Comportamento de formas de nitrogênio e fósforo em sistemas de lagoas facultativas primárias, providas de chicanas, tratando esgotos domésticos.

Abstract

Both nitrogen and phosphorus cycles were studied in primary facultative deep (2.3 m) waste stabilization ponds treating domestic wastewater at EXTRABES-UFPB (Federal University of Paraiba's Experimental Station for the Biological Treatment of Sewage), in Campina Grande city (7° 13' 11" Sul, 35° 52' 31" Oeste, 550 m above s i ) , northeast Brazil. The experimental plant was made up of a control reactor (F28), without baffles, two reactors (F27 and F30) with longitudinal paralell baffles and another one (F29) provided with a round-the-corner baflle, all of them loaded with about 330 kgBOD5/ha.day and having a hydraulic retention time of 15 days. Two types of experiments were carried out in the experimental system: (a) between September and November 1998, studies on the diurnal variations of temperature, pH, dissolved oxygen, chlorophyll a, ammonia, organic nitrogen, total phosphorus and dissolved orthophosphate throughout both the depth and the length of pond F29, (b) from October 1997 to December 1998, monitoring of pond effluents based on analyses of ammonia, organic nitrogen, total phosphorus and soluble orthophosphate in samples collected, at 8 a.m. Lower layers of pond F29 were predominantly anaerobic but the upper layer showed a typical daily cycle of aerobic/anaerobic conditions being pH maintained within a range not sufficiently high to cause both orthophosphate precipitation and ammonia volatilization. The application of a one way-analysis of variance (one way - ANOVA) for the comparison of several sets of data obtained from the investigation of pond F29 water bulk and from the long term pond effluents monitoring demonstrated only a few number of significant (a = 0.05) differences among them. Because significant differences could not be demonstrated in terms of the respective forms of both nitrogen and phosphorus effluent mean concentrations it was concluded that from the point of view of nutrient (N and P) removal baffling is not technically and economically viable in designing deep and highly loaded primary facultative ponds treating sewage.