Making Hydrogen a Competitive Alternative to Fossil Fuels Through Anaerobic Digestion of Waste
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8/16/2019 Making Hydrogen a Competitive Alternative to Fossil Fuels Through Anaerobic Digestion of Waste
Making Hydrogen a Competitive Alternative to Fossil Fuels
through Anaerobic Digestion of Waste
By Neil Scheibelhut
8/16/2019 Making Hydrogen a Competitive Alternative to Fossil Fuels Through Anaerobic Digestion of Waste
Table of Contents
1.3 Current Technologies
2. Current Technologies
2.1 Natural "as #e$or%ing
2.2 Bio%ass "asifcation
2.3 Coal "asifcation
2.' Microbial Bio%ass Conversion
3. (ro)osed Bioreactor
3.1 *)+o, -naerobic Sludge Blan et #eactor
3.2 /ood 0aste as /eedstoc
3.3 (retreat%ent o$ Munici)al Sludge
3.3.1 eat Shoc Treat%ent
3.3.2 -cid -l ali Treat%ent
3.3.4 *ltraviolet Irradiation
3.4 I%)ortance o$ "enetic Se uencing
4. /uture #esearch
8/16/2019 Making Hydrogen a Competitive Alternative to Fossil Fuels Through Anaerobic Digestion of Waste
-ccording to the Intergovern%ental (anel on Cli%ate Change greenhouse
gases $ro% hu%an activities are the %ost signifcant driver o$ observed
cli%ate change since the %id526 th century. Carbon dio7ide $ro% burning
$ossil $uel $or energy and heat is the leading greenhouse gas e%ission
8/igure 19. ver :'; o$ the ,orld. nly China
82?;9 )roduces %ore o$ the ,orld.
0ith no %itigation by the year 2166 the &arth. International concerns over global ,ar%ing
are at an all ti%e high there$ore the need $or alternatives to $ossil $uels as
energy sources has never been greater.
Figure 1 Figure "
ydrogen is considered a )ro%ising $uel source as it )roduces only ,ater
u)on co%bustion and is getting increasing attention as a clean energy
alternative to $ossil $uels. Co%)ared to conventional $ossil $uels hydrogen
has the )otential to )roduce t,o and a hal$ ti%es %ore energy than natural
gas or gasoline ='>. In 266' the *.S. &nergy (olicy -ct ,as )assed and
directed the energy secretary to conduct a research and develo)%ent
)rogra% in consultation ,ith other $ederal agencies and the )rivate sector
on technologies related to the )roduction )urifcation distribution
storage and use o$ hydrogen energy $uel cells and related in$rastructureD
ydrogen $uel cell technology has been around since the N-S- "e%ini
days and they continue to use hydrogen as an energy source to this day. It
is )ollution $ree ,ith only ,ater )roduced as a by)roduct and scalable.
Because a single $uel cell only )roduces about one volt o$ )o,er they are
co%bined in series to $or% a stac ,hen %ore )o,er is needed =:>. So $uel
cells can be custo%iEed $or any a))lication. -dditionally hydrogen $uel
cells are very eFicient co%)ared ,ith $ossil $uel energy generators. -
gasoline co%bustion engine is only about 26; eFicient ,ith %ost o$ the
energy lost as heat. Co%bustion based )o,er )lants are little %ore
eFective at about 3'; eFiciency. o,ever hydrogen $uel cells can be u) to
A6; eFicient =?>. Because o$ this versatility and eFiciency the *.S.
Ge)art%ent o$ &nergy is currently )er$or%ing research to %a e the% %ore
eFicient and less e7)ensive to %anu$acture o)erate and %aintain.
o,ever their research also includes hydrogen )roducing technologies as
the cost o$ hydrogen is currently too e7)ensive to be co%)etitive ,ith $ossil
$uels. The Ge)art%ent o$ &nergy esti%ates that a ilogra% o$ hydrogen
,hich is a))ro7i%ately e uivalent to one gallon o$ gasoline needs to cost
bet,een H2.66 and H4.66 by the year 2626 =@>.
