Ammonia in Wastewater: Environmental and Operational Challenges

By Magazine Team On Jun 3, 2025 392 0

Contents

1 Understanding Ammonia in Wastewater

2 Biological Nitrification Process

3 Nitrification, Denitrification, and Anammox

4 Physicochemical Methods for Ammonia Removal

5 Common Biological Nitrification Treatment Processes

5.1 1- Conventional Activated Sludge (CAS):

5.2 2- Extended Aeration:

5.3 3- Sequencing Batch Reactor (SBR):

5.4 4- Fixed Film:

5.5 5- Membrane Bioreactor (MBR):

5.6 6- Lagoon Systems:

6 References:

Ammonia in wastewater poses significant environmental and operational challenges for treatment facilities. Its presence can lead to eutrophication in aquatic ecosystems and adversely affect marine life. Therefore, effective strategies for ammonia removal are essential for environmental protection and compliance with regulations.

Understanding Ammonia in Wastewater

Ammonia (NH₃) and its ionic form, ammonium (NH₄⁺), are commonly found in wastewater due to sources like domestic sewage, industrial effluents, and agricultural runoff. Ammonia concentrations can vary widely depending on the source and treatment techniques employed. High ammonia levels are particularly problematic as they can deplete dissolved oxygen in receiving waters, resulting in hypoxic conditions detrimental to aquatic organisms.

Biological Nitrification Process

Biological nitrification involves converting ammonia in wastewater to nitrate through aerobic autotrophic bacteria. This process consists of two stages: ammonia is oxidized to nitrite by bacteria such as Nitrosomonas, and then nitrite is oxidized to nitrate by Nitrobacter. Biological nitrification systems aim to fully convert ammonia into nitrate.

Nitrification, Denitrification, and Anammox

Active microorganisms effectively remove ammonia from wastewater by nitrification, transforming it into nitrate. Enzymes encoded by specific gene clusters facilitate the conversion of ammonium to nitrite and subsequently to nitrate. The growth rates of nitrifying and denitrifying organisms differ, affecting carbon demand in treatment systems. High salinity can hinder nitrification, although certain bacteria like Nitrosomonas marina can thrive in such environments. Partial nitrification-denitrification is a cost-effective approach, reducing aeration and carbon requirements. Anammox further enhances efficiency by lowering oxygen demand and sludge production, making it a promising method for nitrogen removal in wastewater treatment.

Physicochemical Methods for Ammonia Removal

Physicochemical processes are the most widely used techniques for ammonia removal from wastewater, offering rapid and efficient removal capabilities. However, these methods have limitations regarding operational conditions and costs, which highlight their characteristics and constraints.

Common Biological Nitrification Treatment Processes

1- Conventional Activated Sludge (CAS):

This method uses an aeration system to eliminate harmful substances from wastewater, ensuring it is safe for environmental release. CAS systems comprise an aeration tank where wastewater is mixed with oxygen, activating microorganisms that digest the waste and form flocs, enhancing the degradation of biological components.

2- Extended Aeration:

Similar to CAS, extended aeration processes include aeration basins, clarifiers, and sludge management. The key difference is the longer hydraulic and solids residence times, typically around 24 hours for hydraulic residence time and over 20 days for sludge residence time. This process facilitates effective nitrification with sufficient air supply.

3- Sequencing Batch Reactor (SBR):

In this activated sludge method, all treatment stages occur in a single tank in batches, including filling, organic matter consumption, settling, and decanting. SBR operates similarly to CAS, but all steps are conducted sequentially within the same tank.

4- Fixed Film:

Biological nitrification and BOD removal can also be achieved through fixed film processes like trickling filters, rotating biological contactors (RBCs), or moving bed bioreactors (MBBRs). Here, microorganisms are attached to fixed media, treating wastewater as it flows through the reactor.

5- Membrane Bioreactor (MBR):

MBRs combine membrane processes such as microfiltration or ultrafiltration with biological treatment methods like activated sludge. These systems are increasingly used for municipal and industrial wastewater treatment, with configurations including submerged and side-stream membrane bioreactors.

6- Lagoon Systems:

While lagoon systems primarily target BOD and total suspended solids (TSS) removal, biological nitrification can occur if hydraulic and solids residence times are adequate, along with optimal environmental conditions (temperature and oxygen). Extended hydraulic residence times of five to seven days or more, higher temperatures, and sufficient oxygen supply are crucial for promoting nitrifying bacteria growth. A mixed liquor recycle system can also be implemented to maintain biomass levels conducive to nitrification.

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References: