Performance evaluation of the ILHA Solteira’s city (SP) sewage treatment plant by primary facultative ponds

Abstract

The main objective of this research was to evaluate the performance of IlhaSolteira­SP Sewage Treatment Plant during the different yearly cli­matic seasons. A bathymetric survey of the primary facultative lagoons, a 24­hour monitoring and the tracking of its performance in 3 stages of collection of 3­month long each were conducted. The plant had almost 40% of its effective volume occupied by sludge; the final effluent registered an average BOD removal efficiency of 80,2%; only 3 samples reported values of MPN of Faecal Coliforms under the limit of 1000/100mL defined by legislation; in the third stage, the effluent recorded settleable solid values above the permissible limit of 1,0 mL/L. Most of the time and despite of the climate variations, the plant met the Brazilian environmental regula­tions in terms of BOD removal and settleable solids, but infringed the regulations in terms of the MPN of fecal coliforms, making the need to set up a post­treatment system to reduce the eventual environmental impact caused by the effluents and the risks to public health in the discharge area and downstream the dumping final point evident.