Long-term effective remediation of black-odorous water via regulating calcium nitrate sustained-release

Nitrate addition is reported as a cost-effective method for remediating black-odorous water, which is mainly induced by the deficiency of electron acceptor. However, excessive release of nitrate and lack of long-term effectiveness significantly limited the application of direct nitrate dosing technology. Herein, for remediating black-odorous water, we constructed a nitrate sustained-release ecological concrete (ecoN-concrete), in which calcium nitrate (Ca(NO 3 ) 2 ) was dosed into concrete block to regulate the release of nitrate. The results showed that chemical oxygen demand (COD), turbidity, ammonia, phosphate, and sulfate were significantly removed in an ecoN-concrete-contained reactor fed with black-odorous water, and its removal efficiency was largely dependent on Ca(NO 3 ) 2 dosage. Meanwhile, the released nitrate was lower than 25% of its total dosage and nitrite was lower than 1.5 mg/L during 14 days remediation. After three recycles, the removal efficiencies of COD and turbidity by using ecoN-concrete were still more than 85%, indicating an excellent nitrate sustained-release performance of ecoN-concrete, which can be applied for preventing water re-blackening and re-stinking. Further investigation illustrated that the ecoN-concrete (1) decreased the abundance of Desulfovibrio , Desulfomonile , and Desulforhabdus in the phylum of Desulfobacterota to alleviate the odorous gas production and (2) significantly increased the abundance of Bacillus and Thermomonas , which utilized the released-nitrate for consuming organic matters and ammonia. This study provided an artful Ca(NO 3 ) 2 dosing strategy and long-term effective method for black-odorous water remediation. Graphical Abstract