d~;i no~ak, rand~jf - vtechworks.lib.vt.edu · figure 10. cake solids of a one and 4 roller belt...

MuniCipal Sludge Dewatering Using a Belt Filter Press

by

Daniel D. Reitz

Thesis submitted to the Faculty of the

Virginia Polytechnic Institute and State University

in partial fulfillment of the requirements for the degree of

Master of Science

m

Environmental Engineering

APPROVED:

D~;i_ T. No~ak, Chairman

Dr. William R. Knocke

August 3, 1988

Blacksburg, Virginia

Dr. Clifford W. Rand~Jf

Municipal Sludge Dewatering Using a Belt Filter Press

by

Daniel D. Reitz

Dr. John T. Novak, Chairman

Environmental Engineering

(ABSTRACT)

Experiments were performed on alum, anaerobically digested and aerobically digested

sludges to determine the optimum polymer conditioning for a belt filter press The op-

timum polymer dosages for all three zones of a belt filter press were compared with each

other to determine the best overall conditioning. The requirements of all three zones

of a belt filter press were the same. However, the gravity rate of drainage seems to under

predict the dosages for optimum belt filter press performance. In addition the total

mixing energy, G (the shear) and t (the mixing time), that represents the laboratory belt

filter press was found to be approximately 45,000. Using a mixing energy input of 45,000

and a standard Buchner funnel apparatus the correct polymer dose for the belt filter

press can be predicted.

ACKNOWLEDGEMENTS

I wish to thank Dr. John Novak for all his help not only in the pursuit of this thesis,

but for his support in attending graduate school. I would also like to thank Dr. Clifford

Randall who helped secure funding for my graduate education.

This research effort would not have happened without the support of

of the Arus Andritz copmany, who provided the belt filter press equipment and loads

of information. His support was sincerely appreciated.

Finally, my wife is to be thanked for putting up with all the trials and tribulations

of leaving a perfectly good job and moving across the country, so that I could attend

school. Without her support this research would not have been possible.

ACKNOWLEDGEMENTS iii

Table of Contents

INl"RODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Lll"ERATURE REVIEW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

CHARACTERIZING SLUDGE DEWATERING IN THE LAB .................... 3

POL YELECTROL YfE CONDITIONING OF SLUDGES . . . . . . . . . . . . . . . . . . . . . . . . 5

EFFECT OF MIXING INTENSITY ON DEWATERING ........................ 6

BELT FILTER PRESSES, PROCESS FUNDAMENTALS . . . . . . . . . . . . . . . . . . . . . . . . 8

LABORATORY ATTEMPTS TO PREDICT BELT PRESS PERFORMANCE ....... 11

MEIBODS AND MAlERIALS ..................................•........ 14

COLLECTION AND PREPARATION OF THE SLUDGE SAMPLES ............. 14

POLYMER PREPARATION ............................................. 15

SLUDGE CONDITIONING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

WEDGE PRESS APPARATUS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

BELT FILTER PRESS SIMULATOR ...................................... 21

MIXING DEVICE ..................................................... 26

DEWATERING TESTING AND APPARATUS ............................... 29

BUCHNER FUNNEL APPARATUS ....................................... 31

Table of Contents jy

RESULTS AND DISCUSSION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

EFFECTS OF POLYMER DOSE ON OPTIMUM SOLIDS CONTENT ............ 33

ALUM SLUDGE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

ANAEROBICALLY DIGESTED SLUDGE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

AEROBICALLY DIGESTED SLUDGE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

DETERMINING Gt OF THE BELT PRESS ................................. 52

USING Gt TO PREDICT POLYMER DOSE ................................. 57

SUMMARY Ai"lD CONCLUSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72

BIBLIOGRAPHY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75

Appendix A. BELT SETilNGS ........•.......................•.....•..... 77

VITA . . . . . . . . . . . . • . . . . • . . • • • . .. . . . . . . . . . • • • . . • . • • . • . . . . . . . . . . . • . • . • • . 81

Table of Contents y

List of Illustrations

Figure 1. Belt Filter Press Schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Figure 2. Astro standard wedge zone simulator used in experiments . . . . . . . . . . 18

Figure 3. Dewatering chamber for the wedge zone simulator ................ 20

Figure 4. Astro laboratory belt filter press simulator .................. 22

Figure 5. Schematic diagram of the belt filter press ....................... 23

Figure 6. Mixing apparatus used for determination of Gt . . . . . . . . . . . . . . . . . . 27

Figure 7. Buchner Funnel apparatus ................................. 32

Figure 8. Cake solids of a seven roller belt press cycle versus Percol 757 polymer dose using alum sludge .................................... 35

Figure 9. Cake solids of a one and 4 roller belt press cycle versus Percol 757 polymer dose using alum sludge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

Figure 10. Cake solids of a one and 4 roller belt press cycle versus Percol 757 polymer dose using alum sludge .............................. 37

Figure 11. Cake solids of a 4 roller belt press cycle versus Percol 757 polymer dose using alum sludge ........................................ 38

Figure 12. Cake solids of all the 4 roller belt press cycles using Percol 757 polymer and alum sludge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

Figure 13. Cake solids of a one and 4 roller belt press cycle versus Betz 1120 polymer dose using alum sludge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

Figure 14. Comparison of filtrate quality, wedge zone solids, and the 30 second filtrate volume of the gravity zone using Percol 757 polymer and alum sludge .................................................. 42

Figure 15. Comparison of filtrate quality, wedge zone solids, and the 30 second filtrate volume of the gravity zone using Betz 1120 polymer and alum sludge ................................................. 43

List of Illustrations vi

Figure 16. Cake solids of a 2 roller belt press cycle versus Percol 757 polymer dose using anaerobically digested sludge ........................... 45

Figure 17. Cake solids of a 2 roller belt press cycle versus Percol 757 polymer dose using anaerobically digested sludge ........................... 46

Figure 18. Cake solids of a 2 roller belt press cycle versus Betz 1167L polymer dose using anaerobically digested sludge ........................... 47

Figure 19. Cake solids of a 2 roller belt press cycle versus polymer E dose using anaerobically digested sludge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Figure 20. Cake solids of a 2 roller belt press cycle versus polymer E dose using aerobically digested sludge .................................. 50

Figure 21. Cake solids of a 2 roller belt press cycle versus polymer D dose using aerobically digested sludge .................................. 51

Figure 22. Capillary suction time versus Gt using alum sludge and Betz 1120 polymer ............................................... 54

Figure 23. Capillary suction time versus Gt using alum sludge and Percol 757 polymer ............................................... 55

Figure 24. Capillary suction time versus G t using alum sludge and Percol 757 polymer ............................................... 56

Figure 25. Capillary suction time versus Gt using anaerobically digested sludge and Percol 757 polymer ....................................... 58

Figure 26. Capillary suction time versus Gt using anaerobically digested sludtge and Betz 1167L polymer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

Figure 27. Capillary suction time versus Gt using anaerobically digested sludge and polymer E . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

Figure 28. Capillary suction time versus Gt using aerobically digested sludge and polymer D . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

Figure 29. Capillary suction time versus Gt using aerobically digested sludge and Polymer E . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62

Figure 30. Time to filter 50 mL through a Buchner Funnel using Alum sludge con-ditioned with Percol 7 57 polymer at a Gt= 45,000 ................ 63

Figure 31. Time to filter 50 mL through a Buchner Funnel using Alum sludge con-ditioned with Betz 1120 polymer at a Gt= 45,000 ................. 64

Figure 32. Time to filter 50 mL through a Buchner Funnel using anaerobically di-gested sludge conditioned with Perea! 757 polymer ................ 66

List of Illustrations vii

Figure 33. Time to filter 50 mL through a Buchner Funnel using anaerobically di-gested sludge conditioned with Betz l l 67L polymer . . . . . . . . . . . . . . . 67

Figure 34. Time to filter 50 mL through a Buchner Funnel using anaerobically di-gested sludge conditioned with polymer E at a Gt= 45,000 .......... 68

Figure 35. Time to filter 50 mL through a Buchner Funnel using aerobically digested sludge conditioned with polymer E at a Gt= 45,000 ............... 69

Figure 36. Time to filter 50 mL through a Buchner Funnel using aerobically di-gested sludge conditioned with polymer D at a Gt= 45,000 .......... 70

List of Illustrations viii

List of Tables

Table I. Labratory Belt Filter Press Technical Data (19) ................... 24

Table 2. Calibration of the mixing apparatus as performed by Chelf ( 15) ....... 30

Table 3. Comparison of Optimum Polymer Dosages as determined by the 30 Sec-ond Drainage Voulme Compared to the Labratory BFP Simulator ..... 53

Table 4. Predicted Polymer Dosages Verses Actual BFP Optimum Polymer Dosages ................................................ 71

Table 5. Labratory Belt Filter Press Settings for a Two Roller Configuration ..... 78

Table 6. Labratory Belt Filter Press Settings for a Four Roller Configuration ... 79

Table 7. Labratory Belt Filter Press Settings for a Seven Roller Configuration ... 80

List of Tables ix

INTRODUCTION

In the modern society in which we live, a substantial quantity of waste in the form of

sludge is produced by various water and wastewater treatment processes. Sludges

produced as a by-product of municipal water and waste water treatment are typically

high in water content which is often difficult to remove. Dewatering of sludges prior to

disposal is required for several reasons. Dewatering reduces the land area necessary for

ultimate disposal, reduces transportation costs and makes the sludge easier to handle.

If incineration is employed for final sludge disposal, dewatering will significantly reduce

associated fuel costs.

One of the more recent developments in the area of sludge dewatering equipment has

been the development of the belt filter press (BFP). The belt filter press makes use of

gravity, pressure, and shear to dewater sludges. In light of the importance of optimizing

performance of the belt filter press to reduce operating costs associated with sludge dis-

posal, this study was under taken.

This study was designed to determine polymer conditioning requirements for different

zones of the belt filter press. Requirements for each of the zones were compared to

determine the best overall conditioning.

INTRODUCTION

Presently, BFP performance for specific sludges is evaluated using a laboratory belt fil-

ter press. This laboratory machine is not only very expensive, but bulky, heavy and ex-

pensive to transport. This research sought to characterize the laboratory belt filter press

by relating its optimum performance to simple laboratory tests to see if proper polymer

dosing could be determined using these simple laboratory techniques. The advantage

being that these characterizations might reduce the need to test a sludge on a laboratory

belt filter press, thereby saving much money and effort.

INTRODUCTION 2

LITERATURE REVIEW

Only a modest amount of literature exists which describes the characteristics and per-

formance of belt filter presses for the dewatering of municipal sludges. Laboratory pa-

rameters CST and specific resistance will be discussed to understand how these

parameters may be related to the belt filter press. This chapter will briefly review how

sludges are characterized and how belt presses operate so that an understanding of how

these parameters might be applied to the belt filter press characterization. This review

will also include a general discussion of polyelectrolytes as they applied to this study, a

· discussion of general features of belt filter presses and a section about the work that has

been done to predict belt filter press performance using laboratory tests.

CHARACTERIZING SLUDGE DEWATERING IN THE LAB

The test parameter, specific resistance to filtration (SRF), is a conunonly used test for

measuring the dewatering rate of sludges. In 1968, Gates and Mcdermott (1) concluded

that specific resistance measurements were a valid characterization for the analysis of

sludge dewatering. The SFR test measures the rate at which a sludge will dewater by

LITERATURE REVIEW 3

vacuum filtration, but it has not been found useful for predicting the actual performance

of belt filter presses or plate and frame filters (2).

Christianson and Dick (3) attempted to refine the SRF so that it could be used uni-

versally with different sludges. Novak and Knocke ( 4) disputed their results, pointing

out the time consuming nature of the SRF test. They felt that the SRF test was an ap-

propriate index for sludge dewatering characteristics but should be used in the same way

that BOD is used as an index for waste water strength.

Baskerville and Gale (5) developed the capillary suction time (CST) apparatus as an al-

ternative to the specific resistance test about 20 years ago. The capillary suction time

test has gained wide spread acceptance for sludge testing mainly due to its ease of op-

eration compared to the SRF test (4). Test results from the CST apparatus are influ-

enced primarily by the settleable solids fraction of a sludge (2). It is limited in its ability

to test all the properties of sludge dewaterability (2).

In 1988, Vesilind (5) studied the CST test and concluded that it is a rapid, simple and

inexpensive test of sludge dewaterability, but that it is unique to specific sludge solids.

Vesilind stated that the CST test should be used to compare a single sludge to itself,

(evaluating conditioners for example) but should not be considered a fundamental sludge

dewatering rate measure and is not appropriate for comparing different sludges. Vesilind

did conclude that a mathematical relationship that describes CST is valid for describing

the sludge dewatering rate.

LITERATURE REVIEW 4

POL YELECTROL YTE CONDITIONING OF SLUDGES

Polyelectrolytes are long chain, water soluble chemicals used for coagulation and

flocculation of colloids in water treatment and sludge (6). Organic polyelectrolytes in-

crease the rate of sludge dewatering, while having little effect on the cake solids con-

centration (7).

During the past 10, years many advances have been made in the manufacture of

polymers for use in sludge conditioning. Organic polyelectrolytes are now widely used

in sludge conditioning (6). They vary greatly in composition and effectiveness (6), and

are characterized using three primary parameters. These characteristics of

polyelectrolytes are: relative charge density, molecular weight, and charge type (8).

Anionic polymers carry a negative electrical charge in aqueous solution, whereas

cationic polymers carry a positive charge. Cationic polymers are the most widely used

in sludge conditioning since most sludge solids carry a net negative surface charge ( 6).

The required charge density of the polymer is affected by the sludge particles. For ex-

ample, as the particle becomes smaller in size, a higher degree of charge is required (6).

As the molecular weight of a polymer is increased, the solubility decreases and the

polymer becomes more sensitive to shear forces (8). Low molecular weight polymers

require higher dosages to obtain the minimum dewatering rate than do longer chained

medium to high weight polymers (8). Novak and Piroozfard (9) found that the mech-

anism through which a polymer functions is by increasing the particle size. The average

particle size is maximized at the optimum polymer dose. Overdosing causes a reduction

in this average particle size.

LITERATURE REVIEW 5

Polyelectrolytes come in basically two forms, dry powdered and liquid, although

emulsified forms are gaining in popularity. Dry polymers must be given adequate mixing

time for the polymer to dissolve completely ( 6). Mixing time also allows for aging, and

for the polymer molecule to uncoil and take the form that promotes flocculation (6).

Liquid polymer must also be adequately mixed to insure a homogenous solution. Once

mixed, the polymer solution is usually stable for about 24 hours(6); however, it is de-

sirable to avoid prolonged stirring or storage of a polymer solution as this can cause a

reduction in effectiveness (I 0).

Typical dosages for a belt filter press were published by the EPA according to sludge

type (6). For primary sludge, polymer dosages range from five to ten pounds of dry

polymer per ton of dry solids. For aerobically digested the typical dose would be ap-

proximately ten pounds per ton of dry solids. For anaerobically digested sludge, the

typical value ranged from three to six pounds of dry polymer per ton of dry solids in the

sludge.

EFFECT OF MIXING INTENSITY ON DEWATERING

In 1969, Birkner and Morgan (11) found that an optimum polymer dose exists for max-

imum flocculation efficiency at a given mixing intensity, G. They found that an increase

in G values tended to break up the floe. Similarly, for sludges it has been found that

increased mixing time tended to deteriorate the dewatering rate of sludges (12).

Werle et al (14) studied the effect of mixing intensity and polymer dose on the dewater-

ing of sludges. A CST apparatus was used for detennining optimum polymer require-

ments over a range of G and time (t) values. They found that polymer dose and total

LITERATURE REVIEW 6

mixing energy input (Gt) are the two most important parameters governing high stress

sludge conditioning. For all the sludges tested, it was found that within "ideal" ranges,

the product of Gt was important as opposed to either parameter G or t since there was

a corresponding product of mix time and intensity that would minimize the filtering time

for that dose. An increased Gt beyond the optimum resulted in deterioration of

dewaterability. As Gt was increased, higher polymer doses were required to maintain the

optimum dewatering properties.

Prendiville (13) also concluded that polymer dose and Gt were important for sludge

conditioning. For a given sludge, it was possible to determine an optimum polymer dose

and Gt value that produced the best filtering rate (13). Like Werle et al, Prendiville also

found that the product of Gt is important and any combination may be used within

practical limits to obtain the same results. Prendiville suggested that dewatering equip-

ment such as belt filter presses are thought to produce G values in the range of 500 to

2500 sec-1, so standard jar testing will not necessarly correctly predict the polymer per-

formance for these machines. In the case of alum sludge, Prendiville found that an op-

timum polymer dose may be selected for the Gt to be encountered with the equipment

being used. Prendiville's final conclusions stated that alum and activated sludges can

be conditioned to resist deterioration and dewater well under high stress; for alum and

activated sludge, as mixing energy increases, polymer dose also increases.

Novak and O'Brien (7) showed that under low mixing energy conditions, polymer re-

quirements are minimized and almost are independent of solids concentration; additional

mixing will lower the dewatering rate of a sludge. High mixing energy increased the

polymer dose required, but produced a more stable sludge (7). Polymer dose predictions

using a jar testing apparatus will underpredict polymer dose. They also observed that

LITERATURE REVIEW 7

an optimal dose exists for each process, depending upon the shear encountered. There-

fore to predict performance, the dose, mixing and dewatering conditions should match

those encountered in actual dewatering process.

Recently, Chelf (15) showed the effect of under and overdosing of polymer on the re-

sponse of sludges to the shear (G) during mixing. Using CST and SRF tests to measure

dewatering rate, she found that at extreme doses (usually thought of as under or over-

doses) an exponent of G may exist. Therefor Gxt may be a better description for the

dewatering response to polymer dose. Under most normal dosing ranges, x would be

equal to one. The exponent x would also be indicative of the relative stability of the

sludge. If xis greater then one, the sludge is less stable (more delicate floes) and if x is

less than one, the floe is more stable.

BELT FILTER PRESSES, PROCESS FUNDAMENTALS

Belt filter presses, of German origin, consist of a pair of continuous belts running be-

tween rollers which dewater sludges by squeezing sludge between the belts (16). The

machines are designed to dewater sludges that have been "super flocculated" with

polyelectrolytes. These super floes are very fragile and susceptible to degradation by

shearing forces (16). If super flocculation cannot be achieved, dewatering of sludge by

belt filter presses if not feasible (I 0).

The super flocculated sludge is introduced to the belt where the free water drains under

the influence of gravity. This is known as the gravity zone of the belt filter press. The

solids concentration in this zone should increase from an initial value of approximately

LITERATURE REVIEW 8

one to three percent to five to ten percent at the end of this zone, depending on many

operating variables (6).

The semi-dewatered sludge then travels through the wedge formed where the two belts

come together (Wedge Zone). Here the sludge is subject to gradually increasing pres-

sure and more water is forced out (16). If free drainage is still occurring when the sludge

enters this compression stage the excess water tends to act as a lubricant, and promotes

the movement of sludge solids both laterally out of the side and through the belt fabric

(10).

In the last zone, the high pressure zone (HPZ), the forces exerted are due to high pres-

sure created by the decreasing diameter of the roller, the relative movement of the belts

to each other, and the drive torque of the machine (6). The sludge cake is then dis-

charged continuously (16). Solids retention is normally 99 percent or better in this stage,

with a majority of the solids coming from the filter wash at the end of the cake discharge

( 16). Figure I shows a simple schematic of a belt filter press diagraming these different

zones.

The EPA ( 6) describes three forces exerted by the high pressure zone on the sludge. The

first {Fl) is the force exerted due to the drive torque of the machine. The second (F2)

is the force of the sludge cake due to belt tension. The third (F3) is the force on the

sludge due to belt elasticity causing the shear action. The total pressure on the cake at

any one roller is related to the sum of the pressures and roller diameter by the equation:

psi = 2{Fl + F2 + F3)/D

where D is the diameter of the roller.

LITERATURE REVIEW 9

Filter belt

Gravity ra1nage

Zone

Press belt

\

Wedge Zone

Figure 1. Belt Filter Press Schematic

LITERATURE REVIEW

Scraper

Hiqh res sure

Zone

10

Several variables influence the performance of the filter belt press. Pressure exerted,

number of rollers, belt speed, belt type, sludge type, sludge conditioning are just a few

( 18).

LABORATORY ATTEMPTS TO PREDICT BELT PRESS

PERFORMANCE

Baskerville et al (I 0) described several laboratory tests that could be used to predict

performance of the belt filter press. The first evaluation that can be performed is a visual

inspection of the "super floe". "Super floe" is a term used to describe a condition where

the water visibly separates from the sludge. This type of evaluation is difficult to quan-

tify, and does not give any indication about the completeness of adsorption of the

polymer by the sludge solids (10).

Another evaluation recommended was one using a CST apparatus in conjunction with

a standard laboratory stirrer to make a prediction of polymer dose. In making this re-

commendation, the CST of each sample were measured at various polymer doses and

stirring times. The change in the CST of each sample over different stirring periods gave

an indication of the strength of the sludge floes and the presence or absence of unab-

sorbed polyelectrolyte. A sharp rise in CST with stirring is an indication of weak floes

with no surplus polymer present. If the CST remains constant or decreases with stirring

time, then excess polymer in the sludge is indicated.

Baskerville et al (10) also suggested a test method for determining rate of drainage under

gravity. The super flocculated sludge was put into a 70mm Hartley funnel fitted with

LITERATURE REVIEW 11

filter media identical to the belt press. A range of sludge loadings were applied and the

volume filtered through was measured versus time. The times required for each respec-

tive sludge loading gave an indication of the maximum belt speed that should be used

in the full scale press and the output which might be obtained.

Baskerville et al (I 0) then characterized the pressure zones with a piston type press.

The sludge was gradually pressurized to simulate the wedge zone. Pressure was main-

tained on the cake until filtrate ilow had ceased. Good correlation was found for solids

obtainable by this method and actual belt presses using the same sludge and polymer

doses.

Halde (I 7) also simulated the belt filter press by pressing sludge in a piston arrangement

while simultaneously simulating shearing action by rotating the piston. For these tests

separate pressing cycles had no significant increase in filter cake solids over one contin-

uous pressing of equal duration, assuming no cake disruption between cycles. If cake -

disruption did occur between cycles of applied pressure, more filtrate could be with-

drawn. Squeezing several thin layers of sludge produced drier cakes then squeezing one

large layer and the application of pressure had to be applied gradually or sludge dewa-

tering was unsatisfactory. He also discovered that measured specific resistance to

filtration did not necessarily predict the dewatering by the filter belt press.

In summary, the belt filter press uses gravity, pressure and shear to dewater sludge.

Characterizing conditioned sludges as to shear and dewatering properities in a labratory

and comparing these to performance of a belt filter press may yield valuable information

as to what shear may actually exist in the belt filter press. If a shear value or Gt could

be determined for a belt filter press, a simple stirring mechanism (with a known G) could


be used to simulate shear of a belt press, to determine the dewatering properties of a

sludge for a belt filter press.


METHODS AND MATERIALS

This research was performed to characterize the labratory belt filter press and to find a

method to determine the conditioning chemical and dose that will optimize BFP per-

formance. Many variables effect the actual performance of the belt filter press including

sludge type, polymer, mixing energy, applied pressures, and belt type. The equipment

and materials used in this study as well as the methods employed are described in this

section.

COLLECTION AND PREPARATION OF THE SLUDGE SAMPLES

Sludges used in these experiments were obtained from water and waste water facilities

in the Blacksburg, VA area. Alum sludge was obtained from the Radford Arsenal in

Radford, VA . Anaerobically digested sludge came from the Roanoke, VA municipal

wastewater treatment plant. Aerobically digested sludge was collected from the

Christiansburg, VA wastewater treatment plant.

METHODS AND MATERIALS 14

Alum sludge was collected from a sludge holding tank at the Radford Arsenal and was

stored in five and ten gallon carboys. The sludge solids content was determined in the

lab using the method described in the 16th Edition of Standard Methods for the Exam-

ination of Water and Waste Water (18). The solids content was adjusted to two percent

by decanting the supernatant liquor after allowing the sludge to settle. This sludge was

used within a one month period after it was collected.

The anaerobically digested sludge was collected from a lagoon at the Roanoke treatment

plant. The sludge was obtained by throwing a bucket with a rope into the lagoon and

pulling in the filled bucket. This sludge was also stored in five and ten gallon carboys

with loose fitting caps. The sludge solids varied but were approximately 12 percent as

collected in the field. This sludge was thinned and standardized to two percent solids

with tap water prior to testing, and was used within a 2 week period after collection.

The aerobically digested sludge was obtained from a sampling valve directly on the

digester at the Christiansburg plant. This sludge was also stored in five and ten gallon

carboys. Since this sludge was susceptible to daily changes, it was kept aerated with

compressed air and a diffuser stone, and was tested the day after it was collected. The

solids concentration of this sludge was adjusted to two percent before use. Prior to

testing all sludges were well mixed to assure good suspension of all particulate matter.

All the sludges used were stored at 20 degrees centigrade in the laboratory.

POLYMER PREPARATION

Several different polymers (both cationic and anionic) were used in the experiments.

Betz 1120 was the only anionic polymer used for the testing. Betz 1120 (dry powder


form) is a high molecular weight, moderate charge density polymer. Percol 757 (dry

powder form), and Betz 1167L, were the cationic polymers used. Polymers E and F were

experimental cationic liquid polymers supplied by the Nalco company.

Solutions of both the Percol 757 and Betz 1120 (both dry powders) were mixed in the

following manner. A 2500 mg/L stock solution of these polymers was prepared by

weighing out 1.25 grams of the dry polymers and mixing them with 0.5 liters of tap wa-

ter. The polymers were mixed by measuring out the water and putting it in a 1.0 liter

beaker which was then placed on a magnetic stirrer turned to high speed. Dry polymer

was then gradually poured into the water. The speed was reduced and the polymers were

allowed to solubilize for 24 hours, after which they were used. This procedure was used

each time one of these polymers was used in conditioning tests to insure the polymers

to be fresh, and eliminate storage requirements.

Liquid polymers were mixed immediately before use each time. Liquid polymer was

measured with a syringe, introduced to the water and mixed as previously described.

For the purpose of determining dry weight of polymer in the stock solution, the polymer

manufacturer indicated that a one percent solution by volume equals 10,000 mg/L con-

centration. From this conversion, dry polymer solids were determined for liquid polymer

doses. The polymers were allowed to mix vigorously for at least 30 minutes before use.

SLUDGE CONDITIONING

Traditionally sludges had to be superflocculated using polymers for the belt filter press

to operate properly. This was to keep the sludges from squeezing through the filter

fabric. The sludges used in this reasearch proved to be no different. Early attempts in


this reasearch to use highly mixed sludge/polymer combinations and unconditioned

sludges were made, but these sludges were characterized by minimal solids retention on

the belt filter.

Sludges were superflocculated with the polymers prior to their testing in the belt filter

press simulators. To dose with polymer, 500 mL of the sludge was measured in a grad-

uated cylinder and poured into a one liter beaker. The sludge \Vas then placed onto a

jar tester and mixed at 100 rpm for ten seconds. Polymer was introduced into the sludge

over a period of about the first one to two seconds of the mixing to distribute it evenly.

The mixing speed was then reduced to 30 rpm for an additional 50 seconds to coagulate

and flocculate the sludge solids. This conditioning was assumed to provide a negligible

mixing energy Gt.

WEDGE PRESS APPARATUS

The wedge zone of the belt filter press was simulated using an Astra Standard Wedge

Zone Simulator provided by the Arus Andritz company, as seen in Figure 2.

The simulator consisted of a pneumatic cylinder fitted over a box type dewatering

chamber. The pneumatic cylinder (Atlas Copoco C4-63-20-300) pressure was regulated

with a standard air pressure regulator. The on-off operation of the pneumatic cylinder

was accomplished with a dual action pneumatic switch (Atlas Copoco VA 15 HB2-5).

The box type dewatering chamber (Figure 3) was a square metal box, 4 inches square

by 3 3/8 inch deep, open at the top, with several 1/8 inch holes in the bottom. The box

bottom was fitted with a piece of the belt fabric placed over the holes. The top "ram"


Air Pressure Regulator

-------------Pneumatic ('ylinder

,-------Box Type Dewatering rharnber

~-----Pneumatic

Switch

To Vacuum Pump

---- r,raduated C'ylinder

Figure 2. Astro standard wedge zone simulater used in experiments


component of the dewatering chamber was similar to the bottom, but was smaller so it

would fit snugly into the first box. This effectively sandwiched the conditioned sludge

in between the two filter cloths.

The conditioned sludge was quickly poured into the bottom box, and the free water was

allowed to drain under the influence of gravity for one minute to simulate the gravity

zone of the BFP. Another piece of the filter fabric was then placed on top of the sludge.

The top "ram" portion of the dewatering chamber was inserted into the bottom box on

top of the sludge. Pressure was then applied to the sludge to simulate the wedge zone

of the belt press. Filtrate was allowed to drain both from the top and the bottom of the

box. Filtrate from the bottom was caught in a funnel arrangement below the box. The

filtrate was pumped by vacuum from both the top and bottom of the box to a graduated

cylinder so that a record could be made of the volume of filtrate expelled. The sludge

remained under this simulated wedge zone pressure for one minute (recommended by

Arus Andritz personnel) to approximate a typical time sludge might be in this zone. The

pressure was released and solids content samples were taken. The sludge cake was then

placed in the belt filter press simulator for testing.

The pressure applied to the sludge in the wedge zone simulator was a function of the

pressure (psig) applied to the cylinder. The manufacturer gave a conversion factor of

0.31 psi applied to the sludge per psi gauge applied to the cylinder. This was confirmed

by setting a scale under the pneumatic ram and measuring the force applied. This force

was related to the 4 inch square surface area of the dewatering chamber and the gauge

pressure applied. The same conversion factor of 0.31 was obtained. The pressure cho-

sen to use in the wedge zone simulator (4.65 psi) was based on the good results obtained


Lott om Pilter

LTop Ram Componen-=.

Box Fitted With Belt Fabric

Figure 3. Dewatering chamber for the wedge zone simulator


at this pressure, the even gauge pressure ( 15 psig) to monitor, and the range of 3 to 10

psi suggested by Arus Andritz ( 19).

The volume of water expelled during the gravity portion of the test as well as final vol-

ume of water expelled was used with the final solids content of the sludge to calculate

the gravity zone solids content. The calculation was as follows:

Sg = Si + (Sw - Si)(Vg/Vt)

where Sg = solids content, gravity zone (% by wt),

Si = initial solids content,

Sw = solids wedge zone,

Vg = volume water expelled by gravity,

Vt = volume water expelled total.

The optimum polymer dose for each respective zone was the dose that corresponded to

the highest solids content in the cake.

BELT FILTER PRESS SIMULATOR

The high pressure zones (HPZ) of the belt filter press was simulated using an Astro

Laboratory Belt Press. A picture of this press is shown in Figure 4, and a schematic of

the simulator is shown in Figure 5. Technical data on the machine are presented in

Table 1.

The machine allowed for adjustment of the belt speed as well as the belt tension. The

belt speed could be controlled to the nearest one foot per minute, and monitored with

a digital read-out. The belt tension was monitored with a pressure gauge that indicated


Figure 4. A stro Jabora tory belt filter press simulator (I 9)

METHODS A;'\D MATERIALS

22

:: ~ = 0 0 Cll

> :z 0 , > -l t"l 22 ~

N l:..i

Schematic Diagram showing Lah Press

z,

;----.----Zz

v,

V2

Figure 5. Schematic diagram of the belt filter press simulator ( 19)

:: ~ 0 c rll > 7. c ~

~ > f;;

t

Table 1. Labratory Belt Filter Press Technical Oat.a ( 19)

Technical Data

Dimensions Length x Width x Height 1800 x 700 x 1600 mm 71x28x63in ---- --------

Machine speed 1 - 17 m/min. 3.3-55 fpm ----- -- ---- ------

Roll diameter 250mm 9.84 in. --·--------------- ·--- -

Length of roll 250mm 9.84 in. -·---·--- ·-------Maximum surface pressure 12.5 N/cm2 18.1 psi

---- --· ----- -------Maximum line pressure 2000 N/cm 11400 pli

--------- --------Length of clothing x width 2000 x 200 rnrn 80x8 in. ------------------ - ·-----Drive Electric motor 0.7 kW, 380 or 440 V. 50 or 60 Hertz ---- --------------------- - -- -Compressed air connection 6 - 10 bars --~_!~5 psi ____________ --- _ Weight 180 kgs 4001bs

pressure applied to the pneumatic cylinder (Z2, Figure 5) and could be adjusted using a

standard air regulator (Rl, Figure 5).

The partially dewatered sludge (from the wedge zone simulator) was placed on the belt

of the simulator. A second piece of filter fabric the width of the belt and two feet long,

was then placed over the top of the sludge and held in place with paper clips. This

sandwiched the sludge between the continuous belt and the piece of fabric.

The number of times the sludge cake was passed through the rollers was dependant upon

which test was being performed. Initially, the sludge was passed many times through the

rollers at various pressures. In later tests, two passes at a slow speed and constant

pressure were chosen to simulate a typical dewatering cycle for municipal sludge. The

dewatered cake was then scraped from the continuous belt and the dry solids concen-

tration determined. The nip roller apparatus of the simulator (roller, cylinder Z2 and

regulator R2) was not used in these tests.

The pressures encountered in this machine are similar to those that occur in the high

pressure zone of a belt filter press according to Arus Andritz company literature ( 19).

To convert applied gauge pressure to surface pressure on the sludge, the manufacturer

of the belt press simulator recommended a conversion factor of 3.11. That is, the gauge

pressure is divided by 3.11 to obtain the pressure applied to the sludge in psi. The vari-

ables involved in this pressure conversion factor supplied by the manufacturer are related

by the formula:

Pa= TI RR

where Pa = pressure applied to the sludge (psi)

T = tension of the belt (lb/in)

RR = roller radius (inches)

METHODS Al\D MATERIALS 25

This formula is simplistic in nature and does not take into account all the forces de-

scribed by the EPA (6) concerning elasticity, drive torque and take up tension. This

simulator has only one continuous belt so force Fl (EPA) would be minimized. Other

parameters necessary to determine force F2 (EPA) and F3 (EPA) were not measured.

Formula 3 does take into account the resultant force P as described by the EPA. Since

the absolute actual pressures applied were not important to this study compared to the

relative pressures and durations, the manufacturers conversion was used to convert

pressure read on the gauge to pressure exerted by the machine.

MIXING DEVICE

Bench type sludge dewatering tests were conducted using a high energy mixer and CST

apparatus. Mixing tests were not performed as a preliminary conditioning step for the

belt filter press but to attempt to relate mixing intensity of a laboratory mixer (with a

known G) to the results of tests using the belt filter press. It was desired to find a Gt

of the mixing device that would minimize the CST of the optimum sludge-polymer

combinations (as determined in previous tests).

The mixing device (Figure 6) consisted of a balled mixing chamber with a stirring

mechanism that fits over the top. The stirring component of the device consisted of a

Eastman Model 3-1800 RPM variable speed motor and stirring paddle. The stirrer was

self supported on the balled mixing chamber. The coupling between the motor and the

paddle was fitted with a magnet which was used to send a signal to a Hewlett Packard

Model 3734A electronic counter. The gate time of the counter was set at one second,

which allowed for the rotational speed of the paddle to be read in revolutions per second.


Stirring romponent, Eastman Model 3 Variable Speed Motor

Powerstat Variable Autotransformer

·--~-

Baffled Mixing rhamber

Hewtett Packard Electronic rounter

"' .......... •. t' ~ · .. ' . . ' .

.. i. ' .. '

Figure 6. Mixing apparatus used for determination of Gt values


The speed of the motor was controlled by a type l 16B Powerstat variable

Autotransformer connected directly to the motor.

The cylindrical plexiglass mixing chamber measured 9.4 cm in diameter and 21.7 cm

high. Four 1.2 cm baffies set 90 degrees apart were installed lengthwise in the cylinder.

The paddle measured 2 inches by .5 inches and was situated 0.6 cm from the bottom of

the mixing chamber. The mixer was previously calibrated by Chelf (15) so that paddle

rotational speed could be directly converted to velocity gradient G. The basic equation

for the velocity gradient that was given by Stump and Novak (19) is:

G = {2[3.143]g NT/60 Vvp}·s [l]

where G = mean velocity gradient, sec-I

g = acceleration of gravity, in/sec,

N = paddle rotational speed, RPM,

T = net torque on paddle, oz-in,

V = sample volume, in3

v = kinematic viscosity, in2/sec, and

p = density of water, oz/in3

Chelf (15) measured the torque on the paddle produced by stirring with a Power In-

struments Model 783 torque meter fitted in between the motor and the stirring phddle.

A Strobotach Strobe light unit was used to read the torque meter. Readings were taken

in air and in two percent anaerobically digested sludge for calibration purposes.

Werle et al (14) found the viscosity of alum and primary sludges to be 5.68 x 10-3in2/sec

and this value was used for the calibration. The value of 0.576 oz/in3 was used for the

density of water at 20 degees C. The volume of sludge used was 0.5 liters.

METHODS MD MATERIALS 28

Using these values reduces equation (1) to:

G = 20.14(NT)-s [2]

Results of the calibration are presented in Table 2. These data were plotted for use

during the testing to determine the G values applied to the sludges in the mixing appa-

ratus.

DEWATERING TESTING AND APPARATUS

Dewatering characteristics of the sludges were measured with a Triton Type 1165

Capillary Suction Time (CST) apparatus. Whatman # 17 chromatography paper was

used as the filter paper. The theory of CST operation is that the filtrate flows through

the paper at a rate that is dependent on the relative dewatering properties of the sludge.

The apparatus measures the time it takes for the filtrate to travel a fixed distance.

The impact of varying mixing energy input (Gt) on sludge dewatering rates was

quantitified using the CST device. The polymer doses used for these tests were the doses

that were detennined as optimum for the belt filter press. One half liter samples of

sludge were placed into the mixing apparatus along with the polymer. The mixer was

then turned to a preset speed and samples were withdrawn from the mixing chamber at

the desired times without turning off the mixer. This was accomplished by withdrawing

the sludge through a hole in the top of the mixing chamber using a pipette fitted with a

suction bulb. The withdrawn sludge was then transferred to the CST apparatus and the

corresponding CST value determined. The amount of sludge withdrawn from the mixing

chamber each time was assumed to be negligible in comparison to the total sludge vol-

METHODS A."ID MATERIALS 29

Table 2. Calibration of the mixing apparatus as performed by Chelf (15)

RP~I Torque Torque net G loJ: loJ: in air in sludge Torque (sec-') Rl'i\I G

(oz-in) (oz-in) (oz-in)

420 2.3 3.5 1.2 452 2.62 2.66

600 2.8 5.2 2.4 764 2.78 2.88

720 3.0 6.3 3.3 982 2.86 2.99

900 3.0 7.3 4.3 1253 2.95 3.IO

30 l\IETHODS A:'\D :\IATUUALS

ume of 0.5 L. Enough samples were taken so that a good relationship between mixing

time and CST could be established.

The Gt vs CST curves were detennined using G values of250 sec-I and 750 sec-I. This

was to check how the dewatering responded to changing the mixing energy, Gt.

BUCHNER FUNNEL APPARATUS

The Buchner funnel apparatus (Figure 7) is most commonly used to detennine the spe-

cific resistance of a sludge sample. However, for this series of tests it was used in a much

more simplistic manner. The Buchner Funnel was fitted with Whatman No. 40, 7 cm

diameter ashless filter paper and a vacuum of 20 psi was applied to the sludge samples.

The time to obtain 50 mL of filtrate was used as an indication of relative dewatering rate.

This test was performed using the values. for G ~nd t that had been defined for the belt

press machine. The test was used to try to predict the dose of polymer required to op-

timize the belt filter press. It was also used to evaluate the validity of defining a Gt value

for the BFP, and how this value might be applied in the lab for predicting belt press

performance. The predicted dose was then checked to see that it corresponded to the

actual polymer dose detennined to be optimal for the belt filter press.


graduated cylinder (, 00 mL)

Buchner funnel

to vacuum pump

water trap

Figure 7. Buchner Funnel apparatus

METHODS A.1\/D MATERIALS 32

RESULTS AND DISCUSSION

Data were collected in the initial part of this research to determine the polymer dose

required to optimize the different zones of the BFP. The doses to optimize gravity

drainage, the wedge zone and the high pressure zone were compared to each other.

Using the optimum polymer doses, shear values were found using a bench top mixing

apparatus to attempt to determine the G and t of the belt filter press. This section will

present the results of the research to support the observations noted.

EFFECTS OF POLYMER DOSE ON OPTIMUM SOLIDS CONTENT

Different zones of the BFP were tested to determine the polymer dose required to opti-

mize dewatering performance for the each zone. These tests were conducted to:

1. Determine if the required polymer dose increases from the gravity to the wedge zone,

and from the wedge zone to the high pressure zone.

2. Determine if polymer requirements increased as the sludge passed through one

roller, four rollers and seven rollers.

RESULTS AND DISCUSSION 33

3. Determine a dose that might adequately optimize the overall BFP performance.

4. Determine how the gravity rate of drainage compares to the belt press performance.

ALUM SLUDGE

The first set of experiments on alum sludge were conducted not only to determine re-

quired doses for a given sludge but also to determine the effects of varying the belt

pressing parameters on the optimum polymer dose. This was accomplished by compar-

ing the optimum dose (as determined by the maximum solids content) of the gravity,

wedge and belt press cycle to determine if a shift towards a higher dose occured at higher

pressures. The number of rollers the sludge was passed through as well as the speed of

the belt and the pressure were also varied. The Appendix contains tables showing

pressures and speed settings for a two roller, four roller and seven roller press cycle.

Data obtained by passing the Alum sludge conditioned with Percol 757 through the belt

press with a seven roller cycle are shown in Figure 8. Data presented in Figures 9 and

11 are the results of tests for the same sludge and polymer using four roller press cycle.

Figure 10 shows the results for the same polymer and sludge arrangement passed

through the belt press rollers four times with a sample taken after the first roller and last

roller. Figure 12 shows the results of all the 4 roller tests conducted on alum sludge

using Percol 757 polymer. Similar studies using a different polymer (Betz 1120) and a

four roller press cycle are presented in Figure 13. This figure contains data showing the

results of two tests conducted in exactly the same manner.

RF.SUL TS AND DISCUSSION

_J I: -_J 0 > > a 0: 0 u w (/)

0 (Y)

I-3

>-m I-z w u 0: w Cl

I-z w I-z 0 u CJ) 0 _J 0 (/)

Figure 8.

200

JOO

Apparent Optimum Dose for Drainage

0 l8

17

18

JS

14

13 !!lGRAVITY

12 (!) llEDGE 6 BELT

l I

10

9

8

7

6

5

4

3

2

JO 20 30 40 50 60

POLYMER DOSE !LBS POLYMER I TON DRY SOLIDSJ

Cake solids of a seven roller belt press cycle versus Percol 757 polymer dose using alum sludge


200

_J l:

_J 0 > > 100 a c: 0

u w "" (j) Apparent Optimum 0 Dose for Drainage (T)

c 15

l 4 +

~Optimum Dose foe Pcess

I 13 I 12 I

A I

l l I- I :t ~ JO I m , .. Polymer Dose Below Which I- Breakthrough of Solids occurs z 9 w I u er w 8 I 0..

l!JGRAVITY

I- 7 (!) IJEOGE z Al ROLLER w I- + 1 ROLLERS z 6 0 I u CD I 0 5 0 _J I 0 (J) 4 . f!J I

3 I I

2

POLYHER DOSE !LBS POLYMER I TON DRY SOLIDS!

Figure 9. Cake solids of a one and 4 roller belt press cycle versus Percol 757 polymer dose using alum sludge


200

...J :!::: ~

...J 0 > > JOO a Cl'.'. 0 u w (J)

0 (T) ol

15

14

l3

l2

l l t-:I

>-00

10

t-z 9 w u a:: w 8 0..

I- 7 z w t-z 6 0 u (.0 5 0

...J 0 (.0 4

3

2

Apparent Dose for

+ +-

10 20

Optimum Drainage

+

30

C!J GRAVITY 0 I/EDGE A 1 ROLL ER + 1 ROLLER

POLYMER DOSE !LBS POLYMER I TON DRY SOLIDSJ 40

Figure 10. Cake solids of a one and 4 roller belt press cycle versus Percol 757 polymer dose using alum sludge

RES UL TS AND DISCUSSION 37

200

_J E -_J Apparent Optimum 0 Dose for Drainage > > JOO I a

i 0:: D

u w (/)

0 (T)

0 18

17

JS

15

l 4 Optimum Dose for Press

- J3 t-3: C!J GRAV I TY >- 12 ~WEDGE CD A BELT t- l I z w u er 10 w a..

9 t-z B w t-z 0 u 7

~ 6 _J 0 5 ID

4

3 [!)

2

10 20 30 40 50 60 POLYMER DOSE !LBS POLYMER I TON DRY SOLIDSJ

Figure 11. Cake solids of a 4 roller belt press cycle versus Percol 757 polymer dose using alum sludge


10 20 30 40 so 60

POLYMER DOSE !LBS POLYMER I TON ORY SOLIOSJ

Figure 12. Cake solids of all the 4 roller belt press cycles using Perea! 757 polymer and alum sludge


200

..J l: -..J 0 > > JOO a: a: 0 u w Apparent Optimum (J) Dose for Drainage 0 en 'i

0 16

15

14

13 for Press

12 .... ::i: I I >-III .... JO z w 0 IJEOGE u 'T'est 1 • a: 9 Al ROLLER w CJ 1 AOL LERS Q.

8 .... z 7 e IJEOGE w .... Test 2 . • l ROLLER z 0 6

• 'I- ROLLERS u Ill 0 ..J

5 0 l.D

4

3

2

POL YNER DOSE I LBS POL YHER I ORY TON SOL IDS l

Figure 13. Cake solids of a one and 4 roller belt press cycle verses Betz 1120 polymer dose using alum sludge

40

IUi:SULTS A:"iD OISCUSSIO;'I;

For most of the tests the filtrate quality of the wedge cycle was monitored by visual in-

spection. If under or overdosed with polymer, the conditioned sludge would tend to

#break through" in the wedge cycle which was visually apparent. For alum sludge con-

ditioned with both Percol 757 and Betz 1120 a single test for each polymer was con-

ducted in which the suspended solids was measured as a function of polymer dose.

These tests gave an indication of the total suspended solids concentration in both clean

filtrate and under "breakthrough" conditions. Results of these tests are shown in Figures

14 and 15 and are compared to the 30 second volume of water expelled in the gravity

cycle and the wedge solids content. When #breakthrough" visually occurred the sus-

pended solids were in the range of 500 to 2000 mg/L. Clean filtrate was considered to

contain total suspended solids less than 100 mg/L. It is interesting to note that when

breakthrough occured, it was during the wedge cycle rather than during the belt pressing.

