EPA/600/D-85/194
                                           August 1985
AUTOTHERMAL THEKMOPHILIC AEROBIC DIGESTION IN
       THE FEDERAL REPUBLIC OF GERMANY
                     by
                 Kevin Deeny
                Roy F. Weston
              West Chester, PA

               James Heidman       --•'•••,•..
   Water Engineering Research Laboratory
     U.S. Environmental Protection Agency
             Cincinnati, OH 45268    "*^:.<  .

                 James Smith
Center .for Environmental Research Information^
     U.S. Environmental Protection Agency
             Cincinnati, OH 45268
            EPA Project Officer
               James Heidman
    WATER ENGINEERING RESEARCH LABORATORY
     OFFICE OF RESEARCH AND DEVELOPMENT
    U.S. ENVIRONMENTAL PROTECTION AGENCY
            CINCINNATI, OH 45268

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TECHNICAL REPORT DATA
(P!c::e rczd fituniciions on r/ic revcnc before co'ir.-ltiinsj
i
4
REPOHTNO. 2.
EPA/600/D-85/194
TITLE AND SUBTITLE
AUTOTHERMAL THERMOPHILIC AEROBIC DIGESTION IN
THE FEDERAL REPUBLIC OF GERMANY
7. AUTHpR(S)
Kevin Deeny, James Heidman, and James Smith
9. PERFORMING ORGANIZATION NAME AND ADDRESS '
Wastewater Research Division
Water Engineering Research Laboratory
U.S. Environmental Protection Agency
26 West St. Clair St. Cincinnati, OH 45268
12
IS.
SPONSORING AGENCY NAME AND ADDRESS
Water Engineering Research Laboratory - cinti OH
Office of Research and Development.
U.S. Environmental Protection Agenty
Cincinnati, OH 45268 .
3-M'rYic?3IT207K I
J *- ^ -* •* f- c- I j^
5. REPORT DATE
August 1985
6. PERFORMING ORGANIZATION CODE 1
8. PERFORMING ORGANIZATION REPORT NO.
TO. PROGRAM ELEMENT NO. 1
CAZBIB 1
11. CONTRACT/GRANT NO. I
13. TYPE OF REPORT AND PERIOD COVERED
14. SPONSORING AGENCY CODE I
EPA/600/14
SUPPLEMENTARY NOTES I
Project Officer: James A. Heidman
               The status of Autothermal  Thermophilic Aerobic Digestion (ATAD) of
          Wastewater Sludges in the Federal  Republic of Germany (FRG)  was evaluated
          via  site visits to operating facilities.
               In the FRG,  three variations  of ATAD systems have been  constructed
          on a  full  scale.   These include systems marketed by Fuchs  Gas and Wasser-
          techmk GmbH and  Co., Theime Umwel  Hecknik GmbH, and Babcock (Deusche
          Babcock Anlagen Aktingesulschaft).   Fuchs is  the leading supplier of
          these  systems  with approximately  13 of the 17  facilities in  FRG and
          Switzerland.
              The ATAD  process in  the FRG is required  to  meet a limitation of
          100 enterobacter/ml in  the  final sludge product.   ATAD maintains  a
          status  of  approval  by the Federal Government  (FRG)  as  a process that is
• - r- — --a - r--pv«! i i_\.
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                      NOTICE

This document has been reviewed in accordance with
U.S. Environmental Protection Agency policy and
approved for publication.  Mention of trade names
or commercial products does not constitute endorse-
ment or recommendation for use.
                       11

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INTRODUCTION AND BACKGROUND

The Autothernal Themophilic Aerobic  Digestion  system is  an  aerobic digestion process
that operates within a  thernophilic  temperature  range (40°C to 80°C)  without the
introduction of supplemental heat.

The potential for conducting autothernal thermophilic aerobic  digestion (ATADJ  of
wastewater sludges has  been known for  some  time.   In 1969,  Kambhu and Andrews
reported the results from computer simulations which showed that ATAD could be
self-sustaining with respect to  temperature.   In simulations with air aeration, it
was predicted (Andrews  and Kambhu )  that sludge  temperatures could increase by  more
than 33°C and that the  percentage of volatile  solids destroyed would  be greater
than 40% at residence times greater  than 7.5 days.

Much of the early experimental work  on tfucfc full-scale  ATAD systems  have been  based
was performed by Popel  and ooworkers.  '  '  '    The process was  demonstrated both
with animal manure and  sludge having high concentrations (10-60 kg/cu m) of organic
solids and using the "Unwalzbelufter"  developed  by Fuchs to provide proper aeration.
Reactor temperatures of 50°C were obtained  even at low ambient temperatures.

The empirical operating characteristics of  this aerator  type (self-aspirating
aerator) were reported  in the late 1960's  .  The  aerator and several  comparable
designs were successfully marketed and implemented for industrial and agricultural
waste treatment in the  US by the DeLaval Company  in  a patented process called the
LIGOM (from liquid compositing)  system.  Studies  on  dairy,  beef and swine wastes in
the US indicated that autoheating to thermophilic temperatures was possible.

