Evaluation of the Full-Scale Application
   of Anaerobic Sludge Digestion at the
Blue Plains Wastewater Treatment Facility
              Washington, D.C.
          U.S. ENVIRONMENTAL PROTECTION AGENCY
          OFFICE OF RESEARCH AND DEVELOPMENT
    OFFICE OF ENVIRONMENTAL ENGINEERING AND TECHNOLOGY
                 401 M STREET S.W.
                 WASHINGTON, D.C.

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                 FINAL REPORT

    Evaluation of the Full-Scale Application
      of Anaerobic Sludge Digestion at the
    Blue Plains Wastewater Treatment Facility
                Washington, D.C.
                 Submitted to:

              Mr. James Basilico
       US Environmental Protection Agency
        Office of Research & Development
Office of Environmental Engineering & Technology
               401 M Street, S.W.
             Washington, D.C.  20460
                Prepared Under:
           USEPA Contract 68-01-5913
               Work Assignment 5
                 WAPORA, Inc.

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                                DISCLAIMER

     This report has been reviewed by the Office of Engineering and Techno-
logy,  US Environmental  Protection Agency,  and approved  for  publication.
Approval does not  signify  that the contents necessarily  reflect  the  views
and policies of the US Environmental Protection Agency, nor does mention of
trade names or commercial products constitute endorsement or recommendation
for use.

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                                  SUMMARY

     This  study  investigated  the  application  of  a new  mesophilic-ther-
mophilic  anaerobic sludge  digestion process  to  the existing  mesophilic
sludge  digestion  system at  the  District of Columbia Wastewater Treatment
Facility  (WWTP).   As  part  of  this  study,  improvements  in the  existing
mesophilic  digestion  operation  and  possible  application  of  thermophilic
digestion  technology  were  also  evaluated.   The  study was  prepared  under
Contract  No.  68-01-5913 for  the US  Environmental  Protection  Agency,  with
the cooperation of the city of Washington DC  and the Wastewater Treatment
Facility's  technical  personnel.   The  analyses  are  presented  in detail to
facilitate  the  use of the approach as  a case  study model for other waste-
water  treatment  facilities  considering  the  application  of  the  process.

     The  mesophilic-thermophilic  digestion  process is a new concept in the
treatment   of  municipal  wastewater  treatment   sludges.   It  involves  a
two-step  digestion process,  where the  first step operates under mesophilic
process  conditions,  (that  is, digestion with anaerobic microorganisms that
thrive  at  90  to  100°F)  and the  second step operates  under  thermophilic
process  conditions (that is, digestion with  anaerobic microorganisms that
thrive  at  120  to  130°F).   The  mesophilic process is the  most commonly
employed  digestion process;  the  thermophilic process  has had limited appli-
cation  in  this country but  is  used regularly in the U.S.S.R.   Use of the
mesophilic-thermophilic  process  has  been documented only  at  the Rockaway
facility  in New York  City.

     The  development of  standard process conditions  for  anaerobic sludge
digestion is described in this  report, including operating conditions and
process  effectiveness for the Rockaway  treatment  facility.

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     The development and application of the mesophilic-thermophilic process
has  been  pioneered  by Mr.  Wilbur Torpey.   A full-scale  application and
evaluation of the effectiveness of this dual process approach has been been
undertaken by the  Rockaway Pollution Control Plant in New  York City.  The
results of  the  Rockaway trials indicate that  the  physical  characteristics
of mesophilic-thermophilic  digested  sludge are improved and that these can
result in (1) a significant reduction in the dewatering requirements of the
stabilized  material,  and  (2) a  more  stabilized  residual  that  is nearly
pasteurized and  inert.   The savings from dewatering improvements appear to
be  significant  and outweigh any increased  costs associated with operating
the  two processes  rather than either of the conventional single processes.
Moreover, there  is the possibility that use of the mesophilic-thermophilic
process  may result  in an overall reduction  in  digestion time.   This is
because  the mesophilic system  tends to dampen  any fluctuations  in waste
sludge  characteristics, thus  providing a  consistent  feed to  the thermo-
philic  system.   As  a  result, the  thermophilic  system can be designed to
operate with a  reduced safety factor for  feed sludge variation.  Since the
thermophilic system is a  higher  rate  process than the  mesophilic,  a net
reduction in the overall detention time may be achieved.

     These  considerations  and the  success  of the Rockaway trial resulted in
the  desire  to  investigate  the  feasibility  of  applying  the mesophilic-
thermophilic  process   to   a  major  wastewater  treatment  facility.   The
District of Columbia WWTF  was selected  because:  1) the influent wastewater
was  mainly  domestic,   as  was the Rockaway  influent;  2) the facility has
anaerobic  digesters in operation; 3)  the facility will require modifica-
tions  to upgrade  the  sludge handling  facilities;  and  4)  the staff at the
facility  were   technically  capable  and  willing  to  cooperate  with the
investigation.

     The   investigations   at  the   District of  Columbia  WWTF  involved   a
detailed  review of  existing  plant operations including the  development of
flow  and  mass  balances  using  existing   data  developed  for  the  sludge
management  area.  It was  necessary  to  develop a detailed  piping  schematic
for the  digester  area,   as  this  was  not available.   A  tracer study was
performed   on  the existing  twelve anaerobic  digesters to  determine  the

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useful volume.   Interviews  with  plant staff were used to further establish
the existing  operating  conditions.   These sludge operating conditions were
characterized  according to  the  solids  generated  per  million  gallons  of
influent wastewater flow.

     The analytic data were evaluated in conjunction with financial data to
identify the  cost  of treatment options.  Such  an  evaluation was performed
to determine  alternative costs for the following five operating conditions:

     1)  Current operating practices  (January to June 1980), with anaerobic
         digestion treatment of a partial sludge stream.

     2)  Spring  1981,  after completion of  plant modifications in progress
         during  the  study,  with anaerobic  digestion treatment of a partial
         sludge  stream.

     3)  Mesophilic  digestion  of all  sludge.

     4)  Thermophilic digestion of all  sludge.

     5)  Mesophilic-thermophilic digestion  of all  sludge.

The  financial analyses  were based on a  mixed primary-secondary sludge, with
sludge processed by gravity thickening,  dissolved air  flotation, anaerobic
digestion,   elutriation,  vacuum  filter  dewatering,   and   final  disposal
through land application.   Undigested  sludge  in excess  of the existing
anaerobic  digestion  system capacity  is  limed, dewatered  and disposed  of
through composting or  land  trenching.

      The engineering and financial  evaluations  of  full-scale application  of
 the  mesophilic-thermophilic anaerobic digestion process  concluded that:   a
 limited expansion  of  digester capacity  is required to  handle  the  entire
 sludge stream;  there  would be digester  gas  available  for  sale to  outside
 interests  after internal heating requirements  were satisfied; and the cost
 of sludge  handling could be  reduced by  $24  to $31 per million gallons  of
 influent flow.  The analysis  also  indicated  that the improved characteris-
                                     111

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tics of  the mesophilic-thermophilic digested sludge could  reduce  chemical
conditioning  requirements  so  cost  would  be almost $7  less  (per  million
gallons of influent flow) than mesophilic digestion and almost $4 less than
thermophilic  digestion.   Moreover,  the  Rockaway  results  indicate  that
additional  savings  may be  incurred during disposal because  the stabilized
material should be appropriate for use as a soil conditioner.
                                     IV

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                              RECOMMENDATION

     Based on our  review  of the anaerobic sludge digestion options and how
they could be adapted  to  the existing facilities,  it  is  our strong recom-
mendation that the thermophilic anaerobic digestion process is the best fit
for  the  District  of  Columbia and  should be implemented  on a  full  scale
basis.  This  recommendation is  based on our thorough review of the present
state of practice within the United States and other countries.  We heavily
weighed the  30  years  of  successful experience  at  the City  of Los Angeles
Hyperion Plant  and their  decision to convert the total digestion system to
the  thermophilic  process.  Another  factor was  the successful conversion,
over  2 1/2  years  ago, of  the  entire mesophilic  digestion system  to the
therraophilic  mode by  the city of  Denver.  The City  of Chicago  has  also
shown  that  the  capacity  of a mesophilic  digestion tank  can be doubled by
converting to thermophilic  operation.

     The  thermophilic  process is  the option that could be initiated with a
minimum of time and money.  Other significant advantages of  the process are
(a)  increased sludge  processing capability, (b) improved sludge dewatering
as  to  coagulant demand and yield, and   (c) increased destruction of patho-
gens,  all  of which are pertinent  to the needs  of  the District of Columbia
Treatment Facility.

     It  is  especially  important  that,  prior  to start up,  an independent
engineer  check  the structural  competency of  the existing digesters and
piping at the thermophilic  temperatures,  as well as the temperature control
system.

     We  strongly recommend and urge  that the transition  from  mesophilic  to
thermophilic operation be  implemented as  rapidly  as  possible in order  to
alleviate  the  solids  handling  problems with  the metropolitan  area.   A
carefully formulated plan for the transition should be prepared so  that the
transition   be  carried  out  with  a minimum  of  interference  with  plant
operations.

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                               CONCLUSIONS

1.    It has  been  found  possible to  process  the  total  waste sludge  flow
     using the existing facilities for the thermophilic anaerobic digestion
     process.    In  that  connection  the  accumulated grit  in the  digester
     tanks will not have to be removed.

2.    Adoption  of  the  thermophilic  digestion  option  requires  the  least
     capital  expenditure,   would  be  the  most  expedient  solution to  the
     sludge management problem and would yield substantial operational cost
     savings.    It  also  offers the potential,  because of the pathogen kill,
     of eliminating the need for composting.

3.    The  mesophilic-thermophilic  digestion process would  not  be  able  to
     handle the entire waste sludge flow without additional capital expendi-
     tures  for new  digestor  tanks  and  separate  heating systems,  and  as
     suchj  it  was not  recommended  at this  time even  though  the  final
     product  would satisfy all criteria for stabilization and disinfection
     comparable to effectively operated composting.

4.   The  amount of grit passing through  the  existing  grit removal facili-
     ties  is  substantial.    This  grit  is  combined with  the primary sludge
     and  both  are pumped  to the  digestion  tanks.   The  grit  accumulates
     within  the digestion,  tank  and  reaches  equilibrium  when about 1/3 of
     the  tank volume is occupied by  grit.   Accordingly, this grit accumu-
     lation has reduced the amount of  sludge that can be processed through
     the  existing  digestion tanks by  at least 1/3.

5.   The  detailed  solids production analysis  prepared  for this study  can be
     incoprorated  into  other sludge management  evaluations performed  by the
     District of Columbia.
                                     VI

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                                 CONTENTS
                                                                      Page
Summary	      i
List of Figures	     ix
List of Tables	     xi
Acknowledgment	    xii
1.   Introduction	      1
2.   Anaerobic Digestion and the Rockaway Story	      3
    2.1. Development of the conventional (mesophilic) process	      3
    2.2. Development of the thermophilic process	      5
    2.3. Development of the mesophilic-thermophilic process	     10
    2.4. Purpose of the Rockaway tests	     11
    2.5. Results of the Rockaway tests	     12
3.   Blue Plains Wastewater Treatment Facility	     26
4.   Evaluation of Current and Future Primary and Secondary
    Sludge Generation	     27
    4.1  Primary sludge production	     27
    4.2  Secondary sludge production	     28
    4.3  Summary	     29
5.   Evaluation of Existing Sludge Management Operations on
    Sludge Processing and Sludge Generation	     31
    5.1  Gravity thickener operation	     31
    5.2  Dissolved air flotation thickener operation	     32
    5.3  Anaerobic digestion operation	     35
    5.4  Elutriation system operation	     47
    5.5  Anaerobic sludge dewatering operation	     51
    5.6  Raw  sludge dewatering operation	     53
    5.7  Final sludge disposal	   56
    5.8  Sumraa ry	   57

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                                                                      Page
6.  Improving Sludge Management Operation Using Anaerobic
    Digestion	    60
    6.1  Existing mesophilic system operation	    61
    6.2  Evaluation of thermophilic system option	    66
    6.3  Evaluation of mesophilic-ttiermophilic system option	    70
    6.4  Summary	    72
7.  Economic Impact	    74
    7.1  Operational cost impact	    75
    7.2  Capital cost impact	    79
    7.3  Economic impact	    81
Appendices
   A.  January to June, 1980 summary of average monthly operating
       data on Blue Plains sludge management operations	   A-l
   B.  Analysis of average primary and secondary sludge production
       per million gallons of influent flow	   B-l
   C.  Analysis of gravity thickener operation	   C-l
   D.  Analysis of dissolved air flotation thickener operation	   D-l
   E.  Analysis of lithium chloride tracer studies, Blue Plains
       digesters	   E-l
   F.  Analysis of grit entry into anaerobic digesters per million
       gallons of influent flow	   F-l
   G.  Anaerobic digestion heat availability and system heal
       requirements	   G-l
   H.  Anaerobic digestion piping schematic	   H-l
   I.  Analysis of anaerobic system volatile matter reduction
       and gas production	   1-1
   J.  Analysis of elutriation system operation	   J-l
   K.  Analysis of digested sludge dewatering  on average sludge
       production per million gallons of  influent  flow	   K-l
   L.  Analysis of  raw  sludge dewatering  on average sludge
       production per million gallons of  influent  flow	  L-l
   M.  Section 6.1  supporting calculations	  M-l
   N.  Section 6.2  supporting calculations	  N-1
   0.  Section 6.3  supporting calculations	  0-1
   P.  Thermophilic  digestion references  for  Section  2.2 and 6.2	  P-l
                                   viii

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                                       FIGURES
Number                                                                Page
 2-1  Summary of operating results	     20
 5-1  Cross-sectional view of spring-operated pressure
      relief valve	     36
 5-2  The effect of secondary sludge on volatile matter
      reduction at the Blue Plains anaerobic digestion
      facility	     41
 5-3  The effect of organic loading on volatile matter
      reduction at the Blue Plains anaerobic digestion
      facility	     44
 5-4  The effect of hydraulic detention time on volatile
      matter reduction at the Blue Plains anaerobic
      digestion facility	     44
 5-5  The effect of feed solids concentration on anaerobic
      digestion gas production at the Blue Plains digestion
      facility	     45
 5-6  The effect of volatile matter loading on anaerobic
      digestion gas production at the Blue Plains digestion
      facility	     46
 5-7  The effect of elutriation feed solids concentration
      on elutriation underflow solids concentration	     48
 5-8  The effect of digested sludge flow rate on
      elutriation underflow solids concentration	     49
5-9   The effect of washwater on elutriation underflow
      solids concentration	     50
                                     IX

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Number                                                                Page

5-10  The effect of ferric chloride addition on filter
      feed solids concentration	   51
5-11  The effect of secondary sludge mass on ferric
      chloride addition for dewatering anaerobically-
      digested sludge	   52
5-12  The effect of feed solid concentration on vacuum
      filtration of anaerobically-digested sludge	   54
5-13  The effect of feed solids concentration on vacuum
      filtration of raw sludge	   55
5-14  The effect of secondary sludge on vacuum filtration
      of raw sludge	   56
 7-1  Average cost for chemicals and final disposal
      per million gallon of influent flow for the
      five conditions given in Table 7-1	  77
 7-2  Average wet tons of sludge produced per day for
      the five conditions given in Table 7-1	  78

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                                  TABLES
Number                                                                Page

 2-1  Rockaway P.C.P. Treatment Efficiency, July 1979 to May 1980	   14
 2-2  Rockaway P.C.P. Influent-Effluent Nitrogen Concentrations,
      July 1979 - May 1980	   15
 2-3  Rockaway P.C.P. Influent-Effluent Phosphorus Concentrations,
      July 1979 - May 1980	   16
 2-4  Rockaway P.C.P. Influent-Effluent Metals Concentrations,
      July 1979 - May 1980	   18
 2-5  Rockaway P.C.P. Amount and Concentration of Solids Passing
      Through System	   21
 2-6  Rockaway P.C.P. Daily Gas Production	   23
 2-7  Gas Production cu ft/lb Volatile Solids Reduced	   24
 2-8  Gas Production and Quality From Anaerobic Digestion of
      Several Pure Compounds	   24
 4-1  Summary of Current and Future Primary and Secondary
      Sludge Generation at Blue Plains	   30
 5-1  Summary of Anaerobic System Heat Requirements	   38
 5-2  Summary of Addition (Reduction) in Solids Production
      due to Various Solids Processing Steps	   58
 5-3  Summary of Blue Plains Sludge Management Process
      Limitations under Current Operation	   59
 6-1  Expected Primary and Secondary Sludge Quantities
      at Current 334 Million Gallon Per Day Influent Flow	   60
 6-2  Summary of Major Process Considerations in Implementing
      Full Anaerobic Digestion of Blue Plains Sludges	   73
 7-1  Summary of Average Sludge Generation Per Million
      Gallons of Influent Flow	   76
 7-2  Summary of Operating and Capital Cost Requirements
      Per Sludge Handling Options	   82

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                         Acknowledgement

     This report  has  been prepared  for the U.S.  Environmental  Protection
Agency,  Office  of  Research  and  Development,   Office  of  Environmental
Engineering  Technology  (OEET).    The  work was   inspired  by  the  highly
successful results obtained under the direction of Mr.  Wilbur Torpey at the
Rockaway Pollution Control Plant,  in New York City.   Mr. Torpey served as
the  principal consultant  on  this  evaluation for  the application  of  the
mesophilic-thermophilic process.   He also contributed the discussion on the
Rockaway test.  Mr.  James  Basilico of OEET, was instrumental in initiating
this study  and in obtaining the cooperation of  the Blue Plains Wastewater
Treatment Facility staff in performing the analysis.  He was also the USEPA
project  officer responsible  for  this study.  The  detailed  analysis of the
sludge   management  system  was   performed  by  Environmental  Technology
Consultants,  Inc., under  the direction of Mr.  Nick Mignone.   Dr.  John
Andrews,  University  of Houston,  assisted in this  study  as a special con-
sultant  on  anaerobic  digestion,  and he  also contributed  the discussion on
the  development of the anaerobic  digestion  processes.  WAPORA,  Inc., per-
formed  the tracer study  on the  anaerobic  digesters  and  provided overall
project  management and  report  preparation under the direction of Mr. Robert
France and  Mr. Robert Stevens.

     Special  acknowledgement is  due to  the District of Columbia management
and  the Wastewater  Treatment  Facility  staff.   In particular to Mr. Steve
Bennett  and Mr. Ed Jones who provided  their  time  and in-depth understanding
of the treatment  facility to  make the analysis of management alternatives
possible,  and to  Mr. John  Zelinski  who spent  so much time on helping  with
 the  process piping.

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                                 SECTION 1
                               INTRODUCTION

     This  study  is an  engineering  evaluation of the application  of  a new
concept in wastewater engineering to a major wastewater treatment facility.
The new  concept involves  the  combination of two anaerobic  digestion pro-
cesses:  the mesophilic  process  (that is, anaerobic digestion operating at
temperatures  from  90  to  100°F),  and the  thermophilic process  (that is,
anaerobic  digestion  operating at  temperatures  from   120  to 130°F).   In
combination, these  represent  a new process  termed  the mesophilic-thermo-
philic process.  Such a  system has been operated at the Rockaway Pollution
Control Plant in New York City with outstanding operational results.

     The  existing  Blue  Plains wastewater  treatment plant  in  Washington,
D.C. treats approximately  330  mgd and uses mesophilic,  anaerobic digestion
for sludge  treatment.   This  system has had operational  constraints and is
limited  in capacity.  As  a  result,  a major portion  of the total sludge
stream generated at  Blue Plains  is disposed  of  without digestion.   Expan-
sions of  sludge  processing unit  operations, now is  progress, will increase
the  system capacity,  but not sufficiently  to  handle  the   entire  sludge
stream as the system now operates.  Finally, there are related planning and
engineering  evaluations  in  progress  that  consider  the long-term sludge
disposal options available at  Blue Plains,  including the complete abandon-
ment of  anaerobic  digestion in  favor of  alternate sludge  treatment pro-
cesses.

     Therefore, the purpose  of these evaluations was to identify the rela-
tive  merit  of  the  mesophilic-thermophilic  process  compared  with  other
anaerobic  digestion  processes.   In particular,  the evaluations  emphasize
the capabilities of  anaerobic  digestion to meet sludge processing needs at
Blue Plains,  the modifications required  to handle  the  full sludge stream

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(operating and equipment), and the costs associated with the systems (mone-
tary  and  energy).   Existing equipment  is  used  to  the maximum  in  these
evaluations, with  the  objective to identify an anaerobic  sludge digestion
process that can be implemented with no major construction.  In this sense,
the study represents an operations evaluation of the  Blue Plains  facility
for the anaerobic digestion system.

     The report  is  organized to follow logically the analyses performed on
the sludge  handling system.   Section 2 presents a perspective on anaerobic
digestion and  relevant data and discussions on the new mesophilic-thermo-
philic process  as  applied by Mr. Torpey at Rockaway.  Section 3 provides a
background  description of the  Blue Plains  wastewater treatment facility.
Section 4  describes the  sludge production  at  Blue Plains,  with  detailed
information  also  provided in Appendixes A and B.   An operations evaluation
of  the  sludge  system is  included as Section 5, with supporting analyses in
Appendixes  C  through  L.  The  comparison  between  anaerobic  processes is
performed  in  Section  6, with  supporting  calculations  and  assumptions in
Appendixes  M,  N,  and 0.  Financial evaluations are presented in Section 7.

     The methods employed in this case study should be generally applicable
to  most  major  wastewater  treatment  facilities.   The  application  of
anaerobic processes,  and in particular the new  raesophilic-anaerobic pro-
cess, may be profitably  analyzed by following these  techniques.

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                                 SECTION 2
                ANAEROBIC DIGESTION AND THE ROCKAWAY STORY

     The technologies currently  used  for the anaerobic digestion of sludge
have evolved  over the  last  100  years as  scientific and  engineering prin-
ciples  have  been  applied.   Tracing  this  development,  there  has  been  a
gradual improvement  in  performance, both with respect to the stabilization
of the waste material and to the associated cost.

2.1. DEVELOPMENT OF THE CONVENTIONAL (MESOPHILIC)  PROCESS

     Anaerobic  digestion is one of  the  oldest wastewater  treatment  pro-
cesses.  This process,  which involves the biological conversion of organic
solids  to  methane and  carbon  dioxide,  is  a natural  process  occurring in
such diverse environments as swamps, stagnant bodies of water,  and stomachs
of  cows.   One of its first  engineered  uses was in the latter  part of the
19th century  when septic  tanks  were first  used  for  wastewater treatment.
In  the  septic  tank,  the solids that settle to the bottom undergo anaerobic
decomposition with  the  liquid passing on  to  a tile  drainage  field.   The
solids  are well  stabilized,  but unfortunately the gas evolved disturbs the
sedimentation  process   by  lifting particles into  the  overflow.  This can
result  in plugging of the tile field,  thus destroying the efficiency of the
field,  and frequently resulting in malodorous conditions.

     This  deficiency of  the  septic  tank  was  recognized  and  a  solution
developed  by  the famous  sanitary engineer, Dr. Karl  Imhoff,  in the early
part  of this  century.   Dr.  Imhoff invented a  two-story tank,  which now
bears  his  name.   The  design  of  this was  such   that the  gas  evolved by
anaerobic  digestion  in the bottom  tank  was  prevented from  entering the
upper  tank where sedimentation  occurred.   The functions  of digestion and
sedimentation were thus effectively separated.

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     A natural evolution  of  this separation of functions, which took place
in the 1920's, was the construction of separate tanks for sedimentation and
digestion with the  solids removed in the sedimentation  basin  being pumped
to the anaerobic  digester.   This decreased the required depth of the tanks
and also permitted the easy application of heating and artificial mixing to
the anaerobic digester.  Both heating and mixing, which began to be applied
in  the  1930's  and  AO's,  accelerate the  rate  at  which  the  solids  are
digested.   They  also  help  to  reduce  stratification  problems  in  the
digester,  thus  increasing  the  effective  volume available  for digestion.
This  increase  in effective  volume  made possible  the use  of  much smaller
digesters.  Instead  of the  three to six months  requirement for anaerobic
digestion in  the  Imhoff  tank,  it was now possible  to accelerate digestion
and complete  the  process  in one  to  two  months.  The  obvious result of this
was a substantial decrease in required capital cost.

     The  application  of   digester mixing soon made  it  obvious that mixing
and separation  of the supernatant  from the digested  sludge were incompa-
tible in much the same sense that sedimentation and digestion in the septic
tank were  incompatible.   This  led to a  further  separation  of functions by
the application of two-stage digestion where the biological reactions (with
mixing  and heating  for   acceleration) occur  in  the first  stage  with  the
digested sludge then going to a separate stage for separation of the solids
from  the liquid.   This  second stage also served two  other valuable func-
tions, these  being the  storage of  the  sludge prior to  disposal  and  as a
source of "seed" sludge for restarting the primary digester in the event of
difficulties  with the biological reactions.  Two pioneers  in  the applica-
tion  of   two-stage  digestion were  A.M.  Buswell  and A.J. Fisher.   With a
two-stage  system, good  digestion  could consistently  be obtained  in  the
first tank in one month or less.

     In  the 1950's, Wilbur Torpey was faced with the necessity of expanding
the capacity  of  the  digesters  used in the New York City plants.  He recog-
nized that the digestion  time could be substantially decreased if a portion
of the water could be removed from the sludge prior to its being fed to the
digester.  He therefore  installed sludge thickeners prior to digestion and

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was able  to quadruple the  loading  of solids to his  digesters.   This  per-
mitted plant  expansion to  be  put off  for several years,  thus  saving the
City of New York a very substantial sum of money.   Energy requirements for
sludge heating   also  were  substantially  reduced  since  it  was  no  longer
necessary to heat  the water that was formerly  associated  with the sludge.

     In  addition to  his  full-scale  work  on thickening,  Torpey conducted
pilot plant studies  that  established three days as the lower limit of time
at which  the  process  could operate.  One  would,  of  course,  not normally
operate at  three days since it allows no margin of safety and digestion is
incomplete.    Also,  the  volume  of  Torpey's  pilot  digester  was  fully
effective, whereas a  portion of the volume of  full-scale  digesters may be
occupied  by  grit deposits  on  the bottom  or scum  at the  top.   The lower
limit  of  time,  with  which  operating  engineers  in  large  cities  feel
comfortable, is about 15 days.

2.2.  PRESENT STATE  OF PRACTICE OF THERMOPHILIC  ANAEROBIC  SLUDGE DIGESTION

     Thermophilic  anaerobic   digestion   is  very   similar  to  mesophilic
anaerobic digestion  except  for  the  temperature at  which  it  is operated,
this being  120-130°  instead of the usual 85-95°F.   It thus takes advantage
of the well known fact that biological reaction rates can be increased by
increasing temperature.   It is only natural, therefore, that conversion of
existing  mesophilic  digesters to  thermophilic operation  should  be  con-
sidered as  a  low cost technique for  increasing  the sludge processing cap-
ability  of  wastewater  treatment  plants.   Full   scale  studies  by  the
Metropolitan Sanitary District of Greater  Chicago  (1),  Ontario  Minstry of
the Environment,  Canada  (2),  and  Moscow,  U.S.S.R.  (3)  all indicated  that
they could at least double  the amount of sludge that could be processed per
unit volume of  digester  capacity by  converting  from  mesophilic  to thermo-
philic operation.  The  actual  amounts of sludge that can  be processed may
be substantially greater than this  since  the upper  limits of the process
have yet to be defined.

     In  addition to  its  increased  sludge processing  capability,  thermo-
philic operation also offers  two  other  significant  advantages  over meso-

-------
philic operation;  these  being (a) improved sludge dewatering (4,5) and (b)
increased destruction of pathogens (3,6).

     An example of how sludge dewatering can be improved through the use of
thermophilic digestion is  afforded  by the work of Garber (4) on the vacuum
filtration of thermophilic sludge at the Hyperion plant in Los Angeles.  He
reported  a  270% increase  in vacuum  filter  yields with a  48%  decrease in
coagulant  dosage  for  thermophilic  as  compared  to  mesophilic  sludge.
Improved  solids-liquid separation is  of substantial value in land applica-
tion of  sludge  through  decreasing the quantity of wet sludge for disposal
and thus  lowering the cost of transport to the disposal site.

     An example  of the  increased destruction of pathogens  through the use
of thermophilic digestion is given in the report of Popova and Bolotina (3)
on the practice  of thermophilic digestion in Moscow,  U.S.S.R.   They state
"The most essential advantage  of this process is  the  sanitary quality of
the thermophilic sludge.   According to the sanitary officials of the health
department, viable  eggs  of helminths  are absent from such a sludge."  This
improvement  in   the  sanitary quality  of the sludge  is of  special  signi-
ficance  in light  of the  current trend toward  land disposal  of  digested
sewage sludge.

     Although mesophilic and  thermophilic anaerobic  digestion are quite
similar in both  design  and operation, there are  differences which must be
taken into account in  adapting mesophilic digesters to thermophilic opera-
tion.  Among  these  are   (a)  additional  sludge  heating  requirements,  (b)
structural  competency of existing  digesters  and  piping  at   the  higher
temperatures,  (c)  potential  odors  at  sludge handling areas,  (d)  closer
attention  to  temperature  control,  (e)  possibly  higher  concentrations of
dissolved  materials   in  the   liquid  streams   from   sludge   dewatering
operations,  (f)  possible  ammonia  inhibition  due to  increased  protein
destruction, and  (g)  removal  of increased amounts  of moisture  from the
digester  gas.

     It  should   also  be  pointed  out  that caution should be exercised in
making the  transition  from mesophilic to  thermophilic  operation since the
maximum rate at which this can be accomplished is unknown.

-------
PROCESS HISTORY

     There has  been an interest in thermophilic  anaerobic  digestion since
at  least  1930.   Buhr  and  Andrews  (7)  prepared a review paper  of  the re-
search aspects  and  full  scale application of the process in 1976 and their
paper  should  be consulted  for  details of this earlier  work.   Since 1976,
there  has  been a  substantial increase of  interest in  the process.  Dif-
ferent organizations  have  either  adopted or are  considering  adopting the
process to obtain  one of the three advantages  previously  mentioned; these
being  (a)  increased sludge processing rates, (b)  improved  sludge dewater-
ing, or  (c)  increased destruction of pathogens.  In additon to these three
reasons for adopting the process, Metro Denver (8) has converted all of its
mesophilic digesters  to  thermophilic  operation in order to compensate for
the  loss  of  capacity when  the  liquid   levels  were lowered  to alleviate
problems  from  the  existing  foaming  conditions.   A  brief summary  of the
experiences of some of these organizations is given below.

Los Angeles

     The most extensive  application of thermophilic anaerobic digestion in
the  U.S.  has been  at the Hyperion plant (340 MOD)  in  Los Angeles.  This
work has been summarized in a recent paper by Garber (9) with more details
of  the work being  covered in  a  series of papers by  Garber and coworkers
(4,5,6,10).   The  primary  advantage of the process for  Los Angeles is the
greatly improved dewatering characteristics of the sludge.

     Thermophilic  anaerobic  digestion was first started in Los  Angeles in
1952 and was  subsequently  extended to one half  of their digestion system.
At  that  time,  the  digested sludge  was vacuum  filtered,  dried, pelletized,
Sacked and  sold as a  soil amendment.   The half and  half  mixture of meso-
philic and  thermophilic sludge  was used  since  thermophilic  sludge  has  a
lower  nitrogen  content  and  could  not  therefore,  alone   meet the  2.5%
nitrogen content guarantee for the soil amendment.

     In  1957, Los  Angeles  commenced discharge of liquid digested sludge to
the  ocean  so dewatering of the sludge was  no  longer necessary.  However,

-------
they have continued  to  operate one or  two  full  sized digesters at thermo-
philic temperatures so as to gain experience with operational stability and
to work  on the  centrifugability and the  pathogen content  of  the thermo-
philic sludge.  In 1985, Los Angeles will be required to cease discharge of
digested sludge  to  the  ocean and turn to land disposal.  At that time they
plan to  operate the  entire digestion  system  at thermophilic temperatures
because they  will  once  again need the improved dewatering characteristics.

     The  work reported  on  by Garber  and  coworkers  in 1975 (5)  and 1977
(6,10) confirmed  their  earlier  work in 1954  in illustrating  that solids
dewatering  (both  vacuum  filtration  and   centrifugation)  was  definitely
benefited by  thermophilic  operation.   They also found that the process was
no more difficult to operate than the mesophilic process except that closer
temperature   control  was  required.   In  a  cooperative  study  with  the
Municipal  Environmental Laboratory of  the  Environmental Protection Agency
(11),  they  also found  that thermophilic  operation resulted in  very sub-
stantial  improvements   in  the  destruction  of  pathogenic  bacteria  and
viruses.   For  example, thermophilic   digestion consistently  reduced  the
Salmonella  densities  to below  the  detectable limits  of  the analytical
procedure.

     The  volatile  acids concentration  in  thermophilic  digesters is higher
than  that  in  mesophilic   digesters  and  this   was  also the  case  in  Los
Angeles.   The  odor  of  thermophilic sludge  is accordingly  also  somewhat
higher.   Although  Garber did not feel  that this was  at  a level which would
be  considered obnoxious, he  did suggest that care  should  be taken in the
solids dewatering step  to contain these odors.   The Los  Angeles experiences
also  indicate that  there  are somewhat  higher concentrations of dissolved
materials in  the liquid  streams  from dewatering  operations.

Moscow, U.S.S.R.

     In  1964, Popova and Bolotina  (3)  reported  on the  use of  thermophilic
digestion  at  the Kur'yanova plant  (260  MGD)  in Moscow.  Plant  scale tests
on thermophilic  operation were first made  at this plant in  1955  and in  1958
the  digestion system was converted  to  thermophilic operation.   The primary

-------
reason for  this  conversion was  the sanitary  quality of  the  thermophilic
sludge.  Research  at the plant  had shown that mesophilic digested sludge
retained up to 20% viable helminth eggs whereas  after  thermophilic diges-
tion no viable eggs could be found.  The sanitary quality of the sludge was
of particular concern  since  it had become the practice to apply the liquid
sludge directly to agricultural land.

