Stabilizowanie przebiegu koagulacji zanieczyszczeń wody o zmiennej jakos̈ci przez zastosowanie recyrkulacji osadu pokoagulacyjnego

Operating conventional treatment systems of mountain waters generates difficulties in immediate coagulant dose adjustment to sudden and significant changes in raw water quality. This is mainly due to poor buffering properties of this type of water and its varying quality, both daily and hourly, over the course of the year. This is the reason why the maintenance of optimum conditions for coagulation process, especially coagulant dose and water pH, is very difficult. Under such conditions, application of typical hydrolyzing coagulants results in uncontrolled pH drops, completely inhibiting the water treatment process. An inability to immediately adjust the coagulant dose to variations in water quality causes overdosing or underdosing of coagulant in relation to its optimal value, leading to deterioration of treated water quality. Therefore, instead of hydrolyzing coagulants at mountain water treatment stations the pre-hydrolyzed coagulants are introduced, such as polyaluminium chlorides (PAC). The pilot study results show that the use of post-coagulation sludge recirculation into flocculation system is an effective method to maintain high and stable coagulation effectiveness, both under an overdose and underdose conditions.