Avaliação das concentrações de nutrientes (N e P) no módulo II da estação de tratamento de esgotos de Mangabeira na grande João Pessoa-PB.

Abstract

The aim of this work was to analyze the concentrations of both nitrogen and phosphorus, in the Module II of the Sewage Treatment Plant of Mangabeira, in the City of João Pessoa (7°10”South; 34°49”West), Paraiba state, northeast Brazil. The Module was designed and, initially, operated with three reactors in series, being the first an aerated pond with complete mixture, followed by a facultative aerated pond and a maturation pond, but, nowadays, it is made up of three stabilization ponds in series, being two anaerobic and a secondary facultative. The full scale system was provided with units for preliminary treatment, a manually raked bar screen and a grit chamber. A parshall flume with a 23cmthroat, situated over the grit chamber, was designed for a maximum flow-rate of 132.4L/s. In the investigation period, mean flow-rate was 35.52L/s. Between March and November 2005 samples of raw sewage (EB) and effluents of anaerobic ponds 1 (A1) and 2 (A2) and of the facultative pond (EF) were collected, weekly, between 8 and 9 a. m., for determining the variables pH, temperature, dissolved oxygen, chlorophyll “a”, BOD5, COD and the nutrient species, total kjeldahl nitrogen (NTK) and ammonia (N-NH3), total phosphorus (P-T) and soluble orthophosphate (O-S). Besides the routine monitoring, the same variables were determined in the influent and effluents of the system throughout two variation studies in the daily cycle (profiles). Based on the daily mean flow-rate, the physical characteristics of the reactors and the influent mean BOD5 value (264mg/L), a total hydraulic retention time of 28.41 days and surface and volumetric organic loadings, in the first anaerobic pond, of 2020.49kgBOD5/ha.d and 54.74gBOD5/m3.d, respectively, were determined. Monitoring data analysis showed that the operation of two anaerobic ponds in series did not introduce any significant differences among mean concentrations of forms of nitrogen as well as forms of phosphorus being not recommended the design of this configuration for the improvement of nutrient removal, mainly in full scale plants. Module II removed nitrogen ammonia (41%) and total phosphorus (25%) similarly to other regional treatment systems (Campina Grande and Guarabira), whose configurations are nearly the same. The final effluent of the system was characterized as being very eutrophic, i. e., mean concentrations of nutrients were greater than the maxima permissible values established by the legislation for discharging the effluent into receiving bodies.