     Conversion from mesophilic  to thermophilic digestion also permitted a
sharp  increase in  the  capacity of the installation with the digestion time
being  shortened from 18 to 9 days.

Chicago

     In  1977,  the  Metropolitan Sanitary District  (MSB)  of Greater Chicago
converted one of their 12 digesters at the West Southwest  plant (1,200 MGD)
to  thermophilic  operation.   The  reason for  this  is  that their mesophilic
digesters  are currently  operating  at a  14  day  detention time  and they
wished to  explore  the possibility of  increasing sludge processing  capacity
by  operation  in   the  thermophilic  range.    Although  their  experimental
program  is  not completed,  they  did report on  the  results of  130 weeks of
operation at  the  1980 Conference  of the Water  Pollution Control Federation
in Las Vegas  (1).

     Their  work   did  demonstrate that  thermophilic  digesters   could  be
operated  successfully  at a 7  day detention  time.   Of particular concern to
USD is the  energy  self-sufficiency of  the  process  since  thermophilic  diges-
tion   does  require more  heat energy  input  than  the  mesophilic  process.
However,  they did  observe  increased  gas  production from  the  thermophilic
process  and believe that this,  with  the  use of a  heat  exhanger to preheat
the  feed sludge 'with the  discharged  thermophilic sludge, will offset  the
increased  energy  requirements.  Just  as  in  Los Angeles,  they  had  no  parti-
cular  difficulty  in operating the process and observed  that it could stand
a change in temperature  of  up to 5°F in  24  hours without adverse effects.

     USD is  particularly  concerned  with sludge  odor  since  the  digested
sludge is initially lagooned  at  a location  with  a high visability.   Their

-------
tests indicated  only a  slightly  greater odor  intensity from  the  thermo-
philic  sludge,  however,  the odor  was  different  and  there were  various
opinions as  to whether  the'\Hrdef was better or worse.  They therefore plan
further investigations  of  the  disposal aspects of the thermophilic sludge.

Ontario Ministry of the Environment, Canada

     In  1977,  Smart  and  Boyko  (2)  of  the  Ontario  Ministry  of  the
Environment, Canada, reported on the results of their full scale studies on
the  thermophilic  anaerobic digestion process.   They had originally planned
to establish the upper limits at which sludge could be processed by thermo-
philic  digestion but due  to difficulties  with their heating  system were
unable  to  do so.   However,  they did obtain good  overall  performance at a
detention  time   of  7.5  days and  stated that  the  thermophilic  digestion
process could be applied in existing plant operations  where solids stabi-
lization  performance is  compromised  by organic  or  hydraulic  overloading
conditons.

     As a  practical matter, they found  that standard gas drying equipment
was  inadequate  for  drying the gas  produced in the  thermophilic digester
since  it  is  at  a  higher  temperature and  thus contains more water vapor.
Several modifications  of this equipment were recommended for accomplishing
additional moisture removal.

2.3. DEVELOPMENT  OF THE MESOPHILIC-THERMOPHILIC PROCESS

     Torpey,  in  his most recent  (1979-80) work  at  the Rockaway plant  in New
York City,  has   found  a  way  to  overcome  the  potential  disadvantages of
thermophilic digestion  as well  as  to  improve upon the  process.   He has
accomplished this by again  going  to two-stage  digestion but this time with
the  two stages  consisting of a mesophilic  stage followed by a  thermophilic
stage.  He also  recycles  a  portion  of  the  thermophilically  digested  sludge
back through the aeration  tanks  to  obtain additional  destruction  of organic
solids.   The advantages of  the  thermophilic process  are thus retained with
the  potential disadvantages  being  decreased.    In addition, a substantial
improvement  in  organic  solids  destruction  is  obtained thus improving  the
                                  10

-------
quality of the  ultimate  product,  the digested sludge.  The  extra  gas pro-
duced from the  destruction of these solids also helps to offset the higher
heating requirements.   However,  a  disadvantage  of the process  is  that it
does require  greater  digester capacity (as compared to thermophilic diges-
tion) .

2.4  PURPOSE AND METHODS OF THE ROCKAWAY TESTS

     The  City of New  York,  which is under Federal mandate  to  cease ocean
dumping  of  sludge  derived   from  the  treatment of  wastewater, has  been
involved  in  studies  of  land-based disposal  techniques  for the past few
years.   These studies  were initially directed towards determination of the
optimal methods for dewatering  digested sludge  and  identification of the
subsequent steps for ultimate land disposal.

     Later  the idea was  advanced that, as a  fundamental  and top priority
item in  the  management program, current plant facilities should be studied
for  use  in   the  reduction of  the  rate of  sludge  production,   both  as to
volume  and  as  to  volatile  matter, from  an activated sludge  plant.   The
method would  be based  on  the  exploitation of biochemical mechanisms, namely
by  exposing  the mesophilically  digested solids  to the enzyme  systems of
thermophilic  digestion  and  activated  sludge.   A  new  method  of sludge
processing  has  been  formulated to  implement  this  idea.   The advantage
gained  in  this  investigation would  be  reflected commensurately  in the
economics of  all sludge  dewatering  and  post-dewatering processes which were
previously studied.

     The  Rockaway Pollution  Control  Plant  (P.C.P.), which  is  connected to  a
population of 100,000  and has a  flow of 25  to  30 mgd, was  chosen for a full
scale  test.   The  plant  uses  conventional  facilities  for  the activated
sludge  process and   the  sludge   generated  undergoes  mixed  primary and
seconary  sludge  thickening  prior  to  mesophilic  digestion.   The  digested
sludge  is transported to sea.   As  presently operated,  the primary  tanks
provide  a detention of  about 2  hours,  the  aeration tanks  of 3.3 hours with
step feed provisions, and the  final tanks  of  3  to  5  hours depending on the
number  in use.   Two   45  ft.  diameter  thickening  tanks  are used for  mixed
                                  11

-------
sludge thickening  and a  1  cu.ft./capita tank  is used  for  the mesophilic
digestion.

     As  required  for this  test,  the  following  steps were  taken:   (1) an
additional 1  cu.ft./capita  digestion tank was placed in service to receive
the  overflow sludge  from  the mesophilic digestor  and its  contents were
heated to 120 - 122°F, the lower limit of the thermophilic digestion range;
(2)  piping  was  installed  to  carry  a portion  of  the  overflow  from the
thermophilic  digestor directly to a single 45 ft. diameter tank, which was
to  be utilized  as  a  rethickening  and  elutriating  tank;  (3)  piping was
installed to  carry the remainder of the flow from the thermophilic digester
into  the primary effluent,  and thereby, directly into  the  aerator of the
secondary treatment  system;  (4) city water was  carried  to the elutriation
tank.  In summary,  the  elements  of  this new method  of sludge processing
involved  (1)  subjecting  the  mesophilically  digested  sludge to subsequent
thermophilic  digestion,  (2) circulating a portion of the sludge leaving the
thermophilic  digester directly to,  and through, the  secondary treatment
system,  and   (3) subjecting  the remainder of the  sludge leaving the  ther-
mophilic digester to a rethickening and elutriation step.

      The  thermophilic digester was placed in operation in September  1979.
However,  it  was not until January  15,  1980 that the necessary piping  addi-
tions  were  completed and the  recirculaation and  rethickening steps of the
new  method  brought  into  service.    Therefore,  although  the thermophilic
digester  was in operation,  test results  on treatment plant effectiveness
before January  1980  do not  include  any effects due to  recirculation.

2.5.  RESULTS  OF THE  ROCKAWAY TESTS

2.5.1    Effect of  Recirculation on  Process Performance (Solids and  BOD)

      When the full  scale test was started, the  activated sludge  was  at  a
low  sludge density  index of  0.6 to  0.7.   Microscopic  examination revealed  a
significant  population  of  bacterial  filaments  present along with  colonies
of stalk ciliates  and rotifers.   After  only a  few  days of  operation,  the
digested sludge recirculation caused  the sludge  density index to rise  to
                                  12

-------
1.0 and  the  bacterial  filaments to diminish substantially.  Throughout the
entirety of  the test  following,  the sludge density  index  remained  in the
stable range of 1.0 to 1.4.

     Since the flow received at the plant is approximately 200 gals/capita/
day, the influent wastewater strength is low, averaging about 100 mg/1 each
of  suspended  solids  and  BOD,..   Prior to the test, the suspended solids and
BOD,,  in  the effluent  averaged 14  and  12 mg/1  respectively.   The monthly
treatment results  for  the period from July  to  December 1979 are presented
in Table 2-1.  For comparative purposes, the treatment effectiveness during
the  course   of  the  test  from  January   15  through  May 29, 1980,  is also
included.   These  data  indicate  that  no  significant  effect  on treatment
efficiency was  experienced as  a result  of  the  continuous recirculation of
digested  sludge through  the  aeration system for  at least the first three
months.   In  the  latter  2 months,  suspended  solids in  the  effluent did
increase by  about  3 mg/1 and  there was  a substantial  increase in the flow
rate from about 20 mgd to 27-29 mgd.

2.5.2.    Nutrient Removal

     To  further  evaluate  whether  the   recirculation  of  digested   sludge
through  the  secondary  system had an adverse  effect on effluent quality, the
data  concerning nitrogen and phosphorous are shown  in Tables 2-2 and 2-3.
The effluent  values  are  of   special  interest  since  the  raw wastewater
samples  did  not  contain the recirculating flow.   Inspection  of the data for
the two periods  (1)  pre-test  and  (2)   test, shows  that the total  average
effluent inorganic  nitrogen  was  9.2   mg/1 and  10.4  mg/1  respectively.
Although data  from  month to  month varies, period  averages show that in-
organic  nitrogen in the  effluent  increased  1.2 mg/1 during  the  test period
over  the pre-test period.  Conversely,  the orgarfic   nitrogen decreased 4.3
mg/1.    Phosphorus  concentrations   in  the  effluent  remained  essentially
unaffected  over  the  two  periods.   It  appears  that  the  digested  sludge
recirculation had a  minor effect  on the  effluent quality with respect  to
the nutrients  nitrogen and phosphorus.
                                  13

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TABLE 2-1.  ROCKAWAY P.C.P.  TREATMENT EFFICIENCY,  JULY 1979 TO MAY 1980

Before Modification
Plant Influent

Month
July 79
Ang
Sept
Oct
Nov
Dec
AVG
Flow
MGD
22
22
23
25
22
21

Suspended Solids BOD,.
mg/1
88
83
93
116
140
125
108
Ibs/day
16,146
15,289
17,839
24,186
25,687
21,892
20,173
mg/1
111
117
90
103
112
124
110
Ibs/day
20,366
21,467
17,264
21,475
20,550
21,717
20,473
Plant Effluent
Suspended Solids
mg/1
12
16
12
18
13
10
14
Ibs/day
2202
2936
2302
3753
2385
1751
2555
BOD
mg/1
13
12
10
12
11
11
12
Ibs/day
2385
2202
1918
2502
2018
1927
2159
After Modification
Jan 80
Fel)
Mar
Apr
Hay
AVG
21
19
23
27
29

86
86
106
94
94
94
15,062
13,628
20,333
21,167
22,734
18,585
91
85
57
49
43
65
15,938
13,469
10,934
11,034
10,400
12,355
8
9
13
15
15
12
1401
1426
2494
3378
3628
2465
8
8
8
6
6
7
1401
1268
1534
1351
1451
1401

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    TABLE  2-2.   ROCKAWAY  P.C P.  INFLUENT-EFFLUENT NITROGEN CONCENTRATIONS, .JULY 1979 TO HAY 1980
\J\
Before Modification
Ammonia Nitrogen
Flow Influent
Month
July
A..g
Sept
(in
Nov
Dec
AVG
M«D ing/1
22 13.0
22 7.8
23 	 a
24 78
22 12 5
21 10 4
10.3
Ibs/day
2385
1431
	
1626
2294
1821
1911
Effluent
"JS/1
1.6
1.8
—
0.6
9.4
9.2
4.5
Ibs/day
294
330
	
125
1724
1611
817
Organic
Influent
rog/1
5.8
8.4
10.5
8.4
15.1
16.0
10.7
Ibs/day
1064
1541
2014
1751
2771
2802
1991
Nitrogen
Effluent
n.g/1
2.9
3.0
9.6
3.0
8 6
14 8
7.0
His/day
532
550
1841
625
1578
2592
IOSO
Nitrate
Influent
mg/i
0
2.3
	
0
0.1
0.3

Ibs/day
0
422
	
0
18
52

Nitrogen
Effluent
•atl l!L-£*z
7.0 1284
S.9 1082
	 	
5.2 1084
0.4 73
0.2 35..
3 7 — -b
Total Inorganic Nitrogen
Influent
"6/1
13 0
10 1
	
7.8
12.8
10.7
10.9
Ibs/day
2385
1851
	
1626
2348
1874
2017
Effluent
nig/ 1 1 bs/day
10.6 1945
9.7 1180


60 1251
10.3 1890
9.4 1646
9 2 IS82
After Modification
1980
Jan
Feb
Mar
Apr
May
AVG
Analytical

21 94
19 11.6
23 9.6
27 7.0
29 9.4
9 4
results not

1646
1838
1841
1576
2273
1835
available.

0.6C
2.6
3.0
1.0
2.4
2.3


105C
412
575
225
580
448


9.8
10.6
15.6
8.6
9.2
10.8


1716
1680
2992
1937
2225
2110


3.0C
2.2
4.2
3 2
1 2
2,7


525C
349
806
721
290
542


0.2
0.3
0.8
0.3
0.3
0.4


35
48
153
68
73
75


6.3C 1IOJC
8.2 1299
10.0 1918
5.6 1261
5.4 1306
7.3 1446


9.6
11.9
10.4
7.3
9 7
9.8


1681
1886
1995
1645
2346
1911


6 9C I208r
10.8 1711
13 2 2532
1.8 2207
7 8 1887
10 4 2084

Averages not calculated
Transition
month-results not included in
averages.











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TABLE 2-3.  ROCKAWAY P.C.P.  INFLUENT-EFFLUENT PHOSPHORUS CONCENTRATIONS, JULY 1979 TO MAY 1980
Before Modification
Total Phosphorus

Month
July
Ang
Sept
Oct
Nov
Dec
AVG
After
Flow
MGD
79 22
22
23
25
22
21

Modification
Jan 80 21
Feb
Mar
Apr
May
AVG
19
23
27
29

Influent
mg/1
2.3
2.5
2.5
2.0
2.7
1.8
2.3

2.7
2.8
3.9
2.9
2.5
3.0
Ibs/day
422
459
480
417
495
315
431

473
444
748
653
604
584
Effluent
mg/1
1.8
2.1
2.1
1.2
1.6
1.6
1.7

1.8a
1.7
2.0
2.4
2.0
2.0
Ibs/day
330
385
403
250
293
280
323

3153
269
384
540
484
419
Ortho Phosphorus
Influent
mg/1
1.7
1.8
1.1
1.4
1.9
3.5
1.9

1.6
1.8
1.9
1.2
1.3
1.6
Ibs/day
312
330
211
292
349
613
351

280
285
364
270
314
303
Effluent
mg/1
1.8
1.4
1.7
1.2
1.2
3.0
1.7

,5a
.4
0.7
.1
.6
.2
Ibs/day
330
257
326
250
220
525
318

2623
222
134
248
387
248

   Transition month results not included in averages.

-------
2.5.3.  Heavy Metals Removal

     The results  of the monthly  metal analyses of  composite  influent and
effluent samples  for  the pre-test period July to December 1979 and for the
test period January  to  May 1980 are presented in Table 2-4.   Comparison of
the overall averages of these test periods for cadmium and mercury, the two
metals  that  have been  shown  to exert a major effect  on  human physiology,
indicate that there  is  not a significant difference between  the  removals.
In fact, the  activated  sludge process does not seem capable  of appreciably
reducing the  already low  concentration of either of  these metals.   Also,
mass balance studies of the metal data, excepting cadimum and  mercury, have
been generally good.  Cadmium and mercury, however, due  to their low con-
centrations and  to  the  sensitivity of the testing procedure,  had  poor mass
balances.   Comparative   inspection of  the  data  for  the remaining  heavy
metals,  indicates  some variable  effects  of  treatment  during  individual
months,  but  with no  significant  changes in  the overall  averages for the
subject periods.

2.5.4.  Effect of Recirculation on Oxygen Requirements

     The effect  of  digested sludge recirculation on air  compressor output
over  the course   of  the test  could not be determined.  The air compressor
was operating at a level to produce more than adequate dissolved oxygen and
its  rate could  not be lowered before  or  during the  test  to attempt  to
evaluate any  demand  changes.   A calculated estimate was  made  based on the
fact  that  meso-digestion,  without  the  benefit  of  subsequent  thermo-
digestion,  destroys  90% of the BOD. present.  The estimate indicates that
the BOD5 in the portion of the digested sludge which is continuously recir-
culated, would  add less  than  5% to  the  oxygen  demand of  the primary
effluent.
                                 17

-------
                       TABLE 2-4.   ROCKAVIAY P C.P.  1NFI.UKNT-EFFLUENT METALS CONCENTRATIONS,  JULY 1979 TO HAY 1980
00
Copper

Before Modification
luly 1979
Aug
Sept
On
Nov
Dec
AVC
After Modification
J.iii 1980
Feh
Mar
Apr
May
AVG
Before Modification
July 1979
A.ig
Sept
Del
Nnv
Dec
AVG
AfLrr Modification
Jnii 1980
Feh
Mar
Api
May
AVG
Inf
0.11
0 II
0.11
0.13
0. 16
0. 11
0.12
0.09S
0.080
0. 110
0.075
F.ff
0 07
0.05
0.03
0.06
0.05
0.05
0.22
0.0035
0.0400
0.0380
0.088 0.027
Iron
Inf
0.8
0.9
5
.5
.6
.1
.2
0.57
0.65
0.55
0 84
0.8J
0.72
Eff
0.2
1 0
0.7
1.2
2.0
0.1
0.9
1.00
0.16
0.21
0.13
0.46
0 24
Cliromc
Inf
0
0
0
0
0
0
0
0
0
0
0
0
0
.001
.020
012
.009
.011
.OJ4
.014
.007
.0012
.0038
.010
.0038
Eff
0 006
0.015
0.008
0.002
0.007
0 008
0.0012
0.001
0.003
0.005
0.001
.0047 0.002
Cadmi lira
I lit
0.0001
0 0001
0.004
0.0001
0.0010
0.0008
0
0
0
0
0
0
0
.0004
0018
.0005
.0011
.0046
.0011
.0018
Eff
0.0001
0.0001
0.0002
0.0001
0 0015
0.0006
0 0004
0.0005
0.0004
0 0009
0 0029
0.0017
0 0015
Nickel
Inf
0.07
0.02
0.02
0.01
0.02
0.01
0.03
0.015
0.009
0 0042
0.0068
0.0086
F.ff
0.04
0.02
0.01
0.01
0.02
0.02
0.02
0.018
0.021
0.0024
0.014
0.011
0.0072 0.012
Calcium
Inf
41
40
41
29
19
13
10
14
16
14
13
23
16
Eff
36
48
32
41
20
15
32
14
17
15
14
21
17
Zinc
InC
0.11
0.26
0.23
0.09
0.12
0.08
0.15
0.066
0.093
0.090
0.21
0.085
Eff
0 14
0.35
0.16
0.17
0.15
0.08
0.17
0.070
0.086
0.065
0.079
0. 10
0.12 0.082
Magnesium
lnj[
94
107
102
94
85
76
93
70
60
58
54
59
58
Eff
98
112
105
101
88
77
97
72
64
59
55
62
60
Lead
Inf
0.017
0.024
0.110
0.014
0.027
0.023
0.036
0.014
0.049
0.0089
0.0088
0.010
0.018
Mercury
Inf
0.0010
0.0007
0.0007
0.0005
0.0026
0.0005
0.0010
0.0009
O-OOOS
0.0009
0.0003
0.0003
0.0005

Eff
0 006
0.006
0 006
0 008
0 020
0 007
0.009
0.030
0.0024
0.0016
0.0034
0.0064
0.0035
Eff
0.0006
0.0006
0 0002
0 0005
0 0028
0 0009
0 0009
0.0011
O.OOOJ
0.0002
0 0005
0.0004
0 0004

-------
2.5.5.  Operating Results

     As was previously noted, a 1 cu. ft./capita tank was placed in service
as a thermo-digester at about 121°F.  Its contents overflowed by gravity to
either  the primary  effluent,  or  to  a  45  ft.  diameter  rethickening  and
elutriating tank  where city water  was  added  to the  influent  sludge  at a
ratio  of  about 3 to  1.   The rethickened underflow sludge was  pumped  by a
duplex plunger pump,  actuated  by time clock,  to  empty digesters where its
volumetric  rate  was  measured  by filling  the tanks  during the  months  of
March and April.   Such procedures did not involve the use of any man power,
except for periodical blowing back of clogged lines.

     The  amount  and concentration  data  are presented  in Table  2-5.   The
volatile  matter   leaving  the  meso-digester averaged  9,000 Ibs/day,  thus
effecting  a reduction  of  7,200  Ibs/day  (16,200  -  9,000).    The  thermo-
digester  accounted  for  a  further  reduction of  1,800  Ibs/day  (9,000  -
7,200).   Such  reductions were effected  on the  combination  of  raw primary
solids, activated sludge  solids  and the recirculating solids (i.e., solids
that had been previously subjected to meso and thermo-digestion).

     The  conventional  activated  sludge  treatment  units  and  the modifica-
tions made  for incorporating the new method of  reducing sludge production
are represented in  Figure 2-1.  Since the  economics  of sludge  disposal is
fundamentally a function  of the  amount of volatile material to be disposed
of, only the rates of production of volatile matter are shown.   Overall, it
can be  seen that  the reduction of volatile matter  by the meso-digester of
7,200 Ibs/day,  added to the 1,800 Ibs/day reduction by the thermo-digester,
results in  a total  of 9,000 Ibs/day.  Additionally,  the aerator destroyed
2,000  Ibs.  V.M./day for  a  total reduction of  11,000 Ibs.V.M./day.  Since
the treatment system  was  removing a total  of  12,900  Ibs.V.M./day, the net
amount requiring disposal was reduced to 1,900 Ibs.V.M./day.  Previous data
show  the  average  amount  of volatile matter  carried  to  sea from April to
July  1979  (the period  just  prior  to this work) was  5,700 pounds.  There-
fore, there was a reduction of two-thirds in the volatile solids requiring
disposal (5700 -  1900 = 2/3).  Volume reduction was in the same proportion;
             5700
that is, 4,800 cu ft/day to 1,650 cu ft/day, or approximately 2/3.
                                 19

-------
N>
O
*1
S PLANI HiriUlHI _
g flow 20-29 HCO
w BOIk OS-IIOng/l
,0 SS 40 90 «9/l
i lllli'N 7.5-11.5 nq/l
^ lotaf P 2.5-1.0mg/l
CO
1

*
tu
rr
H-
P
oo
U>
P
r»
w
















PRIHARY
CIARIFICAIIOII









•

ACIIVAIEO
SLUDGE


REIURH SLUDGE
WASH ACIIVAIED
SLUDGE





FINAL
ClARiriCAIIOII
. 1


4.000 IVH/day
S.IOO cu ft/day
12.900 IVH Iron Incoumlng waslewater
J.300 IVH contributed from thickening over How
17.000 IVH to digestion


S^~^\
/ X
/ ' \ 16.200 ,
/ GnAVIIV ^ IVH/day j
1 liilCKIHinG 1 7.701) *" 1
\ / cu rt/d«y ^
\ /


x^ 	 ^\ /- 	 \

/ \ / \




I/day




1'IAHI IF fl III III





DILUIION UAIER






i





/
2.400 /
TVH/da/
95 F I 7.000*"! 121 r 1 7.700 ' 1
L / cu It/day V /cult/day \
V >/ V X
\
OODc 6-8 my/1
SS D-IS OHJ/I
till, -II 0.6-4.0 mg/l
lolol r 1.7-2.0 nifl/l









^ 	 ~\
X
IIIICKUIIIIG \ 1 .900
AIID \ IVH/Jay
ELIIIRIAIIUII 1 *"'
1 10 FINAI DISPOSAL
/
                                                            IIIICKEIIER ovtnriow
                                                            BOO IVH/Jay	
                                                           IIUIRIAIIOri
                                                           ovtRnow
                                                           500 IVH/day
                                                                                          VOIAIIIE IVUIER 10 DISPOSAL
                                                                             Oefore therwi|ihlllc
                                                                             systca Incoipgraled
                                                                             s./oo r. 4.000 en rt
Alter tlienuo|ililllc
system Incorporated

1.900 I. I.650 cu ft
                                                                             fVH/ilay - PflllllOS VOIAIIIE HAURIAL  FIR DAT

-------
    TABLE 2-5.  ROCKAWAY P.C.P.  AMOUNT AND CONCENTRATION OF SOLIDS PASSING THROUGH SYSTEM
M
t-1

%Conc. V.


Mo.
1980
Jan
Feb
Mar
Apr
May
Avg.
Feb
to
May


Flow
MOD
21
19
23
27
29



25

//VSS
capt.
(75% VM)
10,400
9,500
14,800
13,400
14,200



12,900
Raw
thick.
pump.
cu ft/day
5,900
7,300
8,400
6,500
8,500



7,700


Raw
thick
3.9
3.6
3.3
3.5
3.0



3.4


Meso
dig.
1.6
1.8
1.7
1.9
2.0



1.9
M.


Thermo
dig.
1.1
1.3
1.5
1.5
1.6



1.5


//V.M.
from
thick.
14,500
16,500
17,500
14,500
16,200



16,200



Meso
dig.
6,000
8,200
8,900
8,000
10,800



9,000
//V.M. /day


The rmo
dig
4,100
5,900
7,800
6,400
8,600



7,200
leaving
Rethickencr
lilutriator
Under Over
flow Now
_ _
-
1 ,800 500
2,000 400
600



1,900 500

     Note:   (1)  Calc. of V.M. inventory in digesters after February show the change does not significantly  influence
                the  above data.
            (2)  Measured volume March 1,600 cu  ft/day x 63 x 1.8% = 1,800 ffV.M./rtay
                                April 1,700 cu  ft/day x 63 x 1.9% = 2,000 0V.M./day

-------
     The daily  amount of  gas  generated during  the course  of  the thermo-
digestion  is  shown  in  Table 2-6.   Based  on the  averages for  the  period
February to May,  the meso-digester produced 83,900 cu ft/day gas, slightly
less than  the  comparable  preceding period without digested sludge recircu-
lation  through  the   aerator.   The  gas  generated  by the  thermo-digester
increased  from  an average  of  7,000 cu  ft/day  to  14,000  cu  ft/day  during
recirculation.    Gas  production  per pound  of volatile  solids  reduced  is
presented  in  Table  2-7,   with  gas  production  for several  pure compounds
presented  in Table 2-8 for comparison.

     The  gas  mixers  in  both  digesters were causing  formation  of  large
solids masses  in the digesters with consequent clogging of the overflows.
It  was necessary  to operate  the  mixers  only  a  few  minutes  per  day  to
alleviate  this condition.

     Garber  (1)  in  Los  Angeles  had  determined  that  the thermo-digested
sludge  required  half the  dose of iron coagulant and produced  almost four
times  the  yield  on a vacumm filter  as  meso-digested  sludge.   Accordingly,
to obtain  some estimate of the improvement on coagulability achieved by the
use of the thermo-digestion in this instance, the me so and thermo-digested
sludges were subjected  to polymer treatment.  It was found on a laboratory
scale, that using  a  high molecular  weight,  low  charge  polymer  //2535CH (as
manufactured by American Cynamid)  the  coagulability  improved radically.
Specifically,  dosages of  up  to 4,000  ppm on meso-digested sludge did not
produce an end  point,  although some  flocculation  was  observed.   In con-
trast,  the thermo-digested sludge released 73% of  the  water in 30 minutes
at  1C, at a dose of 2,500  ppm.  Thermo-digested  sludge, after  a  3 to  1
elutriation, required a  lesser  comparative dose of  1,650  ppm  of the same
polymer to release 64% of  the water  within 30 minutes at 1C.
                                 22

-------
TABLE 2-6.  ROCKAWAY P.C.P. DAILY GAS PRODUCTION



Month
September 1979
October
November
December
Mesophilic
digester
cu ft/day
79,200
93,800
90,300
77,200
Thermophilic
digester
cu ft/day
5,300
8,200
6,900
7,500
Average, No
recirculation
January 1980
February
March
April
May

Average, with
recirculation
Feb to May 1980
87,600
79,200
88,000
86,800
76,400
84,300
 7,000
 8,500
12,700
13,600
11,900
17,700
83,900
14,000
                                 23

-------
TABLE 2-7.  GAS PRODUCTION CUBIC FEET/POUND VOLATILE SOLIDS REDUCED


Month
January
February
March
April
May
Mesophilic
digester
9.3
10.6
10.1
11.7
15.6
Thermophilic
digester
4.5
5.5
12.4
7.4
8.4

TABLE 2-8.  GAS PRODUCTION AND QUALITY FROM ANAEROBIC DIGESTION OF SEVERAL
            PURE COMPOUNDS
                         Gas production cubic
                         feet/pound volatile           Percent
Material                   solids reduced              content
Crude fibers                    13                      45-50
Fats                            18-23                   62-72
Grease                          17                      68
Protein                         12                      73
Scum                            14-16                   70-75
                                 24

-------
SUMMARY

     A  full  scale test  was conducted  at  the Rockaway  Plant in New  York
City, which  serves a  population of 100,000, for a period of five months to
evaluate a new  method of reducing the amount and volume of sludge produced
from  the  activated sludge  process.   This method  involved the  use  of (1)
high  stability  thermophilic digestion  following  mesophilic digestion, and
(2)  the recirculation of a portion of such thermo-digested sludge directly
to and  through  the secondary system of  the  activated sludge process while
the   remainder  was   conducted  to  a  rethickening and  elutriation  tank.
Operating  results have   demonstrated  that  the  volatile  matter  normally
transported  to  sea after raeso-digestion was reduced by 2/3.  Moreover, the
volume of sludge produced was lowered by 2/3 without chemical or mechanical
aids.   Using a  laboratory  scale,  it was  shown  that the  residual  solids
exhibited  improved  coagulability after  having undergone thermo-digestion.
This  change  would improve the economics of  all  subsequent dewatering pro-
cesses.   The treatment  process  was performed without  significant adverse
effect  on any  accepted  parameter due  to  the continuing  recirculation of
digested sludge through  the  activated sludge process.

Reference:   (1) Buhr, H.  0. and Andrews, J.  -  The Thermophilic Anaerobic
                Digestion  Process  -  Water  Research.  Vol.  II,  pp!39-l46,
                1977, Permanon Press, Great Britain.
                                  25

-------
                               SECTION 3
               BLUE PLAINS WASTEWATER TREATMENT FACILITY

     The District  of  Columbia  WIT is located in  the  southernmost portion
of Washington,  DC, on the  east  bank of the Potomac River.   The  treatment
facility  receives  flow  from  the  District  of   Columbia,  Virginia,  and
Maryland.   The  plant  has  a  tributary  area of 725  square  miles, with  a
design flow  rate  of 309  mgd and a  peak flow rate of 650 mgd.  It occupies
an area  of  more than 200 acres, and is adjoined by the  US  Naval Research
Laboratory to the north,  the Anacostia Freeway to the east, and the Potomac
River to the south and west.

     The existing  (winter 1980) liquid management treatment scheme consists
of  raw  wastewater  pumping, aerated grit removal,  primary  clarification,
high rate activated sludge, intermediate clarification with chemical addi-
tion  for phosphorus  removal,  nitrification,  final  clarification,  multi-
media  filtration,  and chlorine disinfection.  Discharge  is  to the Potomac
River.

     The existing  (winter 1980) sludge management treatment scheme consists
of the  following.   All primary sludge  is  thickened  in gravity thickeners;
all  waste   activated,  waste  nitrified,  and  filter  backwash   sludge  is
thickened in dissolved air  flotation thickeners.  Approximately half of the
total  sludge  volume  is   pumped   to  the   existing  anaerobic  digesters,
elutriated,  vacuum  filtered,  and   disposed  of on agricultural  land.   The
other  half  of  the total  sludge volume  is  vacuum filtered with excess lime
and is either landfilled  in trenches or  composted.

     The  size  and capacities of the existing  sludge handling  equipment are
discussed in Section  5.
                                 26

-------
                               SECTION 4
        EVALUATION OF CURRENT AND FUTURE PRIMARY AND SECONDARY
                          SLUDGE GENERATION

     The first step in this analysis of ways to improve the existing anaer-
obic digestion operation  at  Blue Plains involved the evaluation of current
and future sludge production.  Current primary and secondary sludge produc-
tion was determined  using operation data supplied by Blue Plains personnel
for  the months  of  January  through  June  1980  (Appendix  A,  Table  A-l).
Future  primary  and  secondary v sludge  production  was  estimated by  using
existing data  plus assumptions  as  to the effects on  sludge  production of
the completion of  current on-going  plant modifications.  All data analyses
relative to sludge production are given in Appendix B.

4.1.  PRIMARY SLUDGE PRODUCTION

     Primary sludge consists  of those solids that settle and are removed in
the primary clarifiers.  Currently,  these solids are generated from the raw
plant   influent after  coarse  screening and grit removal  and  the overflow
from the  gravity thickening and elutriation tanks.   Analysis  of the data
indicates that the average dry solids withdrawn from the primary clarifiers
and pumped  to the gravity thickeners is 0.348 ± 0.057 dry  tons of solids
per million gallons  of influent flow (T/MGIF).l  The  volatile  solids con-
tent averages  79.7 ± 2.9  percent  or  0.277 ± 0.047 dry  tons  of volatile
solids per million gallons of influent flow (VT/MGIF).

