V-/EPA
                                United States
                                Environmental Protection
                                Agency
                                Municipal Environmental Research
                                Laboratory
                                Cincinnati OH 45268
                                Research and Development
                                EPA-600/S2-81-242  Dec. 1981
Project  Summary
                                Physical  and  Chemical
                                Characteristics of  Synthetic
                                Asphalt  Produced  from
                                Liquefaction of Sewage Sludge

                                J. M. Donovan, R. K. Miller, T. R. Batter, and R. P. Lottman
                                  Direct thermochemical liquefaction
                                of  primary  undigested  municipal
                                sewage sludge was carried out to
                                produce  a low molecular weight
                                steam-volatile oil, a high molecular
                                weight  synthetic  asphalt,  and a
                                residual char cake. The latter product
                                is capable of supplying the thermal
                                energy  requirements  of  the
                                conversion  process.  The  steam-
                                volatile oil has immediate value as a
                                synthetic  fuel  oil. The synthetic
                                asphalt  may prove to be a  useful
                                cement  for paving  with  further
                                research, or it can be used as a fuel or
                                coking stock. It is outwardly similar to
                                petroleum asphalt, but chemically
                                different.
                                  The thermochemical liquefaction
                                process should be capable of opera-
                                ting in a technical and environmentally
                                acceptable  manner in conjunction
                                with many existing wastewater treat-
                                ment facilities. The overall feasibility
                                of the process depends on the value of
                                the oil and synthetic asphalt products
                                as petroleum replacements and on the
                                costs associated  with disposal of
                                sludge. Projected economics indicate
                                that  the process has  considerable
                                promise for many potential sites in the
                                United States at the present time.
                                  This Project Summary was develop-
                                ed by EPA's Municipal Environmental
                                Research Laboratory, Cincinnati. OH,
                                to announce key  findings of  the
                                research project that is fully docu-
                                mented in a separate report of the
                                same title fsee Project Report ordering
                                information at back).
                                Introduction
                                 Disposal  of sewage  sludge  is an
                                increasing problem for  many munici-
                                palities in the United States. Currently,
                                there is a need to implement alternative
                                disposal technologies. The alternative
                                technologies need to be energy efficient
                                and,.if possible, some product of value
                                should be recovered from sludge. Direct
                                thermochemical  liquefaction has the
                                capability of meeting these requirements.
                                 Thermochemical liquefaction investi-
                                gations by various authors have shown
                                that organic biomass can be converted
                                to bitumen, heavy oil, and distillate oils
                                having combustion heats closely
                                approximating petroleum products.
                                 The  utility of the high molecular
                                weight fraction  of the  liquefaction
                                product (because it is a substantial part
                                of the  liquefaction products) is often
                                questioned. To  this end, the present
                                study was conducted to determine the
                                value of this fraction  as synthetic
                                asphalt for use as a paving cement. A
                                synthetic asphalt product  would be
                                valuable since petroleum asphalt has
                                increased in value with  escalating

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petroleum costs and it is being increas-
ingly used (e.g., production of olefins) as
a petrochemical feed stock.
  The low molecular weight product of
biomass liquefaction has always been
viewed as a valuable synthetic fuel. In
the case of sludge liquefaction, the low
molecular  weight  oil product was
conveniently  separated  during  the
reaction period  by steam auto-distilla-
tion.  This  steam-volatile  oil  was
obtained in significant quantities using
a relatively simple process. This process
also led   to simplified separation of
excess water present because  of the
use of wet sludge.
Thermochemical  Liquefaction
of Primary Sewage Sludge
  Previous work in the area of direct
thermochemical liquefaction of sewage
sludge and other forms of biomass has
resulted  in the  production  of  high
molecular  weight  fractions  that are
similar  in  appearance  to  petroleum
asphalt.  A high   molecular  weight
fraction derived from pure cellulose  in
our  Battelle-Northwest  laboratory
showed promise as a replacement  or
extender  for  petroleum  asphalt.
Because of the high cost of pure cellu-
lose and other biomass forms,  other
alternative  feed  materials  were
suggested. Primary undigested sewage
sludge,  because of its low or negative
cost, was a logical  choice.
Experimental Procedure
  Although the intended feed stock for
the experimental work was to have been
dried primary sludge from Honolulu, the
actual  feed  stock was fresh, primary
sludge dewatered  with polymer.  The
fresh sludge was preserved by adding
chloroform and, later, by freezing. It was
then sent by  air  to  our  laboratory at
Richland, Washington.
  Fresh   sludge  received  at  our
laboratory was prepared for reaction by
adding a base (either Na2C03 or CaO).
This material was then loaded into an
Inconel linerand blanketed with an inert
gas (Argon). The liner was sealed and
placed into  an autoclave. Water  was
added between the liner and autoclave
to assist in heat transfer and to balance
the differential pressure across the liner
that  would  result  from  heating  to
reaction  temperature.  Pressure inside
the  liner  was controlled to equal  the
vapor pressure of water in the annular
space; this prevented either implosion
or explosion of the liner.
  After being prepared  in this manner,
the autoclave was heated to reaction
temperature  (2 to 3  hours), held at
reaction temperature for 1 hour, and
cooled 4 to 6 hours. During the heating,
reaction,  and cooling periods, gas and
steam were  emitted  from  the  liner
because of the pressure  in  the liner
caused by the gas generation accom-
panying thermochemical liquefaction.
The predominant gas formed and dis-
charged was carbon dioxide, but steam
and steam-volatile oil  were  also dis-
charged with the gas. These gases were
condensed in a water trap and saved for
later   analysis.  Although  hydrogen
sulfide  was   monitored  during  the
reactions,  none was detected.

  After cooling,  the   autoclave  was
opened, the liner removed and opened,
and the product taken out. This product
could  be  separated into an aqueous
supernatant  liquid  and  a char cake
either by settling or centrifugation. In
our laboratory work, the latter was more
convenient and was used most often.
The supernatant liquid was analyzed for
its volatile constituents and-was sub-
jected to treatability analyses. The char
cake  contained the  high molecular
weight fraction  of  the  liquefaction
product, which was intended to become
synthetic asphalt. As a result of being
intermixed with the char and ash,  the
high molecular weight fraction was not
acceptable for use as a replacement or
extender for petroleum asphalt since it
would not  melt when  heated nor mix
with heated petroleum  asphalt.
  To overcome the problems caused by
the char and ash, the  high molecular
weight fraction was separated by sol-
vent  extraction. Previous liquefaction
work, and specifically work with lique-
faction products from  cellulose, indi-
cated that acetone was an acceptable
solvent. Soxhlet extractors were used, and
extraction times were 8 to 24 hours. The
extracted char cake was  crumbly after
the solvent was  removed in a rotary
evaporator under vacuum. The resulting
material, whose appearance resembled
heavy crude oil, was not acceptable for
direct use  as a  petroleum  asphalt
replacement or extender in preliminary
work because its viscosity was not high
enough.
  The use  of  vacuum distillation to
remove residual low molecular weight
liquefaction products from the extracted
product  solved  the  low   viscosity
problem. Although  only a very small
amount  of   low  molecular  weight
material was removed, the viscosity of
the  product  was  substantially
increased.
  Synthetic  asphalt samples  prepared
in this  manner were  sent  to Dr.  R.
Lottman at the University of Idaho for
testing and analysis as paving cements.
Liquefaction Test Results
  Reaction  conditions and resulting
product yields are  given  in Table  1.
Pressure may be estimated from the
vapor pressure - temperature relation-
ship for water. The mean total yield (oil +
asphalt) for  conversions carried out at
320°C with  Na2CO3 was 20.4% with a
standard deviation of 7.1%. Total yield
seemed to increase with temperature
since the yields  at  295°C and 345°C
differ from the mean by 1.5 and 2.3
standard deviations, respectively.
  Several runs at 320°C were  done to
provide the  University of Idaho with a
large, consistent sample for a complete
series  of   asphalt   paving  material
testing. Unfortunately, this limited the.
amount of data taken at other points|
which in turn limited our ability to des-
cribe yield as a function of temperature.
  Lime (CaO) is apparently an excellent
liquefaction   adjunct*  having  yields
approximately  equal  to  those   of
carbonate under the same experimental
conditions.  Unfortunately,  asphalt
testing results indicated  that the one
sample we produced using lime was an
inferior  product.   Because   of  the
inherent variations in using sludge as a
raw material, perhaps additional trials
with lime would give better results.
  Elemental analyses of the products
produced  by  liquefaction (Table  2)
allows a comparison with conventional
feeds and petroleum asphalt. The sulfur
concentration in the synthetic asphalt
and oil samples places them in approxi-
mately a grade four heating oil category.
Both the sulfur and nitrogen contained
in the synthetic asphalt samples and
oils result from the  use of sludge. Our
analyses  of volatiles  (reported  next)
show  that  sulfur  and  nitrogen are
"Previous liquefaction work has referred to alkaline
 adjuncts as catalysts However, our previous work
 has indicated that the alkali is a reactant, and that
 the overall reaction is highly dependent on pH.
 Because of this, alkalis used for liquefaction an
 referred to as adjuncts in this report

