Characteristics of dissolved organic matters in submerged membrane bioreactor with low-concentration Cr(VI)

Abstract

Hexavalent chromium (Cr(VI)) is a common heavy metal, but is hazardous to the environment and human body. Low concentration of Cr(VI) (0.4 mg/L) is ubiquitous in municipal wastewaters of China. However, little is known about its effects on dissolved organic matter (DOM) in submerged membrane bioreactors (MBRs). The effects of low concentration of Cr(VI) on the characteristics of DOM in submerged MBRs were investigated in this study. Compared with control MBR conditions, results showed that low-concentration Cr(VI) caused an increase in concentrations of dissolved organic carbon, polysaccharides, and proteins. Low-concentration Cr(VI) also increased the concentrations of humic substances and protein-like substances, and inhibited the formation of macromolecules (over 500 kDa) in DOM, further enhancing membrane fouling. The low molecular weight (<500 kDa) DOM led to irreversible membrane pore blocking and serious membrane fouling. Additionally, the shifting of DOM functional groups (shift from 3,200 to 3,700 cm⁻¹, shift from 1,640 to 1,626 cm⁻¹, minor change at 1,383.4 and 671–601.4 cm⁻¹) indicated that amino, carboxyl, and sulfonate functionalities were involved in the connection between Cr(VI) and DOM.

Keywords:

• Dissolved organic matter
• Low-concentration Cr(VI)
• Wastewater treatment
• Membrane bioreactor

Acknowledgments

This work was supported by the National Science and Technology Pillar Program (2013BAD21B03) and the Fundamental Research Funds for the Central Universities, China Scholarship Council.