Characterizing shallow secondary clarifier performance where conventional flux theory over-estimates allowable solids loading rate

The performance characteristics of relatively shallow (3.3 and 3.7 m sidewater depth in 30.5 m diameter) activated sludge secondary clarifiers were extensively evaluated during a 2-year testing program at the City of Akron Water Reclamation Facility (WRF), Ohio, USA. Testing included hydraulic and solids loading stress tests, and measurement of sludge characteristics (zone settling velocity (ZSV), dispersed and flocculated total suspended solids), and the results were used to calibrate computational fluid dynamic (CFD) models of the various clarifiers tested. The results demonstrated that good performance could be sustained at surface overflow rates in excess of 3 m/h, as long as the clarifier influent mixed liquor suspended solids (MLSS) concentration was controlled to below critical values. The limiting solids loading rate (SLR) was significantly lower than the value predicted by conventional solids flux analysis based on the measured ZSV/MLSS relationship. CFD analysis suggested that this resulted because mixed liquor entering the clarifier was being directed into the settled sludge blanket, diluting it and also creating a ‘thin’ concentration sludge blanket that overlays the thicker concentration sludge blanket typically expected. These results indicate the need to determine the allowable SLR for shallow clarifiers using approaches other than traditional solids flux analysis. A combination of actual testing and CFD analyses are demonstrated here to be effective in doing so.

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Development of a flocculation sub-model for a 3-D CFD model based on rectangular settling tanks

Water Science & Technology ◽

10.2166/wst.2011.035 ◽

2011 ◽

Vol 63 (2) ◽

pp. 213-219 ◽

Cited By ~ 16

Author(s):

M. Gong ◽

S. Xanthos ◽

K. Ramalingam ◽

J. Fillos ◽

K. Beckmann ◽

...

Keyword(s):

New York ◽

Suspended Solids ◽

Cfd Model ◽

Mixed Liquor ◽

City College ◽

Solids Loading ◽

Before And After ◽

Computational Fluid Dynamics Cfd ◽

3D Computer Model ◽

Relationship Of

To assess performance and evaluate alternatives to improve the efficiency of rectangular Gould II type final settling tanks (FSTs), New York City Department of Environmental Protection and City College of NY developed a 3D computer model depicting the actual structural configuration of the tanks and the current and proposed hydraulic and solids loading rates. Fluent 6.3.26™ was the base platform for the computational fluid dynamics (CFD) model, for which sub-models of the SS settling characteristics, turbulence, flocculation and rheology were incorporated. This was supplemented by field and bench scale experiments to quantify the coefficients integral to the sub-models. The 3D model developed can be used to consider different baffle arrangements, sludge withdrawal mechanisms and loading alternatives to the FSTs. Flocculation in the front half of the rectangular tank especially in the region before and after the inlet baffle is one of the vital parameters that influences the capture efficiency of SS. Flocculation could be further improved by capturing medium and small size particles by creating an additional zone with an in-tank baffle. This was one of the methods that was adopted in optimizing the performance of the tank where the CCNY 3D CFD model was used to locate the in-tank baffle position. This paper describes the development of the flocculation sub-model and the relationship of the flocculation coefficients in the known Parker equation to the initial mixed liquor suspended solids (MLSS) concentration X0. A new modified equation is proposed removing the dependency of the breakup coefficient to the initial value of X0 based on preliminary data using normal and low concentration mixed liquor suspended solids values in flocculation experiments performed.

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Activated Sludge Settlers: Design and Optimization

Water Science & Technology ◽

10.2166/wst.1987.0241 ◽

1987 ◽

Vol 19 (3-4) ◽

pp. 613-623 ◽

Cited By ~ 1

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.

