INSTRUCTIONS FOR ASLO97, US AND MET



STEP BY STEP INSTRUCTIONS FOR ASLO6.0, US AND MET

Model from: “ SLUDGE BLANKET RESPONSE TO STORM SURGE IN AN

ACTIVATED SLUDGE CLARIFIER”

Water Environment Research, July/August, vol. 71, no 4, pp432-442, 1999.

William T. Manning, Jr., P.E.

Manning Engineering Corp., 1425 26th Street, LaPorte, TX 77571

Tel. 281 471 7590, Fax 281 470 9486, e-mail BJmanning@

M. Truett Garrett, Jr., P.E.,Sc.D.

M. T. Garrett & Associates, LLC, 5161 San Felipe #320, Houston, TX 77056

Tel. 713 494 7468, e-mail mtg@

Joseph F. Malina, Jr., P.E., DEE

Rm. 9102 Cockrell Hall, University of Texas at Austin, Austin, TX 78712

Tel. 512 471 4614

Caution: The overflow velocity increases when the blanket

reaches the bottom of the feedwell. Alternatively, the area,

A, could be taken as the total area minus the feedwell area.

Additionally the overflow velocity increases again when the

blanket reaches the bottom of the effluent weir troughs.

The safe way here is to take the MBK as the depth to the

bottom of the weir troughs.

THE PROGRAMS ARE PROTECTED BY M. T. GARRETT, JR. WITH NO PASSWORD.

GENERAL DESCRIPTION OF THE SPREADSHEET PROGRAM

In an activated sludge plant, the solids are carried from the aeration tank to the settling tank by the sum of the incoming and return flows. Simultaneously, solids that have settled in the settling tank are carried back to the aeration tank by the return flow. However, the incoming flow may be so great that more solids are carried to the settling tank than can settle to the floor, and so accumulate in a sludge blanket. The accumulation of solids in the settling tank means depletion of the solids in the aeration tank. Since a reduction in solids concentration usually means an increase in the settling velocity, the time may come when the aeration tank solids concentration is so low that the sludge blanket no longer increases. It is also possible that solids will spill over the settling tank weir before equilibrium is reached.

The spreadsheet program ASLO was prepared to track the changes in solids in the settling tank during dry weather and under various conditions of storm flow.

The program allows several arrangements of flow through the aeration tanks. There are four tanks, and the return sludge is carried to the number one tank. Incoming flow may be divided between the four aeration tanks and a final mixing point. The excess sludge may be taken from aeration tank no. 3 or from the return sludge line.

The area and depth of the settling tank may be entered. The sludge removal mechanism may consist of rakes or a hydraulic removal system. The hydraulic systems have been found to have different efficiencies as indicated by the depth of sludge blanket required for the underflow solids concentration to reach its maximum. The desired depth may be entered. Following a sudden increase in flow, a tank with a rake mechanism produced an underflow sludge concentration that was represented by the moving average of the concentration reaching the tank floor over the time to rake from the circumference to the sump.

The programs ASLO.US.xxx and ASLO.MET.xxx are written for a constant underflow rate. The effect of different underflow rates on the maximum sludge blanket can be observed by the use of different underflow rates in the program. The program ASLO97USFV.xxx is written for the underflow rate to be a fraction of the overflow rate, limited by a selectable maximum underflow rate. Use the power equations of settling for variable underflow rate because the derivative of a power equation is in the program, not so for the exponential equation.

The programs are based on the principals of flux theory. A flux plot is shown in Figure 1. In addition, the data for the settling curve and the operating conditions are shown in a plot of the velocity versus the reciprocal of floc volume in Figure 2. This chart is just to the right of Figure 3, the chart of operating conditions versus time.

The program was originally developed on the basis of two power equations relating the settling velocity to the floc volume of the sludge for a low and a high range of floc volumes:

For DSV30 < 40%, Vs=AL*(1-SV30/100)^NL, and

For DSV30 > 40%, Vs=AH*SV30^-NH.

The program has been modified to allow entry of constants of other power correlations plus exponential correlations of the form:

Vs=AX*e^ (-NX*DSV30).

