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                                 DISCLAIMER
     The information in this document has been funded wholly or in part  by
the United States Environmental Protection Agency under assistance  agreement
*CR811022 to Lehigh University.  It has been subjected  to  the Agency's  peer
and administrative  review  and  has been approved  for  publication as an EPA
document.  Mention of trade names or commerical products does not constitute
endorsement or recommendation for use.
                                     ii

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                                   FOREWORD
      Today's  rapidly developing  and  changing  technologies  and  industrial
products and practices frequently carry with  them the increased  generation of
materials that, if  improperly dealt with,  can threaten both public health and
the environment.  The U.S. Environmental Protection Agency is charged by Congress
with protecting the Nation's land, air, and water resources.   Under a mandate
of national  environmental  laws,  the Agency strives to formulate  and implement
actions leading to a compatible balance between human activities and the ability
of natural systems  to  support and nurture  life.   These laws direct the EPA to
perform research to define our environmental problems,  measure the impacts, and
search for solutions.

      The  Risk Reduction Engineering  Laboratory  is  responsible  for planning,
implementing,  and managing of research, development,  and demonstration programs
to  provide an authoritative, defensible engineering basis in support  of the
policies,  programs, and  regulations of the EPA with respect to drinking water,
wastewater,  pesticides,   toxic  substances, solid and  hazardous wastes,  and
Superfund-related activities.  This publication is one of the products of that
research and provides a vital communication link between the researcher and the
user community.

      One  of the major  procedures  for stabilization  of  municipal  wastewater
sludge  is  anaerobic digestion.   Thermophilic  digestion is of interest because
it  insures pasteurization  of sludge.  This report deals with the  conversion of
mesophilic  digesters  to  thermophilic  conditions  and  evaluates  the  potential
effect of  sudden temperature decreases on thermophilic digester performance.
                              E. Timothy Oppelt, Acting Director
                              Risk Reduction Engineering Laboratory
                                      111

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                                   ABSTRACT


     As part  of  a  larger  study  on the  comparison  between mesophilic  and
thermophilic anaerobic digestion, a study of  the operation of anaerobic systems
under temperature transition was  conducted.  Systems seeded with domestic sewage
sludge, but subsequently fed a chemically defined complex medium, were operated
at 20- and 30-day  detention times  at 35 C.   The temperature was raised to 55C
at rates  varying  from  0.25C  to 2.5C  per day in  duplicate,  parallel  units.
Irrespective of temperature rise rate,  as soon as the temperature exceeded 45C
methane  production  shut  down.   The  units were held  at 45C  until  recovery
occurred.  Once recovery  of methane production ability occurred, transition to
55C took place with little incident except for minor difficulty at 51C.  Data
analysis  indicated that rate of temperature rise had little effect on the total
time  required  to obtain  stable  operation  at  55C;  detention  time  had  a minor
effect with longer detention  times yielding superior results.

     A temperature drop study was  conducted from 55C to as low as 47.5C.  No
adverse effect was observed until the temperature was reduced  to less than 50C.
Washout of methane bacteria seemed to  occur when  the  temperature  was suddenly
dropped below  50C and the system detention time was less than 20  days.

     Comparison of operation  at  55C vs. 35C under steady-state  at  detention
times  ranging from 7.5 days to 30 days indicated that based on effluent volatile
acids  level,  mesophilic operation  was superior and that  this superiority was
greater at the lower detention times.

     The  organisms which  function  under thermophilic conditions  appear  to be
present  in mesophilic  sludge but are  not active  at  low temperature.   When
thermophilic  conditions  are  brought about,  the  thermophilic  organisms  will
multiply  to an adequate level  in several weeks.

     This report was submitted  in  fulfillment of Grant  No.  CR811022  by Lehigh
University under  the sponsorship of the U.S. Environmental  Protection Agency.
This  report  covers  a  period  from October,  1984 to April,  1986  and  work was
completed as of March  31,  1988.
                                      iv

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                                   CONTENTS

Disclaimer 	   ii
Foreword 	  iii
Abstract 	   iv
Figures	   vi
Tables	   ix

     1.   Introduction 	   1
     2.   Conclusions 	   2
     3.   Recommendations 	   3
     4.   Experimental Plan and Details 	   4
     5.   Results  	  10
     6.   Discussions 	  61

References 	  64

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                                   FIGURES

Number	Page

  1       Batch  Daily Feed  Digester  System  	    6

  2       Gas  production  from  Unit  9A  (control):   30  day
          detention time	  11

  3       Gas  production  from  Unit  9B  (control):   30  day
          detention time 	  12

  4       Temperature and volatile acids  concentration vs.  time
          for Unit 9A (control):  30 day detention time 	  13

  5       Temperature and volatile acids  concentration vs.  time
          for Unit 9B (control):  30 day detention time 	  14

  6       Gas  production  from  Unit  10A (control):   20  day
          detention time 	  15

  7       Gas production in Unit 10B (control):  20 day detention
          time 	  16

  8       Temperature and volatile acids  concentration vs.  time
          for Unit 10A (control):  20 day detention time  	  17

  9       Temperature and volatile acids  concentration vs.  time
          for Unit 10B (control):  20 day detention time  	  18

 10       Gas  production in  Unit 3A  (5C increment):  30  day
          detention time 	  19

 11       Gas  production  in Unit 3B (5C  increment):   30  day
          dentention  time 	  20

 12       Temperature and volatile acids  concentration vs.  time
          for Unit 3A (5C increment): 30 day detention  time 	  21

 13       Temperature and volatile acids  concentration vs.  time
          for Unit 3B (5C increment): 30 day detention  time 	  22

 14       Gas production  from Unit 6A  (5C increment):  20 day
          detention time 	  24
                                     vi

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15       Gas production from Unit  6B (5C  increment):  20  day
         detention time  	  25

16       Temperature and volatile  acids  concentration vs.  time
         for Unit 6A (5C increment):  20 day detention  time 	  26

17       Temperature and volatile  acids  concentration vs.  time
         for Unit 6B (5C increment):  20 day detention time 	  27

18       Gas production from Unit  5A (3.5C increment):  30  day
         detention time  	  28

19       Gas production from Unit  5B (3.5C increment):  30  day
         detention time  	  29

20       Temperature and volatile  acids  concentration vs.  time
         for Unit 5A (3.5C  increment):  30  day  detention  time  	  30

21       Temperature and volatile  acids  concentration vs.  time
         for Unit 5B (3.5C  increment): 30 day detention time  	  31

22       Gas production from Unit  7A (3.5C increment):  20  day
         detention time 	  33

23       Gas production from Unit  7B (3.5C  increment):  20 day
         detention time 	  34

24       Temperature and volatile  acids  concentration vs.  time
         for Unit 7A (3.5C  increment): 20 day detention time  	  35

25       Temperature and volatile  acids  concentration vs.  time
         for Unit 7B (3.5C  increment): 20 day detention time  	  36

26       Gas  production from Unit 1A (2C  increment):  30  day
         detention time 	  37

27       Gas  production from Unit IB (2C  increment):  30  day
         detention time 	  38

28       Temperature and volatile  acids  concentration vs.  time
         for Unit 1A  (2C  increment):  30 day detention  time 	  39

29       Temperature and volatile  acids  concentration vs.  time
         for Unit IB  (2C  increment):  30 day detention time 	  40

30       Gas  production from Unit 4A (2C  increment):  20  day
         detention  time 	  41

31       Gas  production from Unit 4B (2C  increment):  20  day
         detention time 	  42
                                 vii

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32       Temperature and volatile  acids  concentration vs. time
         for Unit 4A (2C increment): 20 day detention time  	  43

