DIGESTED
SEWAGE
SLUDGE:
CHARACTERIZATION
OF
A
RESIDUAL
AND
MODELING
FOR
ITS
DISPOSAL
IN
THE
OCEAN
OFF
SOUTHERN
CALIFORNIA
by
William
Karl
Faisst
EQL
REPORT
NO.
13
June
1976
ENVIRONMENTAL
QUALITY
LABORATORY
CALIFORNIA
INSTITUTE
OF
TECHNOLOGY
Pasadena,
California
91125
Supported
by
the
Environmental
Protection
Agency
(Research
Grant
R80069-03-1
and
Research
Contract
68-03-0434)
and
by
the
Environmental
Quality
Laboratory
from
Ford
Foundation
and
other
gift
funds
iii
PREFACE
Sewage
sludge,
the
liquid-solids
suspension
resulting
from
the
sedimentation
phase
of
wastewater
treatment,
contains
a
substantial
portion
of
the
waste
materials
that
enter
the
sewers,
but
only
repre-
sents
one
or
two
percent
of
the
total
plant
flow
by
volume.
The
sludge
is
thus
a
concentration
of
the
municipal
and
industrial
residues
that
are
captured
by
the
treatment
processes
rather
than
being
dispersed
along
with
the
effluent
in
the
environment.
The
quantities
of
sludge
produced
increase
as
the
effectiveness
of
wastewater
treatment
is
im-
proved.
Recent
public
laws
have
mandated
a
general
upgrading
of
waste-
water
treatment
facilities.
The
resulting
sludge
must
be
treated
and
disposed
of,
hopefully
in
the
most
economical
and
environmentally
sound
method
available.
This
document
reports
on
research
on
digested
sewage
sludge
and
modeling
of
sludge
disposal
done
under
the
joint
auspices
of
the
Depart-
ment
of
Environmental
Engineering
Science
and
the
Environmental
Quality
Laboratory
of
the
California
Institute
of
Technology.
This
work
is
part
of
an
ongoing
effort
in
the
area
of
residuals
management
that
includes
basic
laboratory
research,
conceptual
engineering
modeling,
and
economic
analysis
of
important
environmental
problems.
In
the
laboratory
inves-
tigations,
the
'specific
characteristics
of
a
particular
problem
area,
such
as
sewage
sludge
treatment
and
disposal,
are
identified.
Engineer-
ing
modeling
efforts
then
draw
on
laboratory
work
in
order
to
propose
feasible
alternatives
which
can
be
compared
on
a
basis
of
both
potential
environmental
impacts
and
economic
viability.
The
end
results
of
all
efforts
should
be
a
solid
framework
of
facts
and
alternatives
for
use
by
the
decision-makers
who
must
select
the
actual
plan.
This
work
was
submitted
as
a
thesis
under
the
title
Digested
Sludge:
Delineation
and
Modeling
for
Ocean
Disposal,
in
partial
ful-
fillment
for
the
degree
of
Doctor
of
Philosophy
at
the
California
Institute
of
Technology,
May,
1976.
Financial
support
for
this
work
was
generously
provided
by
the
people
of
the
United
States
through
the
Environmental
Protection
Agency
(Research
Grant
R80069-03-l
and
Research
Contract
68-03-0434)
and
by
the
Environmental
Quality
Laboratory
from
Ford
Foundation
and
other
gift
funds.
The
author
wishes
to
thank
Professors
Jack
E.
McKee,
James
J.
Morgan,
and
Norman
H.
Brooks
for
their
help
and
advice
throughout
this
research.
This
manuscript
was
expertly
prepared
by
Ms.
Pat
Rankin
and
Ms.
Pat
McCall;
their
help
and
encouragement
is
greatly
appreciated.
William
K.
Faisst
v
EXECUTIVE
SUMMARY
The
Sludge
Problem
Sewage
sludge
is
a
concentration
of
the
residues
that
our
modern
municipal
and
industrial
society
discharges
to
the
sewerage
system.
