Treatment of Waste Water from Wet Lime (Stone) Flue Gas Desulfurization Plants with Aid of Crossflow Microfiltration

Abstract

Abstract A treatment method has been developed to remove heavy metals such as As, Cd, Cr, Cu, Hg, Ni, Pb, Se and Zn very efficiently from waste water from wet lime(stone)-gypsum flue gas desulfurization plants (FGD). This method has been based on coprecipitation of heavy metal hydroxides and sulfides followed by crossflow microfiltration as a post-treatment. The experiments were carried out on pilot plant scale with actual waste water from a FGD plant downstream of a coal fired boiler. The effect of membrane fouling as a function of several process parameters was investigated. From SEM-EDS analysis it was found that the fouling layer on the membrane surface mainly consists of Mg-, Al-, Si-, Fe-compounds and gypsum. Membrane fouling could be decreased by periodical backwashing and by increasing the liquid velocity in the membranes. Moreover, a computer controlled start up procedure of the crossflow microfiltration unit was developed to minimize the effect of membrane fouling and to increase the operating time before chemical cleaning of the membranes is necessary. The developed chemical cleaning was found to be very successful, because it was possible to achieve the initial permeate flux after each experiment.