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 Table 1.    Reaction Conditions and Yields
Experimental
Designation
HS-3
HS-4
HS-5
HS-6
HS-7
HS-8
HS-9
HS-10
Dry
Ash-Free
Sludge, Kg
2.61
2.52
2.41
3.99
2.01
2.28
2.49
1.33
Steam '
Volatile
Oil gm
330
480
-0-
450
-0-
250
450
250
Synthetic
Asphalt, gm
268
440
250
330
310
50
430
164
Total Yield
%*
23
37
10
20
15
13
35
31
Reaction
Temp. °C
320
345
295
320
320
320
320
320
5% by Weight
NatCOs
/Va2C03
/Va2CO3
/Va2CO3
Na2C03
Na2C03
CaO
NatC03
 * Weight of light oil and synthetic asphalt as percent of dry, ash-free sludge.
 Table 2.    Elemental Analyses (Percent by WeightJ
Element
C
H
N
0
S
Petroleum
Asphalt
AC-10
87.
11.
0.4
1.
-
Synthetic*
Asphalt
74.
10.
4.
9.
0.8
Steam-Volatile^
Oil
77.
12.
3.
7.
0.9
Char Cake
HS-10
26.
3.
0.9
10.
-
 * Average values from Experiments HS-4. HS-5, HS-6, HS-9, and HS-10.
 t Average values from Experiments HS-9 and HS-10.
 substituted  into the aromatic and ali-
 phatic  constituents  of  the  volatile
 products. As a result of this, we suspect
 that  the synthetic asphalt and  oil
 products also contain a wide range of
 substitutecLsulfur and nitrogen com-
 pounds. For use as fuel, this is probably
 of minor concern. For use as synthetic
 asphalt, however, the presence of ni-
 trogen may be limiting because of poten-
 tial  interactions between petroleum
 asphalt and the  more polar synthetic
 asphalt (if synthetic asphalt is to be
 blended with petroleum asphalt). Also,
 since nitrogen ischemically substituted
 and since the average molecular weight
 of synthetic asphalt is lower than petro-
 leum, there may be a more pronounced
 tendency for  synthetic asphalt to be
 soluble in water and for water solubility
_m synthetic asphalt to be higher than
  hat in petroleum asphalt.
  Table  3   illustrates  heats   of
combustion  for  steam-volatile  oils,
synthetic asphalt  and char cake. The
low combustion heat of char cake (Table
3) is due to the large concentration of
ash in the char cake. The HS-10 char
cake  contained- 60% ash  before
combustion.  Heats of combustion  for
the synthetic asphalt and oil reported in
Table 3 are approximately  90% of  the
values  for   petroleum  equivalents.
Although not measured, the viscosity of
steam-volatile  oil was approximately
that of No. 2 heating oil, judging from its
pouring  properties  at  room
temperature.


