Wastewater treatment is an essential process for urban and industrial communities, especially when it comes to removing nitrogen compounds. Nitrogen in wastewater, primarily in the form of ammonia, nitrite, and nitrate, can cause severe environmental damage if not properly treated. High nitrogen discharge into rivers, lakes, and coastal waters leads to eutrophication, fish kills, and unsafe drinking water sources. To tackle these challenges, sewage treatment plants (STPs) have traditionally relied on conventional nitrification-denitrification methods. However, these systems require large amounts of energy, chemicals, and space.
A breakthrough process known as Anammox (Anaerobic Ammonium Oxidation) is now transforming the way STPs remove nitrogen. This biological pathway uses special bacteria to directly convert ammonia and nitrite into nitrogen gas, without requiring organic carbon or high oxygen input. This makes Anammox not only cost-effective but also environmentally sustainable.
In this article, we’ll explore how Anammox works, its benefits, reactor designs, operational challenges, monitoring needs, and its future in wastewater management.
What is Anammox Nitrogen Removal?
Anammox stands for anaerobic ammonium oxidation. It is a microbial process where specific bacteria oxidize ammonia (NH₄⁺) using nitrite (NO₂⁻) as an electron acceptor, producing nitrogen gas (N₂) and a small amount of nitrate (NO₃⁻).
This biological shortcut eliminates the need for conventional two-step processes:
- Nitrification – Oxidizing ammonia into nitrate through aerobic bacteria, which requires large oxygen supply.
- Denitrification – Reducing nitrate to nitrogen gas using organic carbon, which often needs external carbon sources like methanol.
With Anammox, both steps are bypassed, saving oxygen, energy, and chemicals.
👉 Chemical reaction for Anammox:
NH₄⁺ + NO₂⁻ → N₂ + 2H₂O
This simplified process provides the backbone for a sustainable nitrogen removal strategy in sewage treatment plants (STPs).
See here – Sewage Treatment Plant Manufacturer
How Does Anammox Work in STPs?
1. Process Overview
In STPs, wastewater containing ammonia undergoes partial conversion to nitrite through partial nitritation. The effluent containing ammonia and nitrite is then directed to an Anammox reactor. Here, Anammox bacteria convert these compounds into nitrogen gas, which safely escapes into the atmosphere.
2. Reactor Functioning
- Step 1: Wastewater stream with ammonia is introduced.
- Step 2: Controlled oxygen supply ensures partial conversion of ammonia to nitrite (not full nitrification).
- Step 3: Anammox bacteria use the nitrite to oxidize the remaining ammonia.
- Step 4: Nitrogen gas is released, and treated water flows out with minimal nitrogen content.
3. Characteristics of Anammox Bacteria
- Belong to the Planctomycetes group.
- Extremely slow-growing (doubling time of 10–14 days).
- Thrive in oxygen-limited conditions.
- Require careful temperature and pH control for stability.
Benefits of Anammox in Sewage Treatment Plants
The Anammox process offers several clear advantages for municipal and industrial STPs.
1. Energy Savings
- Traditional aeration requires large energy input.
- Anammox reduces oxygen demand by 60–70% because it only needs partial nitritation.
- This translates into significant electricity savings for aeration blowers.
2. Reduced Chemical Usage
- Conventional denitrification needs external organic carbon like methanol or acetate.
- Anammox does not require organic carbon, reducing operational costs.
3. Less Sludge Production
- Anammox bacteria grow slowly and generate less biomass compared to activated sludge systems.
- This lowers sludge handling, disposal, and related costs.
4. Smaller Footprint
- Compact reactor designs allow integration into existing STPs with limited space.
- Ideal for cities where land availability is a challenge.
5. Compliance with Stringent Regulations
- Helps achieve low nitrogen effluent limits as mandated by pollution control boards.
- Supports safe water reuse for irrigation, industrial cooling, and groundwater recharge.
Reactor Designs for Anammox Nitrogen Removal
Different reactor types are used to implement Anammox depending on flow rates, wastewater characteristics, and site constraints.
1. Moving Bed Biofilm Reactor (MBBR)
- Uses plastic carriers for bacteria to attach and form biofilms.
- Provides high surface area and stable performance.
