The invention a residual water treatment plant for small flows, characterized by the combination of a primary sedimentation zone followed by anoxic and aerobic packed zones, placed serially all of them, with packing, alternating descending and ascending flows and aerated according to the oxygen requirement, there being a recirculation of treated water whith sedimented mud between the secondary sedimentator and the first anoxic compartment or primary sedimentation zone, wich produces treated water with enough quality for reutilization activities, after prior disinfecting (for example, watering, auntomobile-washing, flushing of sanitary facilities, floor-washing, and so forth). The plant requires the use of a low energy consumption air compressor, especially specified to minimize its maintenance and noise. The treatment microplant has a compact desing, which requires a small area (of the size of a water cistern for 1100L, 1.5 meters in height), and has an internal water recirculation system, preferably, of the "airlift" type, between compartments, wich prevents use of rotatory equipment additional to the compressor, wich recycles the accumulated mud by permitting its degradation and minimizing its unloading and producction. For purposes of reutilization, the plate requires, additionally, a disinfecting unit and a treated water cistern. 

(Patente MX206841)