Ambien e & Água - An In e disciplina y Jou nal o Applied Science
ISSN 1980-993X – doi:10.4136/1980-993X
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P oduc ion o ene gy (biodiesel) and eco e y o ma e ials (biocha )
om py olysis o u ban was e sludge
ARTICLES doi:10.4136/ambi-agua.2128
Recei ed: 27 Ap . 2017; Accep ed: 05 Jan. 2018
A ianna Callega i1; Pe Hla inek2; And ea Giuseppe Capodaglio1*
1Uni e si à degli S udi di Pa ia, Pa ia, I aly
E-mail: a ianna.callega i@unip .i , and ea.ca[email p o ec ed]
2B no Uni e si y o Technology, B no, Czech Republic
E-mail: hla ine[email p o ec ed]
*Co esponding au ho
ABSTRACT
Sa e disposal o sewage sludge is one o he mos p essing issues in he was ewa e
ea men cycle: a he Eu opean Union le el, sludge p oduc ion is expec ed o each 13 M by
yea 2020. Sludge disposal cos s may cons i u e up o, and some imes abo e, 50% o he o al
cos o ope a ion o a WWTP, and con ibu e o o e 40% o i s GHGs emissions. The mos
common disposal op ions a he momen a e land illing, disposal in ag icul u e (abou 40% EU-
wide), incine a ion o co-incine a ion, and use in he indus ial p oduc ion o b icks, asphal s
and conc e e. Sewage sludge, howe e , s ill con ains bene icial esou ces such as nu ien s, ha
can be eco e ed h ough speci ic p ocesses (e.g. p ecipi a ion as s u i e) and ene gy,
eco e able h ough a a ie y o app oaches. Mic owa e-assis ed py olysis o u ban was e
sludge was applied o he p oduc ion o oil, (Syn)gas, and biocha ha we e a e wa ds
cha ac e ized and compa ed o mains eam al e na i e uels (biodiesels) and o he ma e ial
eco e y op ions. Sus ainabili y issues ela ed o he p oduc ion o biodiesel/biocha s om
u ban was ewa e ea men sludge a e also discussed. The pape shows ha was e u ban sludge
can indeed be a ull componen o he u ban ci cula economy by allowing, i p ope ly
p ocessed, eco e y o ene gy esou ces a mul iple le els: bio-oils (biodiesel), syngas and bio-
cha , all ha ing de ini e ad an ages o inal esidues use and disposal. Biodiesel, in pa icula ,
allowing ene gy eco e y as liquid uel, o e s a much mo e lexible and e icien u iliza ion.
Keywo ds: biocha , biodiesel, ma e ials, mic owa es, py olysis, sus ainable ene gy, u ban was e
sludge.
P odução de ene gia (biodiesel) e ecupe ação de ma e iais (biocha )
a pa i da pi ólise de esíduos de lodo u bano
RESUMO
A eliminação segu a das lamas de esgo o é uma das ques ões mais u gen es no ciclo de
a amen o de águas esiduais: a ní el da União Eu opéia, espe a-se que a p odução de lamas
a inja 13 M a é o ano 2020. Os cus os de disposição das lamas podem cons i ui -se e às ezes
acima de 50% Cus o o al de ope ação de uma ETAR e con ibui pa a mais de 40% das emissões
de GEEs. As opções de eliminação mais comuns no momen o são: a e o, eliminação na
ag icul u a (ce ca de 40% em oda a escala), incine ação ou co-incine ação, uso na p odução
Re . Ambien . Água ol. 13 n. 2, e2128 - Tauba é 2018
2
A ianna Callega i e al.
indus ial de ijolos, as al os, conc e o. As lamas de esgo o, no en an o, ainda con êm ecu sos
bené icos, como nu ien es, que podem se ecupe ados a a és de p ocessos especí icos (po
exemplo, p ecipi ação como es u i a) e ene gia, ecupe á el a a és de uma a iedade de
abo dagens. A pi ólise assis ida po mic oondas de lama de lixo u bano oi aplicada pa a a
p odução de pe óleo, gás (Syn) e biocha que pos e io men e o am ca ac e izados e
compa ados aos p incipais combus í eis al e na i os (biodiesels) e ou as opções de
ecupe ação de ma e iais. São discu idos os p oblemas de sus en abilidade elacionados à
p odução de biodiesel / biocha s de lamas de a amen o de águas esiduais u banas. O
documen o mos a que o lodo u bano esidual pode de a o se um componen e comple o da
economia ci cula u bana, pe mi indo, se de idamen e p ocessado, a ecupe ação de ecu sos
ene gé icos em á ios ní eis: bio-óleos (biodiesel), gás de sín ese e bio-ca bon, odos com
an agens de inidas pa a o uso e eliminação de esíduos inais. O biodiesel, em pa icula , que
pe mi e a ecupe ação de ene gia como combus í el líquido, o e ece uma u ilização mui o mais
lexí el (e e icien e).