     Primary  sludge  production  and volatile content  are not  expected to
change by any significant amount within the near future.
1 It  is  estimated  that 0.07  to 0.1  T/MGIF  is grit,  which is  not  being
  removed in the existing aerated grit chambers.
                                  27

-------
4.2.  SECONDARY SLUDGE PRODUCTION

     Secondary sludge currently consists of those solids that settle out in
the  intermediate  clarifiers  and  are  removed  from  the  system as  waste
sludge. Currently,  these  solids come from the  biological  solids generated
in  the  high rate,  activated  sludge  system;  the suspended  solids  that did
not settle  out  in the primary clarifiers; and the solids produced from the
addition of iron for  phosphorus  removal.  Analysis of  the data indicates
that the  average dry  solids  wasted from the intermediate  clarifiers  and
pumped to the  dissolved  air flotation thickeners is 0.284 ± 0.034 T/MGIF.2
The volatile  solids average  65.3 ±  2.1  percent or  0.185  ± 0.022  VT/MGIF.

     Secondary sludge production will increase in the near future for three
reasons:  increased phosphorus removal,  operation of nitrification systems,
and operation of multi-media filters.

4.2.1.   Increased Phosphorus Removal

     Effluent  limitations  on phosphorus  will  need to be  reduced  from the
current  1.1 mg/1  average to the  NPDES  permit  requirement of  0.53  mg/1.
This  will  increase  chemical  sludge  production  from  iron  addition  by
approximately  0.009  T/MGIF,   assuming   that  the  volatile  fraction  is
negligible.

4.2.2.   Nitrification

     At a minimum,  this  system  will have to  reduce  current total Kjeldahl
nitrogen (TKN)  levels in  the plant  effluent from an average  of 13.8 mg/1
to  5.3  mg/1.   Assuming  a  biological  yield coefficient  of 0.1 pounds  of
solids produced  per pound of TKN reduced, nitrification would generate  an
additional  0.004 T/MGIF,   of  which  70 percent  is  assumed  to  be volatile.
2 Approximately  0.045 ± 0.013  T/MGIF  is  attributed  to  chemical  sludge
  generated by iron addition for phosphorus removal.
                                  28

-------
4.2.3.  Multi-media Filters

     By the end  of 1981,  the new multi-media  polishing  filters will be in
operation.  It  is estimated  that  these filters will  reduce  the suspended
solids being discharged from the current 15 mg/1 average to 7.5 mg/1.  This
will  contribute  approximately  0.031  T/MGIF of which 70  percent is assumed
to be volatile.

     These  three new sources will increase  secondary  sludge  production to
approximately 0.328 + 0.034 tons of dry solids per MG of raw influent flow.
The  volatile  solids content  of the  secondary sludge  would  be reduced to
0.210 ± 0.023 VT/MGIF or 63.8 ± 2.1 percent.

4.3.  SUMMARY

      Table  4-1  summarizes  the information  presented  in  Sections  4.1 and
4.2.  Future  sludge  production  should be  realized by  the  fall  of  1981.
                                   29

-------
          TABLE 4-1.   SUMMARY OF CURRENT AND FUTURE PRIMARY AND SECONDARY  SLUDGE GENERATION AT BLUE PLAINS
Current sludge generation
Dry tons (pounds) per
mill ion gallons of
Sludge type influent flow
Primary 0.348 i 0.057 (696 ± 114)
Secondary
o High rate system 0.239 i 0.034 ( 478 ± 68)
o Chemical 0.045 ± 0.013 ( 90 i 26)


TOTAL 0.632 1 0.068 (1264 ± 136)
Future sludge generation
Volatile dry tons (pounds) Dry tons (pounds) per
per million gallons of million gallons of
Influent flow influent flow
0.277 ± 0.047 (554 t 94) 0.348 i O.O57
0.185 i 0.022 (370 ± 44) 0.239 + 0.034



0.462 ± 0.051 (924 ± 102) 0.676 ± 0.068
(696 ± 114)
( 478 t 68)
( 108 ± 26)
( 62 )
( 8 )
(1352 + 136)
Volatile dty tons (pounds)
per million gallons of
influent flow
0.277 ± 0.047 (544 ±
0.185 ± 0.022 (370 ±
0.022 ( 44
0.003 ( 6
0.487 i 0.051 (974 1
94)
44)
)
)
102)
OJ
o

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                               SECTION 5
         EVALUATION OF EXISTING SLUDGE MANAGEMENT OPERATIONS
              ON SLUDGE PROCESSING AND SLUDGE GENERATION

     The second step in the analysis of ways to improve the existing anaer-
obic digestion operation  at  the District of Columbia  WWTF  was  to evaluate
existing  sludge  management operations.   This  section  evaluates  operating
data supplied  by Blue  Plains  personnel for the months  of  January through
June 1980  (Appendix  A).   Data  analysis, where required, is provided in the
appendix specified in the following discussion.

5.1.  GRAVITY THICKENER OPERATION

     There are six, 65-foot diameter gravity thickeners.  Either primary or
secondary  sludge  can be pumped to these  units,  but  since the installation
of  the  dissolved air  flotation thickeners, only  primary sludge  has  been
thickened  in these  tanks.   Thickened sludge and/or scum collected from the
tank  surface  can  be pumped either  to  the  anaerobic digestion  system or
directly  to  raw  sludge  dewatering.   Overflow from  the thickeners  is  re-
turned  to  primary treatment.   Operational  data for  the  months  of January
through June 1980 is provided  in Appendix A,  Table  A-2.   Data analysis is
provided in Appendix C.

     Current practice  is  to  pump primary sludge 24  hours per day from the
primary clarifiers to  the gravity thickeners  at a solids concentration of
less than  one  percent.   In addition, part of the elutriation tank overflow
is continually returned to the gravity thickeners.   Dilution water from the
intermediate clarifier  overflow is  added.   Experience has  indicated that
the  rate  of dilution water  utilization should be 800  gallons  per day per
                                  31

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square foot of  thickener  tank surface.   Data analysis indicates that under

this mode of operation:


     1.   The average thickened solids concentration that can be expected is
         7.0 ± 0.5 percent.

     2.   The average  thickened  sludge  volume per million gallons  of plant
         influent flow is 1,236 ± 218 gallons.

     3.   The amount of  and  volatile content of primary sludge produced per
         million gallons of influent flow is altered.   After gravity thick-
         ening, the average  dry solids  withdrawn is 0.377 ± 0.060 dry tons
         of  solids  per  million gallons  of  influent  flow  (T/MGIF).1  The
         volatile   solids   content   averages   71.0 ± 5-3   percent   or
         0.268 ± 0.047  dry  tons of volatile solids per million gallons of
         influent flow (VT/MGIF).


     Future  performance of  the gravity  thickeners could  change  signifi-
cantly,  depending on the following conditions:


     1.   Change in  the  amount  of  grit  that is currently getting  into the
         primary sludge stream.

     2.   Change in  the  source and amount of dilution water currently being
         used.

     3.   Change  in the  quantity  of elutriation  tank overflow  presently
         being sent to the gravity thickeners.

     4.   Change in  the  type  of sludge thickened i.e.  thickening  a mixture
         of waste primary and secondary sludge solids.
5.2.  DISSOLVED AIR FLOTATION (DAF) THICKENER OPERATION


     There are  eighteen,  20-foot  wide  by 55-foot  long  (effective length)
DAF  thickeners.  Either primary or secondary sludge can be pumped to these
units, but  currently they  are  only used for thickening  secondary sludge.
Thickened sludge  (float),  and  the heavy solids  that settle and are removed
1 It  is  estimated that  0.07 to 0.1 T/MGIF  is  grit,  that  is not  being
  removed in the existing aerated grit chambers.
                                  32

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from the bottom of the tanks, can be pumped either to the anaerobic  diges-

tion system  or directly  to  raw sludge  dewatering.   Subnatant  from these

units is  returned  to  the high rate, activated sludge process.  Operational

data for  the  months  of January through  June  1980 are provided in Appendix

A, Table A-3.  Data analysis is provided in Appendix D.


     Current  practice  is to  pump  waste secondary sludge 24  hours per day

from the  secondary system clarifiers at the maximum concentration possible

(7,000  to 9,000  mg/1).   Polymer  is utilized  for  the  following reasons:


     1.  Polymer  usage  is  required  to  float  and  thicken  effectively
         secondary waste-activated sludges containing iron salts.

     2.  Polymer  usage  maximizes  solids  recovery,  thus  minimizing  the
         recirculation of solids  via the subnatant  stream that is returned
         to the high-rate, activated sludge process.

     3.  Polymer  usage  maximizes  the   solids  loading  rate  that  can be
         applied  per  unit of  area per  unit  of  tank,  thus minimizing the
         number of DAF units required to be operated.

     4.  Polymer  usage allows the subnatant stream  to  be  used as a source
         of  pressurized  flow  for the  DAF  thickener.   If  the  subnatant
         stream could not be used, plant effluent would have  to be utilized
          requiring extensive piping and  increased operating cost.

Data analysis  indicates  that under  this  mode of operation:

     1.  The  average thickened  solids concentration  that can  be expected is
          4.1  ± 0.3 percent.

     2.  The  average thickened sludge volume  per million gallons of plant
          influent  flow  is   1,644 ± 239  gallons.   If  secondary solids per
         million   gallons  of  influent  flow  increase by  approximately 15
          percent  (as discussed  in  Section  4),  it  is  assumed that  the thick-
          ened sludge volume will  also  increase  proportionately by  15  per-
          cent to  1900 ±  239  gallons.

     3.   Dry  polymer  usage  currently  at  7  to  10  pounds per  ton of dry
          secondary sludge solids is not  expected to change  in the  future.

     4.   At  current average  plant influent  flows,  it is estimated that  7
          DAF  units are required to be operating.   When secondary  solids per
          million  gallons  of  influent  flow  increase in the future it is
          estimated that  8 DAF units will be required.
                                   33

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5.2.1.  Removal of Settled Solids

     Not all  secondary  solids  are capable of being  treated  by DAF.  Those
solids  that  are too heavy to  float,  settle  to  the bottom of  the  DAF unit
and are  conveyed  by a chain and scraper mechanism to a sump located at the
discharge  end of each  tank.   Such solids were planned  to be  removed from
each  sump  by  use  of a  telescopic sludge valve;  however,  there are times
when  insufficient static head  is available to make  the heavy solids flow
upward  and out through the top of the telescopic valve.  When this occurs,
heavy  sludge continues  to  accumulate in  the  bottom of the tank until it
affects  the performance  of  the unit, which then has  to be  taken out of
service.

      Although it is  beyond  the  scope  of this  report  to provide  detailed
solutions  to operating problems,  there are  two possible methods of dealing
with  the problem  that should be  investigated:

      1.  Modifying  each telescopic sludge valve  to  an  air lift pump.   In-
         jecting  about  3  to  5  cfm  of air  near the bottom of each valve
         would permit the movement of sludge through the telescopic  valve.
      2.  Provide  positive sludge removal  through the use of  pumps  discharg-
         ing  into  a  common  header  located  in the  flotation  thickener
         basement gallery.

 5.2.2.   Pressure Regulating Valve

      Until  recently,  pressurized  flow  for  DAF  thickeners  has  been  con-
 trolled through an  air  actuator  and   pneumatic  pressure  device.   This
 automatic  control  system works  very well when  a high  quality  air  supply
 is  available  and  regular  operator  attention   (two  to three  performance
 checks  per  8-hour operating  shift)  is  provided.  When this  actuator  mal-
 functions,  the  float  quality  rapidly  deteriorates,   polymer  usage  in-
 creases, and consequently more DAF units have to be brought on-line to con-
 tinue processing sludge.
                                   3A

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     This  valve  has  been  a  continuous   source  of  operating  problems.
Recently, the manufacturer  of the existing flotation equipment has offered
a new  type of  spring-operated  pressure relief  valve  in place  of the  air
actuated system.  Figure  5-1  shows a cross-sectional view of the valve  as-
sembly.

     This  spring-operated pressure relief  valve relies on  an increase in
fluid pressure  to push the valve diaphragm against  the  spring.   Since  the
spring has  a  set constant of compression,  it permits the diaphragm to open
just far enough to maintain the set pressure and allows flow to pass.  This
valve  has  been tested  at one  facility  for over three years  and has per-
formed very well.   It is recommended that  the  WWTF  personnel consider use
of this new type valve.

5.2.3.  Spare Part Requirements

     As  a  result of the  overall  financial  constraints,  spare parts inven-
tory is  almost  non-existent.   In order to  keep the  required number of DAF
units  in  operation,  several  units  have  been  cannibalized"  for parts.
Currently,  this is  not  a critical  problem because  excess  capacity  for
normal operation  is available,  but if allowed  to  continue this  could lead
to significant  sludge processing problems.

5.3.   ANAEROBIC DIGESTION SYSTEM OPERATION

     The  anaerobic  digestion  system  is  made  up  of  several  major sub-
systems:   digestion tanks, sludge  heating, digestion  tank sludge mixing,
gas collection  and  storage, and sludge piping and pumping capabilities.  At
the present time only a  fraction  of  the  raw sludge is pumped continuously
to  the digestion system.  Operational data  from January 1979 through June
1980 is  provided in Appendix  A, Table A-4.
                                   35

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     Ad (usting screw
     Designed so spring cannot
     be compressed solid.

     Leek nut
     With set screw to lock
     securely in place.
     Spring«
     Carbon steel or aluminum
     pipe. Case and spnng seals
     designed to prevent
     warping of sonngs or
     Interference. Sealed top and
     bottom against moisture or
     dirt

     Adapter bushing
     Carbon steel equipped with
     grease fitting. "0" Ring seal
     in stem.

     Spindle (stem)
     Stainless steel equipped
     with stop collar—acts as a
     stop on opening stroke and
     takes the load off the
     compressor pin on closing
     stroke.

     Fingerplate
     anal compressor
     Finger plates, or flngara
     cast into the bonnet In
     larger valves combine with
     the compressor to provide
     metal support to the dia-
     phragm in all positions.

     Sliding stem bonnet
     Ductile iron.
     Diaphragms are melded
     dosed to reduce required
     closing forces, give longer
     life and provide drop ngnt
     closure without stretching
     or distortion.
FIGURE  5-1.
Cross-sectional  view of  spring-operated
pressure  relief  valve
                                   36

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5.3.1.  Digestion Tanks

     There are  12  earth covered,  concrete, digestion tanks.  Each tank has
an  inside  diameter of  84  feet  and a theoretical  liquid  volume  of 146,500
cubic feet  (1,096,000  gallons).   Though no longer usable, internal heating
coils are  still  located inside  each unit.  Lithium chloride tracer studies
(Appendix  E)  indicate  that  approximately 65 percent  of the  total  actual
volume--!.14 million  cubic  feet (8.54 million gallons)--is available.  The
remaining 35 percent is unusable due to such factors as (1) volume occupied
by scum and grit and (2) inadequate mixing.

     Scum—The  scum thickness is  measured on all tanks on a routine basis.
The  findings  indicate  that the  thickness of  the  layer depends  upon the
operation  of  the  digestion  tank  gas-mixing  system (Section 5.3.3).   When
the gas-mixing  system  is  not operational, the scum layer builds up rapidly
to  a  thickness  of several  feet.   When the  system is in  operation,  very
little scum accumulates.

     Grit—On a  routine basis,  digestion  system operations personnel probe
the tank bottoms for grit buildup.  Grit in the digesters has always been a
problem.  Until  several years  ago, digesters were systematically taken out
of  service for  cleaning,  but this is no  longer  done.   Based on conversa-
tions with  long-time  plant operators, grit accumulates  in  each tank until
it  reaches  a  point of  equilibrium.   Best  estimates  are that 15 to 20 per-
cent  of  each  tank is occupied by  grit.   Using  these assumptions, calcula-
tions  in  Appendix F  indicate  that  for  each million  gallons  of influent
flow, 1.4  to  2.0 cubic feet of grit  passes  through the aerated grit cham-
bers and is removed with the primary  sludge.
                                  37

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5.3.2.   Sludge Heating

     There are six, double inlet, double outlet,  6 inch by 8 inch,  tube and
tube heat  exchangers.   The source  of  hot water  is from  two  steam boilers
and one hot  water  boiler, each fueled by digester gas with diesel  standby.

     Originally designed  to transfer  3,000,000  BTU per hour per  heat ex-
changer (18,000,000 BTU per hour total), current operation is only capable
of  13,000,000 BTU  per  hour total.  Refurbishing of the  existing hot water
boiler  in  1981  will add  another 3,000,000  BTU per hour to  the  total.  In
addition,  the current on-going construction contract will tie in the exist-
ing steam boilers with new steam boilers elsewhere on the plant site. These
new steam boilers will have an approximate total capacity of 17,000,000 BTU
per  hour,  but  how  much  could  be  used  for  sludge  heating is  unknown.
Appendix G gives  a detailed analysis of sludge heating capacity.  Appendix
G also  analyzes  system heat requirements for both summer and winter opera-
tion.  Table 5-1 summarizes the  results.

TABLE 5-1.  SUMMARY OF ANAEROBIC SYSTEM HEAT REQUIREMENTS3
For raw sludge addition in BTU's per MGIF
     Primary sludge only
     Secondary sludge only
Total primary and secondary sludge
                                                   Winter
                                                 operation
  511,808
  636,353
1,148,161
                  Summer
                 operation
255,904
272.723
528,627
For system radiation heat losses in
BTU's per hour
Roof
Walls
Floor
Sludge piping
Total radiation losses


1,453,112
613,276
546,866
582,400
3,195,654


535,358
285,826
546,866
467,200
1,835,250

   Calculations for data are presented in Appendix G.
   MGIF - million gallons influent flow.
                                  38

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     Based on the  information  presented in Appendix G,  there  is  currently
9,800,000 6TU per  hour available for raw sludge addition during the winter
months  and  11,100,000  BTU per  hour  for  raw  sludge  addition during  the
summer  months.   After  refurbishing  the  existing hot  water  boiler,  raw
sludge  heating  capacity  will   increase  to  12,800,000  BTU per  hour  and
14,100,000 BTU per hour, respectively.

5.3.3.  Digestion Tank Sludge Mixing

     Mixing in the anaerobic digestion tanks is primarily done  using recir-
culated  gas.  Three  1,000 gallon per minute recirculation pumps are avail-
able for substitute or supplemental mixing.

     All  gas-mixing  systems are of  the type in which digester gas is  re-
moved  from  the  tank,  compressed, and discharged into the lower part of the
digester  through  vertical 2-inch pipes  (lances)  supported from  the tank
roof.   In some tanks, gas is  discharged through  only one  pipe at a time,
the  point of  discharge being changed to another discharge pipe either man-
ually  or automatically on a timed basis while others discharge through all
points at once.

     There  are  several  conditions  that prevent  the  existing gas mixing
systems  from adequately mixing each tank.

     1.  There  is  a  significant amount of grit  accumulating in each tank.
         Since  grit  has  a specific gravity  of  2.65,  digestion gas-mixing
         systems cannot  cope with these accumulations.
     2.  Since  all tanks  contain their old  internal  heating  coils, which
         completely  circle  the  inside of  the   tank,  the walls   act  as
         barriers  to the  mixing  currents thus allowing material to  build up
         behind  them and  reduce  useable tank volume.
     3.  Eight tanks (3,  4, and  7 through  12) were equipped with gas-mixing
          systems in 1960  that were intended to serve as  scum breakers until
          they  could  be  replaced by a  permanent gas recirculation  system.
                                  39

-------
         Since  1978,  several  of these  tanks have  had newer  systems  in-
         stalled, but they have been unable to operate continuously because
         of the lack of spare parts.

     4.  As a  result  of  the overall financial constraints, spare parts for
         the  gas-mixing  systems have been difficult to obtain  and  one to
         two gas-mixing systems have been inoperative.

5.3.4.  Gas Collection and Storage
     Anaerobic digestion produces a gas with an energy value of roughly 600

BTU  per  cubic foot  and the  District  has the  potential of producing  two

million cubic  feet per  day (see Section 5.3.7  for  analysis of gas produc-

tion capabilities).


     Visual  inspection  of the  existing  gas collection  and storage system
revealed that  there  is  need for appropriate corrective  action at least in
the following instances.


     1.  Some parts  of  the gas piping system show  extensive  corrosion,  to
         the extent that holes have developed in the piping, with duct tape
         wrapping used to prevent leakage.

     2.  Extensive  corrosion  on the  bottom of  the  floating gas  holder
         prevents  the  unit  from  being  used  to  its  fullest  capacity.
         Approximately  20  percent  of the  useable volume  has been  lost.

     3.  Some gas safety equipment was inoperative.

     4.  Where operators must  occasionally  enter several  locations  where
         digester gas can build up.   No gas alarm or portable gas meter has
         been provided for operator safety.

5.3.5.   Sludge Piping and Pumping Capabilities


     The anaerobic digestion  system is provided with an extremely flexible

sludge piping  and pumping  system.   Appendix H contains a  current sludge
piping  schematic that  was developed  as  part  of  this study.   A cursory
review of existing line sizes and pump capabilities indicated that capacity
is adequate to handle all sludge generated.
                                  40

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5.3.6.  Volatile Matter  Reduction

     Due  to  the  conversion of  some of the  biodegradable organic  material
(volatile  solids)  to methane  (CH.)  and  carbon dioxide  (CCL),  anaerobic
digestion  of municipal  wastewater  sludge decreases  the total solids.   The
amount of volatile  material that can be reduced depends primarily on sludge
type,  digestion operating  temperature,  food to  organism  ratio,  and  length
of  time  the sludge  is  kept  within the  digestion  tank  (sludge  residence
time).  In  addition, at similar  digester operating  temperatures  and sludge
residence  times,  a  greater fraction  of primary sludge  will  digest  than
waste activated  sludge.  Figure 5-2 shows a plot  of  percent volatile solids
           SWMWv
          - jivXvivXvX
       70
                                            Blue Plains 1980 Sludge


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•X1
         10
20
                           30
                  40
                                             50
                                    60
                                                               70
                              Percent of Total Sludge Mass Being Digested
                                   That is Secondary Sludge
        FIGURE  5-2.   The effect of secondary sludge on volatile
   matter  reduction  at the blue plains anaerobic digestion  facility2
2See Appendix  I  for development of data points.
                                   41

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reduction versus percent  by  weight of secondary sludge  in  the sludge mass
being digested at digestion temperatures of 93 to 95°F and sludge residence
times generally  from 17  to  21  days.   Each point on  Figure  5-2 represents
the average performance over a one-month period.

     As  the  secondary sludge fraction  of the total  sludge  mass increases
(digestion temperature and sludge residence time  held relatively constant),
the  percent  volatile matter  reduction  decreases  as  would  be  expected
(Figure  5-2).   The curve  drawn  in Figure  5-2 is  of "eye ball"  fit con-
structed under the following assumptions.

     o  The  lack  of accuracy involved  in performing solids  analysis plus
        the  fact that  each data  point represented the average of one month
        of operating  data  dictated that a wide band  curve  incorporating a
        range would be required.
     o  Realization that  without  data  in the region  of  0  to 20 percent on
        the  horizontal axis,  the  curve  would have  to lie  between 60 to 80
        percent volatile  matter  reduction as the secondary sludge fraction
        of the total mass approached zero percent (USEPA, 1979). •
     o  Realization  that  without data  in the region beyond 52 percent on
        the  horizontal axis,  the  curve  would have  to lie  between 30 to 40
        percent volatile  matter  reduction as the secondary sludge fraction
        of the total mass approached 100 percent  (USEPA, 1979).

     Volatile matter reduction as a function of organic loading and hydrau-
lic  residence time  are  given  in Figures 5-3 and 5-4,  respectively.   In
evaluating  the  information shown  in  these figures,  it  must  be remembered
that not  all sludge goes to anaerobic digestion, in  fact not even the same
ratio of  primary  to secondary sludge is  maintained.   The  amount and ratio
pumped  to digestion  is  presently controlled by the  raw and anaerobically
digested sludge dewatering operations.

     Organic  loading  Over the range indicated in Figure  5-3  had little or
no effect on volatile matter reduction.   Analysis of  the raw data indicates
that at  the  higher organic loadings and higher volatile matter reductions,
the  ratio of primary  sludge to  secondary  sludge  was  considerably higher
than  the normal  50:50 to  60:40 split.  These  results would  be expected
since Figure 5-2  showed  that a greater fraction of primary sludge digested
than secondary sludge.
                                  42

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     Evaluation  of  the  raw data  in  Figure  5-4  indicates that  the  four
points beyond  22  days  are for time periods in  which the primary:secondary
sludge ratio was  considerably  higher than the normal 50:50 to 60:40 split.
If  these  data  points  were  removed, the  data would  indicate  no  effect of
hydraulic detention time  on volatile matter reduction over the range indi-
cated.  This would  imply  that  a primary:secondary sludge ratio of 50:50 to
60:40  could operate  at  less  than 16 days hydraulic detention and still
expect 45 to 60 percent  volatile matter reduction.

     Based  on  the curve developed in Figure  5-2  and the data presented in
Figures 5-3 and 5-4, the following can be said about volatile matter reduc-
tion  using  the existing  anaerobic digestion system.   (Assuming  hydraulic
detention times of  16  to 17 days,  operating  temperatures  of 93°F to 95°F,
and organic  loadings  of 0.12 to 0.14 pounds volatile matter per cubic foot
per day.)3

     o  Digestion  at   the  current  secondary  sludge  to  total  sludge  mass
        generation  ratio  of 0.43 should provide  a  56.5  ±6.5 percent vola-
        tile matter reduction.   This  would  give an overall  reduction in
        solids of 0.256 ± 0.042 T/MGIF.
     o  Digestion  at   the  future  secondary  sludge  to  total  sludge  mass
        generation  ratio of  0.465,  should provide  a  53.5 ±  6.5  percent
        volatile matter reduction.  This would give an overall reduction in
        solids of 0.255 ± 0.042 T/MGIF.

5.3.7.  Gas Production
     Anaerobic  digestion  produces  a  gas  with an energy value of approxi-
mately   600   BTU  per   cubic   foot.    As  indicated   in   Appendix   I,
in  order for  the  existing heat  exchangers  to  operate at their maximum
capacity, the  boilers  would require 810,000 cubic feet of digester gas per
day.  In addition, the District WWTF is negotiating with the Naval Research
and Development  Center to sell them excess digester gas at  $0.95 per 1,000
cubic feet.
   Data  analysis for  volatile  matter  reduction  is  given in  Appendix I.
                                  43

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               70
         1-2
         ss ->

         •- ii
         n =1

         -5    60
         — v
         •9 •a
         £
               50
                         0.10
O.L2
0.14
0.16
                                   Organic Loading
                       Pounds Volatile Matter Per Cubic Foot Per Oay
                                                               0.18
  FIGURE 5-3.   The effect of  organic loading on volatile  matter

  reduction  at  the District of Columbia anaerobic digestion WWTF4
           •fi
           31
         II 3
               70
               60
         -T   50
                          16        13         20        22


                             Hydraulic Detention Time - Days
                              24
 FIGURE  5-4.   The effect  of hydraulic  detention time  on volatile

matter  reduction  at  the  District of  Columbia  anaerobic  digestion  WWTF0
 See Appendix I for development of data points.



                                  44

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     Figures  5-5,  5-6, and  5-7 show operating  data on gas  production per
pound of  volatile matter  reduced as a  function of feed  solids  concentra-
tion,  and volatile  matter  loading.   All  data  indicate that  significant
amounts of  gas  production can  be  lost as a  result  of  digestion system pro-
cess  stress,  possibly  caused  by  either poor mixing  or  ammonia  toxicity.

     Gas  production  per  unit  of volatile  matter reduced  declined  with
increasing  digester feed  solids concentration  (Figure  5-5).   This  decline
may  be  attributed  to  the existing systems  inability  to mix the  solids at
higher  solids  concentrations.   Insufficient mixing  allows  concentration
gradients  to  build  up which  tend to  disrupt the  biological process.   Two
possible  solutions  would  be  (1)  increase  the  mixing  intensity  or (2)
operate the system  at  a lower  feed solids  concentration.
          = 3 V
          a o se.
           55
             (^
             O
                   14.0
                   12.0
                   10.0
                    3.0
                         5.0
6.0
7.0
3.0
                             Feed Solids Concentration
                                 Percent Solics
   FIGURE 5-5.  The effect of feed solids concentration on anaerobic
    digestion gas production at the District of Columbia  digestion  WWTF5
 5  See Appendix I for development of data points.
                                   45

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     The  decline  may  also be  attributed  to  ammonia  toxicity.   Ammonia
nitrogen levels  in the digestion  tanks  vary from 1,200 to 1,500 milligrams
per liter  (mg/1).   It is  known  that ammonia  nitrogen  starts to affect the
digestion  process  adversely  above  concentrations  around  1,400  to  1,500
mg/1.   Therefore,  it  may be  concluded  that reduced gas  production at the
higher  feed  solids  concentration is  a  reflection of  the higher potential
for ammonia nitrogen toxicity.

     The solution  to ammonia  toxicity is dilution.   This dilution would be
accomplished  by proper  blending  of  the thickened  primary  and secondary
sludge.  It is desirable  to digest as  concentrated a sludge as possible and
still  maximize  gas  production.    From Figure 5-5,  a value  of six percent
meets  this criterion.   To meet  the six percent  level,  the primary sludge
mass  should  not be  more  than  65 percent of the total sludge mass pumped to
digestion.
     Gas  production  per  unit  of  volatile  matter  reduced  declined with
 increased  volatile matter  loading  (Figure  5-6).  The  current operational
 practice  is to maintain  a  constant liquid volume flow to digestion,  but  to
 vary the primary-secondary sludge mixture.
           §£«
                  li.O-
                  12.Of-
                     L
                  10.0-
                   8.0
                      D.-.O
0.12
                                              0.16
                               Volatile natter Loaemc
                              Pounds volatile Matze" °er
                               Jseole Cubic Feet °er Oay
     FIGURE 5-6.  The effect of volatile matter  loading on anaerobic
     digestion  gas  production  at  the District  of Columbia  digestion WVTF**
 5  See Appendix I for development  of  data  points.
                                    46

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     Increasing the percentage of primary sludge means more volatile matter
per unit  of flow,  thereby increasing the  volatile matter  loading on the
digestion system.  Therefore, the higher volatile matter loadings indicated
in Figure 5-6  are due to a high percentage of primary sludge in the incom-
ing  flow.   This  decline  may  again be  due to poor  mixing at  the higher
feed solids  concentration that  would  develop with the  greater percentage
of primary  sludge being  pumped to the system.  It is desirable to maintain
the highest  volatile matter  loading  possible and  still  maximize  gas pro-
duction.  From Figure 5-6,  a  value between  0.12  to 0.14  meets  this cri-
terion.

5.4.  ELUTRIATION SYSTEM OPERATION

     Elutriation  (washing)  of the  anaerobically  digested  sludge  is prac-
ticed  to  reduce  chemical  conditioning requirements  (reduced  operating
cost)  in  the  vacuum  filter  operation.   River water is used as  the source
of washwater.

     The elutriation  system consists  of two 35-foot wide  by  70-foot long
tanks,   each  equipped with  sludge removal  and  surface  skimming equipment.
The tanks are  operated  in series.  Anaerobically digested  sludge  is mixed
with wash water before entering the first tank.  The sludge that settles to
the bottom is  removed and pumped to the second tank where it is again mixed
with wash  water.   Settled  sludge from  the second tank  is pumped  to the
vacuum  filter.   Part  of  the elutriation tank  overflow  flows by gravity to
the  primary   clarifiers  and  the  remainder  is  pumped  to  the  gravity
thickeners.   Polymer is  added to  improve solids  concentration  and capture.

     Figures 5-7  through 5-9  show the effect of several  variables on the
percent  solids concentration  of the  elutriation  underflow pumped  to the
vacuum  filters.   The data  presented  in  these  figures  are  included  in
Appendix A,  Table  A-5   and  in  Appendix J.   As  will  be  demonstrated  in
Section 5.5, it is important to maintain this solids concentration as high
as possible.
                                  47

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     Figure 5-7  indicates  that a feed solids  concentration  of  at  least 2.7
percent  is  required  to develop  a  five  percent  underflow  concentration.
Because  there  is no digester supernatant,  the solids concentration  out  of
the digesters  is controlled by the solids  concentration  into the digesters.
Assuming  an  average 53 percent volatile  matter reduction (Section  5.3.6),
the feed solids  concentration into the digester must  be  a minimum  of 4.5  to
5 percent.  This also implies that the primary:secondary sludge mixture has
to be a minimum  of  1:6.