The 30 second gravity volume was not affected as drastically by breakthrough condi-

tions. These figures also indicate that the polymer dose that gives the highest 30 second

gravity volume may also be the best dose for the wedge cycle.

Based on the data in Figures 8, 9, 10 and 11 as well as the filtrate quality, it appeared

that the optimum Percol 757 dose for alum sludge was 20 lbs/ton. Although a range of

optimum doses of 10 to 20 lbs/ton may actually exist, the one chosen represented that

with the best solids content most of the time and the best filtrate quality all of the time.

Based on the results shown in Figures 13 and 15 the optimum dose for the alum sludge

conditioned with Betz 1120 was determined to be 11 lb/ton.

The results of this series of tests demonstrated that the optimum dose for all the cycles

appeared to be approximately equal. The expected shift toward a higher optimum dose

under high pressure belt pressing cycles was not apparent. Likewise, the optimum dose


..J 200 :i:: -..J 0 > > a: :oo 0:: CJ

u w Ul

- 0 (T)

I- 5 :t

>-Ill ..; I-z LL.I u 3 a:: LL.I Q. - 2 l.D c i5 l.D

1200

1100

IOOO ..J

' 900 0 :c - 800 lO 0

cl 700

lO 600 0 w ~ 500 w Q. '400 lO ::::> Ill

300

200

100

00 10 20 30 4'0 so POLYMER DOSE ILBS POLYMER I TON ORY SOLIOSJ

Figure 14. Comparison of filtrate quality, wedge zone solids, and the 30 second filtrate volume of the gravity zone using Pcrcol polymer and alum sludge

42 l~ESLl.TS AND DISCUSSION

..J 200 :r -..J 0 > > a: 100 a: 0 u LLJ (J)

0 (Tl

I-3: >- 6 m I- 5 z LLJ u a: .. I.LI 0.. -(J) 3 0 ..J 2 0 (J)

1800

1600

..J 1400 ..... 0 :i:

CJ) 1200 0 ..J 1000 0 CJ)

0 w 800 0 z LLJ 0.. 600 CJ) ::> CJ)

400

200

0 0 ID 20 30 40 50

POLYMER DOSE !LBS POLYMER I TON ORY SOLIOSJ

Figure 15. Comparison of filtrate quality, wedge zone solids, and the 30 second filtrate volume of the gravity zone using Iletz 1120 polymer and alum sludge

RE.SLLTS A~O DISCtJSSIOi\' 43

did not seem to be affected by varying the number of belt cycles or the speed and in-

tensity of the cycles. The number of cycles did effect the absolute value of the optimum

solids content, but this was of no real value to this study. Also, based on these same

figures, the optimum dose could be accurately predicted by the 30 second gravity drain-

age volume, since the dose that gave the maximum volume drained under gravity was

the same dose that optimized performance of the belt press cycle.

Since a shift towards a higher dose at higher applied stresses was not seen in any of these

tests, it was decided to use a 2 roller press test configuration to determine optimum

polymer doses for the duration of the study. The speed of the belt was fairly slow and

the pressure was increased on the second roller for this 2 roller configuration. Since the

time the sludge is under pressure is important as compared to the number of rollers, this

relatively slow speed was chosen to simulate a multi roller condition during the remander

of the study.

ANAEROBICALLY DIGESTED SLUDGE

Three polymers were used to aid in dewatering the anaerobically digested sludge. Percol

757, Betz l 167L and Nalco Polymer E were all used. All tests were performed using the

two roller configuration for the belt cycles previously described.

Results of testing with the Percol 757 are shown in Figure 16 and 17. Betz 1167 L results

are shown in Figure 18. Tests results using Polymer E are found in Figure 19.

Based on the data presented in Figures 16 and 17 the optimum Percol 757 dose for the

anaerobically digested sludge was 10 lbs per ton. A dose of 35 lbs/ton was selected as


<100

_J l:

_J 0 > > 300 er a:: 0 u w Apparent Optimum (/)

Dose for Drainage 0 ('T)

zoo 26

25

24

23 [!)GRAVITY C!I IJEDGE

t- ~BELT 3 22 >-m Optimum Dose for Press t- 21 z w u a:: w 20 a..

t- 18 z w t-z 0 17 u CD 0 _J 16 0 IJ)

15

14

13

120 5 JO 15 20 25

POLYMER DOSE !LBS POLYMER I TON DRY SOLIDS>

Figure 16. Cake solids of a 2 roller belt press cycle verses Percol 7 57 polymer dose using anaerobically digested sludge


.CJD Q Q

_J I: 0 -_J 0 > > 3 OD a: 0:: D Apparent Optimum u Dose for Drainage w U)

0 (T)

200

26 Optimum Dose for Press

25 I ~

24 .!. I

Polymer Dose Below Which 23 Breakthrough of Solids Occurs

I-:I I!! GRAV I TY >- 22 Cl \./EDGE m A BELT I-z w 21 u a:: w a..

20 I-z w

(!) I I- 19 z 0 I u CD 18 ~ I 0 ...J 0 I CD

l7 I ~ [!)

16 I

15 [!) I

14 0 6 10 15 20 26

POLYMER DOSE !LBS POLYMER I TON DRY SOLIDS>

Figure 17. Cake solids of a 2 roller belt press cycle verses Percol 757 polymer dose using anaerobically digested sludge


Figure 18. Cake solids of a 2 roller belt press cycle verses Betz 1l67L polymer dose using anaerobically digested sludge


4'00

_J x: -_J 0 > > 300 a: 0:: D

u w (/) Apparent Optimum 0 Dose for Drainage en

200 26 I 25 I

Z~mDo~ I

24 • 1-I

23 I for Press

I- 22 I :J: l!I GRAVITY >- I (!)WEDGE m 21 A BELT I- I z w u 20 I 0:: (!) w Q. I - 19 I- I z !Polymer Dose Below Which w 18 I- Breakthrough of Solids occur z :/ 0 u c.o 17 0 _J

16 I 0 (/)

15 [!]

14

13

12 0 10 20 30 4'0 50 60

POLYMER DOSE !LBS POLYMER I TON DRY SOLIOSJ

Figure 19. Cake solids of a 2 roller belt press cycle verses polymer E dose using anaerobically digested sludge


the optimum dose of the Betz 1167L polymer; however, a range of doses provided ac-

ceptable results. The high solids content of the sludge conditioned with Betz l l 67L at

low doses (25 lbs/ton) was because breakthrough was occurring at this low dose, re-

sulting in formation of a very thin cake which attained a high solids content. From data

in Figure 19 a dose of 30 lbs/ton was chosen as the optimum dose using Polymer E.

The results of these tests demonstrate no increase in polymer conditioning requirements

as the number of pressing cycles was increased. The 30 second gravity drainage volume

seemed to under predict the Percol dose required to optimize the BFP performance. It

did a fair job in determining the correct range of Betz 1167L doses and accurately pre-

dicted the correct dose for the wedge cycle. The drainage test also seemed to under

predict the optimum dose for polymer E.

AEROBICALLY DIGESTED SLUDGE

A two roller press cycle was again used to determine the optimum belt press doses of the

aerobically digested sludge. Polymer E and Polymer D were used to dewater the

aerobically digested sludge. Figure 20 shows the results obtained using polymer E, and

Figure 21 provides the results obtained using Polymer D.

Based on the data in Figure 20, the optimum dose using Polymer E was selected to be

15 lbs/ton. The optimum dose of Polymer D was 25 lbs/ton based on data in Figure 21.

Both figures indicate no disernable difference in polymer conditioning requirements for

the different zones.


'400

_J

~Appacent l:

_J 0 > Optimum > 300 Dose for Drainage a a:: D

u w CJ)

0 en 200

I-:t

>-00 I-z w u n: w 0...

I-z w I-z 0 u Ill 0

-' 0 Ill

Figure 20.

16

15

14

[!]GRAV I TY

13 (!) IJEOGE A BELT

12

11

JO

9

8

POLYMER DOSE !LBS POLYMER I TON ORY SOLIOSl

Cake solids of a 2 roller belt press cycle verses polymer E dose using aerobically digested sludge

RES UL TS AND DISCUSSION so

400 0

_J l: 0 _J

\Appuent 0 > > 3 00 a Optimum 0:: Dose for Drainage 0

u w CJ)

0 (T)

200 16

15

~

14

I-13 ::i:: !!I GRAVITY

>- <!l \/EDGE CD A BELT I-z 12 w u er w Q_

l l I-z w I-z 10 0 u Ul a _J 9 0 I.I)

8

7

60 lO 20 30 40 50 60

POLYMER DOSE !LBS POLYMER I TON DRY SOLIDS I

Figure 21. Cake solids of a 2 roller belt press cycle verses polymer D dose using aerobically digested sludge

RESULTS AND DISCUSSION SI

The 30 second gravity volumes tended to underpredict Polymer E dose but accurately

predicted polymer D doses.

Table 3 presents a summary of results of these optimum polymer dosage tests performed

on all the sludges.

DETERMINING Gt OF THE BELT PRESS

Since the Gt of the belt press cannot be measured directly an attempt was made to

measure the Gt of the belt pressindirectly. This was accomplished by comparing the

polymer dose requirement for the belt press to the dewatering response using the

labratory mixer over a range of mixing times and intensities. The Gt that gave the best

dewatering rate was assumed to be the Gt that would characterize this laboratory BFP

set up as tested.

