Effects of Na+/H2O2 on nitrogen removal and sludge activity: Performance and mechanism

Abstract

A large amount of wastewater containing Na+ and H2O2 was generated in the pharmaceutical, food and dyeing industries. After entering sewage treatment plant, they could interfere with the growth and metabolism of microorganisms. However, the effects of coexisting Na+/H2O2 on nitrogen removal and sludge flocculation were unclear. In this study, the effects of Na+/H2O2 on removal efficiencies of pollutants and sludge activity were investigated using sequencing batch reactor. The composition and structure of extracellular polymer substance (EPS) were analyzed, and the influencing mechanisms of Na+/H2O2 on the activated sludge were revealed. The results showed that when concentration ratio of Na+/H2O2 was 30, removal efficiencies of COD and TN were the highest values of 96 % and 68 %, ARE, NAR and SAOR were 56.9 %, 35.3 % and 24.08 mg N/(mg MLVSS·h), respectively. The level of oxidative stress was the lowest, and ROS and MDA were 30.78 % and 32.65 %, respectively. Zeta potential, particle size and flocculation capacity of the sludge reached the highest values of -4.1283 mV, 48.73 μm and 8.92 %, respectively. Na+ promoted the decomposition of H2O2, and ·OH, ·O2- and 1O2 produced improved denitrification rate. However, removal efficiencies of pollutants and sludge activity were decreased when Na+/H2O2 concentration ratio was higher and lower than 30. The coexisting Na+/H2O2 could promote the production of EPS and improve fluorescence intensity of protein and humic acids, but main components and functional groups of EPS were not changed. Therefore, removal efficiencies of pollutants and sludge flocculation could be improved by regulating influent concentration ratio of Na+/H2O2.