     The  total  hydraulic  flow  to  the  elutriation  system  is  composed  of
digested  sludge  flow  and washwater flow,  which currently totals 2.2 to 2.4
                 4- WO
                 
                 3
                 LU
      4.0
                               2.5
                       3.5
                           Feed Concentration
                             Percent Solids
          FIGURE 5-7.  The effect of elutriation  feed  solids
     concentration on elutriation underflow  solids  concentration7
7  See Appendix J  for development of  data  points.
                                   48

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                   L.
                   01 C i-
                   •O -r- r—
                   C S- O
                   =3 
                     •M
                   C (TJ 4->
                   O S C
                   •r- 0) 0)
                   •M a o
                   ID   S.
                   •i- o a>
                   s- t— a.
5.0
                          4.0
         40
                                               50
                               Digested Sludge Flow
                              To Elutriation Per Day
                                   Gallons x 104



         FIGURE 5-8.  The effect  of  digested  sludge flow rate

            on elutriation underflow solids concentration7
million  gallons  per  day.   Higher total  flows  are not possible  because of

the  inability to  remove  elutriation  overflow  at higher  flow  rates.   Pre-

liminary  analysis  of  elutriation  underflow  solids  concentration  versus

total  flow  rate  showed no  relationship.  Evaluation  of  the digested  flow

component (Figure 5-8)  indicates  that  elutriation underflow solids concen-

tration  is  quickly  and significantly  reduced  at digested  flow  rates  over

450,000 to 470,000 gallons per  day.
   See Appendix J for development  of  data  points,
                                   49

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     The  addition  of washwater  improves  the  compaction capabilities  of

sludge;  however,  according  to  Figure  5-9,  washwater  usage  beyond  4.5  to

4.7 times  the  incoming digested  sludge flow rate is  of no value.  Because

of the costs to pump washwater  from  the river and treat it after use, it is

best to minimize the quantity of  washwater consumed  for elutriation.
               J- WO
               CD C v
              •O-i- i—
               C S- O
              3 0> 
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5.5.  ANAEROBIC SLUDGE DEWATERING OPERATION

5.5.1.  Solids Generation

     Currently,  anaerobically digested  sludge  is  dewatered  on drum-type
rotary vacuum  filters after  conditioning by  elutriation and the addition
of  ferric  chloride.   The  addition of  ferric  chloride adds  solids  to the
total sludge mass.

     The amount  of ferric  chloride added is  governed by several factors:
the  operators  visual  evaluation  of  cake release  from the  drum  and cake
solids content,  both  of  which will improve with increasing ferric chloride
addition;  and  management's attempt  to keep ferric  chloride  addition at a
minimum level  and still  obtain acceptable results.  Although existing data
are  inconclusive,  there are  indications  that  some relationship is exerted
on  the  ferric chloride  addition by  the  filter feed  solids  concentration
(Figure 5-10)  and by  the percent secondary sludge in  the total sludge mass
(Figure 5-11).
    •a o
    ••- co
    00
       0)
     9) V
    U_ 0.

     0)
    -(-> C
    i— O
       (O
     3 C
     (J O
      c
       o
5.0
                4.0
                                10
                           11
12
                                Ferric  Chloride  Usage
                                  Tons  per  day
         FIGURE 5-10.  The effect of ferric chloride addition
                 on filter feed solids concentration9
9  Filter  operates  24  hours  per day.   See Appendix  K  for development  of
   points.
                                 51

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o
11 ««
0)
H 41
*^ jj
5 §

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     1.  At current conditions for the sludge being anaerobically digested,
         each  million gallons  of  influent  flow  generates an  additional
         0.043 ± 0.009 tons of solids.
     2.  At future  conditions  for the sludge being anaerobically digested,
         each million gallons of influent flow would generate an additional
         0.049 ± 0.009 tons of solids.

5.5.2.  Cake Dryness
     Final disposal of  digested sludge requires truck transport to a final
disposal  site.   Minimizing   the   volume  of  digested  sludge  produced,
minimizes the transporation cost.

     Figure 5-12 indicates that within the range evaluated, increasing feed
solids  concentration  produced  an  increasingly drier  filter  cake.  (Note:
Feed  solids  concentration is  the  same as  that in  the elutriation under-
flow.)   Therefore,  from  the  standpoint  of  the dewatering operation,  the
digested  sludge  should be maintained at the  highest  possible  feed solids
concentration.

5.6.  RAW SLUDGE DEWATERING OPERATIONS

5.6.1.  Solids Generation

     Currently, raw sludge  is dewatered on cloth belt type,  rotary vacuum
filters.  Sludge conditioning consists of addition of both ferric chloride
and lime, which adds substantially to the total sludge mass.

     No analysis was  conducted to  evaluate if any relationship existed for
predicting  ferric  chloride  and lime usage  as a  function of  raw sludge
characteristics, (for  example, feed  solids content,  or secondary fraction
of the total sludge mass).  Lime is currently added in excess of condition-
ing  requirements  to maintain  a high pH  to meet  sludge trenching require-
ments.   In  the near  future  when trenching is  discontinued,  lime require-
ments would  be expected  to  decrease  by  at least 50  percent,  which would
affect the amount of ferric chloride utilized.
                                  53

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     I/)
     •O •!->
     •r- C
     r- 
-------
     4.   In the future,  even if caw sludge  was  not to be trenched but  raw
         secondary  sludge  still  needed  to  be  dewatered,   each million
         gallons  of  influent  flow  would  generate  an additional 0.021 ±
         0.007  tons  of  solids  from ferric  chloride addition and 0.055 ±
         0.018 tons from lime addition.

5.6.2.  Cake Dryness

     As with  digested  sludge,  final disposal  of raw sludge  requires  truck
transport to a final disposal site.  Minimizing  the volume of raw sludge is
again important to minimizing the  transportation cost.

     Figure 5-13  indicates  that within  the  range evaluated,  increasing feed
solids  concentration produced an  increasingly drier cake.   Therefore from
the  standpoint  of the dewatering  operation,  the raw sludge  should be main-
tained  at the  highest possible feed  solids concentration.    In  the  future
when lime and  ferric  chloride additions  are reduced, it is  believed that
the  highest cake  solids  will still be  produced from the highest feed solids
concentration,  but that the cake  dryness  will not  be  as  high as currently
developed for a given  feed  solids  concentration.
           7.0
         S 5.0
       
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     Figure 5-14  indicates that decreasing  amounts  of secondary  solids  in
the mixture  produce drier dewatered cake.   This would  be expected  since
primary  solids  are  gritty and  fibrous,  which compact better  than  gelati-

nous secondary solids.
            70
       V)
       
       a
       a
       £
50
            50
            40
                      13
                    19
20
21
22
                            Raw Sludge Vacuum Filter Cake
                                 Percent Solids
             FIGURE  5-14.   The effect of secondary sludge
                  on  vacuum filtration of raw sludge13
5.7.  FINAL  SLUDGE DISPOSAL


      Currently,  several methods of  final disposal for the sludge generated
      at  the  District of Columbia's WWTF are used:

      o   Dewatered anaerobically digested  sludge  is trucked and disposed of
         on land  for approximtely §15 per wet ton.

      o   Approximately  100  wet  tons per  day  of  dewatered  raw  sludge is
         trucked   to  Beltsville at  an  approximate  trucking  cost of $30 per
         wet  ton.

      o   Between   100  to 150  wet tons  per day of dewatered  raw  sludge is
         trucked   to  MIT for  composting.   The  approximate trucking cost is
         $30  per  wet ton.
     See Appendix I for development of data points.

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          The balance of the dewatered raw sludge is trenched.   Hauling and
          disposal cost are approximately $35 per wet ton.
5.8.  SUMMARY
     The discussions of changes in solids production per MGIF caused by the
various processing  operations  are  summarized in Table 5-2.  Table 5-3 pre-
sents the various limitations noted for the processing steps.
                                   57

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        TABLE 5-2.   SUMMARY OF ADDITION  (REDUCTION)  IN  SOLIDS  PRODUCTION DUE TO VARIOUS
                    SOLIDS PROCESSING  STEPS
        Processing operation
                             Current  sludge  generation,
                                  dry  tons  (pounds)
                                 per million  gallons
                                   of  influent  flow
                               Future sludge generation
                                   dry tons (pounds)
                                 per million gallons
                                   of influent flow
00
Gravity Thickening

Dissolved air flotation
  thickening

Anaerobic digestion

Elutriation

Digested sludge dewatering
o  Ferric chloride

Raw sludge dewatering
o  Ferric chloride
0  Lime
          None


0.001          (  2      )

0.256 ± 0.042 ((512 ± 84))

          None


0.043 ± 0.009 ( 86 1 18)
                                      0.049 ± 0.015 ( 98 ± 30)
                                      0.223 ± 0.042 (446 ± 84)
          None


0.002          (  3      )

0.255 ± 0.042 ((510 ± 84))

               None


0.049 ± 0.009 ( 98 ± 18)
                              0.044 ± 0.015  ( 88 ± 30)
                              0.119 ± 0.040  (238 ± 80)

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                        TABLE 5-3.  SUMMARY OF DISTRICT OF COI.UHUIA'S UwTF SLUDGE NANAGIIMFNT
                                    PROCESS [.IMITATIONS UNDER CURRENT OPERATION
                             Process
                        Gravity thickening
                        Dissolved air  flotation
                          thickening
                                                                               Limitations
                             Average thickened primary  sludge concentration  is 7 0 i 0 5 percent

                             Average thickened primary  sludge volume per MGIF  is 1,236 ± 218  gallons

                             Average primary  solids  production  per MfilF is O.377 i 0 1)60 ton-: (754 *  120
                                  pounds)   The  average volatile  content is  71 ± 5  I percent



                             Average thickened secondary sludge concentration  is 4  I i 0 3 percent

                             Average current  thickened  secondary  sludge volume per  MGIF  is 1,644  i 239
                                  gallons;  in 1981,  it  will  increase  to 1,900  1 239  gallons

                             Average secondary solids production per  MGIF  is 0 284  i 0.034 tons
                                  (568  ± 68 pounds)  with an  average  volatile content of  65 percent;
                                  in  1981,  it will  increase  to  0 328  ± 0 034 tons  (656 t 68 pounds)
                                  with  an average volatile content of 63 9  t 2.1 percent
                         Anaerobic  digestion


                         o    Tankage
                              Approximately 65 percent of the total volume available or 1,142,458
                                   usahle cubic feet (8,545,587 usable gallons)
Ln
10
o    Heating capacity
After meeting system radiation, losses at a 95°F operating temperalnie
     available heating capacity is currently 9,800,000 RTU per hour during
     the winter and 11,100,000 RTU per hour during the summer   In  1981,
     this will increase to 12,800,000 and 14,100,000 BTU per hour,
     respectively
                              For maximum gas          Maximum feed solids coiiccnliation to digestion uoL to exceed six
                                production                  pen en t solids.

                                                       Maximum volatile mailer loading not to exceed 0 14 pounds per usable
                                                            cubic feet per d«iy
                         F.lutnalion
                         Digested sludge
                           dnwalernig
                              Digested sludge  flow  rate to sysli-ra not to exceed 490,000  gallons
                                   per day.

                              Feed sol ills coiiieiilralion to be a minimnnnf 2 7 penent

                              Maximum  percent  take  solids achievable on a consistent  basis  16 to 17
                                   percent
                         Raw sludge dew.itering
                              Maximum current  percent  lake  solids  jclnev.ihle on  a  consistent  h.isis
                                    21 to  22 percent    In  the  Fiiliue,  tins may dui rease  to  IV  to 2O
                                    pel«enl

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                                  SECTION 6
   IMPROVING SLUDGE MANAGEMENT OPERATION USING ANAEROBIC DIGESTION

     Table 6-1  summarizes  expected sludge quantities at the current  average
plant  influent flow rate  of  334 million gallons  per  day.  The purpose of
this  study  was  to  evaluate  the existing  sludge processing operation  with
the  intent  of  determining  if  a  new  two-stage,  mesophilic-thermophilic
anaerobic digestion process  could be  applied  to digest all sludge  produc-
tion  using  the  existing  equipment in conjunction  with  a minimal  capital
expenditure.   If  possible,  then  sludge  processing  and  disposal  cost at
Blue  Plains  would be  reduced by  more  than 50  percent.    In  addition,  the
scope  of  work included recommendations  to  improve the   current anaerobic
digestion  operation and   a brief  evaluation  of  the  use of  thermophilic
digestion.  This  section  of  the report will discuss these three objectives
in the  following  order:

     o   Existing  mesophilic system operation
     o   Evaluation of thermophilic system option
     o   Evaluation of mesophilic-thermophilic  system option.
 TABLE 6-1   EXPECTED PRIMARY AND SECOND-»RV SLUDGE QUANTITIES AT CURREVT 334 ,-ILLIOs GALLO.N PER DA}
          INFLUENT FLOW3

               Gallons of sludge per ia\     Pounds of sludge per das'  \oiaiile pounds sludge pe- o-\
              Minimum  Average  laximum   *!inimao  Average  'Idxuniift   'linimun  Average  Id* mi-.

 Primary sluage   340,012   412,S2i   485,63c   :il.'56   151.836   2»:,916  150,347  ITS 30;  2u7 :»C
 Secondary sludge  55-.77.   634,600   71...-20   196.392   2:9.104   2-.l.?;t  12S.691  140^22^  15- :«.-
     TOTALS     394,786 1,047.424  L.200.062   iOS.143   470.940   53J.732  276.OSS  311.03.,  3oi a::

   Da-.« calculated from Table 5-3
                                      60

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6.1.  EXISTING MESOPHILIC SYSTEM OPERATION1

     Evaluation of  an existing anaerobic digestion process  system  for the
purpose of  improving operations  begins  at the "end and  works  towards the
front."  This  is  done  to  ensure that any  individual  process constraints,
which normally affect the  output of the preceding process,  can be identi-
fied  and  incorporated  into  the  operation of  the  preceding process.   In
addition,   the  evaluation  will be  made  from the viewpoint that  all the
sludge is  to be  processed through the present system.   It is believed that
this  is  the only  impartial way to compare all  three  digestion processes.

6.1.1.  Ultimate Disposal

     Ultimate disposal of anaerobically digested sludge is on the land.  It
is  desirable  to have  the  driest cake  possible to minimize the transpor-
tation costs.

6.1.2.  Digested Sludge Vacuum Filter Operation

     The constraint  from  ultimate disposal is to produce the driest sludge
cake possible.  From the  viewpoint of dewatering management,  it is impor-
tant to minimize  chemical  additions (chemical cost and  extra solids).  In
Section 5.5,  the  data presented indicated  that  maximum cake  solids and
minimum chemical  usage occurred at the  highest  feed  solids  concentration.
The  data  in Section 5.5  also indicated that with proper operation of the
elutriation  system,   a  minimum of  five  percent feed  solids concentration
could  be  obtained  on a regular  basis.   This would  result   in  an  average
16.5 percent cake solids concentration.

Current Operation--
     There are  four  old drum vacuum filters,  each with  500  square feet of
filtering area.   In  1979  when the secondary  to  total  sludge mass ratio of
the  sludge  being digested  was between 0.4 to 0.5,  the  average calculated
yield  was  2.41 pounds  per square  foot  per  hour.  Assuming that all four
1  All  supporting calculations  for  Section 6.1  are  given in  Appendix M.
                                  61

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units were operating  at  the average yield, 115,680 pounds of anaerobically
digested  sludge  could  be  dewatared.   At  an  average  16.5   percent  cake
solids  there  would be 390.5  wet  tons of sludge per  day  needing disposal.
At  the  present,   the  limited  capacity  of these facilities  is a  major
constraint in  processing sludge  through the digestion system.   This will
change shortly with the start-up of six new and larger filters.

Future Operation—
     Sometime in early 1981, six new cloth belt vacuum  filters  will become
operable  for anaerobic  sludge dewatering and the  four existing  units will
be  abandoned.   Each new  unit will have 600 square feet  of  filtering area
and  it  is  assumed the  same  yield.  Under  these conditions the digested
sludge  dewatering  capacity  would  increase to 208,224 pounds per day.   With
these  new filters  in  operation,  dewatering capacity  will  no longer be the
rate-limiting  process.    In  fact,  elutriation  will  be  the  rate limiting
process  and  will  limit  digested solids  requiring   dewatering  to  142,000
pounds  per day (479 wet  tons to  disposal), which would mean only  four of
the six  filters would need to be operated at any one time.

     It  should be  noted  that if  all  primary and  secondary sludge could be
mesophilically digested,  10 of the 15 vacuum filters currently being used to
dewater  raw  sludge could be used to dewater digested sludge, as piping and
valving  exits for  such a  configuration.

6.1.3.   Elutriation

     The  constraints  from the dewatering operation are:   (a) to produce a
solids  concentration  (elutriation  underflow solids  concentration)  of at
least  five percent solids; and, (b) the maximum amount of sludge capable of
being  dewatered in early  1981 is  208,224 dry pounds per day.

     In  Section 5.4,  the data presented indicated that in order to achieve
a  constant five percent solids concentration in the elutriation underflow:

     o   The  flow  rate to the elutriation  system  from the digestion system
         should not exceed 490,000 gallons per day.
     o   The  solids concentration  of the influent  digested sludge stream to
         elutriation had to be a minimum of 2.7 percent.
                                  62

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     With the start-up of the new digested sludge dewatering operation, the
existing elutriation  system would  become  the next  rate-limiting process,
limiting sludge processing  to  490,000 gallons per day (40 to 55 percent of
the total sludge flow).

     Consideration   should   be   given  to   using   some  of   the   spare
dissolved air  flotation tanks  as  elutriation tanks.   Eight of  the  spare
tanks  would provide   an  additional  880,000  gallons  per day  elutriation
capacity under  the constraints specified.  This  additional  capacity would
allow  the elutriation system to process all  sludge  generated.  Appropriate
charges would enable pumping digested sludge and washwater to the flotation
tanks.

6.1.4.   Anaerobic Digestion

     The constraints from the present elutriation facilities are:

     (a)  Digested solids concentration  from  the digesters to be a minimum
          of 2.7 percent.
     (b)  The  flow rate  from  the  digestion  system  cannot  exceed 490,000
          gallons per day.
     (c)  The maximum sludge mass not to exceed 208,224 dry pounds per day.

     From the viewpoint of digestion management it is important to maximize
flow  rate,   solids  reduction,   and  gas  production within  the  constraints
stated.  In  Section  5.3,  the data  presented  indicated  the following addi-
tional operating constraints:

     (d)  Approximately  35  percent of the  existing  tank volume—1,757,856
          cubic feet  (13,148,763  gallons)—is unusable, usable tank volume
          is 1,142,606 cubic feet (8,546,693 gallons).
     (e)  Available sludge  heating  capacity after meeting system radiation
          heat  loss  requirements   is  9,800,000  BTU per  hour  during the
          winter and  11,100,000 BTU per hour during  the  summer.   In  1981,
          this  will   increase  to 12,800,000  and  14,100,000 BTU  per hour.
     (f)  Maximum  gas  production  achievable on a consistent basis required
          that:
                                  63

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          o  Maximum  feed  solids concentration to digestion  not  to exceed
             six percent solids
          o  Maximum volatile matter  loading  not  to exceed 0.14 pounds per
             usable cubic foot per day
     (g)  Existing data  indicate  that hydraulic residence times of 16 days
          present no problem over a wide range of feed combinations.  Lower
          detention times may be possible, but no operating data are avail-
          able.

     Since all  digestion tanks  are  being mixed and  no  supernatant is re-
moved,  the  flow rate  out  of the  digestion tanks  should be  approximately
equal  to the  flow  into the tanks.   The flow rate  through  the  tanks  is
governed  by  one  of three  constraints:  the  elutriation system,  sludge
heating, and vacuum filtration capacity.

     The  calculations  on  sludge  heating capabilities  indicate   that  the
existing heat  exchangers are capable of heating 683,700 gallons per day to
95°F  during  the 1980 winter and 1,549,000 gallons per  day to  95°F during
the summer of 1981.  When the new hot water boiler is put in service during
the  summer  of  1981,  the winter capacity will  increase  to 893,000 gallons
per day and 1,967,000 gallons per day during the summer.

     It  should  be  noted that in order to process all sludge through diges-
tion,  an additional 4,400,000  BTU per  hour  would be  required during the
winter months.   As  explained in Appendix G, 17,000,000 BTU per hour of new
low pressure (9 psi) steam capacity is being interconnected with the exist-
ing  sludge heat exchanger  steam boilers.  If the capacity is  available, it
may be   possible to place steam lines up to the top of the digestion tanks
and inject the  steam directly into the digesters through the roof.

     Based  on  a  minimum  16-day hydraulic detention time and 65 percent
usable digester volume,  the  flow rate would be 534,000 gallons per day.  If
the  grit problem was  solved and all  existing  tank  capacity  became avail-
able, then the  flow  rate would be 821,700 gallons per day.
                                  64

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     It  may  be  possible  to operate  this  mesophilic  system  at a  lower
hydraulic  detention time,  but  operating  data do  not  currently  exist  to
verify this.

     Both heating  capacity  and  hydraulic detention time flow rate maximiuns
are  above  the  elutriation  operation  490,000  gallon per  day  constraint.
Therefore, total raw sludge flow rate through the existing anaerobic diges-
tion  tanks  should be and is  limited to 490,000 gallons per  day under the
present circumstances.

     In  addition  to hydraulic  flow  rate  restrictions  on  the digestion
tanks, volatile matter loading requirements must also be satisfied.  Avail-
able data indicate that the system can be successfully operated at volatile
matter  loading  ratios of  0.16  to 0.17  pounds volatile  matter per usable
cubic foot  per  day, though gas production  seems  to deteriorate over 0.14.
Based  on 0.16  loading and  65  percent  usable  digester volume,  the  total
amount  of volatile solids pumped to the system would be 183,000 pounds per
day.  If  the  grit problem was solved and all existing tank capacity became
available,  then the amount would be 281,000 pounds per day.

     If  all the  existing  digesters  were utilizing  full  capacity, then at
least  four more  tanks  identical  to  the existing  12 would be  required to
meet volatile matter loading requirements.

6.1.5.  Primary -  Secondary Flow Rates To Digestion

     The  ratio  of thickened primary  to  thickened  secondary sludge volumes
is  0.65:1.  At  the current time, the  ratio being processed through diges-
tion  is 1.44:1  (288,000 gallons per  day:200,000  gallons  per day).  As was
discussed in  Section 5 of this report,  operating at high primary  sludge to
total  sludge  mass  ratios  leads to digester  stress  conditions.   It is re-
commended that  for better overall process  operation  the  primary to secon-
dary  flow rate volumes should be altered to  193,000 gallons per  day:297,000
gallons per day (0.65:1).
                                  65

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6.1.6.  Digester Gas Production

     Calculations in  Appendix M  show  that at  the 490,000  gallon  per day
sludge processing rate  under  the conditions previously discussed, more gas
will be generated than  required to meet total sludge heating requirements.
The average daily excess  gas  production is 658,000  cubic  feet per day and
will  range  from 780,000  cubic  feet per  day  during the summer  to  537,000
cubic feet per day during the winter.

6.2.  EVALUATION OF THERMOPHILIC SYSTEM OPTION2

     Review of  thermophilic anaerobic  digestion clearly indicates that the
process should be seriously considered for the least cost,  short term solu-
tion  of the  sludge processing  and disposal  problems  of  the District  of
Columbia's Wastewater Treatment Facility.   The three significant advantages
of  the process  (a)  increased  sludge  processing capability,  (b)  improved
sludge  dewatering,  and  (c)   increased  destruction  of  pathogens,  are all
pertinent to the District's situation.

     More  detailed  checks should  be made  on a number  of items prior  to
deciding  to  convert  the  existing  digesters  to   thermophilic  operation.
These  include  (a)  amount  and type of additional  sludge heating required,
(b) structural  competency  of  existing  digesters and piping at thermophilic
temperatures,   (c)  needed improvements  in  the  temperature  control  system,
(d)  equipment needed  to remove  the increased  amounts  of moisture  to  be
expected from  the  digester gas,  and (e)  how to avoid  possible  inhibition
by ammonia.
2A11  supporting calculations  for  Section  6.2  are given  in Appendix  N.
                                  66

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6.2.1.  Ulitmate Disposal

     Thermophilically  digested  sludge is  generated under  conditions  that
approach disinfection,  thus  allowing for acceptable final  disposal  to the
land.  As with  the  current mesophilic operation, it would  be important to
minimize  transportation  cost,   therefore,  the  driest  cake  possible  is
desirable.

6.2.2.  Digested Sludge Vacuum Filter Operation

     Thermophilically  digested  sludge  exhibits better  filterability  than
straight mesophilically  digested  sludge—some  times as much as double.  In
Appendix N,  the  analysis used a 25  percent  improvement  in yield resulting
from  thermophilic digestion,  a  value considered conservative. Calculations
indicate that  thermophilic digestion  of all Blue  Plains  sludge  would re-
quire  the  use  of 8  of  the 21  new vacuum  filters for  dewatering  of the
digested sludge.

     Another  advantage  would  be  the  elimination  of  the  need  for  sludge
conditioning  by  elutriation or  by  added  iron salts.   Thermophilically
digested  sludges can  be  conditioned  using a  combination of  anionic and
cationic polymers.   This  change  alone would reduce the present  amount of
solids to be disposed of by 94 pounds per million gallon of influent flow—
over  16 dry  (96 wet) tons per day.

     A  disadvantage  to  dewatering  this  sludge is  that  the  sludge  must be
cooled  to under  90°F.   Calculations in Appendix N  indicate that the exist-
ing  elutriation  tanks  might be  used  as  cooling  tanks.   Potential  odor
problems may also be  minimized by  using  the  elutriation  step because of
this  liquid  to liquid cooling.

6.2.3.  Impact of Increased Heat Requirements

     The thermophilic  digestion process  being evaluated operates at 122°F.
The existing heating capabilities at Blue Plains have been calculated to be
inadequate,  with  approximately  16.1 x 10  BTU  per  hour  additional heating
                                  67

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needed during the  winter  months.   It is suggested that direct steam injec-
tion be  considered for supplying  the additional heat  since  this  has been
used successfully  in  Los  Angeles,  Moscow, and the  Canadian  study.   Struc-
tural  competency  should be  checked  by a  structural engineer.  A  control
engineer  should  be   engaged  to  look  at the  temperature control  system
with  a  maximum  variation  of  about  ±1.5°F being permitted  (at  120°F
operation).

6.2.4.  Digestion Tanks

     Calculations indicate that the existing digestion tanks are capable of
taking the  full sludge load in the thermophilic range of operation if they
are cleaned and grit accumulation kept to a minimum.

6.2.5.  Volatile Matter Reduction and Gas Production

     Analysis indicates  that the  percentage  volatile  matter  reduction in
the  thermophilic  system would  be  about the same as the mesophilic system
but  at one  half the  time.   Calculations  in Appendix N  show  that  more gas
will be  generated  than required to meet total sludge heating requirements.
The average daily  excess  gas production  is 840,000  cubic feet per day and
will range  from 1,000,000 cubic feet per  day  during the summer to 600,000
cubic  feet per day during the winter.

6.2.6   Transition from Mesophilic to Thermophilic Operation

     It would be  desirable to make the transition from mesophilic to ther-
mophilic  operation as  rapidly as  possible.    However,  caution  should be
exercised  in making   this  transition  since  very  little  information is
available on  the  maximum  rate at which  this transition can be effected.
In Garber's early work (4), he indicated that almost six months were needed
to establish the first thermophilic unit as a separate culture.  By seeding
and  more rapid increases  in temperature, he was  able to cut  this  time
to three months.
                                  68

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     In  Garber's  later  work,  he  gave  more details  as to  the  transition
procedure.  This  time he  increased  the temperature from 96°F to  126°F at
the  rate  of 1°F  per day  while  maintaining the  load  at  approximately 0.1
pound volatile  solids  per cubic foot per day.   This was not successful and
the digester turned "sour."  He then reduced the loading to a minimum while
maintaining the temperature at  the  126°F level but observed  no  change in
condition  over  a four  month period.  The temperature  was  then  reduced to
120°F  and  over  a  three  week period,  satisfactory  digestion  commenced.

     Because of Garber' experience, personnel in Chicago were more cautious
in raising  the  temperature.   Their procedure was  to  raise  the temperature
at a rate  of 1°F per day for only  five  days  and then to  wait  for two to
three  weeks for  the  digester to  stabilize before  again  increasing the
temperature 1°F per day  until a  final temperature  of 127°F was attained.
During this period the loading on  the digester was maintained at about 0.13
pounds volatile solids  per cubic  foot per  day.   Several  surges  (one up to
2,500  mg/liter)  were  observed  during  the  transition period and  it took
approximately one year for  the digester to stabilize at consistently low
volatile acid concentrations.

     From  the above,  it can be clearly seen that there is still much to be
learned  about  the  correct  procedure  for  making   the  transition  from
mesophilic  to thermophilic digestion.  The three variables involved are (1)
rate  of  change of  temperature,   (2)  rate  of  change  of loading,  and (3)
maximum temperature to be  attained.  Garber's experience indicates that, at
least  inititally,  the maximum temperature  should be limited  to  120°F.

     In  both  the Los  Angeles and Chicago  experiences, the loading on the
digester  was  maintained  at  its   normal  value while  the  temperature was
gradually  increased.  An alternate approach would be to stop the loading to
the  digester, bring  it to the  new temperature  as rapidly as possible, and
then  gradually  increase  the loading.   Limited experience  in Atlanta  (12)
during  the summer of  1980  indicates  that  the transition  might be  accom-
plished more rapidly by following  the latter procedure.
                                  69

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6.3.  EVALUATION OF MESOPHI1IC - THERMOPHILIC SYSTEM OPTION3

     As noted  at the beginning  of  Chapter 6, the primary  purpose  of this
study was  to evaluate  the  existing sludge  processing operation with  the
intent of determining if  a  new, two-stage, mesophilic-thermophilic  anaero-
bic digestion  process  could  be  applied to  digest all sludge   production
using  existing  equipment  and  without  substantial  capital  expenditures.

     The  mesophilic-thermophilic  system  offers  all  the  advantages   of
thermophilic digestion  (disinfection,  increased  volatile  matter reduction,
and improved dewatering) and produces an essentially innocuous sludge.   In
addition,   the  system  is  simple to  operate  and  has  built in  buffering
capacity to  deal with  unusual loading  conditions.  Disadvantages are that
it  requires  heating  of  two  completely separate digestion processes  (one at
95°F, the  other at  122°F)  and  that  there is only one  operational plant,
handling 100,000 people, in the United States.  Both the mesophilic-thermo-
philic and  thermophilic processes  will require that  the  sludge  be cooled
before being dewatered.

6.3.1.  Ultimate Disposal

     The sludge from this process is extremely inert and looks very  similar
to  composted  sludge.  This  quality  should allow for  disposal  to  both pri-
vate and public lands.

6.3.2.  Digested Sludge Vacuum Filter Operation

     The mesophilic-thermophilic  process will have the  same vacuum filter
operation requirements as for the thermophilic option.
   All  supporting  calculations for  Section 6.3 are  given in  Appendix 0.
                                  70

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6.3.3.  Impact of Increased and Dual Heat Requirements

     The total sludge  heating  requirements for this process option are the
same as the previous thermophilic option.  The major difference is that the
mesophilic digestion  tanks are  to  be maintained  at 95°F  and the thermo-
philic  tanks  at 122°F.   The   suggested  method  of sludge  heating is  as
follows:

     o    For  the mesophilic  tanks,  the  existing sludge  heat exchangers
          would  be  used  and  steam  (approximately  500,000 BTU  per  hour)
          would be injected into each of the tanks.

     o    For  the thermophilic tanks,  all heating would be by direct steam
          injection (approximately 5,000,000 BTU per hour per tank).

     As  was  mentioned  earlier,  calculations  indicate that  the  increased
temperature  will have  no  significant impact  on  sludge  piping   and  wall
structural integrity.

6.3.4.  Digestion Tanks

     Calculations indicate  that even if all the  existing  tanks volume was
available, the hydraulic  detention  time under each process condition would
be  inadequate.   In  order  to process all  of  the currently generated sludge
through this process, four more digesters would be  required.

6.3.5.  Volatile Matter Reduction and Gas Production

     Limited   experience  indicates  that  a  50  percent  volatile  matter
reduction  can be  expected from  digesting the  sludge.    Calculations  in
Appendix 0 show  that more gas  will be generated than required  to meet total
sludge  heating requirements.   The  average daily  excess  gas production is
1,109,000 cubic  feet  per  day,   and will range from  1,384,000 cubic  feet per
day during the summer to 833,000 cubic feet during  the winter.
                                  71

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6.4.  SUMMARY

     Table 6-2 summarizes  the  major process considerations in implementing
either of the  three  anaerobic  digestion alternatives to  fully  process the
maximum sludge quantities given in Table 6-1.
                                   72

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TABLE 6-2.  SUMMARY OF MAJOR PROCESS CONSIDERATIONS  IN  IMPLEMENTING FULL ANAEROBIC DIGESTION  OF
            BLUE PLAIN SLUDGES
                                         Mesophilic
                                          digestion
                                        of all sludge
Additional heat requirements

  BTU's x 106
4.4
                    Thermophilic
                      digestion
                    of all sludge
16.1
              Mesophilic-thermophilic
                     digestion
                   of all sludge
Provisions for better grit removal
Digestion tanks required
yes
18
no
12
yes
16
16.1
Average daily revenues from excess
digestion gas production, dollars
Additional elutriation capacity
Vacuum filters required to be
operational
Maximum wet tons per day for disposal

1298
yes

10
1148

802
no

8
1033

1057
no

8
961

     Excess gas production sold to Naval R&D at $.95 per 1,000  cubic  feet.
     Cake solids - 16.5 percent.

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                                 SECTION 7
                              ECONOMIC IMPACT

     Municipal sludge  management is  a  challenging field.   It  is also  an
expensive one.   It is not  unusual these  days  for a  wastewater  treatment
facility to devote over fifty percent of its capital and operational  budget
to "managing" the steadily increasing amounts of wastewater sludge.

     The Blue  Plains  Wastewater Treatment  Plant is at  a  crossroads.   The
Plant's current wastewater  flow  generates almost 500,000 pounds per  day of
sludge.  Several sludge treatment and disposal options  are utilized:

     o    Dewatering  of  thickened  raw sludge  followed by  land  trenching

     o    Dewatering of thickened raw sludge followed by composting

     o    Mesophilic anaerobic digestion  of thickened  raw sludges followed
          by dewatering and application to land.

     In  the near  future,   the  land  trenching  alternative  must  be   dis-
continued.    Composting  with its attendant  problems and  land requirements
is   not  practical.   The   third   existing  disposal  scheme—mesophilic
anaerobic digestion—is a variable option.