Results of the Gt vs CST test conducted on Betz 1120 polymer at the optimum dose of

11 lbs/ton are shown in Figure 22. Figure 23 presents the dewatering results of Alum

sludge conditioned with 20 lbs/ton Percol 757 polymer. The data indicated that one

optimum CST did not exist. The data were then replotted and by trial and error an ex-

ponent of of G of 0. 7 was found to best describe the response to CST. (shown in Figure

24)

Figure 25 shows the relationship between CST and Gt for anaerobically digested sludge

using a Percol polymer dose of IO lbs/ton. Figures 26 and 27 show similar data for Betz

l l 67L polymer and Polymer E. Each of these doses was chosen as the optimum for belt

press performance.


a a ~ 0 0 ;;

m ~

~

Table J. Comparison of Optimum Polymer Dosages as determined by the 30 Sec-ond Drainage Voulme Compared to the Labratory BFP Simulator

Optimal Polymer Dose(lb/ton) Based on1

Wedge Zone HPZ

30 Second rake Cake Reference Sludge Polymer Volume Solids Solids Figures

Alum Percol 757 15 15-20 20 9,10,11,12

Betz 1120 11 11 11 13

Anaerobically Percol 757 5-8 10 10 16,17 Digested

Betz 1167L 30 40 30 18

Polymer E 20 40 30 19

Aerobically Polymer E 10 15 15 20 Digested

Polymer D 20 25 25 21

a C!

~ ~ 0 -(J) 0

~ -en g 0 u en w en (J) -~ w ::c .... ..... z 0 ...... t-u ::> (J)

~ ([ ...J ...J ...... a. ([ u

~

70

60

50

40

30

20 -1

~ 1!J G-250 SEC I _, (!) G-750 SEC

JO

0 I I I I I I I I I I I I I I I I I I I I I I I I I I I I

J 09 1 0 4 105 1 0 8

Gt

Figure 22. Capillary suction time verses Gt using alum sludge and Betz 1120 polymer

~ ~ s ~ 0 0 -I'll a l&J I'll J: I'll -- .... 0 2 ~ ....

...... g '° >-lI _, _, ..... Q. a u

~

32

28

24

20

16

12

8 I

.. I-

0 I04

1!1 G-750 SEC - I (!) G-250 SEC -I

Ja5 101 I07

OT

Figure 23. Capillary suction time verses Gt using alum sludge and Percol 757 polymer

~ ~ s ~ 0 ,... 0

~ -fll a fll u fll l&J - U> 0 z

l&J z: ...... t-

~ ...... t-

~ g: 5 _J ~

8: u

~

32 30 28

26 24 22 20 18

16

14

12

10

8

:~ l!J G-750 SEC - I (!) G-250 SEC -I

2 0

109 104 105

GO.ft

Figure 24. Capillary suction t1me versus ao.71 using alum sludge and Percol 757 polymer

JOe

Figure 28 and 29 present the results of the aerobically digested sludge tested with

Polymer E and D, tested at the optimal dose for belt press operation.

All of these results with the exception of the data in Figures 23 and 24 show that a Gt

in the range 'Of 30,000 to 90,000 is the mixing condition where the CST is minimized.

A range of 30,000 to 80,000 for G0.7r was also found from Figure 24. These data indi-

cate that err for the machine is in the range of 30,000 to 90,000. This also suggests

that if an exponent does exist for any sludge/ polymer combination, the exponent could

be determined and used to help find the optimum polymer dose required for the belt

press.

USING Gt TO PREDICT POLYMER DOSE

Since the Gt of the machine was determined to be in the range of 30,000 to 90,000 a

value of 45,000 (assuming x - 1) was used to see if this mixing condition combined with

Buchner funnel testing would predict the same polymer dose as the belt press. Using the

Gt of 45,000 ( G- 7 50, t- 60) the time to filter 50 mL (TTF 50) using the Buchner funnel

was checked versus the polymer dose. The theory was that the dose determined as op-

timum on the belt press should also give the lowest TTF 50.

Results for the alum sludge tests conditioned with Percol 757 are found in Figure 30.

Figure 31 shows data for the alum sludge conditioned with the Betz 1120. Using this

method to predict an optimum polymer dose, it can be seen that it predicted the Betz

polymer dose, but under predicted the Percol polymer. This may be because an expo-

nent of G other than one existed for the percol polymer and alum sludge.


; c:: s ~ 0 0

~ -fl> a fl> u fl> w - co ~

w :c .... t-z 0 -t-u ::> U>

>-0: CI -I -I .... CL CI u

It:

25

I I (!) rn

20

J5

JO

5~ Q G-750 SEC -I GI G·2SO SEC - I

0 J~ J~ JO"

Ot

Figure 25. Capillary suction time verses Gt using anaerobically digested sludge and Ptrcol 757 polymer

~ s ~ " ..... " co -Cl> ~ ~ 0 u Cl> I.LI - U> ~ ....

l&.I E .... ... z 0 .... ... g U>

>-0:: a: ...I .J .... Q. a u

~

30

25

20

IS

10

61 - l!J G-750 SEC -I

(!) G-1250 SEC-I

105

Ot

0 I iu;.-~~~··~~~'-~-L~ ... ~~'-'-...J~~~~~~~~--'~~._~.._~ .......... ~-10"' I I I p

.. I I I I I I I I - I I I I I 10'

Figure 26. Capillary suction time verses Gt using anaerobically digested sludge and Betz 1I67L polymer ( by Che 1 f, 1 5 )

~ c:: s ~ 0 0 -- U> rJ>

~ g rJ> u rJ> l&J -0 U> z

l&J :c .... t-

~ ~

t-u :::> U>

>-~ a: _. _. .... S: u

g

40

35

30

25

20

JS

10

5

0

I ~-~e/ [!J G.250 SEC - I (!) G-750 SEC - I

104 IO' Ot

Figure 27. Capillary suction time verses Gt using aerobically digested sludge and polymer E•

I08

; c:: ~ ~ 0 U> 0

~ -Cll g u ~ lLI - U>

~ lLI J: ...... .... z 0 .... .... g (J)

>-a: ([ _, _, .... ~ u

~

25

20

16

JO

I 1!1 li·7SO SEC - I [!) (!) li·250 SEC - I

6

o--~~---1~~.._ ......... ___. .......... ~--......... ~~~_,_~__,~_._ .................. __ .......... ~ rn•

Ot

J04 rn•

Figure 28. Capillary suction time verses Gt using aerobically digested sludge and polymer D

~ c: s ~ 0 0 co -fll g a fll u fll - &al

~ co &al ::c ..... ~

~ ..... ~ g UJ

>-0:: <I ..J ..J ..... ~ u

t

26

20

15

IO

I l!I 6°750 SEC (!) G-250 SEC

s

0 I~ I~ 104

Ot

Figure 29. Capillary suction time verses Gt using aerobically digested sludge and Polymer E

~ r-'l en c: ~ en ~ ~

c LO c c z rii 0 n u c: laJ en U> Cll

0 :z ..J z: 0 ID Q: w ..... ..J .... LL

0 t-UJ z: .... t-

e

60

so

40

30

20

10

00 10 20 00

POLYMER DOSE lLBS POLYMER I TON ORY SOLIDS>

Figure 30. Time to filter 50 mL through a Buchner Funnel using Alum sludge conditioned with Percol 757 polymer at a Gt= 45,000

"40

::i:i ~ t": I:""'

Ci! ~ 0 ..... 0 co

0 iii z n 0 t": u rlJ w ~ U> 0 :z _, J: 0 LD 0: w I-..J -~ 0 t-

w J: -I-

z::

JOO

83

67

50

33

J7

00 5 JO 15 20 POLYMER DOSE CLBS POLYMER / TON DRY SOLIDS>

Figure 31. Time to filter 50 mL through a Buchner Funnel using Alum sludge conditioned with Betz 1120 polymer at a Gt= 45,000

Figure 32 presents the results of studies using anaerobically digested sludge conditioned

with the Percol 757 polymer. Figure 33 is the results of the anaerobically digested sludge

conditioned with the Betz l 167L polymer, whereas Figure 34 contains the results using

Polymer E. The test method did a good job in predicting optimum doses for the

anaerobically digested sludge for all three polymers. A very narrow optimum range was

predicted for the Betz l l 67L curve but did not occur for the belt press.

Figure 35 shows the results of aerobically digested sludge conditioned with Polymer E.

Figure 36 is the results of the aerobically digested sludge conditioned with Polymer D.

This test method did a fine job in determining the optimum dose required for the

aerobically digested sludge using these polymers.

From the results presented it appears that using a Gt of 45,000 in conjunction with a

TTF 50 ml vs polymer dose will give a good indication of the range of acceptable

polymer doses, and will predict the optimum dose for the labratory BFP if the exponent

of G is I. Table 4 presents a summary of the optimum doses as found by the belt filter

press verses the optimum doses found by the Buchner funnel-Gt tests.


:::ii::i

~ c: I:"' -l rJJ

~ 0 ~

tO 0 0 Cii z ('") 0 c: u rJJ ~ rJJ

0 2

_J z:: 0 U> 0: LL.I t-_J -u.. 0 t-

LL.I z:: -t-

~

30

25

20

15

10

5

0 0 5 10 15 20 25

POLYMER DOSE lLBS POLYMER I TON ORY SOLIDS>

Figure 32. Time to filter 50 mL through a Buchner Funnel using anaerobically digested sludge conditioned with Percol 757 polymer at a Gt= 45,000

::1:1 &l ~ s ~ 0 0 (ii g Cl> Cl> 0 z

~

.... U) c ~ u w U) ~

_J :c 0 LD Q: L&J ..... _J ..... LL

0 ...... w E ...... t-

80

70

60

50

40

30

20

JO

00 JO 20 30 '40 50 60 POLYMER DOSE lLBS POLYMER I TON DRY SOLIDS>

Figure 33. Time to filter 50 mL through a Buchner Funnel using anaerobically digested sludge conditioned with Betz 1167L polymer at a Gt= 45,000

:::a ~ Cll ~ ~ ~ Cll

~ 0 0 -Cll (") ~ Cll Cll -0 :z

"" QO

Ul

~ u w CJ)

_J J:

0 LO Q:'. w t-_J ...... LL

0 t-w J: ...... t-

25

20

15

10 I-

5

00

lD / [!]

