Feasibility and optimization of a novel upflow denitrification reactor using denitrifying granular sludge for nitric...

Stainless steel is highly valued for its superior resistance to corrosion. However, the pickling process involved in stainless steel production generates abundant NO3--N, causing health and environmental risks. To address this issue, this study proposed a novel solution utilizing an up-flow denitrification reactor and denitrifying granular sludge for treating NO3--N pickling wastewater under high NO3--N loading. It was found that, the denitrifying granular sludge exhibited stable denitrification performance with the highest denitrification rate of 2.79 gN/(gVSS·d) and average removal rates of NO3--N and TN of 99.94% and 99.31%, respectively, under optimal operating conditions of pH 6-9, temperature 35 °C, C/N ratio 3.5, hydraulic retention time (HRT) 11.1 h and ascending flow rate 2.75 m/h. This process reduced carbon source usage by 12.5-41.7% as compared to traditional denitrification methods. These findings demonstrate the efficacy of combining granular sludge and an up-flow denitrification reactor for treating nitric acid pickling wastewater.