     This section  of  the report will not answer  the  question—what  should
be   done?   What it will do is  show  how  economically  attractive  anaerobic
digestion,  in any of three process configurations, can be.
                                  74

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7.1.  OPERATIONAL COST IMPACT

     Table 7-1  presents  average  sludge  generation per million  gallons  of
influent flow for five different sludge management conditions.

CONDITION I  - This is historical  information  and represents the situation
               for the first  six  months  of 1980.  During this  time period,
               approximately  40 percent  of the sludge was  digested,  40  to
               45 percent went  to land trenching, and 15  to 20  percent to
               composting.

CONDITION II - This is a  projection of what the  situation  will  be in late
               1981  based  on  completion  of  current  on-going  process
               changes.   At  this  time,   approximately  40  percent of  the
               sludge will be digested, the rest will be composted.

CONDITION III- This is a  projection of what the  situation  would be if all
               the  sludge  was  processed  through  a mesophilic  anaerobic
               digestion system.

CONDITION IV - This is a  projection of what the  situation  would be if all
               the  sludge was processed  through a  thermophilic anaerobic
               digestion system.

CONDITION V -  This is a  projection of what the  situation  would be if all
               the  sludge  was  processed  through a  proposed  new process
               modification,  mesophilic-thermophilic anaerobic  digestion.

     The  economic impact  of the numbers  shown in  Table  7-1  are better
illustrated in Figures 7-1 and 7-2.

     In Figure  7-1  a  comparison is made of  the average cost for chemicals
and final disposal per million gallons of influent flow for the five condi-
tions given  in  Table  7-1.  The 40  percent  reduction in cost shown between
the existing 1980 and projected 1981 plan is solely due to eliminating land
trenching  and  replacing  it  with  composting.   The  significant  cost reduc-
tions shown  between  the  projected 1981 plan and the three anaerobic diges-
                                  75

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                                     TABLE 7-1.   SUMMARY OF  AVERAGE  SLUDGE GENERATION PER MILLION GALLONS OF INFLUENT FLOW
-vl
cr>
Based on
January to June 1980
Based on
completion of
current
on-going changes
Dlanning-iall 1981
Sludge Sludge
generated Cost generated Cost
per per per per
MGIF,0 MGIF,

Primary sludge
Secondary sludge
Gravity thickening
Dissolved air flotation
thickening
Anaerobic digestion
Eliilri.ition
pounds
696
568
0

2
dollars




3.83b
MGIF, MGIF,
pounds dollars
696
656
0

3
(512) (5.84)L (510)
0
De.walcring digested sludge
0 Iron salt
0 Polymer
Dewalered raw sludge
0 Iron salt
0 Lime
Disposal digested sludge
Disposal raw sludge
86


98
446


a MGIF = million gallons of
Polymer cost
C Based on 12
1 Based on $0.
Basprl on an

averaged $13.
cubic feet per
0685 per pound
average cost


A
5.B9d


6.71
37. 86*
38. IB1
147. 328
influent flow.
0

98


88
238







4.42
(5.81)


6.71


6.03
20.26
42.86
65.36

Based on
mesophil ic-
Based on Based on tliermopliil ir
mesophilic digestion thermophi lie digestion digestion
of all sludge of all sludge of all sludge
Sludge Sludge
generated Cost generated
per per per
MGIF, MGIF,
pounds dollars
696
656
0

3 4.42
(510) (5.81)
0

98 6.71




42.86


MGIF,
pounds
696
656
0

3
(510)
0


2






Sludge
Cost generated
per per
MGIF, MGIF,
dollars pounds
696
656
0

4.42 1
(5.81) (572)
0


8.00 2



38.50


Cost
per
MGIF,
dollars




4.42
(6.52)



8.00



35.54


50 per ton of dry feed solids.
pound volatile
of this sludge
of $0.0849 per

matter reduced
produced.
pound of this

and $0.95 per 1000 cubic feet.

sludge


produced.










                  8  Based on a $35 per wet ton composite cost (some composting, some trenching).

                     Based on a $24 per wet ton composting cost.

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              118.35
      100 -
       80 -
5 1
a 2
2 U.
< =
SI
s-
— 1/1
II
§ ri
UJ
o oe
5 £
60 i
       40 -
       20 -
                                                                 41.44
            EXISTING
              1980
                  CURRENT
                    PLAN
                    1981
   ALL
HESOPHIL1C
  ALL           ALL
THERMOPHIUC  HESOPHILIC-THERMOPHILIC
         Figure 7-1.  Average  cost  for chemicals and final disposal
                per million  gallons of influent flow for the
                     five conditions given in table 7-1.
 tion alternatives  are due to  two  items.   First, in digestion approximately
 37 to 40  percent of  the  raw solids generated  are destroyed so that diges-
 tion of  all  the  sludge will  significantly reduce the mass  of solids  that
 requires  disposal.   Secondly, the  dewatering operation for digested sludge
 at Blue Plains does not require  lime for conditioning:  in the 1981 projec-
 tion, the raw sludge  dewatering  operation will require a significant amount
 of lime,  which will  increase solids by 238 pounds per  million gallons  of
 influent  flow.    The  higher  unit  cost  of mesophilic  over the  other  two
 digestion  alternatives  is mainly  because the  other  two  digestion alterna-
 tives do  not require iron salts in the dewatering operation (equivalent  to
 96  pounds   of   solids  per   million  gallons  of  influent  flow).  Meso-
 thermophilic  digestion  has a  lower overall cost than thermophilic digestion
 because of a  higher volatile  matter reduction.
                                    77

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               1173
                            1129
      1100
      1000 •
I I
§
  I
                                                                  785
               1980
 RENT
PLAN 1981
  ALL
MESOPHILIC
  ALL     MESOPHUIC-THERMOPHILIC
THERMOPH1LIC      DIGESTION
       Figure 7-2.  Average wet tons of sludge produced per  day  for
                   the  five conditions given in table 7-1.
     Figure  7-2  shows  the  difference  in wet  tons  generated  by the  five
different  conditions given in  Table 7-1.  The  large reduction  in wet tons
is due to  two  items.   First,  in the digestion alternatives  approximately 37
to 40  percent of the  raw solids are destroyed  (converted into  methane gas,
carbon  dioxide,  and  water);   secondly,   significantly  less  chemicals  are
required in  the  dewatering operations.   The difference in  wet  tons  between
the  three digestion  alternatives  is  due  to  lower chemical  conditioning
requirements  for the  thermophilic  and meso-thermophilic  options,  and the
higher volatile  matter  reduction  achieved by the meso-thermophilic  option.
     For  every  million  gallons of  flow  into  the  plant,  the  raw  sludge
     dewatering  option must dispose of 738 more  pounds  of  solids.   This is
     equivalent  to  3432 wet pounds or 1.72 wet tons.
                                   78

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     Of  the  three anaerobic  digestion alternatives,  the  mesophilic-ther-
mophilic option is shown to have the lowest operational cost.  In addition,
of the three digestion alternatives only the mesophilic-thermophilic option
produces a  sludge that  is  extremely inert, with  essentially no pathogens
and little to  no  odor potential.  These benefits should allow the District
of Columbia  to develop  a  strong  marketing  campaign to allow disposal of
dewatered digested sludge on public and private lands.

7.2.   CAPITAL COST IMPACT

     In  order  for any  of  the  three  anaerobic systems  to  process  all the
sludge currently  being  generated at Blue Plains, some capital expenditures
would be required to  expand  and  upgrade  existing equipment.   A detailed
cost  analysis  was  not  performed.  However,  the following  unit operation
analysis indicates  that the capital improvement cost would be the greatest
for the  mesophilic  system  and the  least  for  the thermophilic system.  The
mesophilic-thermophilic system would lie between the two.

7.2.1.   Improvements in Grit Removal

     The analyses  in Sections 4 and 5 indicated that 1.4 to 2.0 cubic feet
of grit  per million gallons  of  influent  flow  is  contained in the sludge
stream.   Grit  is  inert, but it  reduces  the anaerobic digestion  process
capacity by  occupying  tank  volume.  The  calculations  of   tank  volume (in
Section  6)   assume  minimal grit   accumulation,  but at the  current time
approximately  25  to 30 percent  of  the  existing  digestion tank capacity
is occupied  by grit.  The best options are to increase grit removal before
the  influent flow  reaches  the digesters  or  to  increase digestor capacity
to  allow  for  accumulation.   The  capital expenditures  for  grit  removal
equipment are approximately equal  for all digestion processes.

     The cost  for the necessary grit  removal  equipment  has not been  esti-
mated  in this study,  but  it  should  be approximately equal for all  three
digestion  options.   However,  if  grit removal  is  not  provided,  then the
digestion  capacity would have  to  be  increased  by about  25% to allow for
accumulation.
                                   79

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7.2.2.   Digestion Tanks

     Assuming that grit  is  removed upstream of the digestors, the need for
additional digestion tanks  to  handle the entire sludge  stream  is approxi-
mately  six  for  mesophilic,  four for the raesophilic-thermophilic,  and none
for  the  thermophilic  process.   A preliminary   analysis  indicated  that
operating  the digesters  at the thermophilic  temperature would  not  cause
structural problems.

7.2.3.  Sludge Heating Requirements

     All  three  processes  would   require  additional  heating  capacity  to
handle  the  entire sludge stream.   The  mesophilic option may be satisfied
by  existing  in-house  heat generation.  The other two  options  would require
auxiliary  steam  generating  equipment  to  allow   direct steam  injection
into each digestion tank  operating at thermophilic  temperatures.

7.2.4.  Improvements in Gas Piping

     The  existing  gas collection  piping  and  safety devices  need  to  be
replaced  or  upgraded  for  any of  the anaerobic  digestion  processes. The
piping  shows corrosion  damage  in places,  and some  of  the gas  protection
equipment  is  not  functional.

7.2.5.  Improvements in  Mixing

     The  existing digestor mixing is  believed  to  be deficient for several
reasons.   First,  the  majority of  the  existing  gas-mixing  equipment was
originally installed in  1960 on a  temporary  basis  and was not designed as  a
complete  tank mixing system.   Secondly,  the  existing  internal heating coils
allow   build  up  of  grit  and   inert material  not  capable  of being  mixed.
Improvements in grit  removal,  removal  of internal  heating coils,  and  an up-
                                   80

-------
grade  of  the  gas-mixing  system to  current standards would  significantly
improve the  mixing  operation and,  hence,  improve  the  tank  utilization.

7.2.6.  Elutriation Capacity

     The mesophilic system would require a 200 percent increase in elutria-
tion tank capacity.  The mesophilic-thermophilic and thermophilic processes
both could not require elutriation.

7.3.  SUMMARIZED ECONOMIC IMPACT

     The operating  cost analysis  has developed a sludge handling unit cost
for the five options considered in this study.  The developed costs are not
necessarily "accurate"  (in  the sense that all minor cost factors have been
included), but they are consistent and reflect the comparative costs of the
options.  The  unit  costs  are presented in Table 7-2, which also includes a
comparative presentation of capital costs for the five options.

     A  qualitative  analysis  of the disposal factors  also is  summarized in
Table  7-2.  This  analysis  is reflected to some extent in the disposal cost
analysis for the current and projected 1981 options, in that disposal costs
of undigested  sludge are included.  The anaerobic digestion options for the
entire  sludge  stream will  result in a  reduced  disposal  cost.   The charac-
teristics of  the sludge  product as indicated  in the  disposal factors in
Table 7-2 will determine the eventual disposal cost.
                                  81

-------
     TABLE 7-2.  SUMMARY OF OPERATING AND CAPITAL COST REQUIREMENTS FOR SLUDGE HANDLING OPTIONS
00
to

Option Operating cost Capital cost items0

1.


2.

3.

4.


5.

($/MGIF) Grit removal Digestion tanks
Current 118.85 NA NA
(January to
June 1980)
Projected 72.12 NA NA
1981
Mesopliilic, 48.18 Yes, even Yes
all sludge
Mesophilie- 41.44 Yes, even Yes
thermopliilic,
all sludge
Thermophilic, 45.41 No No
all sludge
Sludge heating Gas piping Mixing Elutriation
NA NA NA NA


NA NA NA NA

Yes Yes Yes Yes

Yes, + Yes Yes No


Yes, + Yes Yes No

       Current and projected options do not include the digestion of all sludge generated.

      3
       MGIF = million gallons of influent flow.


       Yes = a capital expenditure is required or recommended to handle the entire sludge shown.


       No = existing equipment is adequate or not required to treat the entire sludge stream


       NA = not applicable to the evaluation.


       Even = approximately the same capital would be required


       Number = the number of digestors required.


       + = a significantly greater capital expense than for the other options is expected.

-------
                                REFERENCES
U.S.  EPA  1979.  Process  design  manual:  sludge  treatment  and  disposal.
EPA-625/1-79-001.  U.S. Environmental  Protection Agency,  Cincinnati, Ohio.
                                   83

-------
                                  APPENDIX A

                             JANUARY TO JUNE 1980
                     SUMMARY OF AVERAGE MONTHLY OPERATING
               DATA ON BLUE PLAINS SLUDGE MANAGEMENT OPERATIONS
The data  shown in  Appendix  A were  obtained from operating  log  sheets and
from conversations  held  with Mr.  Ed Jones, Mr.  Steve  Bennett,  and Mr. Walt
Baily.

The purpose of this analysis was to perform solids mass balances around each
unit process and  to segregate the type of solids—primary, waste activated,
lime,  ferric chloride—involved in each situation.  This is possible at Blue
Plains  since  extensive  process   stream  testing  is  conducted on  a  regular
basis.   Analysis  of six  months  of operating data  indicates  the  following:

    1.    On a total solids basis,  mass balance calculations around each unit
         process are generally within 5 to 10 percent of closing.

    2.    Existing  flow  meters  should  be maintained  and  calibrated  on  a
         regular basis.   Many  of  the existing flow meters  have  been out of
         service  for  some time.   Flow calculations are  approximated using
         either pump strokes, pump curves, or changes in tank liquid levels.
         This type of hydraulic data makes for difficult process control and
         is believed to be responsible for some of the difficulty in closing
         the mass balances around each process.

    3.    Numerous  duplication of  data on various  log sheets  is  currently
         required.  In many cases  different data are  indicated  for situa-
         tions  in  which  the  data should be  identical.   It  is  recommended
         that a review of all existing log sheets be conducted,  that they be
         consolidated  where  possible,  and  that  better quality  control  be
         maintained over the logging of data.

    4.    Some  of  the   solids  analyses  are done  by total solids and  some  by
         total  suspended  solids.   Since total solids  is equivalent  to dis-
         solved solids plus  suspended solids, a  difficulty exists in doing
         solids mass balances.

         This difficulty arises for several reasons:

         o    Dissolved  solids do not concentrate, but do  increase  in con-
              centration  as  the   sludge  moves through the  sludge treatment
              process.

         o    Analyses  of  thickened  or  dewatered  sludges  show that the
              amount of dissolved solids is almost insignificant compared to
              the suspended solids.

                                 A-l

-------
Analyses of  clarified liquors,  filtrates,  or  elutriates show
that suspended  solids  normally comprise only 15 to 50 percent
of the  total  solids,  while dissolved solids normally comprise
the majority.
                    A-2

-------
TABLE A-l.    SUMMARY OF  RECENT AVERAGE MONTHLY HISTORICAL DATA ON  RAW  SLUDGE QUANTITIES
Year

1980
Primary sludge
Total dry sol ids


r Month
) Jan
Fob
Mar
Api
May
Jllll

Vo 1 ume ,
MGD
4 2
3.8
3 7
4.4
4 5
3 0


Percent
0.55
0.72
0.61
0 78
0 62
0.92

Tons .per
day
98
116
96
146
119
117
Total dry
volatile sol ids

Percent
volati le
77
81
78
78
79
85

Tons per
day
75
94
75
114
94
99

Volume,
MOD
2.7
3 1
2.9
3.4
2.8
2.7
Waste activated
Total dry sol idsc
Percent
dry
sol ids
0.91
0.72
0.67
0.73
0.68
0.88

Tons per
day
103
94
82
104
80
101
sludge
Total
volatile

PC remit
volatile
66
68
66
66
62
64

dry
sol ids

Tons per
djy
68
63
r,4
69
65
65
   Data obtained from Mr  Walt Rally and Blue Plains operating records.

   There .ire strong indications that significant amounts of grit are  in  the primary  sludge.   Detailed analysis ol  volume w.is
     not made, but currently is estimated at  300 to 350 cubic feet  per day or  approximately  30,000 to 35,000 pounds per day

   Iron is added for phosphorus removal.   The iron - phosphate sludge contribution  is  between It  to 15.5  percent of the total
     mass

   Density of this material  is 8 5 pounds per gallon

   Density of this material  is 8.39 pounds per gallon.

-------
TABLE A-2.   SUMMARY  OF  RECENT AVERAGE  MONTHLY DATA ON GRAVITY  Til ICKEN1NO"
Total gravity thickener inflow
Tul.il dry solids0

Year
I'J80







HoiiLh
.Lin
Fell
Mai
A,..
May
Jim
.liil
Vo 1 time ,
MOD
16 0
15. Q
15.7
15 7
15.3
16.0
16.9

mg/l
1600
1915
1600
2350
I960
184-i

Tons
per day
107
127
105
154
125
123

Total
volatile
Percent
volatile
74. /
67 4
69.4
66 5
72.0
69.7
67.6
dry
solids
Tons
per day
74 7
82.2
70.8
99.1
83.5
82.8

Gravity thickener under (low
To La I dry sol ids
Vo 1 nme .
HGI)
328
437
.165
.521
.135
370


Percent
7.3
6.7
6.7
6 9
6 4
7.9

'Inns .
l>er_da/ 	
105
129
IOR
158
120
129

Tnt a 1
vnl.il I In
Pcrrriil
volatile
79
75
70
65
66
71

dry
sol ior ilny
74
97
7f.
101
70
92
. .
   Data obtained from Mr. Steve Bennett and Blue Plains operating  data.  Data  jre  not  avail.ilile on gravity thickener  ovetflow

   Tnl.il gravity lliirkrncr inflow consiits of flow Irom primary  danders,  dilution water, approximately 50 percent  ol  UIK eliitrialiou tank  ovcillnw

C  Existing d.ila arc* tnnsidered lo be incorrect because they  indicate  a  sludge oass  greater th.in the output being  disposed ol   At this Unit,
     tin: niiinlicrs hliown liir tons per day arc based on primary  sludge production (Table-  A-1) * the suspended solids  LontrilmLion of
     the dilution w.-iter  (0.17 to  1 0 tons per day) + one half of the total  solids  in the elutriate overflow (Table A-5)
                                  •
   Density of this material is 8.B pounds per gallon.

-------
TABLE A-3.   SUMMARY OF RECENT AVERAGE  MONTHLY DATA OH  DISSOLVED AIR FLOTATION  THICKENING
Total dissolved air notation


Year
i?8o







Mould
Jan

Nar
A|ir
H.iy
Jim

Volume,
MCI)
2 7
3 1
2 9
3 4
2 8
2.7
Toldl dry
PcrrenL
dry solids
0 91
0 72
0 70
0.71
0 68
0.89
sol ids
Tons
per day
101
91
85
103
79
100
Lliickc-iicr inflow
Total
volatile
Pcrn-iil
vo 1 a 1 1 1 e
66.0
67 7
65 9
66.0
62 0
64.0
dry
sol ids
Tons
per day
6B
63
56
f.R
49
64

Volume,
MCI)
0 665
0.5/0
0.496
0.582
0.448
0.508
Thickened m.ilciial
Total dry
Percj-iil
diy solids
3.7
3.9
4.1
4.2
4 2
4.7
solids
Tons
per day
102 7
92 7
84.8
101 9
78 4

-------
TABLE A-3.
              SUMMARY  OF RECENT AVERAGE MONTHLY DMA  OH DISSOLVED AIR FLOTATION  THICKENING0  (continued)
	

Subnatant Flow

Total dry
suspended solids,

Year Month
1080 Jan
Feb
Hat
Apr
May
Jun
Volume,
HOD
Z 6
2.9
2.2
7 7
3.1
S.5

EB/I
28
21
21
37
'•4
17
Tons
per day
0.3
0.3
0.3
1.2
0.6
0.4
                      Data obtained from Mr. Steve Bennett and Blue Plains  operating data.

-------
 TABLE A-4.   SUMMARY OF RECENT AVERAGE MONTHLY DATA ON  ANAEROBIC DIGESTION
 Year




  1979
  1980
Primary slmlee


Ion th
J a n
Fell
Mar
Apr
Hay
Inn
Jill
A"g
Sept
OiL
Nov
lire
.Ian
Full
Mnr
Apr
May
.Inn

Vi> 1 nine ,
MCI)
0.242
0. 188
0 . 284
0 301
0. 199
0 225
0 194
0.216
0 177
0 U>6
0 177
0 195
0.228
0.227
0.228
0. 196
0 222
0.169
Tula I dry
IVrtenl
dry solids
8 0
8 6
8 1
7.3
9.8
8 8
7 3
7 8
7 
69.2
66 9
63.8
63.7
66 3
,lry
sol nls 	
Tons
JKT d.iy
29 4
2r> 0
IS 4
20 4
IS 4
28 i
28 8
»2 1
17 1
35 1
_ _ — —
18 5
14 0
il 1
1J.S
10 6
27 0
41 1
Data olitJincil  from Mr  Steve Bennett  and Blue Plains operating data.
                                                                                                                      (continued)

-------
      TABLE  A-4.   SUMMARY OF  RKCENT AVERAGE MONTHLY DATA ON  ANAEROBIC DIGESTION3 (continued)
     Year_

     1970
f
CO
      1980
Hniith_

 .Lin
 Krl>
 M.II
 Apr
 H.iy
 Jim
 In I
 AiiR
 Sopl
 Oct.
 Nov
 l)er
 liin
 Fel>
 Mar
 Ap.
 May
 Jim
Coinliincil digester input


Vn 1 nine ,
MGD
0 416
0 158
0.384
0 461
0.442
0 431
0 42.)
0 455
0.460
0.441
0.357
0.364
0 503
0 521
0.465
0.464
0 485

Total
Percent
diy solids
7.1
7.0
7.6
6.3
7 4
7 1
6.0
6.4
5.9
5 6
5.4
5.9
5.2
5 2
5.3
5.2
5.8

dry solids
'Inns
per il.iy
123.5
104.3
121.6
122.0
116.0
127.3
105. R
121. 1
113.6
102 6
79.7
90.4
108.3
113.8
103.5
101 6
117.7
Total
volatile
IVrcrnL
volatile
67 6
71 6
71.7
73.0
69.1
67 9
64. 1
64 2
62.1
65. J
70.5
75.8
72.6
68. 4
65.2
65.1
68.5
dry
solids
Tuns
per day
83.5
74 7
87.2
89 1
94.0
86.4
6/ 8
77 7
70.6
67.0
56.2
68.5
78.7
77.8
67.5
66.2
80.6
W.isLc activiitril
sludge
I'tirrcnl
by weight
35
35
19
25
40
35
44
42
52
51
15
23
41
44
46
42
51
t ruction
Price-ill
liy vii 1 Hint:
42
48
26
15
55
48
54
51
62
(>t
45
17
r>r>
56
58
52
f>5
        Dal.i nhi nineil  From Mr  Steve lleimrlt jnd Blue Plains operating data
                                                                                                                                                    (cniiLiiiucil)

-------
TABLE A-4.   SUMMARY  OF RECENT AVERAGE  MONTHLY DATA ON  ANAEROBIC DIGESTION   (continued)
Digested sLmlge



Year Mon III
1979 )7
0 364
0 S03
O.S2I
0 465
0 464
0 485

Total dry


Percent
dry solids
3.3
3 3
3.4
2 9
3 2
3.8
3.8
3.6
3 9
3.6
3.6
2 7
2 3
2.6
2.6
2.8
3.1
3.1
3.1
sol ids


Tons
per day
57.2
49.3
54 4
56.0
59.0
68 3
67.0
68.3
74.8
66 2
47.7
40.2
34.9
54.5
56 5
54 3
60.0
62.5

Total
volali le


Percent
volatile
54 2
54.6
54.2
55.7
55 5
53.3
55.3
54.3
52.3
53.8
56 5
56.6
57.6
55.3
55 1
56.1
55.5
54.8
55.3
dry
solids


Tons
per day
31.0
26.9
29.5
11.2
32.7
36.4
37.1
37 1
39 1
35 6
27.0
22.7
20 1
30 2
31 1
30.5
33.3
34.2




Togo.."
95
96
94
95
96
95
95
95
94
95
95
94
92
91
93
90
9J
95
93


Volatile
acids,
mg/l
168
233
204
158
172
260
207
183
176
166
180
225
142
126
284
338
371
323
329



Alk.C
nig/1
5629
6229
5')56
5313
5868
6488
657H
5742
5238
5209
5099
7272
6784
7624
8403
8914
8328
8366
8140



Nil -N
rag/1
1107
1451
1428
1374
1400
1568
1302













Gns j
produced ,'
cubic feet
xlOOO
912
846
834
999
12)6
1205
R86
749
797
849
808
879
1061
1246
1123
888
906
994
928
Digester gas


co2
rontent ,
percent
32.7
31 4
34.4
31 8
32 6
32.6
12.8
29. 1
33 0
31.9
34.9
35.0
35.5
34.3
35 I
34 6
34.2
34.9
34.8

lias prodiHcd
per pound of
void I lie snl ids
reduced
8 7
8.8
7 2
8 6
9.9
12 (I
14 4
9 I
12 6
11 5
	
9 6
1 1 0
12 8
12 0
12 0
13 8
10.7

Data obtained from Sieve Bennett and  Blue (Mains operating data.




Tempornture measured on recycle sludge before entering heat exchanger.




AIK - alkalinity.   Alkalinity is measured on entire solids mass rather than on sulinatant  of  sludge.




Blue Plains is in the process of signing » contract with Naval Research to sell all  excess digester  gas  for  $0.95 per  1000  rnliir  Icet.

-------
TABI.K A-5.    SUMMARY OF  RECENT  AVERAGE MONTHLY HISTORICAL DATA ON ELUTRIATION TANK OPERATIONS
Anacrnhic ill (jesters
ToLal dry solids
Year Nonlli
I'JHO J.in
Kcl)
Mm
Apr
May
Illll
Dnld oli I aincd from
A|i|>rox mini <:!y hall
!*• C Data indicate LliaL
Vo 1 lino ,
NCI)
0.397
0.509
o 509
0.666
0.448
0 492
Percent
dry solids
2.6
2.4
2.4
2 7
3 0
3 3
Tons
per 
-------
TABLE A-5.   SUMMARY  OF RECENT AVERAGE  MONTHLY HISTORICAL DATA ON  ELUTRIAT10N  TANK  OPERATIONS0  (continued)
Elutriation underflow Lo dewatoring
Elutriation overflow
Total diy solids

Year
19 BO





" Data
b TI..I,

HonLh
Jan
Krl>
Mar
A|>r
Nay
Jun
obtained from Mr.

Volume,
MGU
0.227
0 279
0.309
0 187
0 207
0.241
Steve Bennett and
nrmallv in fsunnnfipl
Percent
dry solids
5.4
4.8
3 6
5.5
5.4
5.2
Blue Plains operating
1 to return to nnmarv
Tons d
per day
54
59
49
46
52
55
records.
treatment bv eravitv
Volume,
MGD
2 44
2.57
2.52
2.56
2.41
2.46

' flow. At the preset
h
Total dry
sol ids

n-B/1
1800
I'J74
1652
1517
12f>4
1208

it tune, only par
Tons
per day
IR 3
21 1
17 4
16 2
12.6
12.4

t of
     the overflow flows  by  gravity to primary treatment   The other part  is  pumped to gravity thickening.  Theie are no flow meters
     on cither line,  and it is not possible to tell how much flow is going to gravity thickening or to primary treatment.

c  Suspended solids for  the same  time period in mg/1 were:  Jan-295; Feb-874; Mar-1048; Apr-684; May-479; Jnne-559.

   Density of this material is 8  85 pounds per gallon.

-------
     TABLF. A-6.   SUMMARY  OF RECENT AVERAGE  MONTHLY DATA ON  RAW SLUDGE  DEUATEKING°
M





Primary sludge
From gravity thickener




Waste activated sludge from 1,
dissolved air flotation thickeners a
Total dry solids
Year Month
1980 Inn
rcl>
Mar
Apr
May
Jim
a
b
c

-------
       TABLE  A-6.   SUMMARY  OF RECENT AVERAGE MONTHLY  DATA  ON RAW SLUDGE DBWATERJNG   (continued)

Uewatered raw sludge off vacuum filler



Yeor
1979




1980








Non Hi
Aug
Sept
Oct
Nov
Dec
Jan
Mar
Apr
May
.Inn
Jill


Wei ions
per day





948
490
910
635
695


Total dry
Pei cenl
dry solids
19 6
20 7
19.9
	
17.6
17.2
21.6
21.1
21 1
22.6
22 1

sol ids
Tons .
, d
per day





163
106
192
134
157

Tolal
volali Ic
Percent
volatile
44 6
43.3
44 8
	
48. 1
46.2
41.0
40.9
40 2
42 1
41 4
vacuum filler fillralc
dry
solids Total dry solids
Tons Volumu, Tons ,
per day MOD mg/1 per day





75 0.499
44 	
78 0.574
54 	
66 0 440

washwalui

Tolal diy solids
Volume-, 'Ions
MGD nig/I per day











 I    _ _ .-...—	...--. __.

1-1   a
l*J     Da la obtained from Mr. Steve Bennett and Blue Plains operating data.



       Data base  is extremely limited.



       Wasliwater  volume  is  significant but no data are taken on this stream   Suspended solids are not believed to be significant



       See  footnote c  on Table A-8.



       Analysis based  on several samples indicated that total solids were about 500 ing/1 and that suspended solids about 250 mg/l.



       llascd  on limited  data, it is estimated that the total solids in the filtiate average 2 tons per day and can be considered  insignificant.

-------
TABLE A-7.   SUMMARY  OF RECKNT AVERAGE  MONTHLY DATA OM  DIGESTED  SLUDGE  DBUATERING*

From clutnation


Vn 1 nine ,
Year Month MCI)
Total (ley
Percent
Dry Solids
solids,
Tons
per day
Dry ferric
chloride added

Tons
per day
I'm Ang
Sept
On
Nov

Her
1980 .Ian 0 227






a
b
c
d
c
Fch 0.279
Mar 0 309
Apr 0.187
May 0 207
.Inn 0.241
Jill
Data obtained from
Data indicate that

5 4
It 8
3 6
5.5
5.4
5.2


54
59
49
46
52
55

Mr. Steve Bennett and
solids contributed by
Density of tins material is 8.83
Sunnier of 1980 Blue Plains pays


pounds
$0.0825


10.2
11.9
10.8
10.0
10.7
10.3

Blue Plains
filtrate are
per gallon.
per pound of


Dewatered digested sludge to disposal

Total
to
dry solids
disposal
Total dry
volatile solids
To disposal
Vacuum liltei filtrate
Total diy
so 1 ids
Dollars. Wet tons Percent Tons Perrent Tons Volume, _ Tons
per day per day dry solids per day volatile per day MGD UIR/ 1 per day


740
864
784
726
777
748

operating data
insignificant

368
361
345
290
289
293
395
337
302
314
328
294
.
compa red

17.8
17.9
16.3
16 1
16.0
15 8
15.6
16.7
16.8
16.9
16.8

65.5
64.6
56.2
46.5
49.9
62.4
52.6
50.4
52.7
55.4
49.4

to total mass of

iron (Fe), which comprises 44




percent of

49.5 32
47 . 7 30
49 6 27
54.3 25
56.3 26
57.2 35
54.1 28
51.6 26
51.9 27
52.5 29
53.8 26

solids included.

.4
.8
9
0
4
.7
.4
.0
.4
.1
.6





0.136
0 205 9600 8.2
0.192 8800 7.0
0.130 12000 6.5
0.144 9200 5.5
0.175 8200 6 0




ferric chloride (Fe CI2).



   Suspended solids  [or  this same time period in ng/1 were:   Jan-185;  Feb-66;  Mar-110;  Apr-103;  June-270.

-------
    TABLE  A-8.   SUMMARY OF  RECENT AVERAGE  MONTHLY HISTORICAL DATA ON  RAW  SLUDGE  DISPOSAL
\Jl
Break down of total dry solids to disposal



Year
1980









Month
Jan
Feb
Mar
Apr
Hay
Jim
Jill
Raw sludge
hauled from
plant. D'c
Wet tons
per day
1153
1047
758
1004
862
762
716
Trucking and ,
disposal cost,
Dollars
per day
41,175
37,200
26,362
35,587
30,262
26,512
24,787
Total dry solids,
to disposal ,
Percent
dry solids
as trucked6
14.1
14.5
14.0
19.1
15.5
20.6


Tons
per day
163
152
106
192
134
157

Raw
sludge
solids.
tons
per day
112
106
72
150
93
104

From
lime addition
tons ,
per day
41
36
28
36
35
36

From
ferric chloride addition
tons
per day
11
10
6
6
6
17

Data obtained from Mr.  Ed Jones,  Mr.  Steve  Bennett, and  Blue Plains operating records.