Pala as-cha e: biocha , biodiesel, ene gia sus en á el, lodo de esíduos u banos, mic o-ondas,
pi ólise.
1. INTRODUCTION
Residual u ban sludge disposal cos s may cons i u e up o, and some imes abo e, 50% o
he o al cos o ope a ion o Was ewa e T ea men Plan s (WWTPs) and con ibu e mo e han
40% o he o al g eenhouse gas (GHG) emissions associa ed wi h hei ope a ion (Liu e al.,
2013). The sa e disposal o such sludge is li e ally a “big” issue in u ban was ewa e ea men :
a he Eu opean Union le el, he 2020 sludge p oduc ion is expec ed o each close o 13 M by
yea 2020, an inc ease o mo e han 30% om oday’s le els. Acco ding o Machado (2001),
u ban was e sludge p oduc ion in B azil is much lowe (abou 150 K pe yea ) since abou 80
million people in B azil do no ha e hei was ewa e collec ed by cen alized sys ems, bu
disposed o h ough sepa a e uni a y (sep ic anks) sys ems, in which he e is no cen alized
con ol o e he inal des ina ion o excess o ganic solids. Pa o he popula ion ha e hei
was ewa e collec ed by communal sys ems, bu no ye ea ed. In p ac ice, only less han 45
million B azilians ge hei was ewa e ea ed. Clea ly, he size o he issue will ine i ably
inc ease as was ewa e collec ion and ea men in B azil inc eases, as has been seen elsewhe e
in he wo ld. In 2008, he Uni ed Na ions Human Se lemen P og amme mo e han doubled
he p e ious es ima e by Machado o he coun y, upda ing i o 370 k pe yea (Ma eo-Sagas a
e al., 2015).
T adi ionally, was ewa e sludges a e p ocessed o : a) educ ion o o al weigh and
olume o acili a e hei anspo and subsequen ea men s; b) s abiliza ion o con ained
o ganic ma e ial and des uc ion o pa hogenic mic oo ganisms, elimina ion o noxious odou s,
and educ ion o pu e ac ion po en ial; and, o he las ew decades, and a an inc easing
deg ee, c) alue addi ion by de eloping economically iable eco e y o ene gy and esidual
cons i uen s, such as nu ien s, ha can be eco e ed h ough speci ic p ocesses (e.g.
p ecipi a ion as s u i e), and ene gy, eco e able h ough a a ie y o app oaches.
Was ewa e s ill con ains signi ican amoun s o esou ces (i.e. nu ien s) and ene gy; mos
o hese end up, a e ea men , immobilized in esidual sludge. Acco ding o Shizas and
Bagley (2004) he heo e ical chemical ene gy con en o was ewa e is app oxima ely
3 kJ/g (d y w.), which is oughly 10 imes he ene gy expendi u e necessa y o ea he same
was ewa e in a cu en - echnology WWTP. As o oday, con en ional echnology allows he
eco e y, h ough anae obic sludge diges ion, o jus a small ac ion o ha es ima ed alue,
allowing WWTPs o co e a mos ¼ o ½ o hei ene gy needs (Capodaglio e al., 2017). By
3
P oduc ion o ene gy (biodiesel) and eco e y …
Re . Ambien . Água ol. 13 n. 2, e2128 - Tauba é 2018
shee mass balance p opo ions, was ewa e sludge can be shown o con ain abou 5 imes he
ene gy s o ed in was ewa e . Table 1 illus a es some igu es epo ed by di e en esea che s.
Table 1. Ene gy con en es ima es (kJ/g d y w.) o di e en sludge ypes.
P ima y Sludge
Seconda y Sludge
Diges ed Sludge
Sou ce
15.9
12.4
12.7
Shizas and Bagley (2004)
15
13.5
11.4
Zanoni and Muelle (1982)
n.a.
n.a.
