Process intensification in wastewater treatment: Ferrous iron removal by a sustainable membrane bioreactor system

Biooxidation of ferrous iron (Fe²⁺) from strongly acidic industrial wastewater with a high Fe²⁺ content by Thiobacillus ferrooxidans in a packed bed reactor and subsequent removal of ferric iron (Fe³⁺) by a crossflow microfiltration (membrane) process have been investigated as functions of wastewater flowrate (54-672 cm³ h^-1), Fe²⁺ concentration (1.01-8.06 gam^-3), and pH (1.5-5.0). A natural (vegetable) sponge, Luffa cylindrical, was used as support matrix material. The fastest kinetic performance achieved was about 40 g Fe²⁺ dm^-3 h^-1 at a true dilution rate of 19 h^-1 corresponding to a hydraulic retention time of 3.16 min. Steady state conversion was observed to be about 10% higher at pH 2.3 than that at pH 1.5. Increasing the flowrate of the inlet wastewater caused a reduction in conversion rate. The oxidation rate reduced along the reactor height as the wastewater moved towards the exit at the top but conversion showed the opposite trend. Increasing Fe²⁺ concentration up to a critical point resulted in an increased oxidation rate but beyond the critical point caused the oxidation rate to decrease. Luffa cylindrica displayed suitable characteristics for use as a support matrix for formation of a Thiobacillus ferrooxidans biofilm and showed promising potential as an ecological and sustainable alternative to existing synthetic support materials. Membrane separation was shown to be a very effective means of Fe³⁺ removal from the wastewater with removal changing from 92% at pH 2.3 to complete removal at pH 5.0. © 2003 Society of Chemical Industry.