Abstract: A continuous waste water treatment system comprising a reservoir providing a single, closed, continuous, substantially horizontal path through at least two adjacent substantially concentric loops, each of said loops having a beginning and an end, said reservoir being provided with waste water inlet means, treated liquid outlet means, and aeration and circulation means, and wherein said treated liquid outlet means is connected to clarifying means which removes at least some of the sludge carried by the treated liquid and sludge return means is provided to return at least some of the removed sludge to said reservoir.