Also the choice of stirred or unstirred settling tests is allowed as long as the SVI is consistent with the type of tests. The values are not interchangeable; do not use DSVI with an SSVI settling equation. Also unstirred settling test values above 30% without dilution give a high indication of sludge blanket, and although it is not correct, it is on the safe side.

In the area BG1 to BR19 is a table from the paper by Manning, Garrett and Malina that shows the initial parameters and result of all of the tests at the Turkey Creek WWTP.

TABLE OF CONTENTS

A. Plant Dimensions and Permit Values

A.1 Default, Training Plant (Turkey Creek) Dimensions 5

and Permit Values

A.2 Enter Your Plant’s Dimensions and Permit Values 6

B. Plant Inputs, Wastewater and Sludge Characteristics 10

C. Process Control Values 11

D. Storm Flow Options 14

E. Program Settings, Settling Equation 17

F. Conditional Signs, Warnings, No Entries 20

G. Tabulated Results, No Entries 21

H. Graphical Presentations of Results, No Entries

H.1 Figure 1. Flux Plot of Settling Curve and Storm Results 22

H.2 Figure 2. Relationship Between Settling Velocity and

Reciprocal of Floc Volume with Storm Results 23

H.3 Figure 3. Operating Conditions versus Time 24

H.4 Print Preview 25

I. Special Instructions for ASLO97USFR 26

J. Special Instructions for ASLO97USTHK 29

A. Plant Dimensions and Permit Values

A.1 Default, Training Plant (Turkey Creek) Dimensions

The plant dimensions and permit values are entered in the area with a BLUE background. The programs ASLO.US.6.0, ASLO.MET.6.0, and

ASLO.USFR.6.0 on the CD all initially have the dimensions and permit values of the Training Plant as shown below. Go to VI (press F5, enter VI) to see area.

|No. |Plant Name |Training Plt |pump away |

|1 |VI, volume = |100,530 |gallons |

|1 |VII, volume = |100,530 |gallons |

|1 |VIII, volume = |100,530 |gallons |

|1 |VIV, volume = |100,530 |gallons |

|  |VT volume = |402,120 |gallons |

|1 |Sed. Area, = |4800 |square ft |

|  |SWD = |13.5 |feet |

|  |MBK= |11.5 |feet |

|  |Sludge Mech. |1 |Rake |

|  |  |0 |feet |

|  |Permit QAV |1.20 |mgd |

|  |Permit 2hr QPK |5,400 |gpm |

The model considers each aeration tank as completely mixed. At the Training Plant there are actually two aeration tanks in series. In order to simulate the plug flow aspect of the aeration tanks, each actual tank is entered as two completely mixed tanks in series resulting in the four tanks as shown above.

The clarifier sludge mechanism has rake arms so the necessary entry is 1. Any other entry would indicate a hydraulic sludge mechanism.

Since this was a real plant, designed for CBOD and Ammonia removal, the dimensions are suitable for a general evaluation of the effects of various storm flows and plant operation modes.

A. Plant Dimensions and Permit Values

A.1 Default, Training Plant (Turkey Creek) Dimensions

and Permit Values

A.2 Enter Your Plant’s Dimensions and Permit Values

|No. |Plant Name |  |  |

|  |VI, volume = |1 |gallons |

|  |VII, volume = |1 |gallons |

|  |VIII, volume = |1 |gallons |

|  |VIV, volume = |1 |gallons |

|  |VT volume = |4 |gallons |

|  |Sed Area, = |  |square ft |

|  |SWD = |  |feet |

|  |MBK = |  |feet |

|  |Sludge Mech |  |Hydraulic |

|  |BK for Max RAS |  |feet |

|  |Permit QAV |  |mgd |

|  |Permit 2hr QPK |  |gpm |

On the sheet “Plant Data” there are empty boxes to enter your plant dimensions, which can then be copied to the Blue box location on the “ASLO” sheet (go to VI). Alternatively, you can write over the data on the “ASLO” sheet and then copy it and paste it on the “Plant Data” sheet for data storage The data for the Training Plant is already on the “Plant Data” sheet.