The
sludge
solids
are
removed
from
the
sewage
flow
by
sedimentation
and
then
partially
stabilized
by
biological
digestion.
Typical
digested
sludges
are
95
to
98
percent
water,
with
the
majority
of
their
potential
environ-
mental
contaminates
such
as
trace
metals
associated
with
the
two
to
five
percent
solids
fraction.
This
particulate
matter
has
usually
been
char-
acterized
only
for
such
gross
constituents
as
total
solids,
total
trace
metals,
and
pesticides.
For
this
work,
the
sludge
particle
system
was
approached
on
a
much
more
detailed
level.
There
is
strong
evidence
that
the
particles
in
di-
gested
sludge
may
cause
serious
deleterious
effects
when
discharged
near
the
productive
surface
waters
of
the
ocean.
Such
effects
include
disrup-
tion
of
light
penetration
into
the
water
column.
This
can
drastically
reduce
photosynthesis,
the
primary
productivity
in
the
ocean.
Sludge
particles
discharged
to
the
ocean
are
heavier
than
the
surrounding
water
and
tend
to
settle.
They
may
"blanket"
the
bottom,
interfering
with
the
normal
life
cycles
of
bottom-dwelling
organisms.
The
digested
sludge.
only
partially
stabilized
by
treatment
processes
before
discharge,
may
also
drastically
alter
the
chemistry
of
the
sediments
where
it
settles.
The
very
fine
material
in
the
sludge
does
not
settle
easily
and
may
be
carried
many
kilometers
by
the
prevailing
ocean
currents.
The
vi
trace
metals
and
other
components
incorporated
into
the
particles
are
also
then
carried
great
distances.
Since
many
marine
organisms
such
as
bivalves
and
zooplankton
are
filter
feeders,
the
presence
of
sludge-
particulate
matter
of
the
right
size
in
the
water
column
may
lead
to
uptake
of
sludge
contaminants
in
the
food
chain.
Experimental
Measurements
The
actual
particle
size
distributions
for
two
digested
sludges
were
measured
electronically.
The
measured
number
counts
were
very
high,
approximately
10
12
particles
per
liter;
the
majority
of
the
par-
ticles
had
diameters
of
less
than
10
micrometers.
Particles
of
less
than
10
micrometers
most
readily
disrupt
the
penetration
of
sunlight
in
seawater
and
are
selectively
chosen
by
many
filter
feeders
in
the
ocean.
Such
particle
systems
also
have
very
high
specific
surface
areas
avail-
able
for
chemical
reactions
such
as
adsorption
and
ion
exchanges.
The
total
sludge
surface
area
per
unit
volume,
calculated
from
the
particle-
size
data,
is
several
orders
of
magnitude
greater
than
that
of
natural
seawater.
Experiments
were
carried
out
to
examine
the
interactions
of
sludge
particles
and
trace
metals
during
both
oxic
mixing
and
sedimentation
in
seawater.
These
experiments
simulated
the
discharge
of
sludge
to
the
ocean.
The
sedimentation
experiments
were
run
at
different
dilutions
(volume
of
seawater
to
volume
of
sludge)
to
see
if
sedimentation
char-
acteristics
changed
as
the
particle
concentration
was
decreased.
A
ten-
fold
dilution
increase
slowed
the
particle
settling
velocity
distribution
vii
by
an
order
of
magnitude.
This
result
suggests
that
coagulation
of
the
sludge
particles
may
be
an
important
phenomena
in
the
ocean.
Slower
sedimentation
rates
imply
transport
over
much
larger
distances
in
the
ocean.
To
a
first
approximation,
the
trace
metals
measured
(copper,
chromium,
iron,
nickel,
lead,
and
zinc)
settled
with
the
same
mean
ve-
locity
as
the
particles.
The
miximg
experiments
simulated
the
travel
of
sludge
particles
in
oxygen-rich
seawater.
