municipal anaerobic digesters as regional renewable energy

8/12/2019 Municipal Anaerobic Digesters as Regional Renewable Energy

http://slidepdf.com/reader/full/municipal-anaerobic-digesters-as-regional-renewable-energy 1/78

MUNICIPAL ANAEROBIC DIGESTERS AS

REGIONAL RENEWABLE ENERGY

FACILITIES

For:

Larry Krom

Research a! De"e#o$me%

Foc&s o Eer'y Ree(a)#e Eer'y Pro'ram

P*O* Bo+ ,-.

S$r/' Gree0 WI 121--

By:

Da/e# 3/%omer a! Prasoo A!h/4ar/

Mar5&e%%e U/"ers/%y

De$ar%me% o6 C/"/# a! E"/rome%a# E'/eer/'

Wa%er 7&a#/%y Ce%er

P*O* Bo+ 8--8

M/#(a&4ee0 WI 1298

May, 2005



E;ECUTI<E SUMMARY

Anaerobic co-digestion is defined as the microbiological production of methane from a

mixture of various wastes. he mixing of wastes can result in both synergistic and

antagonistic interactions that influence methane production. !uccessful application of co-

digestion therefore re"uires careful management.

Many municipal wastewater treatment plants have existing anaerobic digesters that may

be used to co-digest high-strength wastes with municipal wastewater solids. #f used for

co-digestion, then the municipal digesters could become regional renewable energy

facilities.

$our high-strength wastes were studied in an effort to determine appropriate operating

conditions for co-digestion, and to perform a simple economic analysis. Municipal

wastewater solids from !outh !hore %astewater reatment &lant '!!%%&(, )a*

+ree*, %# were co-digested with high strength waste from the following facilities 'with

the range of waste +) in parentheses(

Miller /rewery beer filter '000 1 000 mg34(

4esaffre east fermentation '60,000 150,000 mg34(

!outheastern %isconsin &roducts fermentation '70,000 to 80,000 mg34(

&andl9s :estaurant food '200,000 to 500,000 mg34(

i



he food waste was pretreated using the :othenberg %et %aste :ecovery !ystem

mar*eted by ;cology, 44+ of <lendale, %#.

he pro=ect consisted of three phases. $irst, the high-strength wastes were tested for

biochemical methane potential '/M&( and also tested using anaerobic toxicity assays

'AAs(. !econd, bench scale digesters were operated in the laboratory. $inally, a full-

scale demonstration was performed by feeding wastes to the anaerobic digesters at the

!!%%&.

/M& esting. he average maximum /M& values were as follows 'ml +>6 per gram

+)(

Miller /rewery 6?

4esaffre east 22@6

!outheastern %isconsin &roducts 86

&andl9s :estaurant 677

he maximum theoretical /M& for any waste is 85 ml +>6 per gram +) assuming all

the +) is converted to methane. he abnormally high values for 4asaffre east and

!outheastern %isconsin &roducts wastes indicates that they stimulate methane production

from bac*ground +) present in the biomass, which was digested sludge from the

!!%%&. he +) in Miller /rewery and &andl9s :estaurant waste is essentially

completely convertible to methane.

ii



AA esting. At the loadings tested 'typically 0 to 2 g +)34(, the wastes do not pose

toxicity challenges. An unanticipated result was that doses of 4esaffre east +orporation,

!outheastern %isconsin &roducts, and Miller /rewery wastewaters actually caused

methane production rates to significantly increase by as much as ?5 to 20.

/ench-!cale igester esting. $ourteen bench scale, fill-and-draw anaerobic digesters

were operated. ;ach 2-liter digester was fed a different blend of one high strength waste

and municipal wastewater solids '@0 primary sludge and 0 v3v thic*ened waste

activated sludge from !!%%&(. ;ach digester was completely mixed and operated at a

?5-day solids residence time '!:( at @B?o +. #t was determined that 4asaffre east and

!outheastern %isconsin &roducts wastewaters can be successfully co-digested with

municipal wastewater solids at all blend ratios tested 'from 20 to 70 v3v wastewater in

municipal wastewater sludge(. !imilarly, the food waste can be successfully co-digested

at all blend ratios tested 'from to ?? v3v food waste in municipal wastewater sludge(.

he Miller brewery wastewater was not successfully digested by itself in the fill-and-

draw digester utiliCedD however, it was successfully digested when blended with

municipal wastewater solids. Although the brewery wastewater was not successfully

digested alone, it is amenable to anaerobic treatment. #f it is treated alone, then it is

recommended that reactor configurations other than a fill-and-draw digester should be

considered.

iii



All the wastes utiliCed in bench-scale testing had metals concentrations below the

%isconsin epartment of Eatural :esources high "uality limits for biosolids to be land

applied and will not limit the land application of digested biosolids.

$ull-!cale emonstration esting. A full-scale demonstration test was performed by

feeding !outheastern %isconsin &roducts and &andl9s :estaurant wastes to the anaerobic

digesters at the !!%%& at the same time municipal wastewater solids were also being

fed. here was a @0 increase in biogas production when !outheastern %isconsin

&roducts wastewater was co-digested. he waste constituted ? of the total +) loading

to the digesters. herefore, the biogas production increase was not due to additional

+), but may have been due to a synergistic effect resulting from the presence of

bioavailable nutrients 'e.g., iron( re"uired for microbial growth. he additional biogas

can be employed to produce ?,00 *w-hr3day of electricity worth over F200,000 per

year using an existing biogas-powered electric generator set at the treatment plant.

&andl9s :estaurant food waste was also delivered to the digesters at the !!%%&.

>owever, due to the relatively large solid particles 'approximately 20 of solids greater

than 6.@-mm nominal diameter(, the food waste solids could have damaged pumps and

appurtenances. herefore, the &andl9s food waste was discharged to the primary clarifiers

at the plant. he solids that settle in the primary clarifier are screened and pumped to the

anaerobic digesters. 4aboratory settleability testing and sieve analyses data were used to

estimate that @ of the food waste +) would be conveyed to the anaerobic digesters

at !!%%&. #t is estimated that the waste produced by &andl9s :estaurant can be

iv



ACKNOWLEDGEMENTS

he support of the following organiCations is greatly appreciated

$ocus on ;nergy, :enewable ;nergy &rogram

;cology, 44+, <lendale, %isconsin

Mar"uette Gniversity, Milwau*ee, %isconsin

Gnited %ater !ervices, #nc., Milwau*ee, %isconsin

4asaffre east, #nc., Milwau*ee, %isconsin

Miller /rewing, Milwau*ee, %isconsin

&andl9s :estaurant, /ayside, %isconsin

!outheastern %isconsin &roducts, )a* +ree*, %isconsin

vi



TABLE OF CONTENTS

E;ECUTI<E SUMMARY==================*******=====*===*** /

ACKNOWLEDGEMENTS==========================******=* "/

LIST

OF

TABLES

===============================** /+LIST OF FIGURES=============================*=**** +

C>APTER 8: INTRODUCTION==========================** 8

?.? Anaerobic igestionHHHHHHHHHHH...HHHHHHHHHHHHH.H..?.2 Aanaerobic +o-igestionHHHHHHHHH...HHHHHHHHHHHHHHH?. Municipal Anaerobic igesters as :egional :enewable ;nergy $acilitiesHHHH.H..

?6

C>APTER 9: BIOC>EMICAL MET>ANE POTENTIAL ?BMP@ AND ANAEROBIC TO;ICITY

ASSAYS ?ATA@ OF >IG> STRENGT> INDUSTRIAL WASTES=======*=* -

2.? #ntroductionHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH.2.? Materials and MethodsHHHHHHHHHHHHHHHHHHHHHHHH...H.

2.2.? /M&HHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH..2.2.2 AAHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH..

2.2 :esults and iscussionHHHHHHHHHHHHHHHHHHHHH......HH......?.? /M&HHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH..?.2 AAHHHHHHHHHHHHHHH.HHHHHHHHHHHHHHHH.

2.6 +onclusionsHHHHHHHHHHHHHHHHH.HHHHHHHHHHH....H

788???2?2202

C>APTER 2: BENC>SCALE TESTING OF ANAEROBIC CODIGESTION =========** 9.

.? #ntroductionHHHHHHHHHHHHHHHHHHHHHHHHH.HHHHH.2 /ench-!cale igester escriptionHHHHHHHHHHHHHHHHHH...H...H. !ampling and AnalysesHHHHHHHHHHHHHHHHH..H.HHHHHHH.6 :esults and iscussionHHHHHHHHHHHHHHHHHHH.HHHHHH...

.6.? Average !eed /iomass and $eed +haracteristicsHHHHHHHH..HHHHHH......6.2 igester 4oadings3>ydraulic :etention imeHHHHHHHHH..HHHHHHH...6. p> and Al*alinityHHHHHHHHHHHHHHHHHHHHHHHHHHHH.6.6 Iolatile !olid estructionHHHHHHHHHHHH...HHHHHHHHH...HH..6.5 /iogas3Methane HHHHHHHHHHHHHHHHHHHH.HHHHHHHH.

.5 +onclusionsHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH.

2@28?2265@860

C>APTER : FULLSCALE CODIGESTION TESTING AT SOUT> S>ORE WASTEWATER

TREATMENT PLANT========================*

6.? #ntroductionHHHHHHHHHHHHHHHHHHHHHHHHHHH..HHH.....6.2 !outh !hore %astewater reatment &lant '!!%%&(HHHHHHHHHHHHHH..6. Anaerobic igesters at !!%%&HHHHHHHHHHHHHHHHHH..HHH...H

6.6 !outheastern %isconsin east %astewater '!;%%%(HHHHHH...HHHHHHH.6.5 &andl9s :estaurant $ood %aste HHHHHHHHHHHHHHHHHHHHHHHH6.5.? !ettleability estingHHHHHHHHHHHHHHHHHHHHHHHHH...H..6.5.2 !ieve AnalysisHHHHHHHHHHHHHHHHHHHHHHHHHHHH.....6. ;conomic AnalysisHHHHHHHHHHHHHHHHHHHHHHHHHHHHH6..? !outheastern %isconsin east %astewater '!;%%%(HHHHHHHHHHHH6..2 &andl9s :estaurant $ood %asteHHHHHHHHHHHHHHHHHHHHHH6.@ +onclusionsHHHHHHHHHHHHHHHHHHHHHHH...HHHHHHH

6262626

6667505?525655

vii



C>APTER 1: O<ERALL CONCLUSIONS AND R ECOMMENDATIONS======***===*=

5.? /M& and AA estingHHHHHHHHHHHHHHHHHHHHHHHHHHH

5.2 /ench-!cale +o-igestion estingHHHHHHHHHHHHHHHHHHHHHH.

5. $ull-!cale +o-igestion estingHHHHHHHHHHHHHHHHHHHHHHH.

R EFERENCES================================***

BIBLIOGRAP>Y================================

1

58

0

?

6

viii



LIST OF TABLES

able 2.? /M& Miller /rewery %astewaterHHHHHHHHHHH.HHHHHHHHHHH ?

@able 2.2 /M& 4esaffre east +orporation %astewaterHHHHHHHHHH.HHHHHHH.. ?

@able 2. /M& !outheastern %isconsin &roducts %astewaterHHHHHHHHH...HHHHH.. ?

7able 2.6 /M& &andl9s :estaurant $ood %asteHHHHHHHHHHHHHHH...HHHHH. ?

7able 2.5 )verall /M& :esultsHHHHHHHHHHHHHHH.HHHHHHHHHHHH. ?

8able 2. AA Miller /rewery %astewaterHHHHHHHHHHHHHHH.HH...HHHH.. 2

6able 2.@ AA 4esaffre east +orporation %astewaterHHHHHHHHHH.HHHHHHH.. 2

6able 2.7 AA !outheastern %isconsin &roducts %astewaterHHHHHH..HHHHHHHH.. 2

6able .? +ombinations of Municipal %astewater !olids and >igh-!trength %aste $ed toigestersHHH...H.HHHHHHHHHHHHHHHHHHHHHHHHHHHH...

2

8able .2 !ampling !cheduleHHHHHHHHHHHHHHHHHHHHH.HHHHH..H..

0able . <as +hromatographic +onditions for Methane AnalysisHHHHHHHHHHHHH.

?

able .6 Average +haracteristics of &! and %A! in Municipal %astewater !olids HHHH..H.

able .5 Average +haracteristics of >igh-!trength %astesHHHHHHHHHHH...HHHH..

able . /lend of Municipal !ludge and >igh !trength %aste and I! 4oading :atesHHHH...

6able .@ Average p> of >igh-!trength %astes HHHHHHHHHHHHHHHHH.HHH.

able .7 Average p> and Al*alinity of ;ffluent from igestersHHHHHHHHHHHHH...

able .8 otal !olids, Iolatile !olids of the ;ffluent and Iolatile !olids estructionHHHH.H

@able .?0 /iogas &roduction, :ate of /iogas &roduction and &ercentage Methane in Assays HH

8able 6.? Average !;%%% Addition ate and AmountHHHHH.HHHHHHHHH.H... 6

5able 6.2 Average +haracteristics of !;%%% HHHHHHHHHHH..HHHHHH..HH 6

ix



5able 6. /iogas and Methane &roduction /efore and After !;%%% +o-igestionHHHH.. 6

@able 6.6 &andl9s :estaurant $ood %aste +haracteristicsHHHHHHHHHHHHHHHH.H 6

8

able 6.5 &andlt9s $ood %aste and %isconsin 4and Application 4imit Metals+oncentrationsHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHable 6. !ieve Analysis :esults for $ood %aste !olidsHHHHHHHHHHHHHHHHH..

5

0

5

?able 6.@ !ynopsis of the /iogas &roduction and ;nergy !avings uring !;%%% +o-

igestionHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH.... 5

5

LIST OF FIGURES

$igure 2.? /M& Miller /rewery %astewaterHHHHHHHHHHHHHHHHHH.. ?$igure 2.2 /M& 4esaffre east +orporation %astewater HHHHHHHHHHHHH ?6$igure 2. /M& !outheastern %isconsin &roducts %astewaterHHHHHHH.HHHH. ?5$igure 2.6 /M& $ood %asteHHHHHHHHHHHHHHHHHHHHHHHHH ?

$igure 2.5 AA Miller /rewery %astewaterHHHHHHHHHHH.HHHH...HH... 2?$igure 2. AA 4esaffre east +orporation %astewaterHHHH..HHHHHHHHH. 22$igure 2.@ AA !outheastern %isconsin &roducts %astewaterHHHHHHHH.HH.. 2$igure 2.7 :ate of Methane &roduction versus %astewater ose ' v3v(HH..HHHHH.. 25$igure .? +ontrol Anaerobic /ench-!cale igester ':J?( and ifferent /lends of M%!

and M/%% ':J2, :J and :J6(HHHHHHHHHHHHHHHHHHHHHHH..27

$igure .2 +ontrol Anaerobic /ench-!cale igester ':J?( and ifferent /lends of M%!

and 4%% ':J5, :J and :J@(HHHHHHHHHHHHHHHHHHHHHHH...27

$igure . +ontrol Anaerobic /ench-!cale igester ':J?( and ifferent /lends of M%!

and !;%%% ':J7, :J8 and :J?0(HHHHHHHHHHHHHHHHHHHHH...27

$igure .6 +ontrol Anaerobic /ench-!cale igester ':J??( and ifferent /lends of M%!

and $% ':J?2, :J? and :J?6(HHHHHHHHHHHHHHHHHHHHHHHH 27

$igure 6.? /iogas &roduction from $ull-!cale +o-igestion of !;%%%HHHHHH 67

x



xi



C>APTER 8: INTRODUCTION

8*8 ANAEROBIC DIGESTION

Anaerobic digestion 'A( is one of the standard technologies for stabiliCing wastes. A

is the biological decomposition of organic matter in the absence of molecular oxygen.

he A process produces biogas principally composed of methane '+> 6( and carbon

dioxide '+)2( and the undegraded solids and li"uids '4us* and Moser, ?88(. Anaerobic

processes can either occur naturally or in a controlled environment such as a biogas plant.

epending on the waste feedstoc* and the system design, biogas is typically 55 to 70

percent methaneD the remaining composition is primarily carbon dioxide, with trace

"uantities of potentially corrosive hydrogen sulfide and water vapor.

he process of anaerobic digestion can be considered to consist of three steps. he first

step is the decomposition 'hydrolysis( of complex organic matter. his step brea*s down

the organic material to smaller molecules such as sugars. he second step is the

conversion of smaller molecules to organic acids. $inally, the acids are converted to

biogas containing methane '!peece, ?885(.

&rocess temperature affects the rate of digestion and is often maintained in the

mesophillic range '0 to 7o+ or 85 to ?05o $(. #t is also possible to operate in the

thermophillic range '50 to 5@ o+ or ?22to ?o $ 'Metcalf and ;ddy, 200(. here are

usually two reasons why the mesophilic and thermophilic temperatures are preferred over

lower temperatures. $irst, a higher loading rate of organic materials can be processed and

?



increased rates of biogas production typically result. !econd, higher temperatures increase

the destruction rate of pathogens present in raw sanitary wastes.

/enefits of A technology are listed below '!peece, ?885(.

%aste reatment /enefits

•• Eatural waste treatment process

••+an re"uire less land than aerobic wastewater treatment, composting or landfilling

••:educes disposed waste volume and weight of solid waste to be landfilled

•

;nergy /enefits

••+an be a net energy producing process

••<enerates a renewable fuel

•

;conomic /enefits

••#s sometimes more cost-effective than other treatment options, such as aerobic

wastewater treatment

he ma=or applications of A are in the stabiliCation of concentrated sludges produced

from the treatment of municipal wastewater. >owever, the wastes that can be treated by

A cover a wide range and include sewage sludge, agricultural wastes, municipal solid

wastes and industrial wastes 'Metcalf and ;ddy, 200(.

Many industries with organic waste streams use an A process as a pretreatment step to

lower sludge disposal costs and reduce the cost of overall treatment. !ome industries

using A for wastewater treatment are listed below '!peece, ?885(.

2



• $ood process such as vegetable canning, mil* and cheese manufacture, slaughterhouse

wastes and potato processing wastes

• rin* industry, breweries, soft drin*s, distilleries, coffee and fruit =uices production

• #ndustrial products, paper and board, rubber, chemicals, starch and pharmaceuticals

1.2 ANAEROBIC CODIGESTION

#n typical applications, an anaerobic digester is designed and operated to treat waste from

one facility only, such as a food production facility, soft drin* bottling plant, or municipal

wastewater treatment plant. Co-digestion is a modification of this typical application.

Ahring et al. (1992) and others have described co-digestion as a waste treatment

method in which different wastes or wastewaters are mixed and treated together.

The term “co-fermentation” is snonmo!sl !sed for “co-digestion”. When various

wastes are mixed and co-digested, both snergistic and antagonistic outcomes are

possible. "!ccessf!l com#inations of different t$es of wastes and wastewater

re%!ire careful management. $or example, wastes low in nutrients or al*alinity can be

mixed with wastes with high concentrations of these re"uired constituents to increase

overall biogas production. The potential advantages of co-digestion are $resented

#elow (&ra!n' 22).

&otential Advantages of +o-igestion

• #mproved nutrient balance and digestion

• ;"ualiCation of particulate, floating, settling, and acidifying wastes through dilution

by manure, sewage sludge, or other wastes

• Additional biogas production



8*2 MUNICIPAL ANAEROBIC DIGESTERS AS REGIONAL RENEWABLE

ENERGY FACILITIES

%astewater and solid waste management is a challenge faced by communities around the

world. :apid population growth, urbaniCation, and the associated population density

increase are factors that increase the waste disposal challenge. Methods of solid waste

management include recycling of paper, metal, and plastic, incineration and sanitary

landfilling. #n the case of incineration, perceived air pollution and high capital cost are

potential disadvantages. ypically, a large fraction of solid waste is disposed of in

landfills. >owever, in some communities, landfills are approaching capacity. #n addition,

landfills are not designed to maximiCe the rate of methane generation for renewable

energy. #n comparison, anaerobic digestion systems achieve more rapid methane

generation.

&opulation growth and urbaniCation along with industrialiCation have also helped to

increase world energy demand. +onventional non-renewable sources of energy are

limited. !ome researchers predict that petroleum deposits will be depleted in the next few

decades and coal deposits will be depleted within ?50-200 years '!mil, 200(. /esides

this, the environmental damage 'e.g., global warming, mercury pollution( caused by

improper combustion of fossil fuels is a matter of concern. >ence, it is prudent to develop

energy from a variety of sources, including sources of renewable energy.

6



#n this regard, solid waste and industrial wastewater are potential energy sources worth

considering. Many industries dispose of solid wastes in landfills, or discharge high-

strength wastewater to sewers. #f handled through landfills and sewers, the waste

materials are wasted since they are not typically used as feedstoc*s to produce renewable

energy. #f sludge or wastes are disposed of in a landfill, then wastes ta*e up landfill

space, may lead to future groundwater pollution and may not be used to produce energy.

/iological treatment of wastewater and solid waste using anaerobic treatment may be

used to increase renewable energy production. #n this process, wastes are converted to

biogas 'an energy source( and stabiliCed biosolids.

Many of %isconsin9s municipal wastewater treatment plants li*e Milwau*ee, !outh

Milwau*ee, /roo*field, %au*esha, :acine, !heboygan, /urlington, %atertown, %est

/end, Eew 4ondon, Madison, :ichland +enter, %alworth +ounty, +hilton,

elafield3>artland, <rafton, Kiel, &lymouth, and &ort %ashington use anaerobic

digesters to biologically convert municipal wastewater solids to biogas that contains

methane. he methane is often used as a renewable energy source to generate electricity,

run e"uipment, heat the digesters, and heat buildings. he digesters are often very large

and could, under the correct conditions, treat other high-strength industrial byproducts

and economically produce more methane. herefore, existing municipal anaerobic

digesters could become regional renewable energy facilities.

5



:eports of co-digestion have recently become more numerous, and there have been

several applications or research pro=ects regarding co-digestion of municipal wastewater

solids, agricultural wastes, animal wastes, olive oil, pig slurry, swine manure, cattle

manure, paper mill sludge, and municipal solid waste 'Angelida*i et al., ?88@D +arrieri et

al., ?88D +ecchi et al., ?88D i &alma et al., ?888D <avala et al., ?88D <avala et al.,

?888D >amCawi et al., ?887D Mc<rady, ?888D Mavinic et al., ?887D :intala and Laervinen,

?88D !osnows*i et al., 200( . >owever, anaerobic co-digestion of municipal wastewater

solids with high strength wastewater and food waste has not been widely practiced in the

Gnited !tates due to lac* of information regarding implementation, correct operating

conditions, experience and costs.

#n order to determine appropriate operating conditions and experience for co-digestion of

different high strength wastewaters, a practical demonstration pro=ect was performed and

is reported herein. Municipal wastewater solids from the !outh !hore %astewater

reatment &lant '!!%%&(, )a* +ree*, %# were co-digested with high strength

wastewater from #-house beer filters from Miller /rewery, fermentation waste from

4esaffre east production facility, fermentation waste from !outheastern %isconsin

&roducts and $ood %astes from &andl9s :estaurant. he wastes were selected base upon

their high +), probable anaerobic degradability, and generation in proximity of the

!!%%&. #nformation regarding these facilities is presented below.

Miller /rewing +ompany

88 %. >ighland /lvd.