First, enter a Plant Name for future reference.

Second, go to PA (press F5, enter PA) If sludge processing is on site so that the liquid phase of the waste sludge is recycled to the head of the plant, make NO ENTRY in PA, the yellow box to the right of the plant name entry. In case the waste sludge is pumped to another location for processing, make an entry in PA. It is suggested that you enter “pump away” for easy identification.

Third, select the volumes, in gallons or cubic meters depending on the program used, to enter for VI...VIV. Do not enter ZERO! In case you have a single aeration tank that is completely mixed, the volume may be entered at any of the tanks but give the remaining tank a volume of 1 gallon. Make no entry for VT. The sum of tank volumes is programmed for the cell.

[pic]

The above tank arrangement is frequently used when air-lift pumps are used for return sludge. The tank volumes shown provide an example for entering dimensions. FOR THIS EXAMPLE:

VI, Enter RAS in the No. column, and the volume as =226,000 + 336,000.

VII, Enter idc in the No. column, and the volume as 414,000

VIII, Enter 2 in the No. column, and the volume as:

= 2(click the cell in the No. col.)*336000

VIV, Enter edc in the No. column, and the volume as 414000

VT will add the tank volumes and display the total. In the No. column you might enter the number of aeration tanks that could be put in service, i.e. 3. This will remind you of the number of tanks available.

|No. |Plant Name | Your Plant |  |

|RAS  |VI, volume = |562,000 |gallons |

|idc  |VII, volume = |414,000 |gallons |

| 2 |VIII, volume = |672,000 |gallons |

|  |VIV, volume = |414,000 |gallons |

|3  |VT volume = |2062,000 |gallons |

|3 |Sed Area, = |28509 |square ft |

|  |SWD = |12.0 |feet |

|  |MBK = |9.5 |feet |

|  |Sludge Mech |0 |Hydraulic |

|  |BK for Max RAS |3 |feet |

|  |Permit QAV |9.0 |mgd |

|  |Permit 2hr QPK |23750 |gpm |

Sed. Area, There are 3 settling tanks of 110 ft diameter, 9503 sq. ft. each.

If 3 settling tanks are in use, enter 3 in the No. column and enter the area as:

=3(click the cell in the No. col.)*9503.

SWD Enter the side water depth of the settling tanks. In this example, 12 feet.

MBK, the maximum blanket height before solids spill over the weir in the

effluent. This should be the bottom (outside) of the effluent weir troughs. In this example the bottom of the weir troughs is 2.5 ft below the water surface.

Sludge Mech. consider a Hydraulic sludge mechanism. Enter 0 . For example, consider that a blanket depth of 3 feet is required for the underflow concentration to reach its maximum value. In case the sludge mechanism is a rake, enter 1 for Sludge Mech.

Permit QAV The plant has a permit for an annual average flow of 9.0 MGD.

Permit 2hr QPK. The 2hr peak flow is based on the settling tank area and the maximum allowable overflow rate. In this case 23,750 gpm. for a maximum of 1200 gpd/sf. The value depends on the Design Criteria of the regulatory agency.

NOTE

In case you format a cell in the Plant Data as PROTECTED and then copy the Plant Data to ASLO, that cell will transfer as PROTECTED. If you wish to change the value, all you need to do is CLICK on TOOLS, PROTECTION, UNPROTECT SHEET and then make the desired change, no password in required.

B. Plant Inputs, Wastewater and Sludge Characteristics

Go to BR (press F5, enter BR)

|  |BOD, = |150 |mg/L |

|  |XQAV= |150 |mg/L |

|  |QAV = |1.20 |mgd |

|  |SVI= |54.00 |ml /g |

The plant input values are in the Lavender Area as shown above.

BOD The Influent BOD or CBOD value is not involved in the ASLO program.

It is used to calculate the “Mixing channel F/Md value shown in the Light Blue,

Results Area. Enter the value appropriate for your application.

XQAV This is the concentration of solids contributed to the aeration system.

Consider it as the sum of inert solids plus (BOD * yield coefficient).

