An equation for the empirical design of anoxic zones used to eliminate rising sludges at nitrifying activated sludge plants

1996 ◽  
Vol 33 (3) ◽  
pp. 185-194 ◽  
Author(s):  
M. Sarioglu ◽  
N. Horan
Keyword(s):  
Activated Sludge ◽  
Empirical Equation ◽  
Nitrate Nitrogen ◽  
Critical Concentration ◽  
Settling Tank ◽  
Limited Information ◽  
Batch Experiments ◽  
Anoxic Zone ◽  
Secondary Settling ◽  
Anoxic Zones

Anoxic zones are designed for the removal of nitrogen in nitrifying activated sludge plants. This can be carried out either to achieve a nitrogen discharge consent or to eliminate the problem of rising sludges. The rising sludge problem is mostly encountered in medium and small size plants in warm conditions and there is limited information as to the appropriate design of anoxic zones to protect against rising sludges in the secondary sedimentation tanks. Therefore a series of batch experiments were undertaken in order to establish the critical concentration of nitrate-nitrogen which causes rising sludge in the secondary settling tank and the effect of environmental factors such as temperature (15°C to 30°C) and residual carbon source (100 to 600 mg/1 COD) were examined. Based on the results of these experiments an empirical equation was presented which can be used to size an anoxic zone to eliminate rising sludges. The application of this equation at full-scale plants is discussed.

NUMERICAL MODELLING AND MEASUREMENT IN A TEST SECONDARY SETTLING TANK

1994 ◽  
Vol 30 (2) ◽  
pp. 219-228 ◽  
Author(s):  
C. Dahl ◽  
T. Larsen ◽  
O. Petersen
Keyword(s):  
Numerical Model ◽  
Flow Field ◽  
Activated Sludge ◽  
Settling Tank ◽  
Field Pattern ◽  
Model Description ◽  
Bingham Plastic ◽  
Plastic Characteristic ◽  
Test Tank ◽  
Secondary Settling

A numerical model and measurements of flow and settling in activated sludge suspension is presented. The numerical model is an attempt to describe the complex and interrelated hydraulic and sedimentation phenomena by describing the turbulent flow field and the transport/dispersion of suspended sludge. Phenomena such as free and hindered settling and the Bingham plastic characteristic of activated sludge suspensions are included in the numerical model. Further characterisation and test tank experiments are described. The characterisation experiments were designed to measure calibration parameters for model description of settling and density differences. In the test tank experiments, flow velocities and suspended sludge concentrations were measured with different tank inlet geometry and hydraulic and sludge loads. The test tank experiments provided results for the calibration of the numerical model and for comparing measured and calculated results. The numerical model could, fairly accurately, predict the measured results and both the measured and calculated results showed a flow field pattern identical to the flow fields in full-scale secondary settling tanks. A specific calibration of the Bingham plastic characteristic was needed and further knowledge of activated sludge suspension rheology will be necessary to improve the numerical model.

Filter clogging in coarse pore filtration activated sludge process under high MLSS concentration

2006 ◽  
Vol 54 (10) ◽  
pp. 55-66 ◽  
Author(s):  
M.R. Alavi Moghaddam ◽  
Y. Guan ◽  
H. Satoh ◽  
T. Mino
Keyword(s):  
Activated Sludge ◽  
Settling Tank ◽  
Activated Sludge Process ◽  
Filamentous Bacteria ◽  
Membrane Pores ◽  
Conventional Activated Sludge ◽  
Filtration Membrane ◽  
Aerobic Process ◽  
Filter Clogging ◽  
Secondary Settling

Coarse pore filtration activated sludge process is a type of hybrid process in which the secondary settling tank of the conventional activated sludge process is replaced by non- woven and coarse pore filter modules. The filter has pores, which are irregular in shape, and much bigger than micro-filtration membrane pores in size. The objective of the study is to find out the effect of the microbial community structure on filter clogging in the coarse pore filtration activated sludge process under high MLSS concentration in aerobic and anoxic/aerobic (A/A) conditions. Filter clogging started from day 65 and 70 in the A/A and aerobic process, respectively, but it was more severe in the A/A process compared to that in the aerobic process. EPS contents of sludge did not change significantly during the operation in both processes, and did not have a crucial effect on the observed filter clogging. There was no strong evidence for direct effect of the type and number of metazoa on filter clogging. The main difference between aerobic sludge and A/A sludge during the filter clogging period was the relative abundance of filamentous bacteria. According to the obtained results, it can be concluded that a higher presence of filamentous bacteria could reduce the severity of filter clogging in a coarse pore filtration activated sludge process.

