Enhanced denitrification by graphene oxide–modified cathode for the secondary effluent of wastewater treatment plants in three-dimensional biofilm electrode reactors

Abstract

In this study, a novel three-dimensional biofilm electrode reactor (3D-BER) with a graphene oxide (GO)–modified cathode was developed to enhance the denitrification performance of secondary effluent from wastewater treatment plants (SEWTPs). The effects of different hydraulic retention times (HRTs) and currents on the 3D-BER were explored. The results indicated that at the optimal HRT of 4 h and current of 350 mA/m2, the 3D-BER with GO-modified cathode had a higher denitrification rate (2.40 ± 0.1 mg TN/L/h) and less accumulation of intermediate products, especially with 3.34% total nitrogen (TN) molar conversion to N2O. The GO-modified cathode offered a large biocompatible specific surface area and enhanced the conductivity, which favored microbial growth and increased electron transfer efficiency and extracellular enzyme activities. Moreover, the activity of nitrite reductase increased more than that of nitrate reductase to accelerate nitrite reduction, thus facilitating the denitrification process. The proposed 3D-BER provided an effective solution to elevate tertiary denitrification in the SEWTP. HIGHLIGHTS Secondary effluent from wastewater treatment plants are treated by the three-dimensional biofilm electrode reactor (3D-BER) with GO-modified cathode.; The 3D-BER improves the denitrification efficiency at appropriate current and HRT.; A 52.6% N2O greenhouse gas reduction with 3.34% TN molar conversion to N2O was achieved.; The GO-modified 3D-BER enhances denitrifying enzyme activity.;

Keywords

• biofilm electrode reactors
• graphene oxide
• hydrogen autotrophic denitrification
• municipal wastewater