QAV This is the average flow to be evaluated. It is not necessarily the PERMIT QAV.

SVI The SVI is a sludge characteristic to be entered here. Although the programs can display factors that would encourage the growth of floc formers, there are no biological phenomena included in the programs.

C. Process Control Values

Go to WML (press F5, enter WML)

|  |W ML = |0.000 |mgd |

|  |W Ret = |0.015 |mgd |

|  |UR= |200.00 |gpd /sq ft |

|  |HO= |0.00 |feet |

The process control values are entered in the Orange Area.

W ML This is the flow of Mixed Liquor wasted to the sludge processing facility. Enter the quantity desired.

|WRET+WML? |

W Ret This is the flow of Return Sludge wasted to the sludge processing facility. Enter the quantity desired. In case values greater than zero are entered into both W ML and W Ret, a sign will come on in the Yellow cell to the right of WML with the question:

on the basis that you did not intend to waste sludge from both locations.

The effect of various values of waste sludge are shown in the LIGHT BLUE, RESULTS Area in the cells for SRT, ML SRT, END X4 mg/L, and

Equilibrium ML, mg/L as shown below. SEE NEXT PAGE. Adjust waste sludge quantity to produce the desired result.

UR The is the Underflow Rate of the settling tank(s) in gallons/day/sq ft.

The ASLO programs will provide information on the effect of different Underflow Rates. Note the value of L, the maximum underflow concentration, shown in the LIGHT BLUE, RESULTS Area. This depends on the underflow rate and the SVI. The viscosity of the RAS increases rapidly at concentrations above 15,000 mg/L. The viscosity increase will reduce or even stop the flow of return sludge unless the pumping system can generate additional head to maintain the flow. The recommended underflow rates are between 200 and 400 gallons/day/square ft. (0.34 to 0.68 m/hr) for activated sludge clarifiers..

HO Enter the value of the initial sludge blanket in the settling tank(s). If the value entered is greater than 0, the graph may show that it rapidly goes to 0. If so, you must find values for UR, SVI, XA4, W ML, and W RET that will maintain the sludge blanket without storm flow.

RESULTS

|MAX BKT = |3.18 |ft |

|24hr Xe = |0 |mg/L |

|SRT = |WML+WR=0 |days |

|ML SRT = |WML+WR=0 |days |

|Peak Vo, = |1527 |gpd /sq ft |

|Vr_max, = |455 |gpd /sq ft |

|Effluent, 24hr Q= |3.24 |mgd |

|ViC, = |751 |gpd /sq ft |

|END X4 = |7,359 |mg/L |

|Equilibrium ML = |WR+WML=0 |mg/L |

|Mixing Channel F/ Md= |25.58 |%/day |

| L = |22,922 |mg/L |

|RAS = |15,750 |mg/L |

|CB = |13,968 |mg/L |

|U = |0.96 |mgd |

|BOD Loading = |27.90 |#/d/kcf` |

|SUF, = |6 |mgd |

|QPK, = |7.33 |mgd |

|QPK, = |5087 |gpm |

|FVL= |128.4 |mL /dL |

|FVU= |88.2 |mL /dL |

|PLANT F/Md= |6.39 |%/day |

Go to S (press F5, enter S)

|S, iterations/hr = |6 |ML TKS |

|F1F = |1 |1 |

|F2F = |0 |1 |

|F3F = |0 |1 |

|F4F = |0 |1 |

|FCF = |0 |  |

|XA1,mg/L = |7,000 |  |

|XA2,mg/L = |7,000 |  |

|XA3,mg/L = |7,000 |  |

|XA4,mg/L = |7,000 |  |

F1F The Fraction of Influent plus Recycle Flow[1] (not Return Sludge) applied to Aeration Tank VI. With conventional operation all influent is applied to Aeration Tank VI, so the value to enter is 1. If Aeration Tank VI is used for RAS aeration, the value to enter is 0. If STEP AERATION is used, then a decimal fraction is entered.

