awwa seminar
ROCEED1NG/
Minimizing and Recycling
Water Plant Sludge
Presented at the AWWA Conference, May 13,1973
No. 20123
-------
U,S,EPAU
IIIMII1" .. —
RXOODQD^773
-------
PROCEEDINGS
AWWA SEMINAR
ON
MINIMIZING AND RECYCLING
WATER PLANT SLUDGE
Presented by
EDUCATION COMMITTEE OF AMERICAN WATER WORKS ASSOCIATION
AND
UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
Water Supply Division
Las Vegas, Nevada
May 13, 1973
-------
FOREWORD
All materials and information contained herein are published in the
exact form as presented to AWWA by the seminar speakers. Per AWWA
policy for publication of "Proceedings," no attempt is made on the
part of the American Water Works Association to edit, reformat, or
alter the material provided except where obvious errors or discrep-
ancies have been detected. Any statements or views here presented
are totally those of the speakers and are neither condoned nor re-
jected by the American Water Works Association or its members.
Copyrighted 1973
by
American Water Works Association
2 Park Ave., New York, N.V,
ii
-------
CONTENTS
Title of Paper Paper Number
Waste Discharge Regulations and Turbidity Standards I
Use of Organic Polymers and Sludge Volume Reduction II
High Energy Mixing and Flocculation III
Direct Filtration vs. Oxidation IV
Magnesium Carbonate Recycling V
Practice in MgCO^ Recovery and Reuse VI
iii
-------
WASTE DISCHARGE REGULATIONS
AND TURBIDITY STANDARDS*
Gordon G. Robeck**
Edgar A. Jeffrey***
INTRODUCTION
The Federal government through EPA has many new
responsibilities as a result of Public Law 92-500 on pollution control,
and it may soon be establishing new drinking water standards that
would apply to all Community Water Supply Systems. These
standards will be essentially an updating or revising of the existing
PHS 1962 Drinking Water Standards.
PROPOSED NEW TURBIDITY STANDARD
We in the Water Supply Research Lab are always anxious to
demonstrate how a high-quality water can be delivered to the
consumer's tap economically. Hence, much effort has gone into
developing data to show that many surface sources can be treated
by non-conventional arrangements at less than the usual costs.
In reviewing the literature and our experience with evaluating
Interstate Carrier Water Supplies, we noticed several systems have
had trouble controlling coliform when certain biological blooms and
silt loads enter the transmission or distribution lines. Increasing
chlorination many times seems to temporarily suppress the
presence of growth of coliform, but other times it has not been
successful, particularly if there are open finished water reservoirs.
Filtration will usually allow post chlorination to be more effective, but
we are mainly responsible for suggesting a performance standard, not
*For presentation at Seminar, May 13, 1973, Las Vegas, Nevada.
Jointly sponsored by AWWA Education Committee and Water Supply Div.,
USEPA.
**Director, Water Supply Research Laboratory, NERC-CI, USEPA.
***Water Supply Technical Advisor, Water Supply Division, USEPA.
1-1
-------
create a how-to-do policy so we developed a rationale for supporting
a turbidity limit of 1 at the consumers tap. The Public Advisers
suggested some changes including having the limit applied at the
point of entry into the distribution system. The compromise
proposal now reads as follows:
"4. 22 2 3 TURBIDITY
Approval Limit (Health) - 1 Til
Turbidity in drinking water shall not exceed one turbidity unit
at the point where water enters the distribution system except where
it can be demonstrated that a higher turbidity not exceeding 5TU does
not: (1) interfere with disinfection, (2) cause tastes and odors upon
disinfection, (3) prevent the maintenance of an effective disinfection
agent throughout the distribution system, (4) result in deposits in the
distribution system, and (5) cause consumers to question the safety
of their drinking water. "
The Federal Technical Review Committee prepared the
following rationale to support the turbidity limit:
"Drinking water should be low in turbidity prior to disinfection
and at the consumer's tap for the following reasons:
1) Several studies have demonstrated that the presence of particulate
matter in water interferes with effective disinfection. Neefe, Baty,
Reinhold, and Stokes^ added from 40 to 50 ppm of feces containing
the causative agent of infectious hepatitis to distilled water. They
then treated this water by varying techniques and fed the resultant
liquid to human volunteers. One portion of the water that was
disinfected to a total chlorine residual after 30 minutes of 1. 1 mg/l
caused hepatitis in 2 of the 5 volunteers. A similar experiment,
in which the water was first coagulated and then filtered, prior to
disinfection to the same concentration of total residual, produced no
1-2
-------
hepatitis in 5 volunteers. This was repeated with 7 additional
volunteers, and again no infectious hepatitis occurred.
(2)
Chang, Woodward and Kabler showed that nematode worms
can ingest enteric bacterial pathogens as well as virus, and that the
nematode-born organisms are completely protected against chlorin-
ation even when more than 90 percent of the carrier worms are
immobilized.
Walton^ analyzed data from three waterworks treating surface
waters by chlorination only. Coliform bacteria were detected in the
chlorinated water at only one waterworks, the one that treated a
Great Lakes water that usually did not have turbidities greater than
10 TU, but occasionally contained turbidities as great as 100 TU.
(4)
Sanderson and Kelly studied an impounded water supply
receiving no treatment other than chlorination. The concentration
of free chlorine residual in samples from household taps after a
minimum of 30 minutes contact time varied from 0. 1 to 0. 5 mg/l and
the total chlorine residual was between 0, 7 and 1 mg/l . These
samples consistently yielded confirmed coliform organisms.
Turbidities in these samples varied from 4 to 84 TU, and
microscopic examination showed iron rust and plankton to be present.
They concluded ". . .coliform bacteria were imbedded in particles
of turbidity and were probably never in contact with the active agent.
Viruses, being smaller than bacteria, are much more likely to
escape the action of chlorine in a natural water. Thus, it would be
essential to treat water by coagulation and filtration to nearly zero
turbidity if chlorination is to be effective as a viricidal process. "
(^
Hudson reanalyzed the data of Walton, above, relating them
to the hepatitis incidence for some of the cities that Walton studied.
1-3
-------
A summary of his analysis is shown in Table I.
TABLE 1
FILTERED-WATER QUALITY AND HEPATITIS INCIDENCE, 1953
Final
City
Average
Turbidity
TU
Chlorine
Residual
mg/1
Hepatitis
eases/100,
G
0. 15
0. 1
3. 0
C
0. 10
0. 3
4. 7
H
0. 25
0. 3
4. 9
B
0. 2
-
8. 6
M
0. 3
0. 4
31.0
A
1.0
0. 7
130
/ c j
Tracy, Camarena, and Wing noted that during 1963, in
San Francisco, California, 33 percent of all the coliform samples
showed 5 positive tubes, in spite of the presence of chlorine residual.
During the period of greatest coliform persistence, the turbidity of
this unfiltered supply was between 5 and 10 TU.
(7)
Finally, Robeck, Clarke, and Dostal showed that virus
penetration through a granular filter was accompanied by a break-
through of floe, as measured by an increase in effluent turbidity
above 0. 5 turbidity unit in a pilot unit seeded with an abnormally high
dose of virus.
These 7 studies show the importance of having a low turbidity
water prior to disinfection and entrance into the distribution system.
/ o\
2) The 1969 Community Water Supply Survey revealed
that unpleasant tastes and odors were among the most common
customer complaints. While organics and inorganics in finished
water do cause tastes and odors, these problems are often
1-4
-------
aggravated by the reaction of chlorine with foreign substances.
Maintenance of a low turbidity will permit disinfection with
less likelihood of increasing taste and odor problems.
3) Regrowth of microorganisms in a distribution system is
often stimulated if organic matter (food) is present. An example
(9)
of this possibility occurred in a Pittsburgh hospital. One
source of this food is turbidity created by algae and other
biological forms. Therefore, the maintenance of low turbidity
water will reduce the level of this microbial food and maintain
a cleanliness that will help prevent regrowth of bacteria and
the growth of other microorganisms.
4) The purpose of maintaining a chlorine residual in a
distribution system is to have a biocidal material present
throughout the system so that the consumer will be protected
if the integrity of the system is violated. Because the material
causing the turbidity can exert a chlorine demand, the
maintenance of a low turbidity water throughout the distribution
system will facilitate the provision of proper chlorine residual.
For these reasons, the approval limit (health) for turbidity
is one (1) Turbidity Unit (TU) as the water enters the distribution
system, although a properly operated water treatment plant
employing coagulants and granular filtration should consistently
produce a finished water with a turbidity of less than 0. 5 T. U."
The Public Advisers have suggested some changes be made in
this statement, but any re-write will probably still say essentially
the same thing.
Because of the change in the turbidity standard, some surface
sources may have to be managed in a slightly different way in order
1-5
-------
to meet the new limit. Filtration, for example, may have to be used
to remove most of the particulates. In that case, flocculants may
also be necessary and thus sludge will be formed and have to be
processed. Thus we would seem to be complicating the water
utility man's life while striving for a better quality product.
Although new problems are being formed, we think there are
various designs and operating procedures that will create far less
sludge than conventional treatment, so we have invited several
speakers here today to explain how they have been minimizing sludge
production or re-cycling to reduce disposal problems. We in the
Water Supply Research Laboratory of EPA have some ideas about
modified treatment, but we can bring these oat later during the
discussion period.
WASTE DISCHARGE REGULATIONS
The question of discharge permits has received increasing
interest as more water companies are being forced to confront
the problem of waste sludge and brine disposal. The fact is that
water plant wastes have been considered as industrial by many
states for many years. The entrance of the Federal government
into the permit program is fairly recent, and has not as yet been
fully felt by many industries, including water treatment plants.
The history of Federal involvement is rather interesting and
perhaps worthy of a few comments before discussing briefly the
Standards and Enforcement Section of Public Law 92-500 - "Federal
Water Pollution Control Act Amendments of 1972."
In 1966, in a case of the U.S. Government vs. Standard Oil,
the court ruled, in a case involving an oil spill, that oil in a river
1-6
-------
as a result of a spill is refuse. The Oil Company had contended
that it was a valuable product and should not be defined as waste.
Once it was defined as a refuse, it became subject to the 1899 Refuse
Act. .Section 13 of this ACT prohibits the discharge or deposit of
any waste in a waterway. The law authorizes the Chief of the Corps
of Engineers to grant permits for the discharge of waste that will
not be harmful, etc. Environmentalists immediately saw this as a
way to control the discharge of wastes to rivers and in 1970, EPA
was appointed as the technical advisor to the Corps of Engineers on
the issuance of these discharge permits.
There had been no federal permit system prior to 1970. Since
then very few permits have been issued because of the Kalur vs
Itesor case. In this case, the courts handed down a decision that
required an environmental impact statement to be issued before a
permit could be issued. This required that the Corps of Engineers
issue an environmental impact statement for each waste discharge.
This was an extremely difficult task, and the Corps of Engineers
was reluctant to start to issue many permits because its staff was
just not equal to it numerically. In addition, there was strong
evidence that pending water pollution legislation would override the
Kalur decision and release the Corps of Engineers of the responsi-
bility of both issuing permits and making environmental impact
statements.
So, during the period between the Kalur decision and the
passage of the 1972 Amendments to the Water Pollution Control Act,
the Federal permit program had been in a state of suspended
animation.
1-7
-------
An Act, cited as, "Federal Water Pollution Control Act
Amendments of 1972," was passed on October 18, 1972. It did
relieve the Corps of Engineers of regulatory responsibilities for
permit issuances and charged the Administrator of USEPA with
these responsibilities.
During this period, it should be remembered that the states
had their own water quality regulations, and many had permit
regulations that included all waste discharges, including water
treatment plant wastes. The states, as well as the Corps of
Engineers and EPA, were initially interested in the major dis-
charges, and in many instances, water treatment plants were not
included in this category. In some cases they were, and many
larger plants have been aware of these permit regulations for many
years. All will probably be aware of the regulations shortly.
FEDERAL STANDARDS AND PERMIT REGULATIONS
The 1972 law requires the issuance of permits for all
discharges to surface waters. There are no exceptions. Industries
that discharge to sewage collection systems are not included, except
that their wastes are implicit in the waste treatment plant permit.
The parts of the Act (Public Law 92-500)that are of most interest
are Title III - "Standards and Enforcement" and Title IV - "Permits
and Licenses." The specific sections are 301, 302, 307, 318, 402,
and 404. These sections are in the Appendix.
They are written with a lawyer's flair for prosaic verbosity.
What they say in summary is the following:
1. The discharge of any pollutant by anyone is unlawful,
with certain exceptions.
1-8
-------
2. By July 1, 1977, effluent limitations for point sources
must be achieved based on, "the best practicable control
technology currently available, " as defined by the EPA
Administrator. Limitations for publicly owned treatment
works will be based on secondary treatment, as defined
by the Administrator.
3. By July 1, 1983, limitations must be achieved based on
the "best available technology economically achievable, "
as determined by the Administrator for yet to be defined
categories and classes of industries - all to result in
reasonable progress toward the national goal of
eliminating all pollutants.
4. The Administrator is authorized to set water quality-
related effluent limitations following public hearings.
5. Requires the Administrator to set pretreatment standards
for introduction of pollutants into treatment works.
6. The Act provides for criminal penalties of from $2500
to $25, 000/day, or one year in prison, or both; double
these amounts for the second offense; and civil penalties
of up to $10, 000/day.
7. Requires essentially that all dischargers obtain a federal
permit, contingent upon attaining a certificate from state,
interstate agencies, or EPA, showing that they are in
compliance with the law.
8. The EPA Administrator is authorized to issue permits
for pollutant discharge under certain conditions; among
these is a compliance timetable.
1-9
-------
9. Authorizes EPA to approve state programs for conducting
their own permit programs.
10. Where state standards are more stringent than required
federal standards, the state standards will control.
EFFECTS ON SLUDGE DISPOSAL PROCEDURES
The Act applies to the discharge of any pollutant. In many
states, "pollutant" has come to embrace back-wash water as well as
sludge from settling and presettling reservoirs. This is to be
expected since state water quality standards are generally related
to effluent type standards that prohibit the degradation of the quality
of the surface water receiving the discharge.
The situation at Cincinnati may serve as an example of the
extremes that some utilities may have to go to. The water works
is embarking on a program that will eventually relieve the Ohio
River of the onus of any Cincinnati water plant waste discharge.
A $400, 000 pro ject that should be completed in three to four months,
will permit them to recycle the backwash water to presettling
reservoirs. Iron sludge that accumulates in the secondary settling
basins is recycled through the presettling reservoirs. About
once a year it is necessary to clean one of the two primary
settling reservoirs. This sludge is now returned to the Ohio River.
The prospect is that the water plant will be prohibited in the near
future from making these returns. As a solution, the water works
officials plan to construct a storage reservoir that will receive these
annual discharges from the settling reservoirs. The storage
reservoir is going to be built on part of a nearby golf course, and
the water works will acquire the land in early 1974. Following
construction of the reservoir, the water works will have no return
1-10
-------
discharge of any kind to the Ohio River, except perhaps the super-
natant from the sludge storage reservoir. There is some question
now as to whether this can be returned. It depends on the final
definition and EPA approval of a clause in the ORSANCO Standards
which requires "substantially complete removal of settleable solids,"
and "substantial reduction of suspended solids and also any other
material to such a degree that these materials will not affect the
turbidity, color, or odor of the River or impart taste or odor to
water supplies, or taint the fish." If it is ruled that the supernatant
cannot be discharged to the river, then it will probably be recycled
through the primary reservoirs. The ultimate disposal of the sludge
solids may have to be by centrifugation.
These statements and actions being taken by water
plants indicate that the handwriting is on the wall. They are shaped
by legislation, both federal and state. Special consideration will
probably be given to plants having particular problems, but over-all
it appears that there will be little or no return discharge to the
surface waters unless it meets the State's effluent standards.
Checking with the EPA Regional Office or State Pollution Control
Agency is, no doubt, the best way to acquire details that apply to
your own situation. We only hope that citing the new regulations
will help you to understand why the material to be presented in this
seminar plus the information already in the AWWA Journal is
important to you.
1-11
-------
Neefe, J. R., Baty, J. B., Reinhold, J. G., and Stokes, J.
"Inactivation of the virus of infectious hepatitis in
drinking water." Am. Jour, of Public Health, 37,
365-372 (Apr. 1947).
Chang, S. L., Woodward, R. L., arid Kabler, P. K.
"Survey of free-living nematodes and amoebas in
municipal supplies." Jour. AWWA, 52, 5, 613-618
(May 1960).
Walton, G. "Effectiveness of water treatment processes as
measured by coliform reduction." U. S, Dept. of
Health, Education, and Welfare, Public Health Service,
Publ. No. 898, 68 pp. (1961).
Sanderson, W. W. and Kelly, S. Discussion of "Human
enteric viruses in water; source, survival and
removability" by Clarke, N. A., Berg, G., Kabler,
P.K., and Chang, S. L. Internat. Conf. on Water
Poll. Res., 536-541, London, September 1962.
Pergamon Press. (1964).
Hudson, H. E., Jr. "High-quality water production and viral
disease." Jour. AWWA, 54, 10, 1265-1272 (Oct. 1962).
Tracy, H. W., Camarena, V. M., and Wing, F. "Coliform
persistence in highly chlorinated water. " Jour. AWWA,
58, 1151 (1966).
Robeck, G. G., Clarke, N. A., and Dostal, K, A.
"Effectiveness of water treatment processes in virus
removal." Jour. AWWA, 54, 1275-1290 (Oct. 1962).
McCabe* L. J., Symons, J. M., Lee, R, D., and
Robeck, G. G. "Survey of community water supply
systems," Jour. AWWA, 62, 670-687 (Nov. 1970).
Roueche, B. Annals of Medicine. Three sick babies. The
New Yorker, Oct. 5 (1968).
Kispert, Edward C., Private Communication, April 13, 1973.
