Comportamento de formas de enxofre, fósforo e nitrogênio em um reservatório profundo de estabilização tratando águas residuárias domésticas.

Abstract

The objective of this work was to describe the behaviour of forms of phosphorus, nitrogen and sulphur in a batch deep stabilization reservoir fed with raw sewage from the sewerage system of Campina Grande city (7° 13 11" S, 35° 52' 31" W, 550 m above mean sea level), Paraíba state, Northeast Brazil. Also, the importance of operational parameters in designing reservoirs aiming to obtain both an improved mineralization degree of organic nutrients and the elimination of toxic chemical species was evaluated. The pilot - scale reservoir set up at EXTRABES - UFPB (Federal University of Paraiba's Experimental Station for the Biological Treatment of Sewage) was 6.2 m deep and had an internal diameter of 10.76 m. Two experiments comprising each three different phases (filling, resting and emptying) being characterized by distinct operational parameters were carried out between October 1994 and May 1995. The water column of the reservoir was monitored throughout the distinct operational phases but only the results obtained from both filling and resting periods are described herein. All analytical, parameters including forms of nutrients, were determined in samples collected at 8 a.m. from different levels throughout the depth of the reservoir but only pH, dissolved oxygen and temperature were measured in samples collected at 3 p.m. Experimental results demonstrated that the predominance of mechanisms of either mineralization or conservation of nutrients as well as decrease of nuisance chemical species as hydrogen sulphide are dependent on the operational characteristics particularly organic loadings. The performance of the reservoir was compared to that of another batch reservoir fed with anaerobic pond effluent previously operated at EXTRABES being demonstrated that an adequate distribution of the time of operation (i. e., the resting period being much longer than the filling time) is more beneficial for the performance of the reservoir than the use of an anaerobic pretreatment unit.