The numeral 1 in the column to the right, headed ML TKS indicates that Aeration Tank VI receives some influent sewage and return sludge, and thus can be counted as a Mixed Liquor Tank. These are NOT DATA ENTRY POINTS.

F2F The Fraction of Influent plus Recycle Flow applied to Aeration Tank VII.

If Aeration Tank VI is used for RAS aeration, the value may be 1, or if STEP AERATION is used, then a decimal fraction is entered.

F3F The Fraction of Influent plus Recycle Flow applied to Aeration Tank VIII. If STEP AERATION is used , then a decimal fraction is entered. Otherwise the value entered would be 0.

F4F The Fraction of Influent plus Recycle Flow applied to Aeration Tank VIV.

If STEP AERATION is used , then a decimal fraction is entered. Otherwise the value entered would be 0. As a measure to control the sludge blanket during storm flow, all Influent plus Recycle Flow could be applied to this aeration tank by entering 1, and entering 0 is the other tanks.

FCF The Fraction of Influent plus Recycle Flow applied to a mixing point just before the settling tanks. This feature was incorporated in the City of Houston, Sixty-ninth Street Plant. Diverting the flow to this point immediately stops the rise of a sludge blanket in the settling tank.

XA1 Enter the suspended solids concentration in Aeration Tank VI. In case this aeration tank contains RAS, look for the value of RAS in the LIGHT BLUE RESULTS AREA after entry is made for XA4.

XA2 to XA4 Enter the desired suspended solids concentration. In case the Influent and Recycle Flow is distributed between F1F to F4F don’t worry about calculating the suspended solids concentrations, an estimate is OK. Then look at the values in the spreadsheet after 3 hours and re-enter these values.

D. Storm Flow Options

Go to B (press F5, enter B)

|STORM FLOW OPTIONS: |  |

|B, mgd = |0.00 |  |

|  |  |

|XSUF, mg/L = |0 |  |

|SUF / QAV = |0 |  |

|SUF Rise time, hrs = |0 |  |

The STORM FLOW OPTIONS are in the Yellow Area as shown above.

B Is a flow option, but not a Storm Flow. It is the Diurnal Flow Variation, plus and minus, from the Average Flow. B is applied as a sine wave with a value of zero at 6 a.m. and 6 p.m., maximum at 12 noon, and minimum at 12 midnight. The purpose of using B is to give some reality to the daily variation in mixed liquor and return sludge concentration. The influence of B is normally not seen in a hydrograph of a storm event, so a value of zero is appropriate for the study of storm flow effects.

XSUF This is the suspended solids brought in by the STORM (SURGE) FLOW. Analyses of plant influent data indicate the value may be about 25 mg/L. The effect on sludge blanket formation is trivial. Use as you wish.

SUF/QAV This is the ratio of STORM SURGE FLOW TO AVERAGE FLOW, and it determines the STORM SURGE FLOW added to the QAV (plus or minus B). The resulting peak flows are shown in the LIGHT BLUE, RESULTS AREA. Go to SUF (press F5, enter SUF)

|SUF, = |0 |mgd |

|QPK, = |1.80 |mgd |

|QPK, = |1249 |gpm |

SUF Rise time, hrs This is the time for the STORM SURGE FLOW to increase from zero to its maximum value. In the research of William T. Manning, Jr., the storm flow was applied instantly (within 15 minutes). For small collection systems the rise time may be as fast as 1 hour. For large collection systems the rise time is typically 3 hours. You will see that the effect of the longer rise time is to transfer more solids to the settling tank before the peak flow arrives, and thus reduce the formation of a thin blanket.

E. Program Settings, Settling Equation

|S, iterations/hr = |6 |ML TKS |

| | | |

Go to S (press F5, enter S)

There are two GREEN AREAS for PROGRAM SETTINGS. The one shown above is for entry of S.

S, iterations/hr is shown above. The default value is 6. With this value, the spreadsheet and the chart in Figure 3. cover 48 hours and 20 minutes, and the time of the STORM SURGE FLOW is correct. Other values of S may be used, but STORM SURGE FLOW will not be included. Moreover, with low values of S, the spreadsheet loses some accuracy while it covers a greater period of time.