1-12
-------
APPENDIX
1-13
-------
"TITLE III—ST.VXD.VUDS AXD EXFOUCEMENT
Pub. Law 92-500 "kffi.uext limitations October 18, 1972
"Sv.c. SOI. (a) Except as in compliance with this section and sec-
tions 302, 300, 307, 318, 402, mul 404 of this Act, the discharge of any
pollutant by a 113- person shall be unlawful.
"(b) I11 "order to carry out the objective of this Act there shall Ix.
achieved—
66 STAT. ,
"(1)(A) not later than July 1, 1077, efiluent limitations for
point sources, other than publicly owned treatment works, (i)
which shn.lt require the application of the best practicable control
technology currently available as defined by the Administrator
pursuant to section '104(b) of this Act, or (ii) in the case of a dis-
charge into a publicly owned treatment works which meets the
requirements of subparagraph ( B) of this paragraph, which shall
require compliance with any applicable pretreatment requirements
and any requirements under section 307 of this Act; and
"(B) for publicly owned treatment works in existence on
July 1, 1077, or approved pursuant to section 203 of this Act prior
to June 30,1974 (for which construction must be completed within
four years of approval), effluent limitations based upon secondary
treatment us defined by the Administrator pursuant to section
304(d) (1) of this Act; or,
"(C) not later than July 1, 1977, any more stringent limitation,
including those necessary to meet water quality standards, treat-
ment standards, or schedules of compliance, established pursuant
to any State law or refill at ions (under authority preserved by sec-
tion 510) or any other Federal hsw or regulation, or required to
implement nny applicable water quality standard established pur-
suant to this Act.
"(2) (A) not later than July 1, 1083. efiluent limitations for
categories and classes of point sources, other than publicly owned
treatment works, which (i) shall require application of the best
available technology economically achievable for such category
or class, which will result in reasonable further progress toward
the national goal of eliminating the discharge of all pollutants,
as determined in accordance, with regulations issued by the Admin-
istrator pursuant to section 304(b)(2) of this Act, which such
elltuent limitations shall require the elimination of discharges of
all pollutants if the Administrator finds, on the basis of informa-
tion available to him (including information developed pursuant
to section 315), that such elimination is technologically and eco-
nomically achievable for a categorv or class of point sources as
determined in accordance with regulations issued bv the Adminis-
trator pursuant to section 304(b) (2) of this Act. or (ii) in the case
of the introduction of a pollutant into a publicly owned treatment
works which meets the requirements of subparagraph (B) of this
paragraph, shall require compliance with any applicable pretreat-
ment requirements and any other requirement under section 307
of this Act; and
"(B) not later than Julv t, 1083, compliance by all publicly
owned treatment works with the requirements set forth in sec-
tion 201 (g) (2) (A) of this Act.
1-14
-------
"(c) The Administrator may modify the requirements of subsection
(b) (2) (A) of this section with respect to unv point source for which
a permit application is filed sifter July 1. 1977. upon a showing by the
owner or operator of such point source satisfactory to the Administra-
tor that such modified requirements (1) will represent the maximum
use of technology within the economic capability of the owner or
operator; and (2) will result in reasonable further progress toward
the elimination of the discharge of pollutants.
"(d) Any effluent limitation required by paragraph (2) of subsec-
tion (b) of this section shall be reviewed at least every five years and,
if appropriate, revised pursuant to the procedure established under
such paragraph.
"(e) Effluent limitations established pursuant to this section or sec-
tion 302 of this Act shall be applied to all point sources of discharge
of pollutants in accordance with the provisions of this Act.
66 STAT. 846
"(f) Notwithstanding any other provisions of this Act it shall be
unlawful to discharge any radiological, chemical, or biological war-
fare agent or high-level radioactive waste into the navigable waters.
"WAT Kit QUALITY liKl.ATH) EFFLUENT LIMITATIONS
"Sec. 30-2. (a) Whenever, in the judgment of the Administrator, dis-
clm rges of pollutants from a point source or group of point sources,
with the application of effluent limitations required under section 301
(b) (-2) of this Act. would interfere with the attainment or mainte-
nance of that wilt el- quality in a specific portion of the navigable waters
winch shall assure protection of public water supplies, agricultural
and industrial uses, and the protection and propagation of a balanced
population of shellfish, fisfi and wildlife, and allow' recreational activi-
ties in and on the water, effluent limitations (including alternative
eflluent control strategies) for such point source or sources shall be
established which can reasonably be expected to contribute to the,
attainment or maintenance of such water quality.
"(b) (1) Prior to establishment of any effluent limitation pursuant Public hearing,
to subsection (a) of this section, the Administrator shall issue notice
of intent to establish such limitation and within ninety days of such
notice hold a public hearing to determine the relationship of the eco-
nomic and social costs of achieving any such limitation or limitations,
including any economic or social dislocation in the affected community
or communities, to the social and economic benefits to be obtained
(including the attainment of the objective of this Act) and to deter-
mine whether or not such eflluent limitations can be implemented with
available technology or other alternative control strategies.
¦'('2) If a person affected by such limitation demonstrates at such
hearing that (whether or not such technology or other alternative con-
trol strategies are available) there is no reasonable relationship
between the economic and social costs and the benefits to be obtained
(including attainment of the objective of this Act), such limitation
shall not become effective and the Administrator shall adjust such
limitation as it applies to such person.
"(c) The establishment of eflluent limitations under this section shall
not, oiMM'ate to delay the application of any effluent limitation estab-
lished under sect ion :!D1 of this Act.
1-15
-------
''TOXIC ANI) l'HKTKKATMEN'f FITI.UKNT STANDARDS
"Svr.c. 307. (a) (1) Thy Administrator shall, within ninety days after
the date of enactment of this title. publish (and from time to time
thereafter revise") a list which includes any toxic pollutant or combina-
tion of such pollutants for which an effluent standard (which may
include a prohibition of the discharge of such pollutants or combina-
tion of such pollutants) will ho established under this section. The
Administrator in publishing such list shall take into account the toxic-
ity of the pollutant, its persistence, degradability.the usual or potential
presence of the affected organisms in any waters, the importance of
the affected organisms and the nature and extent of the effect of the
toxic pollutant on such organisms.
il('2) "Within one hundred and eighty days after the date of pub- Proposed
lication of any list, or revision thereof, containing toxic pollutants or effluent
combination of pollutants under paragraph (1) of this subsection, the standard.
Administrator, in accordance with section Soft of title o of the I'nited Publication.
States Code, shall publish a proposed effluent standard (or a prohibi- 80 Stat. 38 3.
tion) for such pollutant or combination of pollutants which shall take
into account the toxicity of the pollutant, its persistence, degradability,
86 STAT. B57
the usual or potential presence of the affected organisms in any
waters, the importance of the affected organisms and the nature and
Hearing. extent of the effect of the toxic pollutant on such organisms, and he
shall publish a notice for a public hearing on such proposed standard
to be held within thirty days. As soon as possible after such hearing,
but not later than six months after publication of the proposed effluent
standard (or prohibition), unless the Administrator finds, on the
record, that a modification of such proposed standard (or prohibition)
is justified based upon a preponderance of evidence adduced at such
hearings, such standard (or prohibition) shall be promulgated.
Revised '"(¦*) If after a public hearing the Administrator finds that a modi-
effluent fication of such proposed standard (or prohibition) is justified, a
standard. revised ellluent standard (or prohibition) for such pollutant or com-
bination of pollutants shall be promulgated immediately. Such stand-
ard (or prohibition) shall be reviewed and, if appropriate, revised at
least every three years.
"(4) Anv diluent standard promulgated under this section shall bo
at that level which the Administrator determines provides an ample
margin of safety.
"(5) When proposing or promulgating any effluent standard (or
prohibition) under this section, the Administrator shall designate the
category or categories of sources to which the elllnent standard (or
prohibition) shall apply. Any disposal of dredged material may be
included in such a category of sources after consultation with the
Secretary of the Army.
Efreotive "(6) Any ellluent standard (or prohibition) established pursuant to
date, this section shall take effect on such date or dates as specified in the
order promulgating such standard, but in no case more than one year
from the date of such promulgation.
"(7) Prior to publishing any regulations pursuant to this section
the Administrator shall, to the maximum extent practicable within
the time provided, consult with appropriate advisory committees,
States, independent experts, and Federal departments and agencies.
Pretreatment "(b)(1) The Administrator shall, within one hundred and eighty
standards, days after the date of enactment of this title and from time to time
proposed thereafter, publish proposed regulations establishing pretreatment
regulations, standards for introduction of pollutants into treatment works (as
publloatlon, defined in section 212 of this Act) which are, publicly owned for those
pollutants which are determined not to be susceptible to treatment by
such treatment works or which would interfere with the operation of
such treatment works. Not later than ninety days after such publica-
tion, and after opportunity for public hearing, the Administrator shall
1-16
-------
promulgate such pri'tieatinent standards. Pretmitnieiit standards
under this subsection shall specify a time for com pi in nee. not to exceed
three years from the date of promulgation and shall be established to
prevent the discharge of anv pollutant through treatment works (as
defined in section 212 of this Act) which are publicly owned, which
pollutant interferes with, passes through, or otherwise is incompatible
with such works.
"(2) The Administrator shall, from time to time, as control tech-
nology, processes, operating methods, or other alternatives change,
revise" such standards following the procedure established by this sub-
section for promulgation of such standards.
"(3) When proposing or promulgating nnv pretreatment standard
under this section, the Administrator shall designate the category or
categories of sources to which such standard shall apply.
"(4) Nothing in this subsection shall affect any pretreatment
requirement established by any State or local law not in conflict with
any pretreatment standard established under this subsection.
"(c) In order to insure that any source introducing pollutants into a
publicly owned treatment works, which source would be a new source
subject to section 300 if it were to discharge pollutants, will not cause a
violation of the ellluent limitations established for any such treatment
works, the Administrator shall promulgate pretreatment standards for
the category of such sources simultaneously with the promulgation of
standards of performance under section 300 for the equivalent category
of new sources. Such pretreatment standards shall prevent the dis-
charge of any pollutant into such treatment works, which pollutant
' ire with, pass through, or otherwise be incompatible with
"(d) After the effective date of any ellluent standard or prohibition
or pretreatment standard promulgated under this section, it shall be
unlawful for any owner or operator ol any source to operate any source
in violation of any such ctiluent standard or prohibition or pretreat-
ment standard.
"Sec. 318. (a) The Administrator is authorized, after public hear-
ings, to permit the discharge of a specific pollutant or pollutants under
controlled conditions associated with an approved aquacultnre proj-
ect under Federal or State supervision.
"(b) The Administrator shall by regulation, not later than Janu-
ary 1, 1974. establish anv procedures and guidelines ho deems neces-
sary to carry out this section.
"NATIONAL POU.CTANT D1SCHAHUE >',1.1 >11 NATION SYSTEM
"Sec. 402. (a) (1) Except as provided in sections 318 and 404 of this Permits,
Act, the Administrator may, after opportunity for public hearing, issuance,
issue, a pennit for the discharge of any pollutant, or combination of
pollutants, notwithstanding section 3<)i(u), upon condition that such
discharge will meet cither all applicable requirements under sections
301, 302. 306, 307, 308, and 403 of this Act, or prior to the taking of
necessary implementing actions relating to all such requirements, such
conditions as the Administrator determines arc necessary to carry out
the provisions of this Act.
66 STAT. 858
"aquacci.turk
1-17
-------
"(:!) The Administnitor shall prescribe conditions for such permits
to assure compliance with the requirements of paragraph (1) of this
subsection, including conditions on data mid information collection,
reporting njui such other requirements «s he deems Appropriate.
"(3) The permit program of the Administrator under paragraph
(1) of this subsection, and jjermits issued thereunder, shall be subject
to the same terms, conditions. am! requirements as npplv to a Statu
permit program and ]K'rniiIs issued thereunder under subsection (b)
of this sect-ion.
"(4) All permits for discharges into the navigable watoi-s issued
pursuant to section 1.'! of the, Act of March :i. 18!>!1. shall be deemed to 30 Stat, 1152,
be permits issued under this title, and Hermits is-ued under this title 33 LSC 407.
shall be deemed to be permits issued under section IS of the Act of
Mnrch 'i. 1K!)<). and shall continue in force and effect for their term
unless revoked, modified, or suspended in accordance with the pro-
visions of this Act,
"(5) No permit for a discharge, into the navigable waters shall be
issued under section 5:S of the Act of March 3, after the date of
enactment of this title. Knell application for a permit under section
111 of the Act of March ;i. 1K!)<), pending on the date of enactment of
this Act .shall be deemed to be ad application for a permit under this
section. The Administrator shall authorize a State, which he, deter-
mines has the capability of administering a permit program which
will carry out the object ive of this Act. to issue pennits for discharges
into the navigable waters within the jurisdiction of such State. The
Administrator may exercise the authority granted him bv the pre-
ceding sentence only during the period which begins on the date, of
enactment of this Act and ends either on the ninetieth day after the
date of the first promulgation of guidelines required by section .'Wit
{li) (-J) of this Act. or the date of approv al by the Administrator of
tl permit program for such State under subsection (b) of this sec-
tion. whichever date first occurs, and no such mithoriy.it'ion io a State
shall extend beyond the last day of such period. Each such permit
shall be subject to such conditions as the Administrator determines
all1, necessary to carry out the provisions of this Act. Xo such perm t
shall issue if the Admi uist rator objects to such issuance.
"(b) At any time after the promulgation of the guidelines reqni;od State pennit
by sui.r. f'tioti (h) (2) of section .'iO-t of this .Vet, tlie (ioventor of each progrv 3.
Slate. des'-ing to administer its own permit program for discharges
66 S'fAT. 931 __
into navigable waters within its jurisdiction may submit to the Admin-
istrator a full and complete description of the program it proposes
to establish and administer under State law or under an interstate
compact. In addition, such State shall submit ft statement from the
attorney general (or the attorney for those State water pollution con-
trol agencies which have independent legal counsel), or from the
chief legal officer in the, case of an interstate agency, that the laws
of such State, or the interstate compact, as the case may be, provide
Approval adequate authority to carry out the described program. The Admin-
oondltionu, istrator shall approve, each such submitted program unless he deter-
mines that ndcqniite authority does not exist:
*'(1) To issue permits which—
l" (A) apply, and insure compliance with, any applicable require-
ments of sections jiUl. 30-2, 30(5. ;507, and 40!i;
"(B) are for fixed terms not exceeding five years; nnd
"(C) cun be terminated or modified for cause including, but
not limited to, the following:
"(i) violation of any condition of the permit;
"(ii) obtaining a permit by misrepresentation, or failure
to disclose fully all relevant facts;
1-18
-------
" (iii) change in any condition that requires either a tempo-
rary or permanent. reduction or elimination of tlie permitted
discharge;
"(D) control the disposal of pollutants into wells;
"('2) (A) To issue permits which apply, and insure compliance with,
all applicable requirements of section ;$08 of this Act, or
li( It) To inspect, monitor, enter, and require reports to at least the
same extent as required in section :108 of this Act;
"(3) To insure that the public, and any other State the waters of
which may be atl'eeted. receive, notice of each application for a permit
and to provide an opportunity for public hearing before a ruling on
each such application;
" (4) To insure that the Administrator receives notice of each appli-
cation (including a copy thereof) for a permit;
"(5) To insure that nny State (other than the permitting State),
whose, waters may be atl'eeted by the issuance of a permit may submit
written recommendations to the permitting State (and the Adminis-
trator) with respect to any permit application and, if any part of
such written recommendations are not accepted by the. permitting
State, that the permitting State w ill notify such affected State, (and the
Administrator) in writing of its failure to so accept such recommenda-
tions together with its reasons for so doing;
"(0) To insure that no permit will be issued if, in the judgment
of the Secretary of the Army acting through the Chief of Engineers,
after consultation with the Secretary of the department in which the
Coast Guard is operating, anchorage and navigation of any of the
navigable waters would lie substantially impaired thereby;
"(7) To abate violations of the permit or the permit program,
including civil and criminal penalties and other ways and means of
enforcement;
"(8) To insure that any permit for a discharge from a publicly
owned treatment works includes conditions to require adequate notice
to the, permitting agency of (A) new introductions into such works
of pollutants from any source which would be ft new source as defined
in section liOti if such source were discharging pollutants, (11) new
introductions of pollutants into such works from a source which would
1)0 subject to section -501 if it were discharging such pollutants, or
(C) a substantial change in volume or character of pollutants being
introduced into such works by a source introducing pollutants into
86 STAT. BB2
such works at the time of issuance of the permit. Such notice shall
include information on the quality and quantity of etHuent to be
introduced into such treatment works and any anticipated impact of
such change in the quantity or quality of effluent to be discharged from
such publicly owned treatment works; and
"(0) To insure that any industrial user of any publicly owned
treatment works will comply with sections 201(b), 307, and 308.
"(c) (1) Not later than ninety days after the date on which a State
has submitted a program (or revision thereof) pursuant to subsec-
tion (b) of this section, the Administrator shall suspend the issuance
of permits under subsection (a) of this section as to those navigable
waters subject to such program unless ho determines that the State
permit jirogrnm does not meet the, requirements of sul»section (b) of
this section or docs not conform to the guidelines issued under section
304(h)(2) of this Act. If the Administrator so determines, he shall
notify the State of any revisions or modifications necessary to con-
form to such requirements or guidelines.
"(2) Any State permit program under this section shall at all
times be in accordance with this section and guidelines promulgated
pursuant to section 1104(h) (2) of this Act.
1-19
-------
86 STAT. 683
Publia
Information,
''(3) Whenever the Administrator determines after public hearing
that « State is not administering a program approv ed under this sec-
tion in accordance with requirements oi this section, he shall so notify
the State nnd, if appropriate corrective action is not taken within a
reasonable time, not to exceed ninety days, the Administrator shall
withdraw approval of such program. The Administrator shall not
withdraw approval of any such program unless he shall first have,
notified the State, and made public, in writing, the reasons for sue))
withdrawal.
