The use of air cleaning systems to reduce ammonia emissions from animal houses is increasing. These systems are normally used in order to comply with local or national regulations of ammonia emission. Therefore, accurate determination of the proportion of ammonia being removed by these systems is crucial. There are two main methods available to measure ammonia removal efficiency of scrubbers: air balance (based on the measurement of ammonia concentrations in air) and combined water-air balance (in which it is also necessary to determine the amount of nitrogen recovered in the liquid phase). The first method is simpler to establish, while the second method might provide deeper information about the processes occurring. The main aim of this work was to assess, in terms of the variability of the results, the use of these two methods to evaluate the efficiency of an acid packed bed scrubber on a pig farm. An acid packed bed scrubber (70% NH3 removal) was monitored during ten complete 24 h cycles for ammonia concentrations, airflow rates, and nitrogen accumulation in the acid solution basin. The average efficiency calculated using the air balance method was 71% (Â±4%), close to the design value of 70%, while the average efficiency when using the combined water-air balance method was 255% (Â±53%). The accumulation and precipitation of ammonium salts in the packing material seem to be the main cause of the high variability and inaccuracy of the combined water-air balance method observed for this type of scrubber. According to these results, it is recommended to use the air balance method when determining the ammonia removal efficiency for acid packed bed scrubbers similar to the one studied here. According to the variability of the results observed in this work, at least 24 measurement days are needed in order to keep the relative error below 5% when using the air balance method to determine the ammonia removal efficiency of an acid packed bed scrubber
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