PB31-195160
Liar.e Stabilization and Ultimate Disposal of
Municipal Wastewater Sludges
Camp, Dresser and McKee, Inc.
Boston, MA
Prepared for
¦unicipal Environmental Research Lab
Cincinnati, OH
May 81
3
U.S. OtpartMtt of Cmmm
National Technical Information Service
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pp?l-
c
EPA 600/2-81-076
May 1981
LIME STABILIZATION AND ULTIMATE Dfc?OSaL
OF MUNICIPAL WASTEWATER SLUDGES
fay
Camp Crasser & McKee Inc.
Boston, Massachusetts 02108
Contract No. 68-03-2803
Project Officer
Roland V. Villiers
Wastewater Research Division
Municipal Environmental Research Laboratory
Cincinnati, OH 45268
MUNICIPAL ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
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TECHNICAL REPORT DATA
tPieast reed Imurucnons on the rtvene btfort comnlnmt)
1 REPORT NO. 1 2.
EPA-600/2-81- 076 1 ORP Report
3 RE^TSAj^NgOo
4. TITLK ANO SUBTITLE
LIME STABILIZATION AND ULTIMATE DISPOSAL OF
MUNICIPAL WASTEWATER SLUDGES
S. REPORT DAT*
May littil
«. PERFORMING ORGANIZATION CODE
7, AUTHORiSI
Camp, Dresser, and McKee, Inc.
8. PERVORMlNG ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME ANO AOORESS
Camp, Dresser, and McKee, Inc.
One Center Plaza
Boston, MA 02108
10. PROGRAM ELEMENT NO.
CAZB1B, D.u. 8-113
it. contact/grant no.
68-03-2803
12. SPONSORING AGENCY NAME ANO AOORESS
Municipal Environmental Research Laboratory - Cin.,0H
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati. Ohio 45268
12. TYPE OP REPORT ANO PEntOO COVERED
Final 6/79 to 3/80
14. SPONSORING AGENCY CODE
EPA/600/14
15. supplementary notes
Project Officer: Roland V. Villiers (513) 684-7664
IS. ABSTRACT _ ' ^ . ¦, ^ , , ... 1 — --
Twenty-eight lime stabilization facilities were visited. None of these
jlants were originally designed for sludge lime stabilization. Lime stabilization was
nstituted either as a permanent sludge handling mechanism to replace a more costly
jrocess, as an interim sludge handling technique, as a back-up^process, or as a
seasonal practice. Three general techniques of lime stabilization were observed,
.ime addition to a liquid sludge before land application. Litr.s addition to a liquid
»ludge before cake dewatering. Lime addition to a dewatered sludge cake. Bacterial
analyses performed at some of the facilities demonstrate that Uming a sludge to a pH
>f 12 is an effective means of total and fecal coliform inactivation. The lime stabi-
lized sludge product is either landfilled, land applied as a liquid sludge, applied
•o land as a cake, or stockpiled prior to landfilllng or land application. Stockpiling
>f sludge has in some cases resulted 1n odors upon pile breakdown. Indications are
;hat with pH drop in stockpiles regrowth of organisms can occur. Lime stabilized
liquid sludge and cake sludge are land applied to farms and to test areas. According
:o operators at several facilities, farmers willingly accept the product reporting
•educed soil liming requirements and satisfactory crop growth. Despite this, some
raci1ities encountered difficulties in acquiring suitable land application sites.
"•
Unclassified
33. PRICE '
I» 'win li»t (V7i)
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DISCLAIMER
This report has been reviewed by the Municipal Environmental Research
Laboratory, U. S. Environmental Protection Agency, and approved for publi-
cation. Approval does not signify that the contents necessarily reflect the
views and policies of the U.S. Environmental Protection Agency, nor does
irention of trade names or commercial products constitute endorsement or
recommendation for use.
EPA
600/2 Lime stabilization
81-076 and ultimate
disposal of
9010S£vl4munic ipal
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FOREWORD
The U.S. Environmental Protection Agency was created because of increasing
public and government concern about the dangers of pollution to the
health and welfare of the American people. Noxious air, foul water, and
spoiled land are tragic testimonies to deterioration of our natural
environment. The complexity of that environment and the interplay of
its components require a concentrated and Integrated attack on the
problem.
Research and development is that necessary first step in problem solution
and it involves defining the problem, measuring its impact, and searching
for solutions. The Municipal Environmental Research Laboratory develops
new and improved technology and systems for the prevention, treatment,
and management of wastewater and solid and hazardous waste pollutant
discharges from municipal and community sources, for the preservation and
treatment of public drinking water supplies, and to minimize the adverse
economic, social, health, and aesthetic effects of pollution. This
publication is one of the products of that research; a most vital com-
munications link between the researcher and the user community.
In order to acquire data for this report, 28 municipal wastewater treat-
ment facilities practicing lime stabilization of sludge were visited. In
these visits, various lime stabilization techniques were observed.
Additionally, data regarding bacterial kill and costs were collected.
Three general techniques of lime stabilization practiced at the visited
sites are; (1) lime addition to a liquid sludge in a batch operation
prior to land application; (2) lime addition, in dosages higher than that
needed for sludge conditioning alone, to liquid sludge prior to
dewatering; and (3) lime addition to a dewatered sludge cake. Bacterial
data shows that lime stabilization can be an effective means of reducing
coliform bacteria concentrations when the pH of operation is 12.0 or
greater. Of course, the effectiveness 1n bacterial reduction depends on
the technique being used. The 11me stabilized sludge 1s being landfllled
or land applied in a liquid or cake form.
Francis T. Mayo, Director
Municipal Environmental Research laboratory
111
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ABSTRACT
Lime stabilizstion, the addition of sufficient lime to sludge to produce
a pH of \Z after two hours of contact, has been accepted by EPA a.', a
method of significantly reducinc, pathogens in sludge. It has gained
popularity as c replacement for both incineration and heat conditioning.
Rising costs and uncertain availability of fuel have caused facilities,
many of which are in Connecticut, to seek alternatives like lime stabili-
zation.
Twenty-eight lime stabilization facilities were visited. Fiftren of
these plants are located in Connecticut; twelve are in other N.jw England
states; and one is in New York. None of these plants was originally
designed for sludge lime stabilization. Lime stabilization wis insti-
tuted either as a permanent sludge handling mechanism to replace a more
costly process, as an interim sludge handling technique, as j back-up
process, or as a seasonal practice.
Bacterial analyses performed at snme of the facilities demonstrate that
liming the sludge to a pH of 12 is an effective means of total and fecal
coliform inactivation. Survival of pathogens and other indicator organ-
isms was not tested at the sites visited. The data collected indicate
that to provide for a pH of 12, a line dose (as CaO) of 2J to 3C percent
should be planned for 1f no sludge samples are available for testing. A
dose of greater than 30 percent might be expected for sljdges thinner
than two percent solids.
Three general techniques of lime stabilization were obrerved. These
techniques are: (1) lime addition to a liquid sludge before land
application; (2) lime addition to a liquid sludge befcre sludge
dewatering; and (3) lime addition to a dewatered sludje cake.
Lime addition to a liquid sludge prior to land appli:ation is typically a
batch process in which lime is added to a tankful of sludge. The lime-
stabilized sludge is then pumped to a land application vehicle for remov-
al from site.
At those sites practicing lime addition to a liquid sludge prior to
sludge dewaterlng, stabilization is accomplished '.>y simply increasing the
Hme dose required for sludge conditioning to obtain the required pH.
Conventional sludga conditioning equipment is usad. Equipment provided
for 1n original facility design has been sufficient to handle increased
dosages needed for stabilization.
1v
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Cake sludge is lime rtabilized by the addition of hydrated lime directly
to a sluoge cake screw conveyor. The mixing action of the conveyor is
used to mix tne lime and sludge.
The following three types of lime were purchased at. the sites visited:
(1) quicklime (CaO); (2) bagged hydr-ited lime (Ca(0H)2); and (3) lime
slurry. The lime slurry used most frequently is carbide lime or chemical
lime, a by-product of acetylene production.
Bagaed hydrated lime and carbide lime slurry are the economical forrs to
use in plants smaller than 5 mgd. At larger facilities, the slaking of
quicklime becomes economical. With facilities larger than 5 mgd, high
manpower requirements make the handling of bagged hydrated lime rora
costly and inconvenient than carbide lime slurry or quicklime. With
larger plant size, quicklime becomes more economical because of the
chemical's low cost.
The lime-scabilized sludge product is either landfilled, land applied as
a liquid sludge, applied to land as a ccke, or stockpiled prior to land-
filling or land application. StockpMing of sludge has, in some cases,
resulted in odors upon pile breakdown. Indications are that, with the pH
drop in stockpiles, re§rowth of organisms can occur.
Lime-stabilized liquid sludge and cake sludge are land applied to farms
and to test areas. According to operators at several facilities, farmers
willingly accept the sludge product, reporting reduced soil liming
requirements and satisfactory crop growth. Despite this, some facilities
encountered difficulties in acquiring suitable land application sites.
This report was submitted In fulfillment of Contract No. 68-03-2803,
Work Effort 3, by Camp, Dresser and McKee, Inc., under sponsorship of the
U.S. Environmental Protection.Agency. This report covers the period 6/79
to 3/80, and work was completed as of 12/80.
v
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CONTENTS
Foreword iii
Abstract iv
Tables v<<<
Figures
Acknowledgments x
Section 1. INTRODUCTION 1
General 1
Plants Visited 2
Findings 4
Recommendations for Further Study 9
Section 2. LIME REQUIREMENTS Af.D THE EFFECT OF LIME 11
STABILIZATION
Lime Required to Reach pH 12 11
Pathogen Kill 11
Regrowth of Organ isms 15
Section 3. DETAILED DESCRIPTION OF LIME STABILIZATION 16
Preparation of Lime Slurry 16
Quicklime 16
Hydrated Lime 1/
Ma.-jally Operated Systems for Preparing
Sluivy: Equipment 18
Mamiaily Operated Systems for Preparing
Slurry: Procedures 22
Automatically Fed Systems for Preparing
Slurry 22
Slurried Lime 22
Storage and Delivery of Slurried L1me 24
Day Tanks for Lime Slurry 24
Pumping and Conveyance of Lime Slurry 26
Application" of Lime Slurry Transfer Fumps 26
Applications of Lima Slurry Metering Pumps 27
Piping Systems for Lime Slurry 28
Valving in Lime Slurry Pipeline Systems 30
Application of Lima 30
Lime Application to Liquid Sludge Prior to
Land Application 30
L1me Addition to Sludge Transfer Line 30
L1me Addition to Unmixed Storage Tank 33
L1me Addition to Nixed Storage Tank 33
vi1
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Lime Addition to Batch Aerobic Digester 35
Lime Addition to Liquid Sludge Prior to Dewatering 36
Lime Addition to Dewatered Sludge Cake 38
Lime Addition to Sludge Screw Conveyor 38
Lime Addition to Sludge Cake Storage 41
Disposal and Reuse Alternatives 41
Sludge Removal from Site 41
Stockpiling 41
Landfilling 43
Land Application 43
Uses of the Sludge 43
Techniques Used to Apply Liquid Sludge 44
Equipment Used to Land-Apply C2k« Sludge 46
Results of Land Application 46
Section 4. INNOVATIVE TECHNIQUES 50
Section 5. COSTS OF LIME STABILIZATION 52
Costs Reported at the Sites Visited 52
Analysis of Costs for Lime Stabilization 52
Costs of Providing a Lime Slurry for Existing
Vacuum FiU.ars 54
Cost of Conversion to Lime Stabilization at a
Facility with Vacuum Filtration 54
Cost of New Vacuum Filters with Lime Stabilization 57
Cost of Lime Stabilization of Liquid Sludge In a
Batch Operation 57
Section 6. ACCEPTABILITY OF METHODS 61
L1me Addition to Liquid Sludge Before Land Application 61
Lime Addition to Liquid Sludge Before Dewatering 62
Lime Addition to Dewatered Cake Sludge 62
Section 7. RFFrRENr.FS 63
APPENDIX Data from the Plants Visited 64
Metric Conversion Table 180
TABLES
Number Page
1 Data From L1me Stabilization Facilities 3
2 L1me Doses Used at Sites Visited 12
3 Typical Analysis of Carbttfe Lime 25
4 Criteria Used for Cost Study 53
v111
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FIGURES
Number Page
1 Litre Dosages at Various Sludge Solids Concentrations 13
2 Hydrated Lime Slurry Makeup System (Bath, ME) 18
3 Addition of Bagged Hydrated Lime to Slurry Makeup (Bath, Mt) 20
A Dust Control Added to existing System 'Stafford, CT) 20
5 Slurry Makeup Tank Depressed 'nto Floor (Middletown, CT) 21
6 Automatic Hydrated Lime Slurry Makeup System, Hatches to Day
Bins (Portland-Westbrook, ME) 23
7 Automatic Hydrated Lime Slurry Makeup System, Day Bins
and Feeders (Portland-Westbroek, ME) 23
C Lime Slurry Storage Tank with Grit Screen (Willimantic, CT) 25
9 Lime Scaling of Pipeline (Midnletown, CT) 28
10 Troughs Holding FlexiDle Lime Hoses (Kennebec, ME) 29
11 limo Addition to Liquid Sludge Prior to Land Application 31
12 Hydrated Lime Addition to Sludge Transfer Lime
(Scarborough, ME) 32
13 Aerobic Digester, Digestion Mode (Thompson, CT) 35
14 Aerobic Digester, Used for Lime Stabilization (Thompson, CT) 35
15 Hydrated Lime Addition to Cake Sludge (Glastonbury, CT) 39
16 Hydrated Lime Addition to Cake Sludge, Lime Hopper
(Stamford, CT) 40
7 Hydrated Lime Addition to Cake Sludge, Lime Day Bin
(Stamford, CT) 40
1? Hydrated Lime Addition to Cake Sludge, Lime and Sludge
Conveyors (Stamford, CT) 40
19 Sand Bed Dried Sludge in Stockpiles {Stratford, CT) 42
20 Liquid Sludge Land Application Truck (Falmouth, ME) 45
21 Manure Spreader for Land Applying Sludge Cake (Somersworth, NH) 45
22 Sludge Cake Land Application Equipment, Sludge Hopper
(Rochester, NY) 47
23 Sludge Cake Land Application Equipment, Rear of Hopper
(Rochester. NY) 4*/
24 Sludge Cake Land Application Equipment, Harrcws {Rochester, NY) 47
25 Costs of Preparing Lime Slurry for Addition Prior to Vacuum
Filtration 55
26 Cost of Conversion to Lime Stabilization at a Facility with
Vacuum Filtration 56
27 Cost of New Lfme Stabilization an! New Vacuum Filtration 58
28 Cost of L1me Stabilization cf Liquid Sludge in a Batch
Operation 59
ix
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ACKNOWLEDGMENTS
"Review of Techniques for Stabilization of Municipal Wastewater Sludges
with Lime and Their Ultimate Disposal" was prepared under the direction
of Mr. Paul W. prendiville, officer-in-:harge» and Dr. Albert B. Pincinc.
project manager. Principal investigators were Mr. Robert M. Otoski (pro-
ject engineer) and Mr. David F. Young. The assistance of Ms. Juliette L.
Brown, Mr. John F. Donovan, Ms. Ellen M. Connors, and Ms. Suzanne M.
Balleville is gratefully acknowledged.
EPA project officer was Mr. Roland V. Villiers, who provided valuable
direction and guidance.
x
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SECTION 1
INTRODUCTION
GENERAL
In wastewater treatment, it is often desirable to stabilize sludge,
making it less odorous and putrescible and decreasing its pathogen
concentration. The level of pathoqens in sewage sludge must be
reduced if it is to be applied to the land surface or incorporated
into the soil. Several processes are available to satisfy this
requirement, although they achieve varying levels of pathogen reduc-
tion. These processes include aerobic digestion, air drying, anaero-
bic digestion, composting, and lime stabilization.
Lime stabilization has gained popularity as a replacement for incinera-
tion and heat treatment, processes which have been affected by rising
costs and uncertain availability of fuel. In some locations, lime
stabilization further processes aerobically digested sludge that would
not otherwise have achieved stabilization because of inadequate solids
destruction.
Adding lime to sludge increases its pH and thus discourages tti growth
of organisms that might be harmful or oromote odors. It does not,
however, decrease the content of volatile material. According to EPA,
sludge is lime-stabilized when the addition of lime increases the
sludge's pH to at least 12, two hours or more after the liming occurs.
The addition of more lime is normally required for sludge to reach pH
12 than Is required for it to achieve conditioning, i.e., an altera-
tion of sludge properties to improve dewatering characteristics. This
is an Important point, especially in view of the fact that some plant
operators purporting to be stabilizing sludge are not adding suf-
ficient lime to increase the pH to 12, and therefore are only con-
ditioning it. Some sludtws require such large quantities of lime for
conditioning that stabilization occurs simultaneously.
Because of the concentration of lime stabilization facilities in Con-
necticut, EPA asked Camp Dresser & McKee to Investigate the Connecticut
facilities and, at the same time, those 1n other areas of New England.
(Because of its proximity, Rochester, New York's Northwest Plant was also
Included in the survey.)
This guide was prepared based on information obtained from visits to 28
plants, previously published information, suggestions from manufacturers,
and our past technical experience. It is intended to serve as a prac-
1
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tical source of information for designers, operators, and others, providing
information on design and operation of lime stabilization facilities, describ-
ing the effectiveness of lime stabilization for pathogen kill, and comparing
lime stabilization with other stabilization processes. The work was carried
out under contract No. 68-03-2803 issued by EPA's Municipal Environmental
Research Laboratory, Office of Research and Development.
PLANTS VISITED
We identified facilities practicing lime stabilization in New England by con-
tacting the regulatory agency of each state. Because of the concentration of
lime stabilization plants in Connecticut, we also called each wastewater
treatment plant in that state. We visited all the lime stabilization plants
identified except for two that were not available for study.
Cur visits revealed that some plants reported to be using lime stabilization
vere in "dct only conditioning because the pH in the sludge was less than 12.
Sone irfomation on those plants and their lime conditioning was useful to
r.nis study, hcwever, and for that reason has been retained in this report.
During tho s*te visits we interviewed the plant superintendent or the chief
plant operator to obtain information concerning the entire treatment plant,
the selection and history of the lime stabilization process, and details
regarding the sludge management program. We solicited comments; examined
plant records concerning equipment reliability, system costs, and the final
sludge disposal operation; and collected data from any special studies on
the lime stabilization process or system. With plant personnel, we inspected
lime and sludge handling areas and equipment. We also visited landfill and
land application sites. We did not take our own measurements, relying Instead
on plant records and statements of the operator.
Table 1 summarizes the data collected, including general information on the
plants and their lime stabilization systems. Detailed plant-by-plant compil-
ations of all pertinent data collected through the plant visits are found 1n
the Appendix which contains Information regarding equipment materials and
sizes, techniques, and manpower used in lime handling and loading, cost data,
and results of special studies.
The present average flow of the facilities studied ranges from 0.2 to 20
million gallons per day (mgd).* Fourteen (50 percent) of these plants have
present average flows of less than 3.0 mgd, and twenty (71 percent) have
flows of 6.0 mgd or less. Of those five having a present average flow of
greater than 10 mgd, only the Lewiston-Auburn, Maine and the Rochester, New
York facilities are truly lime stabilization facilities on a full-time
basis. Two of the four plants use lime only 1n a back up capacity:
New Haven, Connecticut (as a back up to Incineration) and
** For convenience of the reader, the English system is mainly used 1n
this report. A metric conversion table 1s given In the Appendix.
2
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?yU*T_l*M
Plant Size (agd)
Average fio* (agd)
Digestion
Type of Oewatertng
Storage of LM
Sludge
Disposal of limed
Sludge
tint smnmntm system
Sources of SI1HI9L Hoed
Type of Sludge lined
Percent Solids of
Sludge Limed
lime llose (percent of
dry sludge solids «s
C«0)
Other Chemicals MM
Hethod of lining
Reported pH
!jjs of Ltae Purchased
Percent Solution of Llae
Applied (as C«(0H)2)
Use of Srsttm
TABIC I
DATA fR«t Line STABILIZATION FACILITIES (page I of 4)
0) (2) (3) «) (5) (6) (?)
Groton Dm Haver.
Infield Glastonbury (low) KillIrtgly Middletown Naugatuck (Cast St.)
CT CT CT CT CT Ct CT
10.5
4.S
Aerobic
Digestion
Vacoua Filter
3.4
I.I
•lone
Centrifuge
5.0
2.5
None
Centrifuge
8 0
?.0
None
Vacuum filter
6-10
4
None
Vacuu* Filter
10.1
5.0
None
22.5
15.5
None
Vacuum filter Vacuum filter
Stockpile
Stockpile/
•PP>y
Stockpile
Pile/Compost/
landfill
Concrete Tank None
landiltl Landfill
None
landfill
Hone
landfill
hone
landfill
Prlaary/
Secondary
Ml* of Ran/
Digested
4-8
Primary/
Secondary
Cake
17-18
Primary/
Secondary
Cake
16
Primary.'
Secondary
Thickened
4.5 - 6.5
Primary/
Secondary
Thickened
3-4
Primary/
Secondary
Thickened
Prlaary
Thickened
10
25-30
ferric Chloride
A; Vlcuua filter
12
Slurry
6
Polymer
Sprinkle Dry
11-12
Hydrtted
20
Polymer
11.i - 12
H>drated
19
1errlc Chloride
23
Ferric Chloride
Bags to Pit At Vacuiai filter At Vacium filter
11.5 - 1?
Hydrated
12
Hytntiia
14-25
Ferric
Ihioride or
Polymer
At Vacuum
filter
11.8 - 12.5
Quick Mae
No Oata
None
At Vacuum
Filter
1?
Hydrated
<0
Permanent
Dry
Interim
0»y
Interim
II
Permanent
Permanent
11
Permanent
1?
Back-up
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TABLE 1 (Cont. )
MIA FROM LIME STABILIZATION FACILITIES (page ? of 4)
runwi
Plant bite (agd)
Average flow (q
-------
TABIC I (Cont.)
DATA FROK LIKE STABILIZATION rACILITIfS (page 3 of
PI ANT I1ATA
Flint Six (ngd)
Average Flow (agd)
DigestIan
Type of Oewatertng
Storage of lined Sludge
Disposal of tiffed
Sludge
11 HE STABILIZATION STSTEH
Source of Sludge lined
Typo of Sludge ltaed
Percent Solids ef
Sludge Ltaed
Itoe Dose (percent of
dry sludge solids as
C»0)
Other Chemicals Added
Method of Lining
deported pH
Type of time Purchased
Percent Solution of Dae
Applied (as Ca(0Hlj,)
Use of Systeu
<151
Uilllaiantic
CT
5.5
2.4
Honi
Vacuus Filter
Mom
Stockpile/
Apply
Prtaary/
Secondary
Thickened
3-4
15
Ferric Chloride
At Vacuun Filter
10.5 - 11.0
Slurry
10
Pereunent
(161
Bath
HI
I.6
2.i
None
Vacuun Filter
None
Landfill/
Arply
Secondary
Thickened
7
10
ferric Chloride
At Vacuun Filter
II.5 - 12.0
Hydrated
4
Peraunent
(<7)
Falmouth
HE
1-5
0.5
Aerobic
Dtnestlon
None
lerited
Appl.
Secondary
Digested
1-3
5
None
(18)
Kt-nnebec
(Udtervllle)
HE
12.7
8 A
None
Vacuun Filter
None
Landfill/
Apply
Primary/
Secondary
Thickened
15
ferric Chloride
(19)
lew Is ton-
Auburn
Ml
14.2
11.0
None
Vacuun Filter
None
Landfill
Primary/
Secondary
Thickened
5-8
16-18
Ferric Chloride
11.5 - 12.5
Hydrated
II
?en
-------
PtAMT BUT*
Mut Site M
Avenge Flo* M)
Hysllai
Type of Oewatering
Star49c of IM Sludge
Disposal of ttaed
Sludge
I I* STA8I1UA7 IM SrSIf M
Source of Sludge LM
'Type of Sludge tlaed
(22)
SversMrtk
tM
2.4
1.6
Vacuus Filter
Stockpile
Apply
Secondary
Thickened
TABU I (Cont.)
DAT* fttOH LIW SmiiWATIOH FACUITIES (p<9<- 4 of 4)
(23)
Rochester
N»
IS
13
Hone
Vacua* Filter
Apply
Primary/
Secondary
Thickened
(2«)
bu^na* Ft.
Rl
(35)
E. Providence
Rl
31 10.4
23 6
Anaerobic Hone
Vacuua Filter Vacuua F11Icr
None None
landfill Landfill
Priis»ry/
Secondary
Olgested
r rlmary/
Secondary
Thickened
(26!
Woonsocket
Rl
16
»
None
Vacuum Filter
Not.c
Landfill
Priaary/
Secondary
Thicker
(27) (28)
Burlington Burlington
(Main) (Riverside)
VT VT
S.O
4.5
'•Wl-robic
1.0
0.7
A^ierobic
Vacuua Filler Vacuua Filter
None
landfill
None
landfill
Secondary Secondary
Thickened Thickened
Percent Solids of
Sludge Lined
tte Imt (perxint of
dry soil* OS
CaO)
Other Chericals
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Stamford, Connecticut (to coincineration). At Buckram Point, Rhode
Island, lime is used primarily as a conditioning agent and for odor
control.
At no facility had lime stabilization been the original design intent.
At two facilities, lime was used as a back-up to sludge incineration;
ten plants are using lime as an interim procedure prior to institution
of composting or Incineration; thirteen are permanently using lime as a
replacement for incineration or heat treatment; and three are using lime
on a seasonal basis.
In addition to these plants using lime on a planned basis, two plants in
Connecticut reported using lime in emergency situations. In both cases,
anaerobic digesters had to be emptied and their contents were lime
stabilized.
FINDINGS
1. Lime stabilization can bv simple and inexpensive. Required equipment
is typically a dry storage area for bagged lime or a storage tank
with a mixer for slurry storage, a cteel tank with a mixer and a dust
collector for slurry makeup (or without dust collection if only for
slurry dilution), a slurry metering pump, and a mixed tank to pro-
vide the sludge/lime detention period. This system is followed with
a dewat.ering system, or sludge can be pumped directly to a land
application truck*
In the simplest of systems, only a sludge/lime mixing tank and a land
application truck is required. Lime slurry is purchased when needed
and used immediately. Running the system requires little training
and little technical knowledge.
2. Lime stabilization Is effective as a back-up or as an interim
system. Lime is widely available, can be stored, and may already
be in use at the plant 1n another capacity. When used as back-up,
a lime stabilization system may be put on-line on short notice and
has a simple start-up procedure. In addition, the capital cost of
the equipment selected can be very economical, especially in a
labor-intensive, back-up system design.
If an Interim sludge handling system Is required, lime stabilization
may be Inexpensively accomplished using equipment already available
at the plant site. At a number of plants visited, lime stabilization
took place 1n available sludge conditioning tanks, in existing aero-
bic digesters, In unused sludge tanks, and by direct application to
sludge conveyance systems.
3. Present systems can be upgraded by applying lime stabilization. At
the sites visited, lime was used to upgrade the previous systems in
three ways* It was used to improve the degree of stabilization
7
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achieved by aerobic and anaerobic digesters; applied to systems that
had been disposing conditioned, but unstabilized sludge; and applied
as an odor control device. Typically, equipment required was either
available onsite or required little expense.
4. Lime stabilization has been instituted as a less costly alternative
both to incineration and to heat treatment. A number of treatment
facilities visited had instituted lime stabilization to replace
sludge incineration or heat treatment, largely because of the
effects rising fuel costs have had on the costs of these two pro-
cesses. In addition, the treatment plant facilities utilizing lime
stabilization were generally small and had difficulty keeping incin-
erators loaded. Fuel is wasted keeping the incinerator temperature
up during low load periods.
5. lime stabilization is well-suited for smaller plants. Twenty of the
28 plants visited (71 percent) have present average flows of 6.0 mgd
or less. Of the five plants receiving more than 10.0 mgd, only one
is truly lime stabilizing on a full-time basis.
Lime stabilization costs are typically operation and maintenance
intensive. Thp costs of chemicals, which are a major oortion of the
total cost, show little economy of scale.
6. The economical form of lime depends on plant size and location.
Bagged hydrated lime or lime slurry are the least expensive forms for
smaller plants (up to about 5 mgd), and quicklime 1s appropriate for
larger plants. If carbide lime (which is a waste product) can be
economically delivered, Its use 1s appropriate for a wide range of
plant sizes.
7. Stockpiling may adversely affect the bacteriological quality of a
lime-stabilized sludge. Although lime stabilization of sludge
results in a high coliform kill, sludge organlcs are not
destroyed and viable organisms do remain. Surviving pathogens can
"regrow" or can recover from 1nact1vat1on If sludge pH drops,
causing the sludge to become "unstabilized". Evidence of this was
noted at various sites. Stockpiles of a few months to a year old,
when broken down, emitted an odor signifying bacteria Infestation.
Stockpiling of sludge that has been lime stabilized, dewatered, and
allowed to dry on sandbeds has shown significant Improvement over the
stockpiling of wet cake.
8
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8. A program for applying lirce stabilized sludge to land can be suc-
cessful .
a. Treatment plant operators have reported that farmers initially
skeptical have come to look forward to receiving the sludge as
their crop growth has improved. In the study area, lime is nor-
mally applied to the land to maintain soil pH.' The addition of
lime-stabilized sludge reduces or eliminates the need for this
Hme addition.
b. The sludge has successfully been used as a soil builder. Stripped
lands are improved by the organic content and moisture holding
capacity of the sludge.
c. Lime-stabilized sludge application operations have had few
problems with odors. The odors emitted have been described as
being less offensive than tiicse emitted when manure is spread.
Odor problems have developed only when stockpiled sludge was
applied on warm days.
9. Lime stabilization systems may be subject to pcor operational proce-
dures. Because the effects of incomplete stabilization are not imme-
diately apparent and do not occur onslte, an improper lime dose may
not be recognized. In addition, where lime 1s added prior to dewa-
tering, the Hme dose required for stabilization may be confused with
the dose required for sludge conditioning* This may result in at-
tainment of lower sludge pH than required for«stab1lization. Cutting
lime dose is an easy, but Improper, means of cutting chemical costs.