33       Temperature and volatile  acids  concentration vs. time
         for Unit 4B (2C increment): 20 day detention time  	  44

34       Gas production from Unit  2A (1C  increment):  30  day
         detention time	  45

35       Gas production from Unit  2B (1C  increment):  20  day
         detention time  	  46

36       Temperature and volatile  acids  concentration vs. time
         for Unit 2A (2C increment): 30 day detention time  	  47

37       Temperature and volatile  acids  concentration vs. time
         for Unit 2B (1C increment): 30 day detention time  	  48

38       Gas  production from Unit  8A (1C  increment):  20  day
         detention time 	  50

39       Gas  production from Unit  8B (1C  increment):  20  day
         detention time 	  51

40       Temperature and volatile  acids  concentration vs. time
         for Unit 8A (1C increment): 20 day detention time  	  52

41       Temperature and volatile  acids  concentration vs. time
         for Unit 8B (1C increment): 20 day detention time  	  53

42       Volatile acids  concentration vs. time: 30 day detention
         time  	  54

43       Volatile acids  concentration vs. time: 20 day detention
         time  	  55

44       Mean  volatile acids concentration  vs. time  for units
         subjected  to  temperature  drops from  55C  to 55, 52.5,
         50,  and 45.5C 	  57

45       Mean  volatile acids concentration  vs. time  for units
         subjected  to  temperature  drops from  55C  to 55, 52.5,
         50,  and 47.5C 	  58

46       Comparison  of mean volatile  acids   concentration  in
         units at 30 day and 30  day  detention  times  subjected  to
         temperature drops  from  55C to 47.5C	  59
                                    viii

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                                    TABLES

Number	Page

    1          Identification of Units in Temperature Rise Study 	  5

    2          Feed Used in Study  	  7

    3          Steady State Performance of Thermophilic and
               Mesophilic Anaerobic Treatment Systems 	 60

    4          Summary  of Performance During Temperature Transition
               from Mesophilic  to  Thermophilic Conditions 	 62
                                      ix

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                                  SECTION 1

                                 INTRODUCTION

     The purpose of  this  study was to  conduct  a comparative evaluation of
the performance of  anaerobic  digestion  systems  under different  temperature
regimes.  The  temperature  regimes chosen were  those  most commonly used in
field  installations (i.e.  mesophilic 35C and thermophilic  50-55C).
Evaluation of performance was  in  terms of  a  number of parameters  including:
stability of  operation, degree  of waste  stabilization,  dewaterability of
digested sludge and odor.

     The  work  has  been divided  into  two phases.   The  first,  which is
reported on here, deals primarily with the operation  of anaerobic  digestion
systems under  situations of  temperature  transition.   The  second phase will
deal with differences between  system performance at steady state in the two
temperature regimes.

     The  primary reason for  conducting  temperature  transition studies
revolves  around  the question  of  how  to start  up  a   thermophilic  digestion
system.   The  most   efficient  procedure  is  to  seed with  sludge  from an
operational thermophilic system.  However, this material may not be readily
available.   In such  a  case  it will  be necessary to convert  a mesophilic
anaerobic  digestion  system  to  a  thermophilic system.    Because methane
forming microorganisms are known  to be quite sensitive to all environmental
conditions,  it" was  felt that  a  rapid change in temperature may not yield
positive  results.   On the  other hand, if  a  very low rate of adjustment of
temperature is used,  the anaerobic treatment system may be out of  operation
for a  long period of time.   Consequently,  an evaluation was made here  into
the  effect of temperature rise  rate when  converting  from  mesophilic to
thermophilic operation.

     Another question which was  addressed in this study  was  the effect of
temperature  decreases on the  performance  of thermophilic systems.   It is
generally  considered that  thermophilic  systems  are  more  sensitive  than
mesophilic systems.   Thus,  small reductions  in temperature may have  severe
consequences on  thermophilic  system  performance.   This part of  Phase I of
the  study  thus,  incorporated experiments  in  which the  temperature  was
intentionally  and rapidly  reduced to  determine  the magnitude of the  effect
on  the  thermophilic anaerobic  systems.   Finally,  limited  steady-state  data
on  system performance  were  collected  at 55C and   35C  to  determine if
thermophilic  anaerobic  digestion  is  superior  in performance  to  the
conventional temperature 35C.    Much more extensive  steady-state  data were
collected during Phase II and  is reported on  in  the Phase  II Report.

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                                  SECTION 2

                                 CONCLUSIONS
1)   Race of temperature increase had little effect on  the  time  required  to
     reach  stable  operation at  55C  during conversion  from mesophilic  to
     thermophilic conditions.

2)   The  transition from  mesophilic  to  thermophilic  conditions occurs  at
     45C  as  operation  is interrupted  (methane  production  halted)  for
     several weeks when this temperature is reached.

3)   Eventual  recovery  occurs  indicating that thermophilic  organisms exist
     in mesophilic sludge but are dormant.

4)   It  takes  several  days  after  reaching  45C for  the  retardation to  be
     fully manifest.

5)   At  longer detention  time  operation temperature  transition  effects are
     not as severe.

6)   When  the  temperature is  rapidly  reduced  from 55C no effect  on
     operation  is  manifest until the  temperature is  reduced below 50C and
     the detention time below 20 dayc.

7)   The temperature drop  effect is probably not a reduction in  the  ability
     of  the methane bacteria  to process substrate but in  the  ability  to
     reproduce.

8)   Steady-state  operation at 35C was  slightly  superior  to operation  at
     55C  at  long detention times  and  clearly superior at  short  detention
     times.

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                                  SECTION  3

                               RECOMMENDATIONS
1)   The data  collected  here  gave some  indication  of  a second retardation
     temperature slightly above 51C,  this  should be  investigated.

2)   These  studies  should  be  repeated  with a  feed of  sewage  sludge  to
     observe  the effect  of  continuous  reseeding  from  organisms   in  raw
     sludge.

3)   The  washout phenomenon observed  when a  temperature  drop  took place
     should be investigated.

4)   Storage of  thennophilic sludge at cold temperature  (approx. 5C) should
     be investigated as a method of saving  thennophilic  sludge for later use
     as seed for starting thermophilic digesters.

5)   The  data  collected here indicated  best performance  of  anaerobic
     digestion  may  be- at  temperatures  in  the  range 40C  to 45C.   This
     should be studied in depth.

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                                  SECTION 4

                     EXPERIMENTAL PLAN AND DETAILS


     Phase I contained four separate periods listed as A through D below:

     A.    Temperature Rise Rate Study

     B.    Steady State at 55C and 35C at 20 & 30 day detention times.

     C.    Temperature Drop Study

     D.    Steady State at 55C &  35C at detention times in the  range  from
          20 to 7.5 days.

     In all studies an artificial feed was used and feed  and withdrawal was
on a periodic batch basis.  In all studies monitoring  of the units was based
on pH, alkalinity, volatile acids, gas volume and gas  composition.   Specific
details  of  A follow,  and specific details  of B, C  & D will  be given  as
necessary when the results of these studies are presented.

TEMPERATURE RISE RATE

     The major goal of Phase  I of the study was to determine the  effect  of
rate  of  temperature  change  on  system performance during  conversion  from
mesophilic  conditions  to thermophilic conditions.   The basic plan used was
to set up  a series of bench  scale  units  at 35C, operate them to a steady
state and  then  raise  the temperature  at  various  rates while maintaining  a
normal feeding pattern as long as possible.

