Estudo da variação cíclica diária de fósforo sedimentável numa lagoa facultativa primária, profunda, provida de chicanas do tipo vai e vem.

Abstract

The aim of this work was to study the daily cycle variation of phosphorus in suspended matter in two different levels (50 and 200 cm) in both inlet and outlet channels of a pilot-scale deep (2.3 m) primary facultative pond provided with round-the-corner baffles treating domestic raw sewage from a municipal sewerage system. The baffled pond was operated, under a mean surface organic loading of 330 kgBODs/ha.day and a mean hydraulic retention time of 15 days, at EXTRABES-UFPB (Experimental Station for the Biological Treatment of Sewage of the Federal University of Paraiba) situated at the City of Campina Grande (7° 13' 11" S, 35° 52' 31" W, 550 m above m.s.l), northeast Brazil. The experimental work, based on 18 experiments (9 throughout light hours and 9 representative of dark hours), was carried out from April to August 2000 being determined pH, total phosphorus (P-total), inorganic phosphorus (P-inorganic), organic phosphorus (Inorganic), mobile phosphorus (P-mobile), phosphorus bound to both iron and aluminum (PFe- Al), phosphorus linked to calcium (P-Ca), residual phosphorus (P-residual) and sedimentation rates in the particulate fraction of the settleable matter and soluble orthophosphate in the pore water. Both P-inorganic and P-organic mean concentrations in settleable particulate matter represented 52 and 48 %, respectively. pH which is considered a key factor in inorganic phosphorus fractionation in stabilization ponds was observed to be within a nearly neutral range (7-8), what favoured the fraction P-Fe-Al to predominate over all other fractions of inorganic phosphorus. Although pH was not high enough to cause P-Ca to predominate concentrations of this fraction were not negligible representing about 30% of inorganic phosphorus. The application of one-way Analysis of Variance to sedimentation rate data demonstrated significant differences between inlet and outlet channels rather than between surface and bottom layers. Also, sedimentation rates were observed to be higher in outlet rather than in inlet channel, particularly during light hours, being this attributed to a much higher concentration of suspended solids due to both algae and cyanobacteria as well as to the resuspension of a lighter sludge from the bottom of this channel.