Degradation efficiency of the azo dye acid orange 2 and microbial community characteristics in a rotating algal biofilm reactor

Abstract

Under the traditional suspended culture system for algae, processing high concentrations of azo dyes is difficult because of poor light transmittance in wastewater. The rotating algal biofilm (RAB) system enables algal biofilms to receive adequate light, even in the presence of high concentrations of dye. The degradation efficiency of acid orange 2 (AO-2) at concentrations of 50–600 mg/L exceeded 95 % within 12–24 h, and the highest removal rate was 592.35 mg/(L·d). Fourier transform infrared spectroscopy showed that the azo bond was broken in AO-2, and the main decomposition products were amines and olefins. The sulfate concentration did not influence the AO-2 removal, whereas the pH had a significant effect (P < 0.001). The dye degradation efficiencies under acidic and neutral conditions were higher than those under alkaline conditions. Decolorization experiments indicated that the extracellular and intracellular enzymes synergistically degraded AO-2. High-throughput sequencing revealed that biofilms in RAB reactors contained a variety of taxa, including cyanobacteria, bacteria, Rotifera, and Cercozoa. The potential cause of AO-2 biodegradation by algae-bacterial systems is that the biofilm can use AO-2 as a nitrogen source for its own growth.