"(d) (J) Kucli State shall transmit to the Administrator a copy of
each permit application received by audi State and provide notice to
the Administrator of every action related to the consideration of sncli
permit application, including each permit proposed to be issued by
such State.
"(2) No permit shall issue (A) if the Administrator within ninety
days of the date of his notification under subsection (b)(5) of this
section objects in writing to the. issuance of such permit, or (B) if
the. Administrator wit hin ninety days of the. date of transmittal of the
proposed permit by the State objects in writing lo the issuance of
such permit its being outside the guidelines and requirements of this
Act.
"(3) The Administrator may, as to any permit application, waive
paragraph ('2) of this subsection.
"(e) In accordance with guidelines promulgated pursuant to sub-
section (h) (2) o{ section "04 of this Act, the Administrator is author-
ized to waive the requirements of subsection (d) of this section at
the time lie approves a program pursuant to-subsection (h) of this
section for any category (including any class, type, or size within such
category) of jx>int sources within the State submitting such program.
"(f) The Administrator shall promulgate regulations establishing
categories of point sources which lie determines shall not be subject to
the requirements of subsection (d) of this section in any State with a
program approved pursuant to subsection (b) of this section. The
Administrator may distinguish among classes, types, and sizes within
apy category of point sources.
ft(g$ Any permit issued under this section for the discharge of pol-
lutants into the navigable waters from a vessel or other floating craft
shall be subject, to any applicable regulations promulgated bv the
Secretary of the department in which the Coast Guard is operating,
request for the purpose of reproduct ion,
"(k) Compliance with a. permit issued
State peimit
program,
approval
withdrawal.
Administrator,
notifioatl&n.
Waiver
authority.
Point aouroes,
DS.tegorieB,
establishing specifications for safe transportation, handling, carriage,
storage, and stowage of pollutants.
"(h) In the event any condition of a permit for discharges from a.
treatment works (as defined in section 212 of this Act) which is
publicly owned is violated, a State with a program approved under
subsection (b) of this section or the Administrator, where no State
program is approved, may proceed in a court of competent jurisdiction
to restrict or prohibit the introduction of any pollutant into euch
treatment works by a source not utilizing such treatment works prior
to the finding that such condition was violated.
" (i) Nothing -in this section shall be construed to limit the author-
ity of the Administrator to take action pursuant to section 309 of this
Act.
"(j) A copy of each permit application nnd each permit issued
under this section shall be available to the public. Such permit appli-
cation or permit, or portion thereof, shall further be available on
pursuant to this section shall
be deemed compliance, for purposes of sections 309 and 505, with sec-
tions 301, 302, 306, 307, and 403. except any standard imposed under
section 307 for a toxic pollutant injurious to human health. Until
1-20
-------
December 31,1074, in any case where a. permit for discharge has been
applied for pursuant to t>)iis section, but final administrative disposition
of such application hns not been made, such discharge shall not be a
violation of (1) section 301, ,106, or 40'2 of this Act, or (2) section 13
stat. 1152. of the Act of March 3, 189!), unless the Administrator or-other plain-
use 407. tiff proves that final administrative disposition of such application has
not Wen made because, of the failure ot the applicant to furnish infor-
mation reasonably required or requested in order to process the Applica-
tion. For the 180-day period beginning on the date of enactment of the
te, p. 816. Federal \Vtiter Pollution Control Act Amendments of 1972, in the case
of any point source discharging any pollutant or combination of pol-
lutants immediately prior to such date of enactment which source 13
not subject to sectio"n 13 of the Act of March 3, 1899, the discharge by
such source shall not be a violation of this Act if such a source applies
for a permit for discharge pursuant- to this section within such 180-day
period.
"permits fob dredged or fill jtaterial
"Sec. 404. (a) The Secretary of the Army, acting through the Chief No*1'*! hearing
of Engineers, may issue permits, after notice and opportunity for opportunity,
public nearings for the discharge of dredged or fill material into the
navigable waters at specified disposal sites.
"(d) Subject to subsection (c) of this section, each such disposal
si to shall bo specified for each such permit by the Secretary of the Army
(1) through the application of guidelines developed by the Adminis-
trator, in conjunction with the Secretary of the Army, which guide-
lines shall be based ujktn criteria comparable to the criteria applicable
to the territorial seas, tlwcontiguous zone, and the ocean under section
403(c), and (2) in anv case where such guidelines under clause (1)
alone would prohibit the specification of a site, through the applica-
tion additionally of the economic impact of the site on navigation and
anchorage.
"(c) The Administrator is authorized to prohibit the specification
(including tho withdrawal of specification) of any defined area as a
disposal site, and he ia authorized to deny or restrict the use of any
defined area for specification (including the withdrawal of specifica-
tion) ns a disposal site, whenever he determines, after notice ana oppor-
tunity for public hearings, that tho discharge of such materials into
such area will have an unacceptable adverse effect on municipal water
supplies, shellfish beds and fishery areas (including spawning and
brooding aveas), wildlife, or recreational areas. Before making such
determination, the Administrator shall consult with the Secretary of
the Army. The Administrator shall set forth in writing and make Pi ridings of
public his findings and his reasons for making any determination Administrator,
under this subsection. publioation.
Disposal slt«j
speolfioation
prohibition*
1-21
-------
USE OF ORGANIC POLYMERS AND SLUDGE VOLUME REDUCTION
by
Lee Streicher
Water Purification Engineer
The Metropolitan Water District of So. Calif.
Los Angeles, California
Disposal of sludge or other process wastes has
always been a part of water treatment plant operation.
Ten or 20 years ago, however, it was more of a nuisance
than a problem as most treatment plants returned the
sludge to their source of water supply, whether river or
lake, downstream or distant from the treatment plant
intake so that it did not interfere with their plant
operation. This was a very simple and inexpensive way to
dispose of the sludge, and was used by 92 percent of the
water treatment plants surveyed in 1953; Table 1.
In recent years, and particularly since
pollution control and protection of our environment have
become subjects for almost daily discussion in newspapers
and at public meetings, various state and local government
agencies have passed regulations to control the discharge
of potential pollutants into natural bodies of water or
watercourses. Public Law 92-500, enacted in October 1972
as an amendment to the Federal Water Pollution Control
Act, prohibits the discharge of pollutants into a
waterway unless such discharge is authorized by a permit
issued by the U.S. Environmental Agency or by an approved
State Agency. Under these various regulations, sludge
disposal is becoming a problem rather than the nuisance
it was just a few years ago.
Il-l
-------
What, then, can be done to ease the burden of
this problem? Several approaches to a solution can be
considered. First, methods of treatment which might
reduce the quantity of sludge produced should be
investigated. If clarification without softening is
required, the recently developed organic polymers may
assist in the attainment of this goal. These polymers are
long-chain, high-molecular-weight organic chemicals that
are available in three types: (a) cationic, or positively
charged; (b) anionic, or negatively charged; and
(c) nonionic, or neutral in charge. As the suspended
matter found in natural waters is usually negatively
charged, the cationic polymers are generally the type
most suitable for use as primary coagulants. If the
suspended matter is of such a nature that these polymers
can be used successfully as primary coagulants, the
dosage required will probably fall within the range of
0.5 to 2.0 ppm. Compared with a dosage of 15 to 30 ppm
or more of alum that might be required to achieve
comparable clarification of the same water, the reduction
in the quantity of sludge produced as a result of polymer
use can be quite significant. Furthermore, unlike the
gelatinous and voluminous aluminum hydroxide sludges, the
polymer sludges are relatively dense and easier to
dewater for subsequent handling and disposal. Although
the unit cost of the cationic polymers is 10 to 15 times
higher than the cost of alum, the dosages required for
treatment are reduced by an even greater ratio, so the
11-2
-------
actual cost of chemicals for coagulation is less with
polymers than with alum.
It is important to point out that not all waters
can be treated with equal success with the same polymer —
or the same dosages. Jar tests should be run with several
different dosages of the various polymers available to
determine the specific material and range of dosages best
suited for each water supply. In addition, for treatment
of potable waters, only the polymers approved by the EPA
for use in such water treatment should be considered.
Even though a cationic polymer alone can, at
times, produce a strong and readily settleable floe, at
other times the floe may be weaker and less dense. A
nonionic polymer may be helpful under these conditions
as a coagulant aid. The nonionic polymer may act as a
bridging material between fine particles of coagulated
material, causing them to agglomerate into larger and
stronger floe that will settle more readily and also be
more easily filtered from the water. The dosage required
to aid coagulation is about 0.1 to 0.25 ppm, so very
little is added to the quantity of sludge produced.
The cationic and nonionic polymers also appear
to be effective as filter aids. In this application they
appear to bridge between the fine particles carried over
from the settling basins and produce a larger, and more
readily filterable material. In fact, these materials
may be very effective filter aids even with a water that
has not been previously coagulated and flocculated.
II-3
-------
Thus, if a natural water of moderately low turbidity (say
less than 5 JTU) is to be clarified and coagulation is not
mandatory, it may be possible to produce a high quality
filtered water simply by using a polymer as a filter aid.
The dosage required may range from about 10 to 30 parts
per billion if a nonionic polymer is used, or from 30
to 90 ppb if a cationic polymer is used. Obviously,
elimination of the prior coagulation and flocculation
will further reduce the quantity of sludge produced for
disposal, thereby limiting it to essentially the suspended
matter removed from the water.
Occasionally, with changes in the quantity and
character of the suspended matter in a water supply, the
usual range of dosages of the normally successful cationic
polymer, even with the help of a nonionic coagulant aid,
may fail to produce a good floe. It has been found that
a very low dosage (about 4 ppm) of alum used in
conjunction with the polymers may promote satisfactory
flocculation. Although this results in an increase in
the quantity of sludge produced and to some degree
introduces the undesirable characteristics of aluminum
hydroxide, the quantity is still substantially less than
if 20 to 30 ppm of alum were used instead, and the alum-
polymer sludge is still easier to handle and dewater than
the alum sludge alone.
Jar tests have indicated that a properly
conditioned polymer sludge, when recirculated to the raw
water channel to increase the suspended solids prior to
II-4
-------
coagulation, can improve floe formation and clarification.
For these tests, the sludge was conditioned by thorough
agitation with about 50 ppm of cationic polymer. This
made the sludge very dense and strong, and so heavy that
it settled almost immediately when agitation was stopped.
When enough conditioned sludge was added to the raw water
to produce a turbidity of about 100 JTU, the floe formed
following coagulation was much denser and the clarifica-
tion of the water more complete than when no recirculated
sludge was used. This proved to be the case even when the
dosage of cationic polymer used for primary coagulation
was reduced from 1.0 or 1.5 ppm to 0.5 ppm. At the time
of writing, this recirculation had not yet been tried on
a full plant scale but work has been started for such a
test in the relatively near future.
No matter what treatment methods or chemicals
are used, if suspended matter has been removed from the
water some sludge residue is left for ultimate disposal.
As discharge to waterways has been or is being phased out,
other methods must be considered. Sludge lagoons will
continue to be used as long as land is available at
moderate cost within a reasonable distance of the
treatment plant. Landfill operations, too, will accept
properly prepared sludge materials. Sewer systems may
accept some sludges, but this merely shifts the burden
for subsequent handling and ultimate disposal from the
water treatment plant to the wastewater treatment plant.
Polymer sludges are also suitable for use as soil
II-5
-------
conditioners, which would be a desirable disposal method
if a demand for such use could be developed.
Incineration would appear to be a very practical
way of reducing the quantity of sludge to an absolute
minimum for ultimate disposal. This method is used with
some sewage sludges, and it should be applicable to some
water treatment plant sludges as well. If the suspended
solids removed from the water are predominantly organic
matter, and polymers are used for coagulation, then the
sludge cake produced may be readily combustible provided
that it is adequately dewatered. The ash remaining after
incineration will represent only 5 to 10 percent of the
original quantity of sludge. Furthermore, the ash should
be easy to handle, it would not be subject to decompo-
sition when applied to a landfill operation, and it may
possibly be suitable for use as a filter aid (instead of
diatomaceous earth) if needed during dewatering of the
sludge prior to incineration.
On the other hand, alum sludges and softening
plant sludges are not well suited for incineration, as
they are primarily non-combustible mineral matter and
would permit very little volume reduction. Furthermore,
the fuel requirement for these sludges would be much
higher than for organic sludges.
From the foregoing, it would appear that the
use of the right polymers at the right dosages could help
in the production of better water, perhaps even with a
saving in chemical costs, and result in a substantial
II-6
-------
reduction in the amount of sludge (and an improvement in
the character of the sludge) produced for disposal.
Unfortunately, however, some treatment plants have been
unable to find a polymer or combination of polymers
that would provide effective clarification with their
waters. Until new polymers which can perform satisfac-
torily with those waters are developed, those plants will
continue to use alum (or, in some cases, iron salts) for
coagulation. What can they do to relieve their sludge
disposal problems?
A reduction in the volume of sludge produced
may be attainable if polymers can be used' as coagulation
aids. It was mentioned eaflier that during times when
polymers alone failed to produce a good floe, the addition
of 4 ppm of alum helped to solve the immediate problem.
In the same manner, the addition of 0,2 to 1.5 ppm of
polymers may permit a substantial reduction in the alum
dosage required to achieve satisfactory flocculation.
This reduction in alum dosage will, of course, be
reflected in a reduction in the quantity of sludge
produced.
But what if polymers are not helpful in the
treatment of certain waters and higher dosages of alum
must be used to obtain satisfactory clarification? If
tests confirm the economic feasibility, recovery of alum
or sodium aluminate from the aluminum hydroxide sludge
might deserve consideration. Alum recovery is not
practiced very widely and, where it is, the efficiency of
II-7
-------
recovery appears to be only about 60 percent. In
addition, if heavy metals are present, they will build up
in concentration with each alum recovery operation. These
factors have tended to discourage wider use of alum
recovery from aluminum hydroxide sludge. Figure 1 shows
a flow diagram of a typical alum recovery system, and
Figure 2 shows a flow diagram of a modified recovery
system which, in small pilot plant tests, yielded 80 to
93 percent recoveries of filtered alum. The modified
system also requires less equipment, less lime (or calcium
carbonate) for pH adjustment of the sludge cake left after
filtration, and leaves less residue for ultimate disposal.
Further tests of this system might be warranted to
investigate its economic feasibility.
An alkaline recovery system (using sodium
hydroxide rather than sulfuric acid) has also been tried
experimentally. This results in the recovery of sodium
aluminate instead of alum. As the heavy metal hydroxides
are not redissolved at the high pH levels maintained in
this recovery process, there is no continuous build-up of
these contaminants. However, the sodium aluminate alone
is not a good primary coagulant, so alum, carbon dioxide,
or other acidic material must be used with it to achieve
proper coagulation.
These recovery processes will, or course,
reduce the quantity of sludge left for ultimate disposal.
On the other hand, if alum or sodium aluminate recovery
is not practicable, other methods for reducing the sludge
II-8
-------
disposal problem should be considered. Alum sludge is
very gelatinous and difficult to dewater, so it is not as
suitable for lagooning as other sludges are. Here, again,
polymers may be useful, in this instance as sludge
conditioning agents to aid in the dewatering process.
Drying beds, if used, must be shallow to permit cracking
to the bottom of the sludge layer; otherwise the bottom
material will remain wet for a long time. Discharge into
a sewer system is a very simple means for disposal, but
some sewage plants are reluctant to accept such sludge
because when it is mixed with sewage sludge the mixture
is much more difficult to dewater than sewage sludge alone
and this, coupled with the voluminous nature of the alum
sludge, tends to tax their digester capacity. Alum sludge
is also less suited for landfill disposal because of its
failure to compress into a hard, dense fill.
Freezing and thawing may be the best way to
reduce the quantity and improve the characteristics of
an alum sludge, particularly if climatic conditions
permit natural freezing. In this process the alum sludge
is first thickened to about 3.5 to 4 percent solids and
then slowly frozen. The ice crystals formed squeeze the
water from the sludge and compress the particles to about
one-sixth of their original volume. The process is
irreversible and, when thawed, the particles are like a
brown powder or sand. These granules could be used as
soil conditioners, or, possibly, as fillers in some
commercial products, but it is questionable whether a
II-9
-------
sufficient demand for this material could be developed.
However, disposal of the greatly reduced volume and
easier to handle sand-like residue would be much easier
than disposal of the original alum sludge.
If softening, rather than just clarification,
is desired in the treatment process, then the sludge
produced will be either calcium carbonate or a mixture of
calcium carbonate and aluminum hydroxide when lime or
lime-soda ash softening is used. Calcium carbonate forms
a dense, granular sludge which is easy to dewater and
quite easy to handle. Magnesium hydroxide, like aluminum
hydroxide, is voluminous and difficult to dewater. With
any substantial degree of softening a great volume of
sludge is produced.
In the operation of large treatment plants,
recovery of lime from calcium carbonate sludge may be
practicable. Table 2 lists a number of plants in the
U.S. where lime recovery is practiced. If the sludge
contains a mixture of calcium carbonate and magnesium
hydroxide, the two can be separated by centrifugation.
(Or the process to be described later today by Kinman
and Thompson may be applicable.) By passing through the
steps of thickening, dewatering, flash drying, and
calcination, the calcium carbonate sludge can be converted
to lime. Generally, about 50 percent more lime can be
recovered than was used in the treatment process, if a
market can be found for this surplus lime, part of the
cost of the reclamation process can be recovered.
11-10
-------
If the sludge is dried by not recalcined, it
may be suitable for soil conditioning. If it is also low
in organic matter, it could be used for road stabilization,
neutralization of acid wastes, as a filler in rubber or
other products, or possibly as a pigment in whitewash
paints. If no use is found for the sludge, it can be much
more easily dewatered and handled than alum sludge and
thus is suitable for lagooning or for landfill disposal.
It has been suggested that the sludge could assist in
phosphate removal during sewage treatment, so that
discharge into a sewer might be acceptable, but some
sewage treatment plants have reported that the sludge
interfered with anaerobic digestion or that it plugged
the digesters.