At the time of this report - Sept.  1980  - dewatered raw  sludge was being disposed of as follows:

  o  Approximately 100  wet tons per day  to  Beltsville  at an approximate trucking cost of $30/wet ton.
  o  Between ISO to 200 wet tons  per  day to HT1  for composting at an approximate trucking cost of $30/wet ton.  Contract on a
       yeai to year basis.  Could possibly  go up to 400  wet tons per 
-------
TAIII.E A-9   SUMMARY OF KKCKNT AVF.RAKK MUNTII1.Y HISTORICAL DATA ON I)IfiKSTKI) SI.UUGK DISPOSAL
                                                             Total dry sol ids
                                                                lo disposal
Break down of_ |-oLJlJ_|lr.y sojids


Year
1979




1980








HonLli
Ang
Sept
Oct
Nov
Dec
Jan
K.-l.
Mar
A|ir
Mjy
Jim
.liil
Deviate red
digested
slmlgp,
we I Lous
|ici day
168
361
145
290
28V
291
395
337
302
116
128
294
Triu king and .
disposal cost,
do 1 1 a rs
per 
4.395
5,925
5,055
4,510
4,710
4,920
4,410
pert nil
dry solids
17.8
17.9 '
16.3
	
16 1
16 0
15 8
15 6
16.7
16 8
16.9
16 8
tons
pi>r day
65.5
64.6
56 2
	
46.5
49 9
62.4
52.6
50.4
52.7
55.4
49.4
Digested Sol i
-------
                                APPENDIX B

        ANALYSIS OF AVERAGE PRIMARY AND SECONDARY SLUDGE PRODUCTION
                   PER MILLION GALLONS OF INFLUENT FLOW
B.I. PRIMARY SLUDGE
                  TABLE B-l.  ANALYSIS OF AVERAGE SLUDGE
             PRODUCTION PER MILLION GALLONS OF INFLUENT FLOW3
                        (January through June 1980)
                          Primary sludge.                Primary sludge
                            production,  'C            volatile solids,
     Month	T/MGIF0	percent
January
February
March
April
May
June
Average
Standard deviation
98/331
116/325
96/345
146/332
119/327
117/330


= 0.296
= 0.357
= 0.278
= 0.440
= 0.364
= 0.355
0.348
0.057
77
81
78
78
79
85
79.7
2.9
     Average dry  ton of  volatile primary  sludge  production per  MGIF is:

            (0.348 ± 0.057) T/MGIF (0.797 ± 0.029) percent volatile

          = (0.348)(0.797) ±   (0.797) (0.057)  + (0.348)2(0.029)2

          = 0.277 ± 0.047 VT/MGIF
     All data taken from Appendix A, Table A-l.

     Sludge  as  withdrawn  from  the  primary  clarifiers  and pumped  to the
     gravity thickeners.
Q
     It is  estimated  that  grit equal to  1.5  to 2.0 cubic feet per million
     gallons of influent flow at 100 pounds per cubic foot is included with
     the primary sludge.
                                    B-l

-------
     MGIF    = million gallons influent flow.
     T/NGIF  = dry tons of solids per million gallons influent flow.
     VT/MGIF = dry  tons  of  volatile  solids  per million  gallons  influent
               flow.

B.2. SECONDARY SLUDGE
B.2.1.  Current Conditions
             TABLE B-2.  ANALYSIS OF AVERAGE SECONDARY SLUDGE
             PRODUCTION PER MILLION GALLONS OF INFLUENT FLOW3
                          (January to June 1980)

                         Secondary sludge              Secondary sludge,
                           production,                 Volatile solids,
     Month	T/MGIF	percent
January
February
March
April
May
June
Average
Standard deviation
103/331
94/325
82/345
104/332
80/327
101/330


= 0.311
= 0.289
= 0.238
= 0.313
= 0.245
= 0.306
0.284
0.034
66
68
66
66
62
64
65.3
2.1
     Average dry tons secondary sludge, volatile solids production per MGIF
     is:
            (0.284 ± 0.034) T/MGIF (0.653 ± 0.021) percent volatile

          = (0.284)(0.653) ±   (0.653)  (0.034)  + (0.284) (0.021)

          = 0.185 ± 0.022 VT/MGIF
a    All data taken from Appendix A, Table A-l.

     Sludge as withdrawn from the secondary clarifiers and pumped to  the
     dissolved air flotation thickeners.

B.2.2.  Future Conditions

Increase Phosphorus Removal —
Effluent  limitations  on phosphorus  will be  reduced from  the  current  1.1
mg/1  average  to  the new NPDES  permit  requirement of 0.53 mg/1.  This will
be  accomplished  by  increasing  the   current  iron  dosage.   Past  records
indicate 3.8  pounds  of chemical  sludge  produced per pound of  P removed  by
iron,  therefore,  every  million gallons  of    influent  will  generate  an
additional:
   (1.1  -  0.53)»g/l P  (8.34)(1  HC)
                                     B-2

-------
It is assumed there are no volatile solids.

Multi-media Filters —
Within the year the new multi-media polishing filters will be in operation.
It is estimated  that these filters will reduce  the  suspended solids being
discharged  from  an average  of  15 to 7.5  mg/1.    Therefore,  every million
gallons of influent will generate an additional:
  (15.0 - 7.5)mg/l (8.3A)(1 MG)          = 0'°31 T/MGIF
It is assumed that 70 percent of the solids will be volatile.

Nitrification--
Within   several   months  the  nitrification  system   will   be  completely
operational.  At  a minimum,  this system will have  to  reduce current total
kjeldahl nitrogen (TKN) levels  in  the plant  effluent from  an  average of
13.8 mg/1  to the NFDES permit  level  of  5.3 mg/1.  Assuming a  biological
yield  coefficient of   0.1  pounds  of  solids   produced  per  pound of  TKN
reduced, the additional dry solids generated would be:
  (13.. - 3.MM/1 (..MXIW                           • °-0"
It is assumed that 70 percent of the solids will be volatile.

Assuming  no  change  in the  standard  deviation,  the  new volatile  solids
content would be:
  (0.185 + 0 + 0.0313(0.7) + 0.0035(0.7) (100)     ,. .
        0.284+0.009+0.031+0.004            ~  J   Percent
                                    B-3

-------
                                APPENDIX C
                 ANALYSIS OF GRAVITY THICKENER OPERATION
There are  six  65-foot diameter units.  Surface area  of each unit is 3,318
square  feet.   Surface area  is 19,908 square  feet.   All  operational  data
taken from Appendix A, Table A-l and A-2.
      TABLE C-l.  AVERAGE MONTHLY HYDRAULIC AND SOLIDS LOADING RATES
            AVERAGE MONTHLY HYDRAULIC AND SOLIDS LOADING RATES
                        (January through June 1980)
     Month
 Hydraulic loading rate,
gallons per day per square
   foot of tank surface
   Solids loading rate,
gallons per day per square
   foot of tank surface
January
February
March
April
May
June
804
799
789
789
769
804
10.7
12.8
10.5
15.5
12.6
12.4

            TABLE C-2.  AVERAGE MONTHLY THICKENING PERFORMANCE
                        (January through June 1980)
     Month
       Thickened sludge volume,
       gallons thickened sludge
        per million gallons of
            plant influent
            Thickened sludge
             concentration,
                percent
                 solids
January
February
March
April
May
June
Average
Standard deviation
328,000/331 =
437,000/325 =
365,000/345 =
521,000/332 =
435,000/327 =
370,000/330 =


991
1,345
1,058
1,569
1,330
1,121
1,236
218
7.3
6.7
6.7
6.9
6.4
7.9
7.0
0.5
                                  C-l

-------
No  relationship  between hydraulic  loading  rate  or  solids  loading  rate
versus thickened sludge concentration could be established.
  TABLE C-3.  ANALYSIS  OF EFFECT OF GRAVITY THICKENING  ON AVERAGE PRIMARY
          SLUDGE PRODUCTION PER MILLION GALLONS OF INFLUENT FLOW
                        (January through June 1980)
                                   sludge.             Thickened sludge
                           production,  '              volatile solids,3
     Month	T/MGIF                         percent
January
February
March
April
May
June
Average
Standard
105/331
129/325
108/345
158/332
120/327
129/330

deviation
= 0.317
= 0.397
= 0.313
= 0.476
= 0.367
= 0.391
0.377
0.060
79
75
70
65
66
71
71
5.3
     Average VT/MGIF  as  removed  from  the  gravity  thickener.

             (0.377 ±  0.060) T/MGIF  (0.71  ±  0.053)  percent  volatile
                                    22           22
           =  (0.377K0.71)  ±    (0.71)  (0.060)   +  (0.377)  (0.053)

           =  0.268 ± 0.047  VT/MGIF
      Sludge  as  withdrawn from the gravity thickeners.

      It is estimated that  grit  equal to 1.5 to  2.0  cubic feet per million
      gallons of influent flow at 100  pounds  per cubic foot is  included with
      the primary sludge.

      MGIF    =   million gallons  influent flow.
      T/MGIF   =   dry ton of solids per million gallons influent flow.
      VT/MGIF =   dry ton of  volatile solids per million gallons  influent
                 flow.
                                   C-2

-------
                                APPENDIX D

      ANALYSIS OF DISSOLVED AIR FLOTATION (DAF) THICKENER OPERATION
There  are  18,  20-foot  wide  by  55-foot  long  (effective length)  units.
Effective thickening surface area of each unit is 1,100 square feet.   Total
effective  surface  area  is  19,800  square  feet.    These  units  operate
continuously at 30 to 34 pounds of secondary solids  per day per square foot
of  effective  thickening  area.   Polymer  is  required  to  operate at  this
loading rate.  Polymer  usage  is 7 to  10 pounds  of  dry polymer per dry ton
of  feed solids.   All operational data taken from Appendix A,  Table A-l and
A-3.
            TABLE D-l.  AVERAGE MONTHLY THICKENING PERFORMANCE
                        (January through June 1980)
                    Thickened sludge volume,          Thickened sludge
                    gallons thickened sludge           concentration,
                     per million gallons of               percent
     Month	plant influent	solids
January
February
March
April
May
June
Average
Standard
665,000/331 =
570,000/325 =
496,000/345 =
582,000/332 =
448,000/327 =
508,000/330 =

deviation
2,009
1,754
1,438
1,753
1,370
1,539
1,644
239
3.7
3.9
4.1
4.2
4.2
4.7
4.1
0.3

Since  float  concentration  is not  expected  to change  in the  future,  the
additional  secondary  solids  generated  in  the  future  (Appendix B)  will
increase  thickened  sludge volume  by  approximately the  same amount  or  15
percent  (from  1,644 ± 239  to 1,900 ± 239 gallons  per million  gallons  of
influent flow).

At 30  pounds of  dry secondary solids per  day  per square foot of effective
thickening area,  each DAF can thicken:

         30 pounds           1100 square feet   _   33,000 pounds
     day-square foot     x       unit                 day-unit
                                  D-l

-------
In  the  future,  each  million  gallons  of  influent  flow will  contribute
0.328 ± 0.034 tons  (656 ± 68  pounds).   Assuming a value of 656 + 68 or 724
pounds  per  million gallons  of  influent  and   an  average  daily  flow  of
334  million  gallons  per  day  (MOD),  then  the  minimum number  of  DAF
thickeners required to be operating is:
        1 unit           724 pounds       334 MOD   _   g   -t
     33,000 pounds   X     1 MGD      X      1      "
                                   D-2

-------
                                APPENDIX E

            ANALYSIS OF LITHIUM CHLORIDE (LiCl) TRACER STUDIES
                           BLUE PLAINS DIGESTERS
E.I.  MECHANICAL DATA

Inside diameter of each digester - 84 feet
Cone depth - 13 feet
Average cylindrical height - 22.1 feet
Theoretical tank volume

     (42)  (3.1416K22.1 + 13/3) =   146,488 cubic feet
                                 = 1,096,000 gallons

Theoretical weight of digester fluid - 9,140,000 pounds
E.2.  TEST PROCEDURE

     Each  day  three digesters  were  taken off  line and 6  pounds  (Ibs)  of
LiCl added  in  approximately four equal fractions at manholes  spaced about
25  feet  from the  center of  the  digester.   On digester No. 1,  two  of the
manholes  could  not be  entered,  so one-fourth  of the LiCl was  added  at a
manhole located  on  a  line between the two manholes that could not be used,
and  one-fourth at  a  location adjacent to  the wall  of the digester.   On
digester No. 9, one manhole could not be entered,  so one-fourth of the LiCl
was added  through  a manhole at the center of the digester instead.  Mixing
was  accomplished by  means of  the  regular  gas-mixing  system and  with a
recycle of  approximately 1,000  gallons per minute (GPM) by means of a pump
for  one  hour  before the  sampling  time.   Samples  were taken  before the
addition of  the  LiCl  (0 time) and at 3, 6,  and 8 hours after the addition.
Gas  compressors  were not  available  on digesters 9 and  10,  so mixing  in
these  digesters  was accomplished  by  means  of  the 1,000  GPM  recycle pump
running continuously during the 8-hour test period.

     Samples were  analyzed for  lithium by means of an atomic  adsorption
instrument,  using  a graphite  furnace.   The available volume was calculated
from the  difference in  concentration between the 0-hour and 8-hour samples
resulting from the  addition of the 6 Ib dose of LiCl.
E.3.  RESULTS

     The results of the tracer studies are presented in Table E-l.
                                  E-l

-------
E.4.  DISCUSSION

     It  is  apparent that  mixing was  a  problem,  as  indicated  by the fact
that in  digesters  3,  4, 6, 9, and 11, the 8-hour and 6-hour concentrations
differed by  more  than  10 percent, indicating that equilibrium may not have
been reached.
TABLE E-l.  LITHIUM TRACER STUDY RESULTS

Lithium


Digester 0-hr
1
2
3
4
5
6
7
8
9
10
11
12
0.00
0.16
0.29
0.52
0.00
0.16
0.39
0.46
0.03
0.19
0.47
0.07

3-hr
0.95
1.15
2.11
4.15
1.50
1.16
2.37
2.17
14.13
1.09
18.20
7.15
Concentrations,

6-hr
0.59
1.13
1.64
1.82
1.20
1.14
1.57
1.00
3.00
0.96
1.50
1.73

mg/1

8-hr 8-hr - 0-hr
0.55
1.09
1.32
0.84
1.20
1.45
1.43
1.09
1.37
0.98
1.12
1.59
0.55
0.93
1.69
0.32
1.20
1.29
1.04
0.63
1.34
0.79
0.65
1.52
Volume ,
gallons
x 1000
1,310
775
699
2,251
600
558
693
1,143
538
912
1,108
474
Usable
volume,
percent
119
71
64
205
55
51
63
104
49
83
101
43
      The value for  digester  No.  1 is also suspect.   As  discussed above,  a
 portion of  the LiCl was added near  the  tank wall of the  digester,  rather
 than at the more  central  addition points used in the other digesters.   The
 very low concentration  of  LiCl  found in digester No. 1  would indicate that
 mixing was not adequate in the area near the tank wall,  and that a portion
 of the LiCl was not recovered.

      The distribution of recycle to the digesters appears to be good, based
 on the  0-time  readings  for digesters 4,  8,  and  11,  the last three tested.
 The  content  of LiCl  in the  digesters  before addition  of LiCl  was 0.52,
 carried to the digesters by the recycle from the other digesters.

      The usable-volume  values obtained in these  tests  exclude portions of
 the  tank volume  occupied  by grit and also  those areas  where mixing was so
 poor  that  the  LiCl  never reached  them.  The  results  of digester  No.   1
 indicate  that this  may be  a factor in  the areas  of  the tanks  near the
 walls.  It  is  also of  note  that  4  of the 9  gas-mixing  tubes  in the No.  1
 digester  were inoperative.   It  should  also be  noted  that a  scum layer,
 which  may  range  from 0 to 12 inches, will also be excluded from the usable
 volume.

      Lithium chloride appears to be  quite satisfactory as  a tracer material
 for  this  test.   More reliable results would be  obtained if the digesters
                                   E-2

-------
were  kept  off-line for a  longer  period to allow more  complete  mixing.   A
test  where  one slug  of  LiCl was  added to the recycle line  would  allow a
determination of the recycle distribution to all tanks,  and a determination
of usable volume  for  the  entire system, but a test of this type would also
have problems in distinguishing between areas occupied by grit and areas of
very  poor  mixing; to  make this determination, longer-term  off-line tests
are probably required.

     The system was simulated by computer analysis, using an average usable
digester volume of 700,000 gallons.  The values predicted by the simulation
agreed very well  with the analyzed values through the end of the third day
of testing,  but  the  analyzed values  were about 20 percent  low  during the
fourth  day.   It  is  not  known  what  problems  could  have  caused  this  dis-
crepancy during the last tests,  those of digesters 4, 8, and 11.
E.5.  COMPUTER SIMULATION

     A computer program  was  developed to simulate the  behavior  of lithium
chloride during the  test period.   For the purposes  of  the simulation, the
digesters  were divided   into  four  groups  of  three   digesters  each,  in
accordance with the test procedure.  Each group was assumed to have a total
volume of  2.1  million gallons  (700,000 gallons per digester) and a recycle
rate  of  1,500 gallons  per minute,  (500  GPM  per  digester).   The  flow  of
fresh sludge into the group and treated sludge out of the tanks was assumed
to be  1/15 of  the total volume per  day.   The program calculated the esti-
mated LiCl  concentrations  each half hour; a  subroutine  was  set  up to cal-
culate the changes in  concentration that would take place  because of the
removal  of tank  contents  by the  recycle,  the addition  of  recycle sludge
that  was composed of mixed  sludge  from  all  four  groups, the  removal  of
treated sludge from the system, and the addition of fresh sludge.  The main
program in turn applied this  subroutine to each group of digesters for each
half-hour  time period,  noting  the change in concentration of each group of
the combined recycle,  taking into account the additions  of  LiCl to a dif-
ferent group  each day,  and  the  fact  that one  group  was off-line  for an
8-hour period  each day.   Results were printed  out from  9:00 AM (time of
LiCl  addition  and removal of  the group  from line) and  5:00  PM (the time
that the group was placed back on-line).

     The results  of  the  simulation are presented  in Table E-2.   It can be
seen  that  there  was  good  correlation  between the  concentrations predicted
by the model and the field results until Sunday at 5:00 PM.

     Both  the  9:00 AM and the 5:00  PM results on Monday, the last day of
the test,  indicated that actual results were substantially lower than those
predicted by the model.  We are unable to explain the apparent loss of LiCl
from  the system  indicated by the 5:00 PM, Monday recycle sample.  In order
to  make  the   computer  simulation agree  with  the field  results,  it  was
necessary  to postulate  a withdrawal of treated sludge and replacement with
fresh  sludge  of  3,300  GPM  starting  at 5:00  PM  on Sunday  and  continuing
through 5:00 PM on Monday or some other addition of several million gallons
of  fresh sludge  to the system.  There are no such upsets reported from the
plant.  One of the digesters  did overflow, but this accident took place the
next  day.   The weight of LiCl left  (23  Ibs)  from the original 100 Ib drum
                                  E-3

-------
TABLE E-2.  MODEL SIMULATION OF DIGESTER ANALYSIS
                                     Lithium concentrations, mg/1
Day Time
Friday 5 PM
Saturday 9 AM
Saturday 5 PM
Sunday 9 AM
Sunday 5 PM
Monday 9 AM
Monday 5 PM
Digester
1 2
i'°
-------
Ibs  of  LiCl in  the  system, as  compared  to  a total weight of  56  Ibs pre-
dicted by the model.   Various explanations are possible:

     o    There was a  large influx of fresh sludge to the system,  flushing
          out the LiCl.   As discussed earlier, this would have had to have
          been on the  order of several million gallons,  and  no such upset
          occurred.

     o    A mistake was  made in the addition of LiCl.  As discussed above,
          a  check  of  the  remaining LiCl indicates that  the  proper amount
          was added.

     o    The average volumes  of the digesters are nearer to the theoreti-
          cal  1,096,000  gallons  than the  assumed 700,000 gallons.   This
          does not appear  reasonable,  in that if  this  assumption  is  made,
          all of the  analyses  for the first  three  days would have been in
          poor agreement  with the  model,  and such an  assumption  does not
          fit with the individual test results.

     o    The missing  12  pounds  of LiCl, which cannot  be accounted for by
          the analyses, may be concentrated in areas of poor mixing so that
          the tracer,  or portion of it, never entered the system.

E.6.  COMPARISON OF RESULTS WITH CANADIAN TRACER STUDIES

     It is  of  interest  to compare results with those obtained by J.  Smart
(1978)  (An  Assessment  of the Mixing Performance of Several Digesters Using
Tracer Response Techniques, Research Publication No. 72, Dec.  1978, Ontario
Ministry of the Environment.)  He used fluoride as a tracer on 10 anaerobic
digesters  ranging  from 165,900  to 1,690,000  gallons  in size,  using both
mechanical  and  gas mixing  with mixing  power ranging  from  0.02  to 0.25
HP/1,000 gallons.

     Smart  found mixing  to  be a  problem,  with an  average of  55  percent
usable volume, as compared to 65 percent found in our study.  He found that
the  tracer  concentration leveled  out  in 4  to 6  hours,  which agrees well
with our finding that in most cases the tracer leveled out in 4 to 8 hours.
He could find no correlation between the amount of dead space and the size,
age,  condition,  applied mixing  power,  or  type  of mixing  used in  the
digester.
E.7  CONCLUSIONS

     The results are  consistent  with an average usable  volume  of about 65
percent of  theoretical,  with the dead space consisting  of  the  grit layer,
the scum layer, and areas where there is little or no mixing.

     A  tracer  study where  the  tracer is  added to  the  recycle  line,  thus
feeding all  12 digesters at once,  will  help to resolve some of  the ques-
tions about short-circuting and total hydraulic detention time.
                                  E-5

-------
                                APPENDIX F

         ANALYSIS OF GRIT ENTRY INTO ANAEROBIC DIGESTERS PER
                MILLION GALLONS OF PLANT INTLUENT FLOW
Based on  discussions with anaerobic system operating personnel:

     o  It takes 2  to  3 years for a digester to accumulate grit to a point
        of  equilibrium,  that is  grit  no  longer  accumulates  but  passes
        through the digestion tanks.

     o  Grit  in  the tank was estimated  to  occupy 15 to 20 percent  of the
        total  tank  volume.    Since  each  tank has  a theoretical volume  of
        146,469 cubic  feet,  then grit occupies 21,970 to 29,294 cubic feet
        of tank volume.

Assuming three years  for grit build-up within  a  tank to reach equilibrium
then:
        21 970 cubic feet off  grit  =  2Q
        (365 day/year)   (3 years)


                                    or

        29,294 cubxc feet of  grit          cub-c                  d
        (365 days/year)   (3 years)                       &    *


Approximately  half  the daily sludge production goes to anaerobic digestion
or the plant influent  flow equivalent of 167 million gallons per day (MGD).

There  are  12  digestion  tanks  and  it  is  assumed  that  sludge  is  pumped
uniformly to  all  of them, therefore each tank  receives raw sluge generated
from:

        12?tanks  =  13'9 MGD °f plant influent flow


At 20  cubic feet of grit per day per tank, each MGD of plant influent flow
is contributing:

        20 cu^c feet  8rit per tank  =   :.4 cubic feet per HGD
              13.9 MGD  per tank                         r

At  100 pounds per  cubic foot,  140 pounds or  0.07  tons of  dry solids per
million  gallons  of  plant   influent  flow  (T/MGIF)  is  being  contributed.

At 26.8  cubic feet it  is 2.0 cubic feet per MGD,  which at  100 pounds per
cubic  foot  is  200 pounds  or  0.1 T/MGIF.

                                  F-l

-------
                                APPENDIX G

    ANAEROBIC DIGESTION HEAT AVAILABILITY AND SYSTEM HEAT REQUIREMENTS


G.I.  DIGESTER HEATING CAPABILITIES

     There are six  double  inlet,  double outlet, 6 inch by 8 inch,  tube and
tube heat exchangers each with a heated exterior sludge tube surface of 360
square feet.   Each unit  is  specified as originally having a  rated output
capacity of 3,000,000 BTU per hour.  The original design criteria could not
be  found, but  knowing how the heat exchanger  supplier  would  have  designed
the units, it is believed that the 3,000,000 BTU per hour output was predi-
cated on the following:

     o  Sludge at each inlet (there are 12) would be at an average  tempera-
        ture of 80°F at a flow rate of 350 gallons per minute  (gpm).

     o  Sludge at  each outlet  (there  are  12)  would be  at  an  average tem-
        perature of 95°F at a flow rate of 350 gpm.

     o  Hot water at  each  inlet (there are 12) would be at 180°F at a flow
        rate of 200 gpm.

     o  Hot water at each outlet (there are 12) would be at 160°F at a flow
        rate of 200 gpm.

     The source of hot water was to be provided by two, 250 horsepower, low
pressure steam boilers;  one,  150  horsepower, hot  water  boiler;  and engine
jacket cooling water.

     Through the years  since  the  sludge heating system was first conceived
and  installed,  changes  have taken  place  that have  altered  the  heating
capabilities as follows:

     o  Sludge at each inlet averages 92 to 95°F at a flow rate of 500 gpm.
        The higher  than  expected  sludge temperature decreases  the expected
        thermal  gradient and therefore  decreases heat  transfer capabili-
        ties.  However,  the  higher flow rate tends to increase heat trans-
        fer capabilities.

        The  original  heat exchanger  design would have  been predicated on
        two standard industry assumptions:

        - Sludge flow through a 6-inch sludge tube would be   approximately
          350 gpm.
                                  G-l

-------
        - Sludge flow  into  the heat  exchanger would  have  consisted of  2
          parts  digested,  recirculated sludge at 95°F and 1  part raw sludge
          at 50°F (assumed winter  conditions).

        At Blue  Plains raw sludge  is added after the heat exchangers rather
        than before.   The addition is  downstream because of  a historical
        problem  with  heat exchanger  plugging  due to  rags  in  the  primary
        sludge.   The  required  screening  of  plant influent,   to  eliminate
        rags in  the raw sludge  has only recently been accomplished.

        Even if  all the  available  raw sludge  (approximately  600 gpm)  was
        added upstream, the  average inlet temperature would be reduced by
        4°F during  the winter and  by 2°F during the summer.  This  small
        decrease is due to  the high digested sludge recycle flow, which is
        10  times  the  raw sludge  flow  instead of  the 2 times originally
        envisioned.

        It is not  known why the recycle flow rate was increased to  500 gpm
        per sludge inlet.   It has  a beneficial effect on the heat exchanger
        in that the high  velocity (5.7 feet  per second)  through the sludge
        tubes prevents tube fouling.*

     o  Hot water at each inlet is at 195°F.   The higher hot water tempera-
        ture tends  to increase the thermal  gradient,  therefore increasing
        heat transfer capabilities.

        Plant operating   experience  indicated  that  the hot   water  being
        utilized could be increased  to  195°F  without causing any  scaling
        problems within the heat exchanger.*

     o  At the present time the source of hot water is provided by two,  250
        horsepower, low pressure steam boilers and one, 150  horsepower,  hot
        water boiler.  Engine  jacket  cooling water is no longer available.
        The 150  horsepower hot water boiler  is  in poor condition and is
        scheduled to be replaced within the next couple of years.  Assuming
        an overall  efficiency  of  80 percent  for the steam boilers and heat
        exchangers, about  13,200,000  BTU per hour are available.   The  new
        hot water  boiler  would add an additional 3,000,000 BTU  per hour.

        In  addition,  the  current  construction contract calls  for  linking
        together the  steam  boilers  in the heat exchanger building with the
        three 150 horsepower, low pressure steam boilers in  the power house
        and the two  100  horsepower, low pressure steam  boilers in  the new
        grit chamber structure being built.  These changes would produce an
        additional 17,000,000 BTU per hour availability,  but how much could
        be used for sludge heating is not known at this time.

G.2.  DIGESTION SYSTEM HEAT REQUIREMENTS

Digestion   system   heat   requirements  consist  of  two  components:  heat
required  for  raw  sludge  addition and heat  required  for radiation  losses.
* Inspection  of  one  unit during  this  study  showed  no scaling  on either
   sludge or hot water side of 6 inch sludge tube.

                                  G-2

-------
G.2.1.  Heat Required For Raw Sludge Addition

     The  amount  of  heat  required  for  raw sludge  addition per  million
gallons of plant influent flow can be calculated as follows:

     (gallons of sludge/MGIF)(Density)(T2 - T^

where:

gallons of sludge/MGIF = gallons of raw sludge per million gallons of plant
                         influent flow

               density = density  of the  liquid  sludge stream,  pounds  per
               gallon

                    T_ = temperature  to  which the raw sludge  stream is to
                    be raised, °F

                    TI  = expected temperature of  the  raw sludge stream, °F


G.2.2.  Heat Required For Primary Sludge Addition Only

     From  Appendix  C,   the  primary  sludge  volume  expected  per MGIF  is
1236 ± 218  gallons.   The  highest value  or 1454  gallons  is used  for  the
following calculations.  Density of primary sludge stream is 8.8 pounds per
gallon.   Sludge  temperature  to  be  raised  to  95°F.   During  the  winter
season,  the coldest  primary  sludge  temperature  is  55°F.   During  summer
operation, the primary sludge temperature is 75°F.

Winter operation:

     1454 gallons     8.8 pounds     (95 - 55)°F
         MGIF      X    gallon    X       1


     =  511,808 BTU's per MGIF

Summer operation:
     1454 gallons     8.8 pounds     (95 - 75)°F
        MGIF       X    gallon    X       1


     =  255,904 BTU's per MGIF
G.2.3.  Heat Required For Secondary Sludge Addition Only

     From Appendix D,  the future secondary sludge volume expected per MGIF
is 1900 ± 239  gallons.   The highest value or  2139  gallons  is used for the
following calculations.   Density of  secondary sludge stream is 8.5 pounds
per  gallon.   Sludge  temperature  to be raised to 95°F.   During the winter
                                  G-3

-------
season, the coldest  secondary sludge temperature expected is 60°F.  During
summer operation, the secondary sludge temperature expected is 80°F.

Winter operation:

     2139 gallons     8.5 pounds     (95 - 60)°F
        MGIF       X    gallon    X        I


     =  636,353 BTU's per MGIF

Summer operation:

     2139 gallons     8.5 pounds     (95 - 80)°F
         MGIF      X    gallon    X       1


     =  272,723 BTU's per MGIF

G.2.4.  Heat Required For All Sludge Addition

     The  heat input  required  for  all  sludge  per  MGIF is  calculated by
totaling the primary and secondary requirements as follows:

                                   Winter               Summer
                                 operation,           operation,
                               BTU's per MGIF       BTU's per MGIF
     Primary sludge               511,808              255,904
     Secondary sludge             636,353              272.723
          TOTAL                 1,148,161              528,627


G.2.5.  Heat Required For Conductive/Convective Losses

     The amount  of  heat required for conductive and convective losses  from
the digestor equipment can be calculated as follows:

     (U)(Area)(T3 - T^)

where:
                  i
     U  = -5=
      ^ = Conductance for a certain thickness of material
          	BTU	
          hour-square foot-°F
     x. = Thickness of material in inches

     k. = Thermal conductivity of material

          	BTU - inch	
          hour-square foot-°F
                                  G-4

-------
     A  = Area  of material  normal  to direction  of heat flow  in  square feet



     T_ = Temperature of inside  boundary, °F



     T, = Temperature of outside boundary, °F



     Figure  G-l  shows a cross  sectional view of  one of the 12  existing anaerobic

digestion  tanks.    In  the   following  analysis  the  assumptions  made  are:
                       Earth Cover
T

 24"

_L
                       *'-l*
                       .»?  Concrete Roof 10.25"
                       Moving, Heated, VJater

                       Saturated Air Space
                                                  ..
                                               ,. -.1 . • ,
                         Liquid at 35°F
            >
                                                •V '.
                                                '
                                                         Concrete Tank Wall
                                Concrete Floor




  FIGURE G-l.  Cross  sectional view of  existing anaerobic  digesters
                                    G-5

-------
     1.    The liquid  contents  of the  tank are being mixed  and maintained
          at an inside boundry temperature of 95°F.

     2.    The average  (several  weeks) coldest outside  temperature (winter
          operation) is 0°F.

     3.    The average  (several  weeks) warmest outside  temperature (summer
          operation) is 60°F.

     4.    All earth is considered to be wet (worst condition).

     5.    The  average temperature  of  the soil  underneath   the  digestion
          tanks is 40°F.

G.2.6.  Heat Loss Through Roof

     T_ is 95°F; T^ for winter is 0°F and for summer is 60°F; area normal to
heat flow is:

     CTT)(one internal tank diameter)2 (12 tanks)
                       4

     = (JT)(84)2 (12)  =  ^
            4


U can be calculated as follows:

     o  liquid-air space interface,       1/C = 0

     o  air space (as indicated),         1/C = 0.5

     o  air space - concrete interface,   1/C = 0.33

                                                10 25
     o  concrete 10.25 inches thick,      x/k = —^ = 0.854


     o  concrete - earth interface,        1/C =1.0

                                                24
     o  wet earth 24  inches thick,         X/T6= — = 1-5
U =
     o  earth - atmosphere interface,     1/C = 0.167

     	1	
     (0 + 0.50 + 0.33 + 1.00 + 0.167) + (0.854 + 1.50)

       1   _ 	0.23 BTU	
      4.35 ~ hour-square foot-°F


Winter operation:

     (0.23 BTU)(66,501 square feet)(95-0)°F =           BTU
             hour-square foot-°F               '   '        *
                                   G-6

-------
Summer operation:

     (0.23 BTU)(66,501 square feet)(95-60)°F _
             hour-square foot-°F


G.2.7.   Heat Loss Through Walls
                                             =  535,333 BTU per hour
T« is 95°; T, for winter is 0°F and for summer is 60°F; area normal to heat
flow is:

     (TT)(one mean tank diameter) (12 tanks) (vertical wall height)

     = (TT)(84 + ^)(12)(22) = 71,154 square feet.
     All  vertical  surface  is not  exposed  to  the  outside.   As  shown in
Figure G-2,  the  grouping of the existing  digestion  tanks  only allows part
of each  tank to  be exposed to the outside environment, the rest is exposed
to each  other. The wide dark lines  in  Figure G-2 indicate the part of the
circumference (59  percent)  that  is  considered exposed to the outside.  The
other 41 percent is exposed to a protected environment with an average year
round temperature of 70°F.
     FIGURE G-2.  Plan view of existing anaerobic digestion tanks.
                                  G-7

-------
U can be calculated as follows:

     o  liquid - concrete interface, 1/C = 0

                                          21 5
     o  concrete 21.5 inches thick, x/k = —=--j- =1.79
     o  concrete - earth interface,  1/C =  1.0

     o  wet earth 72 inches  thick,    x/k  = ||  =  4.5*
U ~
     o   earth - atmosphere interface,  1/C = 0.167

     	1	
       (0 + 1.00 + 0.167)  + (1.79 + 4.5)

       1              0.13 BTU
       7.46        hour-square  feet-°F


Winter operation:

      (0.13  BTU)(71.154  square feet)[(0.59)(95-0)°F + (0.41)(95-70)°F]
                           hour-square foot-°F


      =  613,276  BTU per hour

Summer operation:
      (0.13  BTU)(71.154  square feet)1(0.59)(95-60)°F + (0.41)(95-70)°F]
                            hour-square foot-°F
      =  285,826 BTU per hour
     —  £OJ,O£U O1U pel. 11UUI.

