Aerobic vs. Anaerobic Wastewater Treatment

Untreated wastewater contains a diverse range of contaminants, including harmful pathogens, organic and inorganic substances, and toxic chemicals. It is a mixture of substances that should not be released into the environment untreated.

Discharging wastewater directly into rivers, lakes, oceans or on the land would have severe consequences for natural ecosystems, as well as posing serious health risk, and would circle back to us sooner than later.

This is the reason why wastewater treatment plays a critical role in protecting the environment and human health. The process involves the purification and treatment of wastewater before its release back into natural water bodies or its reuse for other purposes.

Why is it necessary to treat wastewater before disposal?

The necessity of wastewater treatment arises from several factors.

Firstly, the treatment is vital for maintaining public safety, as untreated wastewater often carries pathogens that pose risks to human health. Bacteria, viruses, and parasites found in sewage can cause serious waterborne diseases such as cholera, typhoid fever, hepatitis, and severe gastrointestinal infections.

Through effective treatment processes, including disinfection, wastewater treatment removes or inactivates these pathogens, preventing the spread of diseases and ensuring the safety of public water supplies.

Another crucial aspect is the preservation of water supplies. As freshwater resources become increasingly scarce, treating and reusing wastewater has become imperative.

Advanced treatment methods can produce high-quality reclaimed water that can be utilized for various purposes, such as irrigation, industrial processes, and even drinking water after meeting stringent safety standards.

Wastewater treatment helps alleviate pressure on freshwater sources, promoting sustainable water management and reducing reliance on scarce resources.

Lastly, wastewater often contains high concentrations of nutrients used in daily life, particularly nitrogen and phosphorus, which can contribute to eutrophication in water bodies.

Excessive nutrient levels promote the growth of algae and other aquatic plants, leading to oxygen depletion, harmful algal blooms, and the degradation of aquatic ecosystems. By incorporating processes like biological nutrient removal, the treatment helps decrease nutrient levels in treated water.

Most countries have established standards and regulations to ensure the proper treatment of wastewater before its discharge. Wastewater treatment facilities play a pivotal role in meeting these regulatory requirements, preventing legal and financial consequences for industries and municipalities.

What is the difference between the aerobic process and the anaerobic wastewater treatment process?

The aerobic process and the anaerobic process are two different approaches to wastewater treatment. They are distinguished by their reliance on different environmental conditions and microbial activities.

What is aerobic wastewater treatment?

The aerobic process involves treating wastewater in the presence of oxygen. Oxygen is essential for the growth and activity of aerobic microorganisms, such as bacteria, that thrive in oxygen-rich environments.

In this process, wastewater is mixed with oxygen and supplied to aerobic treatment units, such as activated sludge systems or trickling filters. The microorganisms metabolize organic matter in the wastewater, breaking it down into carbon dioxide, water, and additional microbial biomass.

The oxygen facilitates the efficient breakdown of organic compounds and the removal of nutrients like nitrogen and phosphorus. The aerobic process is particularly effective in treating wastewater with high organic loads, as it promotes rapid degradation and produces a high-quality effluent.

What is anaerobic wastewater treatment?

On the other hand, the anaerobic process operates in the absence of oxygen. This process relies on anaerobic microorganisms, such as bacteria and archaea, that can thrive in low or zero-oxygen conditions.

The absence of oxygen creates an environment where different microbial communities can decompose organic matter through a process called anaerobic digestion.

In anaerobic treatment systems, such as anaerobic digesters or septic tanks, the microorganisms break down organic compounds in the wastewater, producing biogas (mainly methane and carbon dioxide) as a byproduct.

The anaerobic process is particularly effective in treating wastewater with high concentrations of solid organic matter that gets reduced via the digestion process and transformed into the gas. Examples could be sewage sludge or industrial wastewaters. It also has the advantage of producing biogas, which can be utilized as an energy source.

Aerobic versus anaerobic wastewater treatment overview: Which process is more effective?

The following chart explains the main differences between these two treatment processes:

While both processes aim to treat wastewater, they differ in several aspects. Oxygen availability is the primary distinguishing factor. The aerobic process requires a constant supply of oxygen, which can be achieved through mechanical aeration or natural processes like trickling filters.