As mentioned earlier, unlike polymer sludges
neither alum nor lime sludges are suited to incineration
for volume reduction, so either recovery of treatment
chemicals or application to other beneficial uses must
be relied upon if the quantity of sludge left for
ultimate disposal is to be reduced. Therefore, it
appears that at this time the use of polymers, if
applicable, will result in the production of minimal
quantities of sludge or residue for final disposal.
11-11
-------
TABLE 1
Methods for Disposal of Water Treatment Plant Sludges
Point of
Disposal
Percent of Plants Using Indicated Disposal Methods
Softening
(Lime) Sludge
1953*
1969
Coagulation
(Alum) Sludge
1953*
1969
Stream or lake
Sewer or drain
Dry Creek
Landfill
Lagoons
Recycled
92
4
1
0
3
39
6
11
11
33
92
4
1
0
3
49
21
6
6
18
* No distinction made between lime and alum sludges.
Note: 1953 based upon responses from about 1,600 plants: 1969 data
based upon responses from about 80 plants (mainly large plants).
-------
TABLE 2
Recalcination Plants
Location
Water Plant Lime Sludge-
Construction Type of Capacity Type of Capacity Feed to-Lime
Date Fumace(l) ton/day Dewatering(2) mgd Ib/mg Ratio
Plant
Cost(3]
$10*
M
M
I
M
U>
Miami, Fla, 1948
Lansing, Mich. 1954
Dayton, Ohio 1960
San Diego, Calif. 1961
S.D. Warren Company
Muskegon, Mich. 1963
Ann Arbor, Mich. 1968
St. Paul, Minn. 1969
RK
FB
RK
RK
FB
FB
FB
SO
30
150
25
70
24
SO
c
c
c
c
VF
c
c
60
20
96
1,800
2,200
2,460
2.27
2.5
793
1,500
534
100
992
2.4
1,750
(1) RK = rotary kiln; FB = fluidized-bed incinerator.
(2) C = centrifuge: VF = vacuum filter.
(3) Construction cost at date of construction.
-------
Figure 1
Flow Diagram of Typical Alum Recovery Installation
Sulfuric Acid
Lime and Sludge Mixing
Acta ir
Sludge i—j ' i—i
Mixing \_J \_J
M
laked Lime
Thickeners
Sludge from
Settling Basins
Filter C
Sludge
Receiving
Basin
Recla j Tied
Alum Tanks
o>
Trucked away to c
To poJntr. of
alum application site for disposal
-------
Figure 2
Flow Diagram of Experimental Alum Recovery Installation
^^_£uifuric Acid
Acid and Sludge
Mixing
Powdered
Lime
Pressure
FiIters
M
i
f—1
Filter Cake
Sludge from
Settling Basins
Pug
Mill
Neutralised cake
To points of
Reclaimed aluia application hauled to dur.o site
Alum for disposal
-------
HIGH ENERGY MIXING AND FLOCCULATIQN
By
James H. Sullivan, Jr.*, Herbert L. Kaufman**, Wayne Eakins***
In water treatment plant operations we are always looking
at ways to provide the customer with the highest quality product at
the lowest possible price.
In conventional coagulation plants a significant portion
of the capital and operating cost is in the settling basins. Attempts
to accomplish savings here have taken the form of minimizing the
size consistent with the settling characteristics of the floe produced
and/or the utilization of tube settlers. Both these concepts are
consistent with the basic assumption that the floe volume after rapid
mix and flocculation is sufficiently large to require a separation by
gravity sedimentation prior to filtration.
In recent years this basic assumption has been challenged
at at least two points. First, the advent of organic polyelectrolytes
offered the ability to reduce the absolute amount of coagulant re-
quired to produce a comparable amount of destabilization of colloidal
particles by an order of magnitude or more. This correspondingly
resulted in a decrease in total floe volume.
~Vice President, Water and Air Research,Inc., Gainesville, Florida
**Partner, Clinton Bogert Associates, Fort Lee, New Jersey
***Principal Associate, Clinton Bogert Associates,Fort Lee, New Jersey
iii-i
-------
(1 2)
The second challenge grew out of the work of Camp ' 'in which
he suggested that by proper regulation of rapid mixing conditions floe
density could be greatly increased. Camp spoke in terms of floe volume
concentration in which lower values correspond to more dense material.
Using alum and ferric sulfate he demonstrated floe volumes ranging from
less than 50 to over 700 vpm. Floe volumes were determined by visual
examination under a 40 power microscope.
Both these developments suggested that compact floe particles
could be produced. If they could be maintained in this condition it
might be possible to eliminate the sedimentation process altogether and
go directly to filtration. Such floe would penetrate into the filter
bed rather than create a blinding layer on the filter surface. Because
of its small size it might be possible to store a considerable amount
of material in the filter thereby achieving practical filter run
durations.
To be effective in reducing the volume of waste sludge, still yet
another criteria would have to be met. That is, the floe so produced
and removed by the filter must remain 1n a compact condition through
the filter backwash process and settle in a short time to a relatively
high solids concentration. That is the point we are dealing with in
this seminar. Is the final volume of floe to be disposed of reduced by
utilizing the direct filtration process?
For comparison purposes we should examine what happens in a
conventional plant. In reviewing both his own work as well as that
III-2
-------
(3)
of others, Hudson concluded that floe volumes entering a settling basin
are in the range of 2,000 to 7,000 vpm. However, upon settling, the floe
begins to compact and the floe volume decreases. Neubauer^ has reported
values of 1,230 and 2,660 vpm for waste sludge from upflow clarifiers. How-
ever, it was also noted that this sludge was "readily settleable" to floe
volumes of 520 and 1,140 respectively.
Data from plants having settling basins that waste sludge on a batch
basis have reported sludge volumes ranging from 200 to 26,000 vpm. Other
sources^ report only the solids content of the waste sludge. Typical
values range from slightly less than one percent solids up to five percent
or even higher. These are values in the settled sludge mass however and
do not represent the concentration which will result when the basin is
taken out of service and cleaned. When this occurs the overlying water as
well as the settled sludge is wasted together and the resultant sludge
concentration 1s lower. Even so, it is likely that the average sludge
volume actually wasted 1s less on a volume per volume of raw water basis
than the sludge volumes continuously wasted from upflow clarifiers. How-
ever, batch operations suffer in that the waste occurs in slugs which can
make ultimate disposal more troublesome.
Filter backwash water in conventional plants contains a small
fraction of the total solids load but can present disposal problems due to
high solids content.
Against this background let us consider the comparable conditions if
the direct filtration process is utilized. This past summer and fall we
III-3
-------
evaluated the direct filtration process for use by the City of Lynn,
Massachusetts. The characteristics of the raw water are shown in
Table 1. In addition to the obvious potential problems with color,
turbidity, iron, and manganese the water has from time to time strong
taste and odor.
A pilot plant was constructed and operated at Lynn inter-
mittently from August 1972 to April 1973. Raw water temperature
ranged from 3 to 20° C. A total of 76 filter runs were made.
A schematic of the pilot plant is shown in Figure 1. As
can be seen, the pilot plant consisted of up to four stages of rapid
mix with an average detention time per stage of 0.77 minutes. The
flocculators which followed could be either bypassed, operated as a
single unit, or operated as two units in series. The small holding
basin prior to the filters simulated the retention of water that
occurs above the actual filter bed iri a full-scale filter.
Table 1
Typical Raw Water Quality at Lynn, Mass.
Turbidity 1 - 3
Color 35 - 50
pH 7.1-7.3
Alkalinity,mg/l as CaCO^ 15 - 25
Hardness, mg/1 as CaCC^ 45 - 55
Iron, mg/1 0,15
Manganese, mg/1 0.05
III-4
-------
Constant
Head
Standpipe
Alum
Backwash
'lJr^n
Waste
Chlorine
Polymer
Lime
\
I
f
I
| Raw
i Water
~ t±
J—J J L_ L__
Rapid Mix Basins
(may be by-passed)
Pump
r~i
Flocculators
(may be by-passed)
Filter
Holding
Basin
Filtered
Water
Tank
Backwash
Pump
Scale: None
Figure 1. Pilot Plant Set-up
-------
The filters consisted of 6 inch diameter plexiglass tubes, with
appropriate connections for measuring head loss to various depths in the
bed. The early work was all done with dual-media anthracite-sand beds.
Both declining rate and constant rate modes of operation were utilized.
In the latter portion of the study a three media filter was operated in
parallel with one of the dual media units.
The goals selected for finished water quality were less than 0.2
FTU turbidity (preferably less than 0.1 FTU) and color less than 5 units.
These goals are considerably more stringent than the 1962 U. S. Public
Health Service standards of 5 turbidity and 15 color and are only slightly
less stringent than the AWWA goals of 0.1 and 3 respectively.
Alum was used as the primary coagulant throughout the study. How-
ever, it was found to prevent breakthrough of color and turbidity, the
addition of a small amount of a non-ionic polyelectrolyte as a filter aid
was required. With 30 mg/1 of alum, a pol.yelectro7yte dose of about 0.05
to 0.25 mg/1 was found to be sufficient. Increasing the dosage of the
non-ionic polyelectrolyte allowed no significant decrease in alum dosage.
Filter runs were in the range of 5-10 hours depending on the filter
operating conditions. Allowing for backwash water and backwash time, the
most productive mode of operation was to operate declining rate beginning
at 6 gpm/ft , Table 2 shows the relative amounts of water produced under
four modes of operation. It may be significant that higher filtration
rates produced more water per run, at no deterioration in quality, although
the runs were shorter.
III-6
-------
Table 2
Comparison of Productivity of Filters
Under Different Modes of Operation
Rate
Type Operation gpm/ft
Filter Run Length
hrs.
ApproximateProduction
qpd/ft2
Declining rate 6-3
Constant rate 4
6 - 8
5 - 8
6,000
5,300
Declining rate 5-2
Constant rate 3
10 - 11
9 - 10
4,100
4,700
Prechlorination at 4 mg/1 was found to be an effective aid in color
and taste and odor removal. When ozone was substituted for the chlorine,
objectional taste was present in the filtered water, possibly due to re-
action between ozone and the polymer used.
Limited testing revealed that a cationic polymer may be effective
in reducing the amount of alum required. Design of the plant will permit
utilization of both alum and polymers.
Floe volumes within a filter can be estimated by the procedure sug-
gested by Hudson. The procedure is based on Kozeny-Fair-Hatch equation
which relates hydraulic gradient or head loss to filter bed porosity.
o Pt3
^ = head loss at time t
iQ = head loss at time zero
pt = porosity of bed at time t
K = constant
III-7
-------
The constant K is evaluated from the known porosity of the bed at time
zero. If the filtration rate is not constant a correction factor must be
applied to the head loss, i^. This can be done by multiplying i^. by the
ratio of the initial filter rate to the filter rate at time t. The
decrease in apparent porosity of the bed with time can be assumed to be
due to floe accumulation. This floe volume can in turn be related to the
total water filtered and expressed as floe volume per unit quantity of
treated water, usually volumes per million volumes. An obvious short-
coming of this procedure is that the head loss through the filter is
related to the apparent rather than actual porosity of the filter. Hence,
if flow to certain channels in the filter is blocked at the channel entrance
the head loss increase is the same as if the entire channel were filled with
floe. This means that the actual floe volume contained in the filter is
generally somewhat less than calculated by this procedure.
In analyzing the pilot plant data it was found that floe volumes
(vpm) calculated by this procedure generally decreased as the filter runs
progressed. Average values for the filter runs, based on terminal head
loss conditions, ranged from 1,500 to 2,500 vpm. This indicates that the
actual floe volume in the filter bed is significantly more than what Camp
indicated might be produced by high energy mixing. Several factors could
explain this. First the floe density is being measured by two entirely
different means, neither of which has been conclusively verified. Second,
the floe may be small and dense as it enters the filter but may agglomerate
as the filter run proceeds, and water may be entrapped in the process.
III-8
-------
There was visual indication of floe agglomeration in that, as the
filter runs progressed, floe grew from barely visible particles in the
applied water to readily discernible size within the bed and on the
filter bed surface. Also there were large floes in the filter backwash
water.
Let us assume that these figures are reasonably accurate and that
the floe is considerably less dense in the filter bed than when it left
the rapid mix or flocculators. The next question then is, what is the
floe density after backwashing? Although careful measurements were not
made on all runs, it was repeatedly observed that, in general, the floe
in the backwash water settled to a volume of 1 gallon in 1 hour and to
0.5 gallons after standing overnight. Total water filtered per run ranged
from less than 300 gallons on poor runs to about 450 gallons on the best
run. Assuming 375 gallons filtered, a 0.5 gallon settled sludge volume
would convert to 1,335 vpm. This figure is roughly the same as reported
for settled sludge from upflow clarifiers and within the range of values
reported for batch operated settling basins. Hence, although the direct
filtration process using alum offers a number of advantages, the volume
of sludge that must ultimately be disposed of is essentially the same as
can be expected in a conventional plant.
It should be noted that these results are based on work where alum
doses in the order of 30 to 45 mg/1 were required in order to accomplish
color removal. If a significant amount of this alum can be replaced with
a polyelectrolyte, an increase in filter run length and a decrease in floe
volume might occur. The problem to date has been that we have not found a
polyelectrolyte that is really effective in removing color.
III-9
-------
Acknowledgement
The authors gratefully acknowledge the work and efforts of Mr. Alonso
Gutierrez in operating the pilot plant.
References
1. Camp, T. R., "Floe Volume Concentration", Jour. AWWA, 60:656 (June, 1968)
2. Camp, T. R. and Conklin, G. F., "Towards a Rational Jar Test for Coagu-
lation", J. NEWWA, 84:325 (Sept. 1970)
3. Hudson, H. E., Jr., "Physical Aspects of Filtration", Jour. AWWA,
61:3 (Jan. 1969)
4. Neubauer, W. K., "Waste Alum Sludge Treatment"» Jour. AWWA, 60:819
5. Gates, C. D. and McDermott, R. F., "Characterization and Condition of
Water Treatment Plant Sludge", Jour. AWWA, 60:331 (Mar. 1968)
III-IO
-------
REDUCING WATER PLANT SLUDGE BY DIRECT
FILTRATION AND OXIDATION-
Richard L. Woodward**
Direct Filtration
There has been a considerable increase in interest in direct
filtration of water in recent years and it is likely to continue. A
large number of surface water supplies now being used in this
country are troubled by occasional quality problems due to turbidity,
color or plankton growths and direct filtration may provide a more
economical method of treatment than the conventional plant involving
coagulation and sedimentation prior to filtration. In addition to
providing a less expensive plant in first cost, it is frequently found
that coagulant requirements may be lower than with conventional pre-
treatment and that the handling of plant wastes is simplified.
There are limitations to this process, of course. With highly
turbid waters, it is more economical to remove the bulk of the
turbidity by sedimentation than to place the entire load on the filters,
A common guideline as to the upper limit of turbidity suitable for
direct filtration is about 25 Jackson units but direct filtration plants
are successfully treating waters with turbidity in the hundreds of
units. On the other hand, there are plants where very short filter
runs have been experienced even with low turbidity. The filter clog-
ging problems associated with diatoms are well known and if these
organisms are prevalent, it may not be economical to use direct
filtration. The use of a coarse media (1.0-1. 5 mm) in a dual media
*For presentation at AWWA Seminar May 13, 1973, Las Vegas,
Nevada
**Camp Dresser & McKee, Inc., Boston, Massachusetts
rv-i
-------
filter can help to overcome the tendency toward formation of a surface
mat when diatoms are a problem. The use of chlorine or ozone prior
to filtration may also help.
Probably as important as the suspended solids in the raw water
in determining the feasibility of direct filtration is the dosage of
coagulant required to coagulate the suspended matter or color. The
volume of material stored in a filter may be largely the highly
hydrated alum or iron floe. Of course, when color is all that is
being removed, the material clogging the filter is almost entirely
floe. We have found in several instances that where the required
alum dose for coagulation approached 30 mg/f it was necessary to
2 2
reduce filter rates from 5-7 gpm/ft to 3-4 gpm/ft in order to keep
filter runs from dropping below about 10 hours. In such instances,
it is doubtful whether direct filtration is truly economical.
In some instances, the use of a cationic polyelectrolyte as the
prime coagulant rather than a metal salt may make direct filtration
more attractive. In some recent pilot plant tests we found the filter
runs were about doubled when we switched from alum to a cationic
polymer. It was necessary also to add a small amount of a poly-
acrylamide as a filter aid immediately ahead of the filter. The
costs of the coagulant chemicals were about equal as the ratio of
polymer dose to alum dose was abo-ut 1:10 and the cost of the polymer
was about 10 times the cost of alum.
As a rule, the cationic polymers are not economically com-
petitive with metal salts in coagulating true color but in some New
England waters, they have been useful. At the Salem-Beverly,
Mass. water treatment plant which is a soft, low turbidity water with
a color generally below 50, it has been possible to reduce color by
about two-thirds with only 1-2 ppm of Nalco 607 applied immediately
IV-2
-------
ahead of the filters. However, there have been occasions when the
polymer was not effective and it was necessary to use alum as a
coagulant. The washwater from the filters settles well in sludge
lagoons and the supernatant is returned to the raw water sources.
Some of the cationic polymers are attacked by certain oxidizing
agents. At Brockton, Mass. where Nalco 607 was tested, it proved
ineffective probably because potassium permanganate is used there
for oxidation of manganese.
There appears to be little hard information on the dewatering
properties of sludge from direct filtration plants. It is a common
observation, however, that the solids from filter backwash water
are readily settleable whereas the solids reaching the filter were
those that had failed to settle in conventional pretreatment. The only
quantitative information I have seen is from the Fylde Water Board
in England where at their Stocks Plant a colored water is treated
with alum and pressure filters. The plant treats about 26 mgd and the
washwater (about 5 percent of throughput) contains some 300-400 mg/i
of suspended solids. This washwater is settled in horizontal flow
tanks after addition of 1 mg/l of polyacrylamlde. Without poly-
acrylamide, the solids content of the sludge was about 1.7 percent.
