The Efficiency and Mechanisms of Granular Activated Carbon for the Removal of Nitrosodimethylamine and Its Precursors in Reclaimed Water

Abstract

Abstract During the potable reuse of reclaimed water, nitrosodimethylamine (NDMA), as a highly carcinogenic disinfection by-product (DBP), requires critical control. In this study, copper-doped nano zero-valent iron supported on granular activated carbon (nZVI-Cu@GAC) was synthesized via an impregnation-chemical liquid-phase reduction method. Column filtration experiments were performed to evaluate the effects of Cu/Fe loading ratios (0, 5, 10% by weight) and filtration velocities (0.5, 1.0, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" alttext="2.0 normal m divided by normal h" display="inline" overflow="scroll"> <mml:mn>2.0</mml:mn> <mml:mtext> </mml:mtext> <mml:mi mathvariant="normal">m</mml:mi> <mml:mo stretchy="false">/</mml:mo> <mml:mi mathvariant="normal">h</mml:mi> </mml:math> ). Coupled with high-resolution mass spectrometry for degradation pathway identification, this study aimed to explore the removal efficiency and mechanism of nitrosodimethylamine and its typical precursor, dimethylamine (DMA), in reclaimed water. The results showed that after chloramine disinfection, the nitrosodimethylamine concentration in reclaimed water reached <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" alttext="158.4 n g divided by normal upper L" display="inline" overflow="scroll"> <mml:mn>158.4</mml:mn> <mml:mtext> </mml:mtext> <mml:mi>ng</mml:mi> <mml:mo stretchy="false">/</mml:mo> <mml:mi mathvariant="normal">L</mml:mi> </mml:math> , primarily generated from hydrophilic nitrogen-containing organic matter with a molecular weight <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" alttext="1 k upper D a" display="inline" overflow="scroll"> <mml:mn>1</mml:mn> <mml:mtext> </mml:mtext> <mml:mi>kDa</mml:mi> </mml:math> . The removal rate of NDMA by nZVI-Cu@GAC first increased and then decreased with increasing Cu/Fe ratio, reaching the maximum efficiency at 5% by weight. When the Cu/Fe loading ratio increased from 0 to 5% by weight, the removal efficiency of NDMA rose initially from 19.4% to 29.3%. As the Cu/Fe loading ratio was further increased to 10% by weight, the removal efficiency of nitrosodimethylamine decreased to 22.4%. Decreasing the filtration velocity significantly enhanced the removal rate, with the best performance at <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" alttext="0.5 normal m divided by normal h" display="inline" overflow="scroll"> <mml:mn>0.5</mml:mn> <mml:mtext> </mml:mtext> <mml:mi mathvariant="normal">m</mml:mi> <mml:mo stretchy="false">/</mml:mo> <mml:mi mathvariant="normal">h</mml:mi> </mml:math> . Mechanistically, nZVI-Cu@GAC achieved the stepwise degradation of nitrosodimethylamine into intermediates (e.g., unsymmetrical dimethylhydrazine (UDMH) and dimethylamine) via the synergistic effects of GAC adsorption, nZVI-mediated chemical reduction, and nZVI-Cu microelectrolysis. These intermediates were ultimately converted into inorganic ions (e.g., ammonium and nitrate) and low-molecular-weight organic acids [e.g., formic acid (FA)]. In conclusion, this material provides an effective control approach for N-nitrosamines (NAs) pollutants in reclaimed water.