PRELIMINARY STUDIES ON THE INFLUENCE OF NEGATIVE PRESSURE ON ACTIVATED SLUDGE FLOCS

A sludge from municipal wastewater plant operated for biological contaminant removal was exposed to three different negative pressures (-200, -500 and -800 hPa) for three different duration times (30 second, 1 and 2 minutes). Sludge volume index, shear sensitivity of the sludge and activated sludge floc characteristic was the object of the study before and after negative pressure treatment. After the treatment the sludge settled better independently on the pressure value and duration time. The shear sensitivity changed the most when the pressure exposure of -800 hPa was 1 minute and longer. The flocs structure was more open after negative pressur and larger part of activated sludge was comprised by large flocs.

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Hydrophobicity of activated sludge flocs and laboratory-grown bacteria

Water Science & Technology ◽

10.2166/wst.1994.0561 ◽

1994 ◽

Vol 30 (11) ◽

pp. 211-218 ◽

Cited By ~ 43

Author(s):

F. Jorand ◽

P. Guicherd ◽

V. Urbain ◽

J. Manem ◽

J. C. Block

Keyword(s):

Activated Sludge ◽

Environmental Conditions ◽

Hydrophobic Interactions ◽

Volume Index ◽

Sludge Volume Index ◽

Hydrophobic Property ◽

Sludge Flocs ◽

Highly Hydrophobic ◽

Different Strains

The cohesion of activated sludge biological flocs is controlled by the ratio between hydrophilic exopolymers in which bacteria are embedded and hydrophobic interactions. As shown in this study highly hydrophobic bacteria coexist in the flocs with highly hydrophilic bacteria which seem to release large quantities of exopolymers (polysaccharides, DNA, proteins…). Addition to the activated sludge of easily assimilable nutrients such as glucose does not change the hydrophobicity of bacteria but increases both exopolymer production and the sludge volume index. The environmental conditions and the bioavailability of nutrients may considerably shift the hydrophilic/hydrophobic balance. Moreover experiments carried out with four different strains to fourteen isolated from activated sludges have shown that a few strains (variable types) have quite considerable possibilities of hydrophobic property variations in the course of growth.

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On-line measurements of settling characteristics in activated sludge

Water Science & Technology ◽

10.2166/wst.1997.0144 ◽

1997 ◽

Vol 36 (4) ◽

pp. 307-312

Author(s):

Michael R. Rasmussen ◽

Torben Larsen

Keyword(s):

Activated Sludge ◽

Settling Velocity ◽

Continuous Measurement ◽

Batch Reactor ◽

Volume Index ◽

Sludge Volume Index ◽

Dynamic Variations ◽

On Line ◽

Settling Column ◽

Settling Characteristics

An on-line settling column for measuring the dynamic variations of settling velocity of activated sludge has been developed. The settling column is automatic and self-cleansing insuring continuous and reliable measurements. The settling column was tested on sludge from a batch reactor where sucrose was added as an impulse to activated sludge. The continuous measurement of settling velocity revealed a highly dynamic response after the sucrose was added. The results were verified with simultaneous measurement of the initial settling rate. A 200 hour experiment showed variations in settling velocity, which was not apparent in the DSVI (Diluted Sludge Volume Index).

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Long-Term Investigation into the Membrane Fouling Behavior in Anaerobic Membrane Bioreactors for Municipal Wastewater Treatment Operated at Two Different Temperatures

Membranes ◽

10.3390/membranes10090231 ◽

2020 ◽

Vol 10 (9) ◽

pp. 231

Author(s):

Yi Ding ◽

Zhansheng Guo ◽

Zhenlin Liang ◽

Xuguang Hou ◽

Zhipeng Li ◽

...

Keyword(s):

Wastewater Treatment ◽

Activated Sludge ◽

Membrane Fouling ◽

Municipal Wastewater ◽

Membrane Bioreactors ◽

Municipal Wastewater Treatment ◽

Sludge Flocs ◽

Microbial Product ◽

Anaerobic Membrane Bioreactors ◽

Sludge Particle

In this study, the characteristics of activated sludge flocs were investigated and their effects on the evolution of membrane fouling were considered in the anaerobic membrane bioreactors (AnMBR), which were operated at 25 and 35 °C for municipal wastewater treatment. It was found that the membrane fouling rate of the AnMBR at 25 °C was more severe than that at 35 °C. The membrane fouling trends were not consistent with the change in the concentration of soluble microbial product (SMP). The larger amount of SMP in the AnMBR at 35 °C did not induce more severe membrane fouling than that in the AnMBR at 25 °C. However, the polysaccharide and protein concentration of extracellular polymeric substance (EPS) was higher in the AnMBR at 25 °C in comparison with that in the AnMBR at 35 °C, and the protein/polysaccharide ratio of the EPS in the AnMBR at 25 °C was higher in contrast to that in the AnMBR at 35 °C. Meanwhile, the fouling tendencies measured for the AnMBRs could be related to the characteristics of loosely bound EPS and tightly bound EPS. The analysis of the activated sludge flocs characteristics indicated that a smaller sludge particle size and more fine flocs were observed at the AnMBR with 25 °C. Therefore, the membrane fouling potential in the AnMBR could be explained by the characteristics of activated sludge flocs.