10. Treatment plant operators should be educated on the goals of lime
stabilization. Operators need to be made more aware of the import-
ance of adding an appropriate quantity of lime to the sludge and
supplying adequate mixing and detention time. This effort would help
reduce proolems caused by poor operation and could reduce the cases
of Incomplete stabilization. Additionally, 1t 1s Important for the
operators to understand that the primary goal of stabilization is not
for aesthetic odor control, but to protect public health.
RECOMMENDATIONS FOR FURTHER STUDY
1. A study should be perfomed to determine the effectiveness of Hme
addition to conventionally designed dewateHng systems. As shown in
this report, existing plants presently dewatering sludge are con-
verting to lime stabilization with little additional capital expense.
Existing sludge conditioning drums are being used for lime addition.
The mixture of sludge and 11me remains In a liquid form for about IS
minutes in the vacuum filter sludge vat prior to dewatering. Initial
mixing 1s good and pH values are kept at sufficient values for the
required time, but during the detention period the sludge 1s sitting
9
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in >i cake form. It is unknown whether a 15-minute detention of the
liquid is sufficient. A study should be conducted to determine the
required detention time. Cake samples taken at various detentions
would be analyzed for pathogen numbers.
2. Urne stabilization of a cake sludge should be evaluated. A study
should be performed to determine if sludge can be stabilized by
adding lime to a cake form of sludge. The Initial mixing of sludge
and lime and the effects of having only a low proportion of free
water to convey the hydroxy1 icns must be determined. Such systems
are worth evaluating. Operating systems have been low capital, pro-
viding inexpensive stabilization techniques.
3. Regrowth in stockpile; of lime stabilized sludge cake needs to be
quantified. If sludge cake is to be land applied, stockpiling allows
for flexibility in application schedules. Sometimes stockpiled,
lime-stabilized sludge gives off odors when piles are broken down,
depending on stockpile age. These odors may signify bacterial re-
growth. In order to evaluate whether or not stockpiling impacts the
efficiency of lime stabilization, tests should be performed to deter-
mine bacterial regrowth over time.
4. The effects of sand bed drying of sludge prior to stockpiling should
"Ee evaluated. Allowing sludge to dry prior to stockpiling appears to
be effective in reducing cdors that occur when piles are broken down.
A bacterial analysis of the results is recommended.
5* Fecal streptococci should he tested in future studies. The bacterial
analyses performed at the sites visited were for total coliform or
for fecal coliform. Fecal streptococci is an indicator that is more
resistant to inactivation by lime. Researchers should consider
studying fecal streptococci, and possibly actual pathogens as well,
in future studies.
10
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SECTION 2
LIME REQUIREMENTS AND THE EFFECT OF LIME STABILIZATION
LIME REQUIRED TO REACH pH 12
We were able to determine required lime dosages for most of the plants
visited, either through interviews with the operators, or by calculating
the dosage from information available. We found a large variation in
lime dosage — 5 to 35 percent as CaO — for plants reported to reach pH
12. The average dosage was between 20 and 25 percent.
We found little correlation with either sludge type or solids concentra-
tion. Table 2 shows the lack of correlation for sludge type, and the
scatter in Figure 1 shows no correlation with sludge solids for the
plants surveyed. A weak trend develops when data from other sources are
added. The additional data suggest that sludges thicker than 2 percent
can be expected to require between 10 and 25 percent lime; provision for
20 to 30 percent should be sufficient if sludge samples cannot be
tested. For sludge thinner than 2 percent, lime dosages of 30 percent or
more would be required.
PATHOGEN KILL
None of the plants surveyed had conducted extensive studies to assess
the effects of lime stabilization on pathogen concentrations. Only
five plants reported tsstlng: Falmouth, Bath, and Kennebec, Maine;
Enfield, Connecticut; and Rochester, New York. With the exception of
a single test on viruse: at Rochester, all te'ts were on bacteria.
Most cests were with coliform bacteria. There were no attempts to
assess quantities of parasites.
At the Falmouth, Maine treatment facility, bacterial analysis per-
formed on a single, liquid sludge sample, lime-stabilized at a pH of
12.5, showed that no fecal conform, total coliform, or fecal strep-
tococci were present.
Tests at the other four plants were conducted on vacuum filter cake.
Enfield cake, at pH 12, and Rochester cake, at pH 12.2, yielded negative
results in tests for total coliform bacteria. Tests on Rochester sludge
were also negative for fecal coliform.
Tests on cakes at lower pH values yielded positive results for Indica-
tor organisms. At Bath, Maine, sludge cake at a pH of 11.5 contained
100 fecal coliform per 100 ml. While Kennebec, Maine, cake at pH 11.7
U
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TABLE 2
LIHE DOSES USED AT SITES VISITED
(Sites with Complete Record Attaining pH 12)
Sludge Typ®
Number of
Sites
Average
Sludge
Solids
(percent)
Sludge
Solids
Range
(percent)
Average
Lime Dose
(percent
as CaO)
Lime Dose
Range
(percent
as CaO)
Rax Sludges
10
5.7
3.1 - 9.0
22
10 - 35
Primary and Secondary
7
5.7
3.1-9.0
22
17 - 35
Secondary
3
5.6
4.0 - 7.0
20
10 - 25
Aerobically Digested
4
3.3
2.0 - 6.0
17
5 - 27
Sludges
Primary and Secondary
2
4.5
3.1 - 6.0
23
18 - 27
Secondary
2
2.0
2.0
11
5 - 16
-------
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o 8
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X
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w <->
£ IA
2 5
UI a
1 &
40
ss
30
25
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10
1
"T" r 1 "T" "-T1 ~
~
LEGEND
_
#
• DATA FROM 9TE VISITS
(PLANTS ATTAIN *G ph» 12 >
¦ N0LAW5 AND EDWARDS
* PAULSAUO AND CIKUM
-
| RANGE OF VALUES
•
-
•
•
¦ «
>
«
•
m
—
•
•
•
•
•
-
¦
-
¦
t
•
¦ |
a
I
-
•
-
L- I - 1 -1 1
... —1 I 1
• s
SLUDGE SOLIDS CONCENTRATION (PERCENT)
FIG. I UME OOSAGES AT VARIOUS SLUDGE
SOLIDS CONCENTRATIONS
13
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contained 150 fecal coliforms per gram and 460 total coliforms per
yram, the same plant's cake at pH i2 showed no coliform. (Fecal con-
form content of cake without stabilization is roughly 4 x 10° per gram
(2)).
The limited tests on vacuum filter cake at the facilities surveyed
suggest that substantial coliform bacterial kills can be obtained at
pH 12 using conventional vacuum filter conditioning drums and vats.
Nevertheless, further s:udy, including studies using other organisms,
should be conducted. The detention time of the liquid sludge in the
vacuum filter vat 1s only about 15 minutes, but published studies
demonstrating the effectiveness of lime stabilization deal with a
liquia sludge limed to a pH of 12 or greater for a detention period of
30 minutes or more.
Farrell et al (2) showed the importance of holding the sludge in a
liquid state for a contact period prior to sludge filtering. In their
study, a liquid sludge was lime stabilized and held in a liquid state.
A second sample was filtered two minutes after lime addition. One-
half hour after lime addition, the fraction of original bacteria
remaining in the liquid sludge was lower than that in the cake.
Coliform and fecal streptococci were monitored 1n t.hls test.
Studies conducted by Counts and Shuckrow (1), Farrell et al (2) and
Noland et al (4) tested for the inactlvatlon of fecal coliform and
fecal streptococci indicators. The results show fecal streptococci to
be more resistant to inactivation by lime than the coliform species.
The study of fecal streptococci, which was not conducted at the vacuum
filter plants, would be a more stringent test of the effectiveness of
this lime stabilization technique.
The literature is lacking in results with respect to viruses and para-
sites. Me found no citations on the effect of Hme addition on virus
concentrations in sludge. While a single test at Rochester found no
viruses 1n vacuum filter cake, this result needs to be verified to
determine 1f the finding 1s universally true. Other studies (2, 4)
concluded that lime stabilization had little effect on parasites such
as hookworms, amoebic cysts, and as.aris ova* In one study (6),
salmonella and intestinal parasites were killed within two hours after
quicklime addition to pH 13 to a cake sludge. In that study, the sludge
temperature had reached 176°F.
At two of the facilities, Glastonbury and Stamford, Connecticut, lime
stabilization was accomplished by the addition of hydrdted lime directly
to a dewatered sludge cake. These facilities reported that odors were
effectively controlled 1n cake to which lime had been added after dewa-
tering.
While the absance of odors 1s an indirect indicator of stabilization,
there is no dl -<*'t evidence available regarding the effectiveness of
this method for destroying pathogens. Inadequate mixing of the lime
and cake night produce inconsistent kills. We suggest that kill of
14
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organisms obtained when mixing lime with cake be studied inasmuch as
it is inexpensive and readily adaptable to existing facTi ities.
REGROWTH OF ORGANISMS
When organisms remain after stabilization, or when the sludge becomes
reinfected, the organisms will increase in number or recover from
inactlvation as the pH of the sludge decreases with time. Because
these sludges could become hazards or nuisances it' improperly handled,
prompt disposal or application of lime-stabilized sludges is a
desirable precautionary measure.
Of the plants studied, only the Stratford, Connecticut, plant had con-
ducted tests on bacterial regrowth. Some had experience with odors
generated in sludge piles that had been standing for various periods of
time. In general, however, fresh limed sludge and limed sludge that has
been stockpiled for a Jong period of time (three to four years at
Enfield) is inoffensive. There is some intermediate period when odors
can be expected if stockpiles are broken. This period might be variable,
depending on sludge characteristics, amount of lime added, and weather.
Stockpiles at least ?. week old at Kennebec, Maine and Stratford,
Connecticut, and a month old at Somersworth, New Hampshire, produced
offensive odors when they were broken down, but stockpiles less than a
month old were moved without serious odors at Glastonbury and Enfiela,
Connecticut.
The odor generation can be correlated with the drop in pH that occurs
with time. At Enfield, odors were not emitted when stockpiles of less
than seven weeks were broken. The pH values of stockpiles had remained
at about 11 or more until about seven weeks, when they began to drop.
Testing at Stratford suggests that regrowth of organisms is caused by
organisms already in the sludge, rather than by relnfestation from
external sources. The tests consisted of monitoring covered and un-
covered stockpiles of .luctge cake for two months, testing for coliform
bacteria. Both types of stockpiles showed similar rates for pH decay
and similar bacterial numbers.
Air drying of limed sludge before stockpiling can help decrease odors
when the piles are later broken down. This finding is based on experi-
ence at Stratford with sludge air dried for one week on sand beds.
Since stockpiling sludge cake allows organisms to regrow, there might be
some hazard* in addition to nuisance, associated with handling sludge
whose pH has dropped. Studies should be conducted to recommend the
handling of such sludges.
15
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SECTION 3
DETAILED DESCRIPTION OF LIME STABILIZATICN
This section describes equipment and techniques -jsed for lime stabiliza-
tion at the plants surveyed.
PREPARATION OP LIKE SLURRY
The plants surveyed purchase lime in the two available chemical forms:
quicklime (CaO) and slaked lime (CafOHjg). Quicklime is slaked before
use* Plants buying slaked lime normally prepare a slurry from the
hydrate or purchase the lime in a liquid form. A few add unslurried
hydrated lime, however. Some dilute lime purchased in a liquid form
to an even thinner consistency before applying it to sludge.
Quicklime
Five plants receive quicklime: Kennebec and Lewiston-Auburn, Maine;
Naugatuck, Connecticut; Rochester, New York; and Woonsocket, Rhode
Island. They purchase high-calcium quicklime (95 percent as CaO),
which 1s delivered by truck 1n 24-ton loads*
Unloading to conventional lime silos at all the facilities is accom-
plished by pneumatic systems with blowers on the delivery vehicles.
The loading line is typically a four-inch, carbon-steel line running
vertically up the outside of the silo to the top, with long-radius
elbows at bends. Bag filters at the top are used to clean the air
which conveys the lime.
The silos themselves are made of carbon steel, without coating, unless
one had been applied to protect the steel before the tank was placed
in service. The silo bottoms are sloped at about 60 degrees. All
silos have external vibrators for Improving the flow nf quicklime, and
the silo at Woonsocket, Rhode Island has a bin activator. Rotary air
locks at the bottom control the flow of lima and discharge directly to
slakers at Kennebec, Maine, and at Rochester, New York. At other
plants, lime is conveyed to day bins located above the slakers.
Flow from the silos to the day bins 1s pneumatic at Naugatuck,
Connecticut, and at Lewlston-Aubum, Maine; at Woonsocket, Rhode
Island, a screw conveyor 1s used. The pneumatic systems separate lime
from air by two different methods: j cyclonic separator (at
Naugatuck) and diverter plates, which direct the 11me into the day
16
-------
bins (at lewiston-Auburn). At Lewistoii-Auburn, the conveying air con-
tinues to the lime slurry tank on the way to bag filters. Most of the
lime passing the diverter plate falls into the slurry tank.
At Naugatuck, Connecticut, slurry slakers are used. Paste slakers are
used at the other four sites. At all of the installations, lime
slurry tanks are adjacent to the slakers. At the Kennebec plant, the
slakers sit directly on the slurry holding tanks, eliminating the ns«d
for a pipeline. The slurry tank sits below the slaker at Naugatuck,
and the lime slurry flows by gravity to the holding tank through a
clear, flexible, plastic hose, which can be. shaken to break up preci-
pitate. Pumping of slurry from a slaker is required at only one of
the plants visited.
The slurry holding tanks at the plants visited are roughly as wide as
they are high, and they are either cubical and concrete or cylindrical
and steel. Some tanks have high-speed propellers, others have low-
speed turbines, and some have baffles to prevent vortexing. There? was
no clear evidence to suggest that one type of material or mixing would
be inherently better than the others.
All holding tanks had level probes to control slaker operation. At
Woonsocket, which has a high-speed mixer, the probe is protected from
turbulence by a baffle. Probes at all plants are set so that there will
always be sufficient slurry to enable the mixers to work efficiently.
The silos and the slakers do not provide the only way to process lime at
facilities with quicklime. For example, at Lewiston-Auburn, Maine, the
slurry tanks have large openings ta allow use of bagged hydrated lime for
slurry preparation.
Hydrated Lime
The treatment plants visited using hydrated lime receive a high-calcium
grade lime containing 72 to 74 percent calcium oxide and 23 to 24 percent
water in chemical combination with the calcium oxide.
Hydrated lime is normally delivered packed in 50-1b bags* The heavy-
duty paper bags are stacked about 10 high on 4-ft by 4-ft pallets holding
about 50 bags. Plants requiring lime delivery on a regular basis receive
about 900 bags per delivery. Other common delivery loads fre 500 and 200
bags.
At plants receiving Hme 1n Intervals of five weeks or less, a fork-lift
truck Is typically used to unload the pallets of bagged 11me. This
operation takes about 2 labor hours. At the smaller plants, where bags
are typically unloaded manually one at a time, unloading takes 4 to 12
labor hours, depending on delivery size.
The bagged lime storage area 1s conveniently located near the loading
dock at most of the facilities visited. At one large facility, however,
bags are unloaded one at a time, by hand, onto a conveyor taking the
17
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bagged lime down into a basement storage area. With this arrangement, 16
labor nours are required to unload one truckload of lime. Not only is
labor excessive, but some bags fall off the conveyor and break.
Manually Operated Systems for Preparing Slurry: Equipment —
Lime slurry is typically made up from t\yciated lime using a manually
operated batch system. The equipment consists of: a bagged-lime
storage area, a slurry makeup tank, a mechanical mixer, dust control
equipment, a water meter, and a platform from which bags of hydrated
lime can be unloaded As shown in Figure 2, the bag storage area of
a typical system is conveniently located next to the makeup tank.
Lime slurry is pumped directly from the makeup tank to the next treat-
ment process, except at Fast Providence, Rhode Island, where day tanks
are used.
Figure 2. Hydrated lime slurry makeup system
Bath, Maine
18
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The lime slurry makeup tanks are constructed of unlined carbon steel.
They are usually cylindrical with a height-to-diameter ratio of about 1
to 1 and an average volume of 50C to 600 gallons. The tanks include
hatches for lime addition. All had a gravity drain to allow rinsing and
easy removal of any settled grit.
The tanks are mixed to prepare the slurry and then to keep it in
suspension. Two types of mechanical mixers are used: a small-
diameter, high-speed, propeller-type mixer which operates at 150 to
300 rpm; and a large-diameter, low-speed, paddle or turbine-type mixer
which operates at about 15 rpm. For a 500-gallon tank, a motor of
approximately three-quarter horsepower is provided. Operators at the
sites visited have reported that both types of mixers work well.
Another method, mixing with air, is used at the Falmouth, Maine
wastewater treatment facility. Not included in the original design, the
lime slurry makeup tank was later installed outdoors. By simply running
an air line to the tank, mixing was provided without exposing any
electrical equipment to the elements.
Most systems have at least two slurry makeup tanks. In operation,
jlurry is usually being pumped from one tank as it is being prepared
in the other. Some operators choose to pump from both tanks simulta-
neously. In some instances, only one tank is used with the second
tank acting as a back-up. In the latter two operations, lime slurry
is being pumped and prepared simultaneously. The operator starts
making up additional slurry while the tank is still one-quarter to
one-half full.
Because the hydrate is a very fine powdery material, dust control is
provided at most facilities. One facility visited had no dust
control, and the entire area surrounding the lime/slurry makeup tank
was covered with dust. An effective dust control system 1s shown in
Figure 2. In Figure 3 . this dust control system is 1n operation
while 11me 1s being added* Dusty air is drawn into the tank by a fan
and cleaned by a bag filter sitting in the housing on top of the tank
lid. At some facilities, the air cleaned in this way is vented to the
outdoors because some fine materials could escape the bag filter. The
bag filter 1s a low maintenance item requiring bag replacements only
one to two times per year. Although this dust control method 1s
effective, the area still acquires dust and should be cleaned regu-
larly.
A makeshift dust control system 1s in operation at the Stafford,
Connecticut, wastewater treatment facility. This system, shown in
Figure 4, consists of an 8-Inch vertical vent pipe and a fan to draw
the dusty air, with the entrance port of the pipe located just over
the mixing tank 1 Id. This system works quite well.
19
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Figure 3. Addition of bagged hydrated lime to
slurry makeup tank, Bath, Maine
w
t-
. i'r
^"
Figure 4.
tl I
Dust control added to existing
system, Stafford, Connecticut
20
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A platform, as was shown in Figure 2, Is usually provided to allow
the operator to pour In bags of lime from waist level. At New Haven,
Connecticut, the lime slurry makeup tank is taller than those shown in
the figures, having a capacity of about 1,000 gallons. A bag elevator
has been provided to raise the bags to platform height so the operator
does not have to carry them up the stairway.
In the system shown in Figure 5 ; the base of the slurry makeup tank is
depressed two to three feet below the steel grating floor. With this
system, the operator does not have to walk up steps with a 50-1b bag of
lirr.e. Any dust escaping the dust control system falls through the
grating to the concrete slab below.
Figure 5. Slurry makeup tank depressed into ftoor,
Hiddletown, Connecticut
21
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Manually Operated Systetrs for Preparing Slurry: Procedures —
The operator determines the available capacity in the lime slurry
makeup tank by measuring the water depth with a ruler. The operator
th^n turns on the water flow and, as the water fills the tank,
manually adds a predetermined number of bags of lime* Most plants jse
plant water, although some plants use city water in preparing the
slurry. One 50-1b bag of hydrated lime 1s typically added to CO
gallons of water to make an 11 percent lime/slurry solution. TIij?
volume of water added to the slurry makeup tank is measured by one of
two means. A water meter is normally supplied for accurate measure-
ment. When used, the meter should sit clearly visible to the operator
on the top of the tank lid. If no meter 1s supplied, the operator
uses tank depth as a gauge of water volume.
The makeup of one batch of slurry takes about 15 minutes. The slur.y
makeup operation requires regular attention. A low-level probe, not used
at any of the sites visited, could be used to allow the operator co per-
form other tasks between makeups of batches.
After a day's operation, thu tanks should be emptied and rinsed.. At
some facilities, the tank is filled with water which Is held until the
next operating shift.
Automatically Fed Systems far Preparing Slurry —
An automatic slurry makeup system can be used with hydrated lime.
Only at Portland-Westbrook. Maine, was such a system used. The
system, pictured In Figures 6-7,consists of a bagged-lime fsed hopper,
a silo (with vibrator below), a dry-Ume feeder, and a slurry mix tank.
The use of a bag-fed silo and automatic feeder can limit bag handling
to once per shift. The fine-textured hydrated 11me can be difficult
to handle and may clog 1n the silo. This problem may be solved by the
use of properly operated vibrators or air pads on the silo. Another
option 1s to outfit the silo with a I1ve-b1n bottom.
Automatically fed hydrated lime systems are best applied at plants too
large for manual batch slurry makeup and too small to efficiently
handle hulk quicklime*
Slurried Lime
Six of the plants surveyed purchase Hme slurry. Five of these purchase
slurry produced as a by-product 1n acetylene production. This product,
known as carbide Hme or chemical lime, Is available In many aftias and
is readily obtainable 1n the study area. One treatment facility
receives slurried lime commercially prepared by slaking quicklime.
This product Is more expensive than the acetylene by-product, but its
concentration Is more consistent.
22
-------
r*--
*
«V/
-• N»«**
itaiafMNIbAfefc
"-"TCrHil
Figure 6. Automatic hydrated lime slurry
makeup system, hatches to day
bins, Portland-Westbrook, Maine
jiwif wji'wi|Lip!jjl
.¦r-Mki'
...
^.•itiWfrv :*¦
ft--:
Figure 7. Automatic hydrated lime
slurry makeup system, day
bins and feeders, Portland-
Westbrook, Maine
23
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Table 3 gives a typical chemical analysis of carbide lime as
reported by a supplier. The data show that the calcium concentration
is similar to that of high-calcium lime. Carbide lime is normally
delivered at a 35 percent solids concentration. Because operators
report that delivery concentrations can range from 20 to 35 percent,
however, storage facilities should be sized to handle a 20 percent
slurry.
Storage and Delivery of Slurried Lime --
Slurried lime is delivered by tank truck in 4,800-gallon loads. L1me
can be delivered from the delivery truck to storage by gravity. If a
pump is needed, an abrasive handling transfer pump can be used. A
hose should be provided to allow for rinsing settled lime out of the
truck. The slurry usually contains grit. To prevent grit from enter-
ing the treatment plant's lime handling system, the WilHmantic,
Connecticut plant has a screen on the storage tank entry port. Figure
8 shows the type of screen used.
The lime slurry storage tanks at Stratford and WilHmantic,
Connecticut, are constructed of concrete. Unllned carbon steel is
used at other Connecticut plants 1n Enfield and Vernon, and at Bucknam
Point, Rhode Island. No storage 1s required at South Windsor,
Connecticut, where the 11me delivery 1s dumped in one batch to a
sludge/lime mixing tank. At Stratford, Enfield, and Bucknam Point,
the tanks are indoors. The Vernon facility has a 15,000-gallon out-
door storage tank. Underground tanks are also used, as at
WilHmantic.
The storage tanks must be mixed constantly* Large storage tanks at
Enfield and Stratford use a large-diameter, slow-speed paddle mixer.
A high-speed mixer Is used at Bucknam Point, Stratford, and
WilHmantic*
The five plants storing slurry keep a minimum inventory of one to two
weeks' supply and schedule deliveries weekly. The facilities have
either one or two lime slurry storage tanks. Three plants have two
storage tanks, each with the capability of holding one truckload of
lime. Two plants have only one storage tank* In each case, this tank
has capacity of three truckloads.
Day Tanks for Lime Slurry —
All of the five facilities storing lime slurry utilized day tanks 1n
addition to bulk storage* This 1s done for two major reasons:
(1) to locate a storage tank close to the application point of
the lime slurry
(2) to provide for dilution of slurry, if desired.
24
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TABLE 3
TYPICAL ANALYSIS OF CARBIDE LIME
Typical Chemical Analysis Screen Size Distribution
Ca(0H)2 95 Thru 20 Mesn 99.92
CaO Equiv. 72 Thru 48 Mesh 99.2
CaC03 1.5 Thru 100 Mesh 97.0
MgO 0.25 Thru 325 Mesh 85.0
S203 (fe203 t A1z03 1.6
Insolubles 1.1
Source: Che.nline Corporation, 1979
i
Figure 8. Lime slurry storage tank with grit screen,
Wlllimantic, Connecticut
25
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If the slurry, as received, is of a concentration higher than desired
for use, it may be diluted. Additionally, dilution to a constant
slurry concentration simplifies volumetric metering. Although day
tanks at all of the facilities visited :.iz equipped to provide dilu-
tion, it is regularly practiced only Enfield. Here, dilution is a
batch operation. The desired concentration 1s obtained by adding a
metered quantity of water to a concentrated slurry.
Day tanks are typically constructed of carbon steel with no lining.
The tanks are usually sized to hold the capacity for one shift, but
may be sized for some other convenient time interval. During this
time, the tanks must be mixed. The same type of turbine and propeller
mixers used in lime slurry makeup tanks are available for day tanks.
The tank should be fitted with a drain and flusted when empty. At the
Vernon, Connecticut wastewater treatment facility, flexibility has
been built in by designinc the day tanks so that they can be used to
make up lime slurry from bagged hydrated lime. With this capability,
the plant is protected in the event that the source of lime slurry is
temporarily interrupted.
PUMPING AND CONVEYANCE OF LIME SLURRY
The types of pumps, types and configurations of pipelines, and valves
used in the conveyance of lime slurry are discussed in this section.
Applications of Lime Slurry Transfer Pumps
Lime slurry transfer pumps are used to transfer lime slurry to a day
tank or to a batch 11me stabilization tank. Slurry 1s pumped to a day
tank with a slurry pump at Enfield, Stratfprd, and Vernon,
Connecticut; East Providence and Bucknam .'olnt, Rhode Island; and
Rochester, New York. At Thompson, Connecticut, 'im& slurry 1s pumped
to a batch stabilization tank. A portable lime slurry transfer pump
is used at Thompson, employing a procedure described in a later sec-
tion, when bulk lime stabilization Is practiced. The transfer pumps
are only required to operate at a single speed. They operate in an
on/off cycle, delivering lime slurry as required.
Whenever possible, it Is recommended that Hme slurry be transferred
from storage by gravity. Such a configuration Is utilized at the
Wlllimantic facility. Lime slurry 1s transferred from the bulk lime
slurry storage tank to the 11me slurry day tank through a 3-inch-
diameter, 3-foot-long pipeline fitted with a manually controlled gate
valve.
Lime slurry Is non-corrosive but abrasive, and transfer pumps must be
specially designed. Positive displacement pumps are used at Enfield,
Connecticut and at Rochester* New York, but a closed*impeller centri-
fugal pump is normally selected.
26
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The centrifugal pump selected is either hard metal (not simply all
iron) or rubber-lined. A hard-metal pump is very resistant to abra-
sion. While mure resistant than rubber-lined pumps, they are also
more expensive. Rubber-lined pumps do resist abrasion quite veil, and
are sufficient in many applications. Abr?sive particles simply bounce
off or become embedded in the rubber lining. With heavier slurries,
the rubber will wear and shred over time.
To decrease wear due to abrasion, the pump selected should operate at
low speeds -- conventionally about 1,100 rpm or less. Pumps should be
supplied with a maximum size impeller to ensure efficient passage of
solids, reducing the possibility of solids build-up within the pump.
Applications of Lime Slurry Metering Pumps
Lime slurry metering pumps dispense appropriate lime dosages to con-
tinuously operated systems. The pump output is usually controlled by
adjusting pump speed from a control panel located close to the point of
lime application, but output can be manually controlled.
Three types of metering pumps were in use at the treatment plants
visited: plunger or piston puinps; diaphragm pumps; and progressive
cavity pumps.
Plunger pumps were used at nine of the twenty treatment plants using
slurry metering pumps. Operators were generally satisfied with their
operation, citing low maintenance requirements. In one instance these
pumps were used to replace diaphragm pumps that repeatedly failed.
Eight of twenty plants were using diaphragm puinps to meter the Hme
slurry. Most plants use the mechanical type of diaphragm pump.
Operators reported that regular maintenance was required; the rubber
diaphragms reportedly had to be replaced every few months. While
replacement of the rubber diaphragm 1s a relatively simple operation
and most operators do not complain of this regular maintenance
requirement, some operators were upset by iropportune diaphragm
breakage.
Progressive cavity pumps were used at three of the facilities visited.
At one facility the operator reported that rotors and stators were
wearing excessively.
Piping Systems For Lime Slurry
The major problem in the conveyance of lime slurry is that of scaling.
Water carrying the 11me undergoes a softening action and calcium car-
bonate (CaC03) precipitate 1s formed. This results in the formation of a
dense hflnfiL^ scale on the conveying H*e. An example of this 1s shown in
Figure' 9 from Mlddletown, Connecticut. Eventually a pipe has to be
either cleaned or replaced.
27
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Figure 9. L1me scaling of pipeline,
Middletown, Connecticut
As 11me slurry 1s noncorroslve, a wide range of pipe materials can be
used. Carbon steel pipes, plastic pipes, and flexible rubber hoses are
used at the Jites visited. At Thompson, Connecticut, a flexible fire
hose conveys lime slurry to the stabilization tank.
When using rigid pipe, a provision for pipe cleaning should be made at
each pipe bend. Tees or wyes were used In place of bends at maty
sites. These allow access to the pipes' Interior for cleaning with
either a rod or a pipeline reamer "pig". Long-radius, removable
elbows also provide access for cleaning, and are In use at Kennebec,
Maine.
Flexible hoses are used at Enfield, NaugatucK, Stratford, and Vernon,
Connecticut, and at Kennebec* Maine. The hose can be flexed and shaken
to break up any calcium carbonate build-up on the Interior of the pipe
walls.
28
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The system at Kennebec, Maine, is shown or Figure 10 v The hose is laid
in overhead troughs or trays. With this syrtem, a stick can be poked
through the bottom of the trough, allowing the pipe to be shaken from
below. At Stratford and Vernon, Connecticut, the pipeline was simply
tied into place. At these two plants, flexible hose replaced a rigid
pipe installed initially.
Figure 10. Troughs holding flexible lime hoses,
Kennebec, Maine
Another technique of controlling 11me build-up is the use of an inhibi-
tor, such as sodium hexametaphosphate. Inhibitors are used in areas with
hard water to protect dewatering equipment, such as vacuum filters, from
build-up of lime.
A regular flushing schedule should be developed for the entire lime
handling system, including valves, pumps, tanks and mixers as well as
pipelines. At most of the sites surveyed, flushing 1s done at the end of
every lime use. Flushing can be controlled manually or automatically.
Automatic controls are activated upon 11me system shut-down, and should
always be used when the lime system is automatically controlled.
29
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Valvinq in Li;:*; Slurry Pipeline Systems
There are two general types of lime piping system layouts: direct and
loop. In direct systems, lime is pumped directly from one point to
another. All of the plants visited used this system of piping. The
use of loop systems is more popular at large facilities.
When pumping lime slurry directly from one point to another, the use
of one oump and one pipeline is insufficient. Most plants visited are
designed w»th flexibility, with each slurry tank serviced by more than
one pump. A. number of valves are required to achieve flexibility. At
the plants visited, gate valves were commonly used in steel pipelines.
At Willimantic, Connecticut, ball valves were used with the PVC pipes.
These types of valves should not be operated partially opened. In
this position, lime particles would settle out and build up in front
of them.
APPLICATION OF LIME
The points of application can be divided into three major groupings:
(1) to a liquid sludge before land application;
2) to liquid sludge before dewatering; and
3) to a cake sludge after dewatering.
Lime Application to a Liquid Sludge Prior to Land Application
At five treatment facilities, aerotically digested liquid sludge was
lime stabilized prior to land application. The sludge was stored In
an aerobic digester or 1n a separate storage tank prior to batch lime
addition and lime stabilization* Four basic systems developed.
1. Lime Addition to Sludge Transfer Line. At Scarborough, Maine
bagged, hydrfted lime is added to a pipeline transferring aeroblcal!;.,
digested sludge to a land application truck. The treatment plant was
Initially designed so that the sludge could flow by gravity from the
digester to sand drying beds. Because of low volatile solids reduc-
tion in the digester, the stabilization of the sludge had to be
upgraded. L1me stabilization was selected.
The system used at Scarborough 1s shown in Figure 11. The
gravity line from the aerobic digester goes into the bottom of a
tee section. The right hand of the tee section is connected to an
open barrel (see Figure 12 )j the left hand of the tee Is con-
nected to a line leading to i pump on the land application truck.
When sludge is to be removed, the valve to the truck 1s first
closed and all other valves are opened. The barrel fills with
sludge by gravity while the operator adds a few shovels of lime to
the barrel. When the barrel is full, the valve to the truck Is
opened and the pump on the truck is activated. Sludge with lime
1s pulled from the barrel. At the same time, sludge Is being
30
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AEROBIC
OiGESTEP
MVOMTED UME
ADOITIO* TO MUM
LAND
' APPLICATION
-------
pulled from the aerobic digester. When the barrel is emptied, the
valve to the barrel is closed. After the truck is nearly full,
the valve to the barrel is reopened, more lime is added, and the
startup operation is repeated. After the truck is filled, the
pump is temporarily stopped and all valves are closed.
mm
&
¦«
v
.-..J
Figure 12. Hydrated 11me addition to sludge
transfer line, Scarborough, Maine
The land application vehicle Is a converted oil delivery truck*
In the rear of the truck the pump Is valved so that It can pull
sludge from the digester, mix the contents of the truck by re-
circulation pumping, and be used to spray liquid sludge onto
fields. While the truck is being driven to the land application
site, the proper valves are opened and the contents of the truck
are mixed by recirculation pumping.
The technique used at Scarborough obviously requires little capi-
tal Investment. It does hav» some severe limitations, however.
The pH of the I1me-stab1lized sludge can only be accurately deter-
mined after the truck 1s filled and the recirculation pumping has
32
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completely mixed its contents. Whether or not there is complete
mixing is questionable. After pH is determined, it is too late to
add more Time tc correct insufficient pH unless it is added
directly to the truck. Because no provision fcr this has been
made, pH control is limited.
2. Lime Addition to Unmixed Storage Tank. At North Canaan, Connecticut,
aerobically digested sludge is stored all winter in two unmixed
storage tanks. The tanks are primary clarifiers abandoned by a
previous treatment facility. All sludge collection equipment has
been removed. Lime stabilization 1s required at this facility
because of low volatile solids reduction in the aerobic digester.
At North Canaan, lime stabilization is practiced once a year in
the spring. A sludge truck equipped with a pump is parked beside
the storage tank (see Figure 11 ). The pump on the truck is used
to mix the contents of the storage' tank by recirculation pumping
while bagged lime is poured directly into the sludge. pH is moni-
tored and lime is added until the desired level is reached. After
the proper pH is attained, mixing continues for a while. The
truck is then loaded. The truck must make a number of trips to
completely empty the contents of the sludge storage tank.
This system required no capital expenditure, except the purchase
of the sludge truck. The application 1s unique in that a tank
with sufficient capacity to store all sludge created in the winter
was available on site. The acceptability of this type of system
is dependent upon operational procedure. The operator must be
sure that the lime is well-mixed with the sludge and that the con-
tents of the entire tank has reached the required pH. At each
truck loading, pH should be checked and more Hme added If pH
decay has occurred.
3. Lime Addition to Mixed Storage Tank. Lime 1s added to mixed storage
tanks at Falmouth, Ma^ne and at Thompson, Connecticut. At
Falmouth, aerobically digested sludge is stored in the digester.
The digester mixer is periodically stopped to allow the sludge to
settle and the supernatant to be decanted. With this technique,
the digester has sufficient capacity to store sludge produced
during the entire wii.uc Sy spring, the sludge builds up to a
solids concentration of three percent. When weather permits,
batches of winter sludge ar® 1ime-stabilized 1n a separate tank
prior to land application (see Figure-11 j) Sludge collected
during the remainder of year 1s also lTine-stabllized after aerobic
digestion and land-applied as quickly as possible.
L1me stabilization at Falmouth occurs 1n a bulk storage tank
capable cf storing 16,000 gallons of sludge. The tank Is equipped
within an air mixer that completely mixes its contents. The
33
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outlet is fitted with a screen to capture fibers and other
materials that would be unsightly If }and applied.
Sludge is stabilized once per day. In the afternoon, after the
sludge storage tank aas been emptied, the digester is shut off and
the sludge is allowed to settle. The liquid is decanted and the
settled sludge is pumped to the storage tank. Lirre slurry is then
added to Increase the pH to the proper level. The operator
reports that there is an ammonia odor. After overnight storage
with the air mixer kept on, the pH is checked to make sure that it
is sufficiently high. If required, lime is added to adjust the
pH. The sludge is then pumped to a C,G00-gallon land application
vehicle for disposal. Daily operation simplifies operation, and
pro/ides flexibility in scheduling land application.
The fclfTouth plant was originally equipped with the sludge storage
tank and the air mixer. A lime slurry preparation tank, a pump
and pipeline to carry the sludge to the land application truck,
and the land application truck itself were required to convert
this plar.t to lime stabilization* The land application truck was
fabricated by treatment plar.t personnel who affixed a tank to the
bed cf a truck alreacfy owned by the town.
At Thompson, two aerobic digesters were provided in.the original
plant design. These tanks are shown 1n Figures 13 and 14. One of
these tanks is operated as an aerobic digester; the other is operated
as an aerated storage tank. The air to the digester 1s periodically
stopped, supernatant 1$ decanted, and the settled sludge solids are
pumpea with a portable "nud sucker" pump to the storage digester.
The storage digester 1s also occasionally decanted.
Two to four times per year, the contents of the storage tank are
Mme stabilized. Lime slurry is prepared from bagged hydrated
Hrne. The slurry makeup system was included 1n the original plant
design to prepare limn for conditioning prior to sludge vacuum
filtration. Prepared slurry 1s pumped with a portable pump
through a flexible fire hose to the storage digester. The pH of
the tank Is monitored and lima Is added until the desired pH 1s
maintained. The contents of the storage tank are kept completely
mixed until the tank is emptied, one load at a time, to a land
application truck. The lime stabilized sludge Is transferred
u«1ng the same "mud sucker" pump used to transfer the aeroblcally
digested sludge to the storage tank. It takes about one week of
land application to empty a tank full of lime stabilized sludge,
during which time pH 1n the tank Is monitored and maintained.
the systems at Falmouth and Thompson work very well. The sludge
is completely mixed and held at high pH while still 1n the liquid
form, ensuring the greatest pathogen kill. pH control Is very
good. The sludge pH can be accurately measured and adjusted as
the sludge Is completely nixed ami held to the proper detention
time.
-------
*+,. # * '
v
1
1
t
i
f
i
Figure 13. Aerobic digester, digestion mode,
Thompson, Connecticut
Figure 14. Aerobic digester, used for lime
stabilization, Thompson, Connecticut
35
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The system at Thompson required little capital investment. The
plant simply purchased two portable pumps and fabricated a land
application truck by fixing a tank onto a dump truck bed.
4. Lime Addition t.o Batch Aerobic Olaester. At South Windsor,
Connecticut, sludge 1: Time stabilized by adding lime directly
into an aerqbic dlgert.'r. A diagram of the system is provided in
Figure 11.
At South Windsor, sludge sol Ids are allowed to build up In an
aerobic digester. After about one month, a truckload of carbide
lima slurry is ordered and dumped into the digester. Exper
-------
provide lime stabilization, the detention time would be at least 30 min-
utes. A lime conditioning tank design is concerned not with detention
time but only with mixing of lime slurry and sludge.
The vat containing liquid sludgo beneath the vacuum filter does pro-
vide some detention time, but detention ti:ne is not a designed para-
meter for selection of this vat. The vat detention time is a function
of filter submergence, vat geometry, sludge solids concentration, and
the sludge filter rate. Under normal conditions, the detention time
that occurs can be 15 minutes or more.
Because of tha addition of lime, filtrate has a high pH. The operators
of the treatment facilities reported that the increased dose from lime
stabilization caused no adverse effects on the treatment facility from
changed sidestream characteristics. While a few operators did note that
there was an increase in pH of the wastewater being treated, it seemed to
have no effect on wastewater treatment efficiency. Operators also noted
that the solids capture of the vacuum filters and the solids filtering
rate neither degraded nor improved noticeably with the increased dosas of
lime. Operators at some facilities reported an ammonia odor at the
vacuum filters.
In most instances, operators commented that the increased dose resulted
in no effect on maintenance. Two operators commented that vacuum filters
had to be cleaned quite frequently, but that this had also been the case
prior to the institution of lime stabilization.
For proper operation of the lime stabilization system, the dose of
lime nust be sufficient to reach a specified pH and not simply to
achieve efficient sludge dewatering. pH was monitored by using either
litmus p-^er, or a pH probe, or by using litmus paper regularly and occa-
sionally checking its reliability by using a pH probe. pH was typi-
cally measured in cne of three places: on the liquid sludge in the
vacuum filter vat; on the freshly dewatered sludge while still on the
vacuum filter jr conveyor; or on sludge cake that had been allowed to
sit for a while.
Lime stabilization is typically defined as Uming the sludge so that
it has a pH of 12 after two hours detention time. In view of this,
the system should be operated so that the vacuum filter sludge cake
has a pH of 12 after one and three-quarters hours (allowing 15 minutes
detention in the vacuum filter vat). To achieve this goal, some
operators operated the system so that sludge In the filter vat or
freshly dewatered sludge was limed through a pH of slightly greater
than 12, say 12.1 or 12.2. This method was based on individual
experience showing that such a procedure would result in the sludge
maintaining a pH of at least 12.0 after the two-hour detention period.
The lime dose was typically controlled by adjusting lime metering pump
speed from a control panel located near the vacuum filter. At some
treatment plants, the operators conmented that they selected the lime
dose "by eye". Others claimed that, based on past experience, they
37
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could simply add enough lime to achieve 'jood dewaterabi1ity as this
dosage was sufficient to achieve the desired pH. Such shortcuts are
not acceptable, however. The pH must be checked with regularity and
the lime dose adjusted as necessary.
At 16 out of 20 plants dewatering with a vacuum filter, ferric
chloride is normally used in conjunction with lime for conditioning
pirposes. One plant used Hme alone. At three facilities, operators
chose to use polymer instead of ferric chloride as a conditioning aid
with lime. The operates commented that they had a difficult time
finding a polymer that could work well with the high pH of the lime
sludge. Those plants now successfully using polymer are satisfied
that there was some decrease in the required lime dose.
Lime Addition to Dewatered Sludge Cake
Sludge cake is lime-stabilized at three facilities. Two plants add
lime to a sludge screw conveyor; one plant adds lime to sludge cake
stored in a pit.
Lime Addition to Sludge Screw Conveyor —
At two plants, Glastonbury and Stamford, Connecticut, powdered
hydrated lime is added to sludge in a screw conveyor. The conveyor
mixes the sludge with the lime while conveying It to a truck for ulti-
mate disposal.
The system used at Glastonbury 1s shown 1n Figure 15. Bags of lime
are lifted by an elevator and stored on a platform raised about six
feet off the floor. The lime Is poured, one bag at a time, into a 55-
gallon drum, *.t the bottom of which 1s fixed a conventional lawn
spreader. The lawn spreader 1s turned by a belt conveyor that carries
sludge from the centrifuge to the screw conveyor. The sludge falls
off the belt and onto the screw conveyor just below the lawn spreader.
The spreader sprinkles lime onto the screw conveyor, which mixes the
lime with the sludge hhlle conveying It to a truck for ultimate dis-
posal.
L1me dosage is controlled by making an adjustment to the dosing rate of
the lawn spreader. pK was checked by using litmus paper when lime stabil-
ization had been the goal of this facility. At present, lime addition
is being practiced only for odor control, as the sludge is being brought
to a landfill where composting Is being set up.
When the system at Glastonbury was Initially set up, the platform that
holds the system had to be built and the lawn spreader acquired. The
other equipment was available ons1te* The screwrconveyor w«s.tntttallyc '
ustd as an ash conveyor In the Incinerator which has since beer* aban-
doned.
38
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Figure 15. Hydra ted lime additio.. to
cake sludge, Glastonbury,
Connecticut
Stamford* Connecticut's system is also unique. Hydrated lime is poured
one bag at a time into a hopper (Figure 16 [• A flexible screw con-
veyor conveys the hydrated lime from the hopper into a storage silo,
shown in Figure *7. Hydrated lime from the silo is conveyed by a
screw conveyor tj a second screw conveyor moving sludge cake from a belt
press to a truck. The configuration of conveyors is shown in Figure
18.
The pH is occasionally checked by using litmus paper on the sludge-
cake. While the operator aims for a pH of 12.1, actual operation
usually results in a pH after two hours of 11.8. Lime dose is
corrtrolled by setting the ratio of the speed of the lime conveyor ver-
sus that of the sludge conveyor, using a control panel located on an
upper level beside the belt filter.
The system at Stamford, Connecticut is simply a back-up to coincinera-
tion. All equipment was purchased when the system was installed.
39
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«r—mtaiinrmi
Figure 16.
Hydrated lime addi- Figure 17.
tion to cake sludge,
lime hopper,
Stamford, Connecticut
mmmmmmmmmm&r*
Hydrated Hme addi-
tion to cake sludge,
lime day bin,
Stamford, Connecticut
i:
J
J
Figure 18.
Hydrated Hme addition to cake sludge, lime ar.d
sludge conveyors, Stamford, Connecticut
40
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No biological tests have been made to determine whether mixing of cake
and lime is effective. The odor control is so far the only indication
that bacterial activity is inhibited.
Lime Addition to Sludge Cake Storage —
At Groton Town, Connecticut, dewatered sludge cake is stored in an
open tank abandoned from a previous treatment plan*. In a batc.'i
operation, wood chips and bags of lime are added to ti.i pit (N\e wood
chips are used to increase the solids content priit to landfilling).
The sludge is then mixed with a front end loader and loaded ^nto a truck
for removal from the site. This method results in poor pH control anu
poor mixing, and is being replaced by static composting the land-
fill.
DISPOSAL AND REUSE ALTERNATIVES
Sludge Removal From Sitt;
Liquid sludge is disposed of by land application, using trucks
described later in this chapter. Cake sludge '? c.-.rried by a conveyor
to a container that can be lifted and ."ewovea by truck; to a bin that
is unloaded to a dump truck by a front end loader; or co a hopper or
chute discharging directly to the sludge hauling dump Tuck. This
hopper can also temporarily score the cake sludge while the truck* is
in transit. At two facilities using a hopper to ten^orarily store
sludge, operators commented that the sludge would not flow readily
from the hopper to the awaiting truck by gravity alone, but had to be
washed or poked through.
Stockpiling
At a number of the sites visited, cake sludge was trucked to a land
application or landfill site and simply dumped in a stockpile. Sludge
was allowed to sit in piles, to be spread or landfilled at a later
time. Sludge can sit in a stockpile without odors occurring. If
piles are disturbed after short-term stockpiling, they do not emit
highly offensive odors. When somewhat older stockpiles are broken
into, however, a very offensive odor is emitted. Because of this,
operators at Kennebec» Maine and Rochester, New York commented that
they would not allow sludge cake to sit in piles for more than a day.
At Somersworth, New Hampshire, the tern of stockpile storage is also
1imited.
At Enfield, Connecticut, sludge has been successfully stockpiled for
periods of months and even years. Experience at this facility has
shown that the pH drop 1n the stockpiles occurs only gradually. The
operator has commented that odors emitted after breakdown from stock-
piles a few months old are somewhat offensive, but shortlived. Some
41
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sludge stockpiles at Enfield and at Glastonbury had been allowed to
sit for a number of years. When broken into, only a sliyiit musty odor
is emitted from thes1; piles. The sludge in the center of the pile has
been broken down and has the appearance of an organic topsoil.
At Stratford, sludge was at one time simply trucked to the landfill
site and stored in stockpiles. Because of odors emitted when the
stockpiles were broken down, the operator decided to change the stock-
piling procedure. At present, freshly dtwatered sludge is trucked to
the landfill site and spread on sand beds. The sludge is allowed to
sit on these beds for a week or sc.to dry before being scooped up and
stored in a stockpile (see Figure^ IS ). As a result of the drying
procedure prior to stockpiling, the~operator reports that only a
slight odor is emitted when stockpiles are broken down and taken to
the landfill.
¦mm
Figure 19. Sand bed dried sludge 1n stockpiles,
Stratford, Connecticut
42
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Landfilling
Landfilling is the means of sludge disposal at 18 of the 28 plants
visited. At 12 of the facilities, the sludge is simply buried. Landfill
operators ai the six other sites take advantage of the fertilizer and
moisture holding value of the sludge and use it as a cover material. It
was reported that a grass cover grew quite well on the sludge used as a
landfill cover.
The only report of odor problems associated with landfilling of the
sludge was the result of breaking down old stockpiles. At none of the
sites visited was any special monitoring done.
Land Application
At ten of the plants visited, lime stabilized sludge is land-applied.
A liquid sludge :'s applied at four of these plants, and the remainder
land-apply a sludge cake. The sludge is used for its fertilizer value
and for its ability to increase the moisture holding capacity of the
soils.
In many instances, farmprs were initially reluctant to accept the
sludge. A report based on the land application program at Falmouth,
Maine shows how the sludge was gradually accepted by the public. This
was a result of careful planning. The py&'ic was invited to visit
sites where sludge had been applied, to tour t-eatment plant facili-
ties, and to ask any questions concerning ths land application pro-
cess. Responses to questionnaires sent out to chose receiving the
sludge were exceptionally ^avorable.
Uses of the Sludge --
Wastewater treatment plant operators selected application techniques
and reuse options, and made the arrangements with those accepting the
sludge.
At Falmouth, liquid sludge is applied at no charge tu fields where
grass is grown. The sludge has been well-accepted an-, there is a
waiting line for recipients. At Thompson, Connecticut, a similar
arrangement has been made with those receiving the sludge. Lime-
stabilized sludge is applied to fields where silage corn and hay are
grown, lime-stabi»ized si idge from the Scarborough, Maine, treatment
facility is applied to lawns and hay fields, and is also used to
reclaim land that has been stripped of loam. The treatment plant
receives $6.00 per load of sludge. In addition, tiie, farmers sometimes
supply the lime required for stabilization. At North Canaan,
Connecticut, a fanner removes the sludge from the treatment plants
with his own truck. It is mixed with animal wastes and used on fields
where silage corn and hay are grown. Cake sludge from the Enfield,
Connecticut, wastewater treatment plant is spread on town land where
43
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silage corn is grown. A number of experiments h^ve been run at this
site, and wil] be discussed later in this chapter. Willimantic,
Connecticut, sludge is mixed with soil and used as a loam on which
grass is grown. Sludge from the Bath, Maim, wastewater treatment
plant is used to reclaim land stripped of loam. The organic content
of the sludge iinproves the moisture holding capacity of j'oor subsoils.
At Rochester, New York, and at Somersworlh, New Hampshire, the cake
sludge is applied to fields. Treatment plant personnel truck the
sludge to the site, spread it on tha fulds, and harrow it, all at no
charge. A i)ort:on of the sludge from the Kennebec, Maine, wastewater
treatmpnt p(ant is applied to farmlands. The farmers report that they
are very pleased to receive the sludge. Odors are reported tn be
similar to those when manure was spread, as long as sludge is not
stockpiled.
At Somersworth, only 20 percent of the sludge is land-applied as there
is difficulty finding additional land. Much of the sludge from
Rochester and Enfield is applied to lancis owned by the towns.
Operators from these three sites expressed a desire to spread more
sludge on privately owned lands. The difficulty in locating sites is
not one of public .icceptance, but of finding land appropriate for
landspreading of sludge. Such spreading Is regulated when land will
have high human contact.
Techniques Used to Apply Liquid Sludge --
The trucks used to land-apply 1;quid sludge at the sites visited were
fabricated from various types of vehicles.
An amy surplus truck equipped with a pump and tank was used by the
farmer who removed sludge from the North Canaan plant. The truck used
at Scarborough, Maine is a converted oil delivery truck. The pump at
the rear of this truck was revalved so that it couid pump sludge to
the truck, mix the contents of the tank on the truck by recirculation
pumping, and pump sludge from the truck. The truck is also equipped
with a nozzle and splash plate on the rear or the tank so that it can
discharge sludge by gravity.
The trucks used at the Thompson and Falmouth facilities were also
fabricated. The Thompson truck was converted from an old dump truck.
The suspension was built up and a tank fitted to the bed of the tmck.
A nozzle was fixed to the rear of the tank so that the sludge cci:.>. be
discharged.^ gravity. The truck used at Falmouth, Maine is shown in
F1gure(20. Plant personnel completely fabricated this truck from an
old flatbed truck. Sludge is discharged by gravity through the nozzle
shown at the rear of the tank.
44
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V.
<
i
|»» ; • '
J
9
I
_ —. je
Figure 20. Liquid sludge land application truck,
Falmouth, Maine
Figure 21. Manure spreader for land applying
sludge cake, Somersworth, New Hampshire
45
-------
The operator at Falmouth, Maine commented that the sludge disposal
vehicle could improved by fitting the truck with a pump and long
hose, as used at Scarborough, Maine. This would allow more even
spreading of the sludge and would provide access to areas inaccessible
to the truck.
Equipment Used to Land-Apply Cake Sludge —
Farm equipment was usually used to handle the land application of the
cake sludge. Figure 21 is a picture of a marure spreader used at
Somersworth. The blades at the rear of the spreader throw sludge out
of the back of the vehicle. A harrow follow* tne manure spreader,
mixing the soil with the sludge.
Attempts to use a manure spreader at the Rochester facility were
unsuccessful because the cake was sticky. Figure 3-17 shows the cake
sludge application system developed by Rochester treatment plant per-
sonnel. Figures 22 and 23, show the hopper that holds the sludge.
A sliding gate at the bottom of the hopper opens completely and the
cake sludge falls to the ground. The hopper, whicn rests on skids, is
pulled along by a tractor. Sludge falling out of the hopper is left
be.iiM in a mat. Mat depth is controlled by am..adjustable plate on
:he rear of the hopper. As shown in Figure 23 . the mat is broken
up by blades that follow the hopper. Figure 24 shows the harrows
that complete the mixing of sludge with the soil.
Rssults of Land Application —
It was earlier explained that a number of farmers have willingly
accepted lime-stabilized sludge, and some are willing to reimburse the
treatment plant for the expense of spreading the sludge. The sludge's
lime content has been welcomed by New England farmers who normally
have to lime their soil. By using the sludge, th»j need for liming the
soil is reduced or eliminated. The operator at Falmouth, Maine moni-
tors pH of lands to which sludge was applied. If pH were to drop to
less than 6.6, lime would be added, but this has never been necessary.
A controlled test was performed at Enfield to analyze the effects of
1ime-stablllzed sludge on crops. The experiment, conducted on town-owned
lands located about 5 miles from the treatment plant, lasted from July
1976 to September 1979. Much of the data were collected by staff and
students from the University of Connecticut at Storrs. Two separate
field areas were established, each divided Into sections receiving six
different application rates. The sludge was plowed into the soil.
One area received sludge only the first year, and the other received
sludge each year for three years. The application rates used on each
area were 0, 13, 33, 66, 99, and 132 metric tons of sludge per hectare
per year. Field areas also received annual additions of potassium
fertilizer (112 kilograms per hectare) to supplement the low potassium
content of the sludge.
46
-------
i
v. - V
*
ff . 4 .
%.
'&>¦¦¦* &¦
1 •- * •••? •£• is •'- :
4 •' -tef •'¦• '
1 '¦: - w4'::
¦\ • . W •*
~i ' '-ML'V
•» i' rt'f ^,C
: ^wiii'iiAi^ii
M
v't
Figure 22. (left) Sludge cake land
application equipment,
sludge hopper, Rochester,
New York
*r
iv
t'ff-
$• • 3' •:
- 'V
>. . i
. A:'\
f ¦-
mJO - --
Figure 23.
Figure 24.
(above) Sludge cake land
application equipment, rear
of hopper, Rochester, New
York
(left) Sludge cake land
application equipment, harrows,
Rochester, New York
uMihk
¦4ilikaa4<>»MlM
-------
Each Hay, corn ,v
-------
Sludge from the Kennebec, Maine, treatment plant was used to fertilize
hay and corn fields. Samples of these crops and samples of the same
crops taken from fields fertilized only with conventional fertilizer
were analyzed for heavy-metal uptake. Metal uptake was found to be
greater in the fertilized fields than in the fields treated with the
1ime-stabilized sludge. A conclusio.. drawn was that the lime-
stabilized sludge increased the so:l pH, ultimately decreasing the
availability of soluble metals that could be taken up by the piants.
It was recognized that extensive testing in the future will have to be
performed to determine the long-terr effects of using the sludge.
Other plants have checked heavy-metals in crops, soils, ar.d groundwater,
but results have not been documented.
49
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SECTION 4
INNOVATIVE TECHNIQUES
The lime stabilization systems used were generally developed by treat-
ment plant personnel. A number of innovative tecnniques were deve-
loped for the stabilization, handling, and disposal of the sludge.
The plants use screw conveyors to mix centrifuge cake and lime. At
Glastonbury, Connecticut, a common lawn spreader is used to sprinkle
t*e lime onto a screw cunveyor that was taken from an abandoned sludge
incinerator. At Stamford, Connecticut a screw conveyor carries lime
from a storage silo and meters it to cake sludge in a second screw
conveyor.
Two other plants add lime to hatch aerobic digesters. At South
Windsor, Connecticut, a truckload of liquid carbide lime is ordered
when sludge is to he lime-stabilized. The lime is sir.^ly dumped into
the batch digester and mixed with sludge by the mixer provided with
the digester. A truckload of lime is sufficient to 1ime-stabilize the
contents of the d'gester. No lime handling equipment had to be
installed at the olanl.
At Thompson, Connecticut, a lime slurry makeup system was already
available because lime conditioning prior to vacuum filtration had
once been practiced. This system is used to prepare slurry which is
then pumped, by portable pump, to an aerobic digester for lime stabi-
lization. Lime-stabilized sludge is pumped from the digester to a
land application truck by another portable pump. The land application
truck was fabricated by treatment plant personnel. The conversion to
lime stabilization required little capital expenditure.
At Scarborough, Maine, no lime system was Included in the original
plant design. Treatment plant personnel devised a system to add
bagged, hydrated lime directly to a sludge line transferring aerobi-
cally digested sludge from the digester to a land application truck
{Section 3). The land application truck was converted from an old oil
delivery truck. The pump on the back of the truck was valved so that
It could mix the contents of the truck's tank by recirculation
pumping.
At Falmouth, Maina, lime slurry from bagged, hydrated lime 1s prepared
in a slurry makeup tank located just outside of the building housing
the sludge storage tank. An air line was run from the building to the
slurry makeup tank to provide air mixing for the slurry. The air
-------
system was already in use at the plant for another process. No
electrical equipment or lines had to be run outdoors to the lime
slurry makeup. Lime slurry flows by gravity from the slurry makeup
tank to the indoor sludge storage tank, which is used for lime stabi-
1ization.
Treatment plant personnel at Rochester, New York had difficulty land
applying the stabilized sludge cake with conventional faming equip-
ment. Because the sludge is sticky, they installed a sludge holding
hopper on skids (Section 3) Sludge flows readily by gravity from
the hopper as it is pulled along a sludge application site.
At Stratford, Connecticut, the use of stockpiles resulted in odor
problems at the land application site when the stockpiles were broken
down. To solve this problem, sludge was spread on sanu beds at the
land application site and allowed to sit for about one week to dry.
After drying, the sludge was scraped up and placed in stockpiles. By
drying the sludge prior to stockpiling, it was found that no odors were
emitted when the piles were later broken down.
SI
-------
SECTION 5
COST OF LIME STABILIZATION
COSTS REPORTED AT THE SlTES VISITED
The general consensus of treatment plant operators is that lime stabi-
lization offers them the least expensive kludge stabilization alter-
native. Only three plants have made rough estimates comparing the
actual cost of lime stabilization with the cost of incineration,
however. At Rochester, New York, savings realized from lime stabi-
lizing instead of incinerating sludge amount to $10 to $20 per ton dry
sludge solids. At Stratford, Connecticut* savings of almost $60 per
ton dry sludge solids resulted from the conversion to lime stabiliza-
tion because sludge production is too low for efficient operation of
the incinerator. Annual savings of $200,000 reported by the operator
at Enfield, Connecticut are also attributable to an oversized incin-
erator.
ANALYSIS OF COSTS FOR LIME STABILIZATION
This section includes estimates of capital and annual costs which were
prepared to facilitate rough budgeting of lime stabilization systems.
The costs presented here should not be used as a basis for comparison
of lime stabilization costs versus those of alternative processes.
Such an analysis would require the simultaneous estimation of costs of
all systems being compared to ensure that balanced assumptions and
designs are used.
Using data collected from the plant visits we have estimated costs for
the following alternatives:
(1) providing a Hme slurry system (such as for an existing
vacuum filter facility using heat conditioning),
(2) converting a vacuum filter plant capable of lime conditioning
to one capable of stabilizing by either
(a) providing for increased lime dosage in existing facili-
ties, or
(b) providing for Increased lime dosage plus constructing a
new sludge conditioning tank with 30-minute detention;
52
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(3) constructing and operating new vacuum filters with lime
stabilization; and
(4) stabilizing liquid sludge in a batch operation.
The costs for each alternative were estimated using capacities repre-
sentative of the plants surveyed. Costs for vacuum filter plant stu-
dies were estimated for 1- to 20-mgd plants, and costs for batch lime
stabilization were based on capacities of 1 to 5 mgd. Because costs
for sludge transportation and disposal are site-specific, they are not
included in this study.
Table 5-1 presents the criteria used to determine sludge production,
lime usage, and cost for various plant sizes. The capital cost base
and salary and electricity costs used are representative of April 1980
costs. Operation and maintenance costs include power, chemicals,
labor, system maintenance, receipt of lime, and slurry makeup, where
appropriate.
TABLE 4
CRITERIA USED FOR COST STUDY
Sludge Production
Lime Dose for Stabilization
Capital Co;»t Base
Capital Cost Amortization
Salary
Electrical Cost
Maintenance
2000 pounds sludge per million gallons
wastewater treated
20 percent (as CaO)
3135 (ENR, April 1380)
20 years; 7 percent
$13.50 per hour (including benefits)
$ 0.06 per Kwh
3 percent of equipment capital cost
(annually)
Cost of Lime:
Bagged Hydrated Lime $125 per ton CaO delivered
Carbide Linie $ 85 per ton CaO delivered
Quicklime $ 65 per ton CaO delivered
The estimated capital costs, in some cases, do not change with plant
size. This is the result of using the same equipment, but with different
operating schedules. Schedules for operation were selected by analyzing
data from the plants visited.
53
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COSTS OF PROVIDING A LIME SLURRY SYSTEM FOR EXISTING VACUUM FILTERS
We developed and compared costs for three methods of procuring a lime
slurry for use prior to vacuum filtration: (1) preparation of slurry
from bagged hydrated lime; (2) purchase of carbide lime slurry; and
(3) preparation of slurry by slaking quicklime. Costs include the
following variables: chemical purchase, delivery and storage; slurry
makeup; and building space. Because the cost of pumping slurry to
vacuum filter conditioning and the cost of a ferric chloride system do
not vary among the systems under study, they are not included.
Figurei5-a shows fhe capital costs, Figure 25-b shows the operation
costs, and Figure 25-c shows the total annual costs. As illustrated
by Figure 25-c, bagged hydrated lime and prepared carbide lime slurry
are less expensive than slaked quicklime In smaller plants. As seen
in that figure, capital costs for quicklime slaking systems are so
high that their use in small plants would not be considered. At
treatment plants with capacities of about 5 mgd, slaking quicklime
becomes economical. At plants larger than 5 mgd, high manpower
requirements make handling bagged hydrated lime more expensive and
inconvenient than purchasing carbide lime slurry. At larger plants
with greater lime consumption, the use of slaked quicklime becomes the
least expensive alternative because of the low cost of quicklime.
The costs associated with a hydrated lime system include a fork-lift
truck for moving tagged lime; storage; and a slurry makeup system
comprised of tanks, a dust control system, mixers, and loading plat-
forms. The carbide lime system costs include those of storage tanks
with mechanical mixers, transfer pumps, and dilution/day tanks. The
quicklime system costs are based on silo storage, pneumatic conveyance
to day silos, slakers, and slurry tanks.
COST OF CONVERSION TO LIME STABILIZATION AT A FACILITY WITH VACUUM
FILTRATION
Figure 26 reports the costs estimated for institution of lime stabi-
lization at a plant with vacuum filtration by (a) simply increasing
the dose of lime to the existing conditioning drum or (b) both
increasing doses and constructing a larger sludge conditioning/
stabilizing tank with a 30-minute detention tfme. For this analysis,
it was assumed that the increase 1n lime dose between sludge con-
ditioning and s"iudge stabilization was from 12 percent to 20 percent
CaO per dry sludge soiled. At the particular sites visited, no capi-
tal investment was required as lime handling equipment included in the
original design was sufficiently large to handle the increased dosages
needed for lime stabilization. Therefore, Figure 5-2 does not include
costs for Hme handling systems. Costs for a system requiring
installation of a larger conditioning tank are reported in case a
longer liquid sludge detention time is desired.
54
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o
o
QU(CBU«t-<
k(IK —*
100
m
m
< too
x
<
3
O
z
c
£
<
HTMATCO
(MKK I
Mt-v/
I s 10
PLANT FLOW (mgO)
0. CONSTRUCTION COST
It ) '0 20
PLANT FLOW ( mgtf)
b OPERATION AND MAINTENANCE COST
O too
o
o
z
<
z
z
<
MTMATIO
—y/
\—
PLANT FLOW («««)
C TOTAL ANNUAL COST
FIG. 25. COSTS OF PREPARING LIME SLURRY FOR ADDITION
PRIOR TO VACUUM FILTRATION
55
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3 &o
J W
8
COST 0#
TA*«
-
t («
PLANT FLOW ( ">««)
0. CONSTRUCTION COST
b. OPERATION AND MAINTENANCE ( VST
FIG. 26. COST OF CONVERSION TO LIME STABILIZATION AT
A FACILITY WITH VACUUM FILTRATION
56
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The costs of stabilizing lime by simply increasing lime dosage are
essentially determined by the increased chemical cost and the
increased labor costs associated with handling lime and monitoring pH.
The cost of a system with a new, larger conditioning tank includes the
costs of lime; labor for lima handling and pH monitoring; labor and
parts for conditioning tank maintenance; power for conditioning tank
mixing; and the capital cost of conditioning tank, mixer, and building
space.
COST OF NEW VACUUM FILTERS WITH LIME STABILIZATION
Costs for constructing and operating a complete lime stabilization
system with vacuum filtration were developed and are reported on
Figure 27. The slurry systems selected for use are each the least
costly system for a given plant size, as shown in Figure 25. The
flat curve representing capital costs for I- through 5-mgd facilities
reflects the selection of the same number of vacuum filters (two)
with different operating schedules, vacuum filter sizes, and back-up
requirements to handle the various siudge loads.
Costs for the dewatering system include slurry metering pumps; piping;
30-minute, mechanically mixed stabilization tanks; vacuum filters
(with 4 lb/sfAir loading); sludge conveyors; control panels; and build-
ing requiretnents. The cost of constructing and oppriting a ferric
chloride system and the cost of purchasing the chemical are also
included.
COST OF LIME STABILIZATION OF LIQUID SLUDGE IN A EATCH OPERATION
Costs associated with constructing and operating ». system to lime
stabilize a liquid sludge prior to land application were also deve-
loped and are reported in Figure 28. Sludge would be stored in th«
winter and lime stabilized during a seven-month period. Sludge
storage costs are not included. Those plants studied which lime-sta-
bilize liquid sludge in a batch operation either had sufficient winter
sludge storage capacity in initial plant desigr or lime-stabilize
sludge only on a seasonal basis.
Capital costs are broken into two parts: (1) the cost of equipment to
prepare and pump lime slurry and (2) the cost of lime stabilization
tanks. The cost of lime slurry preparation 2nd handling equipment is
reported separately because some plants, such as South Windsor and
Thompson, Connecticut, have aerobic digesters in which stabilization
can be accomplished. The capital cost of the total system reflects
the cost of constructing a complete system operating in a mode similar
to that at Falmouth, Maine.
57
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o
91
O
Z
<
«n
3
z
TOTtt. UintLtMn
Hum Hwnm niTu
t 1 10
punt flow (»»m
o, CONSTRUCTION cost
jT %
\
¦ llM IUM
1 » 10 I
plant plow («*)
b OPERATION AND MAINTENANCE COST
AND TOTAt ANNUAL COSTS
FIG. 27. COST OF NEW LIME STABILIZATION ANO
NEW VACUUM FILTRATION
58
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TfTAC COST
iitfc run
U» liUM
HATlM TAM ^
Vwtit tUHV
|T«M( *MO
a >
PLANT FLOW (*94!
o. CONSTRUCT'IN COST
•o
« W
o »#
<0
I
PLANT FLOW | men )
b OPERATION ANO MAINTENANCE COST
FIG. 28. COST OF LIME STABILIZATION OF LIQUID SLUDGE
IN A BATCH OPERATION
59
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The costs reported are for a system using carbide 1 ir:e slurry because
this is the least expensive alternative for batch iime stabilization.
Capital costs include slurry storage tanks and mixers, lime slurry
transfer pumps, piping, lime stabilization tanks with mechanical
mixers, and pumps and pump gallery for transferring stabilized sludge
to trucks for land application. Operation and maintenance costs
include chemical costs, cost of pumping lime slurry and lime-
stabilized sludge, costs of labor and parts for maintenance of slurry
system and stabilization tanks, and labor costs for runnin? the entire
process.
60
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SECTION 6
ACCEPTABILITY OF METHODS
The degree of pathogen destruction in sludge attained by lime stabili-
zation is effected by the pH reached, the length of time the high pH
is maintained, and the completeness of lime/sludge mixing. Data from
this study and studies from the literature show that indicator and
pathogen numbers are effectively "educed in a liquid sludge limed to a
pH of 12.0 and held at that pH for two hours or more. Deviation from
these operational variables may adversely change the effectiveness of
kill.
Using these variables, we have rated the system observed in the plant
visits. The ratings reflect only a system's ability to attain the
required pH, its degree of lime jnd sludge mixing, its lime and sludge
mixing detention time, and the detention time over which its pH may be
monitored. The ratings (all assuming proper operation of equipment)
are:
(1) Acceptable
(2) Conditionally acceptable (acceptable, but requires attentive
operation)
(3) Requires further study
(4) Not acceptable.
LIME ADDITION TO LIQUID SLUDGE BEFORE LAND APPLICATION
1, Addition of hydrated lime to sludge being pumped to land application
truck (conditionally acceptable). This type of system depends on
the sludge truck's pumping action to recirculate the sludge and
provide the mixing required. With this technique, mixing
throughout the truck might be incomplete. It is acceptable only
with careful operation to ensure complete lime/sludge mixing for
an adequate period.
2. Lime addition to storage tank mixed by recirculation pumping
(conditionally acceptable). This technique requires that sludge
and lime be mixed in a storage tank by recirculation pumping.
Because complete mixing would be difficult to attain, this method
is acceptable only if operation ensures good lime/sludge mixing
and testing for pH.
61
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3. Lime addition to .nixed batch tanks (acceptable). If this system
is designed to provide good mixing, the operation simply requires
that the operator maintain a pH level of 12 for two hours. If
the pH level is not maintained, more lime can be added and pH
ntested later. This type of system can be recommended because
it ensures the time and degree of mixing needed for lime stabili-
zation.
LIME ADDITION TO LIQUID SLUDGE 3EF0RE DEWATERING
1. Lime addition to vacuum filter conditioning drum (conditionally
acceptable). lndicat:ons are that this comnonly Msed technique
is effective when operated properly. Spot bacterial analysis
performed at some plants demonstrated effective bacterial kill.
Odors, a sign uf bacterial infestation, were effectively con-
trolled by this technique. Detention of the lime/liquid sludge
blend is only 15 minutes, but an excess line dose can be added to
ensure that pH 12 will be maintained 1n the cake for two hours.
A disadvantage is that corrective measures are determined after a
sludge is dewatered, with the possible resul: of improperly sta-
bilized cake.
LIME ADDITION TO DEWATERED SLUDGE CAKE
1. Lime addition to sludce screw conveyor (requires further study).
!n this method, lime is added to a cake sludge and the two are
mixed with a screw conveyor. There has been no testing to show
whether there is proper mixing and whether organisms are killed
throughout the sludge. It merits study, however, because of its
simplicity and because of its effectiveness in controlling odors.
2. Lime addition to sludge cake storage. This method has been rated
not acceptable, due to incomplete mixing.
62
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SECTION 7
REFERENCES
1. Counts, C.A. atid A.J. Shuckrow. Lime Stabilized Sludge: Its
Stability and Effect on Agricultural Land. U.S. Environmental
Protection Agency (USEPA)» National Environmental Research Center,
Office of Research and Development. Cincinnati, Ohio. June 1974.
2. Farrell, J.B., J.E. Smir.h, Jr., S.W. Hathaway, and R.B. Dean. "Lime
Stabilization of Primary Sludges." Journal Water Pollution Control
Federation. Vol. 46, p. 113. 1974.
3. Farrell, J.B. and G. Stern. "Methods for Reducing the Infection Hazard
of Wastewater Sludges." P^eserited at the Symposium on the Use of High
Level Radiation in W
-------
APPENDIX
D*TA FROM PLANTS VISITED
1. ENFIELD. CONNECTICUT
(Lime Added to Vacuum Filter Conditioning Tank)
A. PLANT DATA
Plant Type: Conventional activated sludge
Plant Flew: 10.0 mgd design
4.5 mgd present average
Quantity Limed: 3.0 dry tpd present average
B. WASTEWATER PROCESSING TRAIN
Pretreatment
- Conminutors
- Grit removal
Primary Treatment
Secondary Treatment
- Conventional activated sludge
Chlorination
Discharge
- Connecticut River
Comments: Influent wastewater is almost all domestic.
C. SLUDGE PROCESSING TRAIN
Primary Sludge
- ComDined with secondary sludge in primary clarifier
64
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Secondary Sludge
- Aerobic Digester
- Primary influent wastewater stream
Combined Sludges
- Sludge conditioning/lime stabilization
- Vacuum filtration
- Stockpile/land application
Comments: Lime stabilization is practiced because it is too
costly to operate the multiple-hearth furnace.
LIME USE
Type of Sludge: Primary sludge and aerobically digested secondary sludge
Solids Concentration of
Sludge Before Lime Added: 4 to 8 percent
Lime Dosage (as CaO per
weight of dry sludge solids): 25 to 30 percent
Quantity of Lime Used: 33 tons per month, Ca(0H)2
pH Attained: 12.0
Other Chemica's: Ferric chloride added in sludge conditioning, 7
percent.
DETAIL OF LIME SYSTEM
Lime Delivery/Storage
Type of Lime Purchased: Lime slurry, 40 percent concentration.
Concentration varies with truckload but is
usually quite consistent. The slurry is a
byproduct/waste material from acetylene pro-
duction.
Qelivery: Purchase about one 4800-gallon truckload per week. Lime
flows by gravity to storage tanks. Occasionally, there is
a problem with gravel ir. the lime slurry; the operator
depends on the supplier to screen the slurry.
The delivery line is 3 inches in diameter. It has a long
vertical run and has clogged. About 30-40 minutes are
needed to unloed the truck.
Storage: Two, 6000-gallon horizontal, cylindrical iteel tanks.
Constantly mixed with low-speed, rotating paddle mixers.
65
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inventory: One to two weeks' supply always kept on hand. Delivery
schedule is regular, no reported problems.
Liine Slurry Transfer Pumps
Type and Number of Pumps: Two mechanical diaphragm pumps, each with
air cush'ion/standpipe type shock absorp-
tion.
Type of Piping: Vertical exit lines are iron; horizontal lines are
2-1nch hose sitting in troughs. A flushing system
is used daily.
Valvirg: Can pump from any storage tank, with any pump, to any day
tank.
Lime Slurry Dilution/Day Tanks
Type and Number
of Dilution Tanks: Two, 2000-gallon steel cylindrical tanks. The
bottom of each tank forms a cone, at the cone
bottom is the exit port.
Type of Mixing: Low-speed paddle mixers
Method of Dilution: Operator measures quantity of slurry 1n tank by
measuring tank depth. Dilution water Is
measured with a water meter.
Diluted Slurry Concentration: 20 percent as Ca(0H)2
Type of Water Used in Dilution: Plant water
Comments: Lime slurry is diluted at night. The tanks have sufficient
capacity for a day's operation.
Lime Metering Pumps
Type and Number of Pumps: Two mechanical diaphragm pumps
(no shock absorption equipment)
Type of Piping: Vertical e/it lines are steel. Horizontal lines are
hose, sitting in troughs. A flushing system exists
and Is used dally.
Valving: Can pump from any day tank, with any pump, to any con-
ditioning tank.
66
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Lime Application to Sludge Conditioning Tank
Point of Application: Slurry is added to a conventional horizontal
sludge conditioning tank located beside each
vacuum filter.
Dosage Control: Gperator sets the metering pump speed from a control
panel located at the vacuum filters.
Dosage Setting: Dosage is -initially set by past experience. pH is
then measured.
pH Measurement: Frequently measured on the sludge cake using a pH meter.
pH Holding Time: Detention time in filter vat only. Operator has
checked cake pH decay and would expect none over a
short period.
Quantity of Slurry Used: 2000 gallons per day
Comments: Ammonia odors are present in the conditioning tank/vacuum
filter area.
F. DOWNSTREAM PROCESS
Dewatering
Type: Two vacuum filters (coil medium)
Scheduling: Filter 4 days per week, 7 hours per day, one filter.
Loading Rate: 3.5 lb/sq ft-hr
Cake Solids Concentration (includes weight of lime): 20 percent
Comments: The effects of the high lime dose on the treatment plant
operations are negligible. The filtrate (pH 12) is
returned to the primary influent causing a higher
input solids concentration. No problems have resulted
from this. The vacuum filter coils are washed in an acid
bath every 5 to 6 months. Also, lime scale is manually
chiped from the storage tanks every 6 to 8 months. This is
considered to be normal maintenance.
Disposal
Method: Stockpile/land application
67
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Procedure: The stabilized sludge cake is transported by conveyor to
a dump truck and hauled to a field at the town landfill
site. The sludge is stored in 3-foot-hich piles. These
maximize drying. Periodically, sludge is taken from these
stockpiles and applied to experimental corn fields. Some
odors exist when these piles are broken into. This
process and its results are described in the text.
Comments: When lime stabilization was instituted, the procedure was
to incinerate during the winter and to lime stabilize and
stockpile the rest of the year.
G. COST OF LIME STABILIZATION
Equipment
Lime handling equipment was originally installed for chemical con-
ditioning prior to dewatering. The equipment is of sufficient size
to handle doses required for stabilization. Provision for loading
dewatered cake directly to trucks was included in the original
design.
Opetation and Maintenance
The only increase in costs noted is the increased cost for additional
Hme. This cost is much lower thar, the incineration alternative. A
cost study was performed to support this conclusion.
Lime is purchased £t $61 per ton of Ca(0H)2-
Lime cost about $20 per dry ton of sludge treated.
H. SPECIAL STUDIES
See text, Section 3.
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2. GLASTONBURY, CONNECTICU,
(Lime Added to Centrifuge Cake)
plant data
Plant Type: Secondary treatment by activated slud&i
Plant Flow: 3.6 mgd design
1.1 mgd present average
Quantity Limed: 2.0 dry tpd present average
WASTEWATER PROCESSING TRAIN
Pretreatment
Primary Treatment
Secondary Treatment
- Activated sludge
Chlorination
Discharge
- Connecticut River
Comments: Influent wastewater is essentially all domestic
SLUDGE PROCESSING TRAIN
Primary Sludge
- Sludge degritter
- Gravity thickener (with secondary sludge)
Secondary Sludge
- Gf/ity thickener (with primary sludge)
Combined 'iudge
- Centrifuge (polymer added)
- Lime addition to cake
- Compost/Stockpile
- Landfill
Comments: Lime stabilization is practiced because it is too
costly to operate the multiple-hearth furnace. Lime
is used primarily to control odors.
69
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D. LIME USE
Type of Sludye: Centrifuge-dewatered primary and secondary sludge.
Solids Concentration of
Sludge Before Lime Added: 17 to 18 percent
Lime Dosage (as CaO per
weight of dry solids): 6 percent
Quantity of Lime Used: 4.8 tons per month, Ca{0H)2
pH Attained: 11.0 to 12.0
Other Chenicals: Polymer added prior to centrifuging.
Comment: Now that composting has been instituted, lime is added
simply for odor control. A pH of 12.0 is not always
attained.
£• DETAIL OF LIME SYSTEM
Lime Delivery/Storage
lype cf L1me Purchased: 50-1b Dags of high-calcium hydrated lime.
Oelivery: 500 bags about 4 times a year. The^e bags are moved
manually. This takes 4 men about 1.5 hours.
Storage: Bags are stored indoors, stacked about 5 feet high or.
pallets.
Inventory: Operator keeps a minimum of 3 days' supply on haM.
One orcJe** supplies the plant, for about 3 months.
Lime Application to Cake
PoJnt of ^pplicauion: To dewetered cake conveyor.
Type of Applicator Mfethod of Application: This system is described in
detail in the text.
Method of Mixing L1me and Sludge: Screw conveyor.
Lime Dose Control: Spreader can b* opened or closed to adjust the dose.
pH Measurement: Measured twice a day on stabilized v.ake with pH probe.
pH Holding Time: Composites from T hour; of operation are held Average
holding time is 4 hours.
probo.
70
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DOWNSTREAM PROCESS
Disposal
Method: Landfill
Procedure: The stabilized sludge cake falls off the screw conveyor
into a 20 cubic yard steel container. Once a day a con-
tainer truck picks up the sludge container and brings it
to a landfill site. The sludge is then mixed with leaves
ana wood chips. This mixture is stockpiled/composted
until it is utilized as cover material at the site. No
monitoring is done on this sludge.
COST OF LIME STABILIZATION
Equipment
Screw conveyor used to mix lime with sludge is a converted ash
conveyor taken from the shut-down multiple hearth incinerator. No
other equipment purcnased.
Operation and Maintenance
Lime is added using the dewatermg scheme, 8 hours per day, three
days per week. A man must constantly watch the lime system. Lime 1s
purchased at $93 per ton Ca(0H)2« Ihe cost of trucking sludge has
increased. The number of loads has doubled since incinerator shut down.
Lime costs about $7.50 per dry ton of sludge created.
71
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3. GROTON TOWN, CONNECTICUT
(Lime Added to Centrifuge Cake)
A. PLANT DATA
Plant Type: Conventional activated sludge
Plant Flow: 5.0 mgd d.sign
2.5 mgd pre: mt average
Quantity Lim*.*: 2.3 Jry tpd c.-esent average
B. WASTEWATER PROCESSING TRAIN
Primary Treatment
Secondary Treatment
- Conventional activated sludge
Chlorination
Discharge
- Fort Hill Brook
Comments: Influent wastewater is essentially all domestic.
C. SLUDGE PROCESSING TRAIN
Primary Sludge
- Dcgritter
- Gravity thickener (with secondary sludge)
Secondary Sludge
- Holding tank
- Gravity thickener (with primary sludga)
Combined S1udges
- Centrifuge (polymer added)
- Storage
- L1me addition
- Landfill
Comments: Lime stabilization 1s practiced because it is too costly
to operate the heat treatment system and the multiple-
hearth furnace.
72
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D. Li HE US'
Type of Sludge* Centrifuge-dewatered primary and secondary sludge.
Solids Concentration of
Sludge before Lime Added: 16 percent
Lime Dosage (as CaO per
weight of dry solids): "'O percent
Quantity of Lime Used: 27 tons per month, Ca(0H)2
pH Attained: 12.0
Other Chemicals: Polymer added prior to centrifuging, 2-3 percent.
E. DETAIL OF LIME SYSTEM
lime Delivery/Storage
Type of Lime Purchased: 50-1b bags of high-calcium hydrated lime.
Delivery: 800 bags approximately twice a month. The bags are deliv-
ered on pallets and moved around with heavy equipment.
Storage: Stacked 10 bags high on pallets, outdoors. Covered with
plastic only.
Inventory: Operator keeps a minimum supply of 100 bags on hand.
Comments: The lime hardens when it is stored outside. The operator
reports that it is broken apart when it is mixed with
the wood chips and sludge.
lime Application to Cake
Point of Application: Cake storage pit (abandoned trickling filter)
Method of Application: Sludge cake is stored in a pit. Once a
month, a predetermined number of lime bags
are mixed (crushed) with wood chips. This
mixture is applied to the sludge cake. All
of the mixing is done with a rented front-
end loader. Some odors exist during this
process. Studies to consider otner methods
of lime application are being conducted.
Method of Mixing Lir« and Sludge: Front-end loader.
73
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Lime Dose Control: Laboratory pretest of sludge cake. Lime is added
to slurried cake until a pH of 12 is reached in
a test to piedetermine the proper lime dose.
pH Measurement: A pH rrobe is used on sludge cake samples.
pH Holding Time: No specific holding time.
DOWNSTREAM PROCESS
Disposal
Method: Landfill
Procedure: The stabilized sludge cake is taken from the storage/
mixing pit and loaded with the front-end loader into a
dump truck. !t is then hauled to the landfill and stock-
piled, until it is utilized as cover material. No moni-
toring is done on this sludge.
COST OF LIME STABILIZATION
Equipment
No equipment purchased. All of the necessary equipment was on site
or was rented.
Operation and Maintenance
Only the cost of lime and the cost of renting the front-end loader
and dump truck. Additionally, there is more sludge to truck.
The rental equipment costs $5000 per month and the lime stabilization
process requires 3 persons for about 2 days.
Lime is purchased at $80 per ton Ca(0H)2»
Lime costs about $32 per dry ton of sludge treated.
74
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4. TOWN OF KILLIWGLY. CONNECTICUT
(Lime Added to Vacuum Filter Conditioning Tank)
A. PLANT DATA
Plant Type: Conventional activated sludge
Plant Flow: 8.0 mgd design
2.0 mgd present average
Quantity Limeu: 2.3 dry tpd present average
B. WASTEWATER PROCESSING TRAIN
Pretreatment
- Aerated grit removal
Primary Treatment
Secondary Treatment
- Conventional activated sludge
Chiorination
Discharge
- Quinebaug River
Comments: Influent wastewater is 25 percenc industrial, mostly
paper mill wastes, and 75 percent domestic.
C. SLUDGE PROCESSING TRAIN
Primary Sludge
- Sludge blending box
- Gravity thickener
- Mechanically mixed sludge storage tank (5 percent solids)
Secondary Sludge
- Mixed with primary sludge at studge blending box, or
- Flotation thickener and mixed with primary sludge at
storage tank
Combined Sludge
- Sludge conditioning/lime stabilization (ferric chloride
also added)
- Vacuum filtraton
- Landfill
75
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Comments: Lime stabilization is practiced because it is too
costly to operate the multiple-hearth furnace.
LIME USE
Type of Sludge: Mixture of gravity thickened raw primary and
secondary sludge (flotation thickening optional).
Solids Concentration of
Sludge Eefore L1me Added: 4.5 to 6.5 percent
Lime Dosage (as CaO per
weight of dry sludge sol Ids): 19 percent, average
Quantity of Lime Used: 17 tons per month, Ca(0H)2
pH Attained: 11.5 to 12.0
Other Chemicals: Ferric chloride added in sludge conditioning tank,
1 to 3 percent
DETAIL OF LIME SYSTEM
Lime Delivery/Storage
Type of Lime Purchased: 50-1b bags of high-calcium hydrated lime.
Delivery: 900 bags every 5-6 weeks. The bags are stacked on
pallets and moved with a fork lift.
Storage: Sags are stacked about 5 feet high. The storage area 1s
dry, indoors, accessible to heavy equipment, and located
beside the slurry mixing tanks.
Inventory: A minimum of 200 bags (4 days) Is always kept on hand.
Preparation of Lime Slurry
Type and Number of Mixing Tanks: Two 900-gallon unllned stael tanks
Type of Mixing: Low-speed rotating paddle boards.
Mixer Motor Size: 1.5 HP
Dust Control
Equipment: L1me 1s added through a small hatch on top of the tank.
Forced ventilation pulls dust Into the tank. A1r cleaned
by bag filters and vented to outdoors. Despite the use
of this system, area is still fairly dusty.
76
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Method of Slurry
Preparation: Operator manually adds 100 pounds of lime to 100
gallons of water. The bags are opened and poured
manually.
Prepared Lime Slurry Concentration: 10.7 percent as Ca(0H)2
Type of Water Used in Slurry Makeup: Plant water
Frequency of Slurry
Makeup: L"me slurry is continually made up in the mix tanks while
filtering is in progress.
Special Equipment: Bag filters are a low maintenance item, but
require replacement after two years.
Lime Metering Pumps
Type and Number
of Pumps: Two plunger pumps. Pumps are calibrated to be metering
pumps by adjusting pump speed. Air cushion/standpipe type
shock absorption.
Type of Piping: Two-inch galvanized pipe with unions but without
tees. To clean, pipe system is broken down.
Manual full flushing system exists however once
every year lines are broken down and cleaned.
Valving: Can pump froc any mix tank, with any pump, to any
conditioning tank.
Lime Application to Sludge Conditioning Tank
Point of
Application: Slurry is added to a conventional, rotating, horizon-
tal, sludge conditioning tank located beside the
vacuum filter.
Dosage Control: Operator sets metering pump speed from control panel
located at vacuum filters.
Dosage Setting: Operator tests pH of sludge cake and adjusts lime
feed to obtain required pH.
pH Measurement: pH is measured with litmus paper on the vacuum
filter cake. Occasionally a pH probe meter test is
done.
pH Holding Time: Detention time of filter vat only. Cake sometimes
checked for pH after three hours holding.
77
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Quantity of Slurry Used: 4200 gallons per day
Comments: Some ammonia odors exist in the conditioning tank area.
DOWNSTREAM PROCESS
Oewatering
Type: Two vacuum filters (coil medium)
Scheduling: Filter 2 days per week, 8 hours per day, both fillers.
Loading Rate: Average 4 lb/sq ft-hr
Cake Solids Concentration (includes weight of lime): 20 percent
Comments: There have been no major effects reported from using the
high lime dose. The filtrate (pH 9.5) is returned to the
influent. This raises the pH of the influent but no effect
on treatment has been noticed. Lime system is acid washed
every 4 months.
Disposal
Method: Landfill
Procedure: The stabilized sludge cake is transported by conveyor
to a hopper which deposits it 1n a 5 cubit yard dump
truck. The hopper is designed for short-term storage
when the truck is away. The truck hauls the sludge to
a landfill where it is mixed with sand and used as a
final cover material. No monitoring is dene.
COST OF LIME STAB ILIZATI ON .-About $23 per dry ton of sludge treated.
Equipment
Lime handling system was originally installed for chemical con-
ditioning prior to dewatering. The equipment is of sufficient size
to handle the Increased dose required for stabilization. Thus, no
additional capital expense was Incurred.
Operation and Maintenance
No data are available to compare the dose and cost of lime with other
alternatives (existing incinerator never used due to projected
expense). No major cost effects on operation or maintenance were
noted. Lime 1s purchased at $91 per ton Ca(0H)2<
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5. MIDDLETOWN. CONNECTICUT
(Lime Added to Vacuum Filter Conditioning Tank)
A. PLANT DATA
Plant Type: Conventional activated sludge
Plant Flow: 6.0 - 10.0 mad design
4.0 mgd present average
Quantity Limed: 1.7 tpd present average
B. WASTEWATER PROCESSING TRAIN
Pretreatment
- Comminutor
- Aerated grit removal
Primary Treatment
Secondary Treatment
- Conventional activated sludge
Chlorination
Discharge
- Connecticut River
Comments: Infljent wastewater is less than 1.0 percent industrial
flow.
C. SLUOGE PROCESSING TRAIN
Primary Sludge
- Holding tank with secondary sludge
Secondary Sludge
- Gravity thickener or
- Influent wastewater and settled with primary sludge prior to
holding tank.
Combined Sludge
- Sludge conditioning/11me stabilization (ferric chloride also
added)
- Vacuum filtration
- Landfill
79
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Comments: Lime stabilization is practiced because it is too costly
to operate the multiple-hearth furnace.
D. LIME USE
Type of Sludge: Mixture of raw primary and gravity thickened
secondary sludge.
Concentration of
Sludge Before Lime Added: 3.0 - 4.0 percent
Lime Dosage (as CaO per
weight of dry sludqe solids): 23 percent
Quantity of Lime Used: 15.5 tons per month, Ca(0H)2
pH Attained: 12.1
Other Chemicals: Ferric chloride added in sl'jdge conditioning tank,
4-5 percent.
E. OETAIL OF LIME SYSTEM
Lime Dslivery/Storage
Type of Lime Purchased: 50-1b bags of high-calcium hydrated lime.
Delivery: 900 bags about every 5-6 weeks* There are 50 bacs on a
pallet and the pallets are moved with a fork lift.
Storage: Bags are stacked on pallets 5 ft high. The storage area
is dry, indoors, accessible to heavy equipment and located
beside the slurry mixing tanks.
Inventory: A minimum of 60 bags is always kept on hand.
Preparation of lime Slurry
Type and Number of Mixing Tanks: Two 650-gallon unlined steel tanks.
Type of Mixing: High-speed, portable propeller mixer.
Mixer Motor Size: 1.5 HP
80
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Dust Control Equipment: Lime is added through a small hatch on top
of the tank. Forced ventilation pulls dust
into the tank. Air cleaned by bag filters
and vented to outdoors.
Method of Slurry
Preparation: Operator manually adds 50 pounds of lime to 100
gallons of water.
During vacuum filtration/1ime stabi1ization, more
lime slurry must be made up. The slurry is made up
in the mix"tank while the operation is still in pro-
gress.
Prepared Lime Slurry Concentration: 5 percent a* Ca(0H)2»
Type of Water Used in Slurry Makeup: City water.
Frequency of Slurry Makeup: A total of 2 man-hours per filtering day
are required.
Special Equipment: Flooring around the lime mixing tanks consists
of metal grating which is 3 feet from the top
of the 5 foot high tank. This makes the manual
addition of the lime bags much more convenient.
Lime Metering Pumps
Type and Number of Pumps: One mechanical diaphragm pump is used for
metering the lime slurry. No shock
absorption system.
Type of Piping: One-and-a-half-inch galvanized pi;?, with a built-in
flushing system. There are pipe breaks for dis-
asssembly and acid washing.
Valving: The one lime pump can pump from either mix tank.
Lime Application to Sludge Conditioning Tank
Point of Application: Slurry is added to a vertical sludge conditioning
tank located beside the vacuum fllte". Tank
is equipped with a medium speed 3-blade paddle
mixer.
Dcsage Control: Operator sets metering pump speed from panel located
at the vacuum filter.
Dosage Setting; Operator sets lime dose to Attain required pH.
81
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pH Measurement: pH is measured daily with litmus paper at the vacuum
filter conditioning tank.
pH Holding Time: Detention time of filter vat only.
Quantity of Slurry Used: 3400 gallons per day.
DOWNSTREAM PROCESS
Dewatering
Type: One vacuum filter (coil medium).
Scheduling: Filter 5 days per week, 8 hours per day.
Loading Rate: Average 4-5 1b/sq ft - hr
Cake Solids Concentration (includes weight of lime): 20-22 percent.
Comments: There have Oeen no major effects reported from using the
high lime dose. Only the normal maintenance of a lime
system is required.
Disposal
Methoo: Landfill
Procedure: The stabilized sludge cake is transported by belt con-
veyor to a dump truck located outside, hauled to a land-
fill, and buried. No monitoring takes places.
Comments; Outdoor truck loading has problems with frtazing in
the winter.
COST OF LIME STABILIZATION
Equipment
The lime handling system was originally installed to condition the
sludge for vacuum filtering. The system was of sufficient size to
handle the Increased lime requirements for Hme stabilization, thus,
no additional capital expense was incurred.
Operation and Maintenance
Lime stabilization was found to be cheaper than incineration. No
increased dewatering costs other than that due to an increase in Hme
use. Lime is purchased at $91 per ton Ca(0H)2«
Lime cost $27.50 per dry ton of sludge treated.
82
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6. NAUGATUCK. CONNECTICUT
(Lime Added to Vacuum Filter Conditioning Tank)
A. PLANT DATA
Plant Type: Two separate wastewater processing systems, one
municipal and one industrial. Both are conventional
activated sludge. A provision for tertiary clarifica-
tion has been made in the industrial system.
Plant Flow: 6.7 mgd design to municipal treatment
3.0 mgd present average to municipal treatment
3.6 mgd design to industrial treatment
1.5 to 2.0 mgd present average to industrial treatmenet
Quantity Limed: 4.5 dry tpd present average
B* WASTEWATER PROCESSING TRAIN
MUNICIPAL WASTEWATER TREATMENT
Pretreatment
- Screens
Primary Treatment
- Sludge deoritted and scrcaned
Secondary Treatment
- Extended aeration
Ch'orination
- Mixed with industrial wastewater efflusnt prior to
chlorination
Discharge
- Naugatuck River
INDUSTRIAL WASTEWATER TREATMENT
Pretreatment
- Neutralize:*' by indu'trv
- Clarified by industry (polymer addition)
Primary Treatment
Secondary Treatment
- Extended aeration
83
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Tertiary Treatment
- Not used at present
- Provision for clarification with alum and/or polymer
- Combined with treated domestic wastewater
SLUDGE PROCESSING TRAIN
MUNICIPAL WASTEWATER TREATMENT
Primary Sludge
- Degritting and screening
- Gravity thickened with secondary sludge and with industrial
secondary sludge
- Combined with all sludges in mechanically mixed storage
mixing tank
Secondary Sludge
- Gravity thickened with primary sludge and with industrial
secondary sludge
- Combined with all sludges in sludge storage/mixing tank
INDUSTRIAL WASTEWATER TREATMENT
Primary Sludge
- Gravity thickened
- Combined with all sludges in sludge storage/mixing tank
Secondary Sludge
- Gravity thickened with municipal sludges
- Combined with all sludges 1n sludge storage/mixing tank
MUNICIPAL AND INDUSTRIAL WASTEWATER TREATMENT
Combined Sludge
- Stored in mixing tank
- Sludge conditioning/1 line stabilization
- Vacuum filtration
- Landfill
Comments: L1me stabilization 1s practiced because 1t is too costly
to operate the multiple-hearth furnace. Lime is sometimes
added to sludge storage for odor control. This quantity
1s not included In the dosage reported for conditioning.
LIME USE
Type of Sludge: Gravity thickened Industrial and municipal,
primary and secondary sludges
Sol Ids Concentration of
Sludge Before L1me Added: 5 percent
84
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_ime Dosage (as ^aO per wenjht of dry sludge solidr>):
18 to 25 Kercent whe,. usina ferric chloride
14 to 13 percent when using p^lyner
Qumtity of Lfme Used: 28 tons per montfc, CaO, with ferric chloride
cl tons per month, r.aO, with polymer
pH Attained: 11.S to 12.5
Other Chemicals* Added in sludye conditioning tank, ferric chloride,
6.0 percent or polymer 0.1 percent
E. DETAIL OF LIME SYSTEM
Lime Delivery/Storage
Type of Lime Purchased; Quicklime, granular
Delivery: About 24 tons of lime once a month. Truck blows lime into
storage silo.
Storage: One 50-ton capacity storage silo, outdoors. Silo has
vibrclor which is not used. It also has a bag filter to
clean conveyor air.
Inventory: Operator orders a load when he is down to a lwo week
(16 ton) inventory.
Conveyance and Slaking
Conveyance System: Originally used a bucket system which worked
poorly. A pneumatic conveying system has been
installed to move the quicklime from the storage
silo to the day bins, from which lime is loaded
to the slakers.
The storage silo is fitted with a rotary feed
valve which feeds into a 4 inch line. A 15-HP
blower conveys the line to the day bins, which
are about 4b feet above t!:e bottom of the silo.
The tops of the day b^ns have a cyclonic device
to separate the lime solids from the conveying air.
The system works very well.
Type, Size and
Number of Slakes: Two, slurry type slakers
Prepared Lime Slurry: 11.5 percent as Ca(0H)2
85
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Type of Wdter Used iri Slurry Makeup: Plant water
Special Equiprrent: d.iy fair over slaker has automatic level proDes.
Lime Slurry Transfer
Type of Piping: Lime slurry 1s transferred from the slakers to a
storagi'/d.aj tank by gravity. The tank is, located
below/oeside the slakers. The transfer lines are
clear elastic hose, 3-inch diameter.
Lime Day Tank Storage
Type and Number: One, ?0;)-gal1on steel tank
Type of Mixing: High-sneed propeller mixer
Lime Metering Pumps
Type and Number of Pumps: Five mechanical diaphragm puntps
Type of Piping: The lira is pumped through 2-inch flexible hose to
cushior the pipes from the pounding of the diaphragm
pumps. Then the lime flows through 1.5 inch alu-
minum pipe. All lines are flushed after each use.
Origirally the Hme was transferrer through open
fiberciass troughs; these would foam and overflow.
Valving: Flexibility is built in.
Lime Application to SI dqe Conditioning Tank
Puint of Application: Slurry is added to a conventional horizontal
sludge conditioning tank located beside each
vacuum filter-
Dosage Control: Operator sets metering pump speed from control panel
located at the vacuum filters.
Dosage Setting: Operator at first sets dosage to obtain a good cake.
The c&ke 1s tested for pH. If pH 1s low, dosage 1s
Increased. Conditioning dose is frequently adequate
for stabilization.
36
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pH Measurement: Dewatered cake is taken to lab, diluted, and the pH
measured with litmus paper.
pH Holding Time: Detention time in filter vat only.
Quantity of Slurry Used: 3000 gallons per filter day with ferric
chloride; 2200 gallons per filter day witii
polymer.
F. DOWNSTREAM PROCESS
Dewa\.erinq
Type: Five vacuum filters (coil medium)
Scheduling: Filter 6 days par week, 12 hours per day, 3 vacuum
filters.
Loading Rate: 3.0 lb/sq ft-hr, estimate
Cake Solids Concentration (includes weight of lime): 20 percent
Comments: The present lime dose is so close to the dosage needed for
dewatering that n has had little effect on plant
operations. The filtrate is returned to the industrial
primary sludge thickener. This has resulted in better
settling in the thickener. The high pH filtrate also
helps cut odors in the sludge storage. Only nooal
maintenance is required.
Disposal
Method: Landfill
Procedure: The stabilized sludge cake is transported by conveyor to
15 cubic yard steel bins located indoors. Container
trucks, owned by a trucking company, haul about 17 full
bilis to a private landfill whsre the sludge cake is used
as cover material. This system allows for flexibility in
scheduling sludge removal from the site.
Comments: A slight odor an . some flies are present during storage in
the steel bins. A $15 disposal charge per full bin is paid
by the treatment plant.
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G. COST OF LIME STABILIZATION
Equipment
Lime handling equipment was originally installed for chemical con-
ditioning prior to dewatering. The equipment is of sufficient size
to handle doses required for stabilization. Thus, no additional
capital expense was Incurred.
Operation and Maintanance
No increased operation or maintenance costs, versus the cost of
simply lime conditioning sludge, were noted other than the cost of
th* lime. Lime is purchased at $48 per ton CtO.
Lime cost about $12 per dry ton of sludge treated.
H. SPECIAL STUDIES
They are comparing the costs of lime stabilization when using polymer
as a filter aid versus using ferric chloride. The lime dose is typi-
cally 50 percent higher when using ferric chloride.
88
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7. NEW HAVEN (East Street Plant). CONNECTICUT
(Lime Added as a Backup System Prior to Vacuum Filtration)
A* Pi-ANT DATA
Plant Type: Primary treatment only.
Plant Flow; 22.5 mgd design
15.5 mgd present average
Quantity Lined: 15 dry tpd present average
B* WASTEWATER PROCESSING TRAIN
Pretreatment
- Bar racks
- Screens
Primary Treatment
Chlorination
Discharge
- To ocean.
C. SLUDGE PROCESSING TRAIN
Primary Sludge
- Gravity thickener
- L1me Edition (for stabilization when incinerator is down or
for conditioning in the winter months)
- Vacuum filtration
- Landfill or incineration
Comments: The plant only uses lime stabilization when the
incinerator is not working. Strictly a backup system.
Some lime conditioning required in the winter months
which is not required at other times of the year.
0. LIME USE
Type of Sludge: Gravity thickened primary.
Solids Concentration of
Sludge Before Lime Added: 10 percent
Lime Dosage (as CaO per
weight of dry solids): No data, used on emergency basis only.
89
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Quantity of Lime Used: No data.
pH Attained: 12.0 to 12.4
Other Chemicals: None.
E. PLTAIL OF LIME SYSTEM
Lime Delivery/Storage
Type of Lime Purchased: 50-1b bags of high-calcfura hydrated lime.
Celivery: 800 bags e*ery 2-3 months. The bags are delivered
50 to a pallet and handled with a forklift. Takes
approximately 2 persons and 2 hours for this procedure.
Storage: Bags are stacked about 5 feet high on pallets and stored
indoors in a dry area.
Inventory: An 80 bag minimum inventory is always kept on hand.
Maximum storage is about 900 bags. Load orders v*ry due
to the variability in I1me usage.
Preparation of Lime Slurry
Type and Number of Mixing Ttnks: Two 1100-gallon steel tanks.
Type of Mixing: Low-soeed paddle mixer.
Oust Control Equipment: None
Method of Slurry Preparation: Operator manually adds 50 pounds of
lime to 30 gallons of water.
Prepared Lime Slurry Concentration: 17 percent as Ca(0H)2
Special Equipment: An elevator is used to lift bags to the tank
area. Then tha bags are manually lifted into the
mix tank.
Lime Metering Pumps
Type and Number of Pumps: Two plunger pumps.
Type of Piping: Galvanlzed-steel pipes equipped with a flushing
system.
Valving: Can pump from any mix tank, with any pump, to any
conditioning tank.
90
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Lime Application to Sludoe Conditioning Tank
Point of Application: Slurry added to conventional horizontal con-
ditioning tank located beside each vacuum
filter.
Dosage Control: Operator sets metering pump speed from control panel.
Dosage Setting: Dosage is set to obtain the required pH.
pH Measurement: Litmus paper to «Oudge in filter vat, measured
hourly.
pH Holding Time: Detention time in filter vat only.
F. DOWNSTREAM PROCESS
Uewatering
Type: Two vacuum filters (coil medium)
Lime Stabilization Data: No lime scabil izatiori data is kept, baekuD.'
system only.
Disposal
Method: Landfill
Procedure: The stabilized sludge cake is transported by belt
conveyor to a dump truck, it is then hauled to a
landfill and used as fill.
G. COST OF LIME STABILIZATION
Equipment
No equipment purchased, originally installed as conditioning
equipment.
Operation and Maintenance
No ddta are kept, backup system only. Lime is purchased at $74 per
ton Ca(0H)2>
91
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8. NORTH CANAAN. CONNECTICUT
(Lime Added to Liquid Sijdge Storage)
A. PLANT DATA
Plant Type: Secondary treatment by activated sludge
Plant Flow: 0.35 mgd design
0.20 mgd percent average
Quantity Limed: 0.06 dry tpd present average
B. WASTEWATER PROCESSING TRAIN
Pretreatir.ent
- Grit channel
Secondary Treatment
- Activated sludge
Chlorination
Oischarge
- Blackberry River
Consents: Influent wastewater is essentially all domestic.
C. SLUDGE PROCESSING TRAIN
Secondary Sludge
- Aerobic digester
- Storage in winter and land application in spring
after lime stabilization
- Sand drying beds (summer and fall), landfill
Comments: Sludge is aerobically digested. Periodically (1/wk) the
digester mixer is stopped and the sludge is allowed to
settle. In the winter, the settled sludge is pumped to
a storage tank (no mixer) which has sufficient capacity
to hold all sludge produced. Supernate is decanted from
storage. The stored sludge 1s lime stabilized in the
spring and trucked to a dairy farm. In the summer and the
fall, lime is used for odor control and to condition
sludge for sand bed drying.
92
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D* LIME use
Ty~e cf Sludge: Aerobically digested secondary sludge
Solids Concentration of
Sludge Before Lime Added: 2 percent
Lime Dosage (as CaO per
weight of dry solids): 5.0 percent
pH Attained: 12
Other Chemicals: None
E. DETAIL OF LIME SYSTEM
Lime Delivery/Storage
Type of Lime Purchased: 50-1b bags of high-calcium hydrated lime
Delivery: 60 bags are picked up by the operator at the local supply
store once a year.
Storage: Bags are added almost inmedlately to the sludge. Little
storage time.
Inventory: A few bags, no set amount.
Lime Application to Liquid Sludge Storage
Type, Size and Number of Storage Tanks: Two 15,000 gallon primary
concrete tanks from previous
facility.
Method of Operation: Sludge is stored in t*e tanks all winter. When
s'tudge is to be rerr.oved, the contents of the
tank are pumped to mix it while bagged
lime is added. This mixing occurs for one
hour after the proper pH is attained.
Method of L1me Addition: Lime 1s manually poured from the bags
into the tank.
93
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Lime Dosage Control: Batch operation, lime added until desired pH
is reached.
pH Measurement: By pH probe.
pH Holding Time: One hour.
Removal of Sludge: By tank truck.
Comments: The total liquid sludge storage (including aerobic
digester) is 65,000 gallons. This is sufficient capacity
to hold the accumulated sludge over the winter until it is
lime stabilized in the spring.
F. OOWNSTREAM PROCESS
Disposal
Method: Land application
Procedure: During the spring a farmer uses two converted 2,000
gallon capacity tank trucks to haul the stabilized liquid
sludge to his dairy farm. He mixes the liquid sludge
with animal wastes and applies this mixture to silage
grass and hay fields. No monitoring is done.
During the summer and fall no lime is used. The sludge
is dewatered on sand drying beds and landfilled.
Comments: Farmer does the work for free using his own equipment.
G. COST OF LIME STABILIZATION
Equipment
No special equipment purchased by plant personnel. Storage tanks
were taken from previous treatment facility and mixing is
accomplished by using a pump on farmers' tank truck*
Operation and Maintenance
Lime is purchased at $110 per ton CafuH)?.
Cost $700 annually for the complete process of lime stabilization.
H. SPECIAL STUDIES
Farmer had tests done that show s low heavy metals concentration.
No bacteriological studies.
94
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9. SOUTH WINDSOR, CONNECTICUT
(Lime Added to Liquid Sludge Storage)
A. PLANT OATA
Plant Type: Conventional activated sludge.
Plant Flow: 3.75 mgd design
1.3 mgd present average
Quantity Limed: 1.0 dry tpd present average
B. WASTEWATER PROCESSING TRAIN
Pretreatment
- Comminutor
Primary Treatment
Secondary Treatment
- Conventional activated sludge
Chlorination
Discharge
- Connecticut River
Comments: Influent wastewater is 85 percent domestic and 15 percent
industrial.
C. SLUDGE PROCESSING TRAIN
Primary Sludge: Gravity thickener, combined with secondary sludge in
aerobic digester.
Secondary Sludge: Combined with primary sludge in aerobic digester.
Combined Sludge: Aerobic digester (two, operated in parallel), sludge
conditioning/lime stabilization, drying beds, stockpile.
Comments: Lime stabilizition in sunnier only, dewater with belt filter
and send to landfill remainder of year. Lime stabilization
replaced incineration which had mechanical problems. Future
plans call for composting.
95
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Lime Use
Type of Sludge: Aerobically digested sludges, gravity thickened
primary plus secondary sludge.
Solids Concentration of
Sludge Before Lime Added: Approximately 1.2 percent.
Lime Dosage (as CaO per
weight of dry sludge solids): Sparse data, estimated as 21 percent
dose based on 3000 lb of CaO to
14,000 lb of sludge solids. Dose
higher than required to attain pH.
Quantity of Lime Used: Estimated, 8 tons per month, Ca(0H)2.
pH Attained: 12.0 or greater.
Other Chemicals: None.
DETAIL OF LIME SYSTEM
Lime Delivery/Storage
Type of Lime Purchased: Lime slurry, variable concentrations but
always receive 4000 pounds of Ca(0H)2 in
each truckload of slurry.
Delivery: Deliveries vary in size. There is no need for lime
slurry storage as slurry Is added directly from truck
to digester.
Comment: Some bags of hydrated lime are kept on hand to help
control the pH in the digesters.
Lime Application to Liquid Sludge Storage
Type, Si*-? and Number of Storage Tanks: Two aerobic digesters,
156,000 gallon capacity
each, converted aeration
basins.
Type of Mixing: Surface aerators (one per digester)
Method of Operation: The capacity of approximately two full digesters
Is lime stabilized per month. A truckload of
Hme slurry 1s added to a digester. The pH 1s
checked after 1.5 hours of mixing time. If the
pH 1s not 12-.0 or higher then another load of
11me 1s added. Usually more lime is added than
1s needed.
96
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Method of Line Addition: Slurry unloaded b> gravity to the digester.
Lime Dosage Control: fCo control, a full truckload is added.
pH Measurement: A pH probt meter 1s used to check samoles from the
digester.
pH Holding Time: 1.5 hours, minimum mixing time.
Removal of Sludge: The lime stabilized liquid sludge is pumped frcm
the digester to the drying beds with a 4 inch
trash pump.
DOWNSTREAM PROCESS
Disposal
Method: Stockpile or landfill
Procedure: The stabilized liquid sludge is pumped to sand drying beds
located on site to be dewatered. About once a month the
beds are scraped off with a bulldozer and the sludge is
stockpiled in the back of the site.
When Hme is not used, the sludge is dewatered with a belt
filter and hauled to a landfill.
Comments: The lime stabil izatior. system was designed for temporary
use but has been in operation for 3 years.
COST OF LIME STABILIZATION
Equipment
Only piece of equipment purchased was the trash pump and this pump
is used for other purposes throughout the plant.
Operation and Maintenance
System requires very few manhours. Only temporary system. Lime is
purchased st $65 per ton Ca(0H)2«
Lime costs about $18 per dry ton of sludge treated.
97
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10. STAFFORD, CONNECTICUT
(Lime Added to Vacuum Filter Conditioning Tank)
A. PLANT DATA
Plant Type: Secondary treatment by contact stabilization
Plant Flow: 2.0 mgd design
2.5-3.0 mgd present average
Quantity Limed: 1.4 dry ton tpd present average
B. WASTEWATER PROCESSING TRAIN
Pretreatment
- Bar screens
- Grit removal
Secondary Treatment
- Contact stabilization
Filtration
Chlorination
Discharge
- Wlllimantic River
Comments: Influent wastewater 1s 80 percent Industrial flow, dyeing
and printing wastes, and 20 percent domestic.
C. SLUDGE PROCESSING TRAIN
Secondary Sludge
- Gravity thickener (to 5.0 percent solids)
- Sludge conditioning/11me stabilization (ferric chloride
also added)
- Vacuum filtration
- Landfill
Comments: Lime stabilization is practiced because It is too
costly to operate the multiple-hearth furnace.
98
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D. LIME USE
Type of Sludge: Gravity thickened secondary sludge
Solids Concentration of
Sludge Before Lime Added: 5.0 percent
Lime Dosage (as CaO per
weight of dry sludge solids): 16.0 percent
Quantity of Lime Used: 8.9 tons per month, Ca(0H2)
pH Attained: 11.5
Other Chemicals: Ferric chloride added in sludge conditioning,
4 percent
E. DETAIL OF LIME SYSTEM
Lime Delivery/Storage
Type of Lime Purchased: 50-1b bags of high-calcium hydrated lime.
Delivery: 900 bags about 4 times a year. Pallets, with 50 bags
stacked on a pallet are moved with a forklift.
Storage: The pallets are unloaded at the town garage where
they are stored inside in a dry area. As the treatment
plant needs lime, full pallets are mechanically loaded on a
truck and brought to the plant where they are manually
unloaded. The treatment plant has dry indoor storags for
150 bags.
Inventory: A minimum of 3 tons of lime is always kept on hand
(6 days).
Preparation of Lime Slurry
Type and Number of Mixing Tanks: One 3S0-gallon steel tank
Type of Mixing: High-speed propeller mixer
Mixer Motor Size: 0.5 HP
Dust Control Equipment: No dust control in original design. Have
installed a vent to the outdoors above the
lime slurry tank to remove dusty air.
Works quite well.
99
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Method of Slurry Preparation: Aerator adds 50 pounds of lime to
50 gallons of water.
Prepared Lime Slurry Concentration: 11.0 percent as Ca(0H)2
Type of Water Used in Slurry Makeup: Plant water
Frequency of Slurry Makeup: Lime slurry 1s prepared continuously
throughout the day while the filtering
operation is in progress. Operator
notices no problems with this method.
Lime Slurry Metering Pumps
Type and Number of Pumps: One plunger pump.
Type of Piping: line-inch diameter PVC pipe. Have also installed
-ibout one-foot of flexible hose just after pump
:o protect the PVC pipe from the shock of the
positive displacement pump.
Valving: No special valving. Only one slurry tank, one pump, and
one conditioning tank.
Lime Application to Sludge Conditioning Tank
PointUf Application: Slurry is added to a vertical sludge con-
ditioning tank equipped with paddle mixers and
located beside the vacuum filter.
Dosage Control: Set metering pump stroke lengtn. Pump located
beside vacuum filter.
Dosage Setting: Operator sets dosage for good dewatering and
knows from past experience that the pH is 11.5
when a good cake 1s attained.
pH Measurement: Sample taken from filter vat to laboratory, measured
with pH meter.
pH Holding Time: Detention time 1n filter vat only.
Quantity of Slurry Used: 1000 gallons per filter day.
100
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DOWNSTREAM PROCESS
Oewatering
Type: One vacuum filter (cloth medium)
Scheduling: Filter 4 days per week, 6 hours per day
Loading kite: 3.5 1b/sq ft-hr
Cake Solids Concentration (includes weig.it of lime): 23 to 25 percent
Comments: There have been no major effects reported from Lite nigh
lime dose. Some lime caking has been experienced in the
vacuum filter grid and vacuum pump. This has been taken
care of by washing the vacuum filter system with muriatic
acid every 3 months.
Disposal
Method: Landfill
Procedure: The stabilized sludge cake is transported by conveyor to
a dump truck located outdoors and hauled to a landfill.
One trip takes about 30 minutes. At the landfill the
cake is mixed with woodchips and stockpiled. Period-
ically sludge is taken from these piles and used as
final cover at the site. No monitoring is done.
COST OF LIME STABILIZATION
Equipment
Lime handling equipment was originally installed for chemical con-
ditioning prior to dewatering. The equipment is of sufficient size
to handle the increase in lime dose required for stabilization.
Thus, no additional capital expense incurred.
Operation and Maintenance
No increase in costs were noted, other than the increased use of
lime. Lime 1s purchased at $80 per ton Ca(0H)2.
Lime cost about $17 per dry ton of sludge treated.
101
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11. STAh,-Qon. CONNECTICUT
(Lime Added to Belt-Filter Cake)
A* PLAhT DATA
Plant Type: Conventional activated sludge
Plant Flow: 20.0 mgd design
20.0 mgd present average
Quantity Limed: 13 dry tpd present average
B. WASTEWATER PROCESSING TRAIN
Pretreatment
- Comminutor
Primary Treatment
- Sludge to cyclonic degritter
Secondary Treatment
- Conventional activated sludge
Chlorination
Discharge
- Ocean
Comments: Influent wastewater 1s 75 percent domestic and 25 percent
industrial.