     A series of i liter bench scale anaerobic digestion systems were set  up
using digested  sewage  sludge  from the anaerobic digester at the  Allentown,
PA Sewage Treatment Plant.  The liquid volume  used in  each  digester was 750
ml.  Each unit was connected  to a cylindrical  gas collection tube which had
been  calibrated  Jn  increments  of 10 ml.    An  acidified  saturated  salt
solution was  used as  the confining  fluid to  trap  the  gas evolved.   The
confining fluid was held in a reservoir  connected to  the bottom  of the gat
collection  tube.   A diagram  of  this  experimental arrangement  is given  Lrt
Figure 1.   Throughout  this study  these units were operated on  a  batch  feed
and  withdrawal  basis.   At each  feeding  interval  a   small portion of the
contents of the unit were first withdrawn and then replaced by  a like amount
of fresh feed.  The volume fed and withdrawn was a function of  the hydraulic
detention  time  at which  the unit was  being  operated.   Just  prior  to
withdrawal, and also just after  feeding,  each unit was manually  shaken for

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approximately 10-15 seconds  to  insure  complete dispersion of the  contents.
Thus these units  were operated at identical solids and hydraulic  retention
times (SRT-HRT).

     A total of 20 units were  set up,  ten at each detention time used.   In
addition, units  were operated  in pairs.    This  provided for four sets  of
units at each detention time  in which  the temperature would be  raised  plus
one  pair  as  a control.   The control  units  were maintained at  35C.    The
units were numbered 1 through  10 with  duplicates  identified as  A & B.   The
four rates of temperature rise used were 1C, 2C, 3.5C and 5C  per feeding
period (the  term  feeding period will be defined below).   Table  1  lists  the
numbering system used and the conditions of operation for each unit.
         TABLE  1.  IDENTIFICATION OF UNITS IN TEMPERATURE RISE STUDY
 Identification                Detention Time          Temperature Rise  Rate
1A-1B
2A-2B
3A-3B
4A-4B
5A-5B
6A-6B
7A-7B
8A-8B
9A-9B
10A-10P,
30 days
30 days
30 days
20 days
30 days
20 days
20 days
20 days
30 days
20 days
2C
1C
5C
2C
3.5C
5C
3.5C
1C
0C
0C
      All of  the  units were  set  up  in  a  temperature  controlled  room
 maintained  at  35+  0.1C.   The  units in which  the temperature was  to be
 raised were  in addition  immersed  in  temperature  controlled  water baths.
 Each  consisted  of a  10  gallon  glass aquarium  insulated with  sheets of
 polystyrene on all  vertical sides.   Beads of  polystyrene were placed on  top
 of  the   water  surface  to act  as  insulation.    Variable  setting  aquarium
 heaters  were  used  to raise the temperature above amibient  levels  in  the  room
 (35C).   The water in the bath was  kept in circulation by bubbling a small
 quantity of air continuously  into the water.   Prior to actually conducting
 the   experiments  detailed  below,  the settings  on  the   thermostats   were
 manually calibrated.    Mercury   thermometers  were  inserted  into  1  liter
 bottles  containing  750 ml  of water.   These were  placed in  the water  bath and
 used  to  calibrate  heater   setting;  and  thereafter   for   temperature
 measurement.   The  thermometer  units  were kept in  the water baths throughout
 the  study to monitor the temperatures.   Eight water baths were used.    Each
 contained  a pair  of bench  scale  anaerobic units  and  the  temperature
 measurement bottle.

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Figure 1.  Batch daily feed digester system.   Black triangles indicate fluid levels.
          glass
       pressure
     indicating
           tube
withdraw!  tube
                        gas
                        collection
                                                one liter
                                                digesters
                                     airline
                                                             pressure
                                                             reducing
                                                                valve
_J

T
tuoes
V
V
r
n
                                     ?r valve
                                                     20  liter
                                                    reservoir

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     As indicated  above,  these units were originally started  with digested
sludge.   It had been  planned to use raw  sludge from the  Allentown Sewage
Treatment Plant as the feed during these tests.  The initial detention times
chosen were  7.5  and 15 days.   After several weeks it became  apparent that
good operation at  these  conditions  (35C,  7.5 & 15 day  detention time)  was
not achieved.  This was based  on high levels of  volatile acids in the units
(1000 mg/1).  Consequently  the detention times were increased  to  20 and 30
days.  Improvement was observed (the volatile acids fell  to about 500 mg/1)
but operation was not satisfactory because of the high volatile acids level.
It was decided that an inhibitory  substance  or a nutritional deficiency was
manifest  in  the  Allentown Treatment Plant.   Consequently it was  decided to
use an artificial  feed in these studies.  The feed chosen  was a commercial
product  "Carnation Instant  Breakfast"   suspended  in whole milk.    It  was
chosen because when mixed with whole milk in the  recommended  proportion (1
envelope  per 8 fluid ounces  of milk)  it had  a fat, carbohydrate and protein
content similar  to that of raw sludge.   In  addition,  it contained  most of
the  organic and inorganic nutrients required by microorganisms.   The feed
was,  in  addition,  supplemented with several inorganic  materials  for which
methane  fermenting organisms  have  a  high  demand,  i.e.,  Fe,  Co,  Ni.    A
complete  analysis  of  the feed  is  given in Table 2.   Within a few weeks of
this  change  in  feed,  the volatile  acid  level  in the digester  effluents  was
consistently in  the range of  100 to  200 mg/1, and  stable gas production was
observed.    The  units  were  continued  in  operation  for  several months  to
insure washout of  the  original  seed material.


                         TABLE  2.  FEED USED  IN STUDY
Na2HP04                                                25 mg/1
Carnation  Instant Breakfast                            6.5 g/1
NH4HC03                                                1.9 g/1
CoCl2                                                  1 mg/1 as Co
FeCl2                                                  150 mg/1
Ammonium Molybdate                                     0.02 mg/1
MnCl2                                                  0.4 mg/1
Boric Acid                                            0.01 mg/1
Sodium Tungstate                                       0.02 mg/1
NaCl                                                   0.2 g/1
MgCl2                                                  0.1 g/1
Nickel Acetate                                         2 mg/1
K2S04                                                  0.2 g/1
Milk                                                   66.6 ml
Yeast Extract                                          10 mg/1
Bethlehem  Tap H20                                      1 liter
     After  the  washout  period  was  complete  (>3 HRT's),  the  temperature
change period was  initiated.  The  volume  of  feed required  for the detention
times used corresponds to 25 ml per day at a 30  day HRT  and  37.5  ml  per day
at a  20  day  HRT.  It was felt  that  these volumes were too small  to be fed

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accurately.  Thus  during this study the 30 day HRT unit was  fed 50 ml once
every 2 days and the 20  day HRT units were  fed  75  ml  once  every 2 days.  It
was indicated above that nominal temperature changes per feeding period were
to be used.  Thus  a feeding period represents the period  of  2 days after a
feeding event.

     In conducting the  temperature  rise  study  the following  procedure was
used.  At the beginning  of a  feeding period the heater in  the water bath of
the appropriate  units  was adjusted  based on the  prior  calibration and the
normal once per  2  day withdrawal and feed took place.  Periodically over the
next  2  days the temperature  in  the bath was checked  to insure  that  it was
not above  or below the  new set point.   At the end  of the 2  day period a
comparison was made between the  gas  production  from the last 2 days and that
from  the  control units  (which were maintained  at  35C).   If gas production
was close  to  that of the control unit  the  temperature was again raised and
the unit  was given a  normal  feeding.   If  gas  production  was significantly
less  than  in the control unit the  temperature  was not raised and the units
were  not  fed.   The  units were not fed again until gas  production data
indicated  that  most of  the previous feed had been converted to methane and
carbon  dioxide.   The  temperature was not raised again until  most or all of
the  feed  added during the  last  feeding was consumed  in the  standard 2 day
period.   It should be  appreciated  that  judgement of  the experimenter was
used  in determining when to feed and when to raise the  temperature.  No firm
quantifiable rules were  employed.   As each  run  progressed  and experience was
gained  the  decisions on  feeding  and temperature change were modified.