1.3 Current Technologies
Currently the only viable hydrogen )roduction technology is natural gas
re$or%ing ,hich uses a t,o ste) a))roach to convert %ethane 8natural
gas9 into hydrogen. In the frst ste) called stea%5%ethane re$or%ing
natural gas is %i7ed ,ith ,ater va)or to create carbon %ono7ide and
hydrogen gas. The carbon %ono7ide is then %i7ed ,ith ,ater va)or in
,hat is re$erred to as the ,ater5gas shi$t reaction ,hich converts the
carbon %ono7ide and ,ater va)or into carbon dio7ide and hydrogen. This
)rocess )roduces hydrogen at a cost o$ H3.?6 )er gallon o$ gasoline
e uivalent 8gge9 dis)ensed. o,ever there are %any dra,bac s to this
technology ,hich ,ill %a e costs )rohibitively e7)ensive to e7)and into the
%ass %ar et =16>. Because o$ this the Ge)art%ent o$ &nergy is
researching other technologies to create hydrogen through gasifcation o$
bio%ass and coal electrolysis and %icrobial bio%ass conversion. &ach o$
these technologies in their current states ho,ever are )rohibitively
e7)ensive and %ore research %ust be )er$or%ed to %a e the% viable.
In order to %a e hydrogen a co%)etitive $uel source to $ossil $uels research
%ust be )er$or%ed to lo,er the cost o$ )roduction.
" Current Technologies
2.1 Natural Gas Re or!ing
Currently @'; o$ all hydrogen is being )roduced in large central
%anu$acturing )lants ,hich utiliEe natural gas re$or%ing technology. It
,or s by co%bining e7tre%ely hot ,ater va)or 8:66 ° C 5 1666 ° C9 ,ith the
%ethane contained in natural gas at high )ressure. In the )resence o$ a
)ro)er catalyst carbon %ono7ide and hydrogen is $or%ed in a )rocess
called the stea%5%ethane re$or%ing reaction 8& uation 19.
819 C 4 2 eat → C 3 2
Ne7t the carbon %ono7ide is co%bined ,ith stea% in the )resence o$ a
catalyst ,hich converts the carbon %ono7ide into carbon dio7ide and
hydrogen 8& uation 29.
829 C 2 → C 2 2 eat
/inally i%)urities are re%oved $ro% the gas strea% leaving )ure hydrogen
in a )rocess called )ressure5s,ing adsor)tion.
This technology is used currently because natural gas is relatively
ine7)ensive and even though carbon dio7ide is )roduced in the )rocess it
is a relatively s%all a%ount ,hen co%)ared ,ith the co%bustion o$ $ossil
$uels =11>. *n$ortunately there are dra,bac s to this technology. Ca)ital
costs to create satellite re$or%ers a,ay $ro% the large central )lants is too
high to %eet )rice )er gge targets. #e$or%ing units are currently designed
and built one at a ti%e leading to )rohibitively large and e7)ensive units.
-dditionally the re$or%ing stations are too large $or urban settings. nce
built the re$or%ing stations need e7cessive %aintenance and in )erson
%onitoring leading to high o)eration costs. /inally control sa$ety and
environ%ental )rotocols are needed to address concerns ,ithout escalating
costs ,hile %eeting de%ands avoiding lea age and %ini%iEing e%issions
2.2 "io!ass Gasifcation
Bio%ass is considered to be any rene,able organic resource that can be
used to )roduce hydrogen. &7a%)les o$ bio%ass include %unici)al solid
,aste ani%al ,aste agricultural ,aste and even cro)s gro,n $or the
s)ecifc )ur)ose o$ being used $or energy use. Bio%ass gasifcation
converts organic carbon based %atter into hydrogen carbon dio7ide and
other gases by heating the bio%ass to over :66 ° C but not burning it. -
controlled a%ount o$ o7ygen and stea% are used in this )rocess ,hich
yields carbon %ono7ide carbon dio7ide hydrogen and other gases
8& uation 39.