Synthetic Asphalt Test Results
  Data  from   testing  the  various
synthetic asphalts produced by sludge
liquefaction  varied widely. The data
presented here are for sample HS-7,
one of the better samples.
  Before proceeding with the testing,
the HS-7 synthetic asphalt sample was
melted and washed with hot water. The
sample lost 30% of its original weight
during washing; olive-brown solubles
were removed in the wash water. The
synthetic asphalt sample was then dried
at 60°C.
  The washed sample began to melt at
50°C and became completely liquid at
80°C. It  was sticky and adhered well to
cardboard when subjected to freezing
temperatures. When frozen, the sample
was brittle but no more so than petro-
leum  asphalt.  When exposed to room
temperature,  it regained its putty-like
consistency much  more rapidly  than
petroleum asphalt.
  Part of the sample was used directly
with aggregate, and another sample
was prepared  from a mixture of  50%
high-grade (AC-10) petroleum asphalt
and  50% synthetic  asphalt. During
blending, an adverse reaction between
the petroleum and synthetic asphalts
was noticed; there seemed to be a rapid
increase in apparent viscosity when the
two were mixed.
  Both the 100% synthetic and the 50-
50 blend were mixed with hot aggregate
and oven cured at  60°C for 16 hours.
When the loose mixes  were removed
from  the oven, the blend appeared
duller in appearance.
  After the two mixes were subjected to
heating   arid  compaction,  they  were
cooled to room temperature and  bent
and  pulled  apart  for  a   preliminary
assessment  of adhesion.  The 100%
synthetic asphalt showed good adhe-
sion whereas the 50-50 blend mix was

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            Heats of Combustion

              Synthetic Asphalt
                HS-9
HS-10*
  Calculation based on total mass including ash.
poor  and  crumbly.  Further  testing     Table 3.
excluded the blend because of its poor
performance.
  Compacted   mix  specimens  were
made with petroleum asphalt and with      Type
100% synthetic asphalt. Both were sub-
jected to dry and accelerated moisture
conditioning  (vacuum  saturation
followed by 0°C freezing and  60°C
water soaking).  Mechanical properties
of tensile splitting strength and resilient
modulus were obtained for dry speci-
mens,  moisture  saturated  specimens,
and  specimens after  accelerated
moisture conditioning.
  The mechanical property values for
the 100% synthetic mix are close to
those for the petroleum asphalt mix. The
synthetic mix retained only 62% of its
dry tensile  strength after  accelerated
moisture conditioning, compared with
79% retained strength for petroleum
asphalt. Even though no stripping was
noted for the synthetic mix specimen, its
low retained tensile strength puts it on
the lower end of the scale for petroleum
asphalt.  The   resilient  modulus,
however, was relatively unaffected by
moisture. The synthetic mix retained
96% of its dry modulus when saturated
and 100% of its dry modulus after accel-
erated conditioning Petroleum asphalt
under  the  same conditions retained
103% and 76%, respectively.
  Although  the  synthetic   asphalt
appeared to be duller and more putty-
like than petroleum asphalt, it  showed
good bonding behavior with no  strip-
ping.   The   synthetic  asphalt   was     	
inherently  different  from petroleum     *100 Short ton/day

Table 4.   Payback Period for Several Sludge Liquefaction Process Options
          Steam-Volatile Oil Leachate  Char Cake
HS-9   HS-10
HS-6
HS-10
cal/g
Btu/lb
8,730
15,700
9,060
16,300
9,380
16,900
9,410
14,000
7.760
5.400*
3.020*
asphalt but showed promise because of
its  mechanical  performance  during
testing. Blends of synthetic asphalt and
petroleum asphalt will  require more
investigation  because of the  adverse
effect they have on each other when
mixed.
Conceptual Design and Cost
Estimates for a 91 Tonne/Day*
Commercial  Sludge  Thermo-
chemical Liquefaction Plant
  The conceptual plant design and cost
estimate were made to help determine
the overall feasibility of the process and
to encourage further  research  and
development  on continuous liquefac-
tion of sewage sludge. Estimates, made
on  the  basis of the best  available
information at this time, are tentative
since there are  no pilot plant data, or
even  bench-scale continuous process
data,  to support equipment specifica-
tions.
               In the flowsheet of the process (Figure
             1),  approximate  product  flows and
             temperatures are given for reference. A
             more detailed analysis of heat and mass
             balance is not currently warranted since
             heat of reaction, product  yields, and
             processability of some of the streams in
             a continuous process are unknown.

