Biodiversity monitoring in wastewater oxidation ponds

Abstract

In order to study the relationship between Wastewater Oxidation Ponds efficiency and maturation ponds ecological communities, two AGERE systems from Braga neighbouring villages were selected: Cabreiros, CAB and Tebosa, TEB. Every two weeks sampling campaigns were realized (March - July 2007) to gather wastewater simple samples at the systems inflow and outflow. Determinations of Biochemical and Chemical Oxygen Demand and Total Suspended Solids (BOD5, COD and TSS mg/L), Recovered Heterotrophics and Total and Fecal Coliforms (RH, TC and FC, CFU ml/L) were performed at UM-Biology Lab. The removal efficiencies were 10% higher at CAB for BOD5 and COD and 10% higher at TEB for TSS. RH removal was mostly higher than 95%, but on CAB 6 and 9 samples, was respectively null and weak. During almost all the sampling period TC and FC removal were about 100% at both systems, but on samples 6 and 9, TC and FC CFU/ml were higher at CAB outflow than at inflow. Samples from maturation ponds were also gathered and maintained in the lab for a month, as microcosms. The daily microscopic analysis showed that in CAB maturation pond Euglena, Scenedesmus and diatoms are generally predominant whereas in TEB maturation pond the constant presence of Lemna was concomitant with a lesser density and diversity of algae. The samples 6 and 9 from CAB maturation pond, showed an absence of eucaryotic heterotrophics probably associated with the weak or even null removal of TC and FC.