In 1971, substantial increases in temperature  were inadvertently obtained at the
Hamilton, OH wastewater treatment plant when the  covered digesters were converted to
aerobic digesters.   Temperatures of 38°C were obtained  when the 4% feed solids
concentration was fed to the digester  at a  rate of 2 kg/cu m/day.   Insufficient air
was available to maintain a positive DO concentration and odors  were  present.

Other ATAD studies were conducted in the early to.mid 1970's in  the US with high
purity oxygen (Smith et al.   Matsch and Drnevich  ).  Union Carbide  was reported
to have been working on ATAD systems utilizing high  purity oxygen  since 1972.
Studies at the Speedway,  IN treatment  plant indicated that substantial increases in
temperature were possible although thermophilic conditions were  not attained.   Pilot
plant studies at Tcnawanda, NY on both single  and two-stage  digestion systems were
conducted under autothermal thermophilic conditions.   Based  on  these  studies, it was
concluded that an ATAD  system operating at a 5 day HRT could achieve  volatile solids
destructions equivalent to a conventional system at  a 15 to  20 day HRT.  Nitrification
was observed to be inhibited under thermophilic conditions.  It was also concluded
that reductions in pathogenic organisms to  less than detectable  levels could be
achieved when the temperature of the sludge was maintained at  50°C or greater for 5
or more hours.  Similar reductions could be achieved at  temperatures  as  low as  45°C
with longer residence times.  Sludge produced  from an ATAD system was shown to
dewater as well as an anaerobically  digested sludge.

The most extensive study of ATAD using air aeration  in the US was  conducted at
Binghamton, NY in 1977  and 1978  (Jewell et al,  Jewell and Kabrick11).   A
combined primary and waste activated sludge feed between 3 to 6% TS was  fed to  a
single reactor operated with a liquid  volume of 28.4 cu m (1000  gal).   The  design  was
                                        -1-

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 based en the system marketed in this country by DeLaval Inc.  Both a Midland-Prings
 aerator and a DeLaval oentri-rator aerator were studied.  Start up always occurred
 rapidly regardless  of air  and sludge temperatures and following start up, reactor
 temperatures were always in the thermophilic zone (> 43°C) and often above 50°C.
 Oxygen transfer efficiencies always exceeded 12% and the highest values approached
 23%.   There was no  nitrification but there was some NH3-N loss due to stripping.  A
 high  degree of pathogen control with respect to bacteria, viruses and parasites was
 reported.   A significant deterioration in the dewaterability of the treated sludge
 was observed.  Practical operation and maintenance problems were found to be minimal.
 ATAD  was also felt  to be more economical than aerobic or anaerobic digestion
 facilities  at equal solids conversion efficiencies.
                                                                       I O
 Based on the results reported by Jewell et al., Camp Dresser and McKee   performed
 an economic analysis which compared ATAD with conventional aerobic and anaerobic
 digestion at 1, 10  and 100 MOD (sludge handling costs before and after digestion were
 not included). At  the 1 MGD sizing, unit digestion costs in dollars per dry ton
 ($/ton)  of  sludge processed, were estimated to be 160, 260, and 220 for ATAD, aerobic
 digestion and anaerobic digestion respectively.  At 10 MGD and beyond, anaerobic
 digestion was projected to be the most cost effective alternative.  (The value of
 sludge pasteurization by the ATAD process was not considered.)

 More  recent research reported by Wblinski and Bruce   indicated that the ATAD
 process could compete with anaerobic digestion if the aeration/mixing power
 requirements are minimized.

 PURPOSE AND METHODS OF ASSESSMENT

 In support  of  the Innovative and Alternative Technology Program, the Environmental.
 Protection  Agency retained Roy F. \Weston, Inc. (WESTON) to update developments in
 ATAD  technology utilizing  air aeration.  It soon became apparent that there was very
 little interest in  this technology in the United States  .   This contrasted sharply
 with  information available from the Federal Republic of Germany (FRG)  where it was
 reported15  that the process  had been utilized for more than ten years.  It was
 further  indicated that the aeration devices had been substantially modified and
 improved compared to the aerators utilized by Jewell et al.  The aerators  presently
 utilized by Fuchs (an aerator manufacturer in FRG)  were claimed to operate at 95 w/cu
 m of  reactor volume which  is about half the energy input observed by Jewell et al.
 for best operation.   Also  it was reported that ATAD sludges dewater just as well as
 anaerobically  digested sludge in centrifuges or belt presses.   To evaluate these and
 other  claims,  the focus of the ATAD technology assessment was  shifted  to an
 evaluation  of  those systems  presently in  operation  in Europe.