      Each  time  a withdrawal was made from  a unit  the digester mixed liquor
was  analyzed for  pH,   alkalinity and volatile acids.    Daily  gas production
was  determined  and  at  the  end of each feeding period  gas  analysis  for
methane and carbon dioxide was conducted.   Alkalinity, pH  and volatile acids
were  monitored  by the  procedures  given  in Standard  Methods(l)  (volatile
acids by  distillation);  gas analysis  was  conducted using  a  Fisher  Gas
Partioner(2).

STUDIES B,  C, AND D

      Over  a three  month  time  period the temperature of each unit except the
controls  was  raised  to 55C.  At that time  it was decided  to  continue
operation  of  these  units  at  55C &   35C  respectively to  establish  a
comparison between operation at these  temperatures  with  this feed  and at
 these 2 detention times.

      Subsequent  to this  steady state period, a study was conducted in which
the   temperature   was  suddenly  dropped  by  various   amounts  while  normal
operation i.e.,  feed and withdrawal were maintained.   This study determined
the  effect that  a  sudden loss of heat  supply could have on the operation of
a thennophilic  digester.

      Only  some  of the  16 units being  maintained  at  55C  were used  in the
temperature  drop  study.    The remainder  were used in a study  in which the
detention  times  of the  55C and the 35C units were  reduced  down to  as low
as  7.5  days.   The purpose of this  study was again  to  obtain a comparison

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between operation of units In parallel  at  the two temperatures but at much
lower detention times.

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                                  SECTION 5

                                   RESULTS
TRANSITION TO THERMOPHILIC TEMPERATURES

     The results of this study are presented in the 40 figures which follow.
Some  of  these  figures  give  gas production  as  a  function of  time  and
temperature, while others provide plots  of digester volatile acids  versus
time  and temperature.   The results  are  discussed below  grouped  primarily
according to rate  of  temperature  rise and secondarily according to detention
time.    In  the  plots  of gas  production  each vertical  bar  represents  one
feeding period.    During  periods  of good operation  a feeding period
represents  2  days so  the  bar has 2  sections (unmarked  and  crosshatched) .
The unmarked section  is  gas production during the  first  day  after feeding.
The  crosshatched   section represents  the  gas production  on the second  day
after  feeding.  When retarded  operation occurred each bar  had more than  2
sections as it required more than 2 days  to consume the  feed.   Each section
of the bar, either unmarked or crosshatched represents one  day.  Thus,  if  a
vertical  bar has  6  sections  it  means   it required 6  days   to  consume  a
standard feeding.  For the  first  20 days  (10 feeding periods)  of  this  study
no temperature  rise took place.   These  data give  an indication  of  normal
operation at 35C  prior to initiation of the temperature  rise.

Rate of Temperature Rise - 0C -  30 Day Detention Time

     Figures  2-5   present  the  performance  of  the  30  day detention  time
controls  during  the   100  days  of this  study  (units   9A and  9B).    Gas
production was 584 + 37 ml for 9A and 574 + 36 ml for 9B.   Approximately  90%
of  the  gas was   produced  during  the first  day.    The  abnormally high
production of gas  on day 80-82 for 9A was  due to a minor  leak  which occurred
on that day.  Volatile acids  averaged <200  mg/1,  with occasional  excursions
near 400 mg/1.

Rate of Temperature Rise - 0-C - 20 Day Detention Time

     Figures  6-9   present  the  performance   of  the  20  day detention time
controls (units 10A & 10B).  Results  obtained were  similar  to  those  for  the
30 day controls.   Gas production was  consistently  good  and volatile  acids
low;  <200 mg/1.  However, one  unusual event which occurred was that during
the period day 26-28 unit 10A was killed  when the acid-salt confining  fluid
accidentally gained entrance to the unit.   A new unit was  immediately set up
using previous  days effluent from units 10A &  10B which  had been  stored in
the refrigerator  at 4C.   It can be seen  that  this new  unit  started up
almost instantaneously.  This phenomenon  of being able to  start an  anaerobic
                                   10

-------
Figure 2.  Gas production from unit 9A (control): 30 day detention time.




                                                            790 ml
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2  6
                          Time in days

-------
        Figure 3.  Gas  production from unit 9B  (control):  30  day  detention time.
   600-
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-------
  Figure 4.    Temperature and volatile acids concentration  versus
              time for unit 9A (control): 30 day detention  time.
  12r
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-------
 Figure  5.  Temperature and volatile acids concentration versus
             time  for unit  9B  (control):  30 day detention time.
  I2r
  10
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                          Time  in days
                          80
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                              14

-------
       Figure 6.   Gas production from unit 10A  (control):  20  day
                                         detention  time.
  900 -
  800-
   700 - '
  600-
  500-
 OJ
 3300
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  200
  100
                        new unit
                        established
                              Time  in days
                                    15

-------
  Figure  7.
             Gas production  in unit 10B  (control):  20 day
             detention  time.
  too -I
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  200 -J
                          Time in days
                               16

-------
 Figure 8.   Temperature  and volatile acids concentration versus

             time  for  unit 10A (control):  20 day detention time.
  12
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                                                             30
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                          Time in days
80
100
                              17

-------
  Figure 9.   Temperature and volatile acids  concentration versus
              time for unit  10B (control):  20 day detention  time.
                                                            -i 60
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-------
Figure 10.   Gas production in unit 3A (5C increment)
            30 day detention time.
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     Figure  11,
Gas production in unit  3B (5C increment)
30 day  detention time.
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-------
 Figure 12.  Temperature and volatile acids concentration versus
             time  for unit 3A (5C increment): 30 day detention time.
                                                 55C
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                   Time in days
80
100
                               21

-------
 Figure  13.   Temperature and volatile acids  concentration versus
              time for unit 3B (5C increment):  30 day detention time,
  I2r
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                          Time  in  days
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                                22

-------
digestion unit rapidly  from  digester effluent or mixed liquor stored at  4C
was  observed  several  other  times  during  this study.    The  average  gas
production from unit  10B was 837 45 ml.  About 15%  of the gas production
took place on  the  second day of the feeding period.   Data  for 10A were  not
averaged because  of  its  replacement as detailed above.   The ratio  of  gas
production for the 20 day detention time  to that for  the  30  day units  was
1.45 which  is  close  to the  theoretical value  of 1.5.   As indicated  above
volatile acids were always  low except for an excursion to  500 mg/1 in unit
10B on day 54.

Rate of Temperature Rise  - 5C  - 30  Day Detention Time

     Figures 10-13 present the  data for  the 5C rate of rise.    It  can be
seen that  the  units  (3A  & 3B)  exhibited  similar performance.    At 40C  and
45C, performance  was as  good or even better than the control units (35C) .
However the  transition  from  45C to  50C  created an adverse situation both
with respect to the  acid formers  and methane formers.   The effect was  not
immediately  apparent  in the  first feeding period after  the  transition except
in the slight  shift in  proportion  of gas  production on the first and second
days  (90%  first  day  at  45C,   80%  first day  50C).    However,  the  units
essentially  shut down during  the second feeding  period  after the temperature
reached 50C.   It was  not until day 58  (a period  of 30  days)  that  these
units  could  function at  the normal  2  day feeding  period.    Even  then  the
proportion of  gas  production during  the  first  day  was low.   By  day  68  the
units exhibited nearly  normal operation and  low volatile acids.   On day  69-
70 the temperature was  raised to the  target of  55C.   Over  the next 30 days
the normal 2 day  feeding period could be maintained but the volatile  acids
gradually increased (almost  linearly) from 200 mg/1 to 800 mg/1.