             Process Design
               A plant capacity of 91 dry tonne/day
             (100 short ton/day) was chosen as being
             representative of the volume of primary
             sludge produced in large  wastewater
             treatment plants around  the United
             States. Therefore, the estimates are for
             commercial plants, not for pilot or dem-
             onstration plants.
               The  process  would   operate   on I
             primary sludge dewatered  to at least"
             30% solids.  Other sludges could  be
             used, but for  these estimates, only
             primary   sludge  was  considered.
             Dewatering  to  30%  solids is  already
             practiced  in  many wastewater treat-
             ment plants.  Many  of  these  plants
             already use lime to condition the sludge
                              $ Mil/ion
Process
With
Dewatering
Vith Centrifuge
1 vnha/t
\&frjl IGIL
Recovery Without
Dewatering
Centrifuge
With
Dewatering
Without Centrifuge
1 cn/i^/f
i ofJf Idlt
Recover Without
Dewatering
Centrifuge
Facility
Cost

9.8


7.8


7.8


5.8

Manufacturing
Costs

2.97


2.68


2.58


2.29

Sludge
Disposal
Credit

1.98


1.98


1.98


1.98

Oil/Asphalt
Revenue

1.79


1.79


1.36


1.36

Total
Revenue

3.77


3.77


3.34


3.34

Simple
Payback
(Years)

12


7


10


6


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 Primary
  Sludge

    91
Tonne/day
Dry Basis
           Centrifuge  25°l/min
               t
                              Vapor-Liquid Separator
                                                 J[     1 129 l/min
                                                                                                            Waste
                                                                                                            Water
                                                   Gas
                                        121 l/min |  to
                                                   Vent
                              High Pressure
                              Slurry Feeder
                 Water
              to Secondary
               Treatment
                                                           Light Oil
                                                    Centrifuge
                                                                 Waste Water

                                                               Char Cake
                 Dowtherm A
                  Condensate
                         X
Dowtherm A
   Vapor
   350°C
                                                                Cake
                                                            Desolventizer
                                                                       4
                                         Dowtherm
                                          Vaporizer
                                                                              Solvent
                                                                              Recovery
   Ash
to Disposal
                                     Heavy Oil
                                      Washer
                   Light Oil
                  to Storage

               Waste Water
                                               Synthetic
                                                Asphalt
                                               to Storage
                                              6.4 kg/min

Figure 1.   Preliminary schematic for a sludge liquefaction plant
                                                           Waste Water
for dewatering, and, in many cases, add
10% or more lime on a dry weight basis.
In experiment HS-9, lime proved to be
an  effective adjunct  for  producing
steam-volatile oil, but rated poorly for
production of synthetic asphalt. There-
fore, lime-treated sludge can  be used
directly without further treatment if the
primary goal is fuel  production. Syn-
thetic asphalt from lime-treated sludge
would require more investigation based
an current results.
        Because the thermochemical  lique-
      faction yields varied significantly, in the
      design and estimation work, we used
      the sludge characteristics and  yields
      obtained from HS-10 as representative.
      With the use of these data, the  yields
      from a plant processing 91 tonne/day
      would be:
      Synthetic asphalt:
      Steam-volatile oil:
      Char cake:
                                                              9,000 Kg/day
                                                             13,800 Kg/day
                                                             37,000 Kg/day
At a density of a pproxi mately 830 g m / L,
the light oil would amount to approxi-
mately 16,300 L, or just slightly greater
than 100 petroleum barrels/day.
  Process heat requirements for this
plant would be supplied by combustion
of the residual char cake. The extracted
cake,  with  heat  of  combustion  of
approximately 3,020 cal/gm, would be
produced at the rate of 26 Kg/min and,
therefore,  would be  capable  of
supplying 1.56  X 10'° J/hr (1.5 X 107