The role and control of sludge age in biological nutrient removal activated sludge systems

2010 ◽  
Vol 61 (7) ◽  
pp. 1645-1652 ◽  
Author(s):  
G. A. Ekama
Keyword(s):  
Activated Sludge ◽  
Nutrient Removal ◽  
Settling Tank ◽  
Biological Nutrient Removal ◽  
Hydraulic Control ◽  
Dual Purpose ◽  
Waste Sludge ◽  
Secondary Settling ◽  
And Control ◽  
Activated Sludge Systems

The sludge age is the most fundamental and important parameter in the design, operation and control of biological nutrient removal (BNR) activated sludge (AS) systems. Generally, the better the effluent and waste sludge quality required from the system, the longer the sludge age, the larger the biological reactor and the more wastewater characteristics need to be known. Controlling the reactor concentration does not control sludge age, only the mass of sludge in the system. When nitrification is a requirement, sludge age control becomes a requirement and the secondary settling tanks can no longer serve the dual purpose of clarifier and waste activated sludge thickeners. The easiest and most practical way to control sludge age is with hydraulic control by wasting a defined proportion of the reactor volume daily. In AS plants with reactor concentration control, nitrification fails first. With hydraulic control of sludge age, nitrification will not fail, rather the plant fails by shedding solids over the secondary settling tank effluent weirs.

Improving settling dynamics of activated sludge by adding fine talc powder

1996 ◽  
Vol 34 (5-6) ◽  
pp. 11-18 ◽  
Author(s):  
Michael R. Rasmussen ◽  
Torben Larsen ◽  
Frédéric Clauss
Keyword(s):  
Numerical Simulation ◽  
Activated Sludge ◽  
Settling Velocity ◽  
Settling Tank ◽  
Fine Powder ◽  
Average Density ◽  
Overall Performance ◽  
Settling Characteristic ◽  
Settling Column ◽  
Secondary Settling

The effect of adding varying mixtures of talc and chlorite powder to activated sludge in order to improve the settling characteristic has been studied. The powder is found to improve the settling velocity of the sludge, strictly by increasing the average density of the sludge floc aggregate. The settling velocity was measured with a recirculated settling column under different concentrations and turbulence levels. Numerical simulation of a secondary settling tank indicates that adding fine powder will improve the overall performance considerably.

Modeling and Simulation of the Activated Sludge Process at a Full-Scale WWTP

2012 ◽  
Vol 599 ◽  
pp. 505-509
Author(s):  
Pei Li Lu ◽  
Zhen Liang Li
Keyword(s):  
Activated Sludge ◽  
Settling Tank ◽  
Coupling Model ◽  
Full Scale ◽  
Model Parameters ◽  
Activated Sludge Process ◽  
Modeling Methodology ◽  
Sst Model ◽  
Lower Temperature ◽  
Secondary Settling

Model of a full-scale activated sludge process in a WWTP in Chongqing, China was established by coupling Activated Sludge Model No.2 (ASM2) and secondary settling tank (SST) model. Influent COD of the ASM2 was characterized through combined respirometric and physical-chemical assay and the model parameters were calibrated after evaluating their structural identifiability. The SST model is a flux model based on the consistent modeling methodology, in which a more detailed sludge settling velocity function was proposed to describe the most settling phenomena happened in SST, including discrete settling of floc, zone settling, and compression settling. The coupling model was used to simulate and optimize the operation of the activated sludge process It is concluded that: 1) the effluent COD, SS, TN and TP could be simulated well, 2) the sludge recycle ratio in the SST and the sludge concentration in the bioreactor were optimized to reduce waste sludge, increase the capability to resist load shocks and lower temperature, and improve effluent quality, and 3) an A2/O processes was proposed to upgrade the WWTP for improving the efficiency of N and P removal.

scholarly journals Ocena wpływu systemu technologicznego oczyszczania ścieków na charakterystykę osadu czynnego

2017 ◽  
Vol 26 (3) ◽  
pp. 383-393
Author(s):  
Izabela Płonka ◽  
Barbara Pieczykolan
Keyword(s):  
Activated Sludge ◽  
Municipal Wastewater ◽  
Settling Tank ◽  
Operating Conditions ◽  
Volume Index ◽  
Technological Systems ◽  
Tank System ◽  
Bioreactor System ◽  
Secondary Settling ◽  
Biological Methods