Rate of Temperature Rise  - 5C-  20 Day Detention Time

     Figures 14-17 depict the results for these conditions.   Similar results
to those  obtained at 30  day detention time were observed.   Until 45C  no
adverse effect was noted.  A small  drop  in gas production and  concomitant
rise in volatile  acids  occurred during the first feeding period after 50C
was  reached.   During  the  second  feeding  period  a   significant  shutdown
occurred.   Both methane and acid formers were affected but the  effect on the
former was much greater.   It was not for  another 40 days (day 26  -  day 66)
that the normal 2  day feeding period could be resumed,  and 10 more days were
required until it was  felt  that it was  safe  to  raise  the temperature  to
55C.  The  shift   to  55C was not  as uneventful as  at  the  longer detention
time.  Some  retardation which resulted in modest increases in volatile  acids
occurred.   To  keep the  volatile  acids under control  a  4 day feed period was
used during  day 90-94.  Even so volatile acids were quite high, 1100 mg/1 in
unit 6A  while  they were low,  450  mg/1 in  unit 6B.   A short  temperature
excursion to almost  60C due  to a malfunction  of  the heater  in  the  6A-6B
water bath may be  to  blame for the poorer performance of these  units.

Rate of Temperature Rise  - 3.5C - 30 Day Detention Time

     As illustrated in  figures  18-21 the major  adverse  effect was manifest
when the transition from  45.5C  to  49C occurred.    As before in the  first
                                   23

-------
       Figure 14.  Gas  production from  unit 6A (5C
                    increment): 20 day detention time.
                         45
    -35


900 -
   800  .
   700  -
   600  .
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  400 -

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                        Time in days
                          24

-------
Figure 15.   Gas  production from unit  6B (5C
             increment): 20 day detention time.
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                Time in days
                                    82 86 90 $6 300
                        25

-------
Figure 16.   Temperature and volatile acids concentration versus
            time for unit 6A (5C increment):  20  day  detention time.
             20
40        60

Time in days
80
100

-------
 Figure 17.  Temperature  and volatile adds concentration versus
             time  for  unit 6B (5C increment): 20 day detention time.
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                                27

-------
                           Figure 18.  Gas production from unit 5A  (3.5  C
                                      increment): 30 day detention time.
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                                           Time in days

-------
                               Figure  19.   Gas production  from unit 5B  (3.5 C
                                            increment):  30  day detention  time.
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2  6D143S2226306066  7)

                  Time  in  days
                                                                     78 82  86 SO  $*  58

-------
 Figure  20.  Temperature and volatile acids concentration  versus

             time  for  unit 5A (3.5C increment): 30 day detention  time.
  I2r
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80
100
                               30

-------
 Figure 21.   Temperature and volatile  acids concentration versus
              time for unit 5B  (3.5C Increment):  30 day detention time.
                                         52.55
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                        Time  in days
                                                80
100
                                31

-------
feeding  period after  the  transition to  49C,  only  minor  difficulty was
observed  but  during the  second  feeding  the  full  effect  of the  higher
temperature was observed.   It was  24 days before  the normal  2 day feeding
pattern  could be  resumed.    Recovery was  excellent as  the  transition to
52.5C was made in 4 days and that  to 55C in another 4  days.   At 55C some
retardation was observed as volatile  acids started to rise.   The volatile
acids  returned to normal  in unit  5A (200  mg/1)  but became  elevated (700
mg/1)  in unit  5B.

Rate of Temperature  Rise -  3.5C  -  20 Day  Detention Time

     Figures  22-25  illustrate  a pattern  similar  to  that observed  at the
longer detention  time.   All  was  satisfactory until the  transition to 49C
from 45.5C.   In  this case  the  initial result of the change was more severe
than  at the  30  day detention  period.   It took  30  days until  the  normal
feeding  pattern could  resume and 12  more  days until  a  transition to 52.5C
could  take place.   In  another  2  days a transition to 55C  took place, but
this may have  been premature.  A  rapid rise in volatile acids occurred which
was  brought under control  by going through a single 4  day feeding period.
Eventually the normal feeding of  once per 2 days could be continually used,
and  volatile  acid  levels  dropped  to  the  range 200  to  400 mg/1.    An
interesting observation is  that  at  55C  the second day gas volume was close
to 25% of  the  total  versus  about  15%  at  35C.

Rate of Temperature  Rise -  2C  -  30 Day  Detention  Time

     Figure 26-29 illustrates the familiar pattern except that the use of a
slower rate of temperature  rise allows finer delineation of the temperature
effect.   Under these conditions the  initial  adverse effect  is  noted  at the
transition fr   45C to 47C.  Again  the full effect is delayed for at least
one  feeding p^  -id.  It took  only 14  days  till  the normal 2 day feed period
could  be  reinstated, however, 16 more days passed before  the transition to
49C  occurred.   In  retrospect  this  was  excessive as volatile  acid  levels
were normal 8 days  earlier.  However,  at  this stage the  investigators had
become sensitized to being  optimistic about the  ability  of these systems to
avoid  adverse effects  of  temperature  change.   After  6  days  at  49C  the
temperature was pushed  to 55C  in the next 6 days.  Volatile acids rose and
gas  production  fell temporarily,  but  were soon reasonably  satisfactory
without  the need  to  depart  from the 2 day  feed schedule.

Rate of  Temperature  Rise -  2C  -  20 Day Detention Time

     With  these  units,   much  more severe retardation was  observed (Figures
30-33) than at the  30  day  detention  time.   It  was  decided not to stop at
47C but  to go on to 49C.   This caused a 36 day  period  in  which  the  2 day
feed cycle could not be used and a  total  period  of 40  days  before another
temperature   increase   (to 51C)  was  attempted.    At  53C  some  minor
retardation occurred and 55C  was  reached in 6  more  days.   However,  it was
necessary  to  twice use  a 4  day feed cycle before the units operated normally
at 55C.   In  this situation  the  A unit did not do  as well as  the B  unit.
Volatile acids in A  were 800  mg/1 while  they were  300 mg/1 in B after steady
operation  at  55C was achieved.


                                  32

-------
Figure 22.  Gas production from unit 7A (3.5C
            increment): 20, day detention time.
J.UUU -
900 .




800 -
700 _
600 -


^-^
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                    Time in days
                             33

-------
Figure 23.
                    Gas  production from unit 7B (3.5C
                    increment): 20 day detention time.
                           45.5
   1000 -
         35
   900  -
   800  -
    700  -
    600  -
, 500
QJ
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                       #5

                      35
              30 14  18  22.  2b  &  & 58  62  6S


                             Jime  in  days
                                                   '1100 ml
                                           BQ  W  88  ^  9o JDO
                                    34

-------
  Figure 24.   Temperature and volatile adds concentration  versus
              time  for unit 7A (3.5C Increment): 20 day detention time.
^12

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t 10
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                                                              40  o
                                                      30
               20
                  40        60

                  Time  in  days
80
100
                               35

-------
 Figure 25.  Temperature  and volatile acids concentration versus
             time  for  unit 7B  (3.5C  increment):  20 day detention time.
  I2r
  10
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                                                       30
                          40        60

                          Time in days
                                          80
100
                               36

-------
                        Figure  26.   Gas production  from unit 1A  (2C increment):  30 day
                                     detention time.
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-------
                        Figure 27.  Gas  production from unit IB  (2C increment)
                                    30 day  detention time.
CO
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-   f  42 .48  52  56 60

                                                  Time in  days
72 76  82 86 90 S<*  56

-------
Figure 28.  Temperature and volatile acids  concentration versus
            time for unit 1A (2C increment):  30 day detention time.
                        40        60

                        Time in days
80
100
                               39

-------
 Figure 29.   Temperature and volatile acids concentration  versus
              time for unit IB (2C increment): 30 day detention  time.
                                                            -,60
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                                             80
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                                                              30
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                               AO

-------
      Figure  30.   Gas production from unit 4A (2C increment)
                   20 day  detention time.
o
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ro
  900-
   800-
   700.
   600-
   500-
   400-
   300-
   200-
   100-
       35
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                       39
                           43
- 51
49J53
                                              55
                                               i
2  6  10  14  38  22  26  3D 38 50 58 #> <  ?

