A new sewage treatment System was Studied, which consisted of an anaerobic baffled filter reactor and the following aerobic post-treatment. One of the two studied systems (AN-I) was inoculated with psychrophilic digested sludge, the second one (AN-II) was operated without Inoculation. The HRT in anaerobic and aerobic parts of the reactors were about 15 and 4 h, respectively. The temperature in both reactors varied during the year from 4.5 to 23degreesC. All monitored parameters were removed with relatively high efficiencies (COD 78.6-83.0%, BOD5 = 92.5-94.0% and SS = 80.9-92.7%). An intensive nitrification process was observed during the whole year in both reactors (under average temperature of 5.9degreesC in January 2000, also). The average removal of the NH4-N varied during the year from 46.4% to 87.3%. In both systems a partial denitrification process was observed, too.