The settled sludge has a solids content of about 5 percent and the
supernatant has a color of about 10 units and about 10 mg/l of
suspended solids. This sludge is filter-pressed to about 25 percent
solids without further chemical addition. ^ At the Fishmoor plant
of the same Water Board, which also treats a colored water but with
clarifiers prior to filtration, the solids content of the sludge drawn
from the clarifiers is about 0.6 percent. Total sludge production
IV-3
-------
from the two plants is not markedly different running around 18 kg
per megaliter or about 150 pounds per million gallons.
Oxidation
In treating colored waters, the use of oxidants to bleach the
color has considerable potential for reducing the amount of water
plant waste. This has seldom been done very successfully as a sole
method of treatment but has been effectively used along with other
treatment processes. The various oxidants used in water treatment
also serve other functions than decolorizing.
Chlorine is the most widely used oxidizing agent in water
treatment although its principal waterworks use is as a disinfectant.
It is used widely to decolorize water. Riddick has described the use
of chlorine at Ossining, New York,where chlorination to a free
residual of 4 mg/l. This commonly reduced color from about 30-40
units to less than 10. It was necessary to use alum to keep the color
at satisfactorily low levels about 10 percent of the time. Chlorine
dosages were from 10-16 mg/f . Sulfur dioxide was used for
(2)
dechlorination after filtration.
At Miami, Florida, chlorine is used to decolorize a hard
groundwater after softening. Softening reduces the color from about
80 units to 25-30, A dosage of 12 mg/i of chlorine reduces the color
to less than 10. Black and Christman studied the effect of
three oxidants, chlorine, chlorine dioxide and ozone, on colored
waters by bubbling the gases through samples of eight different
colored waters until a constant color value was obtained. They
determined color and C.O. D, on the samples before and after
treatment. Their results are shown in Table 1. These show the
IV-4
-------
TABLE 1. EFFECTS OF CHLORINE, CHLORINE DIOXIDE, AND OZONE
ON COLOR REMOVAL AND CHEMICAL OXYGEN DEMAND
(From Reference 3)
Original
Color Value
after Oxidation
COD of
Sample
Color
Value
Hi
CIO,
Concentrate
(ppm)
A
240
No data
8
0
2,800
B
352
98
u
0
\ ,394
C
156
72
10
0
996
D
108
30
3
0
1,316
£
68
25
0
0
554
H
70
15
15
3
960
1
424
22
18
3
1,320
J
240
5
0
0
1,280
COD after Oxidation (ppm)
Cl2
c\o2
O3
No data
750
615
1,060
80
220
318
40
152
408
120
129
0
0
82
780
751
794
830
652
742
616
514
810
-------
substantially different responses of the various waters to the three
reagents. Under the conditions of this test, ozone was the most
effective.! in reducing color- followed by chlorine dioxide and chlorine.
However, there was no parallelism between color removal and
reduction in C.O.D. Sample J, for instance, was completely
decolorized by ozone but the C.O.D. was reduced by only about
one-third whereas chlorine left a color of 5 units but removed more
than 50 percent of the C.O.D.
Chlorine dioxide has not been widely used in water treatment
in the U.S. except for dealing with phenolic taste problems. It is an
effective bleaching agent and is widely used for bleaching pulp but its
cost is a major drawback to its wide use in water treatment.
Ozone is widely used in Europe in water treatment and there
are a number of ozone installations in Canadian water plants but only
a few plants in the U.S. use ozone. O/.one is a powerful oxidizing
agent and disinfectant. It decomposes to molecular oxygen and
provides only short lived residuals in water. It is manufactured at
the point of use by an electrical discharge in either dry air or oxygen.
It does not react appreciably with ammonia as chlorine* does.
(4 5 6)
A number of plants in Great Britain and elsewhere ' * ' have
used ozone and microstrainers for removal of color from water
rather than using the more conventional coagulation and filtration.
The microstrainer is used to remove algae and other particulate
matter of comparable size and to reduce the amount of ozone required
to decolorize and disinfect the water. Chlorine may be used prior
to ozonation to remove some of the color and further reduce the
ozone requirement. Some hazards are to be guarded against in
using this approach. If iron or manganese is present as either an
IV-6
-------
organic complex or in the soluble reduced state, it will be oxidized
and form deposits in the distribution system. IVIanganese is typically
oxidized rapidly by ozone to the permanganate form, even at near
neutral pi I, but this is reduced by organic matter in the water to the
insoluble manganese dioxide. In addition, the decolorizing action of
ozone evidently results in the breakdown of the organic color mole-
cules into simpler compounds which are more readily available as
food lor bacteria than were the original compounds. Thus, although
ozone may reduce the C.O. D. of the water, it may increase its
B. O. D. This gives rise to biological growths in the distribution
system with attendant customer complaints of dirty water and taste
and odor problems. Maintenance of a chlorine residual in the
distribution system can help to control the problem of biological
growths but iron and manganese problems can best be handled by
removing the offending materials with rapid sand filters. If the con-
centrations are sufficiently low, it may bo possible to stabilize them
by addition of sodium silicate to prevent their deposition in the
(9)
distribution system.
Our firm has recently designed an emergency treatment plant
for one of the water supply sources of Haverhill, Mass., which uses
ozone for color removal and taste and odor control. Johnson's pond
is one of four surface water sources which serve Haverhill and is
essential for supplying the city's needs during summer peak demands.
In the Fall and Winter of 1970 - 1971, it developed a heavy bloom of
Aphanizomenon with 12, 000 - 20, 000 areal standard units per milli-
liter of this blue green algae. The city was anxious to provide an
emergency treatment plant which could be gotten into operation
prior to the 1971 summer season. The water had been used with
IV-7
-------
only chlorination. Pilot plant tests wore run in December, H)70 and
January, lf)7 1, to determine what treatment would ho feasible.
A microstrainor with 24 micron screen removed only about
20 percent of the Aphariizomenon and also showed poor removal, of
odor.
A dual media filter with one foot of 1.0 mm anthracite over
2. 0 feet of 0.4 mm sand was tested briefly at rates of 4 and 7 gpm per
square feet. Although it generally was quite effective, at times
there was serious penetration of the algae even at the 4 gpm rate.
The area of filter needed was greater than was available in an exist-
ing building, an old steam pumping station which had been converted
to electricity leaving the space previously occupied by the boilers
available for other use. It would not have been possible to provide
a new building in time for the coming season.
A diatomite filter was tested and showed generally complete
removal of the algae cells although odor removal was relatively poor.
In fact, at times the threshold odor number was higher in the filter
effluent than in the influent. This treatment was recommended as the
performance was adequate in algae removal and the needed equipment
could be accommodated in the space available in the existing building.
Ozone was provided following filtration to eliminate tastes and
odors. It also reduces the color which ranges generally from 20 to
30 units to a range of 5 to 10 units.
Since the plant has gone into operation, it has been found that
filter runs and filter aid economy can be improved substantially by
prechlorination and this is being done routinely. Post chlorination
is practiced following ozonization as necessary to maintain a
chlorine residual in the distribution system.
IV-8
-------
This type of treatment has been satisfactory in solving
Haverhill's problem although it is more expensive in operation than
a conventional plant would have boon.
SUMMARY
Direct filtration and oxidation afford some opportunities for
reduction in tin? amounts of waste from water treatment plants.
Direct filtration is particularly attractive if cationic polyelectrolytes
a re suitable- for treating the water. Oxidation alone is seldom
adequate- for treatment but in combination with other processes, it
may substantially reduce waste volumes.
11i:; i ;ni :\c• i:s
1 Hilson, !VI. A. Sludge Conditioning by Polyelectrolytes. J. Inst.
Water Eng., 402-416 (1071).
2 Riddick, T. M. Controlling Taste, Odor and Color with Free
Residual Chlorination. J'.A.W.W.A. 43, 545-552 (1951).
¦i B lack, A. P. and Ohristman, R. F. Chemical Characteristics
of Fulvic Acids. J.A.W.W.A. 55, 897-912 (1963).
4 Campbell, R. M. and !Jescod, M. B. The Ozonization of
Turret and other Scottish Waters. J. Inst. Water Eng.
19, 101-162 (1965).
5 O'Donavan, D. C. Treatment with Ozone. J.A.W.W.A. 57,
1167-1192 (1965).
6 Diaper, E. W. .1. Practical Aspects of Water and Waste
Treatment by Ozone. In Ozone in Water and Wastewater
Treatment. F. L. Evans III, Editor. Ann Arbor Science
Publishers, Ann. Arbor, Michigan. (1972)
7 Van Haaren, F. W. J. Processes for the Removal of Organic
Pollutants. Joint Symposium Society for Water Treatment
and Examination and Water Research Assn. 113-122 (1970).
8 Hall, R. I. Discussion of Reference 7, Page 125.
9 Dart, F. J. and Foley, P. D. Silicate as Fe, Mn Deposition
Preventative in Distribution Systems. J.A.W.W.A. 64,
244-249 (1972).
IV-9
-------
MAGNttSUJM CARBONATE RECYCLING
Riley N. Kinman, Ph.D., P. E. :;:
Introduction
Recycling is a new concept to most people engaged in
water treatment, although it is not a new concept in other
industries and it has been practiced by some people in
water treatment. Consider the steel drum reconditioning
industry, which has been reconditioning steel drums and re-
cycling them for 40 years. An 18-gauge 55 gallon steel
drum can be recycled up to 15 times. In 1968"'", 20*10^
new drums were manufactured and 45*10^ drums were recon-
ditioned and recycled. This resulted in 1*10^ tons of
steel used in recycle rather than the use of raw material.
There were only two examples of true recycling in
water treatment prior to the present concept of magnesium
carbonate recycling. One of these, which is closely allied
to the present chemical and indeed will be a part of the
overall process, is the recovery and recycle of lime sludge
as CaCO^ from which high purity CaO can be and has been
reclaimed for many years at certain water softening plants.
This process will be discussed in detail later. The
second example of recycle in water treatment is in the
disinfection of swimming pool water with iodine. In this
process the I ion resulting from reaction of the active
chemical species 1^ or HOI on an organism is recycled many
times in a recirculating swimming pool before it is lost.
This recycle permits economy of operation in swimming pool
disinfection with iodine. Recycle of chemicals is a way
of conserving chemicals and reducing the cost of treatment.
^Department of Civil and Environmental Engineering, University of
Cincinnati, Cincinnati, Ohio
v-1
-------
Alum has been the water coagulant of choice in this
country since the early 1900's and has defied efforts to
recover and recycle the alum. In recent years the iron
salts have been successfully used by many water treatment
plant operators, but again without recovery and recycle of
the iron. Unfortunately perhaps, but maybe not, stringent
anti-pollution measures now require that there be no dis-
charge of waste sludges to receiving waters. The Federal
2
Water Pollution Control Act Amendments of 1972 set forth
a national policy, 1. "It is the national goal that the
discharge of pollutants into the navigable waters be
eliminated by 1985;" and 2. "it is the national goal that
wherever attainable, an interim goal of water quality
which provides for the protection and propagation of fish,
shellfish, and wildlife and provides for recreation in and
on the water be achieved by July 1, 1983;." There are
additional such statements of policy in the act.
This means that all water treatment personnel must
think seriously about recovery, reuse or recycle of all
chemicals used in the treatment process and all chemicals
removed from the water during the treatment process.
Alum, the coagulant of choice in this country, cannot
be recycled on a satisfactory basis, because of the
economics of the recovery process and the acid sludges
which are produced. The iron salts have resisted recovery
3
and recycle for about the same reasons. Black and co-
workers have proposed magnesium carbonate, hydrolyzed with
lime, as a prime candidate coagulant, which can be used,
reclaimed and either be reused immediately or be recycled
V~2
-------
at some future date.
Magnesium Carbonate
What is magnesium carbonate? The compound that is
under consideration for use in water coagulation is the
tri-hydrate form, MgCO^ • 3H2O. Other magnesium compounds
could be used to provide the MgtOH^ floe in water, but
each of the others has problems associated with its use of
one kind or another. For example,some would add non
carbonate hardness to the water, others would increase the
total solids of the finished water and others have solu-
bility problems associated with them. The desired reaction
is as follows:
MgC03 + Ca (OH) ^ »-Mg(0H)2 I + CaC03 ^ (1)
The lime provides sufficient OH to exceed the solubility
product constant for Mg(0H)2 an<^ solid Mg (OH) ^ floe is
formed fa3t and settles fast conveying the impurities from
the water to the sludge.
[V+] [oh*] 2 = Ksp (2)
4 5 6 7
The magnesium hydroxide floe has been shown ' ' ' to be
as effective as alum floe for removal of color, turbidity
and other suspended matter from water. Both of the
products in reaction (1) can be reclaimed from the sludge
for recycle. The turbidity and other impurities removed
from the water can be separated and placed in a landfill
with no major difficulty.
V-3
-------
Significance of Recycle to the Water Industry
Let us forget for a moment that water treatment plant
sludge can no longer be disposed of by sending it to the
receiving water and consider just the savings in chemical
when it is reclaimed and recycled. Let us assume that
10 mg/1 of any chemical is reclaimed and recycled.
Table 1. Chemical Saved For 10 mg/1 Recycle
Plant Size Daily Quantity Dosed Annual Tons Recycled
(mgd) and Reclaimed #
1 83 15
5 417 76
10 834 153
20 1668 307
50 4170 763
100 8340 1525
Even a small plant of 1 mgd capacity would save over 15
tons of chemical yearly, A large 100 mgd plant could save
1525 tons of chemical on an annual basis. Just a small
savings in chemical dosage, 10 mg/1, would result in
tremendous savings of chemical as well as the prevention
of pollution by discharge of the chemical. Recycle is
something to be considered just from the standpoint of
conservation of chemicals.
Consider for a moment the data in Table 2, developed
by Dr. Black^ and co-workers for the City of Dayton, Ohio.
This table contains the values received for recovery and
recycle of lime for the years 1958 to 1970 at their
100 mgd Ottawa Street Softening Plant. The totals
V-4
-------
Year
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
Total
Table 2
Production Figures and Value of Product Lime Recalcining Plant
Dayton, Ohio 1958 - 1970
Lime Produced Value Lime Produced Value Total Lime Total Value Value of
for Water
for Sale to
Produced
of Lime
Carbon
Treatment
Others
Produced
Dioxide
Produced
for Water
Treatment
20,559
$382,397
4,712
$ 49,476
25,271
$431,873
$32,000
22,995
427,707
11,590
121,695
34,585
549,402
32,000
23,353
434,366
11,568
133,032
34,921
567 ,398
32,000
22,115
411,339
11,711
134,677
33,826
546,016
32,000
21,140
393 ,204
3 ,791
42 ,649
24 ,931
435 ,853
32,000
21,246
395,176
3 ,084
35 ,003
24,330
430 ,179
32,000
22,326
415,264
5,265
59,757
27,591
475 ,021
32,000
23,926
445,024
3 ,606
36 ,060
27,532
481 ,084
32,000
25,574
475,676
6 ,174
67 ,914
31,748
543 ,590
32 ,000
26,150
486,390
6,594
69,237
32 ,744
555 ,627
32,000
27,010
502,386
7 ,628
80,094
34 ,638
582 ,480
32,000
29,772
553,759
4 ,905
55,672
34 ,677
609,431
32 ,000
29 ,370
546,282
4 ,976
56,478
34 ,346
602,760
32,000
315,536 $5,868,970 85,604 $941,744 401,140 $6,810,714 $416,000
-------
represent considerable savings both in chemicals recycled
and monies derived. For the 13 year period a total of
315,536 tons of lime were produced for water treatment at
a value of $5,868,970. In addition 85,604 tons were pro-
duced for sale at a value of $941,744. Also $416,000 of
carbon dioxide were produced to make a grand total of
$7,226,714 worth of products reclaimed and recycled.
Lime Recovery for Recycle at Dayton, Ohio
In lime-soda softening plants employing split treat-
ment the calcium and magnesium removed from the water are
precipitated and form two types of sludges. The first or
primary sludge contains principally CaCO^ plus all of the
magnesium as MgCOH^- Secondary sludge, produced by the
reaction of excess lime in the settled primary effluent
with calcium hardness in secondary raw water is practically
pure CaCO^. Figure 1 is a schematic of the Dayton, Ohio
Ottawa Street Water Softening Plant and lime recovery
facility. Primary sludge is produced in basins 1 and 3
and secondary sludge is produced in basins 2 and 4.
Secondary sludge is pumped to one of two sludge storage
tanks designated "P" in the figure. Primary sludge is
pumped to a sludge recarbonation basin designated "N"
where it is mixed with scrubbed kiln gas containing about
20% C02< Most, but not all of the Mg(0H)2 is selectively
dissolved from the calcium carbonate in the 50-mir»ute
retention period provided. The recarbonated slury passes
to a 130 foot diameter thickener from which the clear
supernatant containing the magnesium, now in the form of
soluble magnesium bicarbonate, overflows and is sent to a
V-6
-------
—R
Fig. 1. Ottawa Softening and Sludge-Processing Plant, Dayton, Ohio. Equipment for
Recovery of Magnesium Carbonate Being Designed
A—from well fields, B—plant bypass shaft, C—raw water junction, D~~double-decked
south flume, E—slow-mix basin, F—settling basin, G—recarbonation basin, H—split-
treatment bypass, I—filters, J—covered clear wells, K—wash water tank, L—wash-
water reclaim lagoon, M—sludge pumps, N—sludge recarbonation, 0—sludge thick-
ener, P—sludge-storage tanks, Q—feed-end building, R—rotary lime kiln, S—firing-
end building, T—lime-storage bin, U—chemical unloading building, V—chemical-
storage bins.
