The system consists of a partially aerated facultative pond with a polished area that treats the effluents of a soft drink industry in Brazil. This work concerns on the study of the longitudinal distribution as well as the analysis of the vertical profile of the main control parameters which exerts a direct influence on the metabolism of the system.

The results show the existence of a horizontal thermal gradient between aerated and polishing zones, which is more intense at the surface of the first 40 metres. The vertical profile did not identify a tendency to thermal stratification. The constant gradient vertical of 0.1°C in the aerated and polishing zones characterizes an almost isothermal condition.

The decrease of the effluent pH values was observed in the bottom layer of the pond. This indicates that the anaerobic digestion on the sedimented sludge incorporates acids in the liquid mass.

The dissolved oxygen vertical distribution presents negative clinographic profile. The isolines in the aerated zone indicate good efficiency of oxygen transfer. In the polishing zone, concentrations above 2.0 mg/l were observed down to a depth of 1 m, possibly caused by photosynthetic activities.

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