 Dr. Egon Keller of  ECOSYSTEMS in the FRG  compiled available information  from the
 academic community,  operating plants and  manufacturers.   Following review  of
 information  received from FRG by WESTON and EPA,  a  first hand  evaluation of  operating
 facilities was conducted by WESTON.   The  evaluation was  supplemented through
discussions with operating personnel,  design engineers,  researcher and manufacturers.
The FRG, ATAD assessment primarily  reflects  the findings  of  WESTON in association with
 support  from Dr. Egon Keller.
                                        -2-

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PROCESS DISCUSSION

Detailed discussions of the heat and mass  balance equations necessary for
ATAD system operation are available  (Andrews  and Kambhu,   Kambhu and Andrews,
Jewell et al.)  and will not be repeated here.   The  same  basic analytical approach
has also been utilized in Germany1  .  The  various inputs, outputs and heat
production items to be included in a heat  balance are illustrated in Figure 1.  An
efficient aeration device is essential  if  the latent heat loss in the water vapor is
to be held at an acceptable level.  Systems currently in  operation in Europe do not
use heat exchange between reactor feed  and effluent  to warm the incoming sludge.
Heat exchange is occasionally practiced for waste heat recovery.  Biological heat
production is, by far, the largest beat source with  typical heat production values of
6100 to 6300 BTU/lb O2 utilized ''   being reported or assumed.  Although
variable, carbonaceous oxygen requirements are often considered to be 1.42 Ib 02/lb
VSS oxidized.  Thermophilic temperatures prevent biological nitrification which
results in a substantial reduction in 02 demand  compared  to conventional aerobic
digestion systems. The rate of digestion is commonly described by first order
kinetics with the rate coefficient increasing up to  approximately  60°Cr .  Feed
sludge biodegradable solids concentration  and temperature, biological reaction rates
and efficiency of the aeration device are  key components  in process analysis.

Significant advances have been made in  the optimization and adaptation of the ATAO
technology during the past 15 years.  Much of the experimental work on which the
present full-scale ATAD systems have been  based  was  performed  by Dr. Klaus
Breitenbucher while at the University of Hohenheim.   Much of this work was based upon
the operation of a full-scale ATAD plant at Gemmingen,  FRG1 .   To date, the process
utilization in Europe has been primarily in West Germany  with  a little employment in
Switzerland.

DESIGN

In the FRG, three variations of thermophilic  aerobic digestion systems have been
constructed on a full-scale.  These include systems  marketed by:

o   Fuchs Gas and Wassertechnik GmbH & Co. K.G.
o   Thieme UmwelHecknik GmbH
o   Babcock (Deutsche Babcock Analgen Aktingesulschaft)

Of these manufacturers, Fuchs is the leading  supplier of  these systems with
approximately 13 of the 17 facilities in the  FRG and Switzerland (per the
manufacturer).  An additional 5 facilities are under design for the FRG and
additional orders are anticipated in Switzerland.  Thieme has  two full-scale systems
operating in industrial applications in the FRG.   Limited operating data are
available from these facilities.  Babcock has one full-scale facility located in
Aidlingen, FRG.

Due to the number of systems installed and the early research  and development work
performed by Dr. Breitenbucher, the ATAD systems  that were visited were all  systems
supplied by Fuchs.  Thieme and Babcock installations were discussed with
manufacturer's representatives and data were solicited while in Germany.

There are significant differences among the actual operating ATAD systems.  Typical
design parameters for each of the three versions of  the process are summarized in
Table 1 and are discussed below:


                                        -3-

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                           Figure 1
         Heat Loss to
         Surroundings
                           Mixing
                           teat Input
Feed Sludge
                   Biological  Heat
                   Production
                            i
                                                      Sensible and
                                                      Latent Water
                                                      Vapor Heat
                                                     -Loss in Gas
                                                      Effluent
Heat Loss in
Sludge'
Effluent
               Influent  Gas
    Figure 1:  Heat balance schematic of a thermophilic
               aerobic digester.
                          -4-

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                                                TABLE 1


                                    SUMMARY OF  DESIGN PARAMETERS
DESIGN PARAMETER
Sludge Feed Concentration, percent (%)
Hydraulic Detention Time, Days
Number of Reactors . %
Sludge Storage Capacity, Days
Operating Strategy
Aeration-Requirement,
KWH/M of sludge throughput
Mixing^Requirements ,
W/M reactor volume
MANUFACTURERS
FUCHS
3-5
5-6
2
20
Batch
12-14
86
THIEME
10-12
6-7
2
70
Batch
-
200-300
BABCOCK
3-6
3-6
1
-
Semi Continuous
12-17
-
I
tn
I

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o   Fachs

The Fuchs ATAD system employs two enclosed and insulated sludge digestion reactors
which  are operated  in series.  Typical designs require pre-thickening and post sludge
storage/thickening  prior  to land application.  A typical Fuchs system is illustrated
in Figure 2.  The pre ATAD sludge thickening is sometimes accomplished jointly with
primary  solids removal  as is the case at two facilities reviewed in Germany.  At
those  facilities, primary solids ranoval is accomplished by dissolved air flotation
(which is a frequent practice in Europe).  Waste activated sludge is pumped to the
primary  DAF for thickening and removal with the primary sludge.  This sludge is then
delivered to the ATAD system.