C>APTER 9: BIOC>EMICAL MET>ANE POTENTIAL ?BMP@ ANDANAEROBIC TO;ICITY ASSAYS ?ATA@ OF >IG>STRENGT>

INDUSTRIAL WASTES

9*8 INTRODUCTION

/atch anaerobic bioassay techni"ues have been developed by others as simple and

inexpensive procedures to monitor relative biodegradability and possible toxicity of

wastes to be treated by A. he biochemical methane potential '/M&( and anaerobic

toxicity assay 'AA( are relatively simple bioassays that can be conducted in laboratories

without the need for sophisticated e"uipment ')wen et al ., ?8@8(.

he /M& is a measure of sample biodegradability ')wen et al ., ?8@8(. Lust as the

biochemical oxygen demand '/)( assay indicates how much organic pollution can be

degraded in an aerobic process, the /M& is a measure of what fraction of a given wastes9

+) can be removed anaerobically and what volume of methane can be produced when

treating that waste '!peece, ?88(. he assay provides a simple means to monitor relative

anaerobic biodegradability of substrates. Gses of the /M& are as follows '!peece, ?885(.

7



• Assaying the concentration of organic pollutants in a wastewater which can be

anaerobically converted to methane '+>6(

• ;valuating potential anaerobic process efficiency

• Measuring residual organic pollution amenable to further anaerobic treatment

• esting for non-biodegradable chemical oxygen demand '+)( remaining after

treatment

he AA was developed to determine any toxic effect of a substance on the organisms

that convert acetate to methane ')wen et al., ?8@8(. hese organisms are typically

considered to be the microbes most sensitive to toxicants in the mixed microbial culture

that achieves methane production from complex substrates.

he significant difference between the /M& and AA assays is that the AA is

supplemented with a high concentration of acetate as well as varying wastewater

concentrations, whereas no acetate is added to the /M& system. he total amount of

biogas production is most important in the /M& test, whereas the initial rate of gas

production is of primary interest in the AA test '!peece, ?88(.

he /M& assay was conducted on all of the wastes used for co-digestion. he AA assay

was conducted on #-house beer filter waste from Miller /rewery, fermentation waste

from 4esaffre east +orporation and fermentation waste from !outheastern %isconsin

&roducts.

8



chromatography with a flame ioniCation detector '<owMac <+(, an 7ft. x .?26 in. o.d.

stainless steel column pac*ed with ?!&-?000 on 0370 +arbopac* / '!upelco, #nc.

/ellefonte, &A( and a nitrogen carrier flow of 20 ml3min at an oven temperature of 0o+.

he numerical data are presented herein as the average cumulative volume of gas

production from triplicate bottles.

9*9*9 ATA

he AA protocol of )wen et al. '?8@8( was used to determine the extent to which each

of the high strength wastes might inhibit methane production by aceticlastic

methanogens.

$or the Miller /rewing +ompany AA, studies were run at four organic loadings of 0.5,

?, 2, and 2.5 g+)34. $or 4esaffre east +orporation wastes, the four organic loadings

were 0.5, ?, 2, 2.5 g+)34, and for !outheastern %isconsin &roducts waste the loading

were 0.6, ?.2, ?.7, 2.6 g+)34. +alcium acetate was also added to provide an initial

concentration of ?0,000 mg34 in the bottles. his is a non-limiting substrate concentration

for aceticlastic methanogenic organisms. herefore, any decrease in the rate of biogas

production measured was due to the wastewater toxicity and not due to lac* of acetate

needed by the anaerobic microorganisms. Also to ensure that p> was approximately @,

al*alinity in the form of sodium bicarbonate 'Ea>+)( was added to all the systems at

the concentration of 5g3l. A control bottle receiving no waste was also prepared.

??



All systems were run in triplicate. hus, 8 serum bottles were prepared for AA tests.

/ottles were sparged with 0 +)2 3@0 E2 gas to establish anaerobic conditions, then

sealed with rubber septa. AA bottles were placed on a sha*er table '+25K+ #ncubator

!ha*er, Eew /runswic* !cientific, ;dison, EL, G!A( at 5o + and ?50 rpm. otal biogas

production was measured daily over a period of approximately 0 days using 50-ml or

?00-m4 wetted barrel glass syringes, and biogas methane content was determined by gas

chromatography with a flame ioniCation detector '<owMac <+(, an 7ft. x .?26 in. o.d.

stainless steel column pac*ed with ?!&-?000 on 0370 +arbopac* / '!upelco, #nc.

/ellefonte, &A( and a nitrogen carrier flow of 20 ml3min at an oven temperature of 0

o

+.

he data are presented as the average initial rate of methane production from triplicate

bottles.

9*2 RESULTS AND DISCUSSION

9*2*8 BMP

<as production in /M& serum bottles for Miller /rewing wastewater, 4esaffre east

+orporation wastewater, !outheastern %isconsin &roducts wastewater and &andl9s

:estaurant food waste was monitored for 2, 0, 2 and days respectively. +umulative

methane production in /M& assays for the different wastes is illustrated in $igures 2.?

through 2.6. he +) of wastes used from /M& assays are as follows Miller /rewery

wastewater '5,00mg3l(, 4esaffre east +orporation wastewater '6@,00 mg3l(,

!outheastern %isconsin &roducts wastewater '7,000 mg3l(, and &andl9s :estaurant food

waste '2,700 mg3l(.

?2



$igure 2.? /M& Miller /rewery %astewater

?



$igure 2.2 /M& 4asaffre east +orporation %astewater

?6



$igure 2. /M& !outheastern %isconsin &roducts %astewater

?5



$igure 2.6 /M& $ood %aste

?



Methane production was observed at all the concentration of wastes tested 'see $igures

2.? through 2.6(. he total amount of methane produced and the maximum specific

methane production rates at the various organic loadings are summariCed in able 2.?

through 2.6.

able 2.? /M& Miller /rewery %astewater

4oadings'g +)3l(

Iol.%%'ml(

Methane'ml(

/M&'ml+>63g+)(

/iogas +>6

Max. Methane production rate

'ml3d(

/iomassI! 'g(

Max. !pecificmethane production

rate 'ml +>63gI!- d(

0.0 0 ?B0 EA 6@ 6

0.67 5.6

0.5 6 60B? 608 52

?.0 8 50B 77 5 ?0

2.0 2 75B2 628 2 ?6

2.5 ?08B 62@ 5 ?@

Avg. 6? 57

!td. ?8

able 2.2 /M& 4esaffre east +orporation %astewater

4oadings

'g +)3l(

Iol.%%'ml(

Methane

'ml(

/M&

'ml+>63g+)(

/iogas

+>6

Max. Methane production rate

'ml3d(

/iomass

I! 'g(

Max. !pecificmethane production

rate 'ml +>63gI!- d(

0.0 0 65B6 EA ? 2

0.? 58.0

0.5 0.6 7B 200 5

?.0 0.8 ?62B? 2@2 0 ?7

2.0 ?.7 2??B? ?87 ? 25

2.5 2.2 ?B 2@??

Avg. 22@6 0

!td. 7

?@



able 2.5 )verall /M& :esults

Charac%er/s%/csM/##er

Bre(/'

Lesa66re

Yeas%

SE WI

Pro!&c%sFoo! (as%e

/M& 'ml+>63g+)( 6?±

?8 22@6±

7 86±

656 677±

22/iogas +>6 57± 0± 8±? 7±2

Max. +>6 &roduction rate'ml3day(

?@ ?@ ?8

I! /iomass 'g( 0.67 0.? 0.8 0.56

Max. !p. +>6 &roduction rate'ml+>63g I!-day(

5.6 58.0 6.0 5.2

According to stoichiometric relationships, 85 ml of methane at 5o+ is e"uivalent to ? g

of +) removed from wastewater if the +) is removed via methane production only.

>owever, measured values sometimes vary slightly from that of the stoichiometric

relationship due to biomass growth, sulfate reduction, hydrogen gas generation,

experimental inaccuracies and other factors. Ma=or variation from stoichiometric

relationships should be closely scrutiniCed, and indicate the existence of uni"ue

mechanisms or experimental error.

:egarding the values observed and reported herein, the /M&s for 4esaffre east

+orporation and !outheastern %isconsin &roducts wastewaters are abnormally high 'i.e.,

greater than 800 m43g +)(. )n the other hand, the average /M& values for Miller

/rewery and &andl9s :estaurant wastes are within 22 of the theoretical /M&. he

abnormally high /M& values for the two yeast-containing wastewaters may be due to the

presence of supplementary nutrients 'e.g, iron( in the yeast wastewaters tested. #n

addition, the presence of complexing agents that render the metals more soluble and

bioavailable could cause an increase in biogas production. herefore, nutrients and3or

complexing agents may have stimulated fermentation of residual +) in the seed

?8



biomass slurry employed in the tests. #t is *nown that the addition of trace nutrients, such

as nic*el, cobalt, and iron, can greatly increase methane production rates in nutrient

limited systems, including some municipal digesters '!peece, ?877(. >owever, further

study is re"uired to determine conclusively that trace nutrients in the yeast wastes caused

the extremely high /M& values.

9*2*9 ATA

he results of AA trials for Miller /rewery wastewater, 4esaffre east +orporation

wastewater, and !outheastern %isconsin &roducts wastewater are presented in $igures

2.5 through 2.@ respectively. <as production in serum bottles for Miller /rewing

wastewater, 4esaffre east +orporation %astewater, !outheastern %isconsin &roducts

%astewater and food waste was monitored for 2, 0, 2 and days respectively. he

results of AA tests are presented in $igures 2.5 through 2.@. he total amount of

methane produced and the rates of methane production for the wastes are presented in

ables 2. through 2.7.

20



$igure 2.5 AA Miller /rewery %aste

2?



$igure 2. AA 4asaffre east +orporation %astewater

22



$igure 2.@ AA !outheastern %isconsin &roducts %astewater

2



production rate increased approximately 70 when 4asaffre yeast wastewater was added

at doses of more than 7 volume per volume 'v3v( 'see $igure 2.7(. !imilarly, as

!outheastern %isconsin &roducts wastewater dose increased from Cero to 60 v3v, the

methane production rate increased 60. #n addition, methane production rate also

increased with increasing Miller /rewery wastewater doses as high as 2 v3v. >owever

a dose of 60 Miller /rewery wastewater caused a decrease in methane production 'see

$igure 2.7(.

(

1(

2(

)(

*(

+(

,(

( + 1( 1+ 2( 2+ )( )+ *( *+

% Wastewater

-&.. /0.. "1.0..

$igure 2.7 :ate of Methane &roduction versus %astewater ose ' v3v(

M/%% 'Miller /rewery %astewater(4%%' 4asaffre east %astewater(!;%%% '!outheastern %isconsin east %astewater(

9* CONCLUSIONS

25



Anaerobic bioassay techni"ues '/M& and AA( were used to determine that the four

high strength wastes, namely #-house beer filters from Miller /rewery, fermentation

waste from 4esaffre yeast production facility, fermentation waste from !outheastern

%isconsin &roducts and $ood %astes from &andl9s :estaurant, were amenable to

anaerobic treatment and demonstrated no discernable toxicity to anaerobic

microorganisms at the concentrations studied. #nterestingly, 4esaffre east +orporation

wastewater and !outheastern %isconsin &roducts wastewater demonstrated abnormally

high /M& values. hese values suggest that the two wastes stimulated methane

production from bac*ground +) present in the biomass used in the test, which was

digested sludge from the !!%%&. #n addition, doses of 4asaffre, !outheastern

%isconsin &roducts, and Miller /rewery wastewaters caused methane production rates to

increase by as much as 20 to 70 in systems containing a non-limiting concentration of

acetate 'i.e., AA assays(. he unanticipated stimulatory effects of the wastewaters may

be due to the presence and bioavailability of trace nutrients. he microbes that convert

substrates to methane re"uire nutrients, such as nic*el, cobalt, and iron. he addition of

these nutrients in bioavailable forms and3or the addition of complexing agents that render

the metal nutrients bioavailable often leads to an increase in methane production rate in

nutrient limited systems. Additional research to investigate this stimulatory affect of yeast

production waste is warranted. #t may be that yeast wastes can be used as additives to

significantly increase biogas production in many anaerobic digesters.

