With stricter requirements for wastewater treatment, small-scale individual wastewater treatment plants can provide a financially attractive alternative to a sever connection in locations far from the existing sewer network. Systems operating under the basis of active sludge are considered advanced, and their producers declare high levels of wastewater treatment not only according to BOD, but also under biogenic materials. However, there are hardly any data on how small-scale individual household wastewater treatment facilities operate. This article presents an analysis of the main parameters of wastewater biologically treated in three small-scale household wastewater treatment plants (which operate under the basis of active sludge), namely TSS, COD, BOD₇, Nt, NO₃-N, NH₄-N, Pt, and PO₄-P concentrations. The research lasted for 5.5 months during a cold period. According to TSS, COD, and BOD₇ concentrations in effluent, the wastewater treatment level in the study plants was good. The concentrations of these substances in effluent (TSS<10 mg/L, COD<98 mg/L, BOD₇<20 mg/L) were lower than requirements for treated water. However, NH₄-N in the effluent in winter increased up to 6-7 mg/L and to 26 mg/L. The concentrations of N_t and P_t in treated wastewater exceeded EU requirements for water released from wastewater treatment facilities. PO₄-P removal, in many cases, was ineffective or did not take place at all.