                   Time  in days
                                                       so
                                 Al

-------
       Figure 31.   Gas production  from unit 4B  (2C increment):
                    20 day detention time.
 1000 -,
 900  -
  800
  700  -
  600 -
o>
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1/1
ro
  300 -
  200 -
  100 -
                                                     55
                                                      i
       35
                                                   53

                                               51   J
       2   6  10  14  3B  22  26  30    50 58  70 ?**  73 8^  50  S*  93


                          Time in days
                                 42

-------
 Figure 32.   Temperature and volatile  acids  concentration versus
             time for unit4A (2C increment): 20 day  detention time.
                                                           -i60
                                             53
                                                     55e
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                                                             30
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                          40        60

                          Time in days
80
100
                               43

-------
Figure 33.   Temperature and volatile acids  concentration  versus
            time for unit 4B (2C increment):  20  day  detention time.
                        40         60

                        Time in days
80
100
                            44

-------
Figure 34.   Gas  production from unit

             detention time.
                                    2A
                                         (1C
                                                                     increment):  30 day
                  700 J
                  600 -
                      35
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-------
Figure 35.  Gas production rom unit 2A (1C increment): 20 day
            detention time.

700-
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                        Time in days

-------
 Figure  36.   Temperature and volatile acids  concentration versus
              time for unit 2A  (1C  increment):  30  day detention time.
  12
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1/1
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                                                              40 o
                                                              30
               20
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                    Time in days
80
100
                                  47

-------
 Figure 37.   Temperature and volatile acids concentration versus
              time  for unit 2B (1C increment): 30 day detention time.
  I2r
  10
a
m
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                                    30
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40         60

Time  in  days
80
100

-------
Rate of Temperature Rise - 1C  -  30 Day Detention Time

     Figures  34-37  illustrate  system  performance  under the  lowest rate  of
temperature rise  and  loading stress  used.  Some initial effect was  observed
at 46C  (note  change  in proportion of gas between first and second  day) but
it was  decided to go up to  47C.  At this temperature, retardation started
but  in  only 10 days  a return to the  2  day feed pattern  was possible  and  in 6
more the  temperature  was  increased to  48C.   The system was  fed normally but
held at 48C  for  six days  and then pushed to 53C.  The volatile acids  rose
sharply and  increased during  the rise  to 53C;  but  this  was  overcome  by
holding for 6  days  at  53C.   After  84  days  the  temperature reached  55C
where  satisfactory operation  at the normal  feeding  interval was  attained.
Again  it should be noted that  gas production in the  second  day is  a higher
proportion of the total at 55C than at  35C.

Rate of Temperature  Rise - 1C - 20  Day  Detention  Time

      The data  presented in  figures  38-41 indicate  that  at this  detention
 time temperature  effects were worse  than at the 30 day  detention  time.   Here
 the fault cannot  be  excessive zeal in pushing the  temperature  rise  as it was
 for the 2C units.   As with the 30 day detention time units,  retardation was
 observed at 46C.  Here it  took 28 days until  the normal feed pattern could
 be used and 4 more days till a rise to 47C  was tried.   The  temperature was
 quickly raised 51C  but this  was accompanied by  a  rapid rise  in  volatile
 acids  so the unit was  held  at  51C  for 4 rather than 2 days.   A rapid  rise
 to  54C  was   again  accompanied by  a volatile  acid  rise.   A  feeding  was
 skipped at 54C  leading  to  a significant fall in volatile  acids.   After  6
 days at 54C  the unit  went  to  55C  and  satisfactory  operation seemed to  be
 manifest.
 STEADY STATE AT 55C AND 35C AT 20 & 30 DAY DETENTION TIMES

      Once  all  the  units discussed  above had  reached 55C  and  exhibited
 satisfactory operation,  it was  decided  to  maintain these systems  at  the
 conditions  reached  at  the  end  of  the  temperature  rise  rate  study,   and
 observe their  operation over an  extended period of  time.   A  plot  of  the
 effluent volatile acids for the next ninety days is given in Figures 42  and
 43.     It  can  be seen  that  initially  there was  some  disparity  in  the
 performance of the  units.   Over the first 30 to 40 days  of operation  some
 units exhibited quite good performance (Units 2A and  5A at 30-day  detention
 time and Units 6B,  7A,  and 7B at  20-day  detention  time).   The other  units
 exhibited  an  increase  in volatile acids to  approximately  1200 mg/1.    In
 addition,   it  was noted that the  gas produced  in  these units was rather
 odorous.

      It was apparent  that some thermophilic organisms were present in  Units
 2A,  5A, 6B, 7A and 7B that were not present in the other units.   In order to
 get  all of  the units operating equally,  it was decided  to  seed the poorly
 operating  units  with  organisms  from  the  units  showing  good operation.
 Consequently,  on 45th day for  the  20-day detention  time  units  and the  46th
 day  for the 30-day  detention time units  extra  effluent  was withdrawn  from
                                   49

-------
       Figure 38.   Gas production from unit 8A  (1C  increment):
                   20 day detention time.
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900 -

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700 _x
600 -
500 -
400 -

300 -
200 -
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2 610 J4Ja 222S3D 3if33.4243e06872768D84aiS^9b
Time in days
                                  50

-------
       Figure 39.  Gas  production from  unit 8B (1C increment):
                   20 day detention  time.
                                                         1150 ml 
 1000 _j
  900  -
  800
  700 _
  600 -
500 -j
CO
  ^00 -
  300 -
  200_
  100-
                     35
                                                        53
                                                        15
                                                            55
2  6  10
                      22  26 30' 3^ 38 * W  60  68  72  76  80  S*  88  91*  9B

                            Time in days
                                      51

-------
 Figure 40.   Temperature and volatile acids concentration versus
             time for unit 8A (1C increment):  20  day  detention time.
  12r
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ra

o
              20
40         60

 Time in days
80
                             52

-------
  Figure 41.   Temperature and volatile  acids  concentration versus
              time for unit 8B  (1C  increment):  20 day detention time.
 en
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 C/l
a
 
-------
   Figure 42. Volatile acids concentration versus  time:  30  day  detention time.
  1400 r
O
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  1200
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 C
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 to
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    800
    600
    400
 o  200
        55C reached
         I  in all units
                                         effluent  from  all  units  mixed:
                                              I  mixed effluent  used  to
                                     A       ^        reseed  all  units
                                                          ------  unit  1A  &  IB
                                                          ..........  unit  2A  &  2B
                                                                  unit  3A  &  3B
                                                          ----  unit  5A  &  5B
             '   '	I	I	1	1	1	1	1	1	1	'
                   10     20      30     40       50      60

                                          Time  in days
70     80
                                                                              90

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         Figure 43. Volatile acids concentration versus time: 20 day detention  time.
Ln
        1400 r
         1200
       in
       to
      J!iooo
       c
       o
       2  800
       o
       c
       o
       U
       o
       to
600
          400
       o  200
              55C reached
               I   in all units
' - 1
                                      effluent  from  all  units  mixed;
                                             mixed effluent  used  to
                                                  reseed  all  units
                                                              unit  4A & 4B
                                                              unit  6A & 6B
                                                              unit  7A & 7B
                                                     	  unit  8A & 8B
                                                                                V/0. f
                                                                                  .  \~ss*~
                               1 - 1 - 1 - 1
                                                       1
                                                                                 i    i
                         10     20      30      40       50     60
                                                Time in days
                                                           70
                                              80
90

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all units, pooled and  anaerobically  Inserted back into each unit.   The data
in  Figures 42  and 43  clearly  illustrate  the  efficacy  of  this  strategy.
Within 10  to 15 days the  volatile  acid level in the effluent from all units
was between  200 and 400  mg/1.   For the remainder of  the  time  of operation
satisfactory  performance was  obtained from  all units.   In addition,  the
disagreeable odor disappeared  from the  gas.