V-7
-------
sewer. Thickened sludge, now mainly CaCO^ with some un-
dissolved Mg(0H>2 and some insolubles, passes to a sludge
storage tank from which it passes to three Bird centrifuges,
these concentrate the slury to about 60% solids. This
thick paste is then conveyed to the kiln where it is
calcined into high quality CaO, The gases withdrawn from
the kiln by induced draft fan are freed from particulate
matter in four water fed scrubbers. Some of the scrubbed
and cooled stack gas is then returned to the treatment
plant by two compressors and used for water recarbonation.
A major portion is transferred by two other compressors to
the sludge recarbonation basin. The remainder exits from
the stack. Hence two major products are produced in lime
recovery according to the following reaction:
CaCO, CaO + CO- (3)
heat 1
The quality of the lime produced is excellent, CaO content
ranges between 92 - 93%. The finished lime may contain as
much as 4% MgO at the present time but an improved process
will be employed so that essentially all of the Mg(OH)^
will be dissolved and recovered. Figure 2 is a schematic
of the lime recovery process.
Benefits From Lime Recovery
1. The cost of treating the water has been reduced.
2. Lime values present in the raw water are re-
covered along with the lime used in treatment.
3. Calcium carbonate removed in the softening
process is not discharged as a pollutant.
4. Considerable C02 is produced for use in carbon-
ating the softened water.
V-8
-------
FIGURE 2,
RECOVERY OF CaO FROM CaC03 SLUDGE
PRIMARY SLUDGE
CaC03 + Mg(OH)2 +
INSOLUBLES
CARBONATION
Mg(HCOt)9 TO SEWER
THICKENING
SECONDARY SLUDGE
STORAGE
CaCO? + INSOLUBLES
CENTRIFUGATION
REJECTS
> t
CALCINATION
CaO STORAGE
SELL OR REUSE CaO
V-9
-------
5. A continuous inplant supply of lime is available
at all times.
6. Land is not required for storage of the lime
sludge.
Recovery of MgCO^ • 3H20 fronl M<3 (Q&) 2 Sludge
3
Black and co-workers presented the reactions involved
in the pilot plant production of Magnesium carbonate in
October of 1971 as follows:
Mg (OH) 2 + 2C02 Mg (HC03) 2 (4)
Mg (OH) 2 + C02 + 2H20 MgCQ3 ' 3H20 (5a)
MgC03 • 3H20 + C02^=^ Mg(HC03>2 + 2H20 (5b)
Mg (OH) 2 + Mg(HC03)2 + H20 >- 2MgC03 * 3H20 (6)
Mg(HC03)2 + 2H20 —— ¦? V MgC03 3H20 + C02 (7)
air
Reaction (4) is the overall reaction by which the insoluble
hydroxide is converted to the soluble bicarbonate. Re-
actions (5a) and (5b) are consecutive and represent the
two steps in the overall reaction. The concentration of
bicarbonate steadily increases to an alkalinity of 16,500
ppm as CaC03. This is the equilibrium concentration for a
kiln gas containing 20% C02. Reaction (6) shows that as
carbonation proceeds there will be a tendency for the
undissolved Mg(0H)2 to react with the dissolved Mg(HCO^)2
to form a precipitate of MgC03 * 3H2°" In Pract:i-ce the
Mg (OH)2 could be fed at a rate no greater than the rate at
which the Mg(OH)2 is dissolved by the C02-
Reaction (7) takes place during product recovery.
The clarified Mg(HC03)2 solution passes to a heat
exchanger where it is warmed to 35°C to 45°C. It is then
V-JO
-------
aerated in a basin equipped with mechanical stirrers. Pre-
cipitation of the tri-hydrate is essentially complete in
90 minutes. The white product MgCO^ • vacuum
filtered, dried and bagged for shipment. The filtrate
containing unprecipitated product will be recycled to the
sludge storage tank. The underflow from the clarifier-
thickener in which the carbonated sludge is clarified, is
thickened CaCO^ sludge. This will be passed to a sludge
storage tank for recovery of the CaCO^. When magnesium
recovery is instituted at Dayton the following should
occur:
1. Essentially all of the magnesium in the sludge
will be recovered,
2. All of the water used to convey the sludge will
be saved.
3. There should be no significant discharge of waste
solids.
4. Lime production will be increased.
5. Lime quality will be improved.
Figure 3 is a schematic of the Dayton, Ohio pilot
plant for total recovery of softening sludge. The purity
of the reclaimed magnesium exceeded 99.5 percent.
Application of the Process to Treatment of Hard Turbid
Waters
Most of the large softening plants in this country
are softening hard waters which contain clay turbidity.
This turbidity has prevented the recalcination of the
sludges for recovery of CaO, because the separation of the
clay turbidity from the CaCO^ sludge could not be done in
such a way as to prevent the buildup of insolubles in the
finished lime. Black and co-workers have studied the
V-ll
-------
Waler Plant
Settling Basm
D
~
j
Clear Water
Overflow Can
Be Returned to Plant
Sludge
SoVids
Raw-Sludge
Pump
Ra-A Slodge
V.ifer Plant Setting Ba^jn
a»
Van Speed
Sludge Thickener Pump Lime Kiln Recarbonation Basin
Stack Gas
D
Settlmg Tank
Dewatered Soiids
to Dryer
J Compressed Air
—*
3
Clear Water Return to
,, o , . Water Plant
Magnesium Precipitator
Magnesium Carbonate
Dewatering Vessel
Fig. 3. Total Recovery of Lime-Softening Sludge; Magnesium Carbonate Recovery Pilot Plant
-------
separation of clay turbidity from the combined CaCO^,
Mg(OH)^ and clay sludge by froth flotation. The mining
industry has been using froth flotation for a long time to
purify CaCO^ for use in applications involving a very pure
white inert compound. They float the impurities off in
large multi-unit cells with air and frothing agents.
Thompson and Black^ presented a flow diagram for the appli-
cation of MgCO^ in a turbidity removal plant in February of
1972. Figure 4 is a schematic of the basic steps involved
in the recovery and recycle of lime and magnesium for such
a plant.
The sludge containing CaCO^, MgfOH^ and clay is first
carbonated with kiln stack gas just as the process is con-
ducted at Dayton. The Mg(OII)2 will be solubilized as a
mixture of MgCO^ and MgCHCO^^* Separation of the mag-
nesium from the calcium carbonate and clay is achieved by
means of a vacuum filter. The filtrate containing the
magnesium as MgCO^ and MgdlCO^^ is returned to the
chemical feed point for reuse in the water treatment
process. The filter cake containing CaCO^ and clay is con-
veyed to a flotation unit for removal pf the clay from the
CaCO-j by froth flotation. This froth containing mostly
clay, but with some magnesium and calcium is sent to the
landfill. Bench scale pilot plant tests conducted prior
to this writing have shown that the magnesium remaining in
the filter cake is less than 2%, or greater than 98%
recovery of the magnesium is expected. Greater than 90%
recovery of the CaCO^ is expected in such a process. A
flotation unit will be used for separation of the clay
V-l i
-------
FIGURE 4, LIME AND MAGNESIUM RECOVERY WHEN SOFTENING
A HARD TURBID WATER
WATER
STABILIZATION
CARBONATION
SLUDGE
CaC03 + Mg(OH)2 +
CLAY
COo FROM KILN
FILTRATE TO
VACUUM FILTER
CAKE MAY CONTAIN
1-2% MAGNESIUM
CHEMICAL FEED
(MgCO? + Mg(HOMo)
CLAY TURBIDITY
WITH FROTH
TO LANDFILL
CaCO
CENTRIFUGE
(THICKENING)
CaCO
KILN
FLOTATION UNIT y
(MIXER, ROUGHER,
SEVERAL CLEANING CELLS
CaO FOR CHEMICAL FEED AT PLANT
AND SALE OF RECLAIMED MATERIAL
V-14
-------
from the CaCO^ which contains a mixer for addition of
frothing-agents, a roughing cell and probably two or three
cleaning cells. The cleaned CaCO^ sludge will then be
centrifuged to 60% solids and then sent to the kiln for pro-
duction of CaO. By the time of this presentation larger
scale pilot plant data should be available for this total
recovery and recycle process.
Advantages of Magnesium Carbonate-Lime Process for Hard,
Turbid Water Treatment
1. Reduced cost of treatment.
2. Elimination of Alum sludge.
3. No discharge of pollutants.
4. Clay turbidity is the only material to be disposed
of in a landfill.
The key to the process is the complete or nearly complete
separation of the three components of the sludge, namely
calcium carbonate, magnesium and clay. If this separation
cannot be achieved on a satisfactory basis, then the
process will not be applicable to treatment of hard turbid
waters. Large scale pilot testing should indicate the
degree to which this can be accomplished.
Summary
A whole new technology has been proposed for water
treatment involving the use of magnesium carbonate hydro-
lyzed with lime to replace alum, with subsequent recovery
and recycle of the magnesium and calcium. The process
appears to offer a cheaper water and of the same or better
quality as that produced by use of alum. Use of the
process would eliminate the need for disposal of alum
sludge and would provide for no discharge of pollutants by
V—1 5
-------
the water utility. Use of the process would result in
design changes in a water treatment plant. Key to the
whole process is the ability to separate the components of
the sludge for recovery and recycle. Work underway at the
time of this writing should provide additional data on the
separation process.
Acknowledgements
Appreciation is extended to Mrs. June Schuck for
typing this manuscript.
References
1. News Release, "Drum Reconditioning Industry Reduces
Nation's Solid Waste Disposal Problems by Recycling
One Million Tons of Steel Annually." National Barrel
and Drum Assn., Inc. Wash., D.C. (1970).
2. "Federal Water Pollution Control Act-Amendments of
1972." 92nd Congress 2nd Session, U.S. House of
Representatives, Report No. 92-1465, 1 (1972).
3. Black, A.P., Shuey, B.S., and Fleming, P.J., "Recovery
of Calcium and Magnesium Values from Lime-Soda
Softening Sludges." Jour. AWWA, 6_3, 616 (Oct.,1971).
4. Thompson, C.G., Singley, J.E., and Black, A.P.,
"Magnesium Carbonate - A Recycled Coagulant." Jour.
AWWA, 64_, 93 (Feb., 1972).
5. Dept. of Public Utilities, Gainesville, Florida,
"Magnesium Carbonate, A Recycled Coagulant for Water
Treatment." Water Poll. Control Research Series
12120 ESW, U.S.P.A. Office of Research and Monitoring
(June 1971).
6. Thompson, C.G., Singley, J.E., and Black, A.P.,
"Magnesium Carbonate - A Recycled Coagulant - II."
Jour. AWWA, 64, 93 (Feb. 1972).
7. Kinman, R.N., "Magnesium Carbonate for Water Treatment"
Presented at First Sanitary Engrg. Seminar, Central
Ohio Section, A.S.C.E. (Mar. 1972).
V-16
-------
DEMONSTRATION OF THE MAGNESIUM COAGULATION
SYSTEM AT MONTGOMERY, ALABAMA
C lilT G. Thompson ;!
A. P. mack —
Dr. Kinman, in the previous paper, discussed the theory unci
chemistry involved in this new technology with particular emphasiK
upon recovery of lime and magnesium values from the sludge. This
presentation will, discuss the application of the process for the
removal- of organic color and turbidity from the very soft water used
by Montgomery, Alabama. Before discussing the Montgomery
demonstration project, a brief review will be made of the processes
encompassed by this new technology.
There are three general processes involved: magnesium
recycle, lime recovery, and the production of magnesium compounds.
The decision as to which process should be used is determined by the
characteristics of the raw water as well as the capacity of the water
treatment plant. A series of seven schematic diagrams are pre-
sented to allow better understanding of the processes involved and
the relative positions of the equipment utilized.
Figure 1 illustrates a typical alum water treatment plant with
a sludge flow of approximately one to two percent soLids being returned
to the river. Figure 2 shows the units required for magnesium
recovery, recycle, and sludge dewatering. As discussed by
Dr. Kinman, carbon dioxide is used to solubilize the magnesium as
the bicarbonate with the thickener overflow recycled to the raw water.
The underflow is dewatered using a vacuum filter and the filter cake
land filled. Figure 3 is a schematic of the Montgomery Demon-
*Co-Project Director and Consulting Engineer, Black Crow and
Eidsnes.s, Gainesville, Florida
**Co-Project Director, Consulting Chemical Engineer and Research
Professor Emeritus
VI.-1
-------
stration Plant but also shows the relative position of the magnesium
recovery units. When lime recovery is practicable, generally when
above 15 - 20 tons per day, the additional units shown in Figure 4 are
required. The dewatered filter cake is reslurried, conditioned with the
proper flotation reagents, and the calcium carbonate floated from the
clay in a series of flotation coils. The calcium carbonate float is
concentrated and burned in a kiln producting carbon dioxide and
calcium oxide. As discussed, an excess over plant requirement, of
both carbon dioxide and lime are produced. Figure 5 illustrates lime
recovery with recycle of the magnesium carbonate.
Those plants whose raw water is high in magnesium will be able
to produce magnesium compounds from the recovered magnesium
bicarbonate rather than recycle magnesium back to the raw water.
Figure 6 illustrates two magnesium production processes. Boiling
the clear magnesium bicarbonate liquor produces the basic carbonate
while blowing air to strip the carbon dioxide produces magnesium
carbonate tri-hydrate. Figure 7 illustrates a plant with magnesium
and lime recovery as well as the capability of recycling magnesium
when desired.
The E. P. A. Demonstration Project 12120HMZ underway in
Montgomery was a natural outgrowth of the laboratory research
(1 2^
reported in the January and February issues of the Journal. '
Last June the results of approximately one year of pilot study were
(3)
presented at the A.W.W.A. Conference in Chicago, The project,
funded by the American Water Works Association Research
Foundation, the Environmental Protection Agency, and the
Montgomery Water and Sanitary Sewer Board as shown in Table 1,
is now in the full demonstration phase.
VI-2
-------
TABLE 1
Funding for the Montgomery Demonstration Project June 1,
1971 - June 1, 1973.
Environmental Protection Agency $99, 500
Montgomery Water and Sanitary Sewer Hoard 78, 500
American Water Works Association Research 24, 426
One half of the 20 mgd water treatment plant has been converted to
utilize this new process for comparison of all phases of this new
technology with the existing alum system. A partial analysis of
Montgomery's raw water is shown in Table 2.
TABLE 2
Typical range in raw water characteristics
As CaC03
pll Alkalinity Hardness Magnesium Color Turbidity
6.6 - 7.0 10 - 22 10 - 22 0 - 5 5 - 60 2 - 300
Referring back to Figure 8, it can be seen that the Montgomery Plant,
provides an excellent facility for such a demonstration as with only
minor alterations two parallel plants with identical units results,
Rapid mixing is not being provided for the alum treatment during this
demonstration period.
MAGNESIUM TREATMENT PROCESS - LAYOUT
AND DISCISSION
Rapid-Mix and Flocculation
Figure 8 illustrates the recycle and chemical feed points using
the two rapid mixers in series which provide a total detention time
of four minutes at a five million gallon per day rate. Recycled
magnesium bicarbonate is added to the raw water immediately prior
to rapid mixing while uncarbonated recycled sludge and magnesium
sulfate are added in rapid mixer number 1. Lime is added between
rapid mixers number 1 and 2 adjusting the pH to the desired value.
VI-3
-------
Lime Coed is controlled automatically using a pi I probe in rapid mixer
number two, coupled to a pi I control ler and SC it controlled pump as
shown in Figure 0. Flocculation is carried out using conventional
rod type- variable speed floccuintors normally operated at the
maximum speed.
Recycled sludge has been provided for the following
purposes:
(1) Recycled calcium carbonate increases magnesium pre-
cipitation kinetically as well as quantitatively as reported
i i i ¦ . (4,5,6,7)
by several early investigators.
(2) A. portion of the magnesium hydroxide fraction of the
sludge reacts with the recycled magnesium bicarbonate
as well as the natural bicarbonate alkalinity and carbon
dioxide in the raw water as:
IV1 g (Oil)2 -t Mg (HCOs)9 - 2 Mg CO;) I 2]J,,t)
This solubilif-ed magnesium carbonate is effective for coagulation
when re-precipitated; however, some coagulated turbidity is also
released. The overall effect is difficult to evaluate but is generally
considered to be of some value.
(3) The pre-formed calcium carbonate recycled, acts as a
seed or nucleus for precipitation preventing a buildup on
mechanical equipment.
(4) The excess causticity in the sludge water, pl-1 11.40,
reduces the lime requirements slightly. The pH in rapid
mix number 1 is generally 10.0 or higher. The pre-
cipitation reactions occur rapidly and produce small
dense fLocculant particles. Even at maximum flocculation
speeds the floe tends to settle from suspension.
VI-4
-------
Settling - Carbonatioi)
The Montgomery Plant utilizes conventional horizontal settling
basins with mechanical sLuUgo removal in the first half. Approxi-
mately two-thirds ol' the basin is used for settling with the1 remaining
third used for two stage stabilization. Liquid carbon dioxide is
metered manually into the settled water, dispersed through one inch
PVC pipe1 drilled with small holes approximately two feet apart.
Baffles of polyetheylene film were installed to prevent mixing back
to the settling zone.
The purpose of the two stage carbonation is to first convert the
hydroxide to carbonate alkalinity, precipitating calcium carbonate.
Very little of the calcium carbonate formed settles, however,
the solid phase is relatively stable and does not redissolve upon final
plf stabilization just prior to filtration. The carry over of calcium
carbonate onto the filter does not shorten the length of filter runs and
does not pass through the filter. !'roper adjustment of the settled
water pll prevents calcium carbonate from precipitating on the sand
in the filter. Precipitated calcium carbonate carried onto the filter
is easily removed on back washing.
Settled, stabilized waters from the alum and magnesium
processes are separated and filtered in identical sand filters,
generally at a rate of 1 - 2.5 gallons per square foot per minute. One
of the four filters used on the magnesium process has been con-
verted to a dual media filter, replacing three inches of sand with
anthracite with an effective size of 1.2 mm.
