Feces, commonly known as poop, is the body’s natural digestive waste product, consisting of material the digestive system could not fully process. The breakdown of feces occurs primarily through the work of countless organisms, both microscopic and macroscopic, that recycle the organic matter back into the environment. This natural decomposition process is a fundamental part of the carbon and nutrient cycles on Earth.
What Feces Is Made Of
Feces is a complex biological matrix that is mostly water, making up about 75% of the total mass. The remaining solid matter is a mix of organic and inorganic compounds. Approximately 30% of the dry weight consists of dead and living bacterial biomass, reflecting the microbial activity within the gut.
The rest of the solid portion includes material that was indigestible by the body’s enzymes. This largely features undigested food material like cellulose and other plant fibers, which can account for up to 30% of the dry weight. Fats and cholesterol make up another 10% to 20%, while protein and nitrogenous matter account for 2% to 25%. Dead cellular lining shed from the intestinal tract also passes out of the body, adding to the organic load, alongside inorganic substances such as various phosphate salts.
The Primary Decomposers: Bacteria and Fungi
The chemical dismantling of feces is carried out by microscopic organisms, primarily bacteria and fungi, which utilize enzymes to break down complex molecules. Environmental bacteria are immediately at work, employing different metabolic strategies depending on the presence of oxygen. Aerobic bacteria thrive in oxygen-rich conditions, efficiently converting organic matter into simpler compounds like carbon dioxide, water, and mineralized nutrients. Conversely, anaerobic bacteria operate in oxygen-deprived environments, such as within the core of a large fecal mass or in a septic system. These organisms perform fermentation, breaking down carbohydrates and proteins into end products like methane, carbon dioxide, and volatile fatty acids.
Fungi, including molds and yeasts, play a complementary role by attacking the toughest chemical structures that bacteria often struggle to degrade. They produce and secrete powerful enzymes that break down complex organic molecules through external digestion. This includes recalcitrant compounds like lignin and certain complex carbohydrates found in plant matter.
Accelerating the Process: Detritivores and Environment
While bacteria and fungi are the chemical decomposers, larger organisms known as detritivores act as mechanical accelerators of decomposition. Detritivores like dung beetles, fly larvae, and earthworms consume the feces, serving two important functions. By ingesting the material, they physically fragment the waste into much smaller pieces, a process called comminution. This fragmentation dramatically increases the surface area of the feces, providing the microscopic bacteria and fungi with easier and more widespread access to the organic matter. The detritivores also distribute the material as they move and excrete their own smaller fecal pellets, spreading the microbial activity across a wider area.
The rate at which decomposition occurs is highly dependent on surrounding environmental factors. Moisture is a necessity for all microbial activity, as bacteria and fungi require water to absorb nutrients and perform enzymatic digestion. Temperature also strongly influences the speed of the process; warmer temperatures generally increase the metabolic rate of decomposers, accelerating the breakdown. Finally, the availability of oxygen determines which type of bacteria dominates the process, directly impacting the chemical byproducts released.