Avaliação do desempenho da estação de tratamento de esgotos da zona leste Teresina (PI) e seu impacto no rio Poty.

Abstract

This work presents the evaluation of a sewage treatment system by stabilization ponds named ETE Leste (Teresina City - Piaui State) and the final effluent impact on the receiving body (Poty River) water quality. The sewage treatment plant comprises preliminary treatment (screening and degriting) followed by five ponds of stabilization. The project considered the fist pond as aerated facultative followed by two series in parallel of maturation ponds named 1, 2, 3 and 4: one serie with maturation 1 and 3 and the other with maturation 2 and 4. The system is located in the sity of Teresina (5°5'13"S; 42°48'41"W; 73m above the sea level), capital of Piaui State, Northeast of Brazil. The study was carried out from March 1999 to November of 2001. The sampling point were raw sewage (RS), final effluent (FE) and river up and downstream (RUp and RD) both at 100m from final effluent discharge. Samples were analyzed for temperature, pH, BOD5 , COD, Total Solids (TS) with fixed (TFS) and volatile (TVS) fractions and fecal coliforms (FC). Mean values of BOD5 in the RS and FE were of 351 and 77mg02/l, between 5- 1 Omg02/1 in river upstream with river downstream showing a discrete BOD increase after receiving final effluent discharge (6 to 16mg02/L). During the experimental period organic matter (as BOD and COD) removal efficiencies (as BOD and COD) were 80% (351-77 mg02 /l) and 72% (525-145mg02/l) respectively, showing good performance of pond system. Total solids and fractions varied considerably and no expressive removals were found. Raw sewage FC values were typical for those found in domestic wastewater (5.3xl07MPN/ml) with pond system removing up to 99,9% (5.3xl07- 4.4xl04MPN/100ml), considered appropriate for systems with this configuration. In the receiving water body FC mean values varied between 9.2x102 to 9.3xl03MPN/100ml for upstream samples and between 2.0x103 to 4.4x104MPN/ 100ml to downstream samples. Although the data haven't demonstrated a river impact caused by the final effluent discharge, the analysis of variance (ANOVA-one way) followed by the GT-2 graphic method demonstrated that those alterations were not significant.