C. SLUDGE PROCESSING TRAIN
Primary Sludge
- Gravity thickener
Secondary Sludge
- Gravity thickener
Combined Sludge
- Combined In gravity thickener
- Aerated storage
- Polymer addition
- Belt filter
- Lime added to cake
- Landfill
Comments: New lime stabilization system 1s to be used only when
the co-incineration system 1s inoperative*
102
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LIME USE
Type of Sludge: DewatereJ, mixture of gravity thickened primary and
secondary sludge
Solids Concentration of
Sludge Before Lime Added: 23 percent
Lime Dosage (as CaO per
weight of dry sludge solids): 18 to 20 percent
Quantity of Lime Us'd: 90 tons per month, Ca(OH)2• estimated
pH Attained: 12.1
Other Chemicals: Polymer added prior to dewatering, 6.5 percent
dose.
DETAIL OF LIME SYSTEM
Lime Delivery/Storage
Type of Lime Purchased: 50-1b bags of high-calcium hydrated lime.
Delivery: Bags
Frequency of Delivery: Ordered as needed. 3ackup system.
Storage: Storage area will be improved to an indoor dry facility.
Inventory: No data.
Lime Application to Cake
Point of Application: To dewatered cake conveyor.
T/pe of Applicator/
Method of Application: This system is described in detail in the text.
Method of Mixing
Lime and Sludge: Screw conveyor specially fitted with "pug mill"
type blades to actually push some sludge back and
improve mixing. Operator reports these actually
mix too well, they make the sludge gumny.
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Lime Dose Control: Control of the sludge ca
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12. STRATl-'ORO. CONNECTICUT
(Lime Added to Vacuum Filter Conditioning Tank)
A. PLANT DATA
Plant Type: Conventional activated sludge
Plant Flow: 11.5 mgd design
8.0 mgd present average
Quantity Limed: 8.9 dry tons per day
B. WASTEWATER PROCESSING TRAIN
Pretreatment
- Screens
- Comminution
- Aerated grit removal
Primary Treatment
Secondary Treatment
• Conventional activated sludge
Chlorinat ion
Discharge
- Housatonic River
C. SLUDGE PROCESSING TPAIN
Primary Sludge
- Gravity thickener
Secondary Sludge
- Aerobic digester
- Recycled to primary clarifier
Combined SlcJge
- Settled in primary clarifier
- Gravity thickener
- Sludge conditioning/lime stabilization
(polymer added)
- Vacuum filtration
- Sand drying beds
- Stockpile/landfill
105
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Comments: Lime stabilization is oracticed because it is too costly
to ope-ate the raItipie-hearth furnace- Lim« stabil-
ization is only an interim technique; will be going to
composting. An effort is being made lo improve the effec-
tiveness of lime stabilization. Dewatered sludge is
spread to further dry on sand beds before it is stock-
piled.
LIME USE
Type of Sludge: Combination of aerobically digested and gravity
thickened secondary sludge and gravity thickened
primary sludge
Solids Concentration of
Sludge Before Lime Added: 2.1 percent
Lime Dosije (as CaO per
weight of dr\ iludge solids): 18 percent
Quantity of Lime Used: 64 tens per month, Ca(0H)2
pH Attained: 11.8 - 12.0
Other Chemicals: Polymer added in sludge conditioning, 5 percent.
DETAIL OF LIME SYSTEM
Lime Delivery/Storage
Type of Lime Purcharsd: Lime slurry, waste product from acetylene
proouction. ThJi replaced the purchase of
bagged hydrated lime. Operator notes that
slurry concentration received varies
greatly.
Delivery: Purchase a 4800 gallon truckload about once a week.
Wash out truck after delivery to get out any settled
lime. Plant supplies 3-incn line and centrigual pump to
unload truck.
Storage: Two, 4500-gallon concrete storage tanxs, equipped with
high-speed propeller mixers.
Inventory: A minimum of one weeks Inventory is kept. One delivery
supplies the plant for a little more than one week.
106
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Lime Slurry Transfer Pumps
Type and Number of Pumps: One progressive cavity pump.
Type of Piping: Two-inch diameter PVC pipe. A long (20-ft)
vertical line clogs frequently. Pipes are flushed
daily as preventive maintenance.
Valving: One pump and one pipeline.
Lime Pay Tank Storage
Type and Number: Two, 500-gallon unlined steel tanks
Type of Mixing: High-speed propeller mixers.
Special Equipment: No dust collection equipment. 8agged lime use was
stopped due to dusty conditions and availability
of lime slurry.
Lime Metering Pumps
Type and Number of Pumps: Two plunger pumps
Type of Piping: One-inch rubber hose from pump to sludge
conditioning tank.
Valving: One pump and one pipeline serve each vacuum filter.
Lime Application to Sluoge Conditioning Tank
Point of Application: Slurry is added to a vertical conditioning
tank that 1s mixed with a flocculator - paddle
type mixer.
Dosage Control: Cperator sets the metering pump speed*
Dosage Setting: Dosage is set to attain required pH.
pH Measurement: Measured with litmus paper or a pH meter on a
sample taken from the vacuum filter vat.
pH Holding Time: Detention time 1n filter vat only.
Quantity of Slurry Used: 800 gallons per filtering day
107
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DOWNSTREAM PROCESS
Oewatering
Type: Two vacuum filters (cloth medium)
Scheduling: Filter 4 days per week, about 6 hours per day
Cake Solids Concentration (includes weight of lime): 18 to 22 percent
Comments: The effects of the high lime dose on the treatment plant
operations are minmal. Extra vacuum filter maintenance
has resulted from the high dose. The filter cloths have
to be manually scrubbed nightly. The filters are
thoroughly cleaned every 3 months to eliminate lime
clogging and scaling problems.
Disposal
Method: Landfill
Procedure: The stabilized sludge cake is transported by conveyor to a
dump truck and hauled to drying beds. It is spread 2 to 6
Inches deep on the sand drying beds and allowed to dry for
a week. Then it is scooped up and stockpiled until it is
utilized as a cover material at the landfill.
Comments: The extra drying of the sludge has helped reduce odors.
Before this extra drying was practiced, the stockpiled
sludge piles would turn black, putrefy and emit offensive
odors. Even with the extra drying some ammonia odors are
reportedly given off from the cake.
COST OF LIME STABILIZATION
Equipment
No new equipment was required to implement lime stabilization at this
plant*
Operation and Maintenance
Six loads of sludge are presently trucked per day versus one
truckload when incineration was practiced. Lirre is purchased at $61
per ton Ca(OH)?. A study prepared to compare the costs of incineration
in September of 1975 versus the cost of lime stabilization in September
of 1976 showed the following results: the cost per ton of sludge
handled was $73.21 for incineration and $14.60 for Hme stablHza-
108
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tion. 241 nan-hours were spent during the one fwnth of incineration
versus 149 msn-hours while practicing lime stabilization.
Lime costs about $14.50 per dry ton of sludge treated.
H. SPECIAL STUDIES
A number of bacterial studies have b«en performed at this facility.
Data and discussion are presented in the text.
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13. THOMPSON. CONNECTICUT
(Lime Added to Liquid Sludge Storage)
A. PLANT DATA
Plant Type: Secondary treatment by activated sludge
Plant Flow: 1.5 mgd design
0.15-0.20 mgd present average
Quantity Limed: 0.7 dry tpd present average
B. WASTEWATER PROCESSING TRAIN
Secondary Treatment
- Activated sludge
Chlorination
Discharge
- French River
Comments: Influent wastewater is essentially all domestic.
C. SLUDGE PROCESSING TRAIN
Secondary Sludge
- Aerobic digester (may add polymer)
- Aerobic digester (second staqe, operated as a storage tank)
- Lime addition to second stage digester
- Land application
Comments: The sludge is aerobically digested. Pericdically the
digester is stopped and the sludge is allowed to settle
for four hours. The decant liquid is returned to the
influent channel and the settled sludge is pumped (with a
portable, gas driven centrifugal pump) to the »icond stage
aerobic digester which is operated as a storage tank.
Limp stabilization occurs by lime addition to this holding
tank.
The treatment facility is equipped with a vacuum filter
which 1s not used. Lime stabilization of liquid sludge is
less expensive and more convenient.
110
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LIME USE
Type of Sludge: Aerobically digested secondary sludge
Solids Concentration of
Sludge Before Lime Added: 2 percent
Line Dosage (as CaO per
weight of dry sludge solids): 16 percent
Quantity of Lime Used: Variation in frequency of lime stabilization.
Total lime usage of approximately 11 tons
per year.
Other Chemicals: Polymer
DETAIL OF LIME SYSTEM
Lime Delivery/Storage
Type of Lime Purchased: 50-1b bags of high-calcium hydrated lime
Del-'very: 900 bags approximately every 2 years. The bags are
unloaded manually (2 people, 4 hours).
Storage: Indoors, on i concrete floor. Bags are stacked about 5
feet high.
Inventory: A 20 bag minimum inventory is always kept on hand.
Preparation of lime Slurry
Type and Number of Mixing Tanks: One 300-gallon steel tank
Type of Mixing: High-speed propeller mixer
Mixer Motor Size: 0.5 HP
Dust Control Equipment: Mix tank fitted with ventilation system to
pull dusty air into lime loading hatch. Bay
filter cleans the air. System not vented
to outdoors.
Method of Slurry
Preparation: Operator adds 100 pounds of lime to SO gallons of water.
Prepared Lime Slurry Concentration: 19 percent as Ca(0H)2
Type of Water Used in Slurry Makeup: Plant water
111
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Lime Slurry Transfer Pumps
Type and Nuniber of Pumps: One, portable, gas driven centrifugal pump
Type of Piping: Portable 4-inch firehose.
Lime Application to Liquid Sludge Storage
Type, Size and Number
of Storage Tanks: One 81,000-galIon capacity tank (an old aerobic
digester) plus in the winter months an aeration
basin, (250,000-gallon capacity) is also used.
Type of Mixing: Fine-bubble air diffusers.
Method of Operation: Settled aerooically digested sludge is pumped
to the secondary digester/storage tank. This
tank is kept mixed but occasionally the mixing
is stopped and the sludge settles, allowing
clear liquid to be decanted. When the tank is
full of sludge, it is at 2.0 percent solids.
When sludge is to be stabilized and removed
from the site, 'ime blurry is pumped to the
storage tank until the desired pH is attained.
Method of Lime Addition: Batch operation, lime slurry 1s pumped from
mix tanks.
Lime Dosage Control: Lime is added until a pH of 12.0 is reached.
pH Measurement: Grab samples are tested in the lab with a pH meter.
pH Holding Time: At least one half hour. No pH decay has been
observed after a 3-4 day holding time prior to
land application.
Removal of Sludge: The tcnk truck is loaded using the portable pump
and firehose to pump the stabilized liquid sludge.
DOWNSTREAM PROCESS
Disposal
Method: Land application.
Procedure: The stabilized liquid sludge 1s applied to slleage com <>nd
hay fields with a tank truck. The tank truck 1s a dump truck with a
1200 gallon steel tank. The sludge 1s applied by gravity flow through a
nozzle at & rate of about 1000 gallons per acre per year. Treatment
plant personnel do all of the work. They average about 2-4 round trips
per hour. It takes 5 minutes to load the truck and 3 minutes to empty It.
112
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Comments: Operator estimates that it takes 100 gallons of fuel for
the tank truck to empty the stabilized sludge in the
holding tank.
G. COST OF LIME STABILIZATION
Equipment
The only new pieces of equipment required for lime stabilization were
the portable »ime slurry pump and the land application truck. The
conversion of the dump truck to a land application truck cost $1500.
Operation and Maintenance
A rougn study of vacuum filter versus liquid lime stabilization
showed a supply cost (chemicals and fuel) reduction of 80 percent
when using stabilization. A savings in utility expenses was noted
but not quantified. An annual manpower reduction from 864 to 200
hours per year was reported.
Lime is purchased at $86 per ton Ca(0H)2.
Lime cost about $1B per dry ton of sludge treated.
113
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14. VERNON. CONNECTICUT
(Lime Added no Vacuum Filter Conditioning Tank)
A, PLANT DATA
Plant Type: Powderec activated carbon treatment in activated sludge
process.
Plant Flow: 6.4 mgd design
3.5 mgd oresent average
Quantity Limed: 4 dry tpd present average (primary sludge only)
B. WASTEWATER PROCESSING TRAIN
Pretrectment
- Comminutor
- Grit removal
Primary Treatment
- Clariflrccul3tor (no chemical addition at present)
Secondary Treatment
- Activated cai^on added to activated sludge aeration tank
- Sludge to carbon regeneration
Rapid Sand Filtration
Chiorination
Discharge
- Hockanum River
Comments: Influent wastewater is 30 percent industrial, mostly
plating, dyeing, and textile wastes.
C. SLUDGE PROCESSING TRAIN
Primary Sludge
- Gravity thickener
- Sludge conditioning/lime stabilization (fer. ,c chloride
also added)
- Vacuum filtration
- Landfill
114
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Secondary Sludge
- Carbon regeneration by wet air oxidation of waste activated
sludge
- Regenerated carbon returned to system
Comments: Lime stabilization is only expected to be used until
existing incinerator is started.
LIME USE
Type of Sludge: Gravity thickened raw primary sludge
Solids Concentration of
Sludge Before Lime Added: 9.0 percent
Lime Dosage (as CaO per
weight of dry sludge solids): 22.0 percent
Quantity of Lime Used: 35.0 tons per month, Ca(0H)2
pH Attained: 11.8 to 12.0
Other Chemicals: ferric chloride added in sludge conditioning,
1-2 percent
DETAIL OF LIME SYSTEM
Lime Delivery/Storage
Type of Lime
Purchased: Lime slurry, 35 percent concentration. It is a
byproduct/waste material from acetylene production.
Consistent slurry concentration is received.
Delivery: Purchase a 4,800-gallon truckload about once a week.
Pumping to storage is by a self-priming centrifugal
pump supplied by the treatment plant.
Storage: Outdoors in r;ne 15,000-gallon steel tank, constantly mixed
by a rotating paddle mixar. Loading pump 1s valved so that
it too can mix the stored lime by recirculating the tank
contents. Tank is jaffled to cut down on vcrtexing within
the tank while mixing.
Inventory: As soon as there is room in the storage tank for a
delivery, an order 1s plsced. A full tank will last for
approximately 16 filter days.
115
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Lime Slurry Transfer Pumps
Type and Number of Pumps: Two centrifugal pumps, with a fiberglass
housing. Have operated quite well consid-
ering that a 35 percent slurry is pumped.
Type of Piping: Two-inch diameter PVC pipes ar,» used. They have few
bends and nc cleanouts. Flushirs with plant water is
done at the end of every fiito.iny ley.
Valving: Can pump from the storage tank with my pump to any day
tank.
Lime Day Tank Storage
Type and Number: Two, 700-gallon unified fibsrglass tanks.
Type of Mixing: Low-speed rotating paddle boards.
Mixer Motor Size: 0.75 hp.
Special Equipment: These tanks are also equipped to handle bagged
hydrated lime. The tanks are ventilated for
dust control and have slurry dilution/makeup
water meters (dilution is not practiced at
present).
Lime Metering Pumps
Type and Number
of Pumps: Two plunger pumps (these pumps replaced dianhragm pumps
that failed, likely due to the nigh concentration of
lime slurry being pumped. The plunger pumps have
sheared pins occasionally, but operator is satisfied
with them).
Type of Piping: Two-inch flexible plastic hose with a 0.5-inch wall
thickness. This hose was installed to replace a rigid
PVC pipe. Replacement was required because original
pipes were too small and because a flexible pipe was
desired to absorb shocks from the positive displace-
ment pump. This system 1s flushed daily.
Valving: Can pump from any day tank, with any pump, to any condi-
tioning tank.
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Comments: The day tanks are filled as needed by turning on the pumps
from the storage tank while the filtering process is in
progress.
lime Application to Sludge Conditioning Tank
Point of Application: Slurry 1s added to a vertical, paddle mixed,
sludge conditioning tank located beside the
vacuum filters.
Dosage Control: Operator sets metering pump speed from a panel located
at vacuum filters.
Dosage Setting: Operator sets lime dose to attain required pH.
pH Measurement: pH is measured twice weekly on the filter cake using
litmus paper. Measurement occurs more frequently
if sludge dewaterability changes.
pH Holding Time: Detention time in filter vat only.
Quantity of Slurry Used: 900-1100 gallons per filter day.
F. DOWNSTREAM PROCESS
Dewaterinq
Type: Two vacuum filters (cloth medium)
Scheduling: Filter 5 days per week, 6 hours per day, 1 filter.
Loading Rate: 5 Ib/sq ft-hr
Cake Solids Concentration (Includes weight of Ume): 30 percent
Comments: The effects from the high lime dose on the treatment plant
operations are negligible. Only normal maintenance is
required.
DISPOSAL
Method: Landfill
Procedure: The stabilized sludge cake Is transported by conveyor to a
hopper which deposits 1t 1n a dump truck located outdoors. The hopper
Is designed for short term storage when the truck Is not there. The
sludge is hauled to a private landfill 1n the next town and used as fill.
About 5-6 loads are hauled 1n a day with each round trip taking about
40 minutes. No monitoring 1s done.
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G. COST OF LIME STABILIZATION
Equipment
Lime handling equipment was originally installed for chemical con-
ditioning prior to dewatering. The equipment if, of sufficient size
to handle the increased dose required for stabi!nation. Thus, no
additional capital expense was incurred.
Operation and Maintenance
No data are available tc compare the dose and cost of lime stabil-
izing versus lime conditioning. Lime conditioning alone has not
been used. Lime is purchased at $92 per ton Ca(0H)2»
Lime cost about $27 per dry ton of sludge treated.
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15. W'tLLIHAN'TIC. CONNECTICUT
(Lime Added to Vacuum Filter Conditioning Tank)
A. PLANT DATA
Plant Type: Conventional activated sludge
Plant Flow: 5.5 mgd design
2.4 mgd present average
Quantity Limed: 1.7 dry tpd present average
B. WASTEWATER PROCESSING TRAIN
Pretreatment
- Bar screen
Primary Treatment
Secondary Treatment
- Conventional activated sludge
Chlorination
Discharge
- Shetucket River
C. SLUDGE PROCESSING TRAIN
Primary Sludge: combined with secondary sludge in sludge conditioning
tank.
Secondary Sludge: Flotation thickner (polymer added), combined with
primary sludge in sludge conditioning tank.
Combined Sludge: Sludge conditioning/lime stabilization (ferric chloride
also added, vaccum filtration, stockpile or landfill.
Consents: Lime stabilization 1s practiced because it is too costly to
operate the multiple-hearth furnace.
0. LIME USE
Type of Sludge: Raw primary and flotation thickened secondary sludge.
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Solids Concentration of
Sludge Before Lime Added: 3-4 percent
Lime Dosage (as CaO per
weight of dry sludge solids): 15 percent
Quantity of Lime Used: 10 tons per month, Ca(0H)2
pH Attained: 10.5 to 11.0
Other Chemicals: Ferric chloride added just prior to conditioning,
7.0 percent.
E. DETAIL OF '.iME SYSTEM
Lime Delivery/Storage
Type of Lime Purchased: Lime slurry, 13 to 30 percent (20 percent
average), byproduct/waste material from
acetylene production.
Delivery: Purchase a 4500 gallon trvckload. Delivery by gravity to
an underground concrete storage tank. Delivery port is
fitted with a removable screen to take out any pebbles.
A solids test and a specific gravity test is done on each
load to determine the lime concentration of the batch.
Storage: Underground, outdoor concrete storage tank of 14,500
gallons. Tank is constantly mixed by a propeller type
mixer with a 10-HP motor.
Inventory: Operator orders about 3 truckloads per month. Orders
a shipment when inventory 1s down to 5000 gallons.
Lime Slurry Transfer
Description: Transfer is by gravity to the dilution/day tank.
Flow controlled by a gate valve (manually operated).
Type of Piping: Transfer pipeline is iron, thrae feet long and large
diameter. There Is no provision for cleaning, none
has been needed.
Lime Slurry Oilutlon
Type and Number of Dilution Tanks: One unllned steel tank, 960
gallons.
Type of Mixer: Low-speed rotating paddle boards.
Mixer Motor Size: 1.5 HP
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Water Used for Dilution: Plant water
Diluted S'.urry Concent.rrtion: About 10 percent Ca(0H)2 by weight.
Special Equipment: Taik is only equipped to handle lime slurry.
Thsre is no provision for utilization of
hydrated 1ime.
Lime Metering Pumps
Type and Number of Pumps: One hydraulic-diaphragm pump. Exit line
outfitted with air cushion/surge control
cylinder.
Type of Piping: Two-inch galvanized pipe to pump inlet (gate valves)
and 2-inch PVC pipe at pump outlet (ball valves).
Pipes outfitted for flushing by connecting a
portable hose. Flushing done daily. Pipes
also have unions so that they can be opened for
cleaning, this has not been required, as flushing
has been sufficient.
Lime Application to Sludge Conditioning Tank
Point of Application: Slurry is added to a conventional horizontal
sludge conditioning tank located beside the
vacuum filters.
Dosage Control: Operator sets metering pump speed from panel beside
the vacuum filters.
Dosage Setting: Operator sets lime dose to get a good cake, does
this by eye.
pH Measurement: Measured In lab on sludge cake by using a pH probe.
pH Holding Time: Detention time in filter vat only.
F. DOWNSTREAM PROCESS
Dewatering
Type; Two vacuum filters (coil medium)
Scheduling: Filter 2 to 3 days per week, 6 hours per day.
Loading Rate: 2.5 Ib/sq ft-hr
Cake Solids Concentration: (Includes weight of lime) 17 percent
121
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Comments: The effects from the lime dose on the treatment plant
operations and equipment have not been determined because
lower doses have not been used.
The operator regularly acid-cleans coils attacked by lime.
He removes three coils at a time for cleaning.
Disposal
Method: Stockpile
Procedure: The stabilized sludge cake is transported by belt
conveyor to a dumptruck, hauled to a gravel pit, and
stockpiled. Some sludge is taken from the stock-
pile, mixed with loam, and used to grow grass.
Comments: Process has been in use for a few years and treatment
plant personnel are satisfied with it.
G. COST OF LIME STABILIZATION
Equipment
Lime handling equipment was originally installed for chemical
conditioning prior to dewatering. The equipment is of sufficient
size to handle the increased dose required for stabilization. Thus,
no additional capital expense was incurred.
Operation and Maintenance
Lime doses being used at present time are no greater than would be
used if incineration were practiced. No change in operation and
maintenance costs.
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16. BATH, MAINE
(Lime Added to Vacuum Filter Conditioning Tank)
A. PLANT DATA
Plant Type: Secondary treatment by activated sludge
Plant Flow: 1.6 mgd design
2.6 mgd present average
Quantity Limed: 1.0 dry tpd present average
3. WASTEWATER PROCESSING TRAIN
Pretreatment
- Communitor
- Grit chamber
Secondary Treatment
- Activated sludge
Chiorination
Discharge
- Kennebec River
Comments: Influent wastewater is 90 percent domestic ana 10 percent
industrial.
C. SLUDGE PROCESSING TRAI"
Ssccndary Sludge
- Flotation thickener (polymer added).
- Aerated storage (periodically decanted, 7 percent solids).
- Sludge conditioning/1 ime stabilization (ferric chloride
also added).
- Vacuum filtration
- Landfill or land application
D. LIME USE
Type of Slucige: Thickened and stored secondary sludge.
Solids Concentration of
Sludge Before Lime Added: 7.0 percent.
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Lime Dosage (as CaO per
weight of dry solids): 10.0 percent.
Quantity of Lime Used: 4.0 tons per month, Ca(0H)2
pH Attained: 11.5 to 12.0
Other Chemicals: Ferric chloride added 1n sludge conditioning, 3.0
percent.
E. DETAIL OF LIME SYSTEM
Lime Delivery/Storage
Type of Lime Purchased: 50-1b bags of high-calcium hydrated lime.
Delivery: 200 bags every month and a half. The bags are unloaded
and restacked manually. This takes 2 people less than an
hour.
Storage: Bags are stacked 6-feet high on pallets. The storage area
is dry, indoors, and located beside the slurry mixing
tanks.
Inventory: A 25 bag (about 2.5 filtering days) minimum inventory is
kept at all times. Maximum storage is about 250 bags.
Preparation of Lime Slurry
Type and Number of Mixing Tanks: Two 350-gallon fiberglass-lined
steel tanks.
Type of Mixing: Low-speed paddle mixer.
Dust Control Equipment: Lime is added through a small hatch on the
top of the tank. Forced ventilation pulls
lime dust into the tank. Air is cleaned
with bag filters and vented to the outdoors.
System works well.
Method of Slurry Preparation: Operator manually adds 50 pounds
of lime to 75 gallons of water.
Prepared Lime Slurry Concentration: 7.5 percent as Ca(0H)2*
Type of Water Used 1n Slurry Makeup: Strained plant water.
Frequency of Slurry Makeup: Prepare Hme slurry every 1.5 hours while
filtering. Uses both tanks simulta-
neously during process.
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Lime Metering Pumps
Type and Number of Pumps; Two plunger pumps. Pumps are calibrated
to be metering pumps. Air cushion/stand-
pipe type shock absorber on pumps.
Type of Piping: PVC pipes with breaks and unions for cle-an-outs.
Had trouble with steel pipes clogging. Was using
too strong a slurry (17 percent). Pipes are flushed
every day with plant water for approximately i5
minutes.
Valving: Pumping is froic both tanks simultaneously during the lime
stabilization process.
Lime Application to Sludge Conditioning Tank
Point of Application: Surry is added to a conventional horizontal
sludge conditioning tank located beside each
vacuum filter.
Dosage Control: Operator sets metering pump speed from control panel
located at the vacuum filters.
Qosage Setting: Dosage is set by eye, estimating the pH by looking
at dewaterability.
pH iieasurement: Measured twice a day on the sludge cake with a pH
probe.
pH Holding Time: Detention time in filter vat only.
Quantity of Slurry Used: 1,000 gallons per filter day.
F. DOWNSTREAM PROCESS
Oewatferinq
Type: Two vacuum filters (coil ,nedium)
Scheduling: Filter 2-3 days per week, 6 hours per day.
Loading Rate: 6.0 • 7.0 Ib/sq ft-hr
Cake Solids Concentration (includes weight of lime): 15.0 percent.
Comments: One result of the high Hme dose Is that the sludge cracks
more quickly on the vacuum filter. No ether major effects
were reported. Normal operation does call for washing
the coil filter with muriatic acid every 8 months to get
rid of any lime scaling.
125
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Disoosal
Method: Landfill or land application
Procedure: The stabilized sludge cake is transported by conveyor to
a 5 cubic yard dump trucK park<;d indoors. In the summer
the sludge is hauled to lands stripped of loam and applied
as a soil amendment. It is applied at 3 rate of 33 cubic
yards per acre per year. Monitoring of this procedure is
done to make sure it is mixed in with the soil. The rest
of the year, the sludge is hauled to a landfill, mixed
one part sludge to one part dredge material, and used as
fill.
G. COST OF LIME STABILIZATION
Equipment
Lime handling system was originally installed for chemical conditioning
prior to dewatering. The equipment was of sufficient size to handle
stabilization doses, thus, no capital expense was incurred for the
lime system. A Rototiller is rented for J!25 a week to aid in land
application.
Operation and Maintenance
No available data to compare the dose and cost of lime with other
alternatives. Lime is purchased at $80 per ton Ca(0H)2«
Lime cost about $10.50 per dry ton of sludge treated.
H. SPECIAL STUDIES
One bacteriological study was done. It showed less thar. 100 coionies
of fecal coliforms per 100 milliliters.
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17. FALMOUTH, MAINE
(Lime Added to Liquid Sludge Storage)
A. PLANT DATA
Plant Type: Secondary treatment by extended aeration.
Plant Flow: 1.5 mgd design
0.5 mgd present average.
Quant,cy Limed: 0.35 dry tpd present average
8. WASTEWATER PROCESSING TRAIN
Pretrea tirsnt
- Bar rack
Secondary Treatment
- Extended aeration
Chiorination
Discharge
- Presumpscot River estuary
Comments: Lifluent wastewater is essentially all domestic.
C. SLUDGE PROCESSING V3AIN
Secondary Sludge
- Aerobic digester (settled, decanted)
- Aerated mixing tank for lime stabilization
- Land application
Comments: Original system called for using a gravity dewatering
unit with the addition of polymer. System did not work
well. Abandoned for economical and environmental
reasons.
With the present operation, aerobically digested sludge is
settled, decanted, remixed, and pumped to an aerated
mixing tank. Lime slurry is added and pH is checked the
next day prior to land application.
In the winter, the aerobic digester stores all sludge
produced.
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0. LIME USE
Type of Sludge: Aerobicaliy digested secondary sludge
Solids Concentration of
Sludge Before Lime Added; 1>0 to 3.0 percent
Lime Dosage (as CaO per
weight of dry sludge solids): 5.0 percent
Quantity of Lime Used: 0.7 tons per month, Ca(0H)2
pH Attained: 11.5 to 12.5
Other Chemicals: None
F. DETAIL OF LIME SYSTEM
Lime Pelivery/Storage
Type of Lime Purchased: 50-1b bags of high-calcium hydrated lime
Delivery: 60-80 bags are picked up by the operator at the local
supply store about cnce a month during the 6 months
that land application takes place.
Storage; Bags are stacked in a dry outdoor shed.
Inventory: Always have at least 5 bags on hand. This lasts about
half a week during the land application months.
Preparation of Lime Slurry
Type and Number of Mixing Tanks: Cne 500-gallon fiberglass tank,
located outdoors.
Type of Mixing: Air mixing
Dust Control Equipment: None. Tank is located outdoors.
Method of Slurry Preparation: Operator adds 50 pounds of lime to about
50 gallons of water. All measurements
are done by eye.
Frequency of Slurry Makeup: One batch Is made up for each storage
tank load.