12.6
Vesilind and Ramsey (1996)
In Table 1, diges ed sludge e e s o sludge p ocesses h ough seconda y (anae obic)
diges ion a e a i s -s age liquid ea men . In B azil and o he Sou h Ame ican coun ies, i is
common p ac ice nowadays o ea u ban was ewa e s h ough UASB p ocesses (Capodaglio,
2017) as his p ocess is much less ene gy-in ensi e, and could be almos as e icien as
adi ional ae obic p ocesses used in EU and he USA, due o he local, a o able clima ic
condi ions. UASB p ocesses can, in heo y, also allow ene gy eco e y om was ewa e ;
howe e , in he ew ull-scale applica ions isi ed by he au ho s, his was a ely implemen ed
in p ac ice. In any case, he esidual ene ge ic alue o anae obic sludge a e a UASB p ocess
should be compa able o he alues indica ed in Table 1 o diges ed sludge.
The EU Land ill Di ec i e 99/31/EC se s es ic ions (quan i a i e a ge s) o
biodeg adable municipal was es (such as sewage sludge) disposed o in land ills; in addi ion,
he na ional legisla ion o some Membe S a es ha e se e y s ic limi s o o ganic ma e o
o al o ganic ca bon (TOC) con ained in disposed-o sludge, p ohibi ing de ac o i s land illing.
Acco ding o ecen Eu os a da a, in ac , signi ican abandonmen o sludge land illing
p ac ices is occu ing in mos o Eu ope, excep o I aly, Denma k, and Es onia. Sewage Sludge
Di ec i e 86/278/EEC, conce ning bene icial use o sludge on soils, ini ially sough o
encou age sa e use o sewage sludge in ag icul u e, egula ing his o m o disposal o p e en
ha m ul e ec s. A e conce ns aised abou possible ha m ul accumula ion o compounds in
soils, 16 (ou o 27) EU coun ies ha e se mo e s ingen equi emen s o hea y me als in
sludge, compa ed o he Di ec i e’s p o isions, and 10 coun ies se s ic e limi alues o
hea y me als in soil. Such es ic ions a e being s eng hened pe iodically, while mos EU
coun ies ha e ou igh p ohibi ed he disposal o un ea ed sludge in soil. Compos ing is
applied mo e o en in he new EU-12 coun ies, compa ed o he old EU-15.
Finally, incine a ion is en o ced in mos EU-15 coun ies. G eece, Slo enia, Ge many and
Ne he lands p esen he g ea es inc easing ends, e en hough he i s wo coun ies expo
sludge o incine a ion; Denma k, Aus ia, Belgium and I aly show ins ead dec easing
incine a ion ends (Kelessidis and S asinakis, 2012).
The mal p ocessing o sludge emains, howe e , a con enien and e icien app oach o
he disposal o was e u ban sludge wi hou causing excess seconda y pollu ion, which is used
as much as possible in many coun ies. The mal u iliza ion o sludge comes in o play when he
sludge does no comply wi h, o is in excess o , equi emen s o disposal in ag icul u e, and
allows o ms o ene ge ic eco e y. The mal p ocessing o sludges can ake se e al o ms. Co-
i ing in powe plan s and hea ing plan s wi h coal (app oxima ely 5% sludge) does no
signi ican ly dec ease he empe a u e o he combus ion p ocess, and usually does no equi e
ex a in es men cos s o o -gas cleaning, as exis ing il e s and sepa a o s can handle his
ex a componen . Co- i ing in cemen kilns was conside ed he mos con enien echnology in
e ms o bo h sludge disposal and u iliza ion: one on o d ied sludge can subs i u e up o 0.33
o aw ma e ial and, since ash om sludge is bound o cemen clinke , his can ac ually be
conside ed a was e-less echnology. This is also conside ed a ‘‘was e- o-ene gy’’ sys em, and
is accep able i no o he en i onmen ally iendly echnology can be applied (Capodaglio e al.,
Re . Ambien . Água ol. 13 n. 2, e2128 - Tauba é 2018
4
A ianna Callega i e al.
2016a). Incine a ion (wi h u ban solid was e, o in special sludge incine a o s) is ano he op ion,
whe e he ene gy con ained in he sludge con ibu es o he ene gy balance o he p ocess.
