Activated Sludge Settlers: Design and Optimization

1987 ◽  
Vol 19 (3-4) ◽  
pp. 613-623 ◽  
Author(s):  
P F. C. Catunda ◽  
A. C. van Haandel
Keyword(s):  
Activated Sludge ◽  
Surface Area ◽  
Loading Rate ◽  
Operational Cost ◽  
Design And Optimization ◽  
Mixed Liquor ◽  
Solids Loading ◽  
Solids Concentration ◽  
Sludge Thickening ◽  
Sludge Settling

Activated sludge settlers perform two functions simultaneously: clarification and sludge thickening. Depending on the values of the mixed liquor and return sludge concentrations and on the sludge settling characteristics either one of these functions may limit the solids loading rate that can be applied to the settler, which in turn determines the required settler surface area. A method is developed to establish which of the two functions is determinant for the maximum solids loading rate in a particular design situation. Expressions are derived to calculate the required settler surface area for clarification and for thickening. These expressions are based on the experimentally verfied supposition that the zone settling velocity decreases exponentially with increasing suspended solids concentration. A graphical method to determine the optimal mixed liquor and return sludge concentrations for minimum construction and operational cost is presented.

Understanding the contribution of biofilm in an integrated fixed-film-activated sludge system (IFAS) designed for nitrogen removal

2015 ◽  
Vol 71 (10) ◽  
pp. 1500-1506 ◽  
Author(s):  
P. Moretti ◽  
J. M. Choubert ◽  
J. P. Canler ◽  
O. Petrimaux ◽  
P. Buffiere ◽  
...  
Keyword(s):  
Activated Sludge ◽  
Nitrogen Removal ◽  
Loading Rate ◽  
Pilot Scale ◽  
Operating Conditions ◽  
Biofilm Growth ◽  
Operational Conditions ◽  
Solids Concentration ◽  
Fixed Film ◽  
Autotrophic Biomass

The objective of this study is to improve knowledge on the integrated fixed-film-activated sludge (IFAS) system designed for nitrogen removal. Biofilm growth and its contribution to nitrification were monitored under various operating conditions in a semi-industrial pilot-scale plant. Nitrification rates were observed in biofilms developed on free-floating media and in activated sludge operated under a low sludge retention time (4 days) and at an ammonia loading rate of 45–70 gNH4-N/kgMLVSS/d. Operational conditions, i.e. oxygen concentration, redox potential, suspended solids concentration, ammonium and nitrates, were monitored continuously in the reactors. High removal efficiencies were observed for carbon and ammonium at high-loading rate. The contribution of biofilm to nitrification was determined as 40–70% of total NOx-N production under the operating conditions tested. Optimal conditions to optimize process compacity were determined. The tested configuration responds especially well to winter and summer nitrification conditions. These results help provide a deeper understanding of how autotrophic biomass evolves through environmental and operational conditions in IFAS systems.

Estimation of suspended solids concentrations in activated sludge settling tanks

1997 ◽  
Vol 35 (8) ◽  
pp. 127-135 ◽  
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.

Effect of loading rate and intermittent aeration cycle on nitrogen removal in membrane separation activated sludge process

2002 ◽  
Vol 46 (8) ◽  
pp. 119-126 ◽  
Author(s):  
H. Nagaoka ◽  
C. Kudo
Keyword(s):  
Activated Sludge ◽  
Nitrogen Removal ◽  
Loading Rate ◽  
Membrane Separation ◽  
Organic Loading Rate ◽  
Aeration Tank ◽  
Activated Sludge Process ◽  
Intermittent Aeration ◽  
Organic Loading ◽  
Mixed Liquor

The performance of the submerged membrane separation activated sludge process with intermittent aeration was investigated in a laboratory scale experiment by changing organic loading rate and intermittent aeration cycle. A rectangular PVC tank was used as an aeration tank, in which a flat-sheet type Micro-Filtration membrane made of poly-olefin with a pore size of 0.2 mm was submerged. Organic loading rate to the reactor was set at 0.3 and 0.8 g-TOC/L/day. C/N ratio in the feed was set at around 5.0 for every condition. Aeration cycle was changed from 10 min-10 min (aeration - stop) to 120 min-120 min in different organic loading conditions. Flux through the membrane was set at 0.25 m/day. Membrane fouling proceeded rapidly in 0.8 g-TOC/L/day conditions. However, when organic loading rate was 0.3 g-TOC/L/day, bacterial metabolic substances were degraded rapidly compared to the production, thereby decreasing viscosity in mixed liquor. Nitrogen removal rate was between 60% and 80% for 0.8 g-TOC/L/day loading, and between 50% and 65% for 0.3 g-TOC/L/day loading. And the nitrogen removal was highest in 40 min to 60 min aeration cycle conditions. Too short aeration cycle did not result in sufficiently long anoxic periods for denitrification while too long a cycle resulted in unnecessary anaerobic periods after depletion of nitrate. Intermittent aeration was effective also for decreasing viscosity in mixed liquor.

