Biodegradability Evaluation of Industrial Products

Biodegradability Introduction 

Biodegradability is defined as a material’s capacity to break down through the action of living organisms such as bacteria, fungi, or water molds, allowing the material to be absorbed by the environment. The awareness of biodegradability has become greatly important as industries globally continue to move forward with sustainable development, especially in industrial sectors of manufacturing, textiles, and packaging. 

There are two types of Biodegradation: 

1. Aerobic Biodegradation: In the presence of oxygen, aerobic biodegradation produces carbon dioxide, water, and biomass. i.e., Organic matters 
2.  Anaerobic biodegradation occurs in the absence of oxygen, producing methane, carbon dioxide, and biomass, as well as inorganic materials such as glass and metals.

Biodegradation Natural Stages

1. Biodeterioration: In this process, various organisms, along with abiotic factors such as sunlight and temperature, begin to act and chemically and physically break down the material.
2. Bio-fragmentation: In this process, organisms such as fungi excrete their enzyme, further fragmenting the material into smaller molecules.
3. Assimilation: In this process, the organism takes the fragmented material completely into the cell and stores it for its food and then into ATP (adenosine triphosphate). They also serve as a precursor to other biosynthetic pathways.
4. Mineralization: Finally, in this process, complete biodegradation occurs. The material is completely degraded and converted, or taken into the various elemental cycles.

Biodegradability Testing Introduction 

Biodegradability Testing evaluates the ability of a material to be degraded, under specific environmental conditions (usually by microorganisms), to determine if a product can decompose into harmless materials like biomass, water, and carbon dioxide, indicating sustainability to the environment. 

There are numerous testing Standards, such as ASTM, ISO, OECD, EPA, FTC, and REACH, that also meet the requirements of the organizations.

1. ASTM Biodegradability Testing

ASTM International offers various standards for evaluating the biodegradability of plastics, emphasizing both aerobic and anaerobic environments.

• ASTM D5210– Standard Test Method for Determining the Anaerobic Biodegradation of Plastic Materials in the Presence of Municipal Sewage Sludge
• ASTM D5988– Standard Test Method for Determining Aerobic Biodegradation in Soil of Plastic Materials or Residual Plastic Materials After Composting
• ASTM D5511– Standard Test Method for Determining the Anaerobic Biodegradation of Plastic Materials under High-Solids Digestion Conditions 
• ASTM D6400– Standard Specification for Compostable Plastics

2. ISO Biodegradability Testing 

ISO biodegradation tests are global standards that evaluate the capability of materials, such as plastics, to decompose under particular circumstances, usually in compost or soil.

• ISO 14855– Determination of the ultimate aerobic biodegradability of plastic materials under controlled composting conditions.
• ISO 15985– Determine the anaerobic biodegradability of plastic. 

3. OECD Biodegradability Testing 

The OECD (Organisation for Economic Co-operation and Development) provides a range of standardized approaches for assessing the biodegradability of chemicals and materials. These approaches are divided into three levels: ready biodegradability, inherent biodegradability, and simulation testing.

1. Ready Biodegradability

These evaluations are rapid and uniform tests intended to determine if a substance can be swiftly and thoroughly broken down by microorganisms in aerobic environments. The standards for passing these evaluations are strict, usually necessitating at least 60% biodegradation within 28 days.

OECD 301 series(301A, 301B, 301C, 301D, 301E and 301F) directly evaluates the material  ready biodegradability.

1. OECD 301A– Measures the decrease in dissolved organic carbon.
2. OECD 301B(CO2 Evolution test)- Measures CO2 produced during aerobic degradation.
3. OECD 301C– Assesses oxygen uptake in microorganisms
4. OECD 301D– Measures oxygen consumption in a closed system
5. OECD 301 E- Dissolved organic carbon screening test 
6. OECD 301 F– Manometric Respirometry test, to measure the oxygen uptake over time 

 2. Inherent Biodegradability (OECD 302 series)  

 These tests are not as rapid and aim to determine if a substance can break down biologically in conditions that are more advantageous than those used in “ready” tests. They permit larger microbial inoculate and extended periods.

1. OECD 302A (Modified MITI Test): This is a revised version of the test developed by the Ministry of International Trade and Industry (MITI).  
2. OECD 302B (Zahn-Wellens/EMPA Test): This method assesses inherent biodegradability by evaluating the removal of dissolved organic carbon (DOC) or reduction of chemical oxygen demand (COD) when a test substance comes into contact with activated sludge. It is appropriate for materials that are highly soluble, non-volatile, and non-absorbing.  
3. OECD 302C (Closed Bottle Test): A test conducted in a closed bottle to measure inherent biodegradability.

3. Stimulation Testing

These are created to effectively replicate natural settings like rivers, seawater, soil, or wastewater treatment facilities.

1. OECD 120– Test the behaviour of polymers in water.
2. OECD 207– Test the toxicity of materials 
3. OECD 208– Test the impacts of products on seedling emergence 
4. OECD 209– Test the impact of material on microorganisms.  

Use of Biodegradability Tests In Various Industries 

1. Packaging: Biodegradable bags, films, and containers are in high demand. This testing helps confirm that compostability standards have been met.
2. Agriculture: Biodegradable Films, mulches used for de-composting are tested to ensure they will degrade and not harm the underlying soil.
3. Food: Testing biodegradability can help us understand how food degrades, which influences shelf-life, storage, safety of food, and developing new methods of preservation and refinement of best-before dates, which ultimately will assist in reducing food waste. 
4. Textiles: Natural and semi-synthetic fibers such as viscose undergo testing to know the biodegradation behavior at the end of their life in soil or in water. 
5. Pharmaceuticals: The importance of biodegradability is displayed in the development and testing of temporary implants, surgical stitches and delivery systems for drugs. 
6. Water and Wastewater Treatment: Biodegradation itself is a natural process used in wastewater treatment to degrade the leftover pollutants into less harmful substances.