In contrast, the anaerobic process occurs in the absence of oxygen, and oxygen should be minimized or eliminated from the treatment system.

Additionally, the byproducts of each process differ. The aerobic process produces carbon dioxide and water as end products, whereas the anaerobic process generates biogas (methane and carbon dioxide), which can be harnessed as an energy source.

The choice between aerobic and anaerobic processes depends on various factors, including the characteristics of the wastewater to be treated, treatment goals, and available resources.

Which process is better: aerobic or anaerobic digestion in the wastewater treatment?

Both processes have their strengths and applications, and they can even be combined in certain wastewater treatment scenarios to optimize treatment efficiency and energy recovery.

The effectiveness of the aerobic or anaerobic process in wastewater treatment depends on several factors, including the specific wastewater characteristics, treatment goals, and operational considerations.

The aerobic process is generally more effective in removing wastewater with high organic loads. The presence of oxygen allows aerobic microorganisms to efficiently metabolize organic compounds, leading to rapid degradation and the production of a high-quality effluent.

The aerobic process is effective in reducing biochemical oxygen demand (BOD), which is a measure of the organic material present in wastewater. It is also efficient in removing nutrients like nitrogen and phosphorus.

Additionally, aerobic processes are well-suited for treating wastewater with fluctuating loads or intermittent operation, as they can quickly respond to changes in organic loads.

On the other hand, the anaerobic process is highly effective in treating wastewater with high concentrations of organic matter. Anaerobic microorganisms in the absence of oxygen can break down organic compounds through anaerobic digestion, resulting in the production of biogas as a valuable byproduct.

Anaerobic treatment systems are particularly useful for treating sewage sludge or industrial wastewater that have high organic content. The anaerobic process has the advantage of energy recovery through the utilization of biogas, making it a more sustainable option in certain applications.

Treatment system designers and operators consider the specific wastewater composition, treatment objectives, available resources, and site-specific conditions to determine the most effective approach.

In some cases, a combination of both aerobic and anaerobic processes may be used in a treatment train to achieve optimal results. The selection of the most effective process is a case-by-case evaluation that takes into account the specific requirements and constraints of the wastewater treatment scenario.

Why anaerobic wastewater treatment is often preferred as compared to other processes?

Anaerobic wastewater treatment is preferred in certain scenarios due to several advantages it offers over other processes.

Here are some reasons why anaerobic method is often chosen:

Organic matter removal: Anaerobic processes are highly effective in removing organic matter from wastewater. The anaerobic microorganisms present in these systems can break down complex organic compounds, such as sewage sludge or high-strength industrial wastewaters, into simpler components through anaerobic digestion.

Biogas production and energy recovery: One significant advantage of anaerobic wastewater treatment is the production of biogas as a byproduct. The anaerobic digestion generates biogas, mainly composed of methane and carbon dioxide.

Biogas can be captured and utilized as an energy source for various purposes, such as electricity generation, heat production, or fuel for vehicles. This energy recovery aspect makes anaerobic treatment more sustainable and economically beneficial.

Lower energy requirements: Compared to aerobic processes that require continuous aeration to supply oxygen, anaerobic treatment systems have lower energy requirements.

Since anaerobic microorganisms can function in the absence of oxygen, there is no need for energy-intensive aeration equipment. This results in reduced energy consumption and operational costs, making anaerobic treatment an attractive option, especially in situations where energy efficiency is a priority.

Sludge reduction: Anaerobic treatment typically results in lower sludge production compared to aerobic processes. This is because anaerobic microorganisms convert a significant portion of the organic matter into biogas and microbial biomass.

As a result, the amount of residual sludge generated in anaerobic treatment is reduced, which can lead to cost savings in terms of sludge handling, disposal, and associated environmental impacts.

Anaerobic treatment has been in use for a long period of time to a satisfactory level. One of the most attractive benefits is that the process is simply more economically friendly, as the input of energy is low and the amount of remaining sludge is lower, which further reduces operating costs. 

In developed countries, both anaerobic and aerobic treatment processes are often involved in municipal wastewater treatment. In developing countries, however, only basic treatment of wastewater typically occurs today, utilizing aerobic processes without the digestion of sludge or anaerobic processes that do not include post-treatment of wastewater.