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Btu/hr) of process heat at a combustion
efficiency of 80%. This amount would be
more than adequate to supply process
heat  requirements, especially if heat
recovery were used on the main stream
coming out of the  liquefaction reactor.
The  greatest heat requirement by far
would be to  heat the  liquefaction
reactor, even with heat recovery. For the
flow design presented in Figure 1, the
liquefaction reactor would require heat
input of 1.17  X  1010 J/hr. Other minor
heat  requirements  for solvent
extraction and recycle are estimated to
be less than 04  X 10'°  J/hr. Total
energy  requirements  therefore  are
balanced by the available energy in the
residual char cake. Energy from com-
bustion of the char cake would be
supplied  to the liquefaction reactor by
m Dowtherm* vaporizer. Other process
utility requirements would be limited to
electrical  power of  about  1.8 X  106
KWH/yr and a small amount of cooling
water.
  Estimates given for capital equipment
and  manufacturing costs  are  derived
from a plant that would already include
sludge dewatering equipment (a centri-
fuge) and solvent extraction to recover
synthetic asphalt, since many sites have
dewatering equipment  m  place  and
since some  plants may elect not to
recover synthetic asphalt.


Simple Payback Period for
Different Process Options
  A major cost in this process would be
associated with  primary  sludge  de-
watering. Estimates given  in Table 4
show that if investment for this process
is not required, the payback period for
the plant  will decrease from 10 to 12
years to 6 to 7 years.
  Although synthetic asphalt may be a
valuable product when produced from
sewage  sludge, these  payback esti-
mates (Table 4) show that the payback
period is actually shorter if asphalt were
not  recovered  because the  solvent
extraction  process  adds more capital
and operating cost than could currently
be  recovered  by  sale of synthetic
asphalt.  If synthetic asphalt were  not
recovered, it would be contained in the
char cake and simply burned. The viabil-
ity of  synthetic asphalt recovery will
change depending on the yield of syn-
thetic asphalt (as yet to be determined in
•Mention of trade names or commercial products
 does not constitute endorsement or recommen-
 dation for use.
a continuous process for which these
estimates were made) and depending
on its value as an alternative to petro-
leum  asphalt. Either or both of these
factors could significantly change the
economics of synthetic asphalt recovery
from sludge in future years.
   In Table 4, credit for sludge disposal
was  estimated  at  $66 per dry tonne
($60/short ton). Revenue from sale of
oil was calculated at S0.25/L ($40/bbl)
and   for  the  synthetic  asphalt,
$143/tonne ($130/short  ton).  These
prices are representative of 1980 prices
for equivalent petroleum products.
  At current petroleum prices and with
the capital and operating costs shown, it
is  necessary to  take some credit for
sludge disposal to  make the process
economically viable. As envisioned, the
liquefaction plant would be adjacent to a
wastewater treatment plant and would
take all the primary sludge generated by
the wastewater plant—so, in fact, some
credit is  due since the sludge would
otherwise  have to  be  disposed  of.
Because   the  cost  of  disposal  will
certainly  rise in the future, as will petro-
leum  prices, the  liquefaction process
should become viable  in future years
even  should it  not be thought to be
viable at current  projected payback
periods of 6 to 12 years.
Recommendations
  The potential for direct liquefaction of
sludge  to  produce  liquid  fuel  at a
reasonable cost is very real based on the
data presented  m this report.  Unlike
other thermal processes, such as incin-
eration  with heat recovery or gasifica-
tion, liquefaction produces a fuel that is
eminently  storable and transportable.
The quantity of net energy produced by
liquefaction (i.e., steam-volatile oil and
synthetic asphalt) is likely to be greater
than  the  net  energy produced   by
incineration with heat recovery.
  Batch reaction methods used for this
study are not acceptable for design and
scale-up of even a modest pilot plant.
Therefore,  a  bench-scale continuous
reaction system is needed to:

