Avaliação de espécies de enxofre em lagoas de estabilização facultativas primárias com chicanas tratando esgotos domésticos.

Abstract

An investigation on the sulphur cycle was carried out in two, pilot-scale, 2.3 mdeep primary facultative ponds treating municipal wastewater at EXTRABES - UFPB ( Experimental Station for the Research on Biological Treatment of Sewage - Federal University of Paraiba), Campina Grande City ( 7° 13' 11" S, 35° 52' 11" W, 550 m above m.s.l), Paraiba state, northeast Brazil. Both ponds were operated under a mean surface organic loading of 330 kg BOD5/ha.d and a hydraulic retention time of 15 days, being one of them provided with longitudinal round - the - corner baffles and the other, without baffles, maintained as a control reactor. Effluent concentrations of total sulphide, hydrogen sulphide and sulphate measured in both ponds during a routine monitoring, between 15th October 1997 and 14* December 1998, were respectively compared, being found that no significant difference was observed, demonstrating that from the sulphur cycle point of view baffling has not influenced the facultative pond performance. Between September and November 1998, sulphur transformations were studied within the baffled pond water bulk. The main diurnal transformations were observed in the 5 cm-top layer which showed a typical anaerobic/aerobic daily cycle that determined the predominance of either reduced or oxidized sulphur species. From a general point of view, however, it was found that about 80 percent of the water bulk was predominantly anaerobic and total sulphide concentrations were kept high. Both toxicity and odour nuisance possibly may occur in these circumstances.