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Numerical assessment of nitrogen removal from swine wastewater in activated sludge systems: Comparison between continuous and intermittent aeration

The appropriate conditions needed to achieve nitrogen (N) removal from swine wastewater (SW) in an activated sludge continuous stirred-tank reactor (+settler) were assessed by performing numerical simulations. Air supply was considered through continuous or intermittent aeration (CA vs. IA), and several values were assumed for the SW BOD5-to-N ratio. By considering CA and low dissolved oxygen (DO) levels, feasibility for peforming N removal via nitrite through simultaneous nitrification–denitrification was confirmed. Nitrogen removal via nitrite was also the case when applying IA, even at higher DO ranges. The nitrite short-cut was shown to reduce energy consumption for aeration. However, regardless of the aeration method applied, sensitive DO controls will be required, particularly when the SW BOD5-to-N ratio takes low values. This study allowed to assess the operational conditions required when biologically treating SW to meet N standards and to identify situations in which a final post-treatment is needed before effluent discharge.

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