The feed solids concentration of 3 to 5 percent has been established by Fuchs to
limit  excessive reactor cooling at concentrations below 3 percent and to limit
excessive foaming in the  reactors which reportedly occurs at concentrations greater
than 5 percent.

The hydraulic detention time is established at 5 to 6 days (2.5 to 3 days per re-
actor) to satisfy the process requirements of 40-percent destruction of total organic
solids.  Sixty percent  of this destruction is reported to occur in the first reactor.

A 2-reactor series  configuration is used to provide a means of isolation of the
digested (pasteurized)  sludge from contamination by incoming raw sludge.  Batch
feeding  of the system is  established by design intent and is reflected in the size of
the sludge feed pump which is sized to deliver the daily sludge volume to the ATAD
system within a short «1 hour) time period.

The aeration devices used are aspirator type aerators.   A typical installation
utilizes two side mounted aerators (one center floating aerator nay be included
dependent upon the  reactor sizing) that are easily removed for maintenance.
Relatively high oxygen  transfer efficiencies, in the range of 1.5 to 3.7 Kg 02/kwh
(2.5-6.1 Ib Oj/hp/hr),  are reported by the manufacturer.   It is also indicated that
the aerator erficiency  increases as the solids concentration in the reactor increas-
es.  An  average of  2.1  Kg 02/kwh (3.5 Ib 02/hp/hr)  is used for design purposes.

A rotary blade type  foam  cutter is utilized (usually 2  per reactor)  to limit the
buildup  of foam in  the  reactor.

A 20-day (minimum)  storage capacity is recommended for  the treated (digested)  sludge.
Aside  from storage requirements related to variations in  disposal rates,  a  20-day
period is recommended to  allow adequate cooling of  the  sludge before post thickening
or dewatering.  The  settling (and possibly dewatering)  characteristics are  reported
be greatly improved  if  the sludge is allowed to cool to 20°C.   Sane  Fuch's
facilities utilize heat exchangers to recover excess heat for building heat.   This  is
an optional consideration.

o   Thieme

Design information that was  available regarding the Thieme ATAD system is summarized
in Table 1.  A typical  Thieme system is depicted in Figure 2.

On comparison, the Thieme process is very similar to the  Fuchs  ATAD  system.  A
significant difference  between the systems is that  the  Thieme system prethickens
sludge to a concentration of  10 to 12 percent using a rotary screen.   The increased
feed solids concentration has permitted the manufacturer  to  reduce the digestion
reactors to approximately 30  percent of the volume  used in the  Fuchs  system.

                                         -6-

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Sludge
Sludge
Sludge
^-^
1 C
, Q, .*> „
I '
\/
WJ

^ P.
a /> , 	 ,
^ / ^ ;
— »> To Land Application <;
1 r
A
Thickener ATAD Reactors Sump Sludge Storage
FIGURE 2A FUCHS ATAD SYSTEM
P £*
GTTq ^ r4j 	 .
'""" -4X4—0 — * *
Mazorator
Holding Tank Conditioning
Tank
FIGURE 2B '
I
I r
I
rlj
^x/^ IL
[ C^T^ ^~^ pon ATAD
I)C 1 vj"^ ftft^ Roar*tf%r

Thickener
\ K
^ [>>. ^^
n H|K g
IT
]* "

1 1 /-s ~ w 	 J To Land
— H r-U-W XyX * A«MII..M>.
Rotating Q Sludge
Screen &ump H Storage
ATAD Reactors
FHIEME ATAD SYSTEM
®. . i i
t — r -
Foam Scrubber
Breaker ;
^ Heat Exchanger

1 To Land
....... I .. . "^Application
Heat Exchanger Sludge Storage , ;
FIGURE 2C BABOCK ATAD SYSTEM ^
' , i

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 The hydraulic detention tine,  number  of  reactors,  series operation, and batch feed
 strategy are all  similar to Puchs ATAD system.

 Aeration and mixing  requirements have not  yet been defined by the manufacturer (some
 limited operating information  is available).  An aspirator type aerator is used which
 is  similar  in concept,  but vastly different in mechanical design from the Fuchs
 aerators.

 o   Babcock

 A typical Babcock ATAD  system  is illustrated  in  Figure 2.

 This variation of the ATAD process differs significantly from the Fuchs and Thieme
 systems in  that a single reactor is used and  a continuous or semi-continuous sludge
 feeding method is utilized.  Additionally, a  different type of aeration system
 (submerged  turbine)  is  installed in the  Babcock  ATAD system.