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The effect of mixed liquor suspended solids (MLSS) on biofouling in a hybrid membrane bioreactor for the treatment of high concentration organic wastewater

Water Science & Technology ◽

10.2166/wst.2011.338 ◽

2011 ◽

Vol 63 (8) ◽

pp. 1701-1706 ◽

Cited By ~ 19

Author(s):

A. Damayanti ◽

Z. Ujang ◽

M. R. Salim ◽

G. Olsson

Keyword(s):

Membrane Bioreactor ◽

Suspended Solids ◽

Loading Rate ◽

Removal Rate ◽

Transmembrane Pressure ◽

High Concentration ◽

Critical Flux ◽

Mixed Liquor ◽

Palm Oil Mill ◽

Volumetric Loading

Biofouling is a crucial factor in membrane bioreactor (MBR) applications, particularly for high organic loading operations. This paper reports a study on biofouling in an MBR to establish a relationship between critical flux, Jc, mixed liquor suspended solids (MLSS) (ranging from 5 to 20 g L−1) and volumetric loading rate (6.3 kg COD m−3 h−1) of palm oil mill effluent (POME). A lab-scale 100 L hybrid MBR consisting of anaerobic, anoxic, and aerobic reactors was used with flat sheet microfiltration (MF) submerged in the aerobic compartment. The food-to-microorganism (F/M) ratio was maintained at 0.18 kg COD kg−1 MLSSd−1. The biofouling tendency of the membrane was obtained based on the flux against the transmembrane pressure (TMP) behaviour. The critical flux is sensitive to the MLSS. At the MLSS 20 g L−1 the critical flux is about four times lower than that for the MLSS concentration of 5 g L−1. The results showed high removal efficiency of denitrification and nitrification up to 97% at the MLSS concentration 20 g L−1. The results show that the operation has to compromise between a high and a low MLSS concentration. The former will favour a higher removal rate, while the latter will favour a higher critical flux.

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Improving the Performance of Houston's Southwest Wastewater Treatment Plant, U.S.A.

Water Science & Technology ◽

10.2166/wst.1984.0233 ◽

1984 ◽

Vol 16 (10-11) ◽

pp. 317-329 ◽

Cited By ~ 1

Author(s):

M T Garrett ◽

Josten Ma ◽

William Yang ◽

Gurdip Hyare ◽

Teresa Norman ◽

...

Keyword(s):

Wastewater Treatment ◽

Wastewater Treatment Plant ◽

Suspended Solids ◽

Transition Period ◽

Settling Tank ◽

Treatment Plant ◽

Low Flow ◽

Mixed Liquor ◽

Storm Flow ◽

The City

In 1981, the City of Houston's Southwest Wastewater Treatment Plant (144,000 m3/d) was experiencing occasional afternoon bulking with loss of solids to the effluent. The plant employs sludge reaeration with about even allocation of tank volume to mixed liquor and return sludge aeration. A dynamic model of solids transfer from influent to mixed liquor to settling tank to return sludge aeration and wasting was developed for use on a desk-top computer. The model predicted that a counter-intuitive reduction in the return sludge rate would redistribute the solids to less in the mixed liquor and more in the sludge reaeration tanks, but would also generate a sludge blanket during the transition period. However, if the change were made when there would be several low-flow days, then the blanket would stay within the settling tanks. The Thanksgiving Holidays of 1981 were chosen for the change in the return sludge rate. Low flow occurred as expected and there was no loss of solids. The effluent suspended solids improved as expected, but the SVI also improved from 172 ml/g to 72 ml/g. The reduction in the return sludge flow rate allowed extra hydraulic capacity for storm flows. The improved control of solids was demonstrated by simulating a storm flow of 4.0 m/h overflow rate by taking settling tanks out of service with resulting effluent TSS of less than 20 mg/L.