Prepared L1me Slurry Concentration: About 11 percent, as Ca(0H)2
Type of Water Used in Slurry Makeup: Plant water
128
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Special Equipment: A platform is needed next to the tank so the
operator can dump the lime into the top of the
8-ft high tank.
Lime Slurry Transfer
Type of Transfer: Lime flows by gravity from the mix tank to the
sludge storage tank. A centrifugal pump is used
to pump the conditioned sludge from the storage
tank to the tank truck.
Type of Piping: PVC pipe (4-inch dla.) fs used, abcut 5 ft long.
No flushing system exists.
Valving: No special valving, direct flow by gravity from lime slurry
tank to lime stabilization tank.
Lime Application to liquid Sludge Storage
Type, Size and Number of Storage Tanks:
Type of Mixing: Qlffused air
Method cf Operation:
One 16,000-gallon concrete
storage tank. Entrance
pipe fitted with a strainer
to keep out rags.
Lime Dosage Control:
Settled, aeroblcally digested sludge is pumped
to storage tank. Lime slurry is added to this
tank, which is kept constantly mixed. pH is
checked. The sludge 1s then mixed overnight.
In the morning, pH 1s rechecked and sludge 1s
land-applled.
Manually done by the operator using past
experience. pH 1s checked after loading Hme.
pH Measurement: pH 1s measured after an evening of mixing using a pH
probe.
fH Holding Time: Overnight, average 12-14 hours.
Removal of Sludge: The sludge is pumped from the storage/fc-rtdlnq
tank with a centrifugal pump to the'can* true*.
Comments: Slight ammonia odors exist at the sludge conditioning
tank. Also, some ammonia odors are present for a while
after the stabilized sludge has been land-applied.
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f. DOWNSTREAM PRQCFSS
Disposal
Method: Land applicat ion
Procedure: The stabilized liquid sludge is applied to grasi" fields
during the warm months (May through October). A 2,000-
gallon tank truck, fabricated by the operator, is used to
apply about 800 truckloads annually. There is no flow
regulator on the truck tc control the gravity flow appli-
cation. pH 1s monitored for up to a year after the sludge
1s applied. If pH falls below 6.6 then lime is applied,
but this has not been needed.
Corments: Sludge is applied at no charge to fields within the town.
There is a waiting list for sludge. Application to lawns
has been curtailed.
G. COST OF LIME STABILIZATION
Equipment
A land application truck was fabricated. The truck was donated, but
conversion cost $2700.
Operation and Maintenance
Lime is purchased at $108 per ton Ca(0H)£«
Lime costs about $7 per dry ton of sludge treated.
H. SPECIAL STUDIES
It was found that heavy metals were below state guidelines and that
there were no detectable levels of conforms, fecal streptococci or
salmonella.
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18. KENNEBEC (WATERVILLE). MAINE
(Lime Added to Vacuum Filter Conditioning Tank)
A- plant DATA
Plant Type: Secondary treatment by activated sludge.
Plant Flow: 12.7 mgd design
8.4 mgd present average
Quantity Limed: 6.0 dry tpd present average
B. WASTEWATER PROCESSING TRAIN
Pretreatment
- Bar screens
Primary Treatment
Secondary Treatment
- Activated sludge
Chlorination
Discharge
- Kennebec River
Comments: Influent wastewater is 40 percent industrial, mostly
paper mill wastes, and 60 percent domestic.
C. SLUDGE PROCESSING TRAIN
Primary sludge: grit removal by cyclone, gravity thickener, combined with
secondary sludge in blending box.
Secondary sludge: Flotation thickener (polymer addition), combined
with primary sludge 1n blending box.
Combined sludge: blending box (3.5-4.0 percent solids), sludge condition-
ing/ 11 me stabilization (ferric chloride also added),
stockpile or land application.
Comments: Originally the plan was simply to dewater and landfill, now
stabilization is required.
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LIME USE
Type of Sludge: Gravity thickened primary and flotation thickened
and stored secondary sludge.
SoHds Concentration of
kludge Before Lime Added: 3.5 to 4.0 percent.
Lime Dosage (as CaO per
weight of dry solids): 15.0 percent*
Quantity of Lime Used: 27.0 tons per month, CaO
pH Attained: 11.5
Other Chemicals: Ferric chloride added in sludge conditioning, 2.4
percent.
OETAIL OF LIME SYSTEM
Lime Delivery/Storage
Type of Lime Purchased: Quicklime, granular
Delivery: About 25 tons of lime once a month. Truck blow; lime
into storage silo.
Storage: One 40-ton capacity storage silo, outdoors. Silo is fitted
with a vibrator and lime level prcbes. It is also equipped
with a bag filter to clean the conveyor air.
Inventory: Operator orders a load of lime when the inventory is
down to 10 tons (similar to Z weeks).
Conveyance and Slaking
Conveyance System: The storage silo 1s set right over the slake**,
lime falls by gravity to the feed system. A
valve has been supplied to hold back flow from
the silo.
Type, Size
and Number of Slakers: One, 1000-1b/hr paste type slaker.
Prepared lime Slurry: 11.0 percent as C«(0H)2
Type of Water Used In Slurry Makeup: Plant water.
Special Equipment: The slaker 1s fitted with a belt feeder. Lime
dose 1s controlled by adjusting lime pile depth
with gate.
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Lime Slurry Transfer
Type of Piping: Lime slurry is transferred from the slakers to the
lime slurry storage/day tanks by gravity. The
slakers sit on a platform that covers the tanks so
no piping is required.
Lime Day Tank Storage
Type and Number; Two, 6000-gallon, concrete, square tanks.
Type of Mixing: Low-speed rotating paddle mixers.
Mixer Motor Size: 3 HP.
Special Equipment: Day tanks may be used as dilution tanks, but
this is not practiced.
Concrete tanks are completely covered except for
an access manhole.
There is »io provision for using hydrated lime,
operator would like to have this option for back-
up.
Lime Metering Pumps
Type and Number of Pumps: Two progressive cavity pumps. The
operator reported that the pumps wear
out quickly. This could be attributed
to the high vertical lift (30 feet) and
the abrasive nature of the Hme slurry.
Type of Piping: The inlet line has a box installed 1n it to allow
grit to settle out before 1t reaches the pump.
Minimal effects have resulted because the slurry is
too thick to allow any settlement of the grit. The
outlet line from the pump is fitted with a one-foot
piece of fire hose. This allows for easy dis-
connection so the pumps can be removed.
The vertical runs and short horizontal runs are Iron
pipe. The long horizontal runs are flexible hose.
This hose sits 1n troughs that hang overhead* The
hoses can be cleaned by manually shading them.
A flushing system that uses plant water Is used
dally.
Valvlng: L1me slurry can be pumped from any day tank, with any
pump, to any conditioning tank.
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Lime Application to Sludge Conditioning Tank
Point of Application: Slurry is added to a conventional horizontal
sludge conditioning tank located beside each
vacuum filter. Just in front of this tank is a
small (about 8 cubic foot) box in which pri-
mary and secondary sludges are mixed. No mixer
is provided in the blending box, mixing is
from turbulence only.
Operator sets metering pump speed from vacuum filter
operation panel in a room near the filters.
Operator, from past experience has a rough Idea of
what 11me dose will be required to attain the
required pH. The pH is checked after startup.
If it is too low the lime dose is increased.
Filtrate is checked for pH by taking a sample to
the lab. This is done throughout the day using a
pH meter.
pH Holding Time: Detention time in filter vat cnly. They have
held sludge for an extra 1/2 hour and checked pH
versus time and feel confident that there is no
pH drop.
Quantity of Sludg* Used: 3»400 gallons per filter day.
F. DOWNSTREAM PROCESS
Oewatering
Type: Two vacuum filters (coll medium)
Scheduling: Filter 5 days per week, 6 hours per day, one filter.
Loading Rate: 3.0 lb/sq ft-hr.
Cake Solids Concentration (includes weight of lime): 18 percent.
Corments: There has been a slight Increase In plant effluent pH, but
no major effects have been noticed 1n plant operations.
The filtrate (pH 11.5) Is returned to the Influent. There
TTas been no acid washing of equipment needed.
Disposal
Method: Land application or landfill
Dosage Control:
Dosage Setting:
pH Measurement:
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Procedure: The stabilized sludge cake is transported by conveyor to
a hopper which deposits it in a 10 cubic yard dump truck.
The Hopper is designed for short-term storage but does
not work well In this capacity.
The sludge is hauled to farm fields when they are
available. A manure spreader is used to spread the
sludge cake. It is plowed into corn fields and left
sitting atop hay fields. Some odors have been reported
during this process. The sludge is applied at 40-50
cubic yards per acre per year with a limit of 3C0-400 lb
per acre per year. The fields are monitored for metals,
metals uptake in crops and nitrogen.
When land 1s not available, the sludge is hauled to a
landfill and mixed with gravel at a one to one ratio.
More gravel is mixed in if heavy equipment is to be
driven over the area.
Comments: Area fanners like to get the sludge and report improve-
ments in their crops.
G. COST OF LIME STABILIZATION
Equipment
Lime handling equipment was originally installed for chemical
conditioning prior to dewatering. The equipment is of sufficient
size to handle doses required for stabilization. Thus, ,io additional
capital expense was Incurred for the lime system. A bulldozer which
cost $19,000 did have to be bought for landfill1ng the sludge.
Operation and Maintenance
No Increased operation and maintenance costs, versus the cost of
simply lime conditioning sludge, were noted other than the cost
of the Hme. Lime Is purchased at $67 per ton CaO.
Lime cost about $10 per dry ton of sludge treated.
H. SPECIAL STUDIES
Have compared Hme stabilizing with polymer as a filtering aid
instead of ferric chloride. Polymer use resulted 1n a small lime
dose requirement, but thd filter ran slower and the sludge was
sloppier at the same solids concentration.
135
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They have a little bacteriological data which shows that the sludge
is effectively stabilized after lime addition. pH tests have shown
that sludge pH dropped to 7.0 after 5 months in the landfill.
Data shows that the limed sludge has inhibited metals uptake in
crops. They actually have seen a lower metals concentration in
crops fertilized with lime stabilized sludge than in conventionally
fertilized fields. They recognize that more intensive, long-term,
studies are needed.
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19. LEWISTON-AUBURN. MAINE
(Lime Added to Vacuum Filter Conditioning Tank)
A. PLANT OATA
Plant Type: Conventional activated sludge
Plant Flow: 14.2 mgd design
11.0 mgd present average
Quantity Limed: 7.0 dry tpd present average
B. WASTEWATER PROCESSING TRAIN
Pretreatment
- Bar screen
Primary Treatment
Secondary Treatment
- Conventional activated sludge
Chlorination
Discharge
- Androscoggin River
Comments: Influent wastewater is approximately 15 percent
Industrial, mostly textile wastes with some poultry and
plastics wastes.
C. SLUDGE PROCESSING TRAIN
Primary Sludge
- Gravity thickener
Secondary Sludge
- Flotation thickener (polymer addition)
Combined Sludge
- Blending box
- Sludge conditioning/11me stabilization (ferric chloride
also added)
- Vacuum filtration
- Landfill
Comments: Originally the plan was simply to dewater and landfill,
now stabilization is required.
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LIME USE
Type of Sludge: Gravity thickened primary and flotation thickened
and stored secondary sludge.
Solids Concentration of
Sludge Before Lime Added: 5 to 8 percent
Lime Dosage (as CaO per
weight of dry sludge solids): 16 to 18 percent
Quantity of Lime Used: 3(5 tons per month, CaC
pH Attained: 11.5 to 12.0
Other Chemicals: Ferric chloride added 1n sludge conditioning (3.5
to 5.5 percent)
DETAIL OF LIME SYSTEM
Lime Delivery/Storage
Type of Lime Purchased; Quicklime, pebble
Delivery: About 30 tons of lime once a month. Truck blows lime
into storage silo.
Storage: One 60 ton capacity storage silo, outdoors. S1lo is
fitted with a vibrator and a high/low level sensor. It
also has a bag filter to clesn conveyor air.
Inventory: Operator orders a load when he is down to a two week
(20 ton) inventory.
Conveyance and Slaking
Conveyance System: Pneumatic conveyance system to day bin silo over
slaker.
The air blower Is located outdoors, below the
storage silo. Lime is passed through an air lock
feeder to the conveying line. The pebbled
quicklime is blown through the line to a valve
which diverts the 11me Into the day bin* The air
continues to the slurry tanks, which are fitted
with bag filters* These bag filters are vented
to the outdoors for extra dust control.
Type, Sl2e and Number
of Slakers: One, 1000-lb/hr paste type slaker.
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Prepared Lime Slurry: 5.0 percent Ca(0H)2
Type of Water Used
in Slurry Makeup: City water
Lime Slurry Transfer Pumps
Type and Number of Pumps: Two mechanical diaphragm pumps. There
is no shock absorption equipment on these
pumps.
Type of Piping: Original installation had about 2G-feet of 2-inch
iron pipeline from each pump to the slurry day
tanks. These lines had removable elbows with
flanges to allow for cleaning pipes. In addition,
a manual flushing system was included.
Despite these precautions, they have had clogging
problems in the lines which caused diaphragms to
pop. They have replaced one of the lime slurry
lines with a 2-inch flexible hose. This seems to
work well.
Valving: Lime slurry can be pumped with any pump to any day tank.
Lime Day Tank Storage
Type and Number: Two, 800-gallon steel tanks.
Type of Mixing: Low-speed rotating paddle mixers.
Mixer Motor Size: 1.5 HP
Special Equipment: The day tanks are flttad with dust control equip-
ment and hatch which allows for the use of
hydrated lime as a backuo. About 30 bags of
hydrated lime are kept on hand. Slurry would
be made up at about 6 percent if needed.
Lime Metering Pumps
Type and Number of Pumps: Three mechanical diaphragm pumps. No
shock absorption system in pipelines.
Type of Piping: Two-inch Iron lines to sludge blending box. Manual
flushing by hooking a hose up and running hot city
water through the system 1s done daily. Also remov-
able elbows are in the bends for cleaning the pipes*
139
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Valving: Lime slurry can be pumped from any day tank, with any pump,
to any conditioning tank.
Lime Application to Sludge Conditioning Tank
Point rf Application: Slurry is added to a conventional horizontal
sludge conditioning tank located beside each
vacuum filter. Just prior to these tanks is
a small (about 8 cubic feet) box in which pri-
mary and secondary sludges are mixed. No
mixer is provided in the blending box;
mixing is by turbulence only.
Dosage Control: Operator sets metering pump speed from vacuum
filter control panel.
Dosage Setting: Operator sets lime dose by eye to get a good cake.
pH Measurement: Msasured in lab on slurried cake, using a pH meter
pH Holding Time: Detention time in filter vat only.
Quantity of Slurry used: 7300 gallons per filter day.
Comments: Some ammonia odors have been noticed during warm weather
at the conditioning tanks.
F. DOWNSTREAM PROCESS
Pewaterinq
Type: Two vacuum filters (coil medium)
Scheduling: Filter 7 days per week, 10 hours per day, both filters.
Loading Rate: 2 Ib/sq ft-hr
Cake SoliJs Concentration (includes weight of lime): 16 percent
Comments: The high lime dose has had minimal effects on trsatment
plant operations. filtrate is returned back to the
influent. Only normal Maintenance has been required.
Disposal
Methrd: Landfill
HO
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Procedure: The stabilized sludge cake is transported by conveyor to
a hopper which deposits the sludge in a 4.5 cubic ydrd
dump truck. The hopper was designed for short term
storage but does not work well in this capacity. The
truck hauls about 14 loads of sludge a day to a landfill
where it is mixed with sand at a one to one ratio and
used as fill. The landfill has a clay lining. No moni-
toring is done.
Comments: The treatment plant has to pay an annual disposal fee of
$2000.
G. COST OF LIME STABILIZATION
Equ i pment
Lime handling equipment was originally installed for chemical con-
ditioning prior to dewatering. The equipment is of sufficient size
to handle the increased dose required for stabilization. Thus, no
additional capital expense was incurred.
Operation and Maintenance
No increased operation and maintenance costs, versus the cost of
simply lime conditioning sludge, was noted other than the cost of the
lime. Lime is purchased at $77 dollars per ton CaO.
Lime cost about $13 per dry ton of sludge treated.
Vacuum filter operation requires one person cbout five hours per
filter day. One person is also needed for te.i hours per filter day
to haul the sludge away.
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20. P0RTLAN0-MESTBR00K. MAINE
(Lime Added to Vacuum Kilter 'Jondii "oning Tank)
A. PLANT DATA
Plant Type: Conventional activated sludge
Plant Flow: 4.5 mgd design
1.5-2.0 mgd present ayerage
Quantity Limed: 1.9 dry tpd present average
B. WASTEWATER PROCESSING TRAIN
Pretreatment
- Aerated grit chamber
Secondary Treatment
- Conventional activated sludge
Chlorination
Discharge
- Presumscot River
Comments: Influent wastewater is 100 percent domestic.
C. SLUDGE PROCESSING TRAIN
Secondary Sludge
- Air flotation thickener
- Aerated storage tank
- Sludge conditioning/1ime stabilization (ferric
chloride also added)
- Vacuum filtration
- Landfill/land application
Comments: Original Jesign was for lime conditioning and landfill.
They hope to replace the lime system with a more
efficient one, use lower lime doses, and coiipost.
0. LIME US*
Type of Sludge: Air flotation thickened secondary sludge
Sol Ids Concentration of
Sludge Before L1me Added: 5.0 - 6.0 percent
142
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Lime Dosage (as CaO per
weight of dry sludge solids): 25.0 percent (irregular)
Quantity of Lime Used: 19.0 tons per months, Ca(OH)2
pH Attained: 11.5 to 12.5
Other Chemicals: Ferric chloride added 1n sludge conditioning,
5 percent
E. DETAIL 0- LIME SYSTEM
Lime Delivery/Storage
Type of Lime Purchased: 50-1b bags of high-calcium hydrated lime
Delivery: 300 bags approximately every two weeks.
Storage: Bags are stacked about 5 feet high on pallets. The
storage area is dry, indoors, accessible to heavy
equipment and located beside the lime silo feed/rnix system.
Inventory: A minimum of 100 bags (4 days) is always kept on hand.
Preparation of Lime Slurry
Type and Number of Mixing Tanks: Two 120-1b/hr automatic lime
feeders.
Method of Slurry
Preparation: Two automatic slurry preparation systems are used.
Each system has a hopper, on the upper level, to
' which bagged lime is manually added. In the base-
ment each system has a day silo equipped with a
vibrator, followed by a screw fed automatic slurry
mixing machine. The silo has steep sides and is
equipped with intermittent vibration to allow the
lime to flow. The screw feeder does not feed a con-
sistent quantity of lime, forcing the operator to
use much more lime than is necessary.
Oust Control Equipment: None, fairly dusty at hopper.
Prepared Lime Slurry Concentration: 10 percent, average, as Ca(0H)2
Type of Water Used 1n Slurry Makeup: City water
Comments: The operator plans to replace the automatic system with
two conventional slurry mix tanks.
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Lime Metering Pumps
Type and Number of Pumps: Two diaphragm metering pu'nps. No shock
absorbing equipment exists.
Type of Piping: Two-inch diameter PVC pipe with unions for cleanouts.
Plant water is pumped through the pipes to flush
them out at the end of every filtering day.
Comments: Line clogging is a problem. Higher lime doses than
needed are used (with a greater flow) to keep lines
"flushed".
Lime Application to Sludge Conditioning Tank
Point of Application: Slurry is added to a conventional vertical
conditioning tank located beside each vacuum
filter.
Dosage Control: Operator adjusts feeder/pump speed.
Dosage Setting: Operator sets dosage to obtain an excess to allow
for feeder equipment failure.
pH Measurement: Once a day filter cake is tested with a pH meter.
pH Holding Time: Detention time in filter vat only.
Comments: Some ammonia odors are present at the sludge conditioning
tanks.
Quantity of Lime Used: 1100 gallons per filter day
F. DOWNSTREAM PROCESS
Oewatering
Type: Two vacuum filters (cloth medium)
Scheduling: Filter 7 d«ys per week, 10 hours per day, both filters.
Loading Rate: 2.5 lb/sq ft-hr
Cake Solids Concentration (Includes weight of lime): 20-22 percent
Comments: There have been no major effects reported from using the
high lime dose. The filtrate 1s returned to the aerated
grit chamber without any problem. Only normal maintenance
required.
144
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Disposal
Method: Landfill
Procedure: The stabilized sludge cake is transported by conveyor to
a 14 cubic yard steel container. About 3 times a week
3 of these full containers are brought to a landfill with
a container truck. At the landfill the sludge is mixed
with Sand and used as fill. No monitoring is done.
Comments: They have recently started their composting project and
stopped landfilling the stabilized sludge.
G. COST OF LIME STABILIZATION
Equipment
Lime equipment was installed in original design, no extra equipment
has been purchased.
Operation and Maintenance
No change when going from conditioning to stabilization and back to
conditioning. Problems with lime feeder mask any lime dose changes.
Lime is purchased at $108 per ton Ca(0H)2*
Lime cost about $36 per dry ton of sludge treated.
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21. SCARBOROUGH. MAINE
(Lime Added to Liquid Sludge)
A. PLANT DATA
Plant Type: Secondary treatment by extended aeration.
Plant Flow: 0.4 mgd design
0.3 mgd present average
Quantity Limed: 0.2 dry tpd present average
8. WASTEWATER PROCESSING TRAIN
Pretreatment
- Comminutor
- Bar screen
- Pre-chlorination
Secondary Treatment
- Extended aeration.
Chiorination
Discharge
- Nonesuch River
Comment*: Influent wastewater Is 10 percent industrial and the rest
is domestic.
C. SLUDGE PROCESSING TRAIN
Secondary Sludge
- Aerobic digester (during warm months, in winter remove
sludge to town septage handling facility).
- Lime stabilization.
- land application.
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D. LIME USE
Type of Sludge: Aerobically digested secondary sludge.
Solids Concentration of
Sludge Before Lime Added: 2.0 percent.
Lime Dosage (as CaO per
weight of dry solids): 4.0 percent.
Quantity of Lii.ie Used: 0.3 tons per month, Ca(0H);>
pH Attained: Estimated 11.5 to 12.0
Other Chemicals: None.
E. DETAIL OF LIME SYSTEM
Lime Delivery/Storage
Type of Lime Purchased: 50-1b bags of high-calcium hydrated lime
Delivery: 25-30 bags are picked up by the operator at the local
supply store about once a month during the months land
application takes place.
Storage: Bags are stored indoors, in a dry area on the floor.
Inventory: A minimum of 10 bags are kept on hand, this supplies the
plant for 1.5 weeks during the land application months.
line Application to Liquid Sludge
Description of System: Detailed description appears in text.
F. UOWNSTRFAM PROCESS
Disposal
Method: Land application in summer.
Procedure: A converted oil truck Is used to land apply the stabilized
sludge to hayflelds, lawns, and land stripped of loam.
The 2400-gallon capacity truck 1s equipped with Internal
mixing by recirculation pumping. The truck can be loaded
or unloaded 1n 10 minutes. Sludge Is applied using a
splash plate or spayed with a hose. No regular moni-
toring occurs.
H7
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Comments: Farmers will sometimes supply the lime in exchange for
spraying their fields. Treatment plant personnel do the
land application and usually receive $6 per truckload from
the land owner. New regulations will decrease the number
of acceptable disposal sites.
G. COST OF LIME STABILIZATION
Equipment
The only capital expense for conversion to lime stabilization was the
cost of converting the truck for land applying the liquid sludge.
Operation and Maintenance
One man can run the oseration, taking approximately one hour for
one complete round trip. Only maintenance is on truck. Lime cost
is minimal. Lime is purchased at $120 per ton Ca(0H)2.
Lime cost about $6.50 per dry ton of sludge treated.
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22. SOHERSWORTH. NEW HAMPSHIRE
(Lime Added to Vacuum Filter Conditioning Tank)
A. PLANT DATA
Plant Type: Conventional activated sludge
Plant Flow: 2.6 mgd design
1.6 mgd present average
Quantity Limed: 0.9 dry tpd present average
8. WASTEWATER PROCESSING TRAIN
Pretreatment
- Bar rack
- Comminitor
Secondary Treatment
- Conventional activated sludge (plug flow)
Ch1 orination
Discharge
- Salmon Falls River
Comments: Influent wastewater if 45 percent mixed industrial
and 55 percent domestic.
C. SLUDGE PROCESSING TRAIN
Secondary Sludge
- Flotation thickener in summer (4-6X solids, add polymer,
may also add hydrogen peroxide to control ooors)
- Gravity thickener in winter (3-4% solids)
- Sludge condit1oning/lime stabilization (ferric chloride
or polymer also added)
Comments: When using polymer, a smaller lime dose is required than
when using ferric chloride. Operator reported no savings
in cost. Improved sidestream quality reported when using
polymer with a trace of ferric chloride (85 percent cap-
ture versus 75 percent with ferric chloride alone).
149
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LIME USE
Type of Slmige: Thickened secon..»ry sludge
Solids Concentration of
Sludge Before Lime Added: 3 to 4 percent
Lime Dosage (as CaO per
weight of dry sludge solids): 23 to 25 percent with ferric chloride
18 to 20 percent with polymer and some
ferric chloride
Quantity of Lime Used: 8.6 tons per month, Ca(0H)2, with ferric
6.7 tons per month, Ca(0H)2, with polymer
pH Attained: 11.0 to 12.0
Other Chemicals: ferric chloride, 6.0 percent or polymer 0.5
percent.
DETAIL OF LIME SYSTEM
Lime Delivery/Storage
Type of Lime Purchased: 50-lb bags of high-calcium hydrated lime
Delivery: 900 bags are delivered about every 2.5 months. The
bags are manually unloaded, rolled down a conveyor to the
basement and stacked. During the unload;,ig process many
bags are accidently broken and the storage area is quite
dusty. The process requires 16 man-hours (8 people).
Storage: Bags are stored indoors on a wooden floor.
Invantory: A minimum of 200 bags (about 2.5 weeks) is always kept
on hand.
Preparation of Lime Slurry
Type and Number
of Mixing Tanks: Two 400-gallon unlined steel tanks covered and
fitted with a hatch for lime addition.
Type of Mixing: Low-speed rotating paddle board.
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Mixer Motor Size: 0.75 hp.
Oust Control Equipment: lime is added through a small hatch on top
of the tank, forced ventilation pulls dust
into the tank. Air cleaned by bag filters
but not vented to outdoors. Area remains
dusty.
Method of Slurry
Preparation: Operator manually adds
of water.
Prepared Lime Slurry Concentration
Type of Water Used in Slurry Makeup:
50 pounds of lime to 80 gallons
7.0 percent as Ca(0H)2
City water
Special Equipment: The bags are stored on t. platform which has the
same elevation as the lime slurry makeup tank
top. This allows the operator to lay the bag on
the floor, a»id simply lift the bottom of the bag
to pour the lime into the tank.
The operator replaced the original water lines
(0.5-inch dia.) with lines (2-inch dia.) of a
larger diameter to reduce the tank filling time.
Comments: Lime and water are added proportionally to the mix tanks
throughout a filtering day. The operator reported no
problems with this procedure.
Lime Metering Pumps
Type and Number of Pumps: Two plunger pumps. The outlet line has
an air cushion chamber (surge control
standptpe).
Type of Piping: Two-inch iron pipe. The pipes conveying the lime
slurry from the pumps to the conditioning tank have
numerous elbows. These are a source of frequent
problems for the operator. As a result, a lower
concentration of lime slurry than desired is pumped
(one-half desired concentration). Operator also
flushes the lines daily, attaching a hose to the
lines.
Valving: Can pump from any mix tank, with any pump, to any con-
ditioning tank.
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Lime Application to Sludge Conditioning Tank
Point of Application: Slurry is added to a conventional horizontal
sludge conditioning tank located beside each
vacuum filter.
Dosage Control: Operator sets metering pump speed from control panel
located beside each vacuum filter.
Dosage Setting: Operator sets lime dose to get optimal dewatering as
determined by a buchner funnel test. When
filtering, the pH of the cake is checked; i* pH 1s
not sufficient, the lime dose is increased.
pH Measurement: Measured daily on the filter cake with a pH meter.
ph Holding Time: Detention time in filter vat only.
Quantity of Slurry Used: 2600-3300 gallons per filter day
Comments: Some ammonia odors are present around the conditioning
tank.
F. C0WNST?.£AM PROCESS
Dewatering
Type: Two vacuum filter (coil medium)
Scheduling: Filter 2 days per week, 10 hours per day, both filters.
Loading Rate: 2.0 Ib/sq ft-hr
Cake Sol ids Concentration (includes weight of lime): 12-14 percent
Conments: There have been no major effects reported from using the
high lime dose. The filtrate (pH 10-11) is retjrned to
the Influent. Vacuum filter system receives an acid
cleaning every 6 mcnths.
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Disposal
Method: Land application or stockpile
Procedure: The stabilized sludge c.ike is transported by conveyor to
two, steel container* (3; 4 cubic yards) located indoors.
About 12 times a day one of the sludge containers is
trucked to a farm or stockpile site. At a farm the
sludge is land applied with a manure spreader and
harrowed into the ground. The farmer plows, supplies
lime, seeds, and harvests. Various application rates (4-
12 tons per acre per year) have been experimented with.
The fields are monitored for heavy metals and nitrates.
When the sludge is stockpiled, it is just left sitting irt
open pits. Some odors are reported if the piles are bro-
ken into. If this occurs lime is usually added.
Stockpiles have been monitored for 30 days to check pH
decay. pH was reported to be around 9-10 after that
period.
Comments: Only 20 percent of the sludge is land applied and the rest
is stockpiled. Finding suitable land is a problem.
C. COST OF LIME STABILIZATION
Equipment
Lime handling equipment was originally Installed for chemical con-
ditioning prior to dewatering. The equipment is of sufficient si^e
to handle the increased dose for stabilization. Thus, no addition
capital expense was incurred.
Operation and Maintenance
Operator notes that vacuum filter coils must be cleaned regularly.