Incidence of Sphaerotilus Natans in Laboratory Scale Activated Sludge Systems

1989 ◽  
Vol 21 (4-5) ◽  
pp. 29-41 ◽  
Author(s):  
D. M. D. Gabb ◽  
G. A. Ekama ◽  
D. Jenkins ◽  
G. v. R. Marais
Keyword(s):  
Activated Sludge ◽  
Surface Area ◽  
Volume Ratio ◽  
Full Scale ◽  
Laboratory Scale ◽  
Sphaerotilus Natans ◽  
Attached Growth ◽  
Mixed Liquor ◽  
Activated Sludge Systems

Bulking in activated sludge systems due to proliferation of Sphaerotilus natans is very common in laboratory-scale but rare in full-scale systems. From two laboratory-scale studies it is concluded that a cause for proliferation was attached growth of S.natans on the walls of the feed lines and reactor surfaces continuously seeding the mixed liquor. It is suggested that S.natans bulking in laboratory-scale systems is common compared to full-scale systems because the surface area/volume ratio of the former is orders of magnitude higher than that of the latter so that the potential for seeding from attached growths in laboratory-scale plants is correspondingly higher. It would appear that in laboratory-scale activated sludge systems regular cleaning of the feed lines and daily scrubbing of the reactor and other wetted surfaces will eliminate S.natans bulking due to seeding of the mixed liquor from these surfaces.

Solids routing in an activated sludge process during hydraulic overloads

1996 ◽  
Vol 34 (3-4) ◽  
pp. 9-16 ◽  
Author(s):  
Youngchul Kim ◽  
Wesley O. Pipes
Keyword(s):  
Activated Sludge ◽  
Suspended Solids ◽  
Quantitative Description ◽  
Settling Tank ◽  
Plant Performance ◽  
Activated Sludge Process ◽  
Mixed Liquor ◽  
Solids Concentration ◽  
Storm Flow ◽  
The Individual

In order to provide a quantitative description of solids wash-out from the settling tanks of an activated sludge process, a method for “routing” of the suspended solids through the settling tanks was developed. The objective was to develop a method which can be used to predict the mixed liquor suspended solids concentration (X) and the sludge blanket depth (SBD) in the clarifiers during transient hydraulic overloads. There were 27 individual hydraulic overloading events encountered during 31 months of study. The solids routing and the SBD prediction were performed for the individual storm flow events by using settling tank operating data. The results of solids routing analysis were found to be satisfactory. The mixed liquor solids concentration can be predicted within ± 10%. The application of a solids storage relationship developed for the settling tanks was found to be useful for describing the dynamic behavior of the SBD during transient hydraulic overloads. The solids wash-out predictions for rainstorm periods corresponded with the plant performance. Operational procedures for avoiding solids wash-out are also discussed.

scholarly journals The influence of operating conditions of activated-sludge treatment on the behaviour of f2 coliphage

1979 ◽  
Vol 82 (2) ◽  
pp. 285-291 ◽  
Author(s):  
S. A. Balluz ◽  
M. Butler
Keyword(s):  
High Temperature ◽  
Activated Sludge ◽  
Suspended Solids ◽  
Operating Conditions ◽  
Regression Coefficients ◽  
Sludge Treatment ◽  
Mixed Liquor ◽  
Treatment Conditions ◽  
Solids Concentration ◽  
Flow Through

