The invention relates to a sewage treatment plant for treatment of waste fluid, said plant comprising at least one aeration chamber (2, 3), a settling chamber (4) and a disinfection chamber (5). In order to rationalize the layout and the structure of the sewage treatment plant (1), the at least one aeration chamber (2,3) and the settling chamber (4) are arranged in a structural unit comprising opposite end walls (101, 102), opposite side walls (103, 104), a bottom part (105) and a cover part (106). The disinfection chamber (5) is arranged separately outside one of said end walls (101, 102), side walls (103, 104), bottom part (105) or cover part (106) of the structural unit.