2



Eote that NM%!O is an acronym for municipal wastewater solids.

27



2*9 BENC>SCALE DIGESTER DESCRIPTION

$ourteen different digesters were constructed '2.5 4 glass vessels( and seeded with 2 4 of

digested sludge 'from !outh !hore %astewater reatment &lant(. ;ach digester was fitted

with a rubber stopper and a gas collection bag. ;ach had a magnetic stir bar inside and

was placed on a stirrer so that complete mixing was achieved 'see $igures .? through

.6(. he different combinations of high-strength waste and municipal wastewater solids

fed to each digester are shown in able .?. Municipal wastewater solids were a mix of

0 thic*ened waste activated sludge '%A!( and @0 primary sludge '&!( by volume

from the !!%%&.

able .? +ombinations of Municipal %astewater !olids and >igh-!trength %aste $edto igesters

D/'es%er

>/'h S%re'%h Was%e M&/c/$a# Was%e(a%er S#&!'e

<o#&me Fe!

?m#!@

<o#&me Fe!

?m#!@

? 0 0 ?00 ?

2 20 M/%% 2@ 70 ?0

70 M/%% ?0 20 2@6 ?00 M/%% ? 0 0

5 70 4%% ?0 20 2@

0 4%% 70 60 5

@ 20 4%% 2@ 70 ?0

7 70 !;%%% ?0 20 2@

8 0 !;%%% 70 60 5

?0 20 !;%%% 2@ 70 ?0

?? 0 0 ?00 ?

?2 ?? $% ?5 78 ??7

? 5 $% @ 85 ?2

?6 $% 6 8@ ?28

All digesters were operated in a temperature-controlled room at @±?o+. ;ach was a

batch fed, completely mixed stirred tan* reactor '+M!:( operated for at least 2.

months . ;very day, ? m4 of digester content was removed and immediately replaced

28



with an e"uivalent volume of digester feed. #n addition, al*alinity in the form of sodium

bicarbonate 'Ea>+)( was added to the feed at a concentration of 2.5 g3l. he solids

retention time '!:( and the hydraulic retention time '>:( for all the digesters were

maintained at ?5 days. his !: was employed because the full-scale digesters at the

!!%%& operated at an >: of approximately ?5 days.

he sampling schedule of fre"uently measured parameters is shown in able .2. #n

addition, the concentrations of the following constituents were measured three times for

each waste arsenic, cadmium, chromium, copper, lead, mercury, molybdenum, nic*el,

selenium, Cinc, waste +), total K=eldahl nitrogen 'KE(, ammonia, total phosphorus

and potassium. Metals measurements were performed since land application of digested

biosolids is regulated in %isconsin, in part, based upon the concentration of these

constituents.

able .2 !ampling !chedule

Parame%ers Meas&reme% Fre5&ecy

emperature aily

p> 'effluent( aily

/iogas production volume aily

+>6 in headspace )nce every one to two wee*s

#nfluent solid content '!, I!( hree times a wee*

;ffluent solid content '!, I!( hree times a wee*

Al*alinity '&A, #A( hree times a wee*

;ffluent !+) )nce a wee*

;very seven to fifteen days, assays were performed to determine digester biogas

production rate. A 50-m4 ali"uot was removed from each digester before digester

feeding and placed in a serum bottle '?0-ml total volume(, sparged with gas '03@0

+)23E2 volume per volume blend( to help establish anaerobic conditions, sealed, and

0



placed on a sha*er table in a 5+ incubator. /iogas production from these bottles was

measured daily over approximately 20 days with a 50- or ?00-ml glass syringe.

2*2 SAMPLING AND ANALYSES

emperature was measured with a thermometer placed in the temperature-controlled

room. !ample p> was measured using a p> probe and meter ')rion Model @20A(. he

percentage of methane present in the biogas was measured using a gas chromatograph.

able . shows the gas chromatograph conditions. he total and volatile solids

concentration of the samples was determined by standard methods 2560 / and 2560 ;

'A&>A et. al, ?887(.

able . <as +hromatographic +onditions for Methane Analysis+hromatograph <owMac <+ata Ac"uisition ;P +hrom with &entium &+#n=ector &ac*ed column in=ector, emperatureQ200o++olumn '&ac*ed +olumn( !upelco, +arbopac* ?-?725, 0370 +arbopac* +30.

+arbowax 20M30.? >&)6

)ven ?50o

+etector $lame ioniCation detector at 200 o++arrier <as Gltra high purity >elium 50 ml3min.

Al*alinity in wastewater results from the presence of hydroxides R)>-S, carbonates

R+)2-S, and bicarbonates R>+)

-S and other salts of wea* acids. +alcium and magnesium

bicarbonates are most common. /orates, silicates, and phosphates can also contribute to

the al*alinity. he al*alinity in wastewater helps to resist a decrease in p> caused by

addition of acids 'Metcalf and ;ddy, 200(. itration and buffer intensity curves can

show the relative magnitudes of bicarbonate and volatile acids 'IA(, but the development

of such curves is tedious for routine operation. herefore, titration to two endpoints is

?



more attractive. itration from the original sample p> to p> 5.@5, or partial al*alinity

'&A(, results in an al*alinity that corresponds roughly to bicarbonate al*alinity. itration

from p> 5.@5 to 6., or intermediate al*alinity '#A(, approximates the IA al*alinity.

!uccessful digester operation depends on maintenance of ade"uate bicarbonate buffering

and avoidance of excessive IA concentrationD the IA-to-al*alinity ratio 'IA Al*alinity

or #A &A( has been used to monitor anaerobic digestion of municipal sludge ':ipley et

al., ?87(. he al*alinity titrations were conducted as per standard method 220/ 'A&>A

et. al., ?887(.

!oluble chemical oxygen demand '!+)( was measured by placing 20 ml of effluent in

a centrifuge tube, centrifuging for 0 minutes and then filtering the centrate through a

0.65-Tm cellulose nitrate membrane filter. he filtrate was then used for the +) test as

per standard method 5220A 'A&>A et. al, ?887(.

2* RESULTS AND DISCUSSION

2**8 A<ERAGE SEED BIOMASS AND FEED C>ARACTERISTICS

All igesters were seeded with sludge from the anaerobic digesters at the !!%%&.

igesters ? through ?0 were started using sludge having ! and I! concentrations of

6.7 and 27.0 g3l, respectively. igesters ?? through ?6 were started later with sludge

having ! and I! concentrations of 6?.2 and 25.7 g3l, respectively.

he characteristics of &! and %A! from !!%%& and the individual high-strength

wastes used during bench-scale studies are presented in ables .6 and .5, respectively.

+ontrol digesters 'igester ? and ??( were not fed industrial waste, but only fed a

2



mixture of @0 &! and 0 %A!, which is referred to herein as municipal wastewater

solids.

able .6 Average +haracteristics of &! and %A! in Municipal %astewater !olids

$>? 2@ TS ?'#@?89@ <S ?'#@?89@ <S? 89@

PS8 5.7B0.2 62B?2 ?B8 @5B5PS9 .2B0. 5B?2 2B@ @B?0WAS8 .2B0.? 7B5 5B6 2B7WAS9 .0B0.2 8B 5B2@ 58B6

&!? and %A!? were used for digesters ? to ?0 and &!2 and %A!2 were used for digesters ?? to ?6.

nQ number of samples

able .5 Average +haracteristics of >igh-!trength %astes

Charac%er/s%/cs MBWW LYWW SEWYWW FW

To%a# So#/!s ?'#@ 6B 'nQ 76( ?B2 'nQ@6( ?B2 'nQ5( 267B7

<o#a%/#e So#/!s ?'#@ ?B? 'nQ 76( B2 'nQ@6( ?6B2 'nQ5( 2?@B@

<o#a%/#e 67B27 58B 77B 77B

COD ?m'#@ 6270B?@70 6500B870 7500B20 62700B?600

N>2N ?m'#@ [email protected] 270B267 55B2 560B2780

Or' N ?m'#@ 75.5B5. 2?70B6.8 @?5B6 68600B?700

TKN ?m'#@ 86B7 26@0B250 @@0 B@6 56800B?8800

TP ?m'#@ ? B5.0 5B?7 ?0B6? ?00B6?7

C! ?H'#@ 6.00B.8 0.@B?2.@ U U6.?V

Cr ?H'#@ U?0 8.@B?2? U?0 U.C& ?H'#@ ?67B65.@ 526B8?.5 0B22 U6@V

P) ?H'#@ 5.B82.6 280B25 U5 U2V

N/ ?H'#@ U @B2@5 U U2V

3 ?H'#@ @2B55 60B@@ ?B27 @B

K ?H'#@ 22600B?5800 0@00B@@60 28000B?000 ??600B??@00

>' ?H'#@ 0.5B0.82 U0. U0. U0.0

As ?H'#@ [email protected] [email protected] U0.2 U0.06

Se ?H'#@ U2 U2 0.@B?.?5 U0.0

Mo ?H'#@ 8.@B7.@6 5.@B@.@? U0.2 0.@B?.?5

Three samples were measured to determine COD, TKN, ammonia TP and the metals concentrations.

:egarding metal concentrations, none of the wastes tested contained metals at

concentrations greater than the %isconsin epartment of Eatural :esources high "uality

limits for biosolids to be land applied. herefore, it is probable that land application of

residuals would not be problematic. >owever, it should be pointed out that the



concentration of metals in the residuals could theoretically increase due to sorption onto

the surface of sludge solids.

2**9 DIGESTER LOADINGS >YDRAULIC RETENTION TIME

igesters ? and ?? 'receiving only municipal wastewater solids( were maintained as

controls and were operated for 2@ days '?7.6 !:s( and ?06 days '.8 !:s(,

respectively. igesters 2 through 6 'receiving M/%%( and igesters 5 through @

'receiving 4%%( were operated for 20 days '?.@ !:s(. igesters 7 through ?0

'receiving !;%%%( were operated for @? days '6.@ !:s(. igesters ?2 through ?6

'receiving $%( were operated for ?06 days '.8 !:s(. 4oading rates and the blend of

municipal wastewater solids and different high strength wastes fed are presented in able

..

able . /lend of M%! and >igh !trength %aste and I! 4oading :ates

D/'es%er Was%eWas%eMWS Days o6

O$era%/o

Loa!/' Ra%e

m# '<S#! #)<S6%2!

? M%! 03?00 03? 2@ ?.52B0.6 0.?0B0.0

2 M/%% 20370 2@3?0

20

?.27B0.6? 0.07B0.0

M/%% 70320 ?032@ 0.@B0.?0 0.02B0.0?

6 M/%% ?0030 ?30 0.07B0.06 0.005B0.002

5 4%% 70320 ?032@

20

2.2B0.?6 0.?6B0.0?

4%% 0360 7035 [email protected]? 0.?B0.0?

@ 4%% 20370 2@3?0 [email protected]? 0.??B0.0

7 !;%%% 70320 ?032@

@0

?.0B0.?? 0.0B0.0?

8 !;%%% 0360 7035 ?.?2B0.?2 [email protected]?

?0 !;%%% 20370 2@3?0 ?.0B0.20 0.07B0.0??? M%! 03?00 03?

?06

?.?B0.2 [email protected]

?2 $% ??378 ?53??7 ?.?2B0.28 [email protected]

? $% 5385 @3?2 ?.?0B0.27 [email protected]

?6 $% 38@ 63?28 ?.08B0.28 [email protected]

6



he feeding of bench-scale digesters was not based on volatile solid loading rates per se,

but on hydraulic retention time '>:(. All the digesters employed an >: of ?5 days.

he results obtained from igesters ? and ?? are useful to ma*e comparisons with the

results obtained from other digesters. he percentage of $% fed to igesters ?2, ? and

?6 are low compared to the percentage of high-strength waste fed to other reactors

because the +) and I! of the $% were relatively high 'refer to able .5(.