Biological methods are used for treatment of municipal wastewater. These processes can be conducted in various kinds of technological systems. In the paper the comparison of characteristic of activated sludge from two types of technological systems is shown. A flow bioreactor with secondary settling tank (system I) and sequential bioreactor (system II) were used. The study showed, that more favorable operating conditions of activated sludge were in the SBR reactor. The activated sludge in SBR reactor had better sedimentary properties, as indicated by values of sludge volume index and flocs’ sizes. This can be connected with the fact that sludge in SRB reactor is not pumped (what occurs in flow systems). Therefore the sludge is not subjected to unfavorable conditions during hydraulic transport (flocs do not undergo the dispersion). Moreover the values of flocs’ sizes, respiratory activity and specific surface area of sludge from II system were higher in comparison with system I.

Control of Activated Sludge Circulation and of Secondary Settling Tank Hydraulics

1988 ◽  
Vol 20 (1) ◽  
pp. 287-290
Author(s):  
R. Huster ◽  
C. H. Möbius
Keyword(s):  
Waste Water ◽  
Activated Sludge ◽  
Load Capacity ◽  
Waste Water Treatment ◽  
Settling Tank ◽  
Effluent Treatment ◽  
Volume Index ◽  
Research Centre ◽  
Capacity Limits ◽  
Secondary Settling

The directives issued by the German Waste Water Association (ABWASSERTECHNISCHE VEREINIGUNG (ATV)) and by the British WATER RESEARCH CENTRE (WRC) in respect of the rating and control of activated sludge circuits and of the loading of secondary settling tanks of biological waste water treatment plants were studied for their applicability to papermill effluents. To this end, several years' testing was carried out on an activated sludge pilot plant and on various industrial plants. These tests revealed that secondary settling tanks of papermill effluent treatment plants may safely be rated in accordance with ATV up to a sludge volume index (SVI) of 300 ml/g and a sludge return rate of 3. If SVI values are low, the WRC process permits excessive surface loadings and is thus only practicable for high SVI levels. If sedimentation properties of the activated sludge are poor, load capacity limits are indicated more correctly by the WRC method. A simplified settling velocity method derived from the WRC process gives reliable information on the load capacity of secondary settling tanks and may readily be used for sludge circulation control.

scholarly journals Intensification of activated sludge sedimentation processes by means of vacuuming

Vestnik MGSU ◽  
2021 ◽  
pp. 370-380
Author(s):  
Artem A. Kulakov ◽  
Alina F. Filatova
Keyword(s):  
Wastewater Treatment ◽  
Activated Sludge ◽  
Municipal Wastewater ◽  
Wastewater Treatment Plants ◽  
Settling Tank ◽  
Municipal Wastewater Treatment ◽  
Treated Water ◽  
Mixed Liquor ◽  
Municipal Wastewater Treatment Plants ◽  
Secondary Settling

Introduction. The mixed liquor of nitrogen removal wastewater treatment plants is characterized by a high concentration of nitrates and dissolved oxygen at the inlet to the secondary settling tank. In the sludge layer of secondary sedimentation tanks, conditions of decreased oxygen content and uncontrolled denitrification processes take place. This leads to the floating up and removal of sludge with the effluent and secondary pollution of treated water. The purpose of this article is to study the parameters of activated sludge sedimentation in municipal wastewater treatment plants and their intensification by means of vacuuming. Materials and methods. The studies were carried out under laboratory conditions. Activated sludge vacuuming and sedimentation processes were simulated. Diagrams of the “sludge-water” phase reduction (Kinsh curves) were drawn. Mathematical and graphic processing of the results was carried out. Results. Biological treatment of municipal wastewater (aerotank — secondary settling tank) and methods of its intensification by influencing the activated sludge were considered in this article. Trends of activated sludge (at different concentrations of mixed liquor suspended solids) sedimentation were experimentally obtained for municipal wastewater treatment plants. The process of sludge vacuuming was researched, the process efficiency was determined as a function of the treatment time. Conclusions. Vacuuming allows removing gases from the fluid, which accelerates the process of sludge separation from the treated water and prevents it from floating to the surface. The treated sample is characterized by better sedimentation characteristics, density, coarseness and integrity of flakes. The optimal duration of mixed liquor vacuuming before sedimentation is 0.5 minutes; this accelerates the processes of subsequent sedimentation and reduces the removal of sludge with treated water. The results of laboratory tests can be applied to the design of the mixed liquor vacuuming unit before the secondary sedimentation tanks and its sludge separation.

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