10 20 30 40 50 60 70

POLYMER DOSE ILBS POLYMER I TON DRY SOLIDS>

Figure 34. Time to filter 50 mL through a Buchner Funnel using anaerobically digested sludge conditioned with polymer E at a Gt= 45,000

~ c: s ~ ...... 0 (/)

Cl z 52 0 en u g w (/) en

!!! ~ ...J

I: 0 lD a: w t-...J ...... lL

0 t-w :I: ...... t-

~

30

25

20

15

JO

5

00 10 20 30 40 50

POLYMER DOSE lLBS POLYMER / TON DRY SOLIDS>

Figure 35. Time to filter 50 mL through a Buchner Funnel using aerobically di-gested sludge conditioned with polymer E at a Gt= 45,000

60

; s ~ ......

~ 0 0

0 -u

fll

LIJ a co fll

fll -~ ..J ~

~ It: l&J t-..J ..... l&.

0 t-

~ ..... t-

cf

ao

25

20

JS

JO

5

o--~~~--~~~--~~~---~~~~---~~~--~~~-o 10 20 30 "10 so POLYMER DOSE lLBS POLYMER I TON DRY SOLIDS>

Figure 36. Time to filter 50 mL through a Buchner Funnel using aerobicaliy di-gested sl\ldge conditioned with polymer D at a Gt= 45,000

60

5 c:: 5 ~ 0 0 -Cl> g Cl> Cl> -0 :z

I

:::!

Table 4. Predicted Dosages

Sludge

Alum

Anaerobically Digested

Aerobically Digested

Polymer Dosages Verses Actual BFP Optimum Polymer

Optimum Dose (lb/ton) Polymer Lab BFP Buchner Funnel

Percol 757 20 10-15

Betz 1120 11 10

Percol 757 10 10

Betz 1167L 30 30

Polymer E 30 30

Polymer E 15 20

Polymer D 25 20

SUMMARY AND CONCLUSIONS

The belt filter press has three distinct zones that can be characterized. The first step in

dewatering, gravity drainage, requires super flocculation of the sludge using organic

polyelectrolytes. The gravity zone of the BFP makes use of the super flocculated con-

dition of the sludge and gravity to initially drain off the free water. The transition zone

known as the wedge zone further dewaters the sludge by applying pressure and forms a

sludge cake. The high pressure zone uses high pressure and shearing action to complete

the dewatering process.

The first aspect of the study was to test each zone to find how conditioning requirements

would change. Polymer requirements for one, four and seven belt cycles in the HPZ

were also studied. Each zone in the belt filter press was tested to determine the polymer

dose required to optimize the respective zone tested. The optimal polymer dose for the

gravity drainage rate as compared to BFP performance was also studied in this phase.

The next important task of this study was to assign a Gt value to the lab belt filter press.

The importance of such a characterization is that a simple mixing apparatus used in

conjunction with capillary suction time or a specific resistance test could yield much in-

SUMMARY AND CONCLUSIONS 72

formation about how a sludge will dewater in a belt filter press, without having to test

a field unit, or a laboratory belt press.

The third aspect of the research was to use the Gt value found in the previous

experments to predict an optimum polymer dose for the lab belt filter press. It was

decided to use the polymers and sludges previously tested for this set of experiments, but

to use a different tool, the Buchner funnel to test the dewatering rate of the sludge. It

is assumed that the results would have been similar if a CST device was used instead of

a Buchner funnel.

From the experiments performed and the results obtained, the following important

conclusions were made:

I. Optimum dosages of organic polyelectrolyte required to dewater municipal sludges are

essentially the same for all three zones in the belt filter press. Furthermore, no increase

in dose requirements occured as the sludge was subjected to added belts. In some cases,

however, the optimal dose for 30 second gravity drainage underpredicted the dose for the

wedge zone. These results may indicate that for a BFP, polymer requirements may be

more a function of the super flocculation conditioning than the energy applied to the

sludge to dewater it.

2. The Gxt of the laboratory belt filter press as it was tested appeared to be in the range

of 30,000 to 90,000.

3. Using a Gt of 45,000 in conjunction with a time to filter 50 mL through a Buchner

funnel will predict a polymer dose that would adequately condition sludge for dewater-

ing in the belt filter press simulator. (where the exponent of G equals one)


4. The wedge zone simulator does well in predicting optimum doses for the belt filter

press simulator.


BIBLIOGRAPHY

1. Gates C. D., and McDermott R. F., "Characteristics and Conditioning of Wa-ter Treatment Plant Sludges," Journal of American Water Works Association, 60, pp 331-334 ( 1968).

2. Karr, P. R., and Keinath, T. M., "Limitations of the Specific Resistance and Cst Tests for Sludge Dewaterability," Filtration and Separation, Nov/ Dec 1978, pp 543-544.

3. Christiansen, G. L. and Dick R. I., "Specific Resistance Measurements: Nonparabolic Data," Journal Environmental Engineering Division American So-ciety of Civil Engineers, 111 ( 3); pp 243-247, (1985).

4. Novak, J. T., and Knocke, W. R., "Discussion of Specific Resistance Meas-urements: Nonparabolic Data," Journal Environmental Engineering Division American Society of Civil Engineers, 113; pp 659-650, ( 1987).

5. Veslind, P. A., "Capillary Suction Time as a Fundamental Measure of Sludge Dewaterability," Journal Water Pollution Control/ Federation, 60(2); pp 215-220, ( 1988)

6. United States Environmental Protection Agency, "Dewatering Municipal Wastewater Sludges," EPA. 625/ 1-87/014, September 1987.

7. Novak, J. T., and O'Brien, J. H., "Polymer Conditioning of Chemical Sludges," Journal WPCF. 47( JO); pp 2397-2410, ( 1975).

8. Bowen, P. T., and Keinath, T. M., "Effects of Polymer Molecular Weight and Charge Density on Sludge Conditioning," Discussion Abstracts Int. B .• 43, pp 3338. ( 1982).

9. Novak, J. T., and Piroozfard, M., "Application of Polymers for Water Plant Sludge Conditioning," Proceedings of the AWWA Annual Conference, Part 1, pp 145-166, (1981 ).

BIBLIOGRAPHY 75

10. Baskerville, R. C., Bruce, A. M., and Day, M. C., "Predicting and Evaluating the Performance of a Filterbelt Press," Filtration and Separation, Sept/Oct 1978, pp 445-450.

11. Birkner, F. E., and Morgan, J. J., "Polymer Flocculation Kinetics of Dilute Colloidal Suspensions," Journal Environmental Engineering Division ASCE, 60, pp 175-191, ( 1968).

12. Bugg, H. M., King, P. H., and Randall, C. W., "Polyelectrolyte Conditioning of Alum Sludge," Journal of AWWA, 62, pp 792-795, (1973).

13. Prendiville, J. F., "Effect of High Stress Mixing on Polyelectrolyte Conditioning of Sludges," Masters Thesis, Virginia Polytechnic and State University, ( 1986).

14. Werle, C. P., Novak, J. T., Knocke, W. R., and Sherrard, J. H., "Mixing In-tensity and Polymer Sludge Conditioning," Journal of the Environmental Engi-neering Division - ASCE, 110(5), pp 919-934, ( 1984).

15. Chelf, C., "Unpublished Masters Thesis" Virginia Polytechnic and State Uni-versity, ( 1988).

16. Salmi, M. W., "Choose Dewatering Units According to the Type of Sludge," Water and Wastes Engineering, Sept 1979; pp 103-105.

17. Stump, V. L., and Novak, J.T., "Polyelectrolyte Selection for Direct Filtration," Journal A WW A, Vo/.79, pp 338-342, ( 1979 ).

18. "Standard Methods for the Examination of Water and Wastewater, 16th edi-tion," American Public Health Association, (1986).

19. Arus Andritz Company Brochure,

BIBLIOGRAPHY 76

Appendix A. BELT SETTINGS

Appendix A. BELT SETTINGS 77

Table 5. Labratory Belt Filter Press Settings for a Two Roller Configuration

Roller Number

1 I 2

Gauge Pressure (psi) 17 25

Sludge Pressure (psi) 5.5 8.0

Belt Speed {fpm) 5 5

Appendix A. BELT SETIINGS 78

Table 6. Labratory Belt Filter Press Settings for a Four Roller Configuration

Roller Number

1 I 2 I 3 I 4

Gauge Pressure (psi) 17 25 37 50

Sludge Pressure (psi) 5.5 8.0 11.9 16.0

Belt Speed (fpm) 5 5 8 8

Appendix A. BELT SETTINGS 79

Table 7. Labratory Belt Filter Press Settings for a Seven Roller Configuration

Roller Number

1 I 2 I 3 J 4 r 5 I 6 I 7

Gauge Pressure (psi) 17 17 25 25 35 40 50

Sludge Pressure (psi) 5.5 5.5 8.0 8.0 11.3 12.9 16.0

Belt Speed (fprn) 15 8 8 8 15 20 30

Appendix A. BELT SETTINGS BO

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