SO4 for constant stirring of about 3 hrs at 50°C. Hence, finally we obtain powders of cellulose after the process of freeze drying, also known as lyophilization at a temperature of about -30°C at a pressure of 10-15 Pa.

Biodegradation studies: degradation through marine microbesBiodegradation behavior of the different polymer film samples was examined by the rate of degradation through marine microbes, namely different species of identified fungus: Aspergillus niger sp. And fungi 1 & fungi 11 sp. The bacteria were isolated from the marine waters near Sunderban area. The first film sample was PET (Polyethylene terephthalate) obtained by cutting the kinley mineral water into square sized 1 cm diameter. The second film sample was PMMA (Polymethyl methacrylate) and third sample was PMMA/ cellulose, obtained by the process discussed above and then was cut into small pieces. The polymer film samples were taken out at 1, 2, 3, 4, 5, 6 weeks respectively, washed with ethanol, was vacuum dried and thus weight loss of the samples with respect to biodegradation was speculated.

Weight loss study

The characterization of the various types of polymer films can be speculated by the weight loss study measuring the rate of degradation hence calculating the percentage of weight loss by the given equation, %Weight loss = {(S1-S2)/S1}* 100Where, S1 is the initial weight of the polymer sample before biodegradation (before putting it in media) and S2 is the final weight of the polymer sample after biodegradation (after taking out from media) at different time intervals.

Isolation and identification of degrading bacteria

Media composition and preparation 1 g/L of Potassium di hydrogen phosphate (KH2PO4), 2 g/L of Sodium Nitrate (NaNO3), 0. 5 g/L of Magnesium sulphate heptahydrate (MgSO4. 7H2O), 0. 5 g/L of Potassium chloride (KCl), 0. 01 g/L of Ferrous sulphite heptahydrate (FeSO2. 7H2O), 1 g/L of Ammonium chloride (NH4Cl) were mixed with the required amounts of distilled water so as to prepare the minimal media at pH 6. 0. 2 g /L of Agar powder was added in the prepared media so as to constitute for agar media. Peptone was additionally added with all these quantities of nutrients for making the nutrient agar media. Nutrient agar media was mainly used for plating. Czapex dox and Potato dextrose with agar were also used for making the fungal media.

Isolation of bacterial strain degrading PET, PMMA/ cellulose composites

The fungal strain identified as Aspergillus niger sp 1, 2 and 3, was obtained from the marine waters near Sunderban area, selected for further study for degradation or weight loss of the composite films. The polymer film samples (PET, PMMA, and PMMA/cellulose) were taken out from the conical flasks at intervals of 1 week, 2 weeks, 3 weeks, 4 weeks, 5 weeks and 6 weeks respectively after keeping it in incubator. The culture plates were also prepared on nutrient agar media. PET, PMMA and PMMA/cellulose composite films which were cut in uniform squared dimensions and implanted in the media. A control was made without the films but only containing the required amounts of minimal media was also kept. The fungi which is growing encircling the plastic polymer composite films was used for the characterization.

Weight loss study of the PET, PMMA and PMMA/cellulose composite films by shaking method with the use of incubation

The behavior of the fungal culture isolated from marine waters was evaluated by the procedure, where PET, PMMA and PMMA/cellulose composite polymer films were added to a conical flask( previously sterilized and autoclaved) containing 50 ml of minimal media. The fungal species identified as Aspergillus, was inoculated into the minimal media, and then was properly cotton plugged, and kept for incubation at a temperature of about 36-37 °C with shaking for 1, 2, 3,4,5,6 weeks respectively. The degradation was speculated by obtaining the weight loss of the composite films at stated intervals.