Effects of nitric oxide on the phytoremediation of swine wastewater by Pistia stratiotes under copper stress

Abstract

Nitric oxide (NO) is widely present in wastewater. As a signaling molecule, NO influences many aspects of phytoremediation, especially in response to heavy metal stress. The current understanding of the impact of NO on the tolerance of Pistia stratiotes and other plants to Cu2+ in swine wastewater is limited. This study aimed to investigate the impact of NO on the physiological response of Pistia stratiotes and its efficacy in removing pollutants from swine wastewater under varying concentrations of Cu2+ ranging from 1~4 mg/L. The findings showed that NO treatment reduced copper stress at 2~4 mg/L Cu2+ while increasing oxidative stress at 1 mg/L Cu2+. According to an analysis of physiological parameters and copper concentrations, the results found a significant correlation between increased copper tolerance and elevated levels of antioxidants and transport coefficients. The morphology of copper and the results of the principal component analysis indicate that NO facilitated the humification process of the dissolved organic matter. The investigation found that the removal efficiencies of NH3–N, NO3–N, and total phosphorus in NO treatment were enhanced to 95.76%, 88.72%, and 91.89%, respectively. Collectively, it was determined that NO is a regulator of phytoremediation to copper in wastewater via promoting antioxidative, copper transport, DOM bound, nutrients uptake, thus adequate amount could improve the tolerance of Pistia stratiotes to Cu2+. This study is expected to provide a theoretical basis for rationally regulating NO concentration and effectively improving the removal efficiency of copper in swine wastewater.