| Summary: | It is emphasized that a generalized relationship can be used to predict the ionic nitrogen concentration (i.e., sum of ammonium NH<sub>4</sub><sup>+</sup>, nitrite NO<sub>2</sub><sup>−</sup> and nitrate NO<sub>3</sub><sup>−</sup>) of the scrubbing liquid in a biotrickling filter treating ammonia emissions by measuring the electrical conductivity (EC) of the water directly. From measurements carried out on different water samples from six biotrickling filters in operation in pig husbandries, the generalized relationship is: Σ([NH<sub>4</sub><sup>+</sup>]+[NO<sub>2</sub><sup>−</sup>]+[NO<sub>3</sub><sup>−</sup>]) <sub>g N/L</sub> = 0.22 EC <sub>mS/cm</sub>. This equation is valid provided the fresh water feeding the biotrickling filter has a low electrical conductivity (<1 mS cm<sup>−1</sup>). Moreover, since ammonium, nitrite and nitrate ions are the ultra-majority ions in the liquid phase, the balance between NH<sub>4</sub><sup>+</sup> and (NO<sub>2</sub><sup>−</sup> + NO<sub>3</sub><sup>−</sup>) was confirmed, and consequently the relationship NH<sub>4</sub><sup>+</sup> = 0.11 EC <sub>mS/cm</sub> can also be applied to determine the ammonium concentration from the EC. As a result, EC measurement could be applied extensively to monitor operating biotrickling filters worldwide and used to determine ammonia mass transfer in real time, keeping in mind that the accuracy of the generalized relationship is ±20%.
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