For
mixing
times
of
up
to
28
days,
less
than
ten
percent
of
the
solids
dissolved
or
were
oxidized;
nickel
was
the
only
trace
metal
that
mobilized
away
from
the
particles.
The
concentra-
tion
of
dissolved
trace
metals
was
also
measured
in
the
digested
sludge.
All
the
metals
were
in
the
particle
form
at
greater
than
99
percent
ex-
cept
for
manganese,
which
was
less
than
two
percent
soluble.
The
low
solubility
of
the
trace
metals,
both
in
the
sludge
and
upon
mixing
with
seawater,
suggests
that
the
metals
would
not
be
available
in
their
more
toxic
soluble
forms.
Modeling
for
Ocean
Disposal
The
results
of
the
experimental
work
were
combined
with
existing
information
to
propose
and
model
a
possible
sludge
disposal
scheme
to
the
San
Pedro
and
Santa
Monica
Basins
off
southern
California.
These
deep
geologic
structures
are
close
to
the
shore
and
nearly
devoid
of
life.
It
is
assumed
that
sludge
discharges'near
the
basin
bottoms
would
be
trapped
in
the
sediments.
A
combination
of
hydraulic
computer
simu-
lations
and
sedimentation
calculations
suggests
that
the
initial
plume
viii
would
rise
no
more
than
120
meters
for
releases
at
depths
of
730
meters.
and
that
the
solids
would
reach
the
sediments
within
10
km
of
the
point
discharge.
Initial
dilutions
were
estimated
to
be
450
to
2600.
Mass
balances
on
the
oxidizable
chemical
constituents
in
sludge
indicated
that
the
nearly
anoxic
waters
of
the
basins
would
become
wholly
anoxic
as
a
result
of
proposed
discharges.
From
chemically-equilibrium
computer
modeling
of
the
sludge
digester
and
dilutions
of
sludge
in
an-
oxic
seawater.
it
was
predicted
that
the
chemistry
of
all
trace
metals
except
Cr
and
Mn
will
be
controlled
by
the
precipitation
of
metal
sulfide
solids.
The
net
environmental
impacts
of
this
scheme
should
be
salutary.
The
trace
metals
in
the
sludge
should
be
immobilized
in
the
anaerobic
bottom
sediments
of
the
basins.
Apparently
no
life
forms
higher
than
bacteria
are
there
to
be
disrupted.
The
proposed
deep-water
discharges
would
remove
the
need
for
potentially
expensive
and
energy-intensive
land
disposal
alternatives
and
end
discharge
to
the
highly
productive
water
near
the
ocean
surface.
ix
TABLE
OF
CONTENTS
PREFACE
EXECUTIVE
SUMMARY
LIST
OF
FIGURES
LIST
OF
TABLES
LIST
OF
NOTATION
AND
ABBREVIATIONS
iii
v
xiv
xvii
xx
CHAPTER
1
SEWAGE
SLUDGE
AND
THE
ENVIRONMENT
1.1
The
Sludge
Problem
1.2
Environmental
Impacts
1.3
Research
Objectives
and
Thesis
Organization
1
1
6
13
1.3.1
1.
3.
2
Research
Objectives
Thesis
Organization
13
18
CHAPTER
2
THE
DIGESTED
SLUDGE
PARTICLE-TRACE
METAL
SYSTEM:
I.
SLUDGE
CHARACTERIZATION--A
REVIEW
II.
PHYSICAL
AND
CHEMICAL
MEASUREMENTS
III.
SLUDGE
INTERACTIONS
WITH
SEAWATER
20
PART
I
CHARACTERIZATION
OF
DIGESTED
SEWAGE
SLUDGE:
A
REVIEW
20
2.1
Introduction
2.2
Sludge
Digestion
2.3
Physical
Properties
of
Sludge
20
21
24
2.3.1
2.3.2
2.3.3
2.3.4
Water
Content
Particle
Size
and
Particle
Density
Techniques
for
Particle
Sizing
and
Counting
Particle
Sizing
by
Filtration
24
28
32
33