2**2 $> AND ALKALINITY

Gnacclimated methane-producing organisms re"uire a neutral environment 'p> .7 to

7.5( in order to produce methane '!peece, ?885(. Acid-forming bacteria often grow

faster than methane forming organisms. Acid-producing bacteria may produce acid faster

than methane-producing microorganisms can consume it, and excess acid can build up in

the system, causing a drop in the p> which inhibits the activity of methane-forming

bacteria. #n case of low p>, methane production may stop entirely.

o help ensure proper p>, al*alinity in the form of Ea>+) was added to all the

digesters at a concentration of 2.5 g3l. Most digesters were stable as far as p> was

concerned, but igesters 7 and 8 had average p> values less than .7 and high average

#A3&A ratios irrespective of addition of Ea>+). he standard deviation of p> and

#A&A values were also high. here were periods when the digesters p> values were

above .7 and methane production was not inhibited by low p>. #t appears that these

digesters acclimated to the relatively low p> since their methane production rates were

5



relatively high. ables .@ and .7 show the p> of the wastes as well as the temperature,

p>, and al*alinity '&A, #A and total al*alinity 'A(( of digester effluent, respectively.

able .@ Average p> of >igh-!trength %astes

Was%es $> ?2@

M/%% 5.0±0.20

4%% 5.8±0.?0

!;%%% .?±0.20

$% 6.±0.0

able .7 Average p>, and Al*alinity of ;ffluent from igesters

D/'es%er Was%eDays o6

O$era%/o$>

PA

m'# as

CaCO2

IA

m'# as

CaCO2

TA

m'# as

CaCO2

IAPA

? M%! 2@ @.0±0.? 2507±655 ?72?±27 628±8?7 0.@±0.2?

2 M/%%

20

@.0±0.? 255±?? ?0±?266 6?85±2286 0.2±0.2?

M/%% @.0±0.? 2?76±??0 ??2±5 ?0±?565 0.5±0.?@

6 M/%% @.0±0.2 ?6@5±??0 72±?0?5 22±?72@ 2.2±6.78

5 4%%

20

@.2±0.2 5@±?6@ 5@5±?507 ??62±?702 ?.?5±0.57

4%% @.2±0.2 67?0±?68 505@±?600 87@±?288 ?.25±0.75

@ 4%% @.2±0.2 6057±@0? 257±57 6@±@?@ 0.8±0.5

7 !;%%%

@0

.±?.0 ?065±?76 266±??00 6@8±28? 5.7±@.60

8 !;%%% .0±0.8 755±?65 2@75±68 60±?787 7.77±??.8@

?0 !;%%% @.0±0.? 2685±@82 ?8±52? 6?8?±?278 0.7±0.08

?? M%!

?06

@.6±0.2 587±?26 2277±62 72@0±?6 0.60±0.?2

?2 $% @.5±0.2 7275±?67 @±?86? ?20?7±20 0.6@±0.0

? $% @.±0.2 @@@±?52@ 7±77 ??5?±2222 0.5?±0.?0

?6 $% @.5±0.2 @5@±?@28 ?67±@0 ?0506±?7?5 0.68±0.6

#A &A values for the bench scale digesters are above 0.5. Eotably, igesters 7 and 8

that received !;%%% had #A &A ratios above 5.0. hese digesters also had low

average p> values. he high #A&A ratios and low p> values may be due to high organic

loading rate ')4:( resulting from the high +) of the !;%%% and the relatively

high volume of waste in the feed. he average temperature of all digesters was @ B ?+.



2** <OLATILE SOLIDS DESTRUCTION

#n general, volatile solid destruction is used to measure the performance of municipal

anaerobic digesters. At mesophilic conditions in full-scale appplicaitons, 60 volatile

solid destruction is a reasonable value in the municipal sludge digestion process 'e 4a

:ubia et al., 2002(.

ables .6 and .5 present the solid concentrations in &!, %A! and the different high

strength wastes used for co-digestion. able .8 presents total solids and volatile solids

concentrations of digester effluents and volatile solid destruction achieved in each

digester during the steady-state period 'i.e., after 65 days had passed(.

able .8 otal !olids, Iolatile !olids of the ;ffluent and Iolatile !olid estruction

D/'es%er Was%eWas%eMWS E66#&e% So#/! <S Des%r&c%/o

D&r/' S%ea!y

S%a%e ?@ m# TS ?@ <S ?@ <S

? M%! 03?00 03? ?.8±0.6 ?.0±0.2 56±6 ±?

2 M/%% 20370 2@3?0 ?.@±0.6 0.8±0.2 52± 5±@

M/%% 70320 ?032@ ?.2± 0.6 0.±0.2 65±@ 5?±8

6 M/%% ?0030 ?30 0.7±0.6 0.2±0.2 ?±?2 -56±6?

5 4%% 70320 ?032@ .±0.6 ?.7±0. 68± 6±6

4%% 0360 7035 .±0. ?.7±0. 56±2 60±5

@ 4%% 20370 2@3?0 2.±0. ?.2±0.2 5?±6 56±

7 !;%%% 70320 ?032@ ?.@±0.@ ?.?±0. 6± 5±?

8 !;%%% 0360 7035 ?.8±0.5 ?.?±0. 2±6 5?±?

?0 !;%%% 20370 2@3?0 ?.@±0.5 ?.0±0. 55±2 2±?

?? M%! 03?00 03? 2.2±0. 0.@±0.2 5±? 57±7

?2 $% ??378 ?53??7 .6±0.6 ?.5±0.2 65± ?±6

? $% 5385 @3?2 .?±0.6 ?.±0. 62±6 52±@

?6 $% 38@ 63?28 2.8±0. ?.?±0.2 8± 5±

@



#f 60 volatile solid reduction is considered to be an acceptable value in the performance

of municipal sludge digestion 'e 4a :ubia et al., 2002( then all digesters except for

igester 6 demonstrated good I! destruction. igester 6 which received ?00 Miller

/rewery wastewater demonstrated a negative I! destruction value, meaning that there

was an increase in I!, ostensibly due to growth of biomass. he digester also had a low

p> and produced very little methane. herefore, methane production in the system was

inhibited.

igestion of ?00 Miller /rewery wastewater was not successful in the fill-and-draw

digester configuration employed. >owever, co-digestion of Miller /rewery wastewater

and 20 v3v or more of municipal wastewater solids lead to acceptable solids destruction

and biogas production. herefore, Miller /rewery wastewater can be successfully treated

in a fill-and-draw digester if it is co-digested with approximately 20 v3v or more of

municipal wastewater solids.

#t should be noted that ?00 Miller /rewery wastewater is not intrinsically a poor

candidate for anaerobic treatment without co-digestion of municipal wastewater solids.

>owever, the fill-and-draw digester configuration employed is typically not appropriate

for the comparatively low, mostly soluble +) present in the Miller /rewery wastewater

since no form of biomass immobiliCation is utiliCed. As demonstrated by /M& results in

+hapter 2, Miller /rewery wastewater may be treated anaerobically without co-digestion,

but other reactor configurations, such as a fluidiCed bed or upflow anaerobic sludge

blan*et would be more appropriate reactor configurations.

7



2**1 BIOGASMET>ANE

able .?0 presents biogas production, percentage methane, and rate of biogas production

results measured in serum bottle assays for biomass from each digester during the steady

state period. !teady state was assumed after 65 days 'i.e., !:s( had passed.

able .?0 /iogas &roduction, :ate of /iogas &roduction and &ercentage Methane inAssays

D/'es%er Was%es

Was%e

M&/c/$a#

Was%e(a%er

So#/!s

S%ea!y

S%a%e

B/o'as

Pro!&ce!

?m##!@

S%ea!y

S%a%e

C>

S%ea!y

S%a%e

Me%hae

Pro!&c%/o

Ra%e

S%ea!y

S%a%e

S$ec/6/c

Me%hae

Pro!&c%/o

Ra%e

m# ?m##!@

?m# ' <S

!ay@

? M%! 03?00 03? 75±@ ±2 5@?B 262 5@

2 M/%% 20370 2@3?0 5±228 ?± 87 B ?60 66

M/%% 70320 ?032@ 62±202 57± 25?B ??@ 62

6 M/%% ?0030 ?30 ?27±7@ 0B0 0 B 0 0

5 4%% 70320 ?032@ 827±6 ?±2 5 B 2?? ?

4%% 0360 7035 7±?5 ±2 56B ?87 0

@ 4%% 20370 2@3?0 ?0?7±626 7±2 82B 277 57

7 !;%%% 70320 ?032@ 760±60 6±2 57B 2@ 68

8 !;%%% 0360 7035 760±8 2±2 52?B 26 6@

?0 !;%%% 20370 2@3?0 560±@@ 58±? ?8B 65 2

?? M%! 03?00 03? 628±2?0 ± 2@0B ?2 8

?2 $% ??378 ?53??7 ??56±5@2 5±5 @50B @2 50

? $% 5385 @3?2 80±7@ ± 6B 255 68

?6 $% 38@ 63?28 556±?@ ?±2 7B ?0 ?

uring the steady state period, most of the co-digestion reactors produced biogas at

rates that were not statistically different from those of the control digesters. he

exceptions were igesters , 6 and ?0, which had lower biogas production rates than the

control 'igester ?(, and igesters ?2 and ?, which had higher biogas production rates

8



than the control 'igester ??(. he lower rates from igester and 6 are probably

because the Miller /rewery waste had a relatively low +). #n addition, the +) was

mostly soluble. Again, the fill-and-draw digester configuration employed is typically not

appropriate for low +), soluble wastes. he reason for the lower rate in igester ?0 is

un*nown.

2*1 CONCLUSIONS

All high-strength wastes tested had metals concentrations lower than the %isconsin

epartment of Eatural :esources high "uality limits for biosolids to be land applied.

herefore, most li*ely, none of the wastes will limit land application of resulting

biosolids based upon metal criteria. he 4asaffre east, !outheastern %isconsin

&roducts, and &andl9s :estaurant wastes were successfully co-digested at all blend ratios

tested 'from 20 to 70 by volume(. he !outheastern %isconsin &roducts waste did,

however, cause a decrease in digester p> 'to below .7( and an increase in #A&A ratio

'to above 5( at waste municipal wastewater solids ratios greater than 2070. >owever,

the systems acclimated to these conditions and produce methane at significant rates.

he Miller /rewery wastewater was difficult to co-digest in the fill-and-draw digesters

employed and at the ratios tested due to its relatively low and soluble +). herefore,

although the Miller /rewery waste is amenable to anaerobic digestion 'as evidenced by

/M& results of +hapter 2(, co-digestion at lower ratios of waste municipal wastewater

solids, or in a reactor configuration other than a fill-and-draw digester would be more

appropriate.

60



C>APTER : FULLSCALE CODIGESTION TESTING AT SOUT> S>ORE

WASTEWATER TREATMENT PLANT

*8 INTRODUCTION

!outheastern %isconsin &roducts east %astewater '!;%%%( and &andl9s :estaurant

food waste were selected and used in full-scale co-digestion testing at the !outh !hore

%astewater reatment &lant '!!%%&(, )a* +ree*, %isconsin. hese wastes were

selected based upon their high +) and /M&, appropriate metals concentrations for

land applicaiton, successful bench-scale digester testing, and production within a 20-mile

radius from the !!%%&. ;ach waste was fed to the existing digesters at the plant along

with primary sludge. &articipants in the study included %isconsin $ocus on ;nergy,

Mar"uette Gniversity, ;cology, 44+, mar*eters of the wet waste recovery system used at

&andl9s :estaurant to mechanically shred and store the waste, as well as the Milwau*ee

Metropolitan !ewerage istrict 'MM!( and Gnited %ater !ervices, #nc. 'G%!(, the

owner and contract operator of the treatment plant, respectively. :esults of full-scale co-

digestion testing and an economic analysis are presented in this chapter.