Sewage sludge is usually p ocessed, p io o disposal, in anae obic anks o p oduce biogas,
a mix u e o CH4 and CO2 ha can be used as such, o u he e ined o ob ain bio-me hane, a
enewable uel wi h cha ac e is ics p ac ically iden ical o hose o ossil me hane (Capodaglio
e al., 2016b).
Howe e , ecen wo k has demons a ed ha he p oduc ion o biodiesel using lipids
ex ac ed om sewage sludge could be economically easible because o he ema kably high
yield o oil and low cos o his eeds ock.
Recen wo k has demons a ed ha p oduc ion o biodiesel om lipids con ained in sewage
sludge, la gely ega dless o i s ups eam p oduc ion p ocesses (i.e. WWTP echnology), could
be an al e na i e, economically easible echnique o ene gy eco e y om was e biological
sludges, , as compa ed o con en ional biodiesel eeds ocks (Bha a hi aja e al, 2014), hanks
o high oil yields, as shown in se e al s udies (Olkiewicz e al., 2012; Capodaglio e al., 2016c).
Fu he mo e, while con en ional biodiesel eeds ocks is usually expensi e and compe ing
wi h o he uses (e.g. ood o animals, o people), was e sludge is abundan , cos ly o dispose
o unde adi ional schemes, and he e o e should be a ailable almos e e ywhe e a e y low,
o no cos , as a eeds ock.
B azil has a s anding adi ion o biodiesel uses, de i ed om bo h ood and non- ood
c ops, and om a ious ood-was e p oduc s (e.g. spen ying oils). This ype o solu ion is
widely suppo ed by he B azilian go e nmen wi hin i s Biodiesel P oduc ion and Use P og am
(BPUP), which a ou s enewable ene gies, speci ically add essing ene gy sel -sus ainabili y
o isola ed u al communi ies (To es e al., 2013). No e e ences we e ound, howe e ,
conce ning he eco e y o biodiesel and ma e ials om u ban was e sludge in B azil. This is
p obably due o he ac ha he sludge disposal p oblem has no eached c i ical p opo ions as
i did in se e al in se e al EU membe s a es.
Se e al echnologies ha e been s udied o his pu pose wo ldwide. While
anses e i ica ion is pe haps he mos -used biodiesel-ex ac ion p ocess in B azil, py olysis
could be a echnology o conside , no only in u ban was e sludge p ocessing, bu also in o he
ene gy/ma e ials eco e y chains, as i allows use ul eco e y o ene gy and ma e ials a
di e en le els. These include py olysis, hyd o he mal lique ac ion, we oxida ion, supe c i ical
wa e oxida ion, sequen ial me hane/hexanol dis illa ion (Demi bas, 2001). These, once
p ocess- alida ed and indus ially es ed, could be conside ed no only as iable al e na i e
p ocesses o sludge disposal, bu also sus ainable, en i onmen al-complian biodiesel
p oduc ion p ocesses. In addi ion o biodiesel, was e u ban sludge may p o ide, as by-p oduc s,
o he subs a es o no able ene ge ic and ma e ial alues, such as biocha .
S udies show ha o oil ex ac ed om was e sludge, he ene gy gain is up o 29.7 GJ/ on
(Zhang e al., 2013). Fu he mo e, GHG emissions s udies show ha biodiesel p oduc ion om
sludge is a ne ca bon dioxide cap u e p ocess, wi h he highes cap u e being a ound 40 CO2/
biodiesel p oduced. Sludge-de i ed biodiesel, inally, has a lowe Global Wa ming Po en ial
(GWP) han mos o he enewable biodiesels (Table 2) wi h he excep ion o biodiesel de i ed
om was e ege able oils (Du ou and I iba en, 2012).
Table 2. Compa ison o GWP (kg CO2 equi alen ) o di e en bio uels.
Biodiesel
ype
Was e
ege able
oil
Bee
allow
Poul y
a
Sewage
sludge
Soybean
Rapeseed
Low-
sulphu
Fossil
Diesel
GWP
(kg CO2-eq)
16.97
23.32
23.55
20.84
26.18
63.23
83.69
5
P oduc ion o ene gy (biodiesel) and eco e y …
Re . Ambien . Água ol. 13 n. 2, e2128 - Tauba é 2018
This pape illus a es expe imen al indings om he applica ion o py olysis ea men o
u ban was e sludge, and desc ibes possible eco e y pa hways o ene gy and ma e ials om
ha eeds ock. In addi ion o he bene i s in po en ially con ibu ing o sol e he signi ican
p oblem o he ul ima e disposal o u ban was e sludge, his echnology could be ins umen al
in suppo ing cu en go e nmen commi men s (e.g. EU’s unde Di ec i e 2003/30/EC, on he
p omo ion o bio uels o anspo ) o achie e in he nex coming yea s highe ac ional a ge s
o bio-oils’ con en in comme cial uels (e.g. 10% by 2020 in he EU) (Raboni e al., 2015).