 The hydraulic detention time and aeration  power  requirements are similar to the Fuchs
 ATAD system.

 A heat  exchanger  is  used as  an econimizer  to  extract heat from the effluent sludge
 which is in turn  used to preheat the  influent sludge.   Additionally,  a heat exchanger
 is  used to  extract excess heat from the  process  to be utilized elsewhere
 (i.e..typically for  building heat).   No  information is available from the
 manufacturer to indicate if  the  economizer is required for process reasons to preheat
 the influent sludge.  It is  assumed that the  heat  extraction heat exchanger is
 optional as it is for the Fuch's system.

 OPERABILTTY AND PERFORMANCE

 Table 2 represents a sumnary of  the operating status of 6 ATAD facilities that were
 reviewed in the FRG.  Operability and performance  criteria assessed during the review
 of  these facilities  are discussed below.

 o   General

 A coranon factor identified in  all six ATAD facilities  is  that the process is easy to
 operate.  In all  cases,  very little process   control and  maintenance  is required.
 Normally, process control consists of performing periodic suspended solids analyses,
 monitoring  reactor temperatures,  and  controlling the punping of  specific volumes  of
 sludge  to the ATAD reactors  on a batch basis.  Several of the operating facilities
 reported that less than  1 hour par day was required to operate and maintain the
 system.  The simplicity of the operation implies that  most of  the process  constraints
 are considered during the design phase thus minimizing required  operator attention.

 o   Pathogen Destruction

 The ATAD process  in FRG  is required to meet a limitation  of  100  enterobacteria/ml in
 the final sludge product  as mandated by regulations  in  the FRG  .   This limitation
 is  consistent with JRG regulatory  requirements to become  fully effective in 1987.
 The ATAD process  in the FRG now maintains a status of approval by the Federal
 government as a process that is  capable of producing a  pasteurized (hygienic)  sludge.
 This status is similar to  the designation  in the U.S. as  a Process to Further
Reduce  Pathogens.20

 The  treatment facilities that utilize the ATAD process are sampled twice per year  by
 the  regional health district.  These samples are analyzed for  a number  of parameters

                                         -8-

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                             Table  2
                Summary of ATAD Actual Operating  Conditions
                          	Facility
Parameter                 I       F       N        G
Ho. of Reactors         2         2        2         2       2       1
Dimensions, 0 x H, m    5x3     7.0 x    7.5  x  4   3.5 x   6.5 x   7  x  2.5
                                 3.5                2.5     2.25
Volume^  (Occupied by
  Sludge) Total, m3     120       120      360       48      150     96
Sludge Influent Flow,
  «3/day                9         20       70        8       15      5
Sludge Concentration,   4/3.1     4/3.4    5.5/     5/3.0   3.5/    6/3.6
  TSS/TVSS, percent                       3.6               2.8
Sludge Mass Loading,
  TVSS, kg/day          280       680      2,520     240     420     180
i'Sludge TVSS
  loading tete, kg/day/nr   2.3       5.7      7.0       5.0     2.8     1.8
Keectons) Detention    133       12       5.1       6.0     10      19.2
  Time, days            (6.6)4    (6)
Aeration  Installed
  Power,  kw             8.8       9-5      38        4.4     11.8    5.5
Aeration  Power
  Consumption2,k»h/day   211       228      912       106     284     132
Aeration  Power/
  Sludge  Volume,        23.4      22.8     13.0     13.3    18.9    26.4
  kwh/mVday            (12.0)4   (12.6)4
Aeration  Power/
  Reactor Volume,
  K/m3                  73        ;79       106       92      79      57
Aeration  Power/
  Sludge  Mass,
  TVSS,  kwh/kg          0.75      0.74     0.36     0.44    0.68    0.73

Notes

1.  Tank  volumes refer  to operating volume with  sludge. Additional
    tank  volume  is  installed  in varying amounts  for freeboard.
2.  'Power consumption  is calculated on a 24-hr basis; actual operation
     =23.5 hr/day.
3.. Since July 1984  (after the field visit), Isenbuttel and Fassberg  were
    operated as  a one-stage operation with batch feeding 3  to 4 times/
    week  to maintain pasteurization.
4.  When  operated in single stage.

I = Isenbuttel
F = Fassberg
N = Nettetal-Viersen
G = Genuningen
V •= Vilsbiburg
S = Schontal  (not considered  to be an actual ATAD facility)
                                  -9-

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 including coliform count.   If the sludge is determined to meet the above limitation
 of 100  #/inl  (in  addition to meeting other organic and inorganic criteria), it is
 approved as  being "acceptable" for agricultural utilization.