*9 SOUT>S>ORE WASTEWATER TREATMENT PLANT ?SSWWTP@

!!%%& is located south of Milwau*ee along the 4a*e Michigan shoreline in )a*

+ree*, %isconsin, and was put into operation in ?87. he plant treats an average of 80

million gallons of wastewater each day, most of it from the southern and western portions

of the MM! service area. he facility has a pea* capacity to treat approximately 00

million gallons per day of municipal wastewater.

62



:aw wastewater flows through primary, secondary and disinfection treatment processes.

/iosolids are conveyed to anaerobic digesters where microorganisms stabiliCe the solids

and create biogas containing methane. his biogas is collected, and is typically used to

continuously run blowers for the activated sludge process as well as produce electricity

using an engine generator set for approximately eight hours per day. #f more biogas was

produced, then the engine generator set could be operated for more than eight hours per

day. his may help reduce energy costs at the treatment plant. !tabiliCed biosolids are

applied to farmland as a fertiliCer and soil conditioner *nown as Agri-4ife or dried to

produce a commercial soil amendment called Milorganite.

*2 ANAEROBIC DIGESTERS AT SSWWTP

!!%%& has ?2 single-stage, high-rate, anaerobic digesters. At the time of this study,

igesters ? through 5 and @ were being used to store digested biosolids, igesters and 7

were out of service, and the remaining four digesters '8 through ?2( were active.

igesters 8 through ?2 are ?25 feet in diameter and have a side water depth of 7 feet.

:ecirculation pumps direct sludge through spiral heat exchangers at each digester to

maintain sludge temperatures in the range of 80 to 85 o$ '2 to 5 o+( for mesophilic

digestion. ypically, waste heat from the blowers and engine generator set is used to heat

the digesters. %hen the ambient temperature is very low, natural gas is also used to fire

boilers providing additional heat for the digesters.

he digesters have fixed concrete covers with a gas dome, access manholes and sample

ports. ;ach of the gas domes has a pressure relief valve and a flame trap. he gas domes

6



collect the biogas produced in the anaerobic digestion process. igester biogas is

recirculated through compressors and forced bac* into draft tube mixers to mix digester

contents. ;xcess gas is withdrawn from the digester cover through a gas header. #n

addition, some biogas can be stored in pressuriCed storage vessels for later use.

>istorically, primary sludge '&!( and thic*ened waste activated sludge '%A!( has been

fed to the digesters. >owever, at the time of this study, &! from both !!%%& and

another treatment plant 'Lones #sland %astewater reatment &lant, Milwau*ee,

%isconsin( was fed, whereas no %A! was fed. &! from primary clarifiers was pumped

and fed, alternately, to each of the four operating digesters by automatic opening and

closing of appropriate valves. uring the study, the &! total and volatile solids

concentrations were 62B?2 and ?B8 g34, respectively. he &! p> value was 5.7B0.2.

* SOUT>EASTERN WISCONSIN YEAST WASTEWATER ?SEWYWW@

he first addition of !;%%% to the anaerobic digesters commenced on Lune @, 2006.

he !;%%% was stored in an unmixed tan* at the plant and added into the &! feed

line using a metering pump. he tan* and pump are employed in cold months to handle

waste aircraft deicing fluid from <eneral Mitchell #nternational Airport 'Milwau*ee,

%isconsin( which is seasonally co-digested 'Pitomer et al., 200?(. he used deicer is

truc*ed to the treatment plant and stored in the unmixed tan*. he waste aircraft deicing

fluid solids content is low. herefore, most of the deicer constituents are soluble and,

therefore, mixers are not present in the storage tan* since there are very few solid

66



particles to *eep in suspension. able 6.? presents the date and the average amount of

!;%%% added to the digesters.

he average characteristics of !;%%% added to the digesters are presented in able

6.2.

able 6.? Average !;%%% Addition ate and Amount

ateAverage !;%%% Addition

'gal3min(

@-Lune-06 2.6

8-Lune-06 6.?

?0-Lune-06 .6

??-Lune-06 2.5

?-Lune-06 6.?

?@-Lune-06 6.0?7-Lune-06 2.2

2-Lune-06 .2

26-Lune-06 5.0

25-Lune-06 2.?

8-Luly-06 .0

?0-Luly-06 2.2

able 6.2 Average +haracteristics of !;%%%

Characteristics Fre5&ecy o6meas&reme% SEWYWW

To%a# So#/!s ?'#@ 5 ?B2

<o#a%/#e So#/!s ?'#@ 5 ?6B2

<o#a%/#e 5 77B

COD ?m'#@ 75?8B25@

N>2N ?m'#@ 55B?.86

Or' N ?m'#@ @?5.B62.@7

TKN ?m'#@ @@[email protected]

TP ?m'#@ ?0.00B6?.@

C! ?H'#@ U

Cr ?H'#@ U?0

C& ?H'#@ 0.00B22.25

P) ?H'#@ U5N/ ?H'#@ U

3 ?H'#@ ?.00B2@.@?

K ?H'#@ 285500.00B?6?.@

>' ?H'#@ U0.

As ?H'#@ U0.2

Se ?H'#@ 0.@B?.?5

Mo ?H'#@ U0.2

65



he !;%%% contributed less than ? of the flow and ? of the total +) loading to

the digesters. /iogas production is often proportional to +) loading, assuming +)

removal efficiency does not decline. ue to the relatively low +) contribution of the

!;%%%, it was anticipated that the additional biogas would not be measurable using

the treatment plant biogas flow meters which are accurate to B5.

>owever, a significant increase in biogas production of @0 was observed when

!;%%% was co-digested. $igure 6.? presents the biogas production during and after

addition of !;%%% to the digesters. able 6. presents the biogas and methane

production at periods during and after addition of !;%%%. he average biogas

methane content during all periods was 58B?.. he average biogas production for 2

days '&eriod ? 36306 to @38306( during the addition of !;%%% to the digester was

approximately?200 standard cubic feet per minute '!+$M(, whereas the biogas

production for 65 days '&eriod @3536 to 73?8306( when !;%%% was not added to

the system was only approximately @00 !+$M 'see $igure 6.?(. he extremely large

increase in biogas production was not expected. #t was considered that the increase in

biogas production could have been due to an increase in the mass loading rate of sludge

solids. >owever, the total solids loading to the digesters was approximately 70 tons per

day during both &eriods ? and 'see $igure 6.?(. herefore, the increase in biogas

production was not a result of a significant increase in solids loading to the digesters. #n

addition, the increase in biogas production could not have been a result of the additional

+) provided by the !;%%% since it was negligible in comparison to the primary

sludge +) loading.

6



he unexpected increase in biogas production may have been due to the presence of trace

nutrients and3or complexing agents in the !;%%% that increased the activity of the

anaerobic microbes. )thers have reported that addition of trace nutrients, such as nic*el,

cobalt, and iron, can dramatically increase the rate of biogas production in some

anaerobic digesters that are nutrient limited '!peece, ?885(. #n addition, it is possible that

complexing agents 'i.e., ligands( can form soluble complexes with metals and render the

metals more bioavailable. he biogas production rate of biomass from many municipal

anaerobic digester has been shown to increase upon addition of bioavailable iron and

other nutrients '!peece, ?877(. he microorganisms responsible for anaerobic digestion

re"uire these and other nutrients for optimal growth. >owever, trace nutrients are

sometimes not present in optimal concentrations or are not present in bioavailable forms

that microbes can utiliCe, even in municipal digesters '!peece, ?885(. #n this regard, yeast

extract, which is similar to !;%%%, is often used in microbiology studies to provide

bioavailable nutrients.

able 6. /iogas and Methane &roduction uring and After !;%%% Addition

&eriodW Eo. of

days

/iogas production

'ft+>63tI!-d(

/iogas&roduction

'ft+>63lb I!-d(

Methane&roduction

'ft+>63tI!-d(

Methane&roduction

'ft+>63lb I!-d(

? 2 2?.0B6.0 ?.2B. ?5702.@B60.@ @.8B2.0

2 65 [email protected] 7.8B2.0 ?067?.7B26@?.0 5.2B?.2

? ?@?7@.@[email protected] 7.B?.@ ?0?2.B2026.0 5.2B?.0

W &eriod ? 2 days during which !;%%% was added to the digester '36306 to @38306(. &eriod 2 he 65 days after addition of !;%%% 'i.e., !:s( '@3836 to 73?8306(.

&eriod he ? days after &eriod 2 '73?8306 to 8320306(.

6@



$igure 6.? /iogas &roduction from $ull-!cale +o-igestion of !;%%%& Q tons per day!+$M Q standard cubic feet per minute

%hen !;%%% was added to the anaerobic digesters at the treatment plant, no

adverse affects were observed with regards to the operation of the storage tan*, metering

pump, or anaerobic digesters.

*1 PANDLS RESTAURANT FOOD WASTE

:egarding &andl9s food waste, treatment plant operators expressed initial concern that

large solid particles in the waste could potentially damage pumps and other e"uipment as

well as settle in the unmixed waste storage tan* and3or the digesters at the treatment

plant. #n comparison, the !;%%% did not contain significant settleable, suspended

67



solids and these problems were not anticipated nor observed when it was co-digested. o

preclude potential e"uipment damage, the food waste was added to the primary clarifiers

at the treatment plant, and not directly to the digesters. #t was li*ely that settleable solids

in the food waste would be removed from the bottom of the clarifier as primary sludge.

he sludge would be pumped with other primary solids through an existing sludge screen

to remove particles greater than 5 mm and then safely conveyed to the anaerobic

digesters. o explore this concept, testing including settleability and sieve analyses were

performed on the food waste.

he general data presented in ables 6.6 and 6.5 were measured for &andl9s food waste

samples collected on April ?, 2006 and March 22, 2006, respectively. he samples were

collected from the ;cology 44+ wet waste recovery system '%%:!(, a vacuum system

with grinding that collects and prepares food waste for disposal or recycling. his unit

was installed at &andl9s restaurant in /ayside, %#.

able 6.6 &andl9s :estaurant $ood %aste +haracteristics

Parame%er <a#&e

Des/%y ?K'#@ ?.027

COD ?m'#@ 62,700

TS ?@ 2

<S ? of !( 80

So#/!s re%a/e! o *.,mm scree ?( 20

68



able 6.5 &andl9s $ood %aste and %isconsin 4and Application 4imit Metals+oncentrations 1'mg3*g dry mass( unless otherwise stated

Me%a# Foo! Was%e <a#&eW/scos/ B/oso#/!s La! A$$#/ca%/o >/'h

7&a#/%y L/m/%s

TS ?@ 5. -W

TKN ?@ @.5 -W

To%a# P ?@ ?.? -W

C! U6.? 8

Cr U. -W

C& 26 ?500

P) U67 00

N/ 2? 620

3 ? 2700

>' U0.0 ?@

As U0.0@ 6?

Se U0.? ?00

Mo 2 @5WW

W here is presently no limit.

WW Mo has no Nhigh "ualityO limit. he normal limit is given.

*1*8 SETTLEABILITY TESTING

A ?00-gram wet sample of the food waste described in able 6.5 was mixed with tap

water to bring the total volume to ? liter. he suspension was thoroughly mixed and

allowed to settle for 0 minutes in a ?-liter graduated cylinder. A sample of the

supernatant was then removed with pipette and analyCed for +). he result was that the

settled solids 'i.e., sludge( volume was 00 ml, and the supernatant +) was ?7,600

mg3l. Approximately ? of the waste +) was in the supernatant. herefore, most of

the +) was in the sludge blan*et that would presumably end up at the bottom of the

primary clarifier. here was some floatable fat, oil, and grease observed 'about a ?-cm

layer in the graduated cylinder(.