  •  determine physical properties of
     intermediate products;
  •  determine necessary designs for
     ancillary equipment;
  •  obtain larger samples  for  more
     detailed testing;
  •  determine   liquefaction  product
     characteristics  as a function of
     temperature,  time,  alkali,  and
     incoming sludge composition; and
  •  determine the technical feasibility
     of a continuous  reactor for sludge
     liquefaction.
Reliable data for design, scale-up, and
economic evaluation  would result from
a continuous bench-scale unit. In addi-
tion, if this unit were  located at the site
of  a  wastewater   treatment  plant,
product characteristics as a function of
sludge composition could be measured
and  the  treatability  of  the  residual
aqueous  phase could be determined.
  Therefore,  we recommended that a
small lab-scale continuous liquefaction
facility be built near a wastewater treat-
ment plant. With this  system, emphasis
should be placed on developing fuel oil
from   sludge because  this  option
appears to be more cost-effective in the
near  term.  However, since the high
molecular weight fraction is made along
with the steam-volatile oil, investigating
its utility as a petroleum asphalt  re-
placement or as a coking stock or fuel
can  continue at minimum additional
R&D cost.
Conclusions
  Seventy percent of the combustion \
energy  available  in  sewage sludge
(approximately  5000  cal/g  or  9000
Btu/lb) can be converted to liquid and
solid fuels analogous  to petroleum by
direct thermochemical liquefaction The
solid fuel can be burned to provide all
the necessary process heat requirements
so that  the process  is a  net energy
producer.
  the high molecular weight product of
liquefaction  is,  in some  cases,  an
acceptable  replacement for petroleum
asphalt based on the results obtained so
far. Synthetic  asphalt samples desig-
nated HS-1, 7, and 10 were ranked as
satisfactory by our preliminary asphalt
testing procedures; most others were
ranked  as  unsatisfactory.  Since the
conversion procedure for the satisfac-
tory and unsatisfactory samples was the
same in most cases, the only  plausible
explanation is that inherent differences
in the  composition  of  the  various
samples of sludge used led to physical
differences  in  the synthetic asphalt
products.
  The synthetic asphalt can also be
used as a potential fuel or coking stock
in the event it is not immediately accep-
table as a paving binder. In addition, the
steam-volatile  oil  produced during^

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liquefaction has significant value as a
synfuel,  having 90% of the  heating
value of No. 2 fuel oil. Based on the
current value of petroleum asphalt and
heating oils, the liquefaction  process
would  be economically viable in  many
existing situations, with expected pay-
back periods of less than 12 years.
  If the process objective were changed
to  production  of  fuels  rather   than
asphalt, a reduction in processing cost
would  be likely—the economics would
probably be more favorable and, in addi-
tion, marketing of the products would be
simplified.
  The full report was submitted in ful-
fillment of  Grant No. R-806790-01 by
Battelle-Northwest,   Richland,   WA,
under  the  sponsorship  of the  U.S.
Environmental Protection Agency.
J.  M. Donovan, R. K. Miller, and  T. R.  Batter are with Battelle-Northwest,
  Richland, WA 99352; R. P. Lottman is with the University of Idaho, Moscow, ID
  83843.
Howard Wall is the EPA Project Officer (see below).
The  complete report,  entitled "Physical and Chemical Characteristics of
  Synthetic Asphalt Produced from Liquefaction of Sewage Sludge. "(Order No.
  PB 82-119 082; Cost: $9.00, subject to change) will be available only from:
        National  Technical Information Service
        5285 Port Royal Road
        Springfield, VA 22161
        Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
        Municipal Environmental Research Laboratory
        U.S. Environmental Protection Agency
        Cincinnati, OH 45268
                                                                           •frU.S. GOVERNMENT PRINTING OFFICE:1982--559-092/3364

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Agency                          Cincinnati OH 45268                                         Protection
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