 Pasteurization by definition requires the attainment of a temperature equal to or
 exceeding 70^C,  and the maintenance of that temperature for a 30-minute time
 period.   The ATAD process  does not typically operate at 70°C; however, it attains
 temperatures of  55-65° and maintains these temperatures over a longer period of
 time.  The pathogen destruction achieved, therefore, is reported16 to be comparable
 to the pathogen  destruction from a "pasteurization" process based on the 100
 enterobacteria/ml limitation.  The process has been shown capable of destroying
 salmonella,  parasite eggs  and viruses'provided a temperature of 50°C is maintained
 for 57 hours of  aeration time (Strauch,21 Bohm et al.,22).

 The ATAD operating strategy maximizes the pathogen destruction potential of the
 process  and  minimizes the  chance for contamination.  In order to prevent
 contamination with raw incoming sludge, a specific volume of sludge is removed on a
 daily basis  from the second stage reactor (which is operating in a range of
 55-65°C).  Once  the sludge is removed, sludg§ from the first stage reactor is
 transferred  into it as a batch.  The second stage is then not disturbed until the
 next batch is loaded 24 hours later.  With this operating method, sludge that has
 been transferred over from the first stage reactor is maintained at a thermophilic
 temperature  for  a minimum  period of 24 hours.   Raw sludge is then fed into the first
 stage to make up the volume that was removed when sludge was transferred.  This
 stepwise feeding approach  isolates the sludge  reactors from each other and minimizes
 the potential for contamination of the final sludge product.

o   Temperature

Table 3  summarizes reactor temperatures determined during field visits and review of
 operating  data.

Of particular concern for  meso- and thermophilic- systems is the impact that batch
 feeding  nay  have on the reactor temperature.  Sane concern has been expressed by
 researchers  in the field that batch feeding of the digestion reactor may suppress the
 reactor  temperature significantly, resulting in a loss of digestion and pathogen
destruction  efficiencies.

This potential was considered when the ATAD facilities were visited in Germany.  It
was observed that,  during  the batch feeding into Reactor No. 1,  the temperature was
depressed by approximately 5 to 6°C.  However,  the reactor recovered at a rate of
 1° per hour, resulting in  a complete temperature recovery in 5 to 6 hours after the
 initial  feeding.   The temperature depression in Reactor No. 2 was somewhat less on
 the order  of 3 to 4°C and  recovered at a similar rate as was observed in Reactor
No. 1.

The observed temperature pattern is similar to those illustrated in Figure 3 which is
 based on research findings at Gemmingen.

o   Feed Solids

Operational guidelines  for the feed sludge concentration to the  ATAD process are
typically  specified in  the ATAD plants designed by Fuchs.   Operating personnel
maintain the feed sludge concentrations within  a range of  3 to 5 percent.   It was
 indicated  that below 3  percent solids  concentration,  the temperature drop in Reactor
No. 1 is excessive and  that above 5 percent solids,  excessive foaming may occur in
Reactor  No.  2.

                                         -10-

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                                 Table 3
                 Summary of Reactor Temperatures
Influent
Sludge
. Temperature
Facility
Vilsbiburg
Gemmingen
Nettetal-Viersen
Fassberg
Shontal*
Isenbuttel
Rheinhausen

12
6
10
6
-
8

<°C)
- 18
- 14
- 22
- 15
--
- 20

Reactor
No. 1
<°C)
60
30 - 50
38
40 - 45
___
40 - 55
42**
Reactor
No. 2
<°C)
69
50 - 60
58
50 - 70
___
45-60
60**
 *Not considered an ATAD facility due to open tank design.
  Intended to be retrofitted into an ATAD system by addition
  of a tank cover.
**Arithmetic mean of temperature measurements taken during 14
  weeks.
                             -1]-

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o   Volatile Solids Reduction

Volatile solids reduction is reported to be ^ 40 percent  for  the  ATAD system.
Figure  3 illustrates the volatile solids reduction achieved at the Gemmingen
facility^.  Volatile solids reductions of 40 percent were achieved as the
detention time became greater than four days.

None of the operating facilities routinely perform TVSS analyses  of the influent and
effluent sludge streams for the ATAD systems. However, a limited amount of  data are
available from Health District analyses.  A review of the Health  District analyses
and facility data indicates that the 1VS reduction ranged from 44 to 41 percent for
one of  the typical Fuchs facilities reviewed  (Nettetal- Viersen).  Volatile  solids
reduction for the Thieme ATAD system in Rheinhausen averaged  44 percent over a 14
week period.

o   Odor

Of the six facilities reviewed, none exhibited offensive  odors during the visits.
Discharges from the ATAD reactors could be characterized  as "musty" and very similar
to odors experienced from conventional aerobic digesters.  Three  facilities  reported
occasional odors.  One of these facilities reported occasional odors when the reactor
temperature exceeds 65°C, while the other two experienced some odor only when raw
sludge was pumped to the system.

