Estudo sobre a remoção de fósforo em uma série longa de dez lagoas de estabilização tratando esgotos domésticos em região de clima tropical.

Abstract

This work describes the study of the removal of phosphorus forms carried out in a series of ten stabilization ponds, constituted an anaerobic lagoon followed by a secondary facultative lagoon and eight of maturation, in pilot scale, with a total hydraulic detention time of 19 days and each lagoon with a depth of 1.5 m. The experimental system was located on land belonging to the Companhia de Água e Esgotas do Paraíba (CAGEPA), in the neighborhood of Catingueira, where the domestic wastewater treatment plant in the city of Campina Grande, Northeastern Brazil (7º13 11 ° S, 35 ° 52 31 ° W, 550 m above sea level). The research was conducted under the responsibility of the Experimental Station of Biological Treatment of Sanitary Sewers (EXTRABES), belonging to the Federal University of Paraíba - UFPb. From August to December 1991, the analyzes of the raw sewage that fed the system and the effluents from each lagoon were made. These analyzes were carried out on and done in punctual samples collected at 8 hours and in samples collected during the daily cycle. The crude sewage was also analyzed with daily composite samples. The following parameters were measured: total phosphorus, soluble orthophosphate, temperature, transparency, dissolved oxygen, pH, COD, DB05 and chlorophyll a. The results of the system monitoring showed a total phosphorus removal during the series of only 10% in relation to the concentration present in the raw sewage that fed the system (which was 4.9 mg P / 1), and a concentration of orthophosphate soluble solution of the order of 3.7 mg P / 1, higher than the affluent orthophosphate concentration. These data, when compared to the results obtained in other systems, of the series ponds investigated by EXTRABES indicate that the detention time exerts an influence, on the removal of phosphorus, greater than the number of ponds in the series. In addition, pH values, low concentrations of algae and dissolved oxygen, presented in the effluent during the experiment, contributed to the poor efficiency of the removal mechanisms, particularly the precipitation of orthophosphate in the form of hydroxyapatite. On the other hand, the sanitary quality of the effluent and the high concentrations of phosphorus found indicate that the effluent from the series can be used with advantages in irrigation and aquaculture, avoiding the eutrophication of receptor bodies and collaborating with the community economy.