Pilot-scale field study for ammonia removal from lagoon biogas using an acid wet scrubber

The anaerobic activities in swine slurry storage generate biogas, and this process releases certain amounts of gaseous ammonia to the atmosphere, which is a chemical agent that can cause adverse environmental impacts. This pilot scale study was aimed to trap the ammonia in biogas with a covered lagoon and subsequently absorb ammonia through a sulfuric acid wet scrubber. The data showed that, on average, the biogas contained 43.7 ppm of ammonia and its concentration was found to be exponentially related to the air temperature inside the lagoon; but when the air temperature rose to 35 °C and the biogas ammonia concentration reached 90 ppm, the mass transfer of ammonium/ammonia from the deeper liquid body to the interface between the air and liquid became a limiting factor. The biogas velocity was found to be critical in affecting ammonia removal efficiency of the wet scrubber. A biogas flow velocity controlled within 8 to 12 mm/s was recommended to achieve a removal efficiency of greater than 60%. Stepwise regression revealed that the biogas velocity and air temperature, not the inlet ammonia concentration in biogas, significantly impacted the ammonia removal efficiency. Overall, when 73 g/L (or 0.75 M) sulfuric acid solution was used as the scrubber solution, removal efficiencies, varied from 0-100% with an average of 54.9%, were achieved in a 40-d measurement period. Mass balance calculation based on liquid or biogas showed that about 21.3 or 21.76 g of ammonia was collected in the scrubber solution from a total volume of 1169 m³ of biogas, while the scrubber solution still maintained its ammonia absorbing ability until its concentration reaches 1 M. These results showed promising perspective for using sulfuric acid wet scrubber for ammonia removal in the digester biogas.