2. MATERIALS AND METHODS
Py olysis is a he mal-decomposi ion p ocess, ca ied ou in he absence o O2, ha
con e s biomass in o solid cha coal (biocha ), bio-oil (biodiesel, o SSPO, Sewage Sludge
Py olysis Oil), and gaseous p oduc s (syngas) a ele a ed empe a u es (gene ally mo e han
500oC) and a mosphe ic p essu e. I is one o he mos e icien p ocesses o biomass
con e sion disco e ed and indus ially adop ed o da e. Reco e ed SSPOs a e a complex
mix u e o alipha ic, a oma ic and poly-a oma ic hyd oca bons, long ca bon-chain o ganic
acids and alcohols, e c. (Poko na e al., 2009), e y simila in p ope ies o diesel uel (hence
he al e na i e e m, “biodiesel”).
Py olysis no only can be used o ans o m biomass o a ious o igins and o he was e
ma e ials (e.g. ubbe y es) in o bio-oil, biocha , and syngas, o a ied cha ac e is ics
(depending on ini ial eeds ock and ac ual p ocess ope a ing condi ions), bu also allows o
a ia ion in he a ios be ween di e en p oduc ac ions, acco ding o p ocess empe a u e
p o iles and du a ion. In a sense, py olysis allows he use o choose among he h ee possible
inal p oduc s, acco ding he bes - i ing combina ion equi ed by local euse/ ecycle needs
(Capodaglio e al., 2016c).
While he ad an age o ob aining sludge-de i ed liquid uels is easily ob ious o mos ,
mo e so han gaseous uel, which is subjec o g ea e anspo a ion and use challenges han
he o me , he solid ac ion esidue om he p ocess (biocha ) also has been ound o ha e
se e al use ul, unexpec ed applica ions. Biocha is a new echnical e m indica ing “ he po ous
ca bonaceous solid p oduced by he he mochemical con e sion o o ganic ma e ials in an
oxygen deple ed a mosphe e ha has physicochemical p ope ies sui able o sa e and long-
e m s o age o ca bon in he en i onmen ” (Shackley e al., 2012). Biocha could in heo y be
used o gene a e ene gy (i has an ene gy con en ha , depending on he p ocess used o i s
p oduc ion, can be e en > 18 MJ/kg); howe e , biocha is ecen ly ge ing much a en ion om
he scien i ic communi y due o i s a ious use po en ials. Gi en i s p ope ies, i is clea ha
he concep o biocha p oduc ion om sewage sludge has become inc easingly popula in
ecen yea s.
Mic owa e echnology has ecen ly eme ged as one o he mos p omising me hods o
enhancing and accele a ing chemical eac ions, due o e icien hea - ans e p o iles. I is
he e o e being adop ed as one o he bes echnologies a ailable in py oly ic p ocesses, since
i educes esidence ime and b ings signi ican ene gy sa ings (Mo asemi and Az al, 2013).
Mic owa e-assis ed py olysis (MAP) echnology is an al e na i e hea ing me hod al eady in
use in biomass py olysis o bio uels p oduc ion, p esen ing se e al ad an ages o e
con en ional py olysis, including: uni o m in e nal hea ing o ma e ial pa icles, since
elec omagne ic ene gy is di ec ly con e ed in o hea a a molecula le el; ease o con ol due
o i s ins an aneous esponse; simple se -up, acili a ing i s adap a ion o la ge-scale indus ial
p ocesses; educed need o eeds ock g inding; and low cos , as mic owa e is a ma u e and
ene gy-e icien echnology. The di e en hea ing mechanisms make MAP p oduc s e ain
di e en cha ac e is ics om hose ob ained wi h con en ional hea ing. In addi ion, MAP akes
a much sho e p ocess ime han con en ional py olysis (Menendez e al., 2002; Leszczynski,
2006), as he hea ing o he eeds ock biomass is mo e uni o m.