839 CA 12 A 2 2 → C C 2 2 other gases
Just li e natural gas re$or%ation the ne7t ste) is a ,ater5gas shi$t reaction
to re%ove the )oisonous carbon %ono7ide $ro% the gas strea% 8& uation
29. -dsorbers or %e%branes fnally se)arate the hydrogen $ro% the gas
This technology is )ro%ising because o$ the abundance o$ bio%ass as a
resource. -ccording to the *.S. Ge)art%ent o$ &nergy by the year 2636
the *nited States ,ill )roduce over one billion dry tons o$ bio%ass that
could )otentially be utiliEed $or gasifcation. Sources o$ this bio%ass
include $orestland agricultural ,aste and energy cro)s =13>. -dditionally
because )lants re%ove carbon dio7ide $ro% the at%os)here the carbon
dio7ide )roduced during gasifcation is oFset ,hich results in a recycling o$
carbon dio7ide ,hich lo,ers greenhouse gas e%issions.
The challenges to bio%ass gasifcation center around high ca)ital costs $or
)urchasing e ui)%ent and high costs associated ,ith bio%ass $eedstoc
2.3 Coal Gasifcation
Ki e bio%ass coal can be gasifed through the introduction o$ o7ygen and
stea% under high te%)eratures. This results in synthesis gas ,hich
consists o$ %ostly carbon %ono7ide and hydrogen 8& uation 49. nce
again the ,ater5gas shi$t reaction 8& uation 29 converts the carbon
%ono7ide to carbon dio7ide once the i%)urities o$ the synthesis gas are
849 C 6.? 2 2 → C C 2 2 other gases
The abundance o$ coal resources in the *nited States %a es this technology
attractive due to the lo, cost o$ the coal. o,ever coal gasifcation
)roduces a large a%ount o$ carbon dio7ide. Gevelo)ing carbon ca)ture
technologies to ensure the dangerous greenhouse gas is not released into
the at%os)here during the )roduction )rocess is needed =14>.
0ater can be bro en do,n into hydrogen and o7ygen by introducing it to
electricity. This )rocess is called electrolysis. &lectrolysis is )ro%ising as
it generates hydrogen ,ith no greenhouse gas e%issions. o,ever the
electricity used to s)lit ,ater into its ele%ental co%)onents is usually
generated using $ossil $uels. In addition to fnding green electricity sources
ca)ital costs and hydrogen )ac aging costs are challenges that need to be
overco%e $or electrolysis to beco%e a viable source o$ hydrogen =1'>.
2.% Microbial "io!ass Conversion
*nder anaerobic conditions so%e %icroorganis%s $er%ent organic %atter
and create hydrogen. Because no light is needed by these %icroorganis%s
this )rocess is called dar anaerobic $er%entation. This technology is
attractive $or so%e o$ the sa%e reasons as bio%ass gasifcation bio%ass is
an abundant resource and in %any cases it consists o$ ,aste )roducts
,hich can be obtained at little to no cost. -dditionally the %icroorganis%s
use the bio%ass as an energy source so the bioreactors ,hich are used to
generate hydrogen use little )o,er another cost saving attribute. o,ever
hydrogen )roduction is slo, ,ith this technology. #esearch %ust be
)er$or%ed to i%)rove %icrobial co%%unities reactor syste%s and
$eedstoc sources to create higher yields =1A>.
# $roposed %ioreactor
3.1 &'(o) *naerobic Slu+ge "lan,et Reactor
Gar anaerobic $er%entation has great )otential to create lo, cost
hydrogen. o,ever to ensure hydrogen costs stay lo, the )roduction
)rocess %ust concentrate on using lo, cost $eedstoc and a bioreactor
design ,hich uses lo, energy. The %ost co%%only utiliEed bioreactor
design $or dar anaerobic $er%entation is the u)+o, anaerobic sludge
blan et reactor 8/igure 49. This reactor is good $or lo, cost hydrogen
)roduction because there is no %echanical stirring that %ust be )o,ered.