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Settling Characteristics of Activated Sludge in Danish Treatment Plants with Biological Nutrient Removal

Water Science & Technology ◽

10.2166/wst.1994.0332 ◽

1994 ◽

Vol 29 (7) ◽

pp. 157-165 ◽

Cited By ~ 17

Author(s):

Gert Holm Kristensen ◽

Per Elberg Jørgensen ◽

Per Halkjær Nielsen

Keyword(s):

Activated Sludge ◽

Nutrient Removal ◽

Volume Index ◽

Biological Nutrient Removal ◽

Sludge Volume Index ◽

Filamentous Microorganisms ◽

Best Parameter ◽

One Year ◽

Sludge Settling ◽

Settling Characteristics

In 1989-91, a study was performed to investigate the settling characteristics of activated sludge in Danish treatment plants with biological nutrient removal. The study included three screening series on 38 treatment plants. Furthermore, the study included investigations during one year on seasonal variations in sludge settling characteristics at three treatment plants. The screening investigations were performed in November 1989 and May and September, 1990. Results showed that in the May-screening, 35-45% of the plants had a filament index of 2-2.5 or above, corresponding to a sludge volume index above 150 ml/g. When comparing data for diluted and non-diluted sludge volume indices, a SVI value of 150 ml/g seemed parallel to a DSVI of 110 ml/g. In the November- and September-screenings, some 30% of the plants had activated sludge showing a filament index in or above the critical area. Dominating filamentous microorganisms were found to be (in decreasing order): Microthrix parvicella, Type 0041, Type 021N, Type 0092, Type 0914, and Type 1851. A distinct variation over the year in sludge settling characteristics was found for the three plants. Sludge settling characteristics improved during summer, and deteriorated during winter. For activated sludge with a high content of filamentous microorganisms, the best parameter to follow the variations in sludge settling properties was the filament number. If the activated sludge concentration, the MLSS, varied significantly, the specific filament number was to be applied.

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Effects of Temperature and pH on the Settleability of Activated Sludge Flocs

Water Science & Technology ◽

10.2166/wst.1990.0089 ◽

1990 ◽

Vol 22 (9) ◽

pp. 249-254 ◽

Cited By ~ 15

Author(s):

F. Dilek Çetin ◽

Gülerman Sürücü

Keyword(s):

Activated Sludge ◽

Volume Index ◽

Aeration Tank ◽

Effluent Quality ◽

Sludge Flocs ◽

Secondary Clarifier ◽

Different Temperatures ◽

Effects Of Temperature ◽

Two Parameters ◽

Physiological And Biochemical

In efficient and economical treatment of wastewaters,the settleability of activated sludge is of prime importance. Efficient settlement in the secondary sedimentation tank is required, both to keep the desired effluent quality and to sustain the necessary amount of microorganisms in the aeration tank. On the other hand, the settleability of microorganisms in the secondary clarifier is very dependent on the physiological and biochemical nature of activated sludge flocs, which are determined by the conditions of the aeration tank. In this research, effects of temperature and pH of aeration basin on settleability of activated sludge were studied. Settleability was measured by zone settling velocity and sludge volume index (SVI). Five different temperatures and four different pH values were operated in the aeration basin. It was found that the settleability of activated sludge is greatly affected by these two parameters.

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Impact of septic compounds and operational conditions on the microbiology of an activated sludge system

Water Science & Technology ◽

10.2166/wst.2007.221 ◽

2007 ◽

Vol 55 (6) ◽

pp. 135-142 ◽

Cited By ~ 2

Author(s):

Carl Pelletier ◽

Mary Ann Fitzsimmons ◽

Sophie Deschênes ◽

Michael Paice

Keyword(s):

Activated Sludge ◽

Digital Imaging ◽

Volume Index ◽

Operating Parameters ◽

Sludge Volume Index ◽

Sulphur Compounds ◽

Operational Conditions ◽

Volatile Organic ◽

Volatile Organic Acids ◽

Reduced Sulphur Compounds

In activated sludge (AS) biotreatment, septic compounds such as volatile organic acids and reduced sulphur compounds have been frequently cited as a major cause of Thiothrix and Type 021N filamentous bulking. These filaments are common in Canadian pulp and paper biotreatment systems, where they cause settling problems in secondary clarifiers. We conducted a 14-week study of a TMP/newsprint mill effluent to characterize the septic compounds entering the biotreatment, and to determine correlations with AS biomass characteristics and biotreatment operating parameters. A significant correlation was found between the sludge volume index, the abundance of Type 021N, and the propionic acid (PA) concentration in the primary clarified effluent. PA also induced a significant change in the flocculating bacteria size distribution determined by digital imaging. Consequently, the correlation observed between PA and Type 021N bulking is an indirect effect of inhibition of floc-forming microorganisms, giving a competitive advantage to filaments.

