Simultaneous removal of nitrate and diethyl phthalate using a novel sponge–based biocarrier combined modified walnut shell biochar with Fe3O4 in the immobilized bioreactor

A novel biological carrier combining sponge and modified walnut shell biochar with Fe3O4 ([email protected]3O4) was fabricated to achieve simultaneous removal of nitrate and diethyl phthalate (DEP). The optimal reaction conditions of the immobilized bioreactor were: carbon to nitrogen (C/N) ratio of 1.5, Fe2+ concentration of 20 mg L−1, and hydraulic retention time (HRT) of 8 h. Under the optimal conditions and DEP concentration of 800 μg L−1, the highest removal efficiency of DEP and nitrate in the immobilized bioreactor with the novel biological carrier were 67.87% and 83.97% (68.43 μg L−1 h−1 and 1.71 mg L−1 h−1), respectively. Scanning electron microscopy (SEM) showed that the novel biological carrier in this study carried more bio–sediments which is closely related to the denitrification efficiency. The gas chromatography (GC) data showed that the nitrogen production of the immobilized bioreactor (99.85%) was higher than that of another experimental group (97.84%). Fluorescence excitation–emission matrix (EEM) and Fourier transform infrared spectrometer (FTIR) indicated the immobilized bioreactor emerged more extracellular polymeric substances (EPS) which was related to favourable biological stability under the DEP environment. Moreover, according to high–throughput sequencing data, the Zoogloea sp. L2 responsible for iron–reduction and denitrification was the main strain in this immobilized bioreactor.