Ammonia nitrogen removal in a biological nitrifying system using oyster shells as alkalinity-releasing filling materials

Abstract. The rapid development of shellfish aquaculture produces a large amount of solid waste - shells. In this study, oyster shells (OS) were used as an active filling in a biological nitrifying system treating synthetic wastewater containing ammonia nitrogen with an inoculated sludge concentration of 4 g/L in terms of mixed liquor suspended solids (MLSS). A biological nitrifying system with no OS was operated in parallel as a control. Results showed that OS could enhance the nitrification process by maintaining pH, and the nitrification efficiency could be positively correlated with the mass of OS. In addition, the results from the Fourier transform infrared spectroscopy (FTIR) suggested that the calcium carbonate in OS played an important role for maintaining pH in the nitrifying system. Results from this study showed a good potential of the waste oyster shells as biological filter medium for nitrification and provided a new method for shells disposal and reuse.