Wastewater from wet lime(stone)-gypsum flue gas desulphurization plants (FGD) for coal-fired boilers contains suspended solids (fine gypsum, silica, hydroxides of iron and aluminium) and soluble salts (chlorides and sulphates of calcium, sodium and magnesium). Moreover, traces of heavy metals such as As, Cd, Cr, Cu, Hg, Ni, Pb, Sb, Se, Sn and Zn are present in these wastewater streams. Most of these heavy metals and suspended solids have to be removed before discharging the wastewater, in order to fulfil the demands stated by the Dutch authorities. Therefore, a very efficient treatment method, based on coprecipitation of heavy metal hydroxides and sulphides followed by crossflow microfiltration (CMF) as a posttreatment, has been developed. The experiments were carried out on a pilot plant scale with actual wastewater from a FGD plant downstream of a coal-fired boiler. Two different types of membranes, a hydrophobic and a hydrophilic crossflow microfiltration membrane, were tested and compared with each other. The effect of membrane fouling as a function of fluid velocity and backwashing was investigated. Besides, the heavy metal concentration and the amount of suspended solids were determined before and after the CMF pilot plant. Finally, a simple and highly effective chemical cleaning method was developed.