Long-term effects of hydrocyclone operation on activated sludge morphology and full-scale secondary settling tank wet-weather operation in long sludge age WWTP

Natalia Gemza; Kamil Janiak; Bartosz Zięba; Jacek Przyszlak; Magdalena Kuśnierz

doi:10.1016/j.scitotenv.2022.157224

Long-term effects of hydrocyclone operation on activated sludge morphology and full-scale secondary settling tank wet-weather operation in long sludge age WWTP

Sci Total Environ. 2022 Nov 1:845:157224. doi: 10.1016/j.scitotenv.2022.157224. Epub 2022 Jul 12.

Authors

Natalia Gemza¹, Kamil Janiak², Bartosz Zięba³, Jacek Przyszlak⁴, Magdalena Kuśnierz⁵

Affiliations

¹ Faculty of Environmental Engineering, Wroclaw University of Science and Technology, Wybrzeże Wyspiańskiego 27, 50-370 Wroclaw, Poland; Wroclaw Municipal Water and Sewage Company, Na Grobli 19, 50-421 Wroclaw, Poland. Electronic address: natalia.gemza@pwr.edu.pl.
² Faculty of Environmental Engineering, Wroclaw University of Science and Technology, Wybrzeże Wyspiańskiego 27, 50-370 Wroclaw, Poland; Wroclaw Municipal Water and Sewage Company, Na Grobli 19, 50-421 Wroclaw, Poland.
³ Faculty of Environmental Engineering, Wroclaw University of Science and Technology, Wybrzeże Wyspiańskiego 27, 50-370 Wroclaw, Poland.
⁴ Wroclaw Municipal Water and Sewage Company, Na Grobli 19, 50-421 Wroclaw, Poland.
⁵ The Faculty of Environmental Engineering and Geodesy, Wroclaw University of Environmental and Life Sciences, Norwida 25, 50-375 Wroclaw, Poland.

PMID: 35835188
DOI: 10.1016/j.scitotenv.2022.157224

Abstract

This paper presents the study concerning long-term effects of a full scale hydrocyclone unit implemented in a continuous flow long sludge age system, on sedimentation, treatment efficiency and sludge morphology. The research concentrates on identifying the mechanisms of sludge behaviour within the system. The gravimetric selection of activated sludge via a hydrocyclone is a recent development for enhancing sludge separation, where heavier flocs are retained in the system, and lighter ones are discarded as waste sludge. The effects of implementing hydroclyclones were analysed with the use of SEM imagining and fractal dimensioning through the frequent assessment of sludge settling capabilities, effluent quality, and floc properties. Over the course of 60 weeks of hydrocyclone operation, sedimentation efficiency varied significantly. Sludge volume index values of 40 mL/g, achieved during the warm season, were not sustained when the temperature decreased and an overgrowth of filamentous bacteria occurred. Good settling efficiency was also observed in batch tests, where settling velocity of experimental sludge was app. 1 m/h higher than for the reference train at the same concentrations. This was confirmed during wet weather, as the experimental train sustained safe sludge blanket height in secondary clarifiers. SEM imaging and fractal dimension analysis revealed that the underflow that returned to the system had a more compact and spherical shape, which led to an increased content of granule-like particles in the reactor. The presence of flocs with a diameter exceeding 900 μm in the underflow, which is not observed in the feed, indicated agglomeration within the hydrocyclone. This is contradictory to most of the literature data coming from laboratory experiments. This phenomenon was attributed to differences in the size and geometry of the used hydrocyclones, and the potential process mechanism was presented.

Keywords: Fractal dimension; Hydrocyclone; Sludge granules; Sludge settling.

MeSH terms

Bacteria
Bioreactors
Fractals
Sewage*
Waste Disposal, Fluid* / methods
Weather

Substances

Sewage