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6
A ianna Callega i e al.
Using monomodal mic owa e syn hesize s (MMS) ins ead o mul imodal ones, he need
o p elimina y mixing d y sludge wi h mic owa es ecep o s addi i es epo ed by ea lie
esea che s could also be elimina ed, and he p ocess empe a u e needed o p ocess
comple ion is signi ican ly lowe ed (as low as 270oC), allowing he p oduc ion o a la ge liquid
p oduc (biodiesel) ac ion (Capodaglio e al., 2016c). De ailed desc ip ion o py olysis, MAP
and MMS-d i en py olysis a e gi en by Masek e al. (2013).
The appa a us shown in Figu e 1 was used o expose sludge samples o MAP. The
expe imen al appa a us consis s o a pu e qua z cu e e (Fig. 1[a]), capable o wi hs anding
high empe a u es exceeding 1000oC, wi h a ca i y (Fig. 1 [b]) con aining he sludge sample
(15-25 g) being ea ed. A MMS, unlike a con en ional (mul imodal) cooking mic owa e o en,
is capable o ma ching he impedance be ween he load o be i adia ed and he mic owa e-
gene a o (magne on), hus maximizing he powe ans e o he samples. Wi h an MMS
app op ia ely uned, i is also possible o i adia e d y samples, elimina ing he need epo ed
by p e ious esea che s o add mic owa e ecep o s o he sludge, a ask impossible o achie e
wi h adi ional mic owa e o ens ha hea con en s indi ec ly, by agi a ion o he wa e
molecules con ained in he samples. A iple-s ub ma ching de ice (MD, Al e Sys ems, Fig.
1[e]) connec ed wi h he magne on was used o balance e lec i e coe icien s wi hin he
sys em, allowing he c ea ion o an op imal elec ic ield in ensi y in he ca i y con aining he
sample.
Sludge samples we e p epa ed om dewa e ed was e sludge ob ained om he local
municipal WWTP ha had al eady unde gone an anae obic diges ion p ocess. Samples we e
u he desicca ed a 60oC o 24 hou s in o de o u he educe hei wa e con en o a ound
73.5%, while minimizing any possible eac ion ha could modi y hei o ganic con en . This
desicca ion phase will be he objec o addi ional conside a ions abou he sus ainabili y o he
p ocess a he ull-scale. The desicca ed sample was hen g ound o a ine powde , and
py olyzed in his appa a us.
De e mina ion o oil con en was made a e condensa ion o p ocess e apo a e wi h a
Soxhle ex ac o a e each es (See Tes s 1-7 in Table 3), and i s chemical cha ac e iza ion
was hen pe o med by GC-MS spec ome y. Tes condi ions a ied acco ding o maximum
empe a u e achie ed in he cu e e, ime o sample exposu e o maximum empe a u e, ime-
o maximum empe a u e (hea ing a e o sample). Biocha cha ac e iza ion was achie ed a e
g inding and sie ing o < 0.5 mm he esul ing p oduc . De e mina ion o ola ile ma e and
ash con en was conduc ed acco ding o ASTM-D1752-84, elemen al composi ion (C, H, N)
assessed by an elemen al analyse (The mo Fishe Scien i ic, MA. USA), O con en by Va io
El Cube (Elemen a Analysensys eme, GmbH).
Table 3 shows empe a u e, du a ion and quan i y o ex ac ed oils om he es s
conduc ed. The g ea es oil yields we e obse ed be ween 270 and 500oC. Below 200oC, he
oil quan i y ob ained is e y small; o e 500oC, he e is s ill some p oduc ion.
3. RESULTS AND DISCUSSION
The highes oil yield was ob ained a he es empe a u e o 280ºC (25.0% oil o o ganics
sludge ac ion, 12.52% oil o o al sludge, weigh basis) and sho p ocess du a ion. Highe
empe a u es and longe p ocess imes end o inc ease he amoun s o gene a ed gaseous and
solid ac ions.
