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Transformations of Dissolved and Colloidal Organic Nitrogen in Biological Nutrient Removal Activated Sludge Systems

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The aim of this study was to investigate transformations of colloidal and dissolved organic nitrogen (CON and DON) occurring inside biological nutrient removal (BNR) activated sludge bioreactors. For this purpose, both field measurements (influent vs. effluent fractionation, profiles inside bioreactors) and laboratory batch experiments with the process biomass were carried out at various BNR plants in northern Poland. The survey of the influent and effluent fractions of organic nitrogen and carbon, based on filtration of the samples through three membrane filters including 0.1, 0.45 and 1.2 μm pore size filters, were conducted at eight biological nutrient removal (BNR) plants of different size and configurations. Transformations of organic carbon and nitrogen inside bioreactors were investigated in more detail in two largest plants, i.e. Gdansk (565,000 PE) and Gdynia (515,500 PE). The average influent DON (<0.1 μm) concentrations ranged from 1.1 gN/m3 to 3.9 gN/m3 and DON accounted for only 4–13% of total organic N (TON). In the effluents, this contribution increased to 12–45%. Ultrafiltration on 0.015 μm pore size filters had a minor effect on further reductions of DON. Inside the two studied bioreactors, the largest reductions of the colloidal fraction were found to occur in the anaerobic and anoxic zones, whereas an increase of DON concentrations was observed under aerobic conditions in the last compartment. Batch experiments with the process biomass confirmed that DON was explicitly produced in the aerobic phase and organic N conversion occurred at a significant rate in the anoxic phase.

Keywords: Activated sludge; Biological nutrient removal; CON; Colloidal organic nitrogen; DON; Dissolved organic nitrogen; fractionation; nitrogen removal

Document Type: Research Article


Publication date: 2009-01-01

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