Ammonia Removal - Aquaculture Engineering

Ammonia Removal

Introduction

In aquaculture it is often necessary to reduce the concentration of ammonia in the water, because it is toxic for the fish.  It is particularly important when re-using water or when trans-porting fish long distances without changing the water, since the fish produce ammonium com-pounds as a metabolic waste product.

In water there is an equilibrium between the concentrations of ammonium ion (NH₄⁺) and ammonia (NH₃) (Fig. 9.1):

NH₃+ H⁺⇔ NH₄⁺

This equilibrium depends on pH. The sum of NH₃ and NH₄⁺ is known as the total ammonia nitrogen (TAN). Because of the equilibrium between NH₃ and NH₄⁺, reducing one of them automatically reduces the other. NH₃ is the more toxic substance for fish, and therefore is the substance of interest.