GC-MS analysis o ex ac ed oil samples, dilu ed wi h dichlo ome hane, show he
ollowing composi ion (Figu e 2). Toluene and s y ene do no show in some o he g aph lines
due o he high dilu ion a io adop ed o analysis; howe e , hey we e de ec ed in he aw oil
samples. F om lowe o highe e en ion imes (le o igh in he g aphs) MS iden i ies a oma ic
7
P oduc ion o ene gy (biodiesel) and eco e y …
Re . Ambien . Água ol. 13 n. 2, e2128 - Tauba é 2018
hyd oca bons (con aining one o mo e a oma ic ings in hei molecula s uc u e), ni ogenous
compounds, alkanes, ca boxylic acids (con aining he –COOH o he –OH g oups linked o a
ca bonyl g oup C=O), s e ols and de i a i es.
The lowe calo i ic alue (LCV) o he biodiesel ob ained, is sligh ly lowe han he one
ob ained om ene gy c ops. Sludge-de i ed biodiesel LCV was abou 33 kJ/g (in he ange
33-35 kJ/g o all es s), agains ha om co n and sa lowe a 42-43 kJ/g, o he one om
coconu eeds ock a 38 kJ/g commonly epo ed (Capodaglio e al., 2016c). Compa ed wi h
ossil diesel, he e o e, his sludge-de i ed oil has an LCV ha is abou 30% lowe . LCV will
a y acco ding o p ocess condi ions: a highe p ocess empe a u es, he LCV o ob ained bio-
oil will end o be lowe o he same eeds ock.
Figu e 1. The expe imen al MMS appa a us.
Table 3. Tes s condi ions and oil yields.
Max Tes
Temp. oC
Time a
TMAX
[min]
To al
p ocess
Time [min]
% oil o
o al
sludge
% oil o
sludge
o g. ac ion
SLUDGE AS IS
60
=
=
3.57*
7*
TEST 1
180
28
50
3.30
7
TEST 2
270
20
55
9.68
19
TEST 3
280
2
8
12.52
25
TEST 4
400
2
18
10.77
22
TEST 5
490
1
54
10.25
21
TEST 6
600
3
56
8.71
17
TEST 7
650
-
60
7.38
15
*ex ac ion wi h sol en om o iginal sample.
Re . Ambien . Água ol. 13 n. 2, e2128 - Tauba é 2018
8
A ianna Callega i e al.
Figu e 2. Supe imposed GC-MS analy ical esul s o he oil ex ac ed
in he di e en es s (F om Capodaglio e al., 2016c).
Syngas is p ima ily composed o H2 and CO, wi h smalle quan i ies o CH4, CO2, H2O,
and o he low molecula -weigh ola ile o ganics. While i s hea ing alue is low (~6 MJ kg-1)
compa ed o na u al gas (~54 MJ kg-1), i can p o ide uel o ho wa e , sludge p e-d ying o
elec ici y onsi e. Gi en he low LCV and i s “di y” composi ion, i is usually no conside ed
wo hy o u he p ocessing (unless pu pose ully gene a ed in high quan i ies). Some ime ago,
be o e widesp ead a ailabili y o na u al gas, syngas was gene a ed o p o ide ene gy o home
hea ing, cooking, s ee ligh ing, e c. (a.k.a. “ own gas”). A he momen , al hough p o iding
some esidual ene ge ic alue, syngas is he leas in e es ing p oduc o was e sludge py olysis.
Biocha is he solid esidue o he p ocess, wi h high ene gy con en , ha can be he e o e
bu ned in sys ems ed wi h pul e ized coal. NOx emissions om biocha combus ion a e
compa able o hose o coal, equi ing simila aba emen echnologies. Some ypes o eeds ock
(i.e. u ban sludge) may con ain ela i ely high le els o me als ha concen a e in he biocha
a e py olysis. Biocha s, howe e , may also ha e many o he a ac i e, high alue uses, in
ields such as chemis y, me allu gy, ag icul u e, was e ea men , e c. Table 4 shows
cha ac e is ics o biocha de i ed om sewage sludges wi h adi ional and mic owa e-assis ed
py olysis, by he au ho s and in o he s udies. As i can be seen, he cha ac e is ics o he
ma e ial a y acco ding o he p ocess adop ed and depending on he o igin o he eeds ock
ma e ial. Table 5 shows some o he main ash componen s o sewage sludge biocha om
di e en o igins. P ocess ope a ional empe a u e has a subs an ial e ec on he quali y o
biocha p oduced: biocha p oduced a low empe a u es is mos sui able o ag icul u al uses,
due o ca bon con en and nu ien a ailabili y, while highe empe a u es can imp o e i s
po osi y and hus enhance i s e ec i eness in adso bing con aminan s p esen in soils (Ag a io i
e al., 2013). Resea che s ha e also shown ha he py olysis p ocess can supp ess hea y me al
elease by non-imp egna ed biocha s, esul ing in an ex emely low en i onmen al isk using
sludge-de i ed biocha as soil amendmen (unlike he case o sludge as is). Biocha s can be
ob ained unde di e en p ocesses and eeds ocks; hey signi ican ly di e om one o ano he
in hei p ope ies, depending on he ype o biomass used o p oduce hem, i s g ow h
condi ions and also on py olysis ope a ing condi ions.