Go to SEQ (press F5, enter SEQ)

|SETTLING EQUATION |  |

|POWER EQ |

|1 |UR OK |

|POWER=1, EXPONENTIAL=0 |

|Garrett et al, DSVI |

|APL= |5052 |

|NPL= |3.83 |

|APH= |9.01E+06 |

|NPH= |2.5600 |

→

The other GREEN AREA is shown above. The only entry is at the cell AB41, indicated by the ARROW. Enter 1 for the POWER EQUATION, and 0 for the EXPONENTIAL EQUATION.

The following page shows an excerpt from the ASLO spreadsheet. The colored boxes from AM25 to AT39 contain settling equation constants. See page 3 for the equations

The program was originally developed on the basis of two power equations relating the settling velocity to the floc volume of the sludge for a low and a high range of floc volumes:

For DSV30 < 40%, Vs=AL*(1-SV30/100)^NL, and

For DSV30 > 40%, Vs=AH*SV30^-NH.

Thus for the power equations, the constants are:

For the low range of DSV30, AL and NL,

For the high range of DSV30, AH and NH.

The exponential equation relating the settling velocity to the floc volume of the sludge is:

Vs=AX*e^ (-NX*DSV30).

Thus the constants for the exponential equation are: AX and NX.

| |AM |AN |AO |AP |

|1 |Exponential formula values: |  |  |  |

|2 |=AX*EXP(-NX*(AM4-0.5))*(AM4-0.5)-AX*EXP(-NX*(AM4+0.5| | | |

| |))*(AM4+0.5) | | | |

|3 |XFVB |UR |XCU |UR*XCU |

|4 |93.10 |200.00 |118.97 |23794 |

|5 |  |  |  |  |

|6 |VXCB= |55.56 |  |  |

|7 |XCB*VXCB= |5,173.15 |  |  |

|8 |  |  |  |  |

|9 |UR= |200 |  |  |

|10 |  |  |  |  |

|11 |Use Goal Seek, Solver, or manually adjust AM4 to set|  |  | |

| |AN4 to UR (shown in AN9). | | | |

F. Conditional Signs, Warnings, No Entries

Go to B (press F5, enter B)

|STORM FLOW OPTIONS: |  |

|B, mgd = |0.00 |  |

|S NOT EQUAL 6, SO SUF=0 |  |

| | |

|  | |

|XSUF, mg/L = |0 |  |

|SUF / QAV = |9 |  |

|SUF Rise time, hrs = |0 |  |

|15 hour storm flow |BKT O'FLOW |  |

|WRET+WML? |  |  |

|ADJUST AM4 |20 |  |

The “S NOT EQUAL 6, SO SUF=0” is a warning that STORM SURGE FLOW is NOT applied in case S is not equal 6.

The “15 hour storm flow” sign appears whenever SUF/QAV is > 0.

The “WRET+WML” sign appears whenever both WRET and WML are >0.

The “BKT O’FLOW” sign appears whenever the Blanket Height reaches the value of MBK.

Go to SEQ (press F5, enter SEQ)

|SETTLING EQUATION |  |

|EXPONENTIAL EQ |

|0 |ADJUST AM4 |

|POWER=1, EXPONENTIAL=0 |

|Garrett et al, DSVI |

|  |  |

|  |  |

|AX= |5.52E+03 |

|NX= |0.0494 |

The “ADJUST AM4” sign appears whenever the Exponential Equation is used AND the value in AN4 is not equal to the value of UR.