50



*1*9 SIE<E ANALYSIS

A ?-liter ali"uot 'total dry solids mass Q 22 grams( of the food waste described in able

6.5 was passed through a series of standard sieves. he mass and percent of solids

retained on each sieve are reported in able 6.. he percent of food solids retained on a

6.@-mm screen is similar to that which would be retained on the primary sludge screens

at !!%%&, which have a 5-mm opening. A 5-mm sieve is not a standard siCe and,

therefore, was not available. !ludge from the primary clarifier is pumped through the

primary sludge screen at the treatment plant before entering the digesters to remove large

particles that may damage pumps or collect at the bottom of the digesters. Approximately

20 of the food particles were retained on the 6.@-mm sieve and would be retained on

the sludge screens. herefore, most of the solids would be conveyed to the digester at the

treatment plant.

able 6. !ieve Analysis :esults for $ood %aste !olidsS/e"e o$e/' s/Je ?mm@ Reco"ere! o S/e"e Re%a/e! Pass/'

91* ?.0 ?.0 88.0

8*8 ?.8 2.8 8@.?*1 @.6 ?0. 78.@

*., 8.5 ?8.7 70.2

9*2- . 2.6 @.

9* ?.6 [email protected] @2.2

8*,- ?.? 27.8 @?.?

8*,- @?.? ?00 -

he &andl9s :estaurant food waste fed to the digesters represented less than of the

total +) load fed to the digesters. !ince biogas production is typically proportional to

+) load and the biogas flow meters are accurate to approximately B 5, the extra

biogas produced from food waste was below detection using existing plant gas flow

meters. >owever, the value of biogas that was generated from the waste can be estimated

as follows. &andl9s restaurant produced approximately 20 liters of food waste per day

5?



having an average +) concentration of 2.7 g34. he food waste biochemical methane

potential was 560 m4 of methane '5+, ? atmosphere( per gram of +) as reported in

+hapter 2. herefore, the restaurant produced 0 Kg of +) per day. #t is estimated from

settleability testing that 76 of the food +) can settle as primary sludge. #t is

estimated from sieve analysis that 70 of the food waste solids in the primary sludge

pass through the sludge screen. herefore, approximately @ of the food waste +)

may be conveyed to the digesters, assuming that ? g I! is e"uivalent to ? g +) and the

soluble +) in the food waste is negligible in comparison to the particulate +).

herefore, approximately 60 Kg of food waste +) per day may be conveyed to the

anaerobic digesters and can be theoretically converted to 70 standard cubic feet of

methane per day. his has an energy value of 70,000 /tu per day.

%hen food waste was added to the primary clarifiers at the treatment plant, no adverse

affects were observed with regards to the operation of primary clarifiers, sludge screens,

or anaerobic digesters.

*, ECONOMIC ANALYSIS

%hen high-strength wastes are not co-digested at the !!%%&, it is typical for digester

biogas to be utiliCed to continuously run blowers for the activated sludge process and run

an existing engine generator set for approximately 7 hours per day. he typical rate of

biogas production is not sufficient to run the engine generator set continuously. ;xcess

heat from the blower engines and generator set is used to heat the digesters. Gnder this

typical scenario, the blowers consume 6@5 !+$M of biogas continuously and the

generator set consumes 80 !+$M of biogas for 7 hours a day. herefore, typical biogas

52



utiliCation is 7@?200 standard cubic feet per day. #t should be noted that this is simply a

typical scenario, and biogas utiliCation scenarios can vary depending on how much

biogas is produced and what e"uipment is shut down for maintenance. $or example,

natural gas is purchased to run blowers if biogas production falls short of re"uirements.

#n addition, if the generator set is not operating or the ambient temperature is extremely

low, then biogas or natural gas is used to fuel boilers that heat the digesters. A typical

maximum biogas utiliCation rate is estimated assuming both the blowers and the engine

generator set are operated 26 hours per day, and this typical maximum biogas utiliCation

rate is ?26500 standard cubic feet per day. %hen co-digestion is not practiced, the

digesters produce approximately 7@?200 standard cubic feet per day of biogas. herefore,

existing e"uipment can typically utiliCe an additional @6600 standard cubic feet per day

of biogas.

#t should be noted that !!%%& operators paid F 0.0 per *w-hr of electricity during

pea* hours '?000 am to ?000 pm( and F 0.02 per *w-hr of electricity during off-pea*

hours '?000 pm to ?0.00 am( during the study. &ea* and off pea* demand charges are

also paid. he cost scenarios presented below assume electricity generated from biogas is

worth an average of F0.06 per *w-hr considering pea* and off-pea* demand charges as

well as the cost per *w-hr. #n addition, a natural gas cost of F.50 per decatherm 'where

a decatherm is e"uivalent to one million /ritish thermal units( was assumed based upon

Eew or* Mercantile ;xchange futures prices for natural gas in Lune 2006. A truc*ing

cost of F00 per 5000-gallon truc*load was paid during the full-scale testing.

5



he following simple economic analysis considers waste truc*ing costs and the value of

methane generated form the high-strength wastes. 4andfill tipping fees and wastewater

treatment plant user fees can be significant and vary from facility to facility. he tipping

fees and user fees have not been considered herein.

*,*8 SOUT>EASTERN WISCONSIN YEAST WASTEWATER ?SEWYWW@

he energy value of the !;%%% co-digested can initially be estimated from

biochemical methane potential results of +hapter 2. he waste can be added to the

digesters at an average rate of ?.0 gallon per minute '2 truc*loads per wee*( and had an

average +) concentration of 75. g34. he !;%%% biochemical methane potential

was 86 m4 of methane '5+, ? atmosphere( per gram of +) as reported in +hapter 2.

herefore, the !;%%% +) could be fed at an average rate of 67 Kg per day that

will theoretically be converted to ?,700 standard cubic feet of methane per day. his has

an energy value of ?.7 W ?0@ /tu per day. Assuming this is utiliCed to generate

electricity, the biogas is worth F20,2003year. #f the biogas is used in place of natural gas,

then the energy is estimated to be worth F 2,700 per year. he yearly transportation cost

to transport two truc*loads per wee* would be approximately F?,200. /ased upon the

/M& results of +hapter 2, the truc*ing cost is more than the worth of electricity

generated from the extra biogas as well as the worth of the biogas if it is used to reduce

natural gas purchase.

>owever, when the !;%%% was actually added to the digesters at the treatment plant,

the average methane production increase was nearly ?0 times greater than that predicted

56



by /M& results. %hen the !;%%% was added to the digesters, the biogas production

increased by 600,000 standard cubic feet per day 'see $igure 6.?(. able 6.@ presents the

digester biogas production, treatment plant biogas utiliCation, excess biogas available for

energy generation, and worth of energy generated from excess biogas from the anaerobic

digesters when !;%%% was co-digested.

able 6.@ !ynopsis of /iogas &roduction and ;nergy !avings uring !;%%% +o-igestion

!tage

igester biogas

production

'standardft3day(

igestermethane

production

'standardft3day(

Maximumreatment

plant biogasusage

'standardft3day(

;xcessGsable biogas

'standardft3day(

&otentialelectricitygeneration

from excess

biogas ? '*w-hr3day(

%orth ofelectricity

from excess

biogas

2

'F3yr(

? ?60000 875000 ?26500 2@200 ?00 2@700

8@000 575000 ?26500 0 0 0

? Assuming ? *w-hr generated per ?0,000 /tu and a maximum possible biogasutiliCation of ?26500 standard cubic feet per day2 Assuming F0.06 per *w-hr Assuming F.50 for ?0 /tu.

uring the period when !;%%% waste was added to the digester, biogas production

increasedD electricity worth in excess of F200,000 per year could be generated from the

usable additional biogas. #f the extra biogas was used to off-set natural gas purchase, then

the plant operators could save F?,800 on natural gas purchases per year. he cost to

transport 2 truc*loads per wee* of !;%%% to the treatment plant would be F?,200.

herefore, the worth of the electricity generated or natural gas saved as estimated by the

full-scale testing data, is significantly greater than the truc*ing cost.

55



*,*9 PANDLS RESTAURANT FOOD WASTE

he restaurant produced 0 Kg of +) per day, of which it is estimated that 60 Kg settle

in the primary clarifier, pass the sludge screen, and proceed to the anaerobic digesters.

he 60 Kg of +) is theoretically converted to @70 standard cubic feet of methane per

day. his has an energy value of 70,000 /tu per day.

he methane can be used to generate F8823year of electricity. #f the biogas is used to off-

set the purchase of natural gas, then the energy is worth F?20 per year. he yearly

transportation cost would be approximately F?500 per year. herefore, the truc*ing cost

is more than the worth of the electricity generated, whereas the truc*ing cost is slightly

less than the worth of the biogas if it is used to reduce natural gas purchase.

#t should be noted that economic benefits not considered herein may be accrued if food

waste is anaerobically digested. $or example, &andl9s :estaurant food waste is presently

disposed of in a sanitary landfill. he waste occupies landfill volume and remains as a

potential source of groundwater pollution. Anaerobic digestion with biogas utiliCation

and safe land application of biosolids may be a more economical solution based upon a

detailed life cycle cost comparison. >owever, a more detailed cost comparison is not

within the scope of this report.

*. CONCLUSIONS

/ased on the results of /M&, AA, +) and bench-scale testing as well as proximity to

the treatment plant, &andl9s food waste and !;%%% were chosen and used in full-

5



scale pilot tests of anaerobic co-digestion at the !!%%& in )a* +ree*, %isconsin.

uring the full-scale testing, no adverse impacts were observed regarding operation of

digesters, pumps, heat exchangers or other digestion appurtenances.

!;%%% was truc*ed to the treatment plant and stored in an existing unmixed tan*.

%hen !;%%% was added to the digesters along with primary sludge, there was a @0

increase in biogas production. he extra biogas could be used to generate electricity

worth in excess of F200,000 per year or off-set natural gas purchase worth F?,800 per

year. he yearly cost to transport 2 truc*loads per wee* of the waste to the wastewater

treatment plant would be F?,200. herefore, the worth of the electricity generated or

natural gas saved is significantly greater than the truc*ing cost.

he extremely large increase in biogas production during !;%%% co-digestion was

not anticipated based on the increased +) loading from the waste alone. #t is possible

that trace nutrients in the !;%%% stimulated microbes in the digesters to produce

more biogas from +) in the primary sludge. )thers have reported that biogas

production can significantly increase when trace nutrients are added to anaerobic

biological systems. #t is possible that !;%%% could be used as a trace nutrient

supplement to significantly increase biogas production at anaerobic digestion facilities.

>owever, additional research is re"uired to verify the trace nutrient hypothesis.

$ood waste from &andl9s :estaurant was added to the treatment plant primary clarifiers

and not directly to the anaerobic digesters. his was done to prevent potential damage to

5@



the existing metering pump due to particles in the food waste. #n addition, the larger

particles could adversely affect existing plant operations by settling in the unmixed

storage tan* as well as the digesters themselves. $or these reasons, the food waste was

added to the primary clarifiers where it was ostensibly incorporated into primary sludge.

he primary sludge was passed through a sludge screen with a 5-mm opening, and then

conveyed to the anaerobic digesters. he increase in biogas production due to the

addition of the food waste was estimated from /M& testing, settleability tests, and sieve

analysis to be relatively low as compared to the total treatment plant biogas production,

and could not be observed using existing gas flow meters at the treatment plant which

have an accuracy of B5. /ased upon the amount of food waste produced at &andl9s

restaurant and results of /M&, settleability, and sieve analysis it is estimated that 70

standard cubic feet per day of methane can be produced from the restaurant waste. his

could be used to generate approximately F882 per year of electricity or off-set the

purchase of F?20 per year of natural gas. he estimated cost to truc* the restaurant

waste to the treatment plant is F?500 per year. herefore, the worth of the electricity

generated is less than the truc*ing cost, whereas the worth of the natural gas saved is

greater than the truc*ing cost. #t should be noted that &andl9s :estaurant food waste is

currently disposed of in a sanitary landfill. #t is possible that anaerobic digestion with

biogas utiliCation and safe application of the stabiliCed biosolids would prove to be a

more economical approach than landfilling if detailed lifecycle cost comparison of the

options was performed.