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Occurrence of Microthrix parvicella in sequencing batch reactors

Water Science & Technology ◽

10.2166/wst.2014.106 ◽

2014 ◽

Vol 69 (10) ◽

pp. 1984-1995 ◽

Cited By ~ 2

Author(s):

Lana Mallouhi ◽

Ute Austermann-Haun

Keyword(s):

Activated Sludge ◽

Municipal Wastewater ◽

Batch Reactor ◽

Oxygen Demand ◽

Volume Index ◽

Batch Reactors ◽

Sequencing Batch Reactors ◽

Municipal Wastewater Treatment ◽

Nitrogen And Phosphorus ◽

Microthrix Parvicella

Sequencing batch reactors (SBRs) are known for high process stability and usually have a good sludge volume index (SVI). Nevertheless, in many SBRs in Germany for municipal wastewater treatment, scum and foam problems can occur, and SVI can be larger than 200 mL/g. The microscopic investigations of the activated sludge from plants with nitrogen and phosphorus removal have shown that Microthrix parvicella is dominant in the activated sludge in most of them. Studies showed that the optimum growth of M. parvicella is performed at a high sludge age (>20 d) and low sludge load in the range of 0.05–0.2 kg of biochemical oxygen demand per kg of total suspended solids per day (kg BOD5/(TSS·d)). The investigations in 13 SBRs with simultaneous aerobic sludge stabilization (most of them are operated with a system called differential internal cycle strategy sequential batch reactor (DIC-SBR)) show that M. parvicella is able to grow in sludge loads less than 0.05 kg BOD5/(kg TSS·d) as well. To optimize the operation of those SBRs, long cycle times (8–12 h) and dosing of iron salts to eliminate long-chain fatty acids are both recommended. This leads to better SVI and keeps M. parvicella at a low frequency.

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Estimation of suspended solids concentrations in activated sludge settling tanks

Water Science & Technology ◽

10.2166/wst.1997.0305 ◽

1997 ◽

Vol 35 (8) ◽

pp. 127-135 ◽

Cited By ~ 1

Author(s):

Youngchul Kim ◽

Wesley O. Pipes ◽

Paul-Gene Chung

Keyword(s):

Activated Sludge ◽

Suspended Solids ◽

Marked Effect ◽

Treatment Plant ◽

Accurate Method ◽

Volume Index ◽

Sludge Volume Index ◽

Solids Concentration ◽

Exponential Decrease ◽

Sludge Settling

This is a report of a field study based on data from an activated sludge process in a wastewater treatment plant in Chester, Pennsylvania, USA. The objective was to develop an accurate method for estimation of the average suspended solids concentration (SSB) of the layer of sludge in the settling tanks (the “sludge blanket”). Plant operators estimated SSB by averaging the mixed liquor suspended solids (Sm) and the return sludge suspended solids (Su) concentrations. Measurement of SSB showed that averaging Sm and Su frequently overestimated SSB by a large amount. A different relationship between SSB and parameters which are normally measured for operational purposes was developed. The parameters are Su, the overflow rates and data from the sludge volume index (SVI) measurement. It was found that an increasing overflow rate will result in an exponential decrease in the ratio of SSB to Su. Also, the SVI has a marked effect on the ratio of SSB to Su and thus on the amount of suspended solids which can be stored in the settling tanks. The proposed estimation equation was found to be statistically superior to estimation by averaging the Sm and Su.

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Removal of organic halogens (AOX) from municipal wastewater by powdered activated carbon (PAC)/activated sludge (AS) treatment

Water Science & Technology ◽

10.2166/wst.1997.0377 ◽

1997 ◽

Vol 35 (10) ◽

pp. 147-153 ◽

Cited By ~ 5

Author(s):

C. Bornhardt ◽

J. E. Drewes ◽

M. Jekel

Keyword(s):

Activated Carbon ◽

Activated Sludge ◽

Municipal Wastewater ◽

Activated Carbons ◽

Treatment Plant ◽

Volume Index ◽

Enhancement Effect ◽

Simultaneous Treatment ◽

Volatile Solids ◽

Organic Halogens

The effectiveness of different treatments with powdered activated carbons (PAC) to reduce the AOX-levels in municipal wastewater was investigated in a bench-scale activated sludge (AS) treatment plant. The PAC was added either directly to the aerated basin (simultaneous PAC-treatment), or to a partial stream of clarified effluent, which was treated with PAC in an agitated tank and recirculated to the aerated basin (subsequent PAC-treatment with recirculation). The standard advanced biological treatment reduced the AOX-content by 24%. In the pilot-plant, three types of powdered activated carbons were tested for a simultaneous treatment. The treatment with 100 mg/l PICA PCO Super produced an additional reduction of AOX by 20%, whereas a dosage of 50 mg/l NORIT W-20 showed no enhancement effect, and W-35 led to an additional AOX-removal of about 9%. Also, an improved removal of DOC, NH4-N and PO4-P was observed. In all cases, the PAC addition caused a significantly improved settling of the AS, reducing the sludge-volume-index, and increasing the content of volatile solids of the PAC-sludge. In general, no evidence of a synergistic effect of the PAC addition to activated sludge, nor bioregeneration of the activated carbon, could be observed. This suggests, that the observed effects probably are caused only by simple adsorption.

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