Due to increasing water demand, the use of alternative water resources is an important issue in many parts of the world. Reclamation and reuse of municipal wastewater is considered a feasible option for potable reuse or agricultural irrigation. For this reason, it is considered essential to carry out the economical and efficient treatment of municipal wastewater. For this purpose, ultrafiltration (UF) is used as one of the pressure-driven membrane separation processes. The main aim of this paper was to examine the efficiency of the UF membranes during the treatment of municipal wastewater. Ultrafiltration was performed with five membranes: GK at 5 bar, PT at 4 bar, PU at 2 bar, PW at 2 bar and MW at 1,5 bar. There was a change in the flux over time. Monitored parameters include turbidity, pH value, electrical conductivity (κ), total carbon (TC), inorganic carbon (IC), dissolved organic carbon (DOC) and chemical oxygen demand (COD) of a real sample of municipal wastewater from Čakovec and the obtained permeate. The composition of the wastewater and the content of each substance was determined by qualitative and quantitative analysis using an ionic chromatograph to determine the presence of cations (Ca2+, K+, Na+, Li+, NH4+ and Mg2+) and anions (F-, SO42-, NO2-, NO3-, Br-, Cl- and PO43-) as well as mass spectrometry with inductively coupled plasma to determine the presence of trace elements (Li, Rb, Mo, Cd, Sn, Sb, Cs, Tl, Pb, U2, Al, Ti, V5, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sr, Ba, As). The obtained permeate meets the limit values prescribed by the Ordinance on Limits of Wastewater Emissions (NN 80/2013, NN 3/2016). The ultrafiltration of the KOV satisfied the legal requirements, which confirms the efficiency of the UF membranes and UF as an effective membrane separation process during KOV processing.