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

Abstract

Biooxidation of ferrous iron (Fe(2+)) from strongly acidic industrial wastewater with a high Fe(2+) content by Thiobacillus ferrooxidans in a packed bed reactor and subsequent removal of ferric iron (Fe(3+)) by a crossflow microfiltration (membrane) process have been investigated as functions of wastewater flowrate (54-672 cm(3) h(-1)), Fe(2+) concentration (1.01-8.06 g dm(-3)), and pH (1.5-5.0). A natural (vegetable) sponge, Luffa cylindrica, was used as support matrix material. The fastest kinetic performance achieved was about 40 g Fe(2+) 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 Fe(2+) 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 Fe(3+) removal from the wastewater with removal changing from 92% at pH 2.3 to complete removal at pH 5.0. (C) 2003 Society of Chemical Industry.