How do aerobic and anaerobic processes differ?
Anaerobic and aerobic treatment are two forms of biological treatment that operate on the fundamental principle of using microorganisms to break down organic compounds in wastewater. However, the most obvious difference between these two processes is that aerobic treatment occurs in the presence of oxygen, while anaerobic treatment does not. So, aside from that key difference, what other distinctions exist between these two processes?
What are the similarities between aerobic and anaerobic wastewater treatment?
• Aerobic and anaerobic wastewater treatment are biological wastewater treatment processes that involve living organisms.
• Complex organic materials are broken down in both processes.
• Both processes are primarily driven by bacteria.
What is the difference between aerobic and anaerobic wastewater treatment?
The anaerobic digestion process used for sludge digestion and wastewater treatment offers the following advantages:
• The anaerobic decomposition process does not use oxygen and therefore consumes less energy. At the same time, since these microorganisms use less energy to synthesize new cells, they can channel that energy into the production of CH₄. As a result, the anaerobic decomposition process produces fewer new bacterial cells than the aerobic decomposition process.
• In terms of nutrient requirements, anaerobic decomposition requires fewer nutrients than aerobic decomposition. When calculated based on COD balance, anaerobic bacteria use approximately 90% of the COD to produce methane, with only 10% used to form new cells. In contrast, aerobic bacteria use 50% of the input COD to synthesize new cells, with the remaining 50% used to generate thermal energy.
• The end products of the anaerobic decomposition process are CH₄, CO₂, N₂, H₂, etc., with CH₄ accounting for up to 65%. The anaerobic process produces large amounts of methane, which can be used to fuel boilers. As a result, this process is more odorous and corrosive than the aerobic process.
• Limits the growth of filamentous microorganisms by recirculating sludge and the surface water layer from the anaerobic sludge digestion tank to the activated sludge tank
• Solids in an anaerobic digester can be used as a source of soil-improving fertilizer
• Suitable for treating wastewater with high concentrations of pollutants
Disadvantages of the anaerobic process:
• Long startup time: Because the rate of biomass synthesis is lower, a longer startup time is required to reach the desired biomass concentration.
• Long recovery time: If the anaerobic symbiotic system is disrupted by biomass washout, toxic substances, or shock loading, it may take longer for the bioreactor to return to normal operating conditions.
• Specific nutrients / trace metal requirements: Anaerobic microorganisms, particularly methanogens, have specific nutrient requirements, such as Fe and Ni, and require Co for optimal growth.
• More susceptible to changes in environmental conditions: Anaerobic microorganisms, particularly methanogens, are highly sensitive to changes in conditions such as temperature, pH, redox potential, etc.
• Treatment of sulfate-rich wastewater: The presence of sulfate not only reduces methane production due to substrate competition but also inhibits methanogens through the production of hydrogen sulfide.