Magnesium Recovery and Sludge Handling
Figure 10 illustrates the units comprising the sludge recovery
system. Sludge is pumped at a controlled rate into the carbonation
VT-5
-------
colls using a variable speed Moyno Pump. Four, ten cubic foot flo-
tation cells a re used for sludge carbonation. Again pure carbon
dioxide is used, however, the feed is automated as shown in Figure 11.
Carbonate sludge is pumped into a ten foot diainter thickener with the
overflow returned to the raw water- using an intermediate 1800 gallon
storage tank. The recycled magnesium bicarbonate is pumped at a
controlled rate to give the desired coagulant dosage. The thickener
underflow is vacuum filtered pumping the filtrate to the magnesium
bicarbonate storage tank and land filling the filter cake.
There are .several reasons why pure carbon dioxide should be
considered for use in the smaller plants not recovering lime. The
rate which carbon dioxide solubilizes magnesium has been found to be
first order- with respect to the partial pressure of the carbon
dioxide. in addition pure carbon dioxide will dissolve approxi-
mately 25, 000 mg/t of magnesium bicarbonate, considerably more
than the lower percentage carbon dioxide produced from on site
generation. The feed of liquid carbon dioxide is much simpler, more
flexible, and easier to automate.
Carbon dioxide feed is automatically controlled to achieve a
carbonation pll of 7.3. Near 100 percent absorption efficiency is
possible due to the very fine bubbles produced and the high driving
force between the caustic sludge and the carbonic acid. At pll values
below 7. 3 the reaction has gone to completion with the result being
the loss of carbon dioxide to the atmosphere. The carbon dioxide
bubbles cause foaming which is greatly accentuated by the slightly
surface active organic color released from the sludge in carbonation.
This foaming serves as a good indicator of excess carbonation and
can be used for visual pH control of the process.
VI-6
-------
Table .'•! gives a typical mass balance for the magnesium process
in treating the soft water in Montgomery. It is important to note
that the only caleiurn carbonate precipitated in coagulation is due to
the recycled magnesium bicarbonate. The sludge produced will
have an unusually high ratio of magnesium to calcium carbonate and
low ratio of calcium carbonate to clay turbidity. The total sludge
production on a dry weight basis is 1050 #'S/M.G. which is 66%
calcium carbonate for this example.
Project Limitation
The conversion of the Montgomery Plant was done so on a
temporary basis, limited by a very tight budget. All of the conversion
was accomplished with water works personnel at a cost of less than
twenty thousand dollars. As a result, the facility layout and
mechanical equipment used was less than desirable in some instances.
First stage stabilization of the finished water should be accom-
plished with point source carbon dioxide addition using mechanical
mixing and sludge recycle. As a result of adding carbon dioxide
across the width of the basin an uneven distribution results causing
the pH to vary depending upon gas flow. One side of the basin may
have a pH of 9.6 while the other side, because of less gas flow, a pH
of 10, 8 rather than a uniform pH of 10. 3. The result of this uneven
pll distribution is a slightly higher finished water hardness, in the
range of 65 to 85 mg/£ as calcium carbonate. Two stage carbonation
has been used very successfully at many plants; therefore it was not
of primary concern to this project. A carbonate hardness in the
range of 35 - 50 mg/f is being obtained in plants operated and
equipped properly.
At the time this project was initiated, the city of Dayton, Ohio
intended to supply magnesium carbonate produced from their
VI-7
-------
TAP EE ;•!
Typical Mass MaJance for Magnesium Process in Montgomery
Raw Water' Characteristics
Turbidity
A ika Unity
Carbon Dioxide
Magnesium
Total Hardness
Flow 5 MOD
fiO FTU4 0 nifj/i suspend solids
IS nig/I as CaCO,,
6 mg/i '*
4 tn g/i as CaCO-..
15 mg/f as CaCO,,
Chemical Addition to Rapid iVlix
Uecycled Magnesium
iV'lagnesium Sulfate
F -imt'
- 50 mft/1 as CaCO-j
- 5 nif;/f as CaCO-^
- 105 nift/1 as CaO
Settled Sludge C ha r n c te r is tic s
Turbidity (if/Day)
Magnesium Hydroxide (///Day)
Calcium Carbonate (///Day)
1667
100
3500
646 7
% of Total
25TB
20. 1
54. 1
Stabilization Point 1
Calcium Carbonate - Produced (///Day)
Carbon Dioxide Required (///Day)
- 1650
- 156 0
(ASSUMING 95% ABSORPTION EFFICIENCY)
Stabilization Point 2
Carbon Dioxide Required (#/Day) - 390
(ASSUME 05% ABSORPTION EFFICIENCY)
Carbonated Sludge
Flow - 11. 5 G PiVl
Magnesium Bicarbonate (As CaCO,,) 17, 000 mg/i
Suspended Solids ' = 4.9%
Carbon Dioxide Required (ft/Day) - 2050
(ASSUMING 98% ABSORPTION EFFICIENCY)
VI-8
-------
Cont'd Tlibit.? :-i
Thickener
Over-flow - 17, 000 mg/1 Magnesium as CaCO,,
Flow - 10.3 Gallons Per Minute
Underflow - 40% Total Solids
Flow - 1.2 Gallons Per Minute
Vacuum Kilter
Cake (60% Solids) - 8,769 ///Day 0/
Composition
Water (///Day) - 3500 40.0
Calcium Carbonate (///Day) 3500 - 40.0
Turbidity - (///Day) - 1667 19.0
Magnesium (///Day as CaCO.,) - 102 1.0
Summary of Chemical feed
Lime (///Day) - 4350
Carbon Dioxide (///Day) - 3900
Magnesium Sulfate (///Day) - 5215
Finished Water Analysis
pll -8.5
Total Hardness - 75 (All as CaCO J
CaLcium Hardness - 71
Total Alkalinity - 70
Magnesium Hardness - 4
Vl-9
-------
softening sludge, Knough product was produced and used in the pilot
scale phase, however', Dayton's full scale production plant con-
struction was delayed making it necessary to use magnesium sulfate
as the make-up magnesium source. As pointed out in the previous
paper, magnesium sulfate adds nonearbonate hardness in direct
proportion to the make-up dosage. This increased hardness is of
little concern to the Montgomery project considering the small make-
up dosage required and the fact that the water is blended with the
extremely soft alum treated water following filtration.
The physical layout of the vacuum filter was less than desirable.
The filter could not be operated during cold weather due to freezing
of the filtrate under near vacuum conditions. The filter bed was
manually filled requiring considerable operator attention. The more
desirable and more costly layout would elevate the filter with the
sludge1 pumped from the thickener to the filter bed, the cake
discharged directly into a truck, and the overflow returned to the
thickener.
Results and Discussion
Plant Operation and System Control
These first four months of operation have found the magnesium
coagulation system to be much more stable than the alum system
particularly in the coagulation process. Under certain raw water
conditions, the alum coagulation pll must be maintained within ± . 1 of
a pH unit in order to treat the water satisfactorily. Slight variance
from the optimum pll results in greatly decreased coagulation
efficiency. The low alkalinity water used by Montgomery has a very
poor buffer capacity, particularly after the addition of alum when
the alkalinity is seldom above 1 mg/l as CaCO^. Slight changes in
either pre-lime or alum feed can affect the coagulation pH to a large
Vl-1.0
-------
degree. Automation of the lime feed and carbon dioxide feed for
sludge carbonation has proven to be very satisfactory. Control of
both feeds are such that less than 0. 1 pH from the desired pll occurs.
Recovery of magnesium as the bicarbonate is routinely carried out
at a constant rate sufficient to provide the average coagulation
requirements. When raw water conditions are such that additional
magnesium feed is required, make-up magnesium sulfate is used
which increases the concentration of recovered magnesium after a
period of approximately 24 hoars, excluding the mechanical defi-
ciencies of the temporary installation, the magnesium system has
performed well with a minimum of operator attention.
Included in the appendix is a summary process control points
and a brief discussion as to which tests are performed at the various
sampling locations. Typical results of these tests are also
included.
Pilot vs Actual Results
Excellent correlation has been found between pilot and full scale
results. Magnesium solubility in the finished water agrees closely
with the results reported last year in Chicago^ with similar tur-
bidity removals and filter performance. Leaf filter tests as well as
thickening tests on the carbonated sludge agree closely with results
now being obtained.
Economics
(2 3)
In the January and February issues of the 1972 Journal, *' a
series of curves were presented which could be used to approximate
chemical costs and economically optimum, operating conditions for
any water. To illustrate the simplicity of the use of this approach
for a single water the cost curves for Montgomery have been
prepared.
VI-11
-------
Figure 12 illustrates the effect of coagulation pH on magnesium
replacement costs for both magnesium sulfate and magnesium
carbonate tri-hydrate. An average of 4 mg/I ol' magnesium is
normally present in the raw water. As a result primarily of the high
magnesium content of the cake moisture, 3 0 pounds per day of
magnesium, as C'aCO^, in the vacuum filter cake, is lost each day.
As the coagulation pH increases less magnesium remains in the
finished water therefore less make-up is required, decreasing the
cost per million gallons for magnesium expressed as calcium
carbonate.
Figure 13 illustrates the effect of increased coaguLation pj 1 on
carbon dioxide and lime costs. Fifty mg/i of magnesium as calcium
carbonate were assumed in the recycle with the chemical costs as
noted.
Figure 14 is a summation of Figures 11 and 12 and represent the
total cost for magnesium, carbon dioxide, and linn: as a function of
coagulation pll. An optimum pH of 11.2 was found for the situation
where magnesium carbonate tri-hydrate was used as the magnesium
source with a total chemical cost of approximately $19.00 per
million gallons. Using magnesium sulfate, an optimum pll slightly
higher than 11.3 is found with a chemical cost slightly higher than
$25. 00 per1 million gallons.
Figure 15 illustrates the reduced costs and slightly higher
optimum coagulation pll if a souce of carbon dioxide were available
at the plant site. A cost of approximately $11.00 per million gallons
at a pH of 11. 3 is indicated.
If dolomitic lime will serve as a suitable magnesium source
Figure 12 can be used to calculate chemical costs. The only
restraints on coagulation pll in this case is to keep the magnesium
Vl-12
-------
content in the finished water below some maximum level for hardness
considerations; generally requiring the coagulation p IJ to be kept
above 11.0 which would result in a chemical cost of only $10.00 per
million gallons.
The results thus f'ar would indicate that the cost estimates
published in the earlier papers were conservative. A predicted cost
for Montgomery's water of $18.23 was based on a purchase price for
carbon dioxide of $20/ton rather than the $30/ton now being paid.
From this brief discussion the importance of carbon dioxide is
clearly indicated. Lime recovery becomes attractive even at the
lower tonnages than would have been considered previously. Other
sources such as stack or engine exhaust should be sought. The
production of electrical power at the plant site with the use of
exhaust gases in water treatment is a possibility which should be
explored.
When considering the economics of this process not only
should chemical costs be compared but all water production costs
which include costs for sludge treatment should be considered. The
additional advantages which Dr. Kinman has presented should be
included in process decision making. These advantages arc
summarized and included in the appendix.
Sludge Handling
In previous papers on laboratory studies the release of
organic color on sludge carbonation has been noted. These studies
¦were usually carried out for a single cycle of coagulation and
carbonation of the resulting sludge. There has been concern that
this released organic color will tend to build-up in the recycle
system after several cycles and cause problems.
VI-13
-------
Jn the past four months, many hundreds of cycles of carbonation-
eoagulation have taken place with no problems resulting from organic
color increase. A ratio is made of the magnesium solubilized to the
color released and recorded every two hours of plant operation.
This ratio has varied from 5 to 10 dependent upon the amount of
organic color present in the raw water. There has been no upward
or downward trend established.
As the turbidity in the raw water changes, the ratio of calcium
carbonate to turbidity is affected. The higher the percentage
calcium carbonate the better the thickener performs. The thickener
underflow ranges from 30 to 45 percent total solids dependent upon
this ratio. Carbon dioxide, released from the super saturated
carbonated sludge has caused some difficulties in thickening. Some
solids carry over results, but lias caused no difficulties except in
excessive wear of the recycle pump. The vacuum filter rates range
from three lbs. per square foot per hour to twenty lbs. per square
foot per hour with the higher rates reported for the higher calcium
carbonate. Several daily filter reports are included in the appendix.
A polymer dosage of approximately .25 pounds per tons of dry
solids is added to the carbonated sludge to aid in thickening. High
molecular weight anionic polymers have been found best suited for
conditioning of the carbonated sludge. The costs are low, approxi-
mately $1.00 per day, and the results extremely good. A typical
jar test for sludge conditioning is included in the appendix.
The rate of carbonation using the flotations cells and pure
carbon dioxide, is extremely rapid. On occasions, as much as 175
pounds of magnesium per hour, as CaCO^, has been recovered,
enough to feed 25 mg/i to a plant flow of 20 mgd.
VI-14
-------
Filtration of Stabilized Waters
Filtered water turbidity is recorded on one of the four filters
treating alum processed water and three of the four magnesium
filters. Filters are normally backwashed after one hundred hours
operation or seven Feet of head-loss whichever comes first.
The months of February and March were selected as
representative of normal operation and the records indicated that
the alum filter had an average filter run of 82.2 hours and an average
head-loss of 6.4 feet at the time of washing. During this same time
period the magnesium filters averaged 97.8 hours with a head-loss
of only 3. 3 feet. The filter capped with anthracite processing the
magnesium treated water averaged over 100 hours filter run with
only 1.8 feet of head-loss between washing. There was no noticeable
difference in filtered water turbidities comparing the sand filter
processing magnesium treated waters with the anthracite capped
filter.
During this time period an average of 7 FTU of calcium
carbonate turbidity were being placed on the filters. Ideally, some
15 to 20 FTU of turbidity resulting from calcium carbonate pre-
cipitation will be normal with better carbon dioxide addition. Based
on the experience in Montgomery and the experience of hundreds of
softening plants, problems with shortened filter runs are not
expected.
Filtered turbidities have been generally lower on the magnesium
processed water, however, as with the alum process, coagulation
efficiency generally determines the filter efficiency. The stabi-
lization of th'e settled water and resulting calcium carbonate pre-
cipitation assists filtration in two ways. Unsettled turbidity serves
as a nucleus for precipitation increasing the particle size for
VI-15
-------
removal on tin? filter and the precipitated calcium carbonate con-
ditions the filter surface for more1 efficient operation. No calcium
carbonate penetration through the filter has been found.
Flotation Studies
Flotation separation of the calcium carbonate and the clay
prior to lime recovery has been accomplished only on a laboratory
scale to date. While the Montgomery Plant will not be considering
lime recovery, it is important that this process be demonstrated on
a sizeable scale for the many plants utilizing sufficient lime to
consider recovery.
A flotation system utilizing a string of six cells* has been
constructed by the Wetnco Division of the PJnvirotech Corporation
and will be loaned to the project from April 15 through June 1. The
raw water turbidity changes will be reflected in the calcium
carbonate to turbidity ratio of the sludge. A wide spectrum of con-
ditions will be studied with product purity and recovery efficiency
evaluated.
Additional Magnesium Sources
As discussed, dolomitic lime will be investigated as a supple-
mental source of magnesium. A special blend of high calcium and
dolomitic lime is being produced in Birmingham for the steel
industry. This product would appear ideal for this application,
however, it was not available until these last months of the project,
Dayton, Ohio will soon be producing sufficient quantities of
magnesium carbonate tri-hydrate as well as the basic carbonate
for use in Montgomery. If the basic carbonate serves as a suitable
'"Schematic flow diagram included in Appendix
VI-16
-------
source of magnesium, production of magnesium from water plant
sludges will he simplified. This of course affects those cities
treating high magnesium content waters which find it profitable to
produce magnesium compounds from their sludge.
Summary
The Montgomery Demonstration Project has accomplished
the objectives undertaken at its origin. The magnesium process has
been found to compare favorably with conventional water treatment
methods in both overall operation and in the water quality produced.
As would be expected, slightly increased labor and maintenance costs
could be expected, however, these can be greatly offset by automation
which is quite ameanable to this process. The magnesium process
does more than treat water; it treats the sludge produced as an
integral part of the system. Considering process economics, one
must include chemical costs, capital costs, operating and main-
tenance costs, as well as the various treatment considerations which
includes sludge treatment in many cases. The various advantages
of this new technology must also be factored into the decision making.
Table 4 summarizes the comparisons between the two systems for
soft waters such as found in Montgomery.
The acceptance of this new technology will probably come first
with those cities faced with sludge disposal problems, extremely
high chemical costs for water treatment, or in those cities where
lime and magnesium recovery is economically feasible.
I invite those present, who may be faced with one or more of
these situations, to seriously consider this new technology. There
now exists, for many waters, an acceptable alternative to the age
old alum or iron salts treatment process.
VI-17
-------
TABLE 4
COMPARISON OF THE MAGNESIUM AND ALUM TREATMENT PROCESSES AT MONTGOMERY
PARAMETER
MAGNESIUM
ALUM
CHEMICAL DOSAGES AND
COAGULATION pH
FLOC CHARACTERISTICS
SETTLING CHARACTER-
ISTICS
SLUDGE CHARACTER-
ISTICS
FILTRATION CHARACT-
ISTICS
FINISHED WATER
CHARACTERISTICS
CHEMICAL AND OPERATIONS
ECONOMICS
1 Dependent upon water
Conditions
875 %/M.G. CaC, 800#/M.G. Co2, and
100 #/W.c. of MgsOe, pH 11.z,
highly buffered
Precipitation products, dense,
granual. Form very rapidly and not
as kinetically dependent upon water
temperature.
Rapid, maximum clarifier loading ra-
between lower rate for alum and high
rate for softening plant. High pH
disinfects.
Carbonated sludge thickens to 40%
solid plus. Approximately 1000
#/m.g. produced but all solids are
dewatered as an integral part of the
process. All sludge water recovered
Generally lower filtered water tur-
bidity, calcium carbonate loading
will not shorten filter runs.
