Ammonia vs Ammonium：What is the Difference?

When discussing water quality, ammonia and ammonium are two terms that cannot be ignored. Although they both contain nitrogen, they in fact exhibit completely different characteristics in water and consequently have vastly different effects on the aquatic environment and human health. Therefore, a thorough understanding of the differences between the two can help us better monitor and improve water quality.

Ammonia or Ammonium: Key Structural Differences

The chemical formula for ammonia is NH₃. It is a neutral molecule consisting of one nitrogen atom and three hydrogen atoms, with a triangular pyramidal molecular structure.

Ammonium is NH₄⁺. It carries a positive charge and has four hydrogen atom, with a tetrahedral structure.

This structural difference directly causes them to behave differently in water.

Ammonia vs Ammonium: Water Solubility Explained

Of course. Here is the text revised with transition words to improve flow and clarity:

NH₃ is highly soluble in water, although its solubility decreases as the temperature rises. In this aqueous environment, it mainly exists in a free state, while a small portion undergoes weak reactions with water.

In contrast, NH₄⁺ is in an ionic state and is therefore more stable. As a result, it easily combines with other anions in water to form various ammonium salts.

It is important to note that the two can be converted into each other in water, and pH is the key influencing factor in this equilibrium.

Effect of pH on NH₃/NH₄⁺ Ratio

Related Reactions

Ammonia vs Ammonium: Aquatic Toxicity Differences

NH₃ is extremely toxic to aquatic organisms such as fish and shrimp. Even at very low concentrations, it can damage their gill tissue and impair respiratory function.

NH₄⁺ has relatively low toxicity. At normal concentrations, it can even be absorbed and utilized by aquatic plants as a nutrient source.

Many aquaculture accidents are associated with sudden increases in ammonia concentrations in water.

Differences in detection methods

Tranditionally detecting NH₃ usually requires the use of special reagents, which are used to determine the concentration through a color reaction with the reagent.

NH₄⁺ can be detected using ion-selective electrode methods to directly measure its ion concentration.

In actual detection, it is often necessary to measure the total amount of both substances and then combine the pH value to analyze their respective proportions.

How to choose Ammonia sensor for water？

Selecting a suitable ammonia sensor for water is essential to ensure accurate and reliable water quality monitoring. To address this, distinct specifications in measurement range, accuracy, and functionality are required across various application scenarios. The following section provides a detailed breakdown of selection criteria for four common uses, with emphasis placed on key technical considerations.

 Ammonia Sensor in Water for Wastewater Treatment

Typical range: 0-500 ppm or higher.
An effective ammonia water sensor for wastewater must offer a wide measurement range, robust anti-interference capability, and high durability. Choose electrochemical sensors with IP68-rated protection and automatic cleaning functions to handle high-turbidity conditions. Output signals such as MODBUS protocol enable smooth integration into PLC systems.

Ammonia Sensor for Water in Drinking Water Treatment

Typical range: 0-10 ppm.
For drinking water applications, precision and safety are paramount. An ammonia sensor in water here should be optical-based, deliver accuracy within ±1% F.S., and include automatic temperature compensation. Certifications for drinking water safety must be obtained to eliminate risks of secondary contamination.

Ammonia Water Sensor for Watershed Monitoring

Typical range: 0-100 ppm.
Watershed and environmental monitoring demand sensors that perform reliably in outdoor settings. A suitable ammonia sensor for water in this context should be low-power, use semiconductor technology, and be equipped with solar power support. An IP67 (or higher) protection rating and wireless telemetry for real-time data transmission are critical for continuous field operation.

 Ammonia Sensor in Water for Aquaculture

Typical range: 0-5 ppm.
In aquaculture, high sensitivity and rapid response are vital. The ideal ammonia water sensor should be electrochemical, with a response time under 20 seconds, and feature visual/audible alarm capabilities. Additionally, corrosion-resistant and anti-biofouling designs ensure longevity in aquatic environments.

Removal methods in water treatment

A common method for removing NH₃ from water is aeration. This process introduces air into the water, allowing the NH₃ to escape as a gas.

For NH₄⁺, engineers often use ion exchange. In this method, a special resin adsorbs the ammonium ions from the water, effectively removing them.

Biological treatment offers another effective approach. Microorganisms metabolize both substances, converting them into harmless compounds and reducing their overall concentration.

Relevance to human health​

Long-term consumption of water with high NH₃ concentrations irritates the respiratory and digestive tracts.
Furthermore, while NH₄⁺ causes little direct harm to humans, it often indicates agricultural pollution in water sources. This signal should prompt additional testing for other contaminants.
Ultimately, water treatment plants must control both substances to ensure drinking water safety throughout the treatment process.