Effect of Zn(II) on the biochemical properties of aerobic granules

Aerobic granules were cultivated in sequencing batch reactor (SBR) columns, and the toxic effect of short-term incubation with Zn(II) on the biochemical properties of the granules was investigated. Zn(II) in the SBR affected the granule morphology and extracellular polymeric substances (EPS) content of the granules. Overall, the aerobic granular microorganism system was susceptible to Zn(II)-induced toxicity, but simultaneously exhibited some tolerance to toxicity, which seemed to be mainly due to the interactions of the heavy metal with polysaccharides (PS) and proteins (PN) of the EPS. The EPS and PS/PN ratio increased gradually with Zn(II) concentration, indicating that the granules can adapt to the toxicity of the external environment. Indeed, a significant correlation between EPS content and Zn(II) concentration existed, which could be fitted to an exponential function. In conclusion, EPS content is a sensitive parameter for the characterisation of pollutant toxicity.