SUMMARYThe behaviour of f2 coliphage during activated-sludge treatment was influenced by the temperature, flow-through-time, concentration of mixed liquor suspended solids and the virus load.The most sensitive way to detect behavioural changes was to examine the regression coefficients for the rate of uptake or loss of virus by the mixed liquor solids. This type of analysis revealed, for instance, high values when the solids concentration was high and even greater values occured when high inocula were used. At high temperature the rate of loss of virus titre after inoculation had stopped was greater than the rate of uptake of virus during inoculation although in all other conditions uptake occurred at a greater rate than the loss of virus. The coefficients were relatively low when the flow rate was increased, when the temperature was low or when the inoculum was small.The distribution of virus between the solids and liquid fractions of the mixed liquor varied somewhat for all conditions but was notably different when (a) the plant was incubated at 5 °C when there was much less virus in the solids fraction than usual, and (b) when the inoculum was low and a much higher proportion of virus was found in the solids.The efficiency with which virus was removed across the plant was the least-sensitive determinant of viral behaviour and the value was about the same for most treatment conditions. However, low or high inocula did result in some increased or decreased removal of virus, respectively.

Effects of detergent zeolite in a nitrogen removal activated sludge process

1998 ◽  
Vol 38 (2) ◽  
pp. 41-48 ◽  
Author(s):  
L. Piirtola ◽  
B. Hultman ◽  
M. Löwén
Keyword(s):  
Activated Sludge ◽  
Surface Area ◽  
Nitrogen Removal ◽  
Surface Characteristics ◽  
Activated Sludge Process ◽  
Batch Tests ◽  
Negative Effect ◽  
Negative Surface ◽  
Negative Surface Charge ◽  
Sludge Settling

Two detergent zeolites, Doucil-P and Doucil-A24, were tested for their weighting effect in batch tests and on a nitrogen removal activated sludge process. The batch tests with a long contact time revealed a negative effect of zeolite on sludge filterability. In continuous pilot tests, the zeolite accumulated in sludge causing an increase in sludge suspended solids of up to 25 to 30%. This accumulation improved the activated sludge settling characteristics. The zeolite did not affect the treatment efficiency or the amount of filamentous bacteria. Measurements were made on sludge surface characteristics, i.e. specific surface area, surface potential and surface energy. A slight increase in surface area and decrease in negative surface charge caused by zeolite addition was observed. The aluminium concentrations in sludge increased but there was no correlation to the concentration of the accumulated zeolite in sludge.

Comparison of the 1D flux theory with a 2D hydrodynamic secondary settling tank model

2004 ◽  
Vol 50 (7) ◽  
pp. 195-204 ◽  
Author(s):  
G.A. Ekama ◽  
P. Marais
Keyword(s):  
Surface Area ◽  
Loading Rate ◽  
Settling Tank ◽  
Full Scale ◽  
Tank Model ◽  
Marked Influence ◽  
Solids Loading ◽  
Small Influence ◽  
Secondary Settling ◽  
Sloping Bottom

The applicability of the 1D idealized flux theory (1DFT) for design of secondary settling tanks (SSTs) is evaluated by comparing its predicted maximum surface overflow (SOR) and solids loading (SLR) rates with that calculated from the 2D hydrodynamic model SettlerCAD using as a basis 35 full scale SST tress tests conducted on different SSTs with diameters from 30 to 45m and 2.25 to 4.1m side water depth, with and without Stamford baffles. From the simulations, a relatively consistent pattern appeared, i.e. that the 1DFT can be used for design but its predicted maximum SLR needs to be reduced by an appropriate flux rating, the magnitude of which depends mainly on SST depth and hydraulic loading rate (HLR). Simulations of the sloping bottom shallow (1.5-2.5 m SWD) Dutch SSTs tested by STOWa and the Watts et al. SST, all with doubled SWDs, and the Darvill new (4.1 m) and old (2.5 m) SSTs with interchanged depths, were run to confirm the sensitivity of the flux rating to depth and HLR. Simulations with and without a Stamford baffle were also done. While the design of the internal features of the SST, such as baffling, have a marked influence on the effluent SS concentration for underloaded SSTs, these features appeared to have only a small influence on the flux rating, i.e. capacity, of the SST. In the meantime until more information is obtained, it would appear that from the simulations so far that the flux rating of 0.80 of the 1DFT maximum SLR recommended by Ekama and Marais remains a reasonable value to apply in the design of full scale SSTs – for deep SSTs (4 m SWD) the flux rating could be increased to 0.85 and for shallow SSTs (2.5 m SWD) decreased to 0.75. It is recommended that (i) while the apparent interrelationship between SST flux rating and depth suggests some optimization of the volume of the SST, that this be avoided and that (ii) the depth of the SST be designed independently of the surface area as is usually the practice and once selected, the appropriate flux rating is applied to the 1DFT estimate of the surface area.

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