Performance of a Series of Polishing Ponds in the Treatment of Sanitary Sewage

The main objective of this research was to evaluate the functioning of a system of polishing ponds on a pilot scale in the post-treatment of urban sewage discharged from an up-flow anaerobic sludge blanket reactor and followed by a submerged aerated filter. The following variables were analyzed: transparency, temperature, dissolved oxygen (DO), pH, alkalinity, biochemical oxygen demand (BOD), chemical oxygen demand (COD), total Kjeldahl nitrogen (TKN), ammonia (NH3), organic nitrogen, nitrate (N-NO3), total phosphorus (TP), orthophosphate (PO43-), total suspended solids (TSS) and chlorophylla. In addition, the planktonic communities were also identified and quantified. During the study period, the pond system registered the following mean and standard deviation of the removal efficiencies: 32.9±31.7% of BOD, 26.5±33.9% of COD, and 29.0±49.6% of TSS; good performance was observed in the removal of nitrogen compounds, and the following results were obtained: 58.4±28.1%, 87.5±15.4%, 24.4±42.6%, and 9.4±51.8%, respectively for TKN, NH3, organic nitrogen, and N-NO3; and 26.9±25.8 of TP and 34.3±32.7% of PO4 3-. During the research period, the planktonic community was represented by the following classes: Chlorophyceae, Euglenophyceae, Cyanobacteria, Cryptophyceae, Zygnemaphyceae, Chrysophyceae, and Dinophyceae; concurrently, the zooplankton registered low densities and was represented by the Rotiferous, Copepod, and Cladocera groups. The results help us understand  the performance of polishing ponds in treating sanitary effluents.