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Experiment of Polyester Wastewater Treatment by Aerobic Membrane Bioreactor and an Engineering Application

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.518-523.2130 ◽

2012 ◽

Vol 518-523 ◽

pp. 2130-2137

Author(s):

Si Hao Lv ◽

Hui Chang ◽

Zhi Hui Liang ◽

Yan Yan Zeng ◽

Hong Bo Fan

Keyword(s):

Water Quality ◽

Pilot Study ◽

Membrane Bioreactor ◽

Suspended Solids ◽

Loading Rate ◽

Engineering Application ◽

Full Scale ◽

Effluent Water ◽

Small Influence ◽

Volumetric Loading

A pilot study was carried out to evaluate the application of aerobic submerged MBR in treating polyester wastewater and a full scale system in which MBR was adopted as the key aspect was put forward to treat the polyester wastewater of Zhuhai Yuhua Polyester co., Ltd., China. The pilot study revealed that HRT could be affected by the influent COD, and a HRT larger than 36h was proposed for treating polyester wastewater by MBR. Volumetric loading rate and sludge loading rate ranged in 0.7-2.0 kgCOD/m3•d and 0.09~0.24 kgCOD/ kgMLSS•d respectively were of small influence on the COD removal. DO in the range of 2.5-4.0 mg/L seemed to be optimal for avoiding limitations due to oxygen concentration and creating an effective turbulence. The modified full scale system which includes anaerobic digesting tank and MBR followed by a stabilization pond was verified to be effective to treat the polyester wastewater in the latest two years. The results illustrated that the effluent water quality could meet the discharge limits of water pollutants (DB 44/26-2001) which was established in Guangdong, China. Observed sludge yield of the system fluctuated between 0.10-0.18 gMLSS/gCOD and averaged at 0.137 gMLSS/gCOD. The membrane permeate at around 10 L/m2h, TMP of less than 0.7bar, and total mixed liquor suspended solids (MLSS) between 6-7g/L were suitable to operate the MBR.

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Evaluating the treatment performance of a full scale Activated Sludge Plant in Islamabad, Pakistan

Water Practice & Technology ◽

10.2166/wpt.2012.016 ◽

2012 ◽

Vol 7 (1) ◽

Cited By ~ 1

Author(s):

S. S. Fatima ◽

S. Jamal Khan

Keyword(s):

Wastewater Treatment ◽

Activated Sludge ◽

Wastewater Treatment Plant ◽

Suspended Solids ◽

Treatment Plant ◽

Oxygen Demand ◽

Full Scale ◽

Operational Parameter ◽

Mixed Liquor ◽

Treatment Performance

In this study, the performance of wastewater treatment plant located at sector I-9 Islamabad, Pakistan, was evaluated. This full scale domestic wastewater treatment plant is based on conventional activated sludge process. The parameters which were monitored regularly included total suspended solids (TSS), mixed liquor suspended solids (MLSS), mixed liquor volatile suspended solids (MLVSS), biological oxygen demand (BOD), and chemical oxygen demand (COD). It was found that the biological degradation efficiency of the plant was below the desired levels in terms of COD and BOD. Also the plant operators were not maintaining consistent sludge retention time (SRT). Abrupt discharge of MLSS through the Surplus Activated sludge (SAS) pump was the main reason for the low MLSS in the aeration tank and consequently low treatment performance. In this study the SRT was optimized based on desired MLSS concentration between 3,000–3,500 mg/L and required performance in terms of BOD, COD and TSS. This study revealed that SRT is a very important operational parameter and its knowledge and correct implementation by the plant operators should be mandatory.

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Measurement of flow velocity profiles in tank structures using the prototype device OCM Pro LR

Water Science & Technology ◽

10.2166/wst.2011.173 ◽

2011 ◽

Vol 64 (1) ◽

pp. 263-270 ◽

Cited By ~ 2

Author(s):

K. Klepiszewski ◽

M. Teufel ◽

S. Seiffert ◽

E. Henry

Keyword(s):

