title: Effect of ferric and ferrous iron addition on phosphorus removal and fouling in submerged membrane bioreactors.
abstract: The effect of continuously dosing membrane bioreactors (MBRs) with ferric chloride (Fe(III)) and ferrous sulphate (Fe(II)) on phosphorus (P) removal and membrane fouling is investigated here. Influent phosphorus concentrations of 10 mg/L were consistently reduced to effluent concentrations of less than 0.02 mg/L and 0.03-0.04 mg/L when an Fe(III)/P molar ratio of 4.0 and Fe/P molar ratio (for both Fe(II) and Fe(III)) of 2.0 were used, respectively. In comparison, effluent concentrations did not decrease below 1.35 mg/L in a control reactor to which iron was not added. The concentrations of supernatant organic compounds, particularly polysaccharides, were reduced significantly by iron addition. The sub-critical fouling time (tcrit) after which fouling becomes much more severe was substantially shorter with Fe(III) dosing (672 h) than with Fe(II) dosing (1200-1260 h) at Fe/P molar ratios of 2.0 while the control reactor (no iron dosing) exhibited a tcrit of 960 h. Not surprisingly, membrane fouling was substantially more severe at Fe/P ratios of 4. Fe(II) doses yielding Fe/P molar ratios of 2 or less with dosing to the aerobic chamber were found to be optimal in terms of P removal and fouling mitigation performance. In long term operation, however, the use of iron for maintaining appropriately low effluent P concentrations results in more severe irreversible fouling necessitating the application of an effective membrane cleaning regime.
authors.affiliation: Water Research Centre, School of Civil and Environmental Engineering, The University of New South Wales, Sydney, NSW 2052, Australia.
authors.forename: Zhenghua
authors.initials: Z
authors.lastname: Zhang
authors.affiliation: Water Research Centre, School of Civil and Environmental Engineering, The University of New South Wales, Sydney, NSW 2052, Australia; UNESCO Centre for Membrane Science and Technology, School of Chemical Engineering, The University of New South Wales, Sydney, NSW 2052, Australia.
authors.forename: Yuan
authors.initials: Y
authors.lastname: Wang
authors.affiliation: UNESCO Centre for Membrane Science and Technology, School of Chemical Engineering, The University of New South Wales, Sydney, NSW 2052, Australia.
authors.forename: Greg L
authors.initials: GL
authors.lastname: Leslie
authors.affiliation: Water Research Centre, School of Civil and Environmental Engineering, The University of New South Wales, Sydney, NSW 2052, Australia. Electronic address: d.waite@unsw.edu.au.
authors.forename: T David
authors.initials: TD
authors.lastname: Waite
mesh_terms: D001426:Bacterial Proteins / Q000032:analysis; D057219:Biofouling; D019149:Bioreactors; D002244:Carbon / Q000032:analysis; D017097:Electric Impedance; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000737:chemistry*; D008567:Membranes, Artificial; D010758:Phosphorus / Q000302:isolation & purification*; D011135:Polysaccharides, Bacterial / Q000737:chemistry; D011312:Pressure; D014865:Waste Disposal, Fluid; D062065:Wastewater / Q000737:chemistry; D060753:Water Quality
chemical_list: D001426:Bacterial Proteins; D002244:Carbon; D007501:Iron; D008567:Membranes, Artificial; D010758:Phosphorus; D011135:Polysaccharides, Bacterial; D062065:Wastewater
keywords: Coagulant; Ferric chloride; Ferrous sulphate; Membrane bioreactor; Membrane fouling; Phosphorus removal