G. Tabulated Results, No Entries

Go to SRT (press F5, enter SRT)

|MAX BKT = |11.50 |ft |

|24hr Xe = |13 |mg/L |

|SRT = |12.17 |days |

|ML SRT = |12.17 |days |

|Peak Vo, = |2500 |gpd /sq ft |

|Vr_max, = |472 |gpd /sq ft |

|Effluent, 24hr Q= |5.51 |mgd |

|ViC, = |854 |gpd /sq ft |

|END X4,mg/L= |6,905 |  |

|Equilibrium ML,mg/L= |5,447 |  |

|Mixing Channel F / Md= |0.26 |1/days-1 |

|Limit of RAS= L = |22,031 |mg/L |

|RAS = |14,955 |mg/L |

|CB = |17,241 |mg/L |

|U = |1.06 |mgd |

|#BOD/kcf/d= |27.93 |  |

|SUF, = |10.8 |mgd |

|QPK, = |12.00 |mgd |

|QPK, = |8328 |gpm |

|MIN FVC= |9.5 |ml /dl |

|Max RAS= |22031 |mg/L |

The Results of calculations are tabulated in the LIGHT BLUE, RESULTS area. The results are helpful in choosing a sludge wasting rate by showing the resulting SRT and MLSRT. The wasting rate also controls the Equilibrium ML, mg/L. This value is helpful in choosing the suspended solids, XA1 to XA4.

A value is given in 24hr Xe only if S=6. Otherwise a sign is displayed that “S NOT=6.”

H. Graphical Presentations of Results, No Entries

H.1 Figure 1. Flux Plot of Settling Curve and Storm Results

[pic]

This is a YOSHIOKA plot of the curve of settling flux (settling velocity times concentration) versus concentration. The concentration unit is the floc volume in percent (ml/dl) as determined by SVI x g/dl. See slides 9 through 17 in “Who’s afraid of settling flux.pps.” See “Welcome to ASLO.htm” for a link to “Who’s afraid of settling flux”

The operating conditions illustrated are those of the default values for the Training Plant. The graph does not tell any results, but rather, rates of change. See “Who’s afraid of settling flux.pps.” Conventional wisdom suggests a high anxiety level if the operating point is above the flux curve and a significant anxiety level when the operating point is between the flux curve and the green line representing the flux for which all solids are returned. Only Figure 3 shows the changes in the sludge blanket and other parameters.

H.2 Figure 2. Relationship Between Settling Velocity and

Reciprocal of Floc Volume with Storm Results

[pic]

This type of chart was presented in Manual of Wastewater Treatment, TWUA. [2]

Coe and Clevenger[3] showed the curve in the charts of their tests (zero was on the right) and the abscissa was consistency, the ratio of fluid to solids in the pulp tested. This we recognize as the reciprocal of the concentration.

The chart presents the same information as the Yoshioka flux chart, but without the flux; the overflow rate and underflow rate are read on the Y-axis.

Conditional Signs, Warnings, No

H.3 Figure 3. Operating Conditions versus Time

[pic]

ASLO programs are designed to show the formation and depletion of a sludge blanket. The flux chart and the settling velocity vs. reciprocal of concentration chart indicate the rate of change of a sludge blanket and do not indicate the height of any sludge blanket. In Figure 3 the blanket height is shown in RED as H’.

I. Special Instructions for ASLO97USFR

Go to WML, (press F5, enter WML)

|W ML = |0.030 |mgd | |  |

|W Ret = |0.000 |mgd |UR OK |  |

|MAXIMUM UR= |300.00 |gpd /sq ft |% Return= |60 |

|HO= |0.00 |feet |Initial UR, gpd/sf= |150 |

In this program, you select the % Return and the MAXIMUM Underflow Rate.

Since the underflow rate is now a variable, CB and L also become variables. Extra columns are used for the calculation of these values. The initial values are still in the LIGHT BLUE, RESULTS area.

A plant with the capability of controlling the return sludge flow would normally be able to provide the increased return sludge pumping head to accommodate the increase in sludge viscosity at high concentrations.

The main reason for using a constant percent return is that so long as there is no sludge blanket, the mixed liquor and return sludge concentrations remain quite constant throughout the day. When there is a sludge blanket throughout the day, the return sludge concentration is in opposite phase with the flow, and the mixed liquor concentration leads the flow by about six hours. However this statement is only approximately correct because the sludge blanket formation is based on a constant underflow rate. When the sludge blanket is caused by a storm flow, the underflow rate is normally constant at the MAXIMUM UR entered.