     Analysis  of these  data  do not  indicate  any particular  pattern with
respect  to units  which retained satisfactory organisms in the transition to
55C and those  which did not.   For  example,  in the case  of  Unit  2A and 2B
(duplicates)  one unit exhibited excellent operation, while  the  other
exhibited marginal operation after the  transition to 55C was achieved.  The
same situation  was  manifest for Units 5A and 5B and Units 6A and  6B.   Rate
of  temperature   rise  was   not  a factor  in determination  of  units  which
achieved the proper population at  55C; nor was detention time.
 TEMPERATURE DROP STUDY

      One  of  the concerns  expressed  with  respect  to  utilization  of
 thermophilic digestion systems is the sensitivity which they may exhibit to
 temperature changes.   Since these units operate at temperatures much higher
 than mesophilic  digesters  it  is  feared that a  small  temperature  drop will
 have much more of an  adverse  effect  than  it would on the lower temperature
 systems.    To  determine  the  effect  of  a  temperature drop  on thermophilic
 systems  several of the 55C units were  subjected to a  temperature drop.  The
 temperature was  dropped  from  55C to the  new setpoint  over  night  and then
 maintained at  the new setpoint.   The normal feed and withdrawal pattern was
 maintained.   The performance  of these  systems  was then monitored  for the
 next 25  days.   Units  with detention  times  of both 20  and 30 days were used.
 Temperatures were reduced to:   52.5C,  50C,  and 47.5C.  Controls were run
 with units maintained at 55C  and 35C.

      The results at a 30-day  detention time are  given in Figure  44.   These
 data indicate  that effluent volatile acids remain low in all units and were
 similiar  to  the control  values.   There  was some  early tendency  for the
 volatile  acids  to  increase in  the  unit  whose  temperature  was  reduced  to
 47.5C.    However,  this  trend was soon  reversed.   The  data  for  the 20-day
 detention  time  units,  given  in Figure 45,  exhibits a similar  situation;
 except that both the  50C  and 47.5C units  exhibited an early tendency for
 volatile acids to rise.  The  trend was  reversed for  the 50C unit,  but not
 for the  47.5C unit.   Figure 46  is a replot of the data from the 20-day and
 30-day detention time units in which the  temperature was dropped to 47.5C.
 This plot  clearly shows  the  significant  difference  which resulted.   The
 pattern  of  rise  in  volatile  acids  exhibited  by  the  20-day  detention time
 unit  is   typical of  a  wash-out phenomenon.    That  is,  the  temperature
 reduction does not interfere  with the microorganisms  ability to degrade the
 substrate,  but   for  some  reason  their ability  to reproduce  is  impaired.
 Thus,  the biomass  in  the system  gradually decreases,  and  the  effluent
 volatile  acids  gradually  increase.   To be  sure no  direct  measurement  of
 biomass  was made so   this  is  a  speculation based  on  failure mode.   It is


                                   56

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Figure  44.
Mean volatile acids concentration versus time for
units subjected to temperature drops from 55C to
55, 52.5, 50, and 47.5C.  Units at 35C are con-
trols.  30 day detention time.
  300
                day of      /,
         temperature drops / .

                   '       /  I

   250
 CD
   200
 "3


I 150
 QJ
 (J
 C
 O
 o



$ 100
O)
-4-J
IT:
   50
                            8      12      16

                             Time in days
                                    20
24
                             57

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Figure 45.
    800
     700
   u  600
     500
 400
AJ
TO
!-i


 300
c
o
u
in
% 200
TO
   OJ
   o
   >
     100
          Mean volatile acids concentration versus time for
          units subjected to temperature drops from 55C to
          55,  52.5,  50, and 47.5C.  Units at 35C are con-
          trols.  20 day detebtion  time.
                         55
                        52.5
                         47.5
                        50  '
                         35
                                      V
                   day of
             temperature drops
                                  /
                     1
                            /:
                           .1   I
                                   1
                                       _L
                                             j_
                               8      12      16
                                 Time  in days
                                                  20
24
                               58

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Figure 46.  Comparison of mean volatile acids concentration in
            units  at  20 day and 30 day detention times subjected
            to  temperature drop  from 55C to 47.5C.
   800
    700
 S  600
    500
  l-l

  c  400

  u
  c
  o
  o

  35  300
 "O
 H
  CJ
  TO
  oj
  o
 >
    200
    100
	20 day detention time
	30 day detention time

               J_
     JL
J_
                                     _L
                        J_
                                                _L
                                      J.
               04       8      12      16     20     24

                  Time in days from  temperature drop

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Possible  that  the 30-day  detention  time unit would also  have gone  into  a
tallure mode if the run had been continued for a longer period of time.


     Despite  the  problem  noted  above,  when the temperature was  dropped to
47.5 C, these data  indicate  that operational  problems  from failure  of the
heating  system of a  thermophilic  digester should  not  be a major  concern.
The only  adverse  situation which was manifest  took several weeks to develop.
It  is  unlikely that the heating system of a  digester could  not be repaired
in  a few  days.   In addition,  the rate of temperature drop utilized here was
extreme  compared to that  which would  occur  in the  field.   Field digestion
systems  t. re massive  tanks  with high heat capacity.   It  is unlikely that the
digestion temperature  would  drop by more  than  1C per day even if a complete
failure  of the heating system occurred in the  middle of the winter.


COMPARISON OF MESOPHILIC AND THERMOPHILIC OPERATION

     The  units which  had operated  .t 55C and which  were  not used for  a
 temperature drop  study were  used to  evaluate  the operation  of anaerobic
 treatment  systems  at  55C vs.  35C  for  detention  periods  below  20 days.
Detention periods used here  were 15,  10 and 7.5 days.  The performance at 20
and 30  day detention  time  was similar  based on effluent  volatile  acids;
although the mesophilic units had slightly lower volatile acids levels.  It
was expected  that if there  was  a  difference between  mesophilic  and
 thermophilic operation  it would  be  most  apparent  at  the  lower detention
 times.  Units were converted  to the  lower detention time and then operated
at  the new detention times for a period equal  to at  least 3 detention times.
All units eventually exhibited steady-state operation in which the effluent
volatile  acids stayed relatively constant within a narrow range.  These data
are presented in Table 3 and include  all of the hydraulic detention times in
 this   study (7.5,  10,  15,  20,  30  days).   These  data  show  that  as  the
detention  time  was  decreased  the  disparity in  performance between  the
mesophilic and thermophilic units  increased.   At 10 day  detention time or
 lower  the mesophilic units clearly exhibited  superior performance.


