Characterization of activated sludge settling properties with a sludge collapse-acceleration stage

توضیحات

ABSTRACT

The sedimentability of the activated sludge can be affected by the presence of a large variety of coagulants and polymers from a previous physical-chemical process. In this paper, the activated sludge settling process in industrial wastewater treatment plants where the sludge does not settle in a conventional way is studied. The two observed constant hindered settling velocity stages and the instant the intermediate sludge acceleration period occurs are described. A variation of the Richardson and Zaki model is used to characterize the two stages of constant settling velocity. The concentration of suspended solids, where a sudden decrease of hindered settling velocity was observed, is calculated. Finally, a new hypothesis to explain the processes triggering the collapse of the initial homogeneous sludge structure and the existence of an acceleration period is formulated.

INTRODUCTION

Many secondary settling tanks design methods are based on the experience acquired in the design of urban wastewater treatment plants. It is also common to use models to simulate settling tanks by calculating the hindered settling velocity from standard values or using empirical formulas obtained from urban wastewater treatment plants. However, in some urban wastewater treatment plants, and especially in industrial ones, the sedimentability of activated sludge can be affected by the presence of coagulants and polymers used in a previous physicalchemical process.In a batch settling test with activated sludge it is usual to find an initial induction stage of a few minutes. The increase of the settling velocity during the induction stage is due to the dissipation of the turbulence generated in the filling of the settling column. The presence of cationic polymers in the sludge reduces the length of this induction period and increases the hindered settling velocity of the sludge. The existence of an induction period in settling tests with flocculate suspensions in the compression range has also been described. This induction period is due to the initial increase in the permeability of the suspension resulting from the .formation of channels through which the water rises

Year: ۲۰۱۹

Publisher : ELSEVIER

 By : E. Asensia, E. Alemany, A. Seco, J. Ferrer

File Information: English Language/ 10 Page / size: 1.22 MB

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سال : ۱۳۹۷

ناشر : ELSEVIER

کاری از : E. Asensia، E. Alemany، A. Seco، J. Ferrer

اطلاعات فایل : زبان انگلیسی / 10 صفحه / حجم : MB 1.22

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