All multifunctional units combine flocculation and sedimentation to improve efficiency of treatment process. The characteristic feature of the unit is a contact of raw water with previously generated floes which enhances flocculation by increasing interparticle collisions and sorption ability offloes. On the basis of the authors' experience it was stated that in spite of significant differences between the procedure of conventional treatment and treatment in multifunctional units, an optimum coagulant dose is determined in jar testing which is commonly used for conventional treatment. The influence of sludge recirculation is not taken into consideration resulting in reagent overdosing. In this paper the results of the research on coagulation with postcoagulation sludge recirculation in aspect of sludge age are presented. It was stated that for the tested water, sludge recirculation may result in significant lowering of optimum alum doses provided that a proper degree of fresh sludge recirculation is applied.

The water of the Wisła-Czarne reservoir is of very low hardness and alkalinity. In spite ofhigh SUVA values it is not susceptible to enhanced coagulation. In order to achieve the assumed results, coagulation with ALS (aluminium sulphate) should be conducted in two optional technological systems - in a conventional system and in "in-bed" coagulation dependently ofwater quality and its temperature. Effective treatment with ALS is possible, even at low temperature of the water, but at strict technological parameters. However, because of significant variations of water quality, especially after rainstorms, it is very difficult to meet such requirements. Application of pre-hydrolyzed Flokor 1,2A instead ofALS enables to eliminate reagents to the pH adjustment and to apply "in-bed" coagulation when water supplied to the WTP is of low turbidity. To assure stable technological system operation, in aspect of raw water quality changes, some activities were also undertaken, i.e. modernization of rapid filters, which involved a drainage system and exchange of sand bed for anthracite-sand bed. Treatment based on direct filtration results in decrease of reagents usage and, what is especially important, effective DBPs precursors removal.