Flow Velocity ◽

Large Scale ◽

Fluid Dynamic ◽

Waste Water Treatment ◽

Transport Processes ◽

Treatment Efficiency ◽

Cleaning Efficiency ◽

Cfd Modelling ◽

Ultrasonic Signals ◽

Cfd Models

Generally, studies investigating the treatment efficiency of tank structures for storm water or waste water treatment observe pollutant flows in connection with conditions of hydraulic loading. Further investigations evaluate internal processes in tank structures using computational fluid dynamic (CFD) modelling or lab scale tests. As flow paths inside of tank structures have a considerable influence on the treatment efficiency, flow velocity profile (FVP) measurements can provide a possibility to calibrate CFD models and contribute to a better understanding of pollutant transport processes in these structures. This study focuses on tests carried out with the prototype FVP measurement device OCM Pro LR by NIVUS in a sedimentation tank with combined sewer overflow (CSO) situated in Petange, Luxembourg. The OCM Pro LR measurement system analyses the echo of ultrasonic signals of different flow depths to get a detailed FVP. A comparison of flow velocity measured by OCM Pro LR with a vane measurement showed good conformity. The FVPs measured by OCM Pro LR point out shortcut flows within the tank structure during CSO events, which could cause a reduction of the cleaning efficiency of the structure. The results prove the applicability of FVP measurements in large-scale structures.

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Coarse filters for pond effluent polishing: comparison of loading rates and grain sizes

Water Science & Technology ◽

10.2166/wst.2007.342 ◽

2007 ◽

Vol 55 (11) ◽

pp. 121-126 ◽

Cited By ~ 1

Author(s):

M. von Sperling ◽

J.G.B. de Andrada ◽

W.R. de Melo Júnior

Keyword(s):

Loading Rate ◽

Uasb Reactor ◽

E Coli ◽

Effluent Quality ◽

Loading Rates ◽

Hydraulic Loading ◽

Grain Sizes ◽

Belo Horizonte ◽

The City ◽

Rock Size

A system comprising a UASB reactor, shallow polishing ponds and shallow coarse filters, treating actual wastewater from the city of Belo Horizonte, Brazil, has been evaluated. The main focus of the research was to compare grain sizes and hydraulic loading rates in the coarse filters. Two filters operating in parallel were investigated, with the following grain sizes: Filter 1: 3 to 10 cm; Filter 2: 8 to 20 cm. Two hydraulic loading rates were tested: 0.5 and 1.0 m3/m3.d. The filter with the lower rock size had a better performance than the filter with the larger rock size in the removal of SS and, as a consequence, BOD and COD. A better performance was obtained with the hydraulic loading rate of 0.5 m3/m3.d, as compared to the rate of 1.0 m3/m3.d. The effluent quality during the period with the lower loading rate was very good for discharge into water bodies or for agricultural reuse (median effluent concentrations from Filter 1: BOD: 20 mg/L; COD: 106 mg/L; SS: 28 mg/L; E. coli: 528 MPN/100 mL).

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Improving a one-dimensional centrifugal compressor performance prediction method

Proceedings of the Institution of Mechanical Engineers Part A Journal of Power and Energy ◽

10.1243/095765005x31351 ◽

2005 ◽

Vol 219 (8) ◽

pp. 653-659 ◽

Cited By ~ 16

Author(s):

E Swain

Keyword(s):

Centrifugal Compressor ◽

Performance Prediction ◽

Fluid Dynamic ◽

Three Dimensional ◽

Axial Compressor ◽

Prediction Method ◽

Compressor Cascade ◽

One Dimensional ◽

Compressor Performance ◽

Cfd Analyses

A one-dimensional centrifugal compressor performance prediction technique that has been available for some time is updated as a result of extracting the component performance from three-dimensional computational fluid dynamic (CFD) analyses. Confidence in the CFD results is provided by comparison of overall performance for one of the compressor examples. The extracted impeller characteristic is compared with the original impeller loss model, and this indicated that some improvement was desirable. The position of least impeller loss was determined using a traditional axial compressor cascade method, and suitable algebraic expressions were derived to match the CFD data. The merit of the approach lies with the relative ease that CFD component performance currently can be achieved and adjusting one-dimensional methods to agree with the CFD-derived models.

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