9
P oduc ion o ene gy (biodiesel) and eco e y …
Re . Ambien . Água ol. 13 n. 2, e2128 - Tauba é 2018
I has al eady been ecognized ha oils de i ed om was ewa e sludge a e compa able
eplacemen s o adi ional biodiesel p oduc ion eeds ock (Bha a hi aja e al., 2014). In o de
o assess he sus ainabili y o biodiesel p oduc ion om his sou ce, ene gy balance and
g eenhouse gas (GHG) emissions a e also essen ial ac o s o conside .
I has been epo ed ha biodiesel p oduced om wo majo ood c op eeds ocks, soybean
and sun lowe oils, has an ene ge ically un a o able ene gy balance, due o he low-oil yield o
he c ops, ansla ing o a p ocess ene gy loss o 32% o soybean, and 118% o sun lowe
(Pimen el and Pa zek, 2005). The e o e, eplacemen o adi ional ees ock wi h be e -sui ed
aw o eco e ed ma e ials is con inuously being in es iga ed. Was ewa e sludge ul ils he
basic gene al equi emen s o al e na i e eeds ocks, ha should be abundan , sus ainable, and
ene ge ically a o able (i.e. gene a e a posi i e ene gy balance).
Sludge-de i ed biodiesel hus has a lowe Global Wa ming Po en ial (GWP) han mos
o he enewable biodiesels wi h he excep ion o biodiesel de i ed om was e ege able oils
(Du ou and I iba en, 2012; Capodaglio and Callega i, 2017). Compa ed o con en ional low-
sulphu diesel as a benchma k, a 75.1% educ ion o use o sludge-de i ed biodiesel can be
achie ed.
The ans o ma ion o was e sludge in biocha by py olysis has also some ele an
en i onmen al ad an ages. In he in oduc o y sec ion a b ie e iew o he exis ing me hods o
excess sewage sludge disposal was p esen ed. In addi ion o he sa ed cos s o he o he wise
necessa y disposal o sewage sludge, his sec ion shows he bene icial (added- alues) uses by
which biocha can become a esou ce.
The mos appealing ea u e o biocha is he ac ha i is an inexpensi e, sus ainable and
easily-p oduced ma e ial wi h po en ially ex ensi e applica ions. E en hough mos o hose
applica ions a e s ill in hei in ancy, biocha al eady has a numbe o iden i ied applica ions
wi h po en ially ex ao dina y e ec s, including soil amendmen , ca alysis, wa e pu i ica ion,
and many o he s s ill o be in en ed o disco e ed.
Bene icial e ec s o biocha on ag icul u al c ops yield and p ope ies o soil ha e been
s udied, showing signi ican imp o emen in he yield o c ops (Chan e al., 2008). Biocha
addi ion is known o imp o e ni ogen e ilise -use e iciency by imp o ing he chemical
p ope ies o soil. I signi ican ly inc eases soil C con en , and imp o es c op p oduc i i y.
Was ewa e sludge biocha applica ion was speci ically ound o inc ease soil ca ion exchange
capaci y (CEC) by up o 40%, and soil pH by up o one uni (Hossain e al., 2010), wi h
imp o emen o plan a ailable nu ien s, and ca bon seques a ion.
Biocha s a e ecep i e o complex me al ions p esen in he soil on hei su aces and
he e o e educe hei bioa ailabili y, esul ing in a educed isk. S udies de ec ed insigni ican
bioaccumula ion in c ops o me als p esen in was ewa e -sludge biocha . In addi ion, biocha
is known o ha e posi i e e ec s on soil quali y, as i enhances soil ae a ion, inc easing wa e
holding capaci y and imp o ed en i onmen al condi ions o he g ow h and de elopmen o
plan oo sys ems.