Effect of Starch Pre-treatment on the Microbial Degradation of Low Density Polyethene Carrier Bags

Filed in Articles by on November 4, 2022

Effect of Starch Pre-treatment on the Microbial Degradation of Low-Density Polyethene Carrier Bags.


In this study, a cassava starch/low-density polyethene (LDPE) blend was compounded and the effect of this starch pretreatment on the rate of degradation of synthetic polyethene carrier bags was tested using bacteria and fungi (as singles and as consortia) isolated from dumpsites.

Weight loss and Fourier Transformed Infra-Red Spectroscopy (FTIR) were used as analytical techniques for measuring biodegradation. Fungi were found to degrade both synthetic LDPE and LDPE/Starch blend resulting in a weight loss of 3.54% to 19.68% while that obtained from bacteria gave a weight loss of 1.0% to 18.5% within 30days.

Mixed cultures comprising of both bacteria and fungi gave better results than the individual organisms and the addition of starch was found to greatly enhance the biodegradation of the low-density polyethene carrier bags.

FTIR analysis showed the appearance of carbonyl groups in the LDPE residues after microbial treatments between wavelengths of 1703.67cm-1 and 1872.83cm-1 indicating likely oxidation of the carbon-carbon double bond (C=C) and various oxidation products formed during the biodegradation.

This study, therefore, shows that microorganisms with the ability to degrade low-density polyethene carrier bags exist in our natural environment. It has also shown that blending LDPE with natural polymers such as starch can greatly enhance the biodegradation of this polymer and that microbial consortia can accelerate the rate of degradation of this polymer.

Therefore finding the right microorganisms and/or their enzymes that can efficiently and completely biodegrade the recalcitrant polyethene into carbon dioxide, water and biomass will go a long way in solving this global threat and studying the synergism between them will give more insight for future efforts towards the biodegradation of these polymers.


Title page i

Declaration ii

Certification iii

Acknowledgements iv

Abstract vi

Table of Contents vii

List of Figures x

List of Tables xi

List of Plates xii

List of Appendices xiii

Chapter 1   Introduction

  • Background 1
  • History of Polyethene 1
  • Classification of Polyethene 2
  • Uses of Polyethene 3
  • Disposal of Polyethene 4
  • Hazards of Polyethene 5
  • Degradation of Polyethene 7
    • Biodegradation of Polyethene 8
    • Microorganisms involved in Polyethene Degradation  9
  • Statement of Problem 9
  • Justification of Study 11
  • Aim and Objectives of Study 12

1 10.1 Aim of study 12

1 10.2 Specific Objectives 13

Chapter 2      Literature Review

  1. 1 Polyethene Carrier bags 14
  • Disposal Methods of Polyethene 14
  • Hazards of Polyethene 17 3.1 Environmental Impacts/ Land pollution        18

2 3.2 Impact on livestock and wildlife 18

2 3.3 Impact on human health 19

  • Degradation of Polyethene 20
  • 2.4.1 Types of Degradation of Polyethene 20

2.4.2    Nondegradability of Polyethene 21

  • Degradable Polyethene  22
    • Polyolefin with Pro-oxidant  24

2 5.2 Pretreatments 24

  1. Polymer Blends 26
    • Surface Active Agents- Biosurfactants  27
    • Genetic Modification of Microorganisms  27
  • Starch as an enhancer 28
  • 7 Microbial degradations of Polyethene      29

2.7.1 Biodegradation of Polyethene/Starch Blend  32

2.8.    Mechanism of Microbial Degradation of Polyethene  33

2.9    Measurement of Biodegradation of Polyethene  36

Chapter 3   Materials and Methods

  • Sample Collection 37
  • Media Preparation 37
  • Isolation of Microorganisms from LDPE Samples  37
  • Identification of Microbial Isolates 38

3 4.1 Identification of Bacterial Isolates 38

3 4.2 Identification of Fungal Isolates 42

  • Screening of Microbial Isolates for Polyethene degradation ability  46
  • Preparation of Polyethene/Starch Blend 47
  • Biodegradation of Polyethene Bags using Individual Bacterial and

Fungal Isolates 47

  • Biodegradation of Polyethene Bags Using Bacterial and Fungal Consortium 48
  • Analytical Techniques for determination of the extent of biodegradation of Polyethene bags by the Bacterial and Fungal Isolates 49

3.8.1.Weight Loss   measurement 49

3.8.2 Fourier  Transform Infra-Red Spectrometry (FTIR)  50

Chapter 4 Results

  • Identity of Bacterial and Fungal Isolates with the ability to degrade Low-Density Polyethene Carrier bags 51
    • Polymerase Chain Reaction Amplicons of Bacteria and Fungi  55

4 1.2 Sequencing Profiles of bacteria 56

4 1.3 Sequencing Profiles of Fungi 57

  • Screening of Bacterial and Fungal Isolates for the ability to degrade LDPE    57
  • Biodegradation of untreated and Starch treated synthetic LDPE 57
  • Comparison of Bacterial and Fungal biodegradative ability on untreated

and Starch treated synthetic LDPE  Carrier bags  70

  • Fourier Transform Infra-Red Spectroscopy (FTIR) Analysis of residual

LDPE Strips after microbial degradation  70

Chapter 5   Discussion, Conclusion and Recommendations

Discussion 80

Conclusion 84

Recommendations 85

References       87



One of the most common items in our modern world is the ubiquitous plastic shopping bag which is made out of polyethene.

Polyethene is a member of a large family of polymers called thermoplastic polymers. It consists of long chains of the monomer ethene with its 2CH2 groups connected by a double bond, (H2C=CH2)  (Nanda et al., 2010).

Polyethene, a waxy chemically inert plastic, is one of the simplest and most inexpensive polymers. It contains the chemical elements, Carbon and Hydrogen, (Suseela and Toppo, 2007; Ramesh and Pramila, 2011).

Polyethene is produced by polymerization of ethene gas by allowing the free-roaming ethene gas molecules to bond together to form long chains of polyethene in the presence of a catalyst.

It can be produced through radical polymerization, anionic addition polymerization, ion coordination polymerization or cationic addition polymerization. Each of these methods results in a different type of polyethene.


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