What Is the Role of Bacteria in Sewage Treatment?

Sewage treatment plays a pivotal role in protecting public health, preserving ecosystems, and sustaining water resources. Every day, vast volumes of wastewater are produced from homes, industries, and commercial establishments. Treating this sewage effectively ensures that only safe, clean water is discharged into the environment. At the heart of this entire process lies an invisible workforce—bacteria. These microscopic organisms are the true heroes of sewage treatment, breaking down pollutants and transforming waste into clean water and energy.

As a leading sewage treatment plant manufacturer, 3D Aqua integrates advanced biological processes into every system it designs. Their approach leverages natural microbial activity, reducing the need for energy-intensive or chemical-heavy methods. Let’s explore the critical role bacteria play in sewage treatment and how modern plants are designed to support their activity.

Understanding Biological Sewage Treatment

Biological sewage treatment refers to the use of living microorganisms to decompose organic and inorganic substances in wastewater. It forms the core of secondary treatment, the stage after physical separation processes like screening and sedimentation. Through metabolic activity, bacteria convert complex waste into simpler, stable end products such as carbon dioxide, water, nitrogen gas, and biomass (sludge).

Key benefits of biological treatment include:

• High pollutant removal efficiency
• Lower operational cost compared to chemical treatment
• Environmentally sustainable byproducts (e.g., biogas, biosolids)

Let’s break down the types of bacteria and the processes they power.

Types of Bacteria Involved in Sewage Treatment

Different bacteria are responsible for different biochemical processes in wastewater treatment. These include:

1. Aerobic Bacteria

• Require oxygen to survive and thrive.
• Break down organic matter into carbon dioxide, water, and biomass.
• Most commonly used in conventional sewage treatment systems.

2. Anaerobic Bacteria

• Live in oxygen-free environments.
• Convert organic matter into methane, carbon dioxide, and other gases.
• Commonly used in sludge digesters and high-strength waste treatment.

3. Facultative Bacteria

• Can switch between aerobic and anaerobic modes depending on environmental conditions.
• Useful in lagoon systems and integrated wastewater treatment technologies.

Key Biological Processes in Sewage Treatment

1. Activated Sludge Process (ASP)

This is the most widely used biological treatment process globally. It involves maintaining a high concentration of aerobic bacteria in a tank, called an aeration basin, where sewage is mixed with microorganisms and oxygen.

a. Aeration Tank Function

• Air is pumped into the tank to provide oxygen for aerobic microbes.
• Bacteria digest organic pollutants, forming suspended flocs.
• These flocs contain living microorganisms and absorbed waste particles.

b. Secondary Clarifier

• The mixture flows into a sedimentation tank.
• The biomass (activated sludge) settles to the bottom.
• A portion of the sludge is recycled to the aeration tank to maintain microbial population, and the rest is removed as excess sludge.

c. Sludge Age Control

• Operators manage the mean cell residence time (MCRT) or “sludge age”.
• This controls the population dynamics and ensures the microbial community remains active and diverse.

Benefits of ASP include high BOD removal, adaptability to various loads, and suitability for urban and industrial sewage.

2. Biofilm-Based Systems

Instead of remaining suspended in water, bacteria in these systems grow on surfaces—called media—forming a biofilm. These systems offer compact designs and resilience to load variations.

a. Trickling Filters

• Contain beds of stones or synthetic media.
• Sewage trickles over the media, forming a microbial layer that breaks down pollutants.
• Simple, low-maintenance, and effective for small communities or industrial units.

b. Moving Bed Biofilm Reactors (MBBR)

• Use free-floating plastic carriers inside an aeration tank.
• Bacteria colonize these carriers, forming biofilms.
• Carriers are constantly mixed to ensure contact between sewage and microbes.

c. Integrated Fixed-Film Activated Sludge (IFAS)

• Combines suspended and attached microbial growth.
• Offers high efficiency in a compact footprint.
• Suitable for upgrades to overloaded plants.

Biofilm systems are less sensitive to toxic shocks and work well under fluctuating conditions.