Mi7ing o$ the substrate ,ith the %icroorganis%s is obtained through gas
generation. -s the bacterial sludge $er%ents the organic substrate ,hich is
)u%)ed into the reactor $ro% the botto% bubbles o$ biogas are $or%ed
,hich churn the li uid causing the desired %i7ing eFect and increases the
rate o$ $er%entation =1:>. o,ever there are still challenges to )roducing
lo, cost hydrogen using this technology. /eedstoc costs %ust be e)t lo,
the bacterial co%%unity ,hich $er%ents the $eedstoc %ust be o)ti%iEed to
increase )roduction rates and lo, energy reactor syste%s %ust be
i%)le%ented to ee) o)erating costs lo,.
3.2 -oo+ aste as -ee+stoc,
-naerobic $er%entative bacteria turn a carbon source usually a fve5carbon
sugar li e glucose into hydrogen carbon dio7ide and organic acids acetic
acid butyric acid and )ro)ionic acid. 0hen considering a $eedstoc $or
biohydrogen 8hydrogen )roduced by living organis%s such as bacteria9
)roduction it should be a %aterial that contains a high )ercentage o$ fve5
carbon sugars. In addition because the $eedstoc is consu%ed there is a
uni ue o))ortunity to use ,aste %aterial to )rovide a solution $or ,aste
re%oval and storage. In a,aii )articularly on ahu $ood ,aste %a es u)
the largest )ortion 812.:;9 o$ all ,aste that %a es its ,ay to ,aste
)rocessing $acilities. ver 126 666 tons o$ $ood ,aste are )roduced each
year on ahu %a ing it a )lenti$ul rene,able resource $or biohydrogen
)roduction not to %ention ee)ing 126 666 tons o$ %atter out o$ the
island. -dditionally the local diet is rich in carbohydrates
li e rice and tro)ical $ruits so the )otential $or biohydrogen )roduction
$ro% $ood ,aste on ahu %ay be )otentially greater than that o$ %ainland
3.3 /retreat!ent o Munici'al Slu+ge
Many %unici)al ,aste ,ater treat%ent $acilities utiliEe bacterial sludge in
their treat%ent )rocess but hydrogen is not a %a!or co%)onent o$ the
biogas )roduced by this )rocess. Because o$ the )resence o$ %any %ethane
)roducing %icroorganis%s in %unici)al sludge %ost o$ the hydrogen
)roduced in the $er%entation )rocess gets converted into %ethane ,hich is
a greenhouse gas that gives oF carbon dio7ide ,hen co%busted.
/ortunately there are %any technologies that can be used to inhibit or
eli%inate %ethanogenic %icroorganis%s. In %ost cases the technologies
)rovide harsh conditions $or the %icroorganis%s in the sludge to induce
s)ore $or%ation. Certain %icroorganis%s create s)ores ,hen )laced in an
environ%ent in ,hich they cannot survive. The s)ores they create
ho,ever can survive very harsh conditions and i$ conditions return to a
state in ,hich the %icroorganis%s can thrive the s)ores hatchD into a ne,
version o$ the original. Methanogenic bacteria have sho,n they are non5
s)ore $or%ing and there$ore are illed in such harsh conditions ,hile %any
hydrogenic bacteria are s)ore $or%ing. By creating such harsh conditions
the %ethanogenic bacteria )erish leaving the desirable hydrogenic bacteria
to survive and thrive. Theoretically a sludge that has been )retreated in
this %anner should )roduce biogas rich in hydrogen.
