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
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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.
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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:
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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.
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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
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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.
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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
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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)
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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.
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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.
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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
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u>
I
Legend
OTS
Zulauf
Ablauf
TR II
TR I
40
g"
o20
70
•C
SO
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0
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9uf
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rUrtt
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if
=9*.
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— •—
-"-
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""^
^^
XI
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^—
I Um*rtuchungstogt
= 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.
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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.
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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.
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