G.2.8.  Heat Loss Through Floor

T,. is 95°F; T, is 40°F for both winter and summer; area normal  to heat  flow
is:

      ,__w  one mean  w  one mean    .   vertical height, ,.., ,.__.-*
      [III!             II   .     ,.    T         f.          Jll£ UanKS 1
      ^  yvtank radius 'vtank radius          of cone
      =  90,391 square feet
 *  In  reality,  the  factor  is  larger  since the  earth  cover  is becoming
    thicker.  In calculating heat loss, the effective protection of an earth
    cover  is  never used  as  more than 10  feet;  therefore the maximum value
    is 7.5.
                                   G-8

-------
U can be calculated as follows:

     o  liquid - concrete interface, 1/C = 0

                                        12
     o  concrete 12 inches thick, x/k = -r  = 1.0
     o  concrete - earth interface, 1/C = 1.0
                                           120
     o  wet earth 120 inches thick*, x/k = -rr =7.5
U =
     (0 + 1.0) + (1.0 + 7.5)

         1                0.11 BTU
        9.5        hour-square foot-°F


Winter and summer operation:

     (0.11 BTU)(90,391 square feet) (95-40)°F   =   ^      ^
             hour-square foot-°F


G.2.9.  Heat Losses Through Sludge Piping

All  sludge piping  involved  in  transporting  sludge  from the  sludge heat
exchangers  to  the digesters  and from  the  digesters back to  the heat ex-
changers is made  of  steel pipe of various diameters.  It is estimated that
approximately 600  linear  feet (6,000 square feet  of  surface area) of this
pipe is buried  in shallow concrete galleries located between the digestion
tanks and  heat  exchanger  complexes.   The U  factor for  this  pipe was esti-
mated at  0.32 BTU per hour-square foot-°F.   It  is  estimated  that another
3,600  linear  feet  (10,000  square  feet  of  surface area)  is  located  in
several building   structures,  where  the  temperature  stays  about  70°F all
year  long.   The  U factor for  this pipe is estimated at  1.6 BTU per hour-
square foot-°F.

Winter operation:

    (0.32 BTU)(6000 sq. feet)(95-0)°F + (1.6 BTU)(10000 sq.  feet)(95-70)°F
          hour-square foot - °F              hour-square foot-°F


    =  182,400 + 400,000 = 582,400 BTU per hour

Summer operation:
    (0.32 BTU)(6000 sq. feet)(95-60)°F +  (1.6 BTU)(10000 sq.  feet)(95-70)°F
          hour-square foot-°F                   hour-square  foot-°F


    =  67,200 + 400,000 = 467,200 BTU per hour
   In calculating heat loss, the effective protection of an earth cover is
   never used as more than 10 feet.

                                  G-9

-------
G.2.10.   Summary of Heat Requirements

                                                  Winter        Summer
                                                 operation     operation
For raw sludge addition in BTU's per MGIF:
     o    Primary sludge only                     511,808       255,904

     o    Secondary sludge only                   636,353       272,723

          TOTAL PRIMARY & SECONDARY SLUDGE      1,148,161       528,627

For system conductive/convective heat loss in BTU's
per hour:
     o    Roof                                  1,453,112       535,358

     o    Walls                                   613,276       285,826

     o    Floor                                   546,866       546,866

     o    Sludge piping                           582,400       467,200

          TOTAL HEAT LOSSES                     3,195,654     1,835,250
                                   G-10

-------
                                APPENDIX H

                   ANAEROBIC DIGESTION PIPING SCHEMATIC


In  order  to  perform  this  study  an up-to-date  piping  schematic  of  the
anaerobic  digestion  system was  required.  Enclosed  in this appendix  are
the following three drawings:

     Drawing 117-1-1     Existing Piping Schematic Digesters  1-8

     Drawing 117-1-2     Existing Piping Schematic Digesters  9-12

     Drawing 117-1-3     Existing Exterior Solids  Processing  Piping
                                  H-l

-------
AVAILABLE
DIGITALLY

-------
                                 APPENDIX I

                       ANALYSIS  OF ANAEROBIC SYSTEM
               VOLATILE MATTER REDUCTION AND GAS PRODUCTION3
I.I.  VOLATILE MATTER REDUCTION

     Table 1-1 lists historical volatile matter reduction and several  possible
related variables.  Data  are  plotted in Figures 5-2, 5-3, and 5-4  in Section
5.3.6 of this report.

   TABLE 1-1.  LISTING OF AVERAGE VOLATILE MATTER REDUCTION AND SEVERAL RELATED VARIABLES




Year
1979











1980








Month
January
February
. March
April
May
June
July
August
September
October
Noveober
December
January
February
March
April
May
June


Average volatile.
matter reduction,
percent
62.9
64.0
66.2
65.0
65.2
57.9
45.3
52.2
. 44.6
46.9
—
59.6
70.7
61.6
60.0
54.8
49.7
57.6


Secondary sludge
fraction,
percent by weight
35
35
19
25
40
35
44
42
52
51
—
35
23
41
44
46
42
53
Volatile matter
loading
pounds volatile
matter per
usable cubicc
foot per day
0.15
0.13
0.15
0.16
0.17
0.15
0.12
0.14
0.12
0.12
—
0.10
0.12
0.14
0.14
0.12
0.12
0.14

Hydraulic
detention
time .
days*
20.5
23.9
22.3
18.5
19.3
19.8
20.2
18.8
18.6
19.4
26.9
23.9
23.6
17.0
16.4
18.4
18.4
17.6
a  All data taken  from  Appendix A,  Table A-4.
b  Calculated as follows:

          avg tons volatile  solids  in - avg tons volatile solids out
                          avg tons volatile solids in                   X

c  Based  on the  information  in Appendix  E,  it was  assumed  that only  65
   percent  of  the total  1,757,628  cubic  feet of  digestion  tank  volume
   was usuable.

d  Based on the information  in Appendix E, it was assumed that only
   65 percent of the  total  13,152,000 gallons of digestion  tank was
   usuable.

                                   1-1

-------
1.2.  ANALYSIS OF  ANAEROBIC DIGESTION ON AVERAGE VOLATILE MATTER REDUCTION

      PER MILLION GALLONS OF INFLUENT FLOW*


1.2.1.  Current Conditions - All Sludge To Digestion

     Primary sludge to anaerobic digestion:

               0.377 ± 0.060 T/MGIF**        0.268 ± 0.047 VT/MGIF

     Secondary sludge to anaerobic digestion:

               0.284 ± 0.034 T/MGIF          0.185 ± 0.023 VT/MGIF

     Summation of primary and secondary T/MGIF and VT/MGIF:

          (0.377 + 0.284) ±   (0.060)  + (0.034)   =  0.661 ± 0.069  T/MGIF
                                     2          2
          (0.268 + 0.185) ±   (0.047)  + (0.023)   =  0.453+0.052 VT/MGIF

     Ratio of secondary sludge to total sludge mass:

          (0.284) T (0.661) = 0.43

     From Figure 5-2,  Section 5.3.6, the average volatile solids reduction
     expected is 56.5 ± 6.5 percent or:

          (0.453)(0.565) ±   (0.565)  (0.052)  + (0.453)   (0.065)

          =0.256 ± 0.042 VT/MGIF

     The VT/MGIF  reduction would  be equivalent to  the  T/MGIF reduced for
     the total sludge mass.


1.2.2.  Future Conditions - All Sludge To Digestion

     Primary sludge to anaerobic digestion:

               0.377 ± 0.060 T/MGIF          0.268 ± 0.047 VT/MGIF

     Secondary sludge to anaerobic digestion:

               0.328 ± 0.034 T/MGIF          0.209 ± 0.023 VT/MGIF
*  Data taken from Appendix B, Tables B-l through B-3.
** T/MGIF  =  dry ton of solids per million gallons influent flow.
   VT/MGIF =  dry ton of volatile solids per million gallons influent
              flow.
                                  1-2

-------
Summation of primary and secondary T/MGIF and VT/MGIF:

     (0.377 + 0.328) ±   (0.060)  + (0.034)   =  0.705 ± 0.069  T/MGIF
                                2          2
     (0.268 + 0.209) ±   (0.047)  + (0.023)   =  0.477 ± 0.052 VT/MGIF

Ratio of secondary sludge to total sludge mass:

     (0.328) -=- (0.705)  =  0.465

From Figure 5-2, Section 5.3.6, the average volatile solids reduction
expected is 53.5 ± 6.5 percent or:

     (0.477)(0.535) ±   (0.535)2 (0.052)2 + (0.477)2 (0.065)2

     = 0.255 ± 0.042 VT/MGIF

The VT/MGIF reduction would be equivalent to the T/MGIF reduced for
the total sludge mass.
                             1-3

-------
1.3.   GAS PRODUCTION

Table  1-2  lists  historical gas  production  and  several possible  related
variables.   Data  are plotted  in Figures 5-5,  5-6, and 5-7 in Section 5.3.7
of the report.
TABLE 1-2.  LISTING OF AVERAGE GAS PRODUCTION AND SEVERAL RELATED VARIABLES
Gas production,
cubic feet
per pound of
volatile natter
\ear Month
1979 January
Februarv
.larch
April
Hay
June
July
August
Septenaer
October
N'ovemoer
December
1980 January
February
ttarcb
April
May
June
reduced
8.7
8.S
7.2
8.6
9.9
12.0
14.4
9 2
12 6
13.5
«
9.6
11.0
12 8
12.0
U.O
13.8
10 7
Volatile matter
Fsed to digestion.
solids,
percent
7.1
7 0
7 6
6.3
7 4
7.1
6.0
6.4
5 9
5.6
..
5.4
5.9
5.2
5.2
5.3
5.2
5.S
tons
per day
83.5
J4.7
87.2
89.1
94.0
86.4
67 8
77.7
'0.6
67.0
..
56.2
o8.5
78.7
77.8
67. S
66.2
3C.6
Volatile matter
loading.
pounds volatile Secondary
natter per sludge fraction.
usable cubic
feet per day3
0.15
0.13
0 15
0 16
0.17
0.15
0.12
0.14
0.12
0.12
..
0.10
0.12
0.14
0.14
0 12
0 12
0.14
percent by
weight
35
35
19
25
40
35
44
42
52
51
..
35
:3

to»»
to
42
53
Hydraulic
detention
time,..
days "
20 S
23.9
:2.3
18 5
19 3
19 8
20.:
18 S
-.8.6
19 4
26 9
23.9
23.o
17.0
16 •
IB.i
18 -
17 0
3  Based  on  the  information in  Appendix  E, it  was  assumed  that  only 65
   percent  of the total 1,757,628 cubic feet  of  digestion tank volume was
   usuable.

   Based  on  the  information in  Appendix  E, it  was  assumed  that  only 65
   percent  of the  total  13,152,000 gallons  of digestion  tank  volume was
   usuable.

NOTE:   The  existing hot water source  for  the heat exchangers  are two  steam
        and  one  hot water  boiler (Appendix G).   To  allow  the  boilers to
        operate  at maximum output, approximately  20,250,000  BTU per hour of
        energy is required.   Assuming  digester gas at  600 BTU's per  cubic
        foot,  then the  amount of  digester gas needed is:

                20,250,000  BTU per hour required
                     600 BTU per  cubic  foot
                =   33,750 cubic  feet per hour

                =  810,000 cubic  feet per day

                                   1-4

-------
                                   APPENDIX J

                  ANALYSIS OF ELUTRIATION SYSTEM OPERATION
Table  J-l lists  historical 1980  elutriation underflow  to dewatering solids
concentration  and several  possible  related  variables.   Data are plotted in
Figures  5-8  through  5-10  in  Section  5.4 of this  report.   All data  taken
from Appendix A,  Table A-5.
TABLE  J-l.  LISTING OF ELUTRIATION UNDERFLOW TO DEWATERING SOLIDS
             CONCENTRATION AND  SEVERAL POSSIBLE RELATED  VARIABLES
         Elutciatioo.        Total dry                             Solids loading
         underflow to       solids to     Volume of                    rate,       Ratio of
        dewacenag solids    elutriation,  digested sludge   feed solids     pounds per  tasn water flow
         concentration,        cons       CO elutriacion,  concentration,     day per h   Co digested
  Month   percent solids       per day        MOD*      percent solids   square toot    sludge flow
January
Feoruarv
Marci
April
May
June
5 i
i 3
3 6
5 5
3.i
5.2
45
53
S3
54
SB
70
0 397
0.509
0.509
0 4o6
0.448
0 492
2.6
2.4
2.4
2.7
3.0
3-3
36.7
43.2
43.3
44.1
47.4
57 I
5.7
4 6
4 b
4 9
4 3
i.5
a  MGD - million gallons per day.

b  There are two elutriation tanks each  35-feet wide  by 70-feet  long
   operated  in series;  therefore the  first tank  receives the entire solids
   load.  Loading rate calculated as follows:

           (tons  dry solids  to elutriation per day)  (2000 pounds  per ton)
                           (35) (70) square feet of  tank


                                     J-l

-------
                                APPENDIX K

             ANALYSIS OF DIGESTED SLUDGE DEWATERING ON AVERAGE
          SLUDGE PRODUCTION PER MILLION GALLONS OF INFLUENT FLOW*
TABLE K-l.

Ferric chloride usage
Month
January
February
March
April
May
June
Average
Standard
Tons per
day
10.2
11 9
10.8
10. 0
10.7
10. 1

deviation
Tons per day of dry
solids to filter
10.2/54 = 0.189
11.9/59 s 0.202
10.8/49 = 0 220
10 0/46 = 0.217
10.7/52 = 0.206
10.3/55 - 0.187
0.204
0.014
Feed solids
concentration.
percent
5.4
4.3
3.6
5.5
5.4
5.2


ftetatered cake
percent
solids
16 0
15 8
15.6
16.7
16.6
16 9
16.2
0 6
Secondary sludge
fraction,
percent by weight
23
41
44
46
42
53


     The  amount  of  solids   contributed  by  ferric  chloride  per million
gallons of influent flow is estimated below.

     The  average  amount  of  ferric  chloride added  per ton  of dry solids
pumped to the vacuum  filters  is 0.204 ± 0.014 tons.  It is assumed  that all
iron  solids  (44 percent of the  ferric  chloride) and 16.3 ± 0.5 percent of
the  chloride solids  remain  in the sludge  (the  remainder of the  chlorides
leave with  the filtrate).   Therefore, the  amount  of solids contributed by
ferric chloride would be:

      (0.44 + [0.163 ± 0.006][0.56])(dry weight ferric chloride  added)

     =    (0.53 ±  0.003)(dry  weight ferric  chloride  added)

     =    (0.53 ±  0.003)(0.204 ±  0.014)(dry solids to dewatering)

     =    (0.108 ± 0.007)(dry solids  to dewatering)

     For  current  conditions, sludge  to digestion,  each million gallons of
influent  flow would contribute:
                            .063)2  +  (0.04)
(0.661 - 0.256) ±  s/XO.<

=    0.405 ± 0.075 dry  tons to dewatering  after anaerobic digestion.
    All  data  taken from  Appendix  A,  Table  A-7  or Appendix I.
                                   K-l

-------
The  amount  of solids  contributed  by  ferric  chloride addition   would be:

          (0.108 ± 0.007)(0.405 ± 0.075)	

          =    (0.108X0.405) ±  \A0.405)2(0.007)2 + (0.108)2(0.075)

          =    0.043+0.009 T/MGIF*

For  future  conditions,  sludge  to  digestion,  each million  gallons  of
influent flow would contribute:
          (0.705 - 0.255) ±  xA°-063)2 + (0.04)2

          =    0.450 ± 0.075   dry  tons  to   dewatering  after  anaerobic
               digestion.

The   amount   of   solids   contributed   by   ferric   chloride   addition
would be:

          (0.108 ± 0.007)(0.450 ± 0.075)
          =     (0.108)(0.450) +  \/0.450)2(0.007)2 +  (0.108)2(0.075)2

          =     0.049 ± 0.009 T/MGIF

For    current   and   future   conditions   with   only  primary   sludge
to    digestion,   each   million    gallons    of   influent   flow   would
contribute:
                              /i           f
          (0.377  -  0.188) ±  V(0.055)   +  (0.035)

          =     0.189 ±   0.065   dry   tons  to   dewatering  after  anaerobic
                digestion.

The    amount    of  solids   contributed   by   ferric   chloride    addition
would be:

          (0.108  ±  0.007)(0.189  ±  0.066)
                (0.108)(0.189)  ±  \/(0.189)2(0.007)2  + (0.108)2(0.065)2

           =    0.020 ± 0.007  T/MGIF

 For   future   conditions   with   only   secondary   sludge   to   digestion,
 each million  gallons of influent flow would contribute:
                               /       2           r
           (0.328 - 0.073)  ± V(0.031)  + (0.015)

           =    0.255 ± 0.034   dry   tons  to  dewatering   after   anaerobic
                digestion.
 *  T/MGIF = Dry ton of solids per million gallons of influent flow.
                                   K-2

-------
The   amount   of   solids   contributed   by   ferric   chloride   addition
would be:

          (0.108 ± 0.007)(0.255 ± 0.034)
               (0.108)(0.255) ±  V/(0.255)2(0.007)2 +  (0.108)2(0.065)2

               0.028 ± 0.010 T/MGIF
                                   K-3

-------
                                APPENDIX L

                   ANALYSIS OF RAW SLUDGE DEWATERING ON
      AVERAGE SLUDGE PRODUCTION PER MILLION GALLONS OF INFLUENT FLOW*
TABLE L-l.

r«rrtc chloride usite

.Innch
faniuirv
February
March
April
•lav
June
Weraie
Standard
Tons
per
Tom per ton of dry
Tena per
d»» solids to filter dav
20
17
II
II
II
12

3
a
3
.3
3
3

20 5/114
17 8/1 10
11 5/73
II 3/134
II 5/96
12.5/108

deviation
0 180
0 162
0 133
0.073
0.12(1
0 116
0 134
0 031
55
48
38
i3
47
48


Line usage

Tons p«r ton

if dry
solids to filter
55/114
48/110
38/7S
18/134
47/96
48/108


0
a
a
0
0
!
0
0
482
4)6
307
312
490
_44i
443
071


feed soklda Oraatere-1 cake.
concentration, percent
percent solids
44 17
: 17
) :i
a 21
5 21
6 ZZ_
:o
2
2
9
6
1
1
_6
Z
2

Secondary sludge
fraction.
percent by 'eight
72
44
47
36
38
33



     The  amount  of  solids  currently  contributed  by  lime  addition  per
million gallons of influent flow is estimated below.

     The average amount of lime (CaO) added per ton of dry solids pumped to
the vacuum  filters  is 0.445 t 0.065 tons.  It  is  assumed that all calcium
solids  (71.5  percent  of the CaO) remain in the sludge and that there are 5
percent inerts associated with the high grade CaO utilized.  Therefore, the
amount of solids contributed by lime addition would be:

          (0.71 + 0.05)(dry weight CaO added)

          =    (0.76)(0.445 ± 0.071)(dry solids to dewatering)

          =    (0.338 ± 0.054)(dry solids to dewatering)

     For current conditions, raw sludge to dewatering, the amount of solids
contributed by CaO  addition per million gallons of influent flow would be:

          (0.338 ± 0.054)(0.661 ± 0.063)

          =    (0.338)(0.661) ±   (0.661)  (0.054)  +  (0.338)2 (0.063)2

          =    0.223+0.042 T/MGIF**
*  All data taken from Appendix A, Table A-6

** T/MGIF = Dry ton of solids per million gallons of influent flow.
                                  L-l

-------
     In  the  future, CaO  requirements  per ton of dry  solids  pumped to the
vacuum filter  are  expected to drop by at least 50 percent.  This reduction
is due to  the  current addition of  lime  in excess of conditioning  require-
ments  so that a high  pH  can be developed to meet  land trenching  require-
ments.   In  the  near  future,  trenching  will  not be  utilized and  lime
requirements will  decrease  to  that required to  enhance dewatering opera-
tions  only.   This   50  percent reduction would change  the  amount of solids
contributed   by    lime   addition   from   [(0.338 ± 0.054)(dry   solids  to
dewatering)] to [(0.169 ± 0.054)(dry solids to dewatering)].

     For  future  conditions,  if  raw  sludge  to  dewatering, the  amount  of
solids contributed by CaO  addition per  million  gallons of  influent  flow
would be:

          (0.169 ±  0.054X0.705 ± 0.063)
               (0.169)(0.705) ±  vAO.705)2 (0.054)2 + (0.169)2 (0.063)2

          =    0.119 ± 0.040 T/MGIF

     For  future  conditions,   if only  primary sludge  to  dewatering,  the
amount  of  solids  contributed  by  CaO  addition  per million  gallons  of
influent flow would be:

          (0.169 ± 0.054)(0.377 ± 0.055)
               (0.169)(0.377) ±  \A0.377)2 (0.054)2 + (0.169)2 (0.055)2

               0.064 ± 0.022 T/MGIF

     For  future  conditions,  if only  secondary  sludge to  dewatering,  the
amount  of  solids   contributed  by  CaO  addition  per million  gallons  of
influent flow would be:

          (0.169 ± 0.054)(0.328 ± 0.031)
               (0.169)(0.328) ± x/(0.328)2 (0.054)2 + (0.169)2 (0.031)2

               0.055+0.018 T/MGIF

     The  amount  of  solids  currently  contributed  by ferric  chloride per
million gallons of influent flow is estimated below.

     The  average  amount  of ferric  chloride added per  ton of  dry solids
pumped to the vacuum filters is 0.134 ± 0.038 tons.  It is assumed that all
iron solids  (44 percent  of the ferric chloride)  and  20.2 ± 2.0 percent of
the  chloride  solids remain  in the sludge (the  remainder  of the chlorides
                                  L-2

-------
leaves with the  filtrate).  Therefore, the amount-of solids contributed by
ferric chloride would be:

          (0.44 + [0.202 ± 0.02][0.56](dry weight ferric chloride added)

          =    (0.55 ± 0.011)(dry weight ferric chloride added)

          =    (0.55 ± 0.011)(0.134 + 0.038)(dry solids to dewatering)

          =    (0.074 ± 0.021)(dry solids to dewatering)

     For current conditions, raw sludge to dewatering, the amount of solids
contributed by  ferric chloride  addition per million   gallons of influent
flow would be:

          (0.074 ± 0.021)(0.611 ± 0.063)
               (0.074)(0.66l) ± \A0.66l)2 (0.021)2 + (0.074)2 (0.063)2

          =    0.049+0.015 T/MGIF

     In  the future,  ferric  chloride  requirements per  ton of  dry solids
pumped to the vacuum filter are expected to drop at least 15 percent.  This
reduction is due  to the significant reduction  in  lime  requirement brought
about by elimination of the trenching operation.  This 15 percent reduction
would change the  amount of solids contributed  by  ferric  chloride addition
from  [(0.074 ± 0.021)(dry  solids  to dewatering)]  to [(0.063 ± 0.021)(dry
solids to dewatering)].

     For  future  conditions,  if  raw sludge to dewatering, the  amount of
solids  contributed  by  ferric  chloride  addition  per million   gallons of
influent flow would be:

          (0.063 ± 0.021)(0.705 ± 0.063)
               (0.063)(0.705) ± V(0.705)2 (0.021)2 + (0.063)2 (0.063)2

          =    0.044+0.015 T/MGIF

     For  future  conditions,   if  only  primary sludge  to dewatering,  the
amount  of  solids  contributed  by  ferric  chloride  addition per  million
gallons of influent flow would be:

          (0.063 ± 0.021)(0.377 ± 0.055)
               (0.063X0.377) + \A0.377)2 (0.021)2 + (0.063)2 (0.055)2

               0.024 ± 0.009 T/MGIF
                                  L-3

-------
     For  future  conditions,  if  only secondary  sludge  to dewatering,  the
amount  of  solids  contributed  by  ferric  chloride   addition  per  million
gallons of influent flow would be:

          (0.063 ± 0.020(0.328 ± 0.031)
               (0.063X0.328) ± v/0.328)2 (0.021)2 + (0.063)2 (0.031)2

               0.021 ± 0.007 T/MGIF
                                  L-4

-------
                                APPENDIX M

                    SECTION 6.1 SUPPORTING CALCULATIONS


M.I.  DIGESTED SLUDGE VACUUM FILTER OPERATION

M.I.I.  Current Operation

     There are four existing units each having 500 square feet of filtering
area.  Their yield  depends  upon the ratio of secondary and primary sludge.
In 1974 when the mixture was 40 to 50 percent secondary, the yield averaged
2.41 pounds per square foot per hour.

       2.41 pounds       500 square feet     4 units     24 hours
     square foot-hour X        unit       x     1     x    day


     =  115,680 pounds per day

     Assuming an  average feed  solids  concentration of  five  percent  and a
density of 8.85 pounds per gallon, the volume of digested sludge capable of
being dewatered is:

     115,680 pounds       1 gallon
                     x
          day           8.85 pounds        0.05


     =  261,423 gallons per day

     Assuming  an  average cake  solids  of 16.5  percent,  the number  of  wet
tons to  be hauled  away  including the ferric  chloride  (FeCl_)  conditioner
would be:


t 115,680 pounds sludge  +  13,180 pounds Fed- ,   x     1 ton     x    1
          day                       day         J      2000 pounds     0.165

     =  390.5 wet tons per day

M.I.2.   Future Operation

     If six new filter units (600 square feet filtering area each with the same
yield of 2.41 pounds per square foot per hour)  are placed into operation, then:

        2.41 pounds        600 square feet     6 units     24 hours
     square foot-hour           unit              1     x     day


     =  208,224 pounds per day
                                  M-l

-------
     Assuming  same  feed  solids  concentration and  density as  before,  the
volume of sludge capable of being dewatered is:

     208.224 pounds      1 gallons   „    1
                     X
          day           8.85 pounds      0.05


     =  470,563 gallons per day

     Assuming  an  average cake  solids  of  16.5  percent,  the  number of wet
tons  to  be hauled  away including the ferric  chloride  (FeCl_)  conditioner
would be:


r 208.224 pounds sludge  +  23,725 pounds Fed. ,  x     1 ton     x    1
           day                      day         J     2000 pounds     0.165

     =  703 wet tons per day

     If the maximum  sludge  production generated at 334 million gallons per
day  influent   flow  was  mesophilically  digested  under  the  conditions  de-
scribed in Section  M.5 of this Appendix, there would be 340,050 pounds per
day to dewater.  The maximum number of filters required would be:

     340,050 pounds     1 filter - day
          day           34,704 pounds


     =  9.8,  or 10 filters required

     Assuming an average cake solids at 16.5 percent, the maximum number of
wet  tons  to  be hauled away  including  the ferric  chloride  (FeCl_) condi-
tioner would be:


  340,050 pounds sludge  +   38,744 pounds Fed,    x     1 ton     x    1
         day                        day               2000 pounds     0.165

     =  1,148 wet tons per day maximum
M.2.  ELUTRIATION OPERATION

     In order to generate 115,680 pounds of solids per day in the elutriate
underflow at a maximum hydraulic flow rate of 490,000 gallons per day and a
density of 8.64  pounds  per gallon, the incoming digested solids concentra-
tion would have to be:
     115,680 pounds       1 gallon            1 day          100
         day         X  8.64 pounds   X  490,000 gallons  X   1

     =  2.7 percent solids

     For any  flow  less  than 490,000 gallons per day, the solids concentra-
tion would have to be proportionately higher.
                                  M-2

-------
     In order  to  generate  208,224 pounds of  solids  per day under the same
stated conditions, the incoming digested solids concentration would have to
be:

     208,224 pounds       1 gallon            1 day          100
          day        x  8.64 pounds   x  490,000 gallons  x   1


     =  4.9 percent solids
M.3.  HEAT EXCHANGER OPERATION*

     Available  heating  capacity limits  the amount  of  sludge that  can be
hydraulically  processed.   The maximum  flow rate possible  based solely on
sludge heating capacity is:

1980 winter operation

     (9,800,000 BTU per hour)	(24 hours)
     (8.6 pounds per gallon)(95 - 55°F) (day)


     =  683,721 gallons per day

1981 summer operation
     (11.100,000 BTU per hour)	(24 hours)
     (8.6 pounds per gallon)(95 - 75°F) (day)

     =  1,548,837 gallons per day

1981 winter operation

     (12,800,000 BTU per hour)	(24 hours)
     (8.6 pounds per gallon)(95 - 55°F)  (day)


     =  893,023 gallons per day

1982 summer operation

     (14.100.000 BTU per hour)	(24 hours)
     (8.6 pounds per gallon)(95 - 75°F) (day)


     =  1,967,442 gallons per day


M.4.  DIGESTION TANK OPERATION

     The available  data  indicate that the  system can  be operated success-
fully at an  average hydraulic residence time of 16 days.  The maximum flow
rate possible based solely on usable tank capacity is:
*  See Appendix G for discussion of calculation performed.
                                  M-3

-------
     8,545,581 gallons of usable tank volume
                      16 days


     =  534,099 gallons per day

     If  the  digestion tanks  were cleaned and  grit  accumulation kept  to  a
minimum, the maximum flow rate possible would increase  to:

     13,147,055 gallons of usable tank volume
                      16 days


     =  821,691 gallons per day

     If  the maximum sludge production generated at  334 million  gallons per
day influent  flow  rate  was mesophilically digested  at a minimum hydraulic
detention time of 16 days, and if the existing  digesters were  clean of  grit
and  grit accumulation was  kept  to  a minimum  in  the  system, the  maximum
number  of digestion  tanks  required (all  the  same  dimensions) would  be:

     1,200.062 gallons     16 days     	1 digester	
            day               1      x  1,096,000 gallon capacity


     =   17.5, or 18 tanks required;  six new tanks would be  required to  meet
     this condition.

     Operating data at Blue Plains indicate that the  system can  be  operated
successfully  at volatile  matter  loading ratios  averaging  0.16   to 0.17,
though gas production seems to deteriorate over 0.14.   The  maximum  volatile
matter loading based on 0.16 pounds  per usable  cubic  foot per  day would be:
1.142,458 cubic feet of usable tank  volume      0.16  pound volatile  matter
                      1                              usable  cubic foot

=  182,793 pounds volatile matter per day

     If  the digestion  tanks  were cleaned and grit accumulation  was kept to
a minimum,  the maximum  volatile matter  loading  based  on  0.16 pounds  per
usable cubic foot per day would be:

1,757,628 cubic feet of usable tank  volume       0.16 pound volatile matter
                      1                               usable  cubic   foot

=  281,220 pounds volatile matter per day

     If  the maximum sludge production generated at  334 million  gallons per
day  influent  flow  rate  was  mesophilically digested at a  maximum  volatile
matter loading  of  0.16  pounds per cubic  foot per day, and if the  existing
digesters were clean of grit and grit accumulation was  kept to a minimum in
the  system,  the maximum  number of  digestion tanks  required  (all  the  same
dimensions) would be:

      362,022 pounds volatile matter    	1 cubic foot -  day       	1  tank
            day                  0 16 pounds volatile matter  x  146,469  cabic feet

     =   15.4, or 16 tanks required;  hydraulic flow rate governs.

                                  M-4

-------
M.S.  GALLONS OF  PRIMARY AND SECONDARY SLUDGE PUMPED  TO DIGESTION

     If  the existing  digestion  system was  processing all the  Blue Plains
sludge,  the  ratio of thickened secondary sludge volume to thickened primary
sludge volume  would be  1.54:1.   Using this  ratio  for allocating the 490,00
gallons  gives:
Gallons
per day
192,913
297,087
490,000
Pounds
per day
118,834
103,683
222,517
Volatile Pounds
per day
84,373
66.254
150,627
Primary sludge

Secondary sludge

         TOTAL


     The following  constraints apply to the above  calculations:

     o  Total  flow  to  digestion  system  to  be  no greater  than  490,000
        gallons per  day -  ok

     o  Minimum  ratio  of  secondary sludge mass  to total sludge  mass to be
        0.35

        103,683 pounds secondary sludge per day        ,_
          222,517 pounds total sludge per day    =     '  "  °K


     o  Concentration  of feed solids into digestion  tanks not  to exceed six
        percent

              (222,517  pounds total sludge per day)(100)            .,
          (8.6 pounds  per  gallon) (490,000 gallons  per day)   ~   *"** " OK


     o    Concentration of  solids into  elutriation  system from digestion
          tanks to  exceed  2.7 percent

          From  Figure  5-2,  at  a  secondary:total  mass  ratio  of 0.46  an
          average  volatile  matter reduction  of 53.5  percent  is expected.

      1(222.517 pounds of sludge per day) - 0.535(150.627 pounds volatile sludge  per dap]'. 100'
                    (3.50 pounds per jalion)(490,000 gallons per day)

          "=   3.4 percent - ok

     o    Sludge mass  from  digestion tank not to  exceed  115,680 pounds per
          day  using the existing  drum filters  for dewatering  and 208,234
          pounds per day using the six new belt  type filters for dewatering.

