Biodegradation

Biodegradation is the process by which organic substances are broken down by the metabolic activity of living organisms, primarily microorganisms such as bacteria and fungi. Through enzymatic reactions, complex molecules are depolymerized and metabolized into smaller compounds, often culminating in mineralization to carbon dioxide, water, and biomass. Biodegradation can occur under aerobic conditions, using oxygen, or under anaerobic conditions, without oxygen, with different microbial communities and end products such as methane in some digestion processes.

Rates and pathways depend on environmental conditions and material properties. Factors include temperature, moisture, pH, oxygen availability, nutrients, and the chemical structure of the substance (for example, molecular weight and the presence of certain functional groups). Some materials biodegrade readily in soil or compost, while others resist degradation or break down only under industrial or marine conditions. Incomplete biodegradation can yield intermediate metabolites that may be toxic or persist.

Biodegradation has applications in waste management and environmental remediation. Composting, wastewater treatment, and anaerobic digestion rely on microbial degradation to convert organic waste into stable products and energy. Bioremediation uses microorganisms to degrade contaminants in soils, sediments, or groundwater, often assisted by aeration, nutrient addition, or bioaugmentation. In aquatic systems, natural attenuation can reduce pollutant loads over time, though rates are highly variable.

Labeling of materials as biodegradable varies by standard and environment; a substance deemed biodegradable may require industrial composting or specific conditions to degrade efficiently. Plastics and polymers pose particular challenges, as slow or incomplete degradation can generate microplastics or toxic byproducts. Some bioplastics, such as polylactic acid (PLA) or polyhydroxyalkanoates (PHA), are designed to biodegrade under certain conditions, not necessarily in the open environment.