Impact of nZVI on the formation of aerobic granules, bacterial growth and nutrient removal using aerobic sequencing batch reactor

Abstract The aim of this study was to investigate the effect of nanoscale zero-valent iron (nZVI) on aerobic granulation, nutrient removal and bacterial growth in sequencing batch reactors (SBRs). For this purpose, two reactors were operated simultaneously for sixty days with and without adding nZVI. The reactors were fed with synthetic wastewater and acclimated with seed sludge collected from a full-scale municipal wastewater treatment plant in Istanbul. Effluent concentrations of nitrate, nitrite, ammonia, phosphate and COD were regularly measured, and their removal pathways including the direct adsorption to nZVI, utilization by microorganisms and adsorption within the generated granules were discussed. The removal efficiency of COD, ammonia and phosphate kept increasing, and almost a complete removal was observed after the formation of aerobic granules on day 50. Furthermore, after the addition of nZVI to R2 on day 24th, the removal efficiency of ammonia, COD and phosphate slightly improved. The addition of nZVI stimulated the production of Extracellular Polymeric Substances (EPS) in the reactor. NGS analysis showed that the addition of nZVI into R2 increased the growth rate of some bacterial species such as Rhizobiales and Xanthomonadales and decreased others such as Clostridiales, confirming that the effect of nZVI on the bacterial growth was genera dependent. The aerobic granules were successfully formed in the reactors in less than 50 days and the addition of nZVI improved to some extent the size and settling rate of the formed granules in R2.