Simultaneous nitritation-denitritation for the treatment of high-strength nitrogen in hypersaline wastewater by aerobic granular sludge

Fish processing industries produce wastewater containing high amount of salt, organic matter and nitrogen. Biological treatment of such wastewaters could be problematic due to inhibitory effects exerted by high salinity level. In detail, as is known, high salt concentration leads to accumulation of nitrite due to inhibition of nitrite-oxidizing bacteria. The feasibility of performing simultaneous nitritation and denitritation in treating of fish canning wastewater by aerobic granular sludge was evaluated, and simultaneous nitritation-denitritation was successfully sustained up to 50 gNaCl L-1. Nitritation collapsed above which nitritation, and the only nitrogen removal mechanism was represented by heterotrophic synthesis. Conversely, organic matter removal was not affected by salinity, but rather by organic loading rate (OLR). COD fractionation analysis highlighted that aerobic granules exhibited excellent removal capacity toward particulate organic matter. Finally, results obtained in this work pointed out that aerobic granular sludge had excellent ability of adapting in adverse environmental conditions.