TABLE  3.   STEADY STATE PERFORMANCE OF  THERMOPHILIC AND MESOPHILIC
           ANAEROBIC  TREATMENT SYSTEMS


           HRT                      Effluent Volatile Acids   mg/1

                                    55C                35C
30
20
15
10
7.5
100-150
150-250
200-300
300-600
1000-1200
50-100
75-100
100-150
100-200
200-300
                                   60

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                                  SECTION 6

                                 DISCUSSIONS

TRANSITION TO THERMOPHILIC TEMPERATURES

     The major  question explored in  this  part of  the  research effort  was
what is the best procedure for converting a mesophilic anaerobic digester to
a thermophilic unit?  Table 4 presents a summary of pertinent data  which can
be  used to  address  this  question.   For  each temperature  rise  rate  and
detention  time  the  following  data  are presented:   time in  days  to  first
reach 55C,  time  in days  to  achieve stable operation at 55C,  time  in days
to the  first temperature inhibition, time in days to be  able  to return to a
normal  2  day  feed  pattern  after  inhibition, time  in  days  to  the  next
temperature  change  after  the  first  temperature inhibition and the  number of
2 day periods during  which feeding  took place  until  55C was  achieved.   The
figures  presented  in  the  table except  for  the  first and  last  columns
represent  days after  the first change from 35C.  The following major points
can be  deduced from this table and from Figures 2-41.

     1.    The slower  the  temperature  rise the longer it takes  to  initially
           reach 55C.

     2.    The rate  of temperature rise has  only a minor effect  on the time
           to reach  stability at 55C.

     3.    Irrespective  of the  rate  of  temperature rise,  a major retardation
           occurs when ever the temperature exceeds 45C.

     4.    The  effect of  this  retardation is  less  at low  temperature  rise
           rates.

     5.    At  high  temperature  rise  rates  once  acclimation   to  the
           thermophilic  conditions occur, few problems are manifest.

     6.    At  low  temperature  rise  rates  small periods  of acclimation  are
           needed as  the unit proceeds from 45C to 55C.

     7.    At  low  temperature rise  rates the  unit  can be  fed  a  high
           percentage  of time during the transition procedure.

     8.    At high  temperature  rise  rates the  unit  can  be fed  only  a small
           percentage  of time during the transition period.

     9.    There  seems  to be  a  zone  of  minor retardation  in  the  50-55C
           range.


                                     61

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     10.   Temperature changes  adversely affect  the  methane bacteria  to a
          much greater extent than the acid formers.

     11.   Temperature effects are not  Instantaneous.  During the first feed
          period  after  45C  is  exceeded  almost normal  operation occurs.
          Retardation is manifest during the next feeding period.

     12.   Temperature effects are magnified at lower  detention  time.
TABLE 4.  SUMMARY OF PERFORMANCE DURING TEMPERATURE TRANSITION
          FROM MESOPHILIC TO THERMOPHILIC CONDITIONS
Temp.
Change -
Detention
Time
5-30
5-20
3.5-30
3.5-20
2-30
2-20
1-30
1-20

Time to
Reach
55C
52
56
54
48
54
60
64
74
Time to
Reach
Stability
at 55C
52
72
54
56
62
68
64
74

Time to
First Major
Inhibition
6
6
10
8
14
12
24
22

Time to
Resume 2 day
Feed Pattern
38
48
44
34
26
48
36
48

Time Till
Next Temp.
Change
52
56
48
46
42
52
42
50
# of
Feeding
Periods
to 55C
13
13
13
14
23
21
30
27
     Overall it does not seem that  the rate  of  temperature rise affects  the
speed of conversion  to  thermophilic  conditions.   A decision on the rate  to
use will depend on another major factor,  i.e.,  what can be done with the  raw
sludge  during  the  conversion  process.    If there  is  no alternate  sludge
handling procedure  the  slow rate of rise should be used,  as  for the most
part, feeding of the digester can continue.   If an alternate  sludge handling
procedure exists the rapid rise method would achieve operation at 55C in a
shorter period of time.    Since operation is satisfactory between 35C  and
45C, perhaps  a  combination  procedure would be best;  a rapid  rise to 45C
followed by a slow rise to 55C.

     In this study it was observed that once the temperature  increased above
45C the units suffered retardation.  The retardation was more dramatic when
the temperature increment was high than when modest increments were used.The
5C increment units  virtually  shut  down for several weeks and then started
to recover.   The units  with lower  temperature  increments  did  not exhibit
such  a  complete  shutdown,  rather  they  suffered some  degree  of  temporary
retardation.    All of the  units  eventually completely recovered  and
demonstrated the  ability to operate  satisfactorily  at temperatures   in  the
range of  45C  to 55C.   It  is probable that  the  units contain  organisms
which  are  thermophilic, but which  do  not  function  at  temperatures below
                                     62

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    .   Once the temperature enters a range that these organisms  can function
 n. they  begin  to  function.   The  amount  of  time  required to  build  the
population of thermophiles to the level required for optimum performance  was
the several  weeks noted  above.   This  time period  is  consistent with  the
known doubling  time  of methane  bacteria  which is  in the range  of 3 to  4
days.   Since most of  the  original seed sludge had been washed out  of these
units  prior  to  starting  the  rise-rate  study,  and was  replaced with
mesophilic  organisms  which  could reproduce  on the  substrate  used,  it  is
probable that  very  few  thermophilic  organisms  were  present  when  tlie
temperature initially reached thermophilic levels.  Thus,  if domestic  sewage
sludge had  been the  feed transition to thermophilic conditions  would have
been  easier because  the  units  would have  been  continually reseeded with
dormant  thermophilic  microorganisms.   It is  unlikely  that the  artificial
substrate  actually  used  here  contained thermophiles because the Carnation
Instant Breakfast is  radiation sterilized by the  manufacturer,  and the milk
used is pasturized at elevated temperatures (much higher  than 55C).   Thus,
the presence of  thermophilic methane bacteria  in the feed is unlikely.


STABILITY OF OPERATION  AT 55C

     After  the  temperature  transition  to  55C was  achieved the  units were
maintained  at this temperature  for  the  next 3 months.   It was observed that
some  of  the units exhibited good operation while others  exhibited marginal
operation  (volatile acids of approximately 1,000).    It was  found that some
of the microflora required for  optimum operation at 55C did not survive  the
transition.   Seeding  from units  which had  this microflora restored optimum
operation.  Thus, while it is  apparent that thermophilic  organisms exist in
anaerobic  treatment  systems which  are operating at  mesophilic  conditions,
some may have  difficulty  surviving the transition.   Thus, some seed  from a
thermophilic digester exhibiting good operation may be necessary in order to
insure trouble  free transition  to thermophilic conditions.

TEMPERATURE DROP  STUDIES

     The data  collected  indicate that a  temporary  temperature  reduction to
as low  as  47.5C will  not  have an adverse effect on a  thermophilic  system
which has been operating  at  55C.  A temperature drop to as low  as 50C will
not have an adverse effect  even if this temperature drop  is  permanent.   The
magnitude of the  effect observed when the temperature drops  below 50C will
depend upon the detention time  of  the  system.  Because  the adverse  effect
noted appeared  to be  related primarily to  washout  rather than  an inability
of the organisms  to  degrade the  substrate,  the adverse  effect  is magnified
at lower detention times.

COMPARISON OF MESOPHILIC  VS. THERMOPHILIC OPERATION

     At  long  detention times it  was  found  that mesophilic and  thermophilic
anaerobic  digestion  systems exhibited  similar  operation;    although  the
mesophilic  systems  were  slightly superior.   Once  the  detention  time  was
reduced  below  10  days  significant performance  advantage  accrued  to  the
mesophilic system.


                                  63

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                                  REFERENCES
1.    Standard Methods  for  the  Examination of  Water  and  Wastewater APHA,
     AWWA, WPCF, 15th Ed. (1985).

2.    Fisher Scientific Co., Catalogue (1986),  Model #1200,  p.  250.
                                      64

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