3.3.1 0eat Shoc, Treat!ent
eat Shoc Treat%ent 8 ST9 is the %ost co%%only used )retreat%ent
%ethod. It uses heat to create a harsh environ%ent ,hich induces s)ore
creation by hydrogenic bacteria "acillus and Clostri+iu! ,hile illing oF
%ethanogenic bacteria. o,ever as ,ith %any )retreat%ent %ethods that
rely on inducing s)orulation other s)ore )roducing bacteria survive the
)retreat%ent )rocess ,hich )roduces a %i7ed culture that includes
acetogenic bacteria such as "acterioi+es and #ubacteriu! ,hich utiliEe
hydrogen =1@>. Most o$ the ti%e an increase o$ hydrogen yield is seen a$ter
ST co%)ared to an untreated control ,ith a %a7i%u% re)orted yield o$
2.3 %ol hydrogen )er %ol glucose. =26>. Ty)ically sludge is )retreated at a
te%)erature bet,een @65166 ° C $ro% any,here bet,een 16%in to 1h =21>.
3.3.2 *ci+ *l,ali Treat!ent
Because %ethanogenic bacteria survive at neutral ) the addition o$ acid
or al ali to )retreat sludge has been investigated. Ty)ically hydrogen
)roducing bacteria can survive at a ,ider ) range than %ethanogenic
bacteria. Because s)ore $or%ers are not the only bacteria to survive a
%ore diverse %icrobial co%%unity e7ists a$ter acid al ali )retreat%ent =26>.
The %ost co%%on acidic )retreat%ent uses Cl 2S 4 N 3 and Cl 4
=22 23> ,ith Na being the %ost )o)ular al aline treat%ent %ethod =24>.
Ty)ically the )retreat%ent lasts $or 24h =2'> ,ith a %a7i%u% observed
yield o$ 1.' %ol hydrogen )er %ol glucose =2A>.
The )ur)ose o$ aeration is to a))ly o7idative stress to obligate anaerobes
,hich causes the% to die. Most %ethanogenic bacteria are obligate
anaerobes ho,ever %any hydrogen )roducing bacteria are also obligate
anaerobes ,hich %a es this %ethod rather ineFicient. -$ter aeration $or
24 hours %a7i%u% hydrogen yield ,as very lo, at 6.: %ol hydrogen )er
%ol glucose =2A>. o,ever aeration has sho,n a very large acetate to
butyrate ratio co%)ared ,ith other %ethods 826.'? L 6.2'9 =24>. This is
signifcant because the acetate )ath,ay )roduces $our %oles o$ hydrogen to
every %ole o$ glucose ,hile the butyrate )ath,ay only )roduces t,o.
-dditionally because o$ the diFerent ind o$ stress this treat%ent )laces on
the sludge co%)ared to other %ethods it results in a diFerent %icrobial
co%%unity. Most )hysical )retreat%ents sho, Clostri+iu! s)). as the
do%inant s)ecies a$ter )retreat%ent but aeration sees #nterobacter s)).
and lebsiella s)) =2A>. This )rovides a uni ue o))ortunity to co%bine
sludge that has been )retreated ,ith o7idative stress ,ith heat shoc ed
sludge $or e7a%)le %a ing $or a %ore robust %icrobial co%%unity.
3.3.4 <raviolet rra+iation
*ltraviolet irradiation bo%bards the sludge ,ith ,avelengths $ro% 16n% to
3?6n% creating an environ%ent ,hich sti%ulates s)orulation o$ hydrogenic
bacteria and inhibition or eli%ination o$ %ethanogenic bacteria. This
%ethod is )roven to increase hydrogen yield by 6.3@ $old co%)ared to
untreated sludge ,hen irradiated $or 1' %in =2:>. The co%)lication o$ this
%ethod is that sludge is usually dar and o)a ue ,hich bloc s the * light
$ro% )enetrating $arther than !ust the sur$ace %a ing this an ineFicient
%ethod. n the other hand this %ethod )resents a uni ue )ossibility to
ee) costs do,n. Solar irradiation could )otentially be used as a substitute
$or * irradiation through electric )o,ered la%)s. #esearch %ust be
)er$or%ed to deter%ine the )ro)er )ara%eters $or this %ethod such as
translucence o$ sludge de)th o$ sludge and ti%e o$ e7)osure to solar
3.4 !'ortance o Genetic Se uencing
"enetic se uencing can be an i%)ortant tool in %a7i%iEing hydrogen