Conditioning drum had to be epoxy coated. Lime is purchased at $86
per ton Ca(0H)2-
Lime cost about $24 per dry ton of sludge treated.
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23. ROCHESTER (Northwest). HEW YORK
(Lime Added to Vacuum Filter Conditioning Tank)
A. PLANT DATA
Plant Type: Conventional activated sludge
Plant Flow: 15.0 mgd design
12.0 mgd present average
Quantity Limed: 10 to 12 dry tpd present average
B. WASTEWATER PROCESSING TRAIN
Pretreatment
- Aerated grit removal
- Mechanical bar screen
Primary Treatment
- Chemical addition for phosphorus removal, normally alum is added.
Secondary Treatment
- Conventional activated sludge
Chiorination
Discharge
- Lake Erie
Comments: Have two stage secondary clarification, originally
designed for niiosphorus removal.
C. SLUDGE PROCESSING TRAIN'
Primary Sludge
- Gravity thickener
Secondary Sludge
- Wasted from mixed liquor
- Gravity thickener
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Combined Sludge:
- Gravity thickener (to 5 percent).
- Unmixed storage tank, no decanting required.
- Sludge conditioning/1ime stabilization (polymer added).
- Vacuum filtration.
- Land application.
Comnents: Original design was to dewater primary sludge by vacuum
filter and centrifuge the secondary sludge prior to
incineration. Presently lime stabilize and vacuum filter
combined sludges in summer and centrifuge and incinerate
in winter.
LIKE USE
Type of Sludge: Gravity thickened mix of primary and secondary sludge.
Solids Concentration of
Sludge Before Lime Added: 5.0 percent.
Lime Dosage (as CaO per
weight of dry solids): 30 to 40 percent, higher than desired, but
sometimes sludge is backlogged and the lime
demand of the sludge increases durir.g storage.
Quantity of Lime Used: 120 tons per month, CaO
pH Attained: 12.2
Other Chemicals: Polymer added in sludge conditioning, 3 percent.
No reported effect on lime dose.
DETAIL OF LIME SYSTEM
Lime Delivery/Storage
Type of Lime Purchased: Quicklime, pebble
Delivery: About 22 tons of lime twice a week. Truck blows lime
into storage silo.
Storage: Three storage silos, one 20-ton capacity and two 80-ton
capacity. Bag filters on storage silos' clean conveyance
air.
Inventory: Purchase one to two loads per week, but as much as three
loads per week at the end of the summer. An order is
placed as soon as space is available.
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Conveyance and Slaking
Conveyance System: Each silo is equipped with a vibrator to aid the
movement of lime. One silo directly over each
slaker. Screw feeders are used.
Type, Size and
Number of Slakers: Three slurry type slakers.
Prepared Lime Slurry: Up to 45 percent (as high as possible) as
Ca(0H)2
Lime Slurry Transfer
Method: Gravity.
Piping: Fifteen feet of pipe from each slaker to slurry storage.
Pipes flushed daily, rodded as required.
Lime Slurry Storage
Type and Number of Storage Tanks; Two 250-gallon steel storage tanks.
Type of Mixing: Medium-speed paddle mixers.
Mixer Motor Size: 0.5 HP.
Dilution: None practiced.
Lime Slurry Transfer Pumps
Tyne and Number of Pumps: Three progressive cavity pumps (use only
one fit a time).
Type of Piping: Four-Inch reduced to 2-Inch steel pipe, no cleanouts.
Flush daily. Few clogging problems, high pressure
system.
Valving: Valved so that two pumps serve one storage tank and one
pump serves the other storage tank.
L1me Day Tank Storage
Type and Number: One, steel tank (estimated at 800-gallon capacity).
Type of Mixing: High-speed propeller uilxer.
Comments: Have to occasionally clean grit out cf tank.
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Lime Metering Pumps
Type and Number of Pumps: Progressive cavity pump (this pump replaced
a plunger pump, operator prefers the
progressive cavity pump's ability to
pump grit).
Type of Piping: Steel piping, 1.5-inch diameter reduced from 2-inch.
No cieanouts or bends.
Litre Application to Sludge Conditioning Tank
Point of Application: Slurry is added to a sludge line about
twenty feet before the conditioning tank.
Vertical conditioning tank is beside vacuum
filter.
Dosage Control: Operator sets metering pump speed from control panel
located beside the vacuum filter.
Dosage Setting: Dosago is set to obtain required pH of 12.2.
pH Measurement: Measurement taken with a pH meter.
pH Holding Time: Detention time in filter vat only. Tests have
shown pH to remain at 12.0 or greater after 3
hours.
Quantity of Slurry Used: 2800 gallons per filter day.
F. DOWNSTREAM PROCESS
Dewatering
Type: One vacuum filter (cloth medium).
Scheduling: Filter 5 days per week, 14 hours per day.
Cake Solids Concentration (includes weight of lime): 24 percent.
Comments: The sludge requires a pH of 12 to dewater well, therefore
a high lime dose has always been useds. No major effects
from the high dose were reported.
Sldestream quality 1s better when farric chloride is used,
but want to keep from adding metals. Polymer 1s also
cheaper to use.
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Disposal
Method; Land applicatIon
Procedure: The stabilized sludge cake is transported by conveyor to
a 10 cubic yard hopper which drops sludge into a 4 cubic
yard dump truck. The hopper Is not used for long-term
storage because sludge sticking results. The operation
requires 3 trucks. They haul the sludge to town lands,
farms and orchards. There it is applied at a rate of 20
to 30 tons per acre per year. It is applied by a tractor
pulling a sled that deposits a 1.5-inch layer of cake
to the land. Also attached to the tractor, behind the
sled, is a set of blades and a harrow to plow the cake
into the land.
Well points are installed on most of the sites to check
for metals and coliforms. The Health Department monitors
all operations closely.
Comments: Most of the sludge presently goes to town land. A farmer
uses this land to grow corn for cattle feed.
The treatment plant personnel do all the spreading of the
sludge cake.
G. COST OF LIME STABILIZATION
Equipment
Operation and Maintenance
No abnormal operation and maintenance costs. They did a cost study
that showed lime stabilization to be cheaper than incinerating. The
stucty reported incineration and disposal to cost $102 per ton dry
solids versus $80 to $90 per ton dry solids for lime stabi11z?t1orr
(these costs don't include maintenance). They are looking at the
possibility of charging customers for the stabilized sludge 1n the
future.
lime is purchased at $50-60 per ton CaO.
time costs about $15-24 per dry ton of sludge treated.
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H. SPECIAL STUDIES
A viral study showed that none were present just after lime stabilization.
Fecal and total coliform were also absent.
Total and fecal coliform are monitored. Background samples (prior to
any sludge addition) showed that there were very few fecal coliform
and some total coliform present in the soil. There were essentially
no coliform in the well water. Raw sludge was appliad and there were
significant quantities of total and fecal coliform in the soil, but
only a slight coliform count in the well water. Coliform counts in
soil and water decreased with the onset of lime stabilization.
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24. BUCKNAM POINT. RHODE ISLAND
(L1me Added to Vacuum Filter Conditioning Tank)
A. PLANT DATA
Plant Type: Conventional activated sludge
Plant Flow: 31.0 mgd design
23.0 mgd present average
Quantity Limed: 8.5 dry tpd present average
8. WASTEWATER PROCESSING TRAIN
Pretreatment
- Bar rack
- Comminutor
- Grit channel
- Preaeration
Primary Treatment
Secondary Treatment
- Conventional activated sludge
Chlorination
Discharge
- Seekonk River
Comments: Influent wastewater is 50 percent mixed industrial
flow and 50 percent domestic flow.
C. SLUDGE PROCESSING TRAIN
Primary Sludge
- Mixed with secondary sludge 1n primary clarifier
Secondary Sludge
- Sludge re-settled with primary sludge 1n primary cl«ritier
Combined Sludges
- Two stage anaerobic digestion
- Sludge conditioning/Hire stabilization
- Vacuum filtration
- Landfill
160
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LIME USE
Type of Sludge: Anaerobically digested primary and secondary sludge
Solids Concentration of
Sludge 3efore Lime Added: 3.0 percent
Lime Dosage (as CaO per
weight of dry sludge solids): .18-19 percent
Quantity of Lime Used: 47.0 tons per month, Ca(0H)2
pH Attained: 11.0
Other Chemicals: Ferric chloride added in sludge conditioning.
Operator reports using insufficient ferric chloride,
and thus, using extra lime.
DETAIL OF LIME SYSTEM
Lime Delivery/Storage
Type of Lime
Purchased: L1nie slurry (33 percent concentration) is purchased from
a supplier who makes up the slurry from hydrated lime. A
consistent concentration is received.
Delivery: Purchase a 5000 gallon truckload 1-2 times a week. The
slurry is unloaded with a centrifugal pump; the same pump
that is useds for transfering slurry to the day tanks.
This process takes about one half hour.
Storage: Four, 1500-gallon, horizontal, steel storage tanks,
equipped with high-speed propeller mixers. Two of these
tanks are located in one room and serve that part of the
lime sysfm, while the other two tanks are located in
another room and serve a duplicate system. Four 1500
gallon vertical day tanks can also be used for storage.
Inventory: A minimum of 3000 gallons is always kept on hand,
is about 2 filtering days.
This
Comments: The purchase of lime slurry replaced the original system
of making up lime slurry from bagged, hydrated lime. The
bagged system was difficult to handle, the system was
dusty and not equipped with dust control. Also the
system was very labor intensive. Bags were moved manually
to the mixing area and batches had to be mixed frequently
because only two 250 gallon mix tanks existed.
A chemical additive is added to the slurry to prevent lime
scaling in pipes. It has worked well.
161
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Lime Slurry Transfer Pumps
Type and Number of Pumps: Four centrifugal pumps, equipped for
abrasive handling.
Type of Piping: Galvanized steel pipes (2-inch diameter). The
system is equipped for flushing and this is done
every filtering day.
Lime Day Tank Storage
Type and Number: Four 1500-gallon, vertical, steel tanks.
Type of Mixing: High-speed propeller mixer.
Mixer Motor Size: 5.0 HP
Lime Metering Pumps
Type and Number of Pumps: Four plunger pumps
Type of Piping: Two-inch galvanized steel pipe to pumps. One-and-
a-quarter-1nch PVC to conditioning tank. Pipes are
equipped with an automatic flushing system and
unions for cleaning. System flushed daily.
Lime Application to Sludge Conditioning Tank
Point of Application: Slurry is added to vertical, propeller
mixed, sludge conditioning tanks located bfside
the vacuum filters*
Oosage Control: Operator sets metering pump speed from control p.inel
located at day tanks (downstairs from filter).
Oosage Setting: Operator adds lime as required to obtain good
dewatering.
pH Measurement: Measured on filter cake with a pH meter.
pH Holding Time: Detention time 1n filter vat only.
Quantity of Slurry Used: 1700 gallons per filter day.
F. DOWNSTREAM PROCESS
Dewatering
Type: Four vacuum filters (cloth medium]
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Scheduling: Filter 5 days per week, 7 hours per day, 2 filters.
Loading Rate: 2-3 lb/sq ft-hr
Cake Solids Concentration (includes weight of lime): 20 percent
Comments: The effects from the high lime dose on the treatment plant
operations am negligible. Only normal maintenance has
been required.
Disposal
Method: Landfill
Procedure: The stabilized sludge cake is transported by conveyor to
a dump truck and hauled to a landfill. There it is used
as fill and covered with foundry slag that is obtained
nearby for free. Some pH monitoring of the cake was
reported.
G. COST OF LIME STABILIZATION
Equipment
Lime system was converted from a small bag system to a lime slurry
system. It was cost effective.
Operation and Maintenance
Lime is purchased at $125 per ton Ca(0H)2.
Lime cost about $30 per dry ton of sludge treated.
163
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25. FAST PROVIDENCE, RHODE ISLAND
(Lime Added to Vacuum Filter Conditioning Tank)
A. PLANT DATA
Plant Type: Conventional activated sludge
Plant Flow: 10.4 mgd design
6.0 mgd present average
Quantity Limed: 3.2 dry tpd present average
B. WASTEWATER PROCESSING TRAIN
Pretreatment
- Bar rack
- Comminutor
- Aerated grit channel
Primary Treatment
Secondary Treatment
- Conventional activated sludge
Chi or-nation
Discharge
- .'terragansett Bay
Comments: Influent wastewater is 60 percent industrial and 40 per-
cent domestic. Also high infiltration.
C. SLUDGE PROCESSING TRAIN
Primary Sludge
- Holding tanu
Secondary Sludge
- Centrifuge thickening (normally bypassed)
- Holding tank
Combined
- Holding tar«
- Sludge conditioning/lime stabilization (ferric chloride-
also added)
- Vacuum filtration
- Landfill
164
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Comments: Lime system originally designed as a backup to heat
treatmert system. Conditioning problems and cost of fuel
resulted in heat treatment abandonment. Will compost in
future.
LIME USE
Type of Sludge: Mixture of raw primary and thickened secondary
sludge.
Solids Concentration of
Sludge Before Lime Added: 4.5 percent
Lime Dosage (as CaO per
weight of dry sludge solids): 20-22 percent
Quantity of Lime Used- 27.0 tons par month, Cd(QH)2
pH Attained: 12.0
Other Chemicals: Ferric chloride added prior to sludge conditioning
tanks, 6.0 percent.
DETAIL OF LINE SYSTEM
Lime Delivery/Storaqe
Type of Lime Purchased: 50-1 b bags of high--alciui.i hydrated lime
Delivery: 200 bags approximately every 3 days. The bags are
stacked 50 bags to a pallet and unloaded with heavy
equipment.
Storage: Bags are stacked 4 feet high on a wooden platform,
"indoors, accessible to heavy equipment, and located
beside the slurry niixing tank.
Inventory: Operator keeps a minimum of 200 bags of lime on hand
(4 c!ays).
Comments: Plans are being made to convert to a lime slurry (33 per-
cent) system. This will be more cost effective and help
solve the lack of lime storage problem.
165
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Preparation of Lime Slurry
Type and Number of Mixing Tanks: One 200-gallon steel mixing tank
Type of Mixing: High-speed propeller mixer
Oust Control Equipment: None, area is dusty
Method of Slurry Preparation: Operator manually adds 50 oounds of
lime to 25 gallons of water.
Prepared Lime Slurry Concentration: 19 percent as Ca(0H)2
Type of Water Used in Slurry Makeup: City water
Frequency of Slurry
Makeup: Approximately eight times a day. The day tanks are always
kept full so batch mixes are made up in the mix tank and
pumped to the day tank as needed throughout the day.
Lime Slurry Transfer Pumps
Type and Number of Pumps: One, progressive cavity pump. No
vibration absorption equipment.
Type of Piping: Three-inch diameter PVC pipe with unions for
cleanouts. Pipes are flushed with plant water
every day after filtering is complete.
Valving: Only one tank and one pump.
Lime Day Tank Storage
Type and Number: Two 375-gallon fiberglass tanks. No dilution takes
place in these tanks.
Type of Mixing: High-speed propeller mixer
Lime Meteri.iq Pumps
Type and Number of Pumps: Two positive displacement chemical feed
pumps.
Type of Piping: One-inch diameter PVC pipe with unions for
cleanouts. Pipes are flushed witli plant water
every day after filtering 1s coirplete.
166
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Valving: Can pump from any day tank, with any pimp, to any
conditioning tank.
Lime Application to Sludge Conditioning Tank
Point of Application: Slurry is added to a vertical sludge con-
ditioning tank equipped with a large impeller
slow-speed mixer. A tank is located beside each
vacuum filter.
Dosage Control: Operator sets the metering pump speed from a
control panel located at the vacuum filters.
Dosage Setting: Dosage is set to obtain a good filter cake and to
obtain the required pH.
pH Measurement: pH is checked every hour with a pH meter.
pH Holding Time: Detention time in filter vat only.
Quantity of Slurry Used: 1600 gallons per filter day.
F. DOWNSTREAM PROCESS
Dewatering
Type: Two vacuum filters (cloth medium)
Scheduling: Filter 5 days per week, 8 hours per day.
Loading Rate: 4.0 Ib/sq ft-hr
Cake Solids Concentration (includes weight of lime): 20-25 percent
Comments: There have been no major effects reported from using the
high lime dose. The filtrate is returned to the primary
influent. Only normal maintenance required.
Disposal
Method: Landfill
Procedure: The stabilized sludge cake 1s transported by conveyor
to a 6 cubic yard dump truck equipped with a water sealed
gate* The truck hauls the sludge 15 miles to a landfill
where 1t 1s used as fill and covered with gravel. No
monitoring is done.
167
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Commerts: Disposal fee for dumping sludge is $5 per u'ry ten. Future
plans call for composting.
G. COST OF LIME STABILIZATION
Equipment
The lime equipment was oriqinully installed as a backup sludge con-
ditioning system to heat treatment. Currently, no expense incurred
in conversion to lime stabilization.
Operation and Maintenance
No unusual operation and maintenance effects noted. The costs are
much lower than the heat treatment alternative. Lime is purchased at
$119 per ton Ca(0H^•
Lime cost about $33 per dry ton of slu.tge treated.
H- SPECIAL STUDIES
A three week study of pH versus time was conducted. A sample limed
to pH of 12.2 remained at 12.1 or greater for the entire period.
168
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26. WIONSOCKET. RHODE ISLANJ
(Lime Added to Vacuum Filter Conditioning Tank)
A. PLANT DATA
Plant Type: Conventional activated sludge.
Plant Flow: 16.0 mgd design
8.0 mgd present average
Quantity Limed: 6.0 dry tpd present average.
B. WASTEWATER PROCESSING TRAIN
Pretreatment
- Bar screen
- Comminutor
- Aerated grit removal
Primary Treatment
Secondary Treatment
- Conventional activated sludge
Chlorination
Discharge
- Blackstone River
Comments: Influent wastewater is 75 percent domestic and 25 percent
i ndustrial.
C. SLUDGE PROCESSING TRAIN
Primary Sludoe
- Gravity thickener (with secondary sludge).
Secondary Sludge
- Gravity thickener (with primary sludge).
Combined Sludge
- Gravity thickener (to 5 percent solids).
- Storage
- SluJga cond1tior.incj/l1m'S stabilization (ferric
chloride also added)
- Vacuum fi'tration
- Landfill
169
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Comments: Multiple-hearth furnace «ot in use because sludge prouuction
presently is not high enough to make it economical to use.
If used 1n future, sludge will not be lime stabilized.
LIMt USE
Type of Sludge: Gravity thickened primary and secondary sludges.
Solids Concentration of
Sludge Before Lime Added: 5 percent
Lime Dosage (as CaO per
weight of dry solids): 10 to 12 percent
pH Attained: 11.0, not checked regularly.
Other Chemicals: Ferric chloride added in sludge conditioning,
3 to 4 percent.
DETAIL OF LIME SYSTEM
Lime Delivery/Storage
Type of Lime Purchased: Quicklime, granular
Delivery: 25 tons delivery. Truck blows lime into storage silo.
Storage: One 60-ton capacity storage silo. The silo has a bin acti-
vator (live bin bottom) with a bridge breaker. There is no
gate to hold lime back from the conveyance system.
Inventory: Order for more lime placed when silo gets down to about
25 tons of 1ime.
Conveyance and Slaking
Conveyance System: A single screw conveyor moves the 11me to the
two day bins located above the slakers. Con-
veyor works well with granular lime, but clogged
when a pebble lime was used.
Type, Size and Number of Slekers: Two, 1000-lb/hr paste t>pe slakers.
Prepared Lime Slurry: 12.0 percent as Ca(0H)2
Type of Water Used 1n Slurry Mceup: City water.
170
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Special Equipment: Frequently the operator overrides the gravimetric
fender and simply varies the belt speed.
The day bins have been fitted with vibrators
(electromagnetic type) attached to a timer.
These vibrators have worked well. Before they
were installed, the operator had to watch to make
sure lime wasn't clogging. The clogging had been
partially attributed to a new lime supplier who
is supplying a lime with more powder and grit.
Lime Slurry Transfer
Type of Piping: Lime slurry is transferred froir the slaker to a
small day tank by gravity. The transfer line is
2-inch galvanized pipe with no provision for flushing
but with crosses at each bend to allow for cleaning
with a rod. Cleaning has not been required.
Slurry can be pumped from a small day tank to two
larger day tanks.
of Pumps: Three double-diapragm pumps equipped with
air cushion/surge control cylinders.
The piping system is interconnected between transfer
pumps and day tanks. Any pump can pump lime slurry
to any day tank.
Type and Number
Valving:
Lime Day Tank Storage
Type and Number: Three steel tanks, (2) 800 gallons capacity and (1)
350 gallon capacity.
Type of Mixing: High-speed propeller mixer.
Mixer Motor Size: 0.5 HP
' Special Equipment: Smaller day tank Is fitted with a capacitance
type level probe. A baffle surrounds the
probe to reduce turbulence.
Tank is fitted with a 2-inch gravity drain/overflow
line.
171
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Lime Metering Pumps
Type and Number of Pumps: Two plunger pumps. Replaced diaphragm
pumps which frequently clogged with lime
grit (these pumps had smaller check valves
than those in the plunger pumps). The
pumps are equipped with air cushion/surge
control cylinders.
Type of Pipina: Installing PVC piping w1tn a built-in flushing
system. Flushing is done at the end of every
shift.
Valving: Lime slurry can be pumped from any day tank, with any pump,
to any conditioning tank.
Limq Application to Sludge Conditioning Tank
Point of Application: Slurry is added tc * conventional horizontal
sludge conditioning tank located beside each
vacuum filter.
Dosage Control: Operator sets metering pump speed from control panel
located at the vacuum filters.
Dosage Setting: Judce by eye to obtain good dewecering.
pH Measurement: Not regularly measured.
pH Holding T%e: Detention tlira 1n filter vat only.
Ouantlty of Slurry Used: 4400 gallons per filter day.
F. DOWNSTREAM PROCESS
De*atering
Type: Two vacuum filter*, one cloth and one coil medium. The coll
filter 1s being converted to cloth.
Scheduling: Filter 6 days per week, 6 hours per day, one filter.
Loading Rate: 4.5-5.0 lb/sq ft-hr
Cake Solids Concentration (Includes weight of lima): 20 to 22 percent
Comments: No higher 11me dose than required for dewaterlng has been
used. There are no abnormal effects reported from the
high dosage* System works well.
172
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Di:pcsa1
Method: Landfill
Procedure: The stabilized sludge cake is transported by belt con-
veyor to a sludge hopper, dropped into a dump truck, and
hauled to a landfill site. At the landfill the sludge
is used for fill and covered with 6-12 inches of gravel
daily.
Comnents: No disposal fee.
G. COST OF LIME STABILIZATION
Equipment
No equipment needed other than that originally installed for lime
conditioning of sludge.
Operation and Maintenance
No higher dose than needed for dewatering.
Lime is purchased at $76 per ton CaO.
Lime cost about $20 per dry ton of sludge treated.
173
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27. BURLINGTON, VFRMONT (Main Plant)
(Lime Added to Vacuum Filter Co. ditinni-g Tank)
A. PLANT DATA
Plant Type: Conventional activated sludge
Plant Flow: 5.0 mgd design
4.5 mgd present average
Quantity Limed: 1,0 dry tpd present average
B. WASTEWATER PROCESSING TRAIN
Pretreatment
- Bar rack
- Screening
- Grit removal
Primary Treatment
»
Secondary Treatment
- Conventional activated sludge
Chlorination
Discharge
- Lake Champlaln
Comments: Influent wastewater is 50 percent industrial and
50 percent domestic.
C. SLUDGE PROCESSING TRAIN
Primary Sludge
• Two stage anaerobic digestion
- Vacuum filtration (in winter only)
- Landfill (In winter), Land Apply (warm months)
Secondary Sludge
- Flotation thickener (polymer added)
- Anaerobic digestion (optional, nay be practiced 1n summer
prior to land application)
- Sludge conditioning/11me stabilization
- Vacuum filtration (In winter only)
- Landfill (in winter)
174
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Comments: In the winter, if waste activated sludge is not digested,
it is stabilized prior to vacuum filtration. In one
summer exDeriment, thickened waste activated sludge was
lime stabilized by simultaneously pumping the sludge and
lime slurry to a land application vehicle. Enough lime
was added to reech a pH of 11.5. (There is no lime dose
data fran this test.) The lime and sludge were mixed in
the truck by recirculation pumping.
LIME USE
Type of Sludge: Flotation thickened secondary sludge (a high lime
dose to the anaerobically digested primary sludge
is also reported)
Solids Concentration of
Sludge Before Lime Added: 4.5 percent
Lime Dosage (as CaO per
weight of dry sludge solids): 20 to 30 percent
pH Attained: 11.5
Other Chemicals: Ferric Chloride
DETAIL OF LIME SYSTEM
Lime Delivery/Storaqe
Type of Lime Purchased: 50-lb bags of high-calcium hyarated lime
Preparation or i.i,r.e Slurry and Lime Metering Purees
Type and Number of Mixing Tanks: One steel tank, 400 gallons.
Method of Slurry Preparation: Batch mix prepared as needed.
Prepared Lime Slurry Concentration: 17 percent as Ca(0H)2» estimate
Type of Water Used in Slurry Makeup: Plant water
Slurry Metering Pump Type: Ofapragm
175
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Lime Application to Sludge Conditioning Tank
Point of Application: Slurry is added to a conventional horizontal
sludge conditioning tank located beside the
vacuum filter.
Dosage Control: Operator sets metering pump speed.
pH Measurement: pH is occasionally checked with a pH meter.
F. DOWNSTREAM PROCESS
Dewatering
Type: One vaccum filter (coil medium). Vacuum filtration is used
during the winter months when land application cannot be prac-
ticed. Lagooning is being considered as a possible alter-
native to this practice.
Disposal
Method: Land application (one week experiment) or landfill (normal)
Comments: Liquid digested sludge Is land applied 1n the warm
months. Sludge is dewatered and landfilled the rest of
the year. The plant is reclaiming a town dump by land-
filling.
G. COST OF LIME STABILIZATION
Equipment
Lime handling equipment was originally Installed for chemical con-
ditioning prior to vacuum filtration. No new equipment was needed.
Operation and Maintenance
Lime is purchased at $64 per ton Ca(0H)2* Not cost effective to lime
stabilize versus anaeroblcally digesting all of the sludge.
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28. BURLINGTON, VERMONT (Riverside Plant)
(Lime Added to Vacuum Filter Conditioning Tank)
A. °LANT DATA
Plant Type: Conventional activated sludge
Plant Flow: 2.0 mgd design
fj-7 mgd present average
Quantity Limed: 0.2 flry tpd present average
B. WASTEWATER PROCFSSING TRAIN
Pretreatment
- Screening
- Coiranunition
- Grit removal
Primary Treatment
Secondary Treatment
- Conventional activated sludge
Chlorination
Discharge
- Winooski River
Comments: Ir.fluent wastewater is 80 percent hospital and university
wastes and 20 percent domestic.
C. SLUDGE PROCESSING TRAIN
Primes^ Sludge
- Two stage anaerobic digestion
- Vacuum filtration (in winter only)
- Landfill (ir. winter), land apply (warm months)
secondary Sludge
- Flotation thickener (polymer added)
- Anaerobic digestion (optional, may be practiced in summer
prior to land application)
- Sludge conditioning/1ime stabilization
- Vacuum filtration (1n winter only)
- Landfill (in winter)
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Comments: In the winter, if wasts activated sludge is net digested,
it is lime-stabilized prior to vacuum filtrat on. In one
summer experiment, thickened waste rctivateu sludge was
lime-stabilized by simultaneously pumping the sludge and
lime slurry to a land application vehicle (there is no
lime dose data from this test). The lime aid sludge were
mixed in the truck by recirculation pumping.
LIME USE
Type of Sludge: Flotation thickened secondjry sludge (a high lime
dose to the anaerobical ly digested primary sludge
is also reported)
Solids Concentration of
Sludge Before Lime Added: 4.5 percent
Lime Dosage (as CaO per
weight of dry sludge solids): 20 to 30 percent
pH Attained: 11.5
Other Chemicals: Ferric Chloride
OETAIL OF LIME SYSTEM
Lime Delivery/Storage
Type of Lime Purchased: 50-1b bags of high-calcium hydrated lime
Preparation of Lime Slurry and Lime Metering Pumps
Type and Number of Mixing Tanks: One steel tank, 400 gallons.
Method of Slurry Preparation: Batch mix prepared as needed
Prepared Lime Slurry Concentration: 17 percent as Cd(0H)2, estimate
Type of Water Used 1n Slurry Makeup:. Plant water
Slurry Metering Pump Type: Diaphragm
178
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Ume Application to Sludge Conditioning Tank
Point of Application: Slurry is auded to a conventional horizontal
sludge conditioning tank located beside the
vacuum filter.
Dosage Control: Operator sets metering pump speed.
pH Measurement: pH is occasionally checked with a pH meter.
F. DOWNSTREAM PROCESS
Dewatering
Type: One vacuum filter (coil medium). Vacuum filtration is used
during the winter months when land application cannot be prac-
ticed. Lagooning is being considered as a possible alter-
native tu this practice.
Disposal
Method: Land application (one week experiment) or landfill (normal)
Comments: Liquid digested sludge is land applied in the warm months.
Sludge is dewatered and landfilled the rest of the year.
The p'tort is reclaiming a town dump by landfilling.
G- COST OF LIME STABILIZATION
Emipment
Lire handling equipment was orgirally installed for chemical con-
ditioning prior to vacuum filtration. No new equipment was needed.
Operation and Maintenance
Lime is purchased at $64 per ton Ca(0H>2. Not cost effective to lime
stabilize versus anacrobically digesting all of the sludge.
179
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ENGLISH TO METRIC CONVERSION FACTORS
Multiply by To obtain
mgd 157 m^/hr
°F °F-32/1.8 °C
ton 907 kg
lb 0.454 kg
ft 0.305 m
gallon 3.78 1
inch .0254 m
Hp 746 watt
mile 1852 ra
acre 4046 m2
Kwh 3.6 X 106 joule
yd3 0.764 m3
lb/ft2/hr 4.88 kg/n^/hr
tons/day 907 kg/day
Ib/hr 0.454 kg/hr
180
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