Two of  the facilities in close proximity to residential areas  are equipped with
exhaust gas scrubbers for the ATAD reactors.   The application  of  these scrubbers is
considered to be somewhat experimental.  Performance is reported  to be good;  however,
occasional odors have been noted even with the scrubbers  in place.

o   Sludge Dewaterability

Dewatering trials were conducted at the Vilsbiburg ATAD facility  using a belt press
and decanter centrifuges.  Preliminary (unpublished) results for  centrification and
belt filtration include the following:

    ATAD Reactor Effluent;  TS = 2.5 percent
                                 influent to dewatering

    Sludge Cake;                 TS = 30 to 35 percent

    Polymer Dose;                4 to 6 g of polymer/kg of
                                 sludge

    Feed Temperature;            48 to 63°C


These results indicate acceptable dewatering performance.  Indeed, for
centrification, exceptionally high cake solids are experienced.  It has been
hypothesized that the high cake solids achieved may be due to reduced sludge
viscosity at higher temperatures.  It was also reported that the centrifuge centrate
was dirtier than would normally be expected for a mesophically-digested sludge.

POST

Capital cost data were provided by manufacturers and facility engineers for eight
ATAD installations.  These cost data were limited to the system components which the
manufacturers supplied.  This information was utilized along with separate cost

                                        -12-

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                                           =  Organic total solids
                                           =  Influent
                                           =  Effluent
                                           =  Reactor No.  2 Temperature
                                           =  Reactor No.  1 Temperature
                                           =  Air  Temperature
                                     FIGURE 3  GEMMINGEN DATA
                                                              17

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estimates  for processes  not included in the manufacturers1  cost information to
estimate the capital cost of a complete ATAD  system of: 1)  prethickening to 3-5% IS,
2) ATAD system with 6 days hydraulic detention  time,  3) 20  days post storage,  4)
pumping system, and 5) concrete slab for tankage.   All costs were adjusted to  US
dollars; March 1984.

These costs are compared in Figure 4 to capital cost  estimates  for aerobic and
anaerobic  digestion systems with similar sludge throughput  capacities as those
observed for the ATAD systems.  Conventional  aerobic  and anaerobic digestion system
cost estimates were developed from a U.S. cost  source^ which was similarly
adjusted to the March 1984 cost base.  For estimating purposes, aerobic  digestion
costs include pre and post thickening while anaerobic digestion costs only include
pre-thickening (post-thickening is assumed to occur in the  second stage  of the
anaerobic  digestion system).  Prethickening to  3-5% solids  was  assumed for both
aerobic and anaerobic digestion systems with  hydraulic detention times of 20 and 12.5
days (first stage), respectively.

OONCUUSION

All of the people with whom this process was  discussed, and who had direct knowledge
of the system operation  in FRG, indicated that  the ATAD system  was operated with
relative ease.  These comments were made by plant operating personnel, design
engineers, and by the manufacturer's representative.  The on-site review of the  ATAD
system operation confirmed this view.

The process performance  factors were generally  found  to be  acceptable.   These
included:  volatile solids reductions >40 percent,  thermophilic (>43°C)  temperature
conditions in the second stage reactor,  apparent pathogen reduction equivalent to a
Process to Further Reduce Pathogens,  and infrequent incidence of  odors.

Additionally, cost analyses  performed in the  FRG have indicated that the ATAD system
is the most cost effective alternative for sludge digestion (compared to conventional
aerobic and anaerobic digestion)  for facilities of  small to medium size  K4MGD).24
The cost comparison made as  a result of  this  recent ATAD assessment indicates that
this relationship may hold true for the  U.S.  as well.  It is important to note that
no consideration was given to the benefit of  achieving "pasteurization"  of  the sludge
during cost comparisons  performed in the FRG  or in the U.S.  Typically,  an  additional
process (i.e., gamma irradiation) may be required to  achieve similar  levels  of sludge
quality.  This benefit nay significantly increase the apparent  cost benefits of  the
ATAD process.
                                        -14-

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                                    FIGURE 4  COMPARATIVE DIGESTION CAPITAL COSTS
   600,000!
   500.000!—
   400,000;^-
2

= ! 300,000!'
O :
O
V)
    200,doo!<
    100,000!—
                     r
                     250
 I
500
 I
750
  I
1000
1250
  I
1500
 J
1750
  I
2000
  17
2250
 JT
i 2500
                                                       Kg/Day of f S Throughout
!2750

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                                     REFERENCES
1.  Kambhu, K and Andrews, J.F., "Aerobic Thermophilic Process for the Biological
    Treatment of Wastes - Simulation Studies," Jour, Waster Pollution Control
    Fed., 41, R127, 1969.

2.  Andrews, J.F. and Kambhu, K., "Thermophilic Aerobic Digestion of Organic Solid
    Wastes," EPA-670/2-73-061, August, 1973.   Available from National Technical
    Information Service, PB 222 396.

3.  Popel, P., W. Ruprich D. Strauch, W. Miiller und E. Best,  Flussigkompostierung
    von Flussigmist und Abwasserschlaram durch Urowaltzbeluftung.  Landtechnische
    Forschung 18 (1970) Nr 5.

