MEVE 013: Unit 05 - Degradation of Natural Compound

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 UNIT 5: DEGRADATION OF NATURAL COMPOUNDS

5.1 Introduction

Natural organic compounds such as cellulose, hemicellulose, chitin, and lignin are major components of agricultural and forestry biomass. Their effective degradation is essential for sustainable waste management and resource recovery. Environmental biotechnology provides efficient biological tools—mainly microbial and enzymatic—for breaking down these complex polymers, contributing to composting, bioenergy, and value-added product generation.

5.2 Objectives

After studying this unit, learners will be able to:

  • Understand the structure and degradation of key natural polymers.
  • Identify the role of microorganisms and enzymes in biodegradation.
  • Explore composting and vermicomposting methods for agro-waste.
  • Examine agro-waste reuse in mushroom cultivation and emerging biotechnologies.
  • Analyze environmental factors and cost-related considerations.

5.3 Degradation of Cellulose, Hemicellulose, and Chitin

Cellulose

  • Structure: A polysaccharide made of β-1,4-linked glucose units.
  • Degradation: Carried out by cellulase enzymes—endoglucanases, exoglucanases, and β-glucosidases.
  • Microorganisms: Trichoderma, Aspergillus, Bacillus, Cellulomonas.

Hemicellulose

  • Structure: Branched heteropolymers of pentoses and hexoses.
  • Enzymes: Xylanases, mannanases, arabinofuranosidases.
  • Microorganisms: Bacillus subtilis, Paenibacillus, certain fungi.

Chitin

  • Structure: Polymer of N-acetylglucosamine found in fungal cell walls and arthropod exoskeletons.
  • Degradation: By chitinases and N-acetylglucosaminidases.
  • Microorganisms: Streptomyces, Vibrio, Serratia, Trichoderma.

5.4 Degradation of Lignin Compounds

  • Lignin: Complex aromatic polymer providing rigidity to plant cell walls; highly resistant to degradation.
  • Microbial Degradation: Mostly by white-rot fungi (Phanerochaete chrysosporium) and actinomycetes.
  • Enzymes involved:
    • Lignin peroxidase (LiP)
    • Manganese peroxidase (MnP)
    • Laccase
  • Lignin degradation is crucial for efficient lignocellulosic biomass utilization in bioenergy and composting.

5.5 Environmental Factors Influencing Biodegradation

  • Temperature: Affects microbial growth and enzyme activity (optimal ~25–55°C for composting).
  • pH: Most microbes prefer neutral to slightly acidic conditions.
  • Moisture content: 50–60% ideal for microbial metabolism in composting.
  • Oxygen availability: Aerobic vs. anaerobic degradation.
  • C:N Ratio: 25–30:1 is optimal for composting; imbalance slows degradation.
  • Presence of inhibitors: Some compounds (e.g., phenols, heavy metals) can suppress microbial action.

5.6 Lignocellulolytic Enzymes

These enzymes degrade lignocellulose, a composite of cellulose, hemicellulose, and lignin.

Enzyme

Substrate

Function

Cellulase

Cellulose

Hydrolyzes β-1,4-glycosidic bonds

Xylanase

Hemicellulose

Breaks down xylan into xylose

Laccase

Lignin

Oxidizes phenolic structures

Lignin Peroxidase

Lignin

Cleaves non-phenolic lignin bonds

Mannanase

Hemicellulose

Acts on mannans and glucomannans

These enzymes are widely used in composting, paper pulp treatment, and biofuel production.

5.7 Composting and Vermicomposting of Agro-residues

Composting

  • Aerobic process that converts organic waste into nutrient-rich compost.
  • Involves thermophilic and mesophilic microbial phases.
  • Reduces pathogen load and waste volume.

Vermicomposting

  • Uses earthworms (e.g., Eisenia fetida) and microbes to break down organic waste.
  • Produces fine-grained, nutrient-rich vermi-compost.
  • Faster and more nutrient-rich than traditional compost.

Agro-residues suitable for composting:

  • Straw, husks, leaves, sugarcane bagasse, fruit/vegetable peels, etc.

5.8 Use of Agro Waste in Mushroom Cultivation

  • Agro-waste like wheat straw, rice husk, cotton waste, and sawdust are used as substrates for mushroom growth.
  • Pleurotus spp. (oyster mushroom) and Agaricus bisporus commonly cultivated.
  • Fungi degrade cellulose and lignin to absorb nutrients.
  • Provides a low-cost, sustainable option for waste reuse and income generation in rural areas.

5.9 Process and Newly Emerging Technologies

Emerging Technologies for Biomass Utilization

  • Solid-State Fermentation (SSF): Used for enzyme production on solid agro-residues.
  • Biorefineries: Integrated approach to convert biomass into fuels, chemicals, and bio-products.
  • Enzyme Engineering: Tailoring enzymes for better activity and stability in lignocellulose breakdown.
  • CRISPR and Genetic Engineering: Used to enhance microbial capabilities for biodegradation.

5.10 Advantages and Cost Considerations

Advantages

  • Reduces environmental pollution and landfill usage.
  • Converts waste into valuable products (compost, biogas, mushrooms).
  • Promotes circular economy in agriculture.
  • Low energy requirement compared to thermal or chemical processes.

Cost Considerations

  • Initial setup for composting/vermi-units or mushroom farms is low.
  • Operational costs are minimal, often limited to labor and maintenance.
  • Profitability improves with scale and by-product utilization (e.g., vermiwash, mushroom spawn).

5.11 Let Us Sum Up

  • Natural compounds such as cellulose, chitin, and lignin can be effectively degraded by microbial action.
  • Composting and vermicomposting provide practical and eco-friendly ways to manage agro-waste.
  • Agro-residues can be converted into high-value products like compost, mushrooms, enzymes, and fuels.
  • Environmental factors and enzymatic systems are key to efficient biodegradation.
  • Biotechnology continues to advance solid waste management through enzyme optimization, process engineering, and waste valorization.

5.12 Key Words with Definitions

  • Cellulose-A plant polysaccharide composed of glucose units, degraded by cellulases.
  • Hemicellulose-A branched plant polymer of various sugars, more easily degradable than cellulose.
  • Chitin-A nitrogen-containing polysaccharide found in fungi and arthropods.
  • Lignin-A complex aromatic polymer in plant cell walls, resistant to microbial degradation.
  • Composting-Aerobic microbial decomposition of organic matter into stable humus.
  • Vermicomposting-Bioconversion of organic waste into compost using earthworms.
  • Laccase-An oxidative enzyme involved in lignin breakdown.
  • Lignin Peroxidase-Enzyme that breaks down complex lignin structures in white-rot fungi.
  • Agro-residues-Agricultural waste products like straw, husks, or bagasse.
  • Mushroom Cultivation-Growing edible fungi on organic waste substrates.
  • Solid-State Fermentation-Fermentation process on solid materials without free-flowing water.
  • Biorefinery-A facility that converts biomass into fuels, energy, and value-added products.

 

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