J. Special Instructions for ASLO97USTHK

First select and enter the desired settling equation information as shown on pages 18 and 19. Then,

Go to VI, (press F5, enter VI)

|No. |Plant Name |Training Plt |PUMP AWAY |

|  |  |  |  |

|  |XQAV= |8,000.00 |mg/L |

|  |QAV = |1.10 |mgd |

|  |SVI= |100.00 |ml /g |

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|  |UR= |55.00 |gpd /sq ft |

|  |HO= |5.00 |feet |

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|1 |Sed Area, = |4,800 |square ft |

|  |SWD = |13.5 |feet |

|  |MBK= |11.5 |feet |

|  |Sludge Mech |1 |Rake |

|  |  |0 |feet |

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Enter the DSVI or the SSVI of the sludge according to the settling equation selected.

When a settling tank is used as a thickener the objective is to produce a thickened sludge of a desired concentration by controlling the underflow rate.

Therefore the next step is to enter the desired Thick Sludge conc. in g/dL(%), e.g.3.20 in the figure above. The program will calculate the underflow rate[4],[5], UR, gpd/sf, and the flow rate of the underflow based on the Sed Area, as shown above. Normally none of the thickened sludge is recycled directly back to the influent of the settling tank (some solids may be recycled to the process ahead of the thickener, e.g. centrate from a centrifuge, or wash water from a belt press.) Therefore the value in W Ret is made equal to the underflow and the cell is locked. Since the W Ret and UR are calculated results, their background has been changed to LIGHT BLUE.

The aeration tank volumes have been set at 1 gallon each and locked since they serve as a pipeline using the ASLO spreadsheet.

Most thickeners have Rake type of sludge removal mechanisms, but this can be changed if needed.

The values of F1F through FC have been locked as shown.

The values of XIA through XIVA have been set to reflect the value input for XQAV.

The input sludge flow and concentration are entered in XQAV and QAV.

An initial sludge blanket height may be entered at HO.

Go to M27 (press F5, enter M27)

|M27 |SCRATCH PAD |  |  |

|M28 |  |  |  |  |

|  |POWER SETTLING EQUATION |  |  |  |

|  |  |  |  |  |

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|Sludge Load |200,160 |pounds/day |100.1 |Tons/day |

|Cu |32,000 |mg/L |  |  |

|U |0.75 |MGD |521 |gpm |

|UR |34.2 |gpd/sf |  |  |

|Cu flux |9.12 |lb/d/sf |  |  |

|U'flow solids |200,160 |pounds/day |100.1 |Tons/day |

|Min Area |21,954 |sq. ft. |  |  |

|  |  |  |  |  |

|Min Diameter |167.2 |ft. |  |  |

A number of formulas have been entered into the SCRATCH PAD area as an aid in the design of a thickener. The background color has been changed to LIGHT BLUE to indicate Results, and the cells locked. When the SED AREA is changed to the value in the Min Area above, the blanket height will be constant in Figure 3.

Go to B, (press F5, enter B)

|B, mgd = |0.00 |  |

|BLANKET DET TIME = |19.2 |Hours |

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|H, Rate of Change= |0.000 |Ft/hour |

|H, END= |6.00 |Ft |

BLANKET DET TIME is the time to deplete the sludge blanket in case the inflow is stopped.

The value in H, Rate of Change= can be useful in determining how long an operation can continue before a change needs to be made.

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[1] Recycle Flows include return flow from sludge processing, filter backwash etc., returned to the plant influent.

[2] Billings, Clayton H, Ed., (1991) Manual of Wastewater Treatment, 6th Edition. Texas Water Utilities Association, Austin. p. 683.

[3] Coe, H. S. and G. H. Clevenger.” Methods for Determining the Capacities of Slime Settling Tanks.” Trans. Am. Inst. Mining Engrs. 55, p 356-383. (1916).

[4] Dick, Richard I. and K. W. Young. “Analysis of Thickening Performance of Final Settling Tanks,” Proc. 27th Industrial Waste Conf., Purdue University, p 34 (1972).

[5] Tiller, F. M. and S. L. Tarng. “Try Deep Thickeners and Clarifiers,” Chem. Eng. Prog., p 75 (March 1995).

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