4.  Popel, F, Energieerzeugung beim biologischen Abbau organischer Stoffe,
    gwf-wasser/abwasser, 112 (1971) H.8.                    /

5.  Popel, F., Die theoretischen und praktischen Grunlagen der Flussigkompostierung
    Hochkonzentrierten Substrate, ausgearbeitet fur die Badische Anilin-und
    Sodafabrik Ludwigshafen; Stuttgart, im November 1971.

6.  Popel, F. and C. Ohnnacht.  "Thermophilic Bacterial Oxidation of Highly
    Concentrated Substrates."  Water Research, 6_, 807-815, 1972.

7.  Jewell, W.J. et al, "Autoheated Aerobic Thermophilic Digestion with Air
    Aeration," EPA Project No. R 804636, MERL Report, NTIS PB 82-196908.

8.  Hamilton, Ohio, City of. "Full-Scale Conversion of Anaerobic Digestions to
    Heated Aerobic Digesters."  EPA Project No. R2-72-050, 1971.

9.  Smith, J.E., K.W. Young and R.B. Dean.  "Biological Oxidation and Disinfection
    of Sludge".  Water Research, £, 17-24, 1975.

10. Matsch, L.C. and R.F. Drnevich.  "Autothermal Aerobic Digestion."  Journal
    Water Pollution Control Federation, 49 296-310, 1977.

11. Jewell, W.J. and Kabrick, R.M., "Autoheated Aerobic Thermophilic Digestion with
    Air Aeration," Jour, Waster Pollution Control Fed., 52, 512, 1980.  -

12. Camp, Dresser, and McKee, Inc.  "Engineering and Economic Assessment of
    Autoheated Thermophilic Aerobic Digestion with Air Aeration."  EPA Contract No.
    68-03-2803, Municipal Environmental Research Laboratory, Cincinnati, Ohio,
    February 1981.

13. Wolinski, W. and Bruce, A., "Thermophilic Oxidative Sludge Digestion; A Critical
    Assessment of Performance and Costs" European Sewage and Refuse Symposium,  1984.

14. Phone conversation with W.  Jewell.  Cornell University, Ithaca,  New York,  24 May
    1983.

15. Breitenbucher, K.  Personal Correspondence with on 24 March, 8 June and 14
    October 1983; F.G.W. Fuchs-und-Wassertechnik, Mayen,  West Germany.


                                        -16-

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16. Breitenbucher, K. Aerob-therraophile Stabilisierung von Abwasserschlamnen
    Ergenbnisse verfahrenstechnischen Untersuchungen zur unweltfreundlichen
    Aufbereitung and Verwertung, Verlag Eurgen Ulmer, Stuttgart, 1983.

17. Cooney C.L., Wang, D.I.C., Mateles. R.I. "Measurement of Heat Evolution
    and Correlation with Oxygen Consunption During Microbrial Growth",
    Biotechnology & Bioenqineering, 11, 269, 1968.

18. Environnental Protection Agency.  Process Design Manual; Sludge Treatment and
    Disposal.  EPA 625A-79-011, September 1979.

19. Bundesgesundheitsamt Merkblatt Nr 7:  Die Behandlung und Beseitigung von
    Klarschlanmen unter besondere Berucksichtigung ihrer seuchenhygienisch
    unbedenklucher Verwertung im Landban.  Bundesgesundheitsblatt 15 (1972).  S
    234/237.

20. USEPA, Technology Transfer Environnental Regulations and Technology - Use and
    Disposal of Municipal Wastewater Sludge, EPA 625/10-84-003, September 1984,
    Center for Environnental Research Information, Cincinnati, Ohio.

21. Strauch, D., 7 Mitteilung:  Wei tare Untersuchungen an einem Verfahren zur
    aerob-thermophilen Schlammstabilisierung, in Mikrobiologische Untersuchungen zur
    Hygienisierung von Klarschlamm, gwf-vBSser/abwasser 121, Jahrgang 1980.

22. Bohm H. 0. and D. Strauch, Das Unwalzbeluftungsverfahren (System Fuchs) zur
    Behandlung von flussiger und Koimunalen Abfalien - In Mitteilung:
    Untersuchungen uber die WirJcung der Unmalzbeluftung auf der Erreger der
    vesikularen Schweinkrankheit, Berl. Much. Tierarztl. Wsch. 96, 57-60 (1983).

23. USEPA, Innovative and Alternative Technology Assessment Manual, EPA
    430/9-78-009, February 1980, Municipal Environmental Research Laboratory,
    Cincinnati, Ohio.

24. Wolf, P, Wirtschaftlichkeitsvergleich von Schlammfaulung und aerob-thermophiler
    Schlammstabilisation auf kleinen und mitteren klaranlagen, Wasser/Abwasser,
    March 1982.
                                        -17-

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