Advances in enhanced biological phosphorus removalamino acids as carbon source and envisaging its integration in high-rate systems

Resumen

Urban wastewater treatment plants (WWTPs) are widely implemented in industrialized countries and they must incorporate processes for nutrients removal (nitrogen (N) and phosphorus (P)). Enhanced biological phosphorus removal (EBPR) has been highly studied at lab scale using simple substrates as carbon source, i.e. volatile fatty acids. As a result, a microbial population enriched in polyphosphate accumulating organisms (PAO) is developed, being Candidatus Accumulibacter phosphatis the species of PAO most frequently found. However, the new microbial identification technologies have demonstrated the presence of other PAO different than Accumulibacter in WWTPs. Since real wastewater is a complex matrix, mainly composed of lipids, proteins and carbohydrates, the need to study EBPR process using complex substrates has arisen. Furthermore, studies on a larger scale than lab-scale should be also performed. In this thesis, the operation of a pilot plant with A2/O configuration for simultaneous removal of organic matter, N and P using glutamate as carbon and nitrogen source was proposed. Moreover, a sequencing batch reactor (SBR) using casein hydrolysate as sole carbon source was operated. As a result, a microbial community enriched in Thiothrix (37%) and Comamonadaceae (15.6%) in the case of A2/O system and a biomass enriched in Tetrasphaera in the SBR were developed. These microbial communities present important differences in comparison to Accumulibacter-enriched systems. Conventional activated sludge process presents high energy consumption, mainly associated to aeration and sludge treatment. In addition, organic matter is mineralized or used for denitrification instead of being utilized for biogas production. For these reasons, WWTPs are energy consuming facilities. Nowadays, the transformation of conventional WWTPs into energy self-sufficient facilities is feasible by implementing the A/B process, which consist of a first step, A-stage, which aims at maximizing the carbon capture into the sludge for being treated through an anaerobic digestion system for biogas production; and a second step, B-stage, where the nitrogen is removed through an autotrophic process. However, this process does not include biological P removal. Therefore, this thesis aims to investigate the possible integration of the EBPR in the A-stage of the A/B process, by incorporating an anaerobic zone in order to allow PAO growth. But, PAO bacteria are washed from the system when the SRT is lower than 4 days, so it was needed to work at higher SRTs than those typically used in high-rate systems (SRT<2 days). In addition, real influent was also used in this study, but an external contribution of organic matter was required for the development of the PAO activity.