While the effects of calcium addition on membrane fouling by alginate have been extensively investigated, there exists little research into the impact of iron concentrations on the fouling behavior of this model polysaccharide. In this paper, the bulk solution characteristics of Fe-alginate assemblages such as size and zeta-potential were determined as were the properties of the materials deposited on flat sheet membranes at different iron and alginate concentrations under steady-state constant pressure filtration conditions. Biphasic filtration behavior of Fe-alginate was observed with highly impermeable gels formed at low iron concentrations, and reduced fouling at high iron concentrations with increased particle sizes observed in bulk solution. Any beneficial effects of iron addition, however, were strongly dependent on the concentration of alginate present. Increased alginate concentrations led to increased Fe-alginate complexation, stabilization of Fe-alginate aggregates and thus more severe fouling. Furthermore, calcium additions were found to strongly influence the properties of the Fe-alginate fouling layer with the presence of calcium inducing the formation of larger aggregates which formed fouling layers with greater surface roughness and lower specific cake resistance and porosity. The material properties of the Fe-alginate, Ca-alginate and Fe-Ca-alginate assemblages formed on flat sheet membranes were also compared and empirical expressions describing the hydraulic conductivity and compressibility of fouling layers developed as a function of trans-membrane pressure. (C) 2015 Elsevier B.V. All rights reserved.