SIightly increased hardness and
alkalinity; 40 - 50 mg/1 as CaCOj,
allows pH adjustment for corrosion
control.
Less favorable for low alkalinity
waters, increased chemical cost
unless COj source becomes available
or dolomitic lime proves successful
250 # / M, G. of alum, 206 P/m.g. of Ca (cH) 2
pH from 6,0 - 6.4 more difficult tc main-
tain.
Hydrolysis products, flocculant, much longer
in size , form slowly with gentle mixing
much slower at colder temperatures.
leGer.erally less than .75 gal/ft^/min loading
rate, sensitive to velocity gradients in
settli r.g basin .
Gelatinous sludge normally less than 1%
solids which can be thickened only to about
6% solids. Less pounds per million gals,
produced, approximately 400'. kpprox-
.imately 1% of total water treated lost due
to sludge discharge.
Filter runs dependent upon amount of floe
carry over.
Very low alkalinity and hardness, generals
more red water, corrosion problems.
Lower chemical cost and less operating and
maintenance expense when alum sludge is
not treated for disposal.
2
Assuming more effi-
cient first stage
carbonation
-------
PRE-CHL0R1NE
RAW WATER
POST LIME
SETTLING
SLUDGE TO WASTE
SETTLING
ALUM
TYPICAL ALUM WATER TREATMENT PLANT
FIGURE 1
-------
TO RAW WATER
C02 FROM STORAGE
OR OTHER SOURCE
MgiHCO,)- STORAGE
F I LTRATE
SOL IDS
30 40 SOLIDS
TO IANOFILL
THICKENER
MAGNESIUM RECYCLE AND RECOVERY UNITS
MAGNES IUM PROCESS FLOW DIAGRAM
FIGURE 2
-------
C02 STORAGE
F
1
LIT 1 E ! ft
I 1 1
s!
i
KJ
STABILIZATION
KglHCOa )2
)¦¦ RAW
WATER
RECYCLE
PUMP
SETTl/ING
MAGNPSIUM
CARBONATI ON
FILTH
SETTLING
ALUM
SLUDGE
TO WASTE
MgtHCCh); STORAGE
THICKENER
SLUDGE UNDERFLO*
i^Oi
\CAKE TO LANDFILL
VACUUM FILTER
MAGNESIUM RECYCLE
HAGNESIUM PROCESS FLOW DIAGRAM
FIGURE 3
-------
DEWATERED
CARBONATED SLUDGE
REPULP
CaO FOR REUSE OR SALE
CaCO
FLOTATION
KILN
(FLOAT)
VACUUM
F ILTER
(UNDERFLOW)
TURBIDITY FOR DISPOSAL
LIME RECOVERY
WITH USE OF CARBON DIOXIDE PRODUCED FOR
SLUDGE CARBONATI ON AND SETTLED WATER STABILIZATION
MAGNES IUM PROCESS FLOW DIAGRAM
FICUP.E 4
-------
I
fo
U3
F
1
L
T
E
R
S
STABILIZATION
RAW WATER
M«m°u ST0R*GE
SETT ulNG
MAGNUS I UM —
C4RB0NATI ON
S E T T L/l N G
THICKENER
VACtlU#
FILTER
REPULP
KILN
FLOTATION
VACUUM
FILTER
TURBIDITY
LIME RECOVERY
MAGNESIUM PROCESS FLOW DIAGRAM
FIGURE b
-------
HEAT EXCHANGER
\
to
¦fr-
AERAT ION
CELLS
BASIC CARBONATE
KETTLE
35
PRODUCTiON OF MAGNESIUM CARBONATE TRl-HYDRATE
OR BASIC CARBONATE FROM WATER PLANT SLUDGE
MAGNESIUM PROCESS FLOW DIAGRAM
FIGURE 6
-------
F
1
L!T i
. s
STABILIZATION
I
to
Ul
RAW WATER
AERATION
CELLS
HEAT
EXCHANGER
o
Vc &- STGRAG£
SETTUING
MAGNPS i {IM
CARBQNATI ON
THICKENER
SETT Li! NG
VACUUM
FILTER
-±C>
CaCOi
FLOTATION
PRODUCT
0EWATER1NG
REPULP
VACUUM
FILTER
MeC03»3H20
TURBIDITY
Li ME AND MAGNESIUM RECOVERY
MAGNESIUM PROCESS FLOW DIAGRAM
C L t. l, 7
-------
Raw Water
L'reatec! Water
tt///// /V)rrrr
V///////YJ/////////-T7
Lime
1'LAN VIEW
zzzzz
Treated ''ater
htpf// // ////////////// ///////////////// / //
R,
SECTION VIEW
RAPID MIX AND CHEMICAL ADDITION POINTS
FIGURE 8
VI-26
-------
10-50 mA SIGNAL
oo
pH METER
RECORDER CONTROLLER
RAPID MIX
LIME FEED
PUMP
LIME
SLAKER
<
I
FLOCCULATION pH CONTROL SYSTEM
-------
SETTLED
SLUDGE
MgC03 to RAW WATER
CARBONATED
SLUDGE
FILTRATE
ELECTRICAL
PANEL
SUPERNATANT
THICKENER UNDER FLOW
DEWATERED
CAKE |
STORAGE
H
MONTGOMERY WTP
SOLIDS HANDLING FACILITIES
Figure 10
-------
Legend for Figure 10
Units Comprising Solids Handling System (See Diagram)
0-15 GPM Variable Speed Moyno Pump
2 dual ccl.1, 2' X 2' each, flotation cells with a total detention
time of 45 minutes with a sludge flow rate of 7 GPM
30 GP1VI submersible pump to the thickener
10 foot diameter reactor-clarifier used as thickener
Vacuum filter station
1) 3' >' 3' vacuum filter
2) Vacuum pump
3) Filtrate pump
4) Filtrate receiver
1800 gallon magnesium bicarbonate storage tank
Recycle pumping system, 0-15 GPM
Sludge drying beds, 8' / 8', 6" of gravel and four inches of
sand
VT.-29
-------
f PH
10-50 mA SIGNAL METER
CURRENT TO
AIR TRANSDUCER
CONTROLLER
RECORDER
SLUDGE
SLUDGE
CARBONATER
O
oo
SLUDGE CARBONATION
pH CONTROL SYSTEM
AIR VALVE
:C02
Figure- 11
-------
$ 20.00-
Mg = 4mg/I in raw water
30#/D LOSS IN FILTER CAKE
(Mg as CaC03>
$ 15.00-
$/mg
$ 10.00
< $ 5.00
I
• ¦ « i »
11.0 11.2 11.4 11.6
pH
MAKE-UP MAGNESIUM COST
AS A FUNCTION OF COAGULATION pH
Figure 12
-------
50 Mg/I MgCo3 RECYCLE
CaO @ $.01/ #
C02 @ $.015/ # ^
$ 40.00-
$ 30.00-
$ 20.00-
$ 10.00-
11.0 11.2 11.4 11.6 11.8
PH
LIME AND C02 COSTS AS
A FUNCTION OF COAGULATION pH
Figure 13
-------
50mg/f MgC03 RECYCLE
CaO (5) $.01/#
C02 @ $.015/#
30.00-
$/mg
20.00-
10.00-
11.0 11.1 11.2
11.3 11.4 11.5 11.6
PH
LIME, C02, and MAGNESIUM TOTAL
COST AS A FUNCTION OF COAGULATION
pH
Figure 14
-------
RECYCLE
$ 20.00-
$ 15.00-
$/mg
$ 10.00 H
50 mg/l MgC03 RECYCLE
CaO <§) $.01/ #
M g C O 3
<
Z $ 5.00
i I 1 1 1 1 1
11.0 11.1 11.2 11.3 11.4 11.5 11.6
pH
LIME AND MAGNESIUM COSTS
AS A FUNCTION OF COAGULATION pH
Figure 15
-------
I
u>
PUMPER CELL
PUMPER CELL
.. _ PUMPER CELL
Reagents
nV
T
DEWATERED CAKE
CaC03 )
a
CLAYS
CONDITIONING AND RESLURRY CELL
^ ft Pi
TAILINGS
I"O LANDFILL
CLEANER #2
CONCENTRATE
CLEANER #1
CONCENTRATE
ROUGHER CONCENTRATE
CLAYS,
INERTS,
LO-CaCO^
FINAL CONCENTRATE f Hl-CaCO-, )
TO DEWATERING. I LO-INERTS >
£ LIME KILN & CLAY
MAGNESIUM CARBONATE PROCESS
FLOTATION CIRCUIT
Figure 11
-------
REFERENCES
Thompson, C. G., Singley, J. E., and Black, A. P.
"Magnesium Carbonate — A Recycled Coagulant," Journal
AWWA, 64:1:11 {January, 1972).
Thompson, C. G., Singley, J. E,, and Black, A, P.
"Magnesium Carbonate — A Recycled Coagulant Part II, "
Journal AWWA, 64:1:94 (February, 1.972).
Thompson, C. G. and Black, A. P. "Progress Report of the
Magnesium Carbonate Project, Montgomery, Alabama,"
presented to 92nd Annual AWWA Conference, June, 1972.
Sperry, W. A, "The Lime Softening of Water and the Use of th
Sludge as an Aid Thereto," Journal AWWA, 6:215
(June, 1919).
Hartung, H. O. "Experience With Up-Flow Type Basins,"
Water and Sewer Works, 1:91 (January, 1944).
McCauley, R. F., and Eliassen, R. "Accelerating Calcium
Carbonate Precipitation in Softening Plants, " Journal
AWWA, 47:487 (May, 1955).
Tuepker, J. L.f and Hartung, H. O. "Effect of Accumulated
Lime-Softening Slurry on Magnesium Reduction, "
Journal AWWA, 52:106 (January, 1960),
Lawrence, R. W. "Equilibrium and Kinetics for the
Carbonation of Magnesium Hydroxide Slurries, "
Research and Development Progress Report No. 754,
U.S. Department of Interior, (December, 1971).
VI-36
-------
APPENDIX
VI-37
-------
CONTROL SYSTEMS AND SAMPLING LOCATION
A) Rapid Mixer number 1. Total and calcium hardness are
determined on a filtered sample from which the magnesium
feed can be determined.
B) Rapid mixer number 2. Automatic pi I control of lime feed.
C) Carbonation point 1. pH measurement and manual control of
COg rotameter to maintain a pH of 10. 3. When the pH is too
low or too high, the water is clear indicating that calcium
carbonate precipitation is not taking place.
D) Settled magnesium water flume. pH, turbidity, total hardness,
calcium hardness, alkalinities, and acid turbidity are
determined on a routine basis.
E) Filtered magnesium treated water - continuous turbidity
monitoring along with alkalinities, pH, and hardness deter-
mined on a routine basis.
F) Carbonated Sludge - Automatic pIT control of the carbon
dioxide flow along with alkalinity titrations on a routine basis.
G) Recycled magnesium control system - alkalinities measurement
and flow control.
H) Vacuum filter - filter rates, solids inflow, filtrate alkalinities,
filter cake solids, and filter cake composition are determined
on a routine basis.
Suggested Automatic Control Systems
I) Total hardness recorder at point A. This would relate directly
to the magnesium concentration and could be used to automate
the magnesium recycle.
2) pH Control system at points C and D to record and control the
stabilization pH.
VI-38
-------
C02 STORAGE
RAW
WATER
U2(HC03); storage
STABILIZATION
CARBONATldN
SETTLING
ALUM
ATE
-SLUDGE
TO WASTE
SLUDGE UNDERFLOW
\CARE TO LANDFILL
VACUUM FILTER
MAGNESIUM RECYCLE
MAGNESIUM PROCESS FLOW DIAGRAM
-------
TYPICAL CONTROL TESTS
M agnesium
Rapid mix number 1
pH 10.3
Total Hardness 100
Calcium Hardness 25
Magnesium Hardness 75
Rapid mix number 2
pi J 11.60
Magnesium Stabilized Water
. g ^ Q
T o t a! II a r d n e s s 70
Calcium Hardness 65
Total Alkalinity 65
(Non-carbonate hardness i.s equal to the mg/i of magnesium sulfate
feed)
Turbidity 7.0 FTU
Aeid Turbidity 1.5 FTU
Carbonated Sludge
pi I 7.3
Total Alkalinity 14, 000 mg/i
Color 7 00 Ft. -Co. units
Alum
l'Toccu la to r
pit 5.9
Total Alkalinity 2.0
Settled Stabilized (lime) Water
pH 9.0
Total Alkalinity 20.0
Total Hardness 28. 0
Turbidity 6.0
VI-A0
-------
Advantages oJ' the Magnesium Carbonate Process
Soft Turbid and jar Colored Waters
1. Provides an economical and practical solution to the problem
of the disposal of water treatment plant sludges.
2. Provides For the first time a coagulant which can he recycled
and reused,
3. Increase settling rate of the floe produced should allow higher
clarifier loading rates,
4. Produces a treated water which is noncorrosive since it can
be stabilized by pU control.
5. Coagulates water in the pll range 11.2 - 11.5 which inactivates
most viruses and destroys bacteria.
6. Should in most cases eliminate prechlorination where used.
7. In many cases, reduces chemical treatment costs.
8. Requires no important changes in treatment plant.
9. Simple to operate and may be automated.
10. Removes both iron and manganese where present.
11. Improves filterability of settled water.
Additional Advantages t'or Hard Water
1. Makes it possible to reduce lime costs by about 50% by
recalcining with excess lime to be sold for some waters.
2. Recovers the magnesium values from the sludge which may be
sold.
3. Substantially reduces present chemical treatment costs, in
some cases by $200, 000 - $700, 000 per year.
VI-41
-------
MAGNESIUM CARBONATE PROCESS
SLUDGE HANDLING DATA DATEFRIDAY, FEBRUARY 23, 1973
TIME
SIudge
Solids (X)
Filtrate
Alkali nity
Solids
g/ft2
Drum
Speed
ft/ft^/hr.
Co
Ca
ke Anal t,
3s caco
Mg
iszs
f. -
% Moisture
3:15
Started
9 AM
43 .4
--
303 .0
.88
3 .9109
--
_
36 . 796
10 AM
—
--
.88
—
--
-
11 AM
TS 36 8
¦ CH 300
7 ,400
307 .2
.88
3,9648
344
34
37 .408
12 N
MH 6 8
—
.88
—
--
-
—
1:30
39 . 9
—
353 .4
.88
4.5614
--
-
36.393
2 PM
--
--
--
.88
—
--
-
—
3 PM
--
—
--
.88
--
__
-
--
4 PM
24.2
169.S
. 88
2.2857
(This
s low d
e to a low J
evei
Ul
1
Closed
rn ¦ ni
trer sen
6 PM
REMARKS: LEAF FILTER TEST 4:15 Form Wet 58.8
5:30 Dry Pry 37.0
21.8 % Moist = 37.07%
370 g/f+2 «¦ 4.74 #/f+2/hr
-------
NAGKBSIl'tl CARSON ATE PROCESS
SLVDGE HANDLING DATA DATE MONDAY, MARCH 5, 1973
TIKE
SIudge
Solids (%,)
Fi1trate
A1 kalini t u
Solids
q/ft2
(fpm}
Prom
Speed
#/f t2/hi-
Cake Analysis
(as daCO-%}
Bel t
Setting
Ca
Mq
% Moisture
8 AH
49.5
--
450.6
1,666
ll . 02 66
38 .08
1 . 0
9 AM
10 AM
11 AM
48 . 8
529 . 2
1 . 25
9.7094
37.84
. 5
12 W
1 PM
TTI 570
jo 5 Cii 530
MM 40
9,000
409 . 2
1 .66 6
10.0134
524
35
39.05
1 . 0
2 PM
43 . 9
367 ,2
J .666
8.9857
40 .29
1 .0
3 PM
4 PM
5 PM
6 PM
REMARKS: LEAF FILTER TESTS
Cake #
Tine(Sec)
Wei gilt
(Grams)
Cake % Moist
Filtrate
Eqaiv. Belt
Filter Fate
Sludg &
Form
Dry
Wet
Dry
M.I.
Setting
(*/f+z/hr)
Solids
1
25 5
330
97 .5
57.7
40 . 82
?&.0
i>
! .44
48 . U%
2
160
230
77.2
45.8
40 .67
64 . 0
. 5
8.40
48 . 8%
3
115
170
65,2
38.7
40.64
59.0
1 .0
9 .47
45.3%
-------
.Jar Test
iJ(.)I ,Y:VI!¦]K CONDITIONING OF CARBONATED SLFDGE
Polymer - Dow A2'5
To determine1 the optimum polymer dosage for sludge con-
ditioning, a jar test is run each day. A.s the sludge solids change in
character and concentration, so does the required polymer dosage.
Following .settling, the jars are rapidly mixed, and the time to
filter 100 mi of the mixed sludge determined for each polymer
dosage. The results from a typical jar test is a.s follows:
Polymer - Dow A23
¦Jar No. 1 2 3 4 5 6
Polymer Dosage (Mg/i) 013579
Sludge Level After 10 IVIin.
Settling (inches) 43/8 4 3/8 4 1/8 2 1/4 2 2
Time for filtration of
100 mi (Sec) 327 265 279 189 192 185
At the present polymer feed levels of 4-7 mg/1 , a cost of
less than 30 cents per million gallons of water treated results. The
polymer acts to produce a clearer supernatent, increase the solids
concentration to the vacuum filter, and increase the filterability of
the1 sludge.
VI-44
-------
FiIter Cake
-Flotation Reagents
Condi tioner
Rougher
Rougher Concentrate
Rougher Tails
First Cleaner
1st Cleaner Concentrate 1st Cleaner Tails
"V/
Second Cleaner
2nd Cleaner Concentrate
(Product)
2nd Cleaner Tails
SCHEMATIC DIAGRAM OF FLOTATION CIRCUIT USED AT MONTGOMERY, ALABAMA
VI-45
-------
NOTES
-------
NOTES
-------
NOTES
-------
NOTES
------- |