New biological treatment method of domestic wastewater with simultaneous nitrification and denitrification based on detached biofilm

Abstract

The paper relates to the treatment of municipal wastewater by intensifying simultaneous nitrification and denitrification processes. The obtained results can be applied to the construction of new treatment plants as well as the upgrading of existing facilities to enhance the nitrogen removal efficiency from treated water. The developed method and corresponding installation leverage the potential of floating biofilm within activated sludge systems to initiate and sustain simultaneous nitrification and denitrification processes throughout the entire volume of the biological reactor. The floating biological film is obtained and supplied in the technological flow based on periodic aeration of the submerged biofilter compartment located in the post-aeration zone with a periodicity shorter than the residence time in the biological reactor. Nitrification achieves an efficiency of up to 99.3%. Simultaneously, denitrification occurs with an efficiency ranging from 19.9 to 91.1%, which is fundamentally correlated with the temperatures of the treated wastewater. The presence of microorganism conglomerates in the activated sludge, based on detached biofilm through an innovative method, initiates and enhances the denitrification process during continuous aeration, due to the functioning of the biological film formed by these conglomerates. Denitrification has been observed both in terms of substrate consumption of the available substrate (COD) in the aeration compartment and as a result of substrate consumption within the conglomerates formed by bacterial lysis in the anaerobic interfloccular zone, without an external carbon substrate. The denitrification process has been evaluated by analyzing the consumption of available substrate (COD) in the aeration compartments and the substrate consumption from within cocoons of microorganism conglomerates, which are formed through bacterial lysis in the anaerobic interflocular zone. This process becomes more prominent in compartments where there is a deficiency of carbon sources (COD_Cr) in the wastewater, especially at temperatures of 17.6 °C and 20.4 °C. The developed method and corresponding installation were implemented on a wastewater treatment line at the Causeni city Wastewater Treatment Plant (Republic of Moldova).