Impacts of nanoscale zero-valent iron on nitrite accumulation performance of nitritation granular sludges with different spatial morphologies and its biosorption behavior

Abstract

To explore the potential impacts of nanoscale zero-valent iron (nZVI) particles on nitrite accumulation performance of nitritation granular sludge (NGS), two types of NGS (NGSA and NGSH) with different spatial morphologies were employed to exposure under a wide dosage of nZVI in batch tests. The biosorption behavior of nZVI was also investigated by determining adsorption isotherm. Results showed that the ecotoxic effect of nZVI was ascribed to its fast adsorption to the granules. Although NGSA and NGSH shared a similar bacterial community structure dominated by genus Nitrosomonas based on high-throughput pyrosequencing, the compact and small granules of NGSA showed a stronger tolerance for nZVI exposure than NGSH with loose spatial structure. The 50% inhibition dosage of nZVI for ammonium-oxidizing bacteria activity in NGSA and NGSH was 88.5 and 21.3 mg g−1 VSS, respectively. As a crucial self-protection mechanism of microbes, the secretion of extracellular polymeric substances was dramatically enhanced with nZVI exposure at a low dosage, and a simultaneous decrease in both extracellular polymeric substances contents and ammonium-oxidizing activity of NGS was observed with a high accumulation of total iron in sludge phase. Overall, the results suggested that ammonium-oxidizing bacteria in granules were susceptible to inhibition by nZVI exposure, and release of engineered nanoparticles into wastewater treatment system increased the risk of failure in autotrophic nitrogen removal process.