The topic of the diploma thesis is the treatment of sludge water after biological purification by dosing of flocculants and their various kinds, so that the sludge produced is best drained and that the concentrated sludge which undergoes the flocculation process is best absorbed by the colloids in the flocs. This will potentially reduce the amount of generated sludge, due to a lower water content, which is finally dumped.The work is divided into six parts. The first chapter is devoted generally to wastewater treatment. It discusses processes and phenomena that occur during wastewater treatment, most often in sewage treatment plants.The second chapter focuses more specifically on the sludge processing, its treatment, use and disposalThe third chapter deals with the process of flocculation and flocculants, their characteristics and their division of their types.Next chapter focuses on legislation of wastewater treatment in the Slovak Republic. A description of the operation, chemical substances, sludge and discharged water from the studied WWTP is described in the fifth chapter. It also includes a description of the methods of research in the practical part of the thesis.The results of the thesis are processed in the last chapter. Based on experiments with different dosing of flocculants, we have found that Praestol K 232 L flocculant is more suitable as Praestol 835 BC to optimize sludge dewatering. We improved the flocculation process, when optimizing dosing and pH of concentrated sludge.