Nitrogen Removal from Anaerobically Digested Swine Waste Centrate Using a Laboratory-Scale Chabazite-Sequencing Batch Reactor

Anaerobic digestion (AD) is widely used for the treatment of livestock waste because the biogas produced can be utilized as energy source. Further treatment of AD effluents is often required for total nitrogen (TN) removal, which is typically carried out using biological nitrogen removal processes. However, the high free ammonia (FA) concentrations present in AD effluents can inhibit nitrification processes. This research tested a sequencing batch reactor (SBR) amended with particulate chabazite (chabazite-SBR) for removal of TN from anaerobically digested swine waste centrate. In the chabazite-SBR, zeolitic material with a high ion exchange (IX) capacity for NH4+ is used to ease nitrification inhibition. Once nitrification is complete, an external organic electron donor is supplied during an anoxic stage to promote denitrification. An overall TN removal efficiency of 84% was achieved in a laboratory-scale chabazite-SBR, with specific nitrification and denitrification rates of 0.43 and 1.49mg-N/(g-VSSh), respectively. Simultaneous nitrification-denitrification was observed in the biofilm surrounding the chabazite particles, resulting in improved TN removal and alkalinity control. TN and chemical oxygen demand (COD) removal were dependent on external organic carbon dose, with a COD/N ratio of 3.2g-COD/g-N resulting in both high TN (97%) and COD (51%) removal efficiencies. Over the 40 cycles of operation, the IX stage was able to reduce FA concentrations to below the inhibitory level for nitrification. No loss in IX efficiency was observed, and no fresh zeolite was added to the reactor. The chabazite-SBR is a promising technology for treatment of high NH4+ strength wastewaters.