Full-scale biological phosphorus removal: quantification of storage polymers, microbial performance and metabolic modelling

Dissertação para obtenção do Grau de Doutor em Engenharia Química e Bioquímica

Enhanced biological phosphorus removal (EBPR) can be applied in wastewater treatment plants (WWTPs), as a sustainable and efficient way to remove phosphorus from wastewater and hence reduce its impact on eutrophication. This work characterises the performance, metabolism and identity of the microbial EBPR communities in full-scale WWTPs. The accurate quantification of the internal storage compounds, namely polyhydroxyalkanoate (PHA) and glycogen, is crucial to the characterisation of EBPR. The optimal glycogen and PHA quantification methods were sensitive to the heterogeneity of the sample, in terms of its microbial structure (floccular or granular) and, for PHA, in terms of the size and the number of substituents of the monomers forming the copolymer. Additionally, by characterising six full-scale EBPR WWTPs, in terms of their overall performance, microbial identity and metabolism, the composition of polyphosphate accumulating organisms (PAOs) was fairly similar in all plants. Also, a warmer climate was not sufficient to justify a higher presence of glycogen accumulating organisms (GAOs). Differing levels of denitrifying PAOs were obtained in different plants and the involvement of the tricarboxylic acid (TCA) cycle in the anaerobic metabolism of PAOs was observed. Furthermore, a metabolic model developed in this study, which incorporates the involvement of the anaerobic TCA cycle and a new description of the aerobic maintenance processes, was able to accurately describe the chemical cycling of soluble and intracellular compounds, while requiring a simple calibration procedure. A series of simulations demonstrated that lower acetate concentrations in the feed and higher aeration retention times would favour the TCA cycle metabolism over the glycolysis pathway, which would explain why the former has been more frequently encountered in WWTPs and the latter in lab-scale enriched cultures.

Fundação para a Ciência e Tecnologia - PhD grant (SFRH/BD/29477/2006)