Problem 47 - Chemistry: The Central Science in SI Units, Global Edition

Question

List the common products formed when an organic material containing the elements carbon, hydrogen, oxygen, sulfur, and nitrogen decomposes (a) under aerobic conditions, (b) under anaerobic conditions.

Step-by-Step Solution

Answer

When organic materials containing carbon, hydrogen, oxygen, sulfur, and nitrogen decompose under aerobic conditions, the common products formed are CO2, H2O, heat, inorganic nutrients (e.g., NO3-, SO4^2-), and biomass. Under anaerobic conditions, the common products are CH4, CO2, H2O, H2S, NH3, biomass, organic acids, and alcohols.

Step 1: Aerobic Decomposition

Aerobic decomposition is the process of breaking down organic material in the presence of oxygen. The primary microorganisms responsible for this decomposition process are bacteria and fungi. They metabolize organic compounds in the material and consume oxygen, releasing various products, including: 1. Carbon dioxide (CO2): Some carbon molecules in the decomposing material are converted into carbon dioxide during aerobic respiration. 2. Water (H2O): Hydrogen molecules combine with oxygen during the decomposition process to form water. 3. Heat: Energy is released during the oxidation process in the form of heat. 4. Inorganic nutrients like nitrates (NO3-) and sulfates (SO4^2-): Microorganisms break down nitrogen and sulfur-containing compounds, releasing nitrogen and sulfur in their oxidized forms. 5. Biomass: The microorganisms reproduce and increase their biomass, which becomes part of the decomposed material.

Step 2: Anaerobic Decomposition

Anaerobic decomposition occurs in the absence of oxygen. The primary microorganisms responsible for anaerobic decomposition are methane-producing bacteria, known as methanogens, and sulfate-reducing bacteria. During this process, various products are formed, including: 1. Methane (CH4) and carbon dioxide (CO2): In the absence of oxygen, carbon molecules in the decomposing material are primarily converted into methane and carbon dioxide. 2. Water (H2O): Hydrogen molecules combine with other atoms during the anaerobic decomposition process to form water. 3. Hydrogen sulfide (H2S): Sulfate-reducing bacteria break down sulfur-containing compounds into hydrogen sulfide. 4. Ammonia (NH3): Nitrogen molecules are converted into ammonia during the anaerobic decomposition process. 5. Biomass: The microorganisms reproduce and increase their biomass, which becomes part of the decomposed material. 6. Acids and alcohols: Some organic acids (e.g., acetic acid) and alcohols (e.g., ethanol) are produced as intermediate products of anaerobic decomposition. In conclusion, the common products formed when organic materials containing carbon, hydrogen, oxygen, sulfur, and nitrogen decompose under aerobic conditions are CO2, H2O, heat, inorganic nutrients, and biomass. Under anaerobic conditions, the common products are CH4, CO2, H2O, H2S, NH3, biomass, organic acids, and alcohols.

Key Concepts

Aerobic Decomposition

Aerobic decomposition is a natural process where organic material breaks down in the presence of oxygen. This method is efficient and commonly observed in environments like compost piles and well-aerated soils. During this process, microorganisms such as bacteria and fungi play a crucial role in breaking down complex organic molecules.

Key products of aerobic decomposition include:

• Carbon Dioxide (CO2): Carbon from the organic material combines with oxygen, resulting in CO2, a gas naturally released in the atmosphere.
• Water (H2O): As microorganisms degrade organic materials, they produce water as a byproduct.
• Heat: The chemical reactions generate heat, making the decomposition process faster and assisting in killing harmful pathogens.
• Inorganic Nutrients: Elements like nitrogen and sulfur are broken down into nitrates (NO3-) and sulfates (SO4^2-), which enrich the soil.
• Biomass: The microorganisms themselves grow, increasing their biomass as part of the decomposition material. This biomass can further contribute to soil health.

Overall, aerobic decomposition is a vital ecological process, aiding in nutrient recycling and soil enrichment.

Anaerobic Decomposition

Anaerobic decomposition occurs in environments lacking oxygen, like sealed garbage bags or waterlogged soils. This slower process involves different types of microorganisms that thrive without oxygen, primarily methanogens and sulfate-reducing bacteria.

The typical products of anaerobic decomposition are:

• Methane (CH4) and Carbon Dioxide (CO2): Without oxygen, organic carbon is mainly converted into methane, a potent greenhouse gas, along with some CO2.
• Water (H2O): Similar to aerobic processes, water is still a major byproduct.
• Hydrogen Sulfide (H2S): Produced by sulfate-reducing bacteria, this gas has a characteristic foul smell.
• Ammonia (NH3): Anaerobic conditions convert nitrogen in organic material to ammonia, important for nutrient cycling.
• Biomass: Microorganisms grow and multiply, adding their own biomass to the decomposing material.
• Organic Acids and Alcohols: Intermediate products such as acetic acid and ethanol form during anaerobic processes.

Anaerobic decomposition plays an essential role in organic waste management and biogas production, providing both challenges and opportunities.

Microorganisms

Microorganisms are a vital part of the decomposition process. They are tiny organisms, like bacteria and fungi, responsible for breaking down dead organic matter. In aerobic decomposition, bacteria and fungi work together by digesting organic material in oxygen-rich environments. Their activity ensures quick breakdown and nutrient recycling.

In anaerobic decomposition, other specialized microorganisms such as methanogens and sulfate-reducers take over in oxygen-poor conditions.

Important roles of microorganisms include:

• Accelerating the breakdown of complex molecules.
• Converting organic matter into simpler molecules and gases.
• Recycling nutrients back into the ecosystem.
• Assisting in the production of energy sources like methane in anaerobic conditions.

Without microorganisms, organic decomposition would be impossible, leading to waste accumulation and nutrient depletion in ecosystems.

Decomposition Products

The decomposition of organic materials results in various products formed through either aerobic or anaerobic processes. These products differ based on the availability of oxygen and types of microorganisms involved.

During aerobic decomposition:

• Carbon Dioxide (CO2): A natural byproduct of aerobic respiration.
• Water (H2O): Essential for microorganism growth and function.
• Inorganic Nutrients: Compounds like nitrates and sulfates that enrich soil.
• Biomass: Microbial growth contributing to soil structure.

In anaerobic decomposition, products include:

• Methane (CH4): Used as a renewable energy source in biogas.
• Hydrogen Sulfide (H2S): Known for its pungent smell.
• Ammonia (NH3): Important for nitrogen cycling.
• Organic Acids and Alcohols: Act as intermediates and potential alternative energy sources.

Each decomposition type contributes uniquely to nutrient cycling, energy production, and ecological balance.