Simultaneous removal of refractory organic pollutants and nitrogen using electron shuttle suspended biofilm carriers in an integrated hydrolysis/acidification-anoxic/aerobic process

Abstract

Azo dyes wastewater contains refractory pollutant and nitrogen, which threatens human health and ecological environment when discharged into environment directly. Electron shuttle (ES) is able to participate in the extracellular electron transfer, and thus enhances the removal efficiency of refractory pollutant. However, the continuous dosing of soluble ES would rise operation cost and cause contamination inevitably. In this study, a type of insoluble ES (carbonylated graphene oxide (C-GO)) was developed and melt blended into polyethylene (PE) to prepare novel C-GO-modified suspended carriers. Compared to those of conventional carrier (31.60%), the surface active sites of novel C-GO-modified carrier increased to 52.95%. An integrated hydrolysis/acidification (HA, filled with C-GO-modified carrier) - anoxic/aerobic (AO, filled with clinoptilolite-modified carrier) process was applied to remove azo dye acid red B (ARB) and nitrogen simultaneously. ARB removal efficiency was significantly improved in the reactor filled with C-GO-modified carriers (HA2) compared to the reactor filled with conventional PE carriers (HA1) or activated sludge (HA0). Total nitrogen (TN) removal efficiency of the proposed process increased by 25.95–32.64% compared to the reactor filled with activated sludge. Moreover, the intermediates of ARB were identified by liquid chromatograph-mass spectrometer (LC-MS), and the degradation pathway of ARB through ES was proposed. C-GO-modified carriers induced ARB-removal-related bacterial enrichment (such as Chloroflexi, Lactivibrio, Longilinea, Bacteroidales and Anaerolineaceae). Besides, the relative abundance of denitrifiers and nitrifiers in the AO reactor filled with clinoptilolite-modified carrier was increased by 11.60% compared with activated sludge. Copy numbers of genes related to membrane transport, carbon/energy metabolism and nitrogen metabolism increased significantly on the surface-modified carriers. This study proposed an efficient approach for simultaneous azo dyes and nitrogen removal, showing potential in actual application.