)roduction ,hen utiliEing )retreat%ent technologies. ne se uencing
techni ue called bar coding can be a valuable tool in identi$ying the
%icrobial co%%unity o$ )retreated %unici)al sludge. Bar coding utiliEes
s)ecifc areas o$ the geno%e ,hich are co%)letely uni ue to each s)ecies o$
bacteria. nce such area o$ the geno%e is the 1AS region o$ the riboso%al
#N- =2?>. Isolating this region is uite %anageable and it can be a%)lifed
through (C# easily so the se uence can be obtained %ulti)le ti%es over to
ensure accuracy. -nother se uencing techni ue that can be use$ul is ,hole
geno%e se uencing. -lthough it is a longer %ore e7)ensive and diFicult
)rocess it yields %ore accurate results because entire geno%es are being
co%)ared to database in$o not !ust a short se uence li e those utiliEed in
bar coding. By using genetic se uencing techni ues to identi$y the
%icrobial co%%unity o$ )retreated sludge a )ossible correlation can be
%ade by co%)aring the hydrogen )roduction o$ each ty)e o$ )retreated
sludge ,ith the %icrobial co%%unity )resent in the sludge. This ,ay
individual s)ecies o$ bacteria can be identifed as vital to the hydrogen
)roducing )rocess. nce the i%)ortant bacteria are identifed an o)ti%al
%icrobial co%%unity %ay be designed to %a7i%iEe hydrogen )roduction.
& Future 'esearch
Ma7i%iEing hydrogen yield through dar anaerobic $er%entation ,hile
%ini%iEing cost is a $uture reality. Many )ara%eters %ust be researched
be$ore this technology is ready $or )roduction on an industrial scale. The
)otential %icrobial co%%unities that could be utiliEed are al%ost infnite
and research %ust be done to identi$y not only the %ost eFicient bacterial
co%%unity $or hydrogen )roduction but also the right co%%unity $or the
s)ecifc $eedstoc being considered. #esearch %ust also be )er$or%ed to
identi$y lo, cost $eedstoc o)tions and ,hether they are better $or dar
anaerobic $er%entation as a )ure $eedstoc or one that has been %i7ed ,ith
another $or%. #eactor designs %ust be researched to o)ti%iEe hydrogen
)roduction ,hile ee)ing o)erating and ca)ital costs lo,. )ti%al
$eedstoc concentration #T te%)erature and ) %ust be identifed.
-dditionally lo, energy reactor syste%s %ust be integrated to re%ove and
)uri$y the hydrogen and drive the syste%.
0ith research being )er$or%ed to decrease the cost o$ hydrogen
)roduction biohydrogen is a )ro%ising technology. Biohydrogen $ro%
,aste is even %ore enticing because it solves t,o )otential )roble%s
,aste %anage%ent and $eedstoc cost. (retreat%ent o$ %unici)al sludge
to %a7i%iEe biohydrogen )roduction can be utiliEed to this end. o,ever
%ore research %ust be )er$or%ed to o)ti%iEe hydrogen yields and drive
hydrogen costs do,n. By using genetic se uencing techni ues %ore
insight can be gained into the co%%unity o$ %icroorganis%s that %ay be
best $or hydrogen )roduction. This techni ue can )otentially be used to
o)ti%iEe %icrobial co%%unities $or each ty)e o$ $eedstoc in order to use
ine7)ensive %aterials or even ,aste to %a e hydrogen even %ore
aFordable. Ko, energy bioreactors such as an u)+o, anaerobic sludge
blan et reactor can be used to ee) o)erating costs do,n. o,ever
research %ust be )er$or%ed to identi$y the o)ti%al o)erating s)ecifcations
and reactor syste%s ,hile ee)ing energy invest%ent lo,. I$ hydrogen can
beco%e a lo,er cost alternative to burning $ossil $uels $or energy it %ay be
utiliEed %ore ta ing a,ay the need $or $ossil $uels and turning to a %ore
sustainable and clean source o$ energy. Microbial bio%ass conversion could
be the %eans to this end.
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