      222,517 pounds of sludge per day - (0.535)(150,627 pounds volatile sludga per day}

          =   141,932 pounds per  day  -  not ok for  current operation of drum
              filters;   ok  for  future  operation with new  vacuum  filters.
                                   M-5

-------
M.6.  GAS  PRODUCTION

M.6.1.   490,000 Gallon Per Day  Sludge Processing Rate

     Under the constraints imposed in developing the 490,000 gallon per day
flow rate,  gas production is  expected to range from  12 to 14 cubic feet per
pound of volatile matter reduced.

Volatile matter reduced:

     (0.535) (150, 627)  =  80,585  pounds per day


     80,585 pounds     12 cubic feet       „,_ no.   , .   -  t      ,
        1 day -  x     pound -  =    967'020 cubic feet per day

     80,585 pounds     14 cubic feet     . ,-„ inn   , .   ,  .       ,
        ' day -  X  - pTSnd -  =  1.128,190 cubic feet per day


     Gas consumption to meet  winter and summer sludge  heating requirements
are:

Winter  operation:


      690.000 gallons    8.6 pounds     (95-55)"F    24 hours    5.195.656 3TU radiation  loss
           day          gallon   *     1        day    x            -
                              600 BTU        0.8 heat efficiency factor
                          cubic foot of gas              1
      =   510,949 cubic feet  per day

Summer  operation:
       690.000 gallons    8.6 pounds    (95-75)T  t  24 hours    1,835.250 3T1' radiation loss
           day          gallon    x     1         day   x         hour

                              600 BTU        0 8 heat efficiency factor
                          cubic fooc of gas              1


      =  267,346 cubic  feet per day

Average expected excess:

      (967.Q20 + 1,128.190) cubic feet  _   (510,949  + 267,346)  cubic  feet
                   2 day                 "                2 day


      =  658,458 cubic  feet per day available  to  be  sold

M.6.2.  Maximum Gallon Per Day Sludge Processing Rate

      Again,   gas  production  is expected  to range  from  12  to  14  cubic  feet
per  pound of volatile  matter reduced.

                                    M-6

-------
Volatile  matter reduced:

      (0.535)(319,030)  = 170,681 pounds per day


      170.681 pounds        12  cubic feet       . ...  ._,     , .    ,  ,.
      -      -    x     pound -   =   2>OA8>172   cublc  feet  P"
      170,681 pounds        14  cubic feet       „ ,on  _0/     , .    ,
      -      -    X     pound -   =   2>389>534   cublc  feet
Gas  consumption  to  meet  winter  and  summer  sludge  heating  requirements
(based  on 18 digestion tanks) would  be:


Winter  operation:


      1.200.062 gallons    8.6 pounds    (95-5STT  .  2i hours     5.272.829 BTU radiation loss
        - d^ -  X    galloD    x     1          day              hour
                              600 BTU        0.8 beat efficiency factor
                          cubic feet, of gas




      =  1,123,686  cubic feet per day


Summer operation:



       1 200.062 gallons    8.6 pounds    (95-75)°F    26 hours    3.C2S.162 BTU radiation loss
       -	day	  *    gallon   x    1          day               hour

   	600 STU0.8 heat efficiency factor
                          cubic feet of gas             1



      =  581,430  cubic  feet per  day


Average expected excess:


      (2.048,172  +  2,389,534) cubic  feet  _  (1,123,686  + 581,430) cubic  feet
                  2                  day    "                2                day


      =  1,366,295  cubic feet per day available to be sold
                                     M-7

-------
                                APPENDIX N

                    SECTION 6.2 SUPPORTING CALCULATIONS


N.I.  DIGESTED SLUDGE VACUUM FILTER OPERATION

     Each vacuum  filter  has  600 square feet of filtering area.  Assuming a
minimum yield for this sludge, thermophilically digested, of 3.0 pounds per
hour per square foot, each filter would be able to dewater:

        3.0 pounds        600 square feet     24 hours
     square foot-hour         filter            day


     =  43,200 pounds per day

     As indicated elsewhere in this Appendix, if the maximum sludge produc-
tion  generated  at  334  million gallons  per  day influent  flow  rate  was
thermophilically  digested,  there would  be  340,050 pounds  per day  to  de-
water.  The maximum number of filters required would be:

     340,050 pounds     1 filter-day
          day        x  43,200 pounds


     =  7.9, or 8 filters required

     Assuming an average cake solids of 16.5 percent,  the maximum number of
wet  tons  to  be hauled  away including  the  polymer conditioner  would  be:
  340,050 pounds sludge + 680 pounds polymer solids   x    1 ton    x   1
          day                         day               2000 pounds   0.165

     =  1,033 wet tons per day maximum


N.2.  ELUTRIATION (COOLING) OPERATION

     Sludge  elutriation  is  not required,  instead,  the  elutriation tanks
would  be  utilized  as sludge cooling  tanks.   The  system would  still be
operated as  a  two-stage  series,   co-current, washing  operation but under
different washing  rates.   The maximum hydraulic  flow  through digestion at
334 million gallon per day influent flow rate is 1,200,062 gallons per day.
The temperature  of  digested  sludge is 122°F.  Cooling  water  on a 1:1 flow
basis would  be  mixed with digested  sludge before entering the elutriation
tanks.  The warmest  cooling  water is  assumed to be  60°F.    In  the first
stage,  1,200,062  gallons  of  sludge at 122°F  is mixed  with 600,031 gallons
of  wash water  at  60°F.   Under  these  conditions, the  minimum sludge dis-
charge temperature would be:

     (1.200.062 gallons)(122°F) + (600,031 gallons)(60°F)  _       0
           (1,200,062 + 600,031) gallons                   ~      J


     If we  assume that  the  sludge concentrates  to 75  percent of its ori-
ginal  volume,   is  pumped  to  the  second stage,  and  blended  with 600,031
gallons of  wash water at 60°F, the minimum sludge temperature discharge to
dewatering would be:

                                    N-l

-------
     (1,200.062 gallons)(0.75)(101.3°F) + (600,031 gallons)(60°F)        .„.
                [(1,200,062)(0.75) + 600,031] gallons              ~  8^tt *
NOTE:  It  may be  economically attractive  to  build a  tube and  tube heat
exchanger  for raw sludge  going to digestion  and digested  sludge leaving
digestion.
N.3.   EFFECT ON  SYSTEM HEATING  CAPABILITIES  DUE  TO  INCREASE  IN  SLUDGE
      OPERATING TEMPERATURE"

N.3.1.  Heat Required for Primary Sludge Addition Only
Winter operation:
     1454 gallons     8.8 pounds     (122 - 55)°F
                   A              X  ^"^^^^^^^^—
        MGIF**           gallon            1
     =  857,278 BTU's per MGIF
Summer operation:
     1454 gallons     8.8 pounds     (122 -
         MGIF      x    gallon    x       1
75)°F
     =  601,374 BTU's per MGIF
N.3.2.  Heat Required for Secondary Sludge Addition
Winter operation:
     2139 gallons     8.5 pounds     (122 - 60)°F
        MGIF       X    gallon    X       1
     =  1,127,253 BTU's per MGIF
Summer operation:
     2139 gallons     8.5 pounds     (122 - 80)°F
         MGIF      x    gallon    X       1
     =  763,623 BTU's per MGIF
*  Assumptions  and calculations  are  as  per  Appendix G  except digestion
  operating temperature at 122°F rather than 95°F.
** MGIF - million gallons influent flow.
                                    N-2

-------
N.3.3.  Heat Required for Conductive/Convective Losses

Roof - winter operation:

     (0.23 BTU)(66,501 square feet)(122 - 0)°F  _     „
     - hour:squarj foot.oF -  -  1,866,018 BTU per hour


Roof - summer operation:

                                        '    °                   per hour
Walls - winter operation:

     (0.13 BTU) (71. 154 square feet) [ (0.59) (122-0)°F + (0.4l)(122-70)°F3
                          hour-square foot-°F


     =  863,027 BTU per hour

Walls - summer operation:

     (0.13 BTU) (71. 154 square feet) [ (0.59) (122-60)°F + (0.4l)(122-70)°F]
                          hour-square foot-°F


     =  535,576 BTU per hour

Floor - summer and winter operation:

     (0.11 BTU) (90.391 square feet)(122-40)°F  _  ft
              hour:squar^ f00t-oF -  -  815,327 BTU per hour


Sludge piping - winter operation:

(0.32 BTU) (6000 square ft)(122-0)°F + (1.6 BTU)(10,000 square ft) (122-70)°F
       hour-square foot-°F                     hour-square foot-°F

=  234,240 + 832,000 = 1,066,240 BTU per hour

Sludge piping - summer operation:

(0.32 BTU) (6000 square ft) (122-60)°F + (1.6 BTU) (10000 square ft) (122-70)°F
      hour-square foot-°F                    hour-square foot-°F


=  119,040 + 832,000 = 951,040 BTU per hour

N.3.4.  Summary of Heat Requirements

                                                       Winter      Summer
                                                     operation    operation
For raw sludge addition in BTU's per MGIF

          Primary sludge only                         857,278      601,374
          Secondary sludge only                     1,127,253      763,623

          TOTAL PRIMARY & SECONDARY SLUDGE          1,984,531    1,364,997

                                    N-3

-------
Winter
operation
1,866,018
863,027
815,327
1,066,240
Summer
operation
948,304
535,576
815,327
951,040
For system heat loss in BTU's per hour
     0    Roof
     0    Walls
     0    Floor
     0    Sludge piping

          TOTAL HEAT      LOSSES                    4,610,612    3,250,247

     Based  on a 334  million gallon  per day  (MGD)  of influent  flow,  the
total digestion sludge heating requirements would be:

Winter operation:

     (1.984,531 BTU's)(334 MGIF)  +  (4,610.612 BTU)(24 hours)
           (MGIF)       (day)            (MGIF)        (day)

     =  7/8 x 108 BTU's per day (32.2 x  106 BTU per hour)

Summer operation:

     (1.364,997 BTU's)(334 MGIF)  +  (3,250,247 BTU)(24 hours)
          (MGIF)         (day)           (hour)         (day)

     =  5.3 x 108 BTU's per day (22.2 x  106 BTU per hour)
N.4.  EFFECT ON SLUDGE PIPING DUE TO INCREASE IN SLUDGE OPERATING
      TEMPERATURE

     All sludge piping involved in transporting sludge from the sludge heat
exchangers  to  the digesters and  from  the digesters back to  the  heat  ex-
changers is made of steel, located in pipe galleries protected from outside
weather conditions, and not ridgidly anchored at the ends.  Any increase in
sludge operating  temperature  will cause a corresponding  increase  in pipe
expansion.  Linear expansion would  be  of primary concern at this installa-
tion.

     The additional linear expansion of the sludge piping due to increasing
the sludge  temperature  from  the existing operating temperature to a higher
operating temperature can be calculated using the equation.

          L = (o)(L)(AT)

  where

          L = the change in length of the piping system being considered,
                inches.

          a  = the coefficient of linear expansion, for steel it is
                78 x 10"  inches per foot per °F
                                    N-4

-------
          L = length of piping being  considered,  feet

         A T = increase in  temperature,  °F

     The sludge piping involved  currently operates at a temperature of 90°F
to 93°F.  Operating at a maximum  sludge temperature  of  130°F,  the maximum
increased temperature,    T, would  be 40°F.

     Maximum linear expansion would occur on the  longest pipe segment.  The
longest pipe  segment  is 400 feet  long and  is  located on the north side of
the  digestion facility  where  it  carries  heated  sludge to  the  anaerobic
digesters.

     The  maximum  increased  linear  expansion,    L,  is  calculated  to  be

                 78 x  10"6  inches   x  400 feet x 40°F
                     foot - °F

or 1.25 inches

     Based  on calculations  for  expansion  of  all  other pipe  segments and
best  engineering judgement, the  increase in temperature  and the  resultant
pipe expansion will not adversely  effect the sludge piping involved.
N.5.  EFFECT ON ANAEROBIC DIGESTION TANKS DUE TO INCREASE IN SLUDGE
      OPERATING TEMPERATURE
     Increasing  the  sludge temperature within the existing concrete diges-
tion tanks  will  create increased  stresses on the  outer  face of the diges-
tion tank walls.  The amount of  stress  developed in the  concrete and the
amount of reinforcing  steel  required needs to be calculated and compared to
the existing  situation to make  sure a structural  failure  would not occur.

     Figures  N-l and N-2  show  the situation that would occur on the exist-
ing structure assuming  that the  maximum sludge  temperature is  130°F and
the coldest ambient  air temperature is 0°F.
          TQ - DIGESTER TEMP.

           ASSUME 130°F
          HORIZONTAL STEEL
           REINFORCEMENT

           *8 99" EF •
                             72
         TA ' AMBIENT AIR TEMP.
            ASSUME 0°F
     SOIL

FIGURE  N-l.    Cross  section  of  existing

          anaerobic  digestion  tank  wall.
                           -•— t = WALL THICKNESS
                               =• 21.5"
                                     N-5

-------
           V 130°F
              DIGESTER
                  CONCRETE
                   WALL -
                          t«ZI.S
                                            SOIL
                      TEMPERATURE
                          GRADIENT
                                        72"
                                                         AIR
                                                           TA- 0°F
FIGURE  N2.   Assumed  temperature gradient  through  digester wall and  soil.


     As  indicated in Figures  N-l  and N-2,  the existing tank walls  are 21.5
inches  thick  with #8 rebar  placed every 9  inches.  In addition,  the entire
structure  is  buried;  the minimum  soil  cover on  the side walls being  72
inches.

     The stress  in the outer  concrete wall  is  calculated on  the following
two pages.

     Temperature  difference  through  the  wall, T,  can be  found by  the fol-
lowing equations.

               T  =  (Tn  -  TJ  t/K
     and
     where:
               1/K =  1/S  + t/K + t./K
T. =

 K =

K- =

 t =

t. =

 S =
                                      1
               digester  temperature (°F)

               ambient air temp (°F)

               coefficient of conductivity for concrete

               coefficient of conductivity for soil

               thickness of concrete (inches)

               thickness of soil (inches)

               outside surface coefficient

                                     21.5
               T =  (130-0)
                            12
= 22°F
                     1
                     6
                                   21.5 .  72
                                   ~12~   ~~8
                                     N-6

-------
        18.   T*
in Cylindrical Tank Wall* *
      Tanks  containing  lioc  liquids  ire  subiect  co
cefflpennire stresses. Assume  chat the temperature is
Ti in the inner face, T- at the oucer face, ma that the
cempenruK decreases uniformly from inner to  outer
face. Ti - T, being denoted as T Fig J7 shows a seg-
ment of i tank  wall in two positions, one before and
one after a uniform increase in temperature. Tie anginal
length of the  are of the will has been increased, but an
increase chat is uniform throughout will not create
JUT stresses as long as the nng  is supposed to be free
tod unrestrained at its edges.  It is the cemperanue
differential onlv, T, which  creates stresses.
               Aftor
                       no. 37
       Toe >*frr fibers  being noner  cend  :o  expand
 note than the outer fibers, so if the segment is cut loose
 from the adjacent portions of the  wail. Point A m
 Fig 38 will move to iV. 3 will move to B', and section
                  X ourjiOQ
 rlB, which, represents the itreuless condition due to 4
 uniform temperature cnange throughout, will move to
 i new position A'B'  Actually tne movements cram A
 co A' and 3 to B' ire prevented since the circle must
 remain i circle, ind  irresses will  be created caac ire
 proportional co che horizontal distances between A3
 mo A'B'
      It is dear that AA' - SB' - movement due to a
temperature change of \%T or wnen > is tne coefficient
of expansion, chat
      AA'  • SB' » Yit X • per unit length of arc.
and

                 4.~.TX *
                     \fy      i
      In i homogeneous section, the moment  ,V(  re-
quired co produce an angle change * in an element of
unit length mav be written as
                    M - Elt
      Eliminating 9 gives
                 ..   El X  T X i
                 m • —^———
                           i
      The stresses in che extreme nben created bv M are

           /-^X--M£XrX,

      The  stress distribution across the cross section
is as indicated in Fig.  38. The stresses are numerically
equal at the two  faces but have opposite signs. Note
chat che equation applies to uncracked sections onlv,
and that this  procedure of stress  calculation is co be
considered  merely as a method bv which the problem
can be approached.  The variables £ and I in che equa-
tions  are  uncertain quantities.  E  mav  vary  from
1,300.000 up to 4,300.000 p.s.i.. and / may also varv
considerably because of deviations tram che assumption
of linear relation between stress and strain.  Finally, if
che concrete cracks, M can ao longer be set equal co

Eli, nor / equal to -j X —  As  a  result, the equation

/ - yftt is to be regarded as merely indicative rather
chan formally correct.
      The value of « may be taken as 0.000006, and for
che purpose of this problem choose £ • 1.300,000 p.s.i.
Then  £  X i - 9 and/ - 4.jr
      The value of T a the difference between tempera-
tures in  che two surfaces of che concrete which mav be
computed  from che temperature of cne  stored  liquid
and che  outside air.
                      HO. If
 a  circular Concrete Tanks  Wlthouc  Preacreaaing.
    5420 Old Orchard Road,  Statue,  111.  60076.
                                                               Portland  Generic  Association.
                                                   N-7

-------
      M'hen (he ilow of he-ic n uniform from the inside
co the outside of che wall section in Ftp. )9. the tem-
 perature difference,  T -  7"i  - Ti.  a smaller than  che
 difference. T, — T.. becweea che inside  liquid  and  che
 ouoide  air Standard cextbooki give
                 T - (T, - T.)
 in which
     i
                             4-  !
                       /    i ^ i,
        • coefficient of conductivity of stone or
          jravel coocrete - U B.C. it. per hour per
          sq.ft. per deg. F. per to. of chicknai
     ii - coefficient of conductivity of insulating
          material
     i • ctuckneu of concrete in in.
     'i - thickness of insulating material
     ; - outside surface confident • 6 B.t.u. per
          hour per sq.ft. per deg. F

 Assuming an anuuulated wall
                    6    12
      Consider a "«fc with wall thickness / •  10 m.
which holds a liquid with a temperanire T, - 120 deg
F while che temperature of che ouoide air 7".  - 30
deg. F Then
                            10
, (120 - 30^^-75 deg. F
and
        / - 4 ST - 4 5 X 75 - 37J p 1.1.

      The stress of / •  373 p.s.i. is tension in che out*
side and compression in the inside face. If ue uniformly
distributed nag tension due to load in che tank is. sav,
300 p.s.i.. che combined stress will be:
Ouoide fiber: 300 -r 375 -   «75 p.s.i. (tension)
Inside aber:   300 - 375 -  -75 p.s.i. (compression)
      In realicv,  coo much significance should not be
attached to  che temperature stress computed from che
equation derived. The stress equation is developed from
che strain equation. AA' - >$ Ti, based on the'assump-
tion chat stress is proportional to strain.  This assump-
tion is rather inaccurate for the case under ducussioa.
The inaccuracy mav be reclined co some extent by using
i relatively  low  value for £<,  such as £, - 1,300.000
p 1.1., whica  is  used in this section. An even lower
value may be iiuuned.
                                                            Ai  computed  in che example,  a  temperature
                                                      differential of 75 deg  r. jives a stress  at  375 p.s.i. m
                                                      che extreme fiber. This is probaoiy more than che con-
                                                      crete can cake in addition co che regular  nng tension
                                                      strew without  cracking  on che colder  surface. The
                                                      temperature stress may be reduced bv  means of insu-
                                                      lation. which serves co decrease the temperature dif-
                                                      ferential. or additional horizontal reinforcement mav be
                                                      provided dose to che colder surface. A procedure will
                                                      be illustrated for determination  of tempera cure  steel.
                                                      Ic is not based awn a rigorous mathematical analysis
                                                      but will be helpful as a guide and as an aid to engineer-
                                                      ing judgment.
                                                            It u proposed to base che design on the moment
                                                      derived in  this  section. M. -  EJTi/i,  in which  che
                                                      value of £< is taken aa 1. JOO.000 p.s.i. If / is taken for a
                                                      secaoa 1 ft. high. I equal* r*. and M  is  the moment
                                                      per ft. Then
                                                            M - 1,300,000 X  r1 X T X  O.OOOOOfi  -  9rT
                                                      ui.lb. per ft. in which
                                                             f m thickness of wall in in.
                                                             r • temperature differencial in deg. F.
                                                            The area of horizontal steel at the colder face
                                                      computed as for a cracker! section is
                                                                                M
                                                                                      "3552
                                                            For example, assume t - 15 m., T • 75 deg. F ,
                                                      and d m 13 in., which gives
                                                                      This area is in addition co che tegular nng steel.
                                                         N-8

-------
     The  stress,  f,  on the  concrete  can be  determined by  the equation:

               f = 4.5 T = 4.5 (22°F) = 99 psi

     The maximum stress on the wall should be less than 300 psi as dictated
by  common engineering practice.   Since  the temperature  stress  is  only 99
psi, the concrete will not crack.

     The  amount of  reinforcing  steel required  to resist  the temperature
stress can be calculated from the following equation:

          A  =   9t2T
               17,500d

where     A,, = cross  sectional  area  of  steel per  foot  of  wall - square
               inches (sq. in.)

          d  = effective concrete thickness (21.5" - 2(3") = 15.5")

          A_ = 9(21.5)2(22)   = 0.34 sq. in.
               17,500 (15.5)

     The maximum  temperature stress  occurs in the  outer wall  face.   The
amount of  steel  in that face is one //8 bar every 9 inches.  Since a #8 bar
equals 1 inch  diameter  or 0.79 sq. in., there is 0.79 x 1.33 or 1.05   sq.
in.  of  steel in the outer  face.   This  is more than  is  required to resist
the temperature stress,  therefore, the wall will not crack.


N.6.  DIGESTION TANK OPERATION

     If  the existing digestion tanks  were cleaned and  grit  accumulation
kept  to  a  minimum, the  following hydraulic  and volatile  matter loading
conditions would prevail.


N.6.1.  Hydraulic Residence Time
     Maximum               13,147,055 gallons of capacity
                         894,786 gallons of sludge per day

                         =  14.7 days
     Average               13,147,055 gallons of capacity
          8              1,047,424 gallons of sludge per day

                         =  12.6 days

     M. .                   13,147,055 gallons of capacity
     ninimum             1,200,062 gallons of sludge per day

                         =  11.0 days


                                    N-9

-------
N.6.2.  Volatile Matter Loading


     M. .                 276,038 pounds volatile matter per day
     Minimum             	*—___r.-0	r-.—•=—-—-     *\	*•
                            1,757,628 cubic feet of capacity

                         =  0.157 pounds volatile matter per cubic
                                  foot per day
     .                   319,030 pounds volatile matter per day
         age                1,757,628 cubic feet of capacity

                         =  0.182 pounds volatile matter per cubic
                                  foot per day
     M   .                362,022 pounds volatile matter per day
                            1,757,628 cubic feet of capacity

                         =  0.206 pounds volatile matter per cubic
                                  foot per day
N.7.  GAS PRODUCTION

     Gas production is expected to range from 12 to 14 cubic feet per pound
of  volatile  matter reduced.   Volatile matter  reduction  is  expected to be
53.5 percent (same as mesophilic system but with a shorter hydraulic deten-
tion period).

Volatile matter reduced

     (0.535X319,030)  =   170,681 pounds per day

     170,681 pounds x 12 cubic feet    „ rt/0 -,„   , .  c   .      ,
     	L—-,—*-	   	-;	 =  2,048.172 cubic feet per day
          day              pound        '    '               *     i

     170,681 pounds x 14 cubic feet =         4 cubic
          day              pound        '    '               v     3


     Gas consumption  to  meet winter and summer sludge heating requirements
(based on  12 digestion tanks) would be:

Winter operation:
             0
     7.8 xlO  BTU  x  1 cubic foot gas  x   1  BTU delivered
         day               600 BTU           0.8  BTU utilized

     =   1,625,000  cubic feet per day
                                    N-10

-------
Summer operation:
            c
     5.4 xlO  BTU  x  1 cubic foot gas  x  1  BTU delivered
         day              600 BTU          0.8 BTU utilized

     =  1,125,000 cubic feet per day

Average expected excess:

(2,048,172 + 2,389.534) cubic feet  _  (1.625,000 + 1.125.QQQ) cubic feet
           2               day                    2               day  .

=  843,853 cubic feet per day available to be sold
                                     N-ll

-------
                                APPENDIX 0

                    SECTION 6.3 SUPPORTING CALCULATIONS


0.1.  DIGESTED SLUDGE VACUUM FILTER OPERATION

     Each vacuum  filter  has  600 square feet of filtering area.  Assuming a
minimum  yield   for  this   sludge,   mesophilically  and  thermophilically
digested, of 3.0 pounds per hour per square foot, each filter would be able
to dewater:

        3.0 pounds        600 square feet     24 hours
     square foot-hour          filter            day

     =  43,200 pounds per day

     As indicated elsewhere in this Appendix, if the maximum sludge produc-
tion  generated  at  334  million gallons  per  day   influent  flow  rate  was
mesophilically-thermophilically digested  there  would  be 316,519 pounds per
day to dewater.  The maximum number of filters required would be:
     316,519 pounds     1 filter-day
          day        x  43,200 pounds

     =  7.3, or 8 filters required

     Assuming an average cake solids of 16.5 percent,  the maximum number of
wet  tons to  be hauled  away including the  polymer conditioner  would  be:

 {"316,519 pound sludge    640 pounds polymer solids'!       1  ton        1
        day                        day             J x 2000  pounds X 0.165

=  961 wet tons per day maximum
0.2.  EFFECT  ON SYSTEMS  HEATING CAPABILITIES DUE  TO DUAL  HEATING SYSTEM
      REQUIREMENTS
0.2.1.  Mesophilic System Heat Requirements

     The  following  calculations and  numbers  are  derived  and discussed in
Appendix G.
                                  0-1

-------
Winter operation:

      r 1,148. 161 BTU     334 MGIF •>      3,195.654 ,BTU
      L               *          J
          MGIF*          24 hours            hour

     =  19,174,228 BTUs per hour

Summer operation:

      r 528. 627 BTU     334 MGIFi      1.835.250 BTU
      L   MGIF      x  24 hours J          hour


     =  9,191,976 BTUs per hour


0.2.2.  Thermophilic System Heat Requirements

Heat required for sludge both winter and summer:

     1,200.062 gallons     8.64 pounds     (122-95)°F       1 day
            day         x    gallon     X      1       x  24 hours


     =  11,664,603 BTU per hour

Heat required for conductive/convective losses:

Roof - winter operation:

     (0.23 BTU) (33.205 square feet)(122-0)°F  _              ner
               hour-square foot-°F -  ~  931'732 BTU Per hour


Roof - summer operation:

                                       '                  «»  « hour
Walls - winter operation:

     (0.13 BTU)(35.577 square feet) [(0.59)(122-0)°F + (0.4l)(122-70)°F]
                           hour-square foot-°F


     =  431,513 BTU per hour

Walls - summer operation:

     (0.13 BTU)(35.577 square feet) [(0.59)(122-60)°F + (0.41) (122-70)°F]
                           hour-square foot-°F

     =  267,788 BTU per hour
" MGIF = million gallons influent flow.
                                  0-2

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Floor  -  summer and winter operation:

     (0.11  BTU)(45,195  square feet)(122-40)°F
                 hour-square foot-°F
                                       =  407,659  BTU per hour
Sludge  piping heat losses in thermophilic section are  minimal.

Total hourly winter heat requirements:
      11.664,603 BTU
           hour
               1.772.186 BTU      13,436,789  BTU
                    hour
  hour
0.3.  DIGESTION TANK OPERATION

     At  the  present  time,  the existing  tank layout lends  itself to  using
digesters  1 through 8  as  the mesophilic  units and digesters 9 through  12 as
the  thermophilic  units.   If all the  existing digestion tanks were   cleaned
and  grit   accumulation  kept   to  a  minimum,  the  following  hydraulic  and
volatile matter loading conditions would prevail.
0.3.1.   Hydraulic Residence Time

                  MesoohiHc System
                    Olcesters 1-3
                                         Thennopnlllc System
                                           Olqestara 3-12
  Maximum
  Average
  Minimum
  8.768,000 gallons of capacity
.394,786 gallons of sluge per day

 » 9.3 days

   8.763.000 gallons of capacity
 1,047,424 gallons of sluge per day

 • 8.2 days

   8.768.000 gallons of capacity
 1,200,062 gallons of sluge per day

 • 7.2 days
  a.384.Oflfi gallons cf capacity
394,786 gallons of sludge per day

•  4.9 days

   4.384.000 gallons of capacity
 1,047,424 gallons of sludqe per day

 - 4.1 days

   4.384.000 gallons of capacity
 1,200,062 gallons of jludqe oer day

 • 3.5 days
     Hydraulic  residence  times are  too  short for  both a  mesophilic  and a
thermophilic  system.   If  two digesters of  same  size  were added to  both
processes,  the new hydraulic residence  times  would  be:
           Maximum
           Average
           Minimum
                             Mesophilic
                                system
                               10  tanks

                                 12.2
                                 10.5
                                  9.1
         Thermophilic
            system
           6 tanks

              7.3
              6.3
              5.5
                                    0-3

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0.3.2.  Volatile Matter Loading

     Volatile matter loading based on 10 mesophilic tanks only:
        .                      276,038 pounds volatile matter per day
     ninimum                     1,464,690 cubic feet of capacity

                              =  0.19 pounds volatile matter per cubic
                                      foot per day

                         319,030 pounds volatile matter per day
     Average               1,464,690 cubic feet of capacity


                         =  0.22 pounds volatile matter per
                            cubic foot per day
                         362,022 pounds volatile matter per day
     tlaximum               1,464,690 cubic feet of capacity

                         =  0.25 pounds volatile matter per
                            cubic foot per day
0.4.  GAS PRODUCTION

     Gas production is expected  to range from 12 to  14 cubic feet per pound
of  volatile  matter  reduced.   The volatile  matter reduction  should  be a
minimum of  60 percent.

Volatile matter  reduced:

     (0.60)(319,030)  =   191,418 pounds per day

     191,418  pounds       12  cubic  feet  =           fi cubi{.              d
          day               pound            '    '                  r

     191,418  pounds       14  cubic  feet                ^ic  f^        d
          day               pound

     Gas  consumption  to meet winter  and summer  sludge heating  requirements
 (based  on  16  digestion  tanks) would be:

Winter  operation:

     7.9  x  10  BTU x   1  cubic  foot gas  x  1 BTU  delivered
          day               600 BTU            0.8  BTU utilized

     =   1,645,833  cubic  feet per day
                                   0-4

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Summer operation:

     5.3 x 108 BTU  x  1 cubic foot gas  x  1 BTU delivered
         day              600 BTU           0.8 BTU utilized

     =  1,104,167 cubic feet per day

Average expected excess:

    (2,297.016 + 2,679,852) cubic feet   (1.654.833 + 1.104,167) cubic feet
               2               day                  2                day


     =  1,108,934 cubic feet per day available to be sold.
                                   0-5

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                                APPENDIX P

        THERMOPHILIC DIGESTION REFERENCES FOR SECTION 2.2 AND 6.2
1.   Rimkus, R.R.,  J.M.  Ryan and E.J.  Cook,  "Full Scale Thermophilic Diges-
          tion  at  the  West-Southwest   Sewage   Treatment  Works,"  Paper
          presented  at  the  Annual  Water   Pollution  Control  Federation
          Conference,  Las Vegas, October,  1980.

2.   Smart,  J.  and  B.I.   Boyko,   Full  Scale  Studies on the Thermophilic
          Anaerobic Digestion Process, Report No.  59, Ontario Ministry  of
          the Environment,  Toronto (1977).

3.   Popova, N.M. and O.T.  Bolotina,  "The Present State of Purification  of
          Town  Sewage  and  the  Trend  in  Research  Work  in  the  City  of
          Moscow,"     Advances in Water Pollution Research, Vol.  2     (W.W.
          Eckenfelder, ed.).  MacMillan Co., New York (1964).

4.   Garber, W.F.,  "Plant  Scale  Studies  of Thermophilic  Digestion  at Los
          Angeles,"  Sewage and Industrial Wastes,  26,  1202-1216   (1954).

5.   Garber, W.F.,  G.T.  Ohara, J.E.  Colbaugh and S.K. Raksit,  "Thermophilic
          Digestion  at   the  Hyperion   Treatment   Plant,"   Journal Water
          Pollution Control Federation. 47,  950-961 (1975).

6.   Garber, W.F.,  "Certain Aspects  of  Anaerobic Digestion  of  Wastewater
          Solids  in  the  Thermophilic Range  at  the  Hyperion Treatment
          Plant," Progress  in Water Technology,  8,  No.  6,  401-406  (1977).

7.   Buhr,  H.O.  and   J.F.   Andrews,  "Review  Paper:   The  Thermophilic
          Anaerobic Digestion Process," Water Research, 11, 129-143  (1977).

8.   Puntenney, J.L.,  Personal communication, January, 1981.

9.   Garber, W.F.,   "Thirty  Years  of Experience  with Thermophilic Anaerobic
          Digestion  at  the  Hyperion  Treatment  Plant  in  Los Angeles,
          California," Unpublished manuscript.

10.  Garber, W.F.,  G.T.  Ohara,  S.K.  Raksit and  D.R.  Olson, "Studies  of
          Dewatering  Anaerobically   Digested  Wastewater   Solids   at  the
          Hyperion  Treatment  Plant,"  Progress in Water Technology,   8, No.
          6, 371-378 (1977).

11.  Stern, G.  and  J.B.  Farrell, "Sludge Disinfection Techniques," Proceed-
          ings National Conference on Composting of Municipal Residues and
          Sludges,  Information Transfer,  Inc.,  Maryland  (1977).

12.  Karr, P.R., Personal communication,  December, 1980.

13.  Heukelekian, H. and A.  J.  Kaplovsky, "Effect of Change of Temperature
          on  Thermophilic  Digestion,"  Sewage  Works Journal, 20,   806-816
          (1948).


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