The aim of the research was to determine the possibility of using and adapting regression models for a description of constructed wetland systems treating reject water from aerobic sewage sludge stabilization. The P-k-C* model was investigated along with related models. The research was carried out using reject water from aerobic sewage sludge stabilization in dairy wastewater treatment plant (WWTP) belonging to Mlekovita in Wysokie Mazowieckie. The main components of the research installation were two vertical flow constructed wetland beds with passive aeration operating at 0.1 m/d hydraulic load. The following parameters were used for modeling: BOD5, COD, N-NH4+ and temperature. Air temperature was also monitored.