Impact of ferrous iron dosing on iron and phosphorus solids speciation and transformation in a pilot scale membrane bioreactor

Abstract

In this study, the distributions of iron and phosphorus species in a 1.25 m³ pilot scale submerged membrane bioreactor dosed with Fe(II) salts to either the membrane chamber or the 1st anoxic chamber were determined using X-ray absorption spectroscopy (XAS) at the iron and phosphorus K-edges. Significant differences in the distribution of Fe species were evident at the commencement of dosing depending on the chamber to which Fe(II) was dosed though these differences were much less distinct by the time steady state conditions were achieved. Both the co-precipitation of P with Fe and adsorption of phosphorus to iron oxides play important roles with regard to the removal of phosphorus from the MBR supernatant with the results of this work suggesting that P removal via formation of Fe(III)–phosphate mineral species is preferred if Fe(II) is dosed to the membrane chamber rather than the 1st anoxic chamber.