Abstract
Phosphorus has been successfully eliminated from wastewater by biological techniques of enhanced biological phosphorus removal (EBPR) process, which relies on a specific microbiota of polyphosphate accumulating organisms (PAOs) that accumulate phosphate as polyphosphates (poly-P). Most methods for quantification of poly-P pools suffer from low accuracy and specificity. More powerful and implementable P-analysis tools are required for poly-P quantification, which will help in improved evaluation of processes in laboratory and full-scale EBPR systems. This study developed two methods to quantify poly-P pools by releasing the poly-P from the cell. During experimental optimization, it was observed that two different methods resulted in the highest phosphate release: acetate addition at a pH of 4.8 and exposure to EDTA solution with a concentration of 1% (w/v). Treatment with EDTA resulted in a higher amount of phosphate release from all sludge samples. This was characterized by P-release of 1.5–2.5 times higher than the control tests. In contrast, treatments with acetate addition at a low pH exhibited that P-release depended upon the types of the sludge samples. The highest P-release amount and rate were found in highly-enriched PAO sludge samples, but with fewer influences on the sludge collected from WWTP, which may be attributed to the lower fraction of PAOs in the sludge. Overall, the proposed approaches to quantify the poly-P concentration can be applied in simple, user-friendly, and cost-effective ways.
Highlights
Phosphorus (P) is one of the most abundant elements in the Earth’s crust and is present in a large variety of forms, either in organic or inorganic forms, and as a monomer or as a constituent part of macromolecules
The presence of EDTA causes P release regardless of aerobic or anaerobic conditions supporting the hypothesis that EDTA has a stressful effect on polyphosphate accumulating organisms (PAOs)
Substantial P release occurred in the EDTA addition tests, where the P release amount rose in the tests with increased EDTA addition, ranging from 1.3 to 10.4 mg P/g total suspended solids (TSS)
Summary
Phosphorus (P) is one of the most abundant elements in the Earth’s crust and is present in a large variety of forms, either in organic or inorganic forms, and as a monomer (phosphate) or as a constituent part of macromolecules (polyphosphates, referred to poly-P). The poly-P content in sludge is an important parameter to study at a fundamental level including its role in the metabolism of specific PAO and the niche differentiation of different PAO clades. Reliable quantification of the poly-P content is of great importance to understand process performance and nutrient recovery potential of wastewater treatment systems. To investigate the effect of poly-P on the metabolism of different types of PAO clades in laboratory studies and modelling approaches (Saia et al, 2017), reliable methods for the determination of poly-P are needed. During the application of EBPR in full-scale wastewater treatment systems or nutrient reclamation facilities, the P-removal capacity of the process can be indicated by the level of poly-P content. To facilitate future studies and optimization of full-scale processes, developing simple and user-friendly methods are required for quantification of intracellular poly-P
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