57



C>APTER 1: O<ERALL CONCLUSIONS AND RECOMMENDATIONS

he research reported herein pertains to co-digestion of three high-strength wastewaters

'i.e., Miller /rewing +ompany, 4asaffre east +orporation, and !outheastern %isconsin

&roducts wastewaters( as well as restaurant food waste with municipal wastewater solids.

$irst, biochemical methane potential '/M&( tests and anaerobic toxicity assays 'AA( of

the wastes were performed. !econd, bench-scale testing of anaerobic co-digestion was

performed for each waste. $inally, full-scale anaerobic co-digestion pilot testing of

!outheastern %isconsin &roducts wastewater and food waste was accomplished using

existing digesters at the !outh !hore %astewater reatment &lant, )a* +ree*, %isconsin.

+onclusions and recommendations based on results of these tests follows.

1*8 BMP AND ATA TESTING

:esults of /M& and AA testing indicate that all four wastes are amenable to anaerobic

digestion and, at the concentrations studied, exhibit no significant toxicity to the

aceticlastic methanogenic organisms that convert acetate to methane. An unanticipated

outcome was that doses of 4asaffre, !outheastern %isconsin &roducts, and Miller

/rewery wastewaters cause methane production rates to increase by as much as 20 to

70 in AA tests. #n addition, 4asaffre and !outheastern %isconsin &roducts

wastewaters yielded abnormally high /M& values 'i.e., greater than 800 m4 methane per

gram +)(. herefore, each of the two wastes had a synergistic effect when digested

with municipal sludge biomass, increasing methane production from bac*ground +)

present in the sludge biomass use in the test. he unanticipated synergistic effect of these

58



wastes may be due to the presence and bioavailability of trace nutrients, such as iron. #n

addition, the wastes may contain ligands that form complexes with trace metals and

render them more bioavailable, thus stimulating methanogenic organisms and increasing

the rate of methane production from all substrates present.

1*9 BENC>SCALE CODIGESTION TESTING

:egarding bench-scale co-digestion testing, the 4asaffre east and !outheastern

%isconsin &roducts wastewaters can be successfully co-digested with municipal

wastewater solids at all blend ratios tested 'from 20 to 70 v3v wastewater in municipal

wastewater sludge(. !imilarly, the food waste can be successfully co-digested at all blend

ratios tested 'from to ?? v3v food waste in municipal wastewater sludge(.

he Miller brewery wastewater was not successfully digested by itself in the fill-and-

draw digester configuration utiliCedD however, it was successfully digested when blended

with municipal wastewater solids. Although the Miller /rewery wastewater was not

successfully digested alone, it is amenable to anaerobic digestion, as indicated by /M&

test results. #f it is treated alone, then it is recommended that a reactor configuration other

than a fill-and-draw digester should be considered.

#t is notable that all the wastes utiliCed in bench-scale testing had metals concentrations

below the %isconsin epartment of Eatural :esources high "uality limits for biosolids to

be land applied. herefore, it is li*ely that none of the wastes will limit the land

application of digested biosolids.

0



municipal wastewater solids may lead to a sustained increase in biogas production. #n

addition, full-scale investigations regarding the use of !outheastern %isconsin &roducts

and other similar yeast production3fermentation wastes as supplements to increase biogas

production at other anaerobic digestion facilities is recommended.

$ood waste from &andl9s :estaurant was added to the treatment plant primary clarifiers

and not directly to the anaerobic digesters. his was done to prevent potential damage to

the existing e"uipment and appurtenances due to large particles in the food waste. he

increase in biogas production due to the addition of the food waste was estimated from

/M& testing, settleability tests, and sieve analysis. #t is estimated that 70 standard cubic

feet per day of methane can be produced from the restaurant waste. his could be used to

generate approximately F882 per year of electricity or off-set the purchase of F?20 per

year of natural gas. he estimated cost to truc* the restaurant waste to the treatment plant

is F?500 per year. herefore, the worth of the electricity generated is less than the

truc*ing cost, whereas the worth of the natural gas saved is greater than the truc*ing cost.

#t should be noted that &andl9s :estaurant food waste is currently disposed of in a

sanitary landfill. #t is possible that anaerobic digestion with biogas utiliCation and safe

application of the stabiliCed biosolids would prove to be a more economical approach

than landfilling if a detailed lifecycle cost comparison of the two options was performed.

#n addition, if more restaurants, mar*ets, cafeterias, and similar facilities began to

practice waste shredding and storage, then it is probable that economy-of-scale savings

2



could be accrued, and that anaerobic digestion of food residuals would become more

cost-effective.



REFERENCES

Ahring, /. K., Angelida*i, #., and Lohansen, K. '?882(. Anaerobic treatment of manure

together with industial waste. Wat. Sci. Tech., vol. 25, no. @, pp. ??-?7.

Angelida*i, #., ;llegaard, 4., and Ahiring, /.K. '?88@(. Modelling anaerobic co-digestionof manure with olive oil mill effluent. Wat. Sci. Tech., vol. , no. -@, pp. 2-2@0.

A&>A 'American &ublic >ealth Association(, A%%A 'American %aterwor*sAssociation(, and %;$ '%ater ;nvironment federation( '?887(. Standard Methods for

the Eamination of Water and Wastewater , 20th ;dition.

+arrieri, +., i &into, A., :oCCi, A., and !antori, M. '?88(. Anaerobic co-digestion ofsewage sludge and concentrated soluble wastewaters. Wat. Sci. Tech., vol. 27, no. 2, pp.

?7@-?78.

+ecchi, $., &avan, &., and Mata-AlvareC, L. '?88(. Anaerobic co-digestion of sewagesludge application to the macroalgae from the Ienice lagoon. !esources, Conser"ation

and !ec#clin$, vol. ?@, no.?, pp. 5@-.

e 4a :ubia, M.A., &ereC, M., :omero, 4.#., !ales, . '2002(. Anaerobic mesophilic andthermophilic municipal sludge digestion. Chem. %iochem. En$., vol. ?, no. , pp. ??8-?26.

i &alma, 4., Medici, $., Merli, +., and &etrucci, ;. '?888(. Anaerobic co-digestion ofsewage sludge and municipal solid waste from mar*ets experimental results. &ournal ofSolid Waste Technolo$# and Mana$ement, vol.2, no. ?, pp. ?0-?.

<avala, >., !*iadas, #., and 4yberatos, <. '?88(. Anaerobic co-digestion of agriculturalindustires9 wastewater. Wat. Sci. Tech., vol.6, no. ??, pp. @-@5.

<avala, >., !*iadas, #., and 4yberatos, <. '?888(. )n the performance of a centraliseddigestion facility receiving seasonal agroindustrial wastewaters. Wat. Sci. Tech., vol.60,no. ?, pp. 8-6.

>amCawi, E., Kennedy, K., and Mc4ean, .. '?887(. Anaerobic digestion of co-mingled municipal solid waste and sewage sludge. Wat. Sci. Tech., vol. 7, no. 2, pp.

?2@-?2.

4us*, &. and Moser, M. '?88(. Anaerobic igestion- esterday, oday and omorrow. Einth ;uropean /ioenergy +onferenceD Lune 26-2@, ?88, +openhagen, enmar*. GK&ergamon &ressD pp. 276-278.

6



Mavinic, . !., Koch, $. A., >all, ;. :., Abraham, K., and Eiedbala, . '?887(.Anaerobic co-digestion of combined sludges from a /E: wastewater treatment plant. En"ironmental Technolo$#., vol.?8, no.?, pp. 5-66.

Metcalf and ;ddy '200(. Wastewater En$ineerin$' Treatment and !euse, Mc<raw >ill,

/oston, MA.

)wen, %. $., !tuc*ey, . +., >ealy Lr, L. /., oung, 4. ., and Mc+arty, &. 4. '?8@8(./ioassay for monitoring biochemical methane potential and anaerobic toxicity. Water !esearch, vol. ?, pp. 675-682.

:intala, L. A., and Laervinen, K. . '?88(. $ull-scale mesophilic anaerobic co-digestionof municipal solid waste and sewage sludge methane production characteristics. Waste Mana$ement ( !esearch, vol. ?6, no. 2, pp. ?-?@0.

:ipley, 4. ;., /oyle, %. +., and +onverse, L. +. '?87(. #mproved al*alimetric

monitoring for anaerobic digestion of high-strength wastes. &ournal WPC) , vol. 57, no.5, pp. 60-6??.

!mil, I. '200(. Ener$# at the Crossroads' *lo+al Perspecti"es and ncertainties. heMassachusetts #nstitute of echnology &ress, +ambridge, MA.

!osnows*i, &., %iecCore*, A., and 4eda*owicC, !. '200(. Anaerobic co-digestion ofsewage sludge and organic fraction of municipal solid wastes. -d"ances in En"ironmental !esearch, vol. @, no., pp. 08-?.

!peece, :. ;. '?877(. A survey of municipal anaerobic sludge digesters and diagnosticactivity assays. Wat. !es., vol. 22, no. , pp. 5-@2.

!peece, :. ;. '?885(. -naero+ic %iotechnolo$# for ndustrial Wastewaters. Archae &ress, Eashville, E.

Pitomer, ., $erguson, E., Mc<rady, K., and !chilling, L. '200?(. Anaerobic co-digestionof aircraft deicing fluid and municipal wastewater sludge. Water En"ironment !esearch, vol.@, no., pp. 65 1 56.

5



BIBLIOGRAP>Y

+ecchi, $., Iallini, <., &avan, &., /assetti, A., and Mata-AlvareC, L. '?88(. #n +ecchi, $.,Mata-AlvareC L. and &ohland $. <.';ds.(, Management of macroalgae from Ienicelagoon through anaerobic co-digestion and co-composting with municipal solid waste'M!%(.

emirer, <.E., uran, M., ;rguder, .>., eCel, G., <ueven, ;., and Ggurul, ). '2000(.Anaerobic treatibility and biogas production potential studies of different agro-industrialwastewaters in ur*ey. Proceedin$ of the /th nternational S#mposium on En"ironmental %iotechnolo$#.

;. &. A. ';nvironmental &rotection Agency( '2006(. - Plain En$lish *uide to the EP-

part 012 %iosolids !ule, ;&A 723:-8-00, %ashington, . +.

$erguson, 4.E. '?888(. -naero+ic Co3Di$estion of -ircraft Deicin$ )luid and

Microaero+ic Studies. M. !. thesis, epartment of +ivil and ;nvironmental ;ngineering,Mar"uette Gniversity, Milwau*ee, %#.

$ruteau de 4aclos, >., esbois, !. and !aint-Loly, +. '?88@(. Anaerobic digestion ofmunicipal organic waste +alorga full-scale plant in ilburg, he Eetherlands. Wat. Sci.

Tech., vol. , no. -@, pp. 65@-62.

Mc+arty, &.4. '200?(. he development of anaerobic treatment and its future, Wat. Sci.Tech., vol. 66, no. 7, pp.?68-?5.

Mc<rady, K. '?888(. -naero+ic Co3Di$estion and Phasin$ for -ircraft De3cin$ )luidTreatment . M. !. thesis, epartment of +ivil and ;nvironmental ;ngineering, Mar"uetteGniversity, Milwau*ee, %#.

Eagel, &., A. Grtubia, A., Aroca, <., +hamy, :. and Achiappacasse, M. '?888(.Methanogenic toxicity and anaerobic biodegradation of chemical products in use in a brewery. Wat. Sci. Tech., vol. 60, no. 7, pp. ?8-?@.

)lesC*iewicC, L., and Mavinic, . !. '2002(. %astewater biosolids an overview of processing, treatment, and management. &. En"iron. En$. Sci., vol. ?, pp. @5-77.

municipal anaerobic digesters as regional renewable energy

Documents