# STATE POINT ANALYSIS

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```					  STATE POINT
ANALYSIS
WesTech Engineering, Inc.
Salt Lake City, Utah, USA

1
Simplified Activated
Sludge Flow Sheet

Q + RAS                 Q
Q     Aeration
Basin                  Clarifier

RAS

WAS

State Point Analysis

2
Key Parameters used in
State Point Analysis
Factor / Parameter                  Symbol
Influent flow rate                    Q
Return activated sludge flow rate     RAS
Mixed liquor concentration            Xmlss
Sludge settling characteristics       V o, k
Clarifier surface area                A

3
State Point Diagram
8.0
7.0
Solids Flux Axis
G, Kg/m2-hr

6.0
5.0
4.0
3.0
2.0                   Solids Concentration Axis
1.0
0.0
0   2   4   6     8    10 12   14   16   18   20
X, g/l

4
What is Solids Flux?
Solids flux is the movement
of solids through a clarifier
Solids Flux = mass per unit area per unit time
kg / m2 - hr

Solids Loading Rate (SLR)
is one type of solids flux
5
State Point Diagram
We will plot three elements
8.0
7.0
- Overflow rate line
G, Kg/m2-hr

6.0
5.0           - Underflow rate line
4.0           - Settling flux curve
3.0
2.0
1.0
0.0
0   2   4   6   8    10 12   14   16   18   20
X, g/l

6
State Point Diagram
8.0
7.0
G, Kg/m2-hr

6.0
Overflow rate line
5.0
4.0                       Slope = SOR = Q/A
3.0
2.0
1.0
0.0
0   2   4   6   8    10 12   14   16     18   20
X, g/l

7
State Point Diagram
8.0
7.0                                   Xmlss(Q+RAS)
Solids loading rate
G, Kg/m2-hr

6.0                                         A
5.0
4.0                     State Point
3.0                          Underflow rate line
2.0
1.0                            Slope = SUR = RAS/A
0.0
0   2     4   6    8    10 12    14   16   18   20
X, g/l
mlss                                      Expected underflow conc.
concentration                                                           8
Settling Flux

Settling Flux, Gs = X Vs
Where:   X = Solids concentration
Vs = Settling velocity at
that concentration

Determine Vs with settling tests

9
Settling Flux
Settling tests at various
solids concentrations
Interface height

We record
interface
height
vs
time

10
Settling Curve
1600
1400                             Vs is the slope of the
Interface Height (mm)

1200                             straight section of
1000                             the settling curve
800
600
400
200
0
0   5   10   15   20     25 30      35   40   45    50
Time (min)
11
Settling Flux
Now that we have the settling
velocity Vs we can calculate Gs
Gs = X Vs
This gives us one (1) point on the flux curve.
To get more points we need to run more tests
at different solids concentrations.

12
Settling Flux
For most activated sludge there
exists the following relationship
Vs = Vo e-kX
Substitution gives
Gs = X Vo e-kX

With a few settling tests we can solve for
Vo and k and define the whole flux curve.
13
Veslund Relationship
2.0
1.5
1.0                             Vo = y intercept
0.5                             k = line slope
ln Vs

0.0
-0.5
-1.0
-1.5
-2.0
0.0     1.0   2.0            3.0   4.0      5.0
X, g/l
14
State Point Diagram
8.0
7.0
Now we plot the
G, Kg/m2-hr

6.0
5.0                        three elements
4.0                        together to form the
3.0                        State Point Diagram
2.0
1.0
0.0
0   2   4   6   8    10 12   14   16   18   20
X, g/l

15
Thickening Failure
8.0
7.0
G, Kg/m2-hr

6.0                         Thickening failure
5.0
4.0
3.0
2.0
1.0
0.0
0   2    4   6   8    10 12   14   16   18   20
X, g/l

16
Inventory Shift
8.0
7.0
G, Kg/m2-hr

6.0
5.0
4.0               1
3.0           2
2.0
1.0
0.0
0   2       4   6   8    10 12   14   16   18   20
X, g/l

17
Clarification Failure
8.0
7.0
G, Kg/m2-hr

6.0                        Clarification failure
5.0
4.0
3.0
2.0
1.0
0.0
0   2   4   6   8    10 12   14   16   18    20
X, g/l

18
Flow Increase
8.0
7.0
G, Kg/m2-hr

6.0                    Overflow line gets steeper
5.0
4.0
State point moves up
3.0
2.0
1.0
0.0
0   2   4   6    8    10 12   14   16   18   20
X, g/l

19
Change Settling Properties
8.0
7.0
G, Kg/m2-hr

6.0
5.0
4.0
3.0
2.0
1.0
0.0
0   2   4   6   8    10 12   14   16   18   20
X, g/l

20
Optimizing RAS Rate
8.0
7.0
G, Kg/m2-hr

6.0
5.0
4.0
3.0                   RAS rate too high
2.0
1.0
0.0
0   2   4   6   8    10 12    14   16   18   20
X, g/l

Underflow conc. too low   21
Optimizing RAS Rate
8.0
7.0
G, Kg/m2-hr

6.0
5.0                        Lower RAS
4.0                        pumping, higher
3.0                        RAS concentration
2.0
1.0
0.0
0   2   4   6   8    10 12   14   16   18   20
X, g/l

22
State Point Analysis
8.0
7.0
State Point Analysis is a useful
G, Kg/m2-hr

6.0
5.0           tool for both designers and
4.0           operators to graphically
3.0           understand the dynamics of an
2.0           activated sludge clarifier.
1.0
0.0
0   2   4   6   8    10 12   14   16   18   20
X, g/l

23
State Point Analysis

Questions ?

24

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Description: STATE POINT ANALYSIS