3. Anaerobic Digestion

Anaerobic bacteria are utilized to treat sewage sludge or highly concentrated industrial wastewater. They break down organic matter in the absence of oxygen, producing biogas—a mix of methane and carbon dioxide—that can be captured and used as renewable energy.

a. Stages of Anaerobic Digestion

• Hydrolysis: Large molecules like fats, proteins, and carbohydrates are broken into smaller compounds.
• Acidogenesis: These compounds are converted into volatile fatty acids, ammonia, hydrogen, and carbon dioxide.
• Acetogenesis: Volatile fatty acids are converted into acetic acid, hydrogen, and CO₂.
• Methanogenesis: Methanogenic bacteria convert acetic acid and hydrogen into methane (CH₄) and CO₂.

b. Digestate Management

• The leftover material, called digestate, is rich in nutrients.
• It can be dewatered and used as fertilizer or safely disposed of.

This method not only treats waste but also contributes to energy recovery, promoting sustainability in treatment plants.

Bacteria and Nutrient Removal

Bacteria don’t just remove organic matter—they also play a vital role in nutrient removal, particularly nitrogen and phosphorus.

1. Nitrogen Removal

• Nitrification: Ammonia (NH₃) is oxidized to nitrate (NO₃⁻) by nitrifying bacteria (Nitrosomonas and Nitrobacter).
• Denitrification: Under anoxic conditions, denitrifying bacteria convert nitrate to nitrogen gas (N₂), which is released into the air.

This process protects rivers and lakes from eutrophication, where excess nitrogen causes algal blooms that deplete oxygen.

2. Phosphorus Removal

• Certain bacteria known as polyphosphate accumulating organisms (PAOs) absorb phosphorus in large quantities.
• In Enhanced Biological Phosphorus Removal (EBPR) systems, these microbes help reduce phosphorus levels without chemicals.

Supporting Bacterial Activity: Environmental Conditions

To keep bacteria active and effective, sewage treatment plants must control several environmental factors:

1. Dissolved Oxygen (DO)

• Essential for aerobic processes.
• Typically maintained at 2–4 mg/L in aeration tanks.

2. pH

• Most bacteria thrive between pH 6.5 and 8.5.
• Sudden pH shifts can kill microbial populations.

3. Temperature

• Ideal range: 20–35°C for mesophilic bacteria.
• Higher temperatures accelerate metabolism but may also reduce oxygen solubility.

4. Nutrient Balance

• Bacteria require nitrogen and phosphorus in proper ratios to function efficiently.
• Typical BOD:N:P ratio is 100:5:1.

Challenges in Biological Treatment

Despite their benefits, bacterial treatment systems face several challenges:

• Toxic Loads: Heavy metals, solvents, and disinfectants can inhibit or kill bacteria.
• Shock Loads: Sudden increases in organic or hydraulic load can destabilize microbial communities.
• Foaming or Bulking Sludge: Caused by filamentous bacteria or poor sludge settling.

Advanced monitoring systems and skilled operators are key to managing these issues.

Innovations and Future of Bacterial Treatment

Modern sewage treatment is increasingly focused on optimizing bacterial processes for:

• Resource Recovery: Producing energy (biogas), water reuse, and biosolids.
• Automation and AI: Sensors monitor microbial performance in real-time.
• Bioaugmentation: Adding specialized bacteria to enhance treatment.

Technologies such as membrane bioreactors (MBR) and sequencing batch reactors (SBR) are integrating bacterial treatment with automation and filtration, delivering compact and highly efficient treatment systems.

Conclusion

From breaking down organic waste to recovering nutrients and energy, bacteria are the backbone of sewage treatment. Their role is central in transforming polluted water into a clean and usable resource. Treatment systems designed by companies like 3D Aqua leverage this biological power to build eco-friendly, cost-effective, and high-performance sewage solutions.

Whether you’re planning a new facility or upgrading an existing plant, understanding and harnessing bacterial processes is crucial. 3D Aqua brings decades of experience in deploying microbial treatment systems that are both innovative and reliable.

Contact 3D Aqua Today

To learn more about how bacteria-based sewage treatment can benefit your community or industry, reach out to 3D Aqua for a custom consultation:

• Phone: +91-6262629090
• Email: info@3daqua.in
• Website: www.3daqua.in

Harness the natural power of bacteria with 3D Aqua’s trusted sewage treatment solutions.