Abstract
Aeration is an energy-intensive process of aerobic biological treatment in wastewater treatment plants (WWTP). Two-stage processes enable energy-efficient operation, but oxygen transfer has not been studied in depth before. In this study, α-factors were determined with long-term ex situ steady-state off-gas measurements in pilot-scale test reactors (5.8 m height, 8.3 m3) coupled to full-scale activated sludge basins. A two-stage WWTP with more than 1 Mio population equivalent was studied over 13 months including rain and dry weather conditions. Operating data, surfactant concentrations throughout the two-stage process, and the effect of reverse flexing on pressure loss of diffusers were examined. The values of αmean, αmin, and αmax for design load cases of aeration systems were determined as 0.45, 0.33, and 0.54 in the first high-rate carbon removal stage and as 0.80, 0.69, and 0.91 in the second nitrification stage, respectively. The first stage is characterized by a distinct diurnal variation and decrease in α-factor during stormwater treatment. Surfactants and the majority of the total organic carbon (TOC) load are effectively removed in the first stage; hence, α-factors in the second stage are higher and have a more consistent diurnal pattern. Proposed α-factors enable more accurate aeration system design of two-stage WWTPs. Fouling-induced diffuser pressure loss can be restored effectively with reverse flexing in both treatment stages.
Highlights
Aeration is an essential process in aerobic biological wastewater treatment
On the basis of our long-term off-gas measurements, we summarize below our findOn the basis our long-term off-gas measurements, summarize below our findings relevant for of design and operation of aeration systems in we two-stage activated sludge ings relevant for design and operation of aeration systems in two-stage activated sludge
Thepaper underlying off-gas measurements on aand pilot scale covered a typical range of op- The
Summary
Aeration is an essential process in aerobic biological wastewater treatment. In most wastewater treatment plants (WWTPs), it accounts for more than half of the net energy consumption [1,2,3]. Engineers rely on technical standards providing design guidelines to properly design aeration systems [4,5,6]. Various WWTP process configurations are possible depending on wastewater composition and required effluent target. Each process configuration demands individual design considerations for the aeration system. Provide α-factors to consider inhibiting effects on oxygen transfer in the activated sludge (AS). Comprehensive research on oxygen transfer in two-stage AS processes is not available. This study provides planners with α-factors required for the design of aeration systems in a two-stage configuration. We discuss the impact of stormwater treatment and fluctuations of operating parameters such as TOC
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