- Suitable for both sidestream and mainstream applications.
2. Granular Sludge Reactors
- Encourage formation of dense microbial granules.
- High settling ability and compact design.
- Allows higher biomass concentration, making them efficient for nitrogen removal.
3. Sequencing Batch Reactors (SBRs)
- Operates in cycles of filling, reacting, settling, and decanting.
- Flexible and easy to control for variable loads.
4. Sidestream Anammox Systems
- Treat concentrated ammonia-rich streams from sludge dewatering.
- Smaller in size, easier to control, and cost-effective.
- Often used as pilot projects before full-scale adoption.
5. Mainstream Anammox Systems
- Treats the main sewage flow directly.
- More challenging due to lower temperatures and fluctuating loads.
- Emerging as a future-ready solution for municipal STPs.
Implementation in STP Plants
1. Retrofitting Existing Plants
- Old aeration tanks can be modified to host Anammox biofilms.
- Ideal for plants facing nitrogen compliance challenges.
2. Side Stream Applications
- Treats sludge liquor, which has high ammonia concentration.
- Helps reduce overall nitrogen load before mainstream treatment.
3. Full Scale Mainstream Application
- Requires advanced control systems for stable operation.
- Currently being adopted in Europe and Asia, with promising results.
Operational Challenges of Anammox
Despite its advantages, Anammox comes with some operational challenges.
- Slow Growth of Bacteria
- Requires long start-up time (weeks to months).
- Seeding with enriched biomass can accelerate start-up.
- Process Sensitivity
- Sensitive to oxygen intrusion, temperature changes, and toxic compounds.
- Requires tight monitoring of dissolved oxygen and pH.
- Maintaining Nitrite-Ammonia Balance
- Imbalanced feeds can reduce efficiency or wash out bacteria.
- Cold Climate Limitations
- Activity reduces at temperatures below 15°C, requiring insulation or heating.
Monitoring and Process Control
1. Routine Sampling and Testing
- Ammonia, nitrite, nitrate, and alkalinity levels must be monitored daily.
- Indicator organisms can confirm bacterial activity.
2. Online Sensors
- Dissolved oxygen, oxidation-reduction potential (ORP), and pH probes provide real-time control.
3. Molecular Monitoring
- DNA-based tools confirm the presence and stability of Anammox bacteria.
- Helps predict performance drops before they occur.
Case Studies of Anammox in Action
- Europe: Several full-scale municipal STPs in the Netherlands and Germany have adopted Anammox in sidestream reactors, reporting 40% operational cost savings.
- Asia: Pilot-scale projects in China and India have demonstrated successful mainstream Anammox treatment, showing potential for large urban deployments.
- Industrial Use: Food and beverage industries use Anammox for high-strength wastewater treatment, reducing nitrogen loads at lower costs.
Future of Anammox in India
With rising urban populations and strict CPCB (Central Pollution Control Board) norms for nitrogen discharge, Indian STPs are under pressure to upgrade. Anammox offers a sustainable pathway to:
- Meet zero liquid discharge (ZLD) requirements.
- Reduce dependency on energy-intensive aeration.
- Enable treated water reuse for industries and agriculture.
3D AQUA, a leading wastewater treatment company in India, is actively working on integrating Anammox-based systems into STPs, offering consultancy, design, and retrofitting services.
Conclusion
Anammox Nitrogen Removal represents a paradigm shift in wastewater treatment technology. By directly converting ammonia and nitrite into nitrogen gas, it reduces oxygen demand, eliminates the need for external carbon, minimizes sludge production, and saves operational costs. Although challenges like slow bacterial growth and process sensitivity remain, advancements in reactor design and monitoring tools are making Anammox a reliable and scalable solution for STPs worldwide.
For Indian cities struggling with rising wastewater volumes and stringent nitrogen limits, Anammox offers a practical, future-ready, and eco-friendly approach.
📞 Contact 3D AQUA for Anammox STP Solutions
- Phone: +91-6262629090
- Email: info@3daqua.in
Whether you need retrofitting of your existing plant, pilot testing, or full-scale STP design, our team of experts can help you implement Anammox successfully and ensure compliance with all regulatory standards.
Discover more from 3D Aqua
Subscribe to get the latest posts sent to your email.