Methodological guide and roadmap to assess the compliance of wastewater treatment plants with sustainability and circularity criteria

Me hodological guide and oadmap o assess he compliance o was ewa e
ea men plan s wi h sus ainabili y and ci cula i y c i e ia
So ía Es ´
e ez
*
, Ana A ias, Gume sindo Feijoo, Ma ía Te esa Mo ei a
CRETUS, Depa men o Chemical Enginee ing. Uni e sidade de San iago de Compos ela, San iago de Compos ela, 15782, Spain
ARTICLE INFO
Keywo ds:
Was ewa e
Ce i ica ion scheme
Sus ainabili y
Ci cula i y
Me hodology
ABSTRACT
En i onmen al ce i ica ion has come up as a olun a y ac ion o demons a e a minimum quali y le el when i
comes o he in oduc ion o ecological- iendly p inciples in decision-making. Howe e , mos o he wo k done
so a has ocused on he ood and ag o o es y sec o s and on he p oduc ion and p ocessing s ages o he alue
chain a he han end-o li e s a egies. The p esen s udy aims o p o ide a oadmap ha acili a es he e al-
ua ion o he pe o mance was ewa e acili ies om sus ainable and ci cula i y pe spec i es. A six-s ep
amewo k has been p oposed wi h he objec i e o se ing as he basis o a u u e ce i ica ion sys em o
his sec o . Fi s , manda o y equi emen s we e collec ed om Eu opean legisla i e documen s o iden i y he
a ge s o be me . Subsequen ly, he collec ed da a ha e been classi ied in o i e le els anging om he de i-
ni ion o pilla s, p inciples, c i e ia, equi emen s o he compliance o indica o s. The selec ion o indica o s was
ca ied ou aking in o accoun he exis ing li e a u e o ga he bo h sus ainabili y (167) and ci cula i y (32)
indica o s, which we e hen associa ed wi h he de ined equi emen s. The inal s ep is o conside he es ing o
alida ion o he me hodology o case s udies, in his case, he design and ope a ion o wo la ge-scale was e-
wa e ea men plan s. The esul s indica ed ha mos o he indica o s a e quali a i e and abou 61 % o he
quan i a i e equi emen s o he amewo k could be calcula ed wi h ou ine plan in o ma ion. Fo hose in-
dica o s o which es ima ion was no possible due o lack o da a, an easily manageable, ac shee - ype empla e
was c ea ed so ha companies we e awa e o da a equi ed o add ess he amewo k. Mo eo e , he applica ion
o his assessmen amewo k o was ewa e ea men plan s iden i ied some gaps o conside : (1) h esholds
could no be de ined o many o he indica o s, (2) he e is a lack o guidelines o da a collec ion, (3) legisla ion
needs imp o emen ega ding ci cula i y me ics in his sec o and (4) he equi emen s should be s eng hened
o accoun o he speci ic cha ac e is ics o acili ies ope a ing a di e en scales and using a ious echnologies.
1. In oduc ion
The uns oppable inc ease in popula ion and he accele a ed de el-
opmen o indus ializa ion has jeopa dized he supply possibili ies o
u u e gene a ions and has also led o an escala ion o en i onmen al
isks (Wang and Azam, 2024). To a oid his, he manu ac u ing sec o
has d i en a ans o ma ion o he ac ual alue chains o p oduc ion and
dis ibu ion o p oduc s o achie e a g eene , sus ainable and deca -
bonized indus y (Mehmood e al., 2024). Apa om his, socie y has
become awa e o how i s consump ion habi s also in luence he use and
demand o esou ces, p oduc s and se ices, as well as he ma ke and
he willingness o companies o go g een. Led by hese changes, many
companies ha e pa icipa ed in and demanded en i onmen al ce i i-
ca ion sys ems o olun a y sus ainabili y s anda ds o highligh
compliance wi h minimum en i onmen al c i e ia (Gomes e al., 2023).
Any o hese ce i ica ion schemes equi e he de elopmen o a se o
speci ica ions o equi emen s o de e mine whe he o no a p oduc o
p ocess is in line wi h policies, s anda ds o legisla ion h oughou i s li e
cycle (Pa lo skaia, 2014). The e o e, he equi emen s a e he basic
elemen s in he s uc u e o any ce i ica ion scheme (Poncib`
o, 2007).
Subsequen ly, hey can be ca ego ized acco ding o he objec i es pu -
sued and c ea e a quan i a i e o quali a i e amewo k (Lee, 2013).
This se o hie a chical equi emen s is hen es ed h ough a con o mi y
assessmen based on he audi me hodology, e i ica ion guide and/o
es me hods o he s anda d (Liepin¸a e al., 2014).
In mos known ce i ica ion schemes (e.g. Fo es S ewa dship
Council o FSC, In e na ional Sus ainabili y and ca bon ce i ica ion o
ISSC, P og amme o he Endo semen o Fo es Ce i ica ion o PEFC
and Be e Biomass), he e alua ion p ocess is quali a i e and equi es
* Co esponding au ho .
E-mail add ess: [email p o ec ed] (S. Es ´
e ez).
Con en s lis s a ailable a ScienceDi ec
Wa e Resea ch
jou nal homepage: www.else ie .com/loca e/wa es
h ps://doi.o g/10.1016/j.wa es.2025.123125
Recei ed 17 Sep embe 2024; Recei ed in e ised o m 17 Decembe 2024; Accep ed 9 Janua y 2025
Wa e Resea ch 274 (2025) 123125
A ailable online 11 Janua y 2025
0043-1354/© 2025 The Au ho s. Published by Else ie L d. This is an open access a icle unde he CC BY-NC-ND license ( h p://c ea i ecommons.o g/licenses/by-
nc-nd/4.0/ ).
he use o checklis s wi h yes o no ques ions o indica o s whose an-
swe s mus be con i med by an audi o . Despi e he expe ience o au-
di o s, he use o quali a i e indica o s is s ill unde a ce ain deg ee o
subjec i i y. I is he e o e ecommended ha a igo ous and sys ema ic
ool be de eloped ha can p o ide objec i e quali a i e and quan i a-
i e in o ma ion.
O e he pas yea s, he e has been a blooming in he p oposal o
indica o s o measu e he implemen a ion o bo h sus ainable and ci -
cula p ac ices since hey can be used as policy-making ins umen s
(Nowaczek e al., 2023). Also, hey a e use ul o assess c i e ia a
di e en le els, allowing o a mul i-c i e ia analysis (de Oli ei a and
Oli ei a, 2023). When implemen ed in ce i ica ion schemes, hey can
con ibu e o he educ ion o bu eauc acy, cos s and g eenwashing, and
acili a e he digi aliza ion o con o mi y assessmen s (Flags ad e al.,
2022; Rossi e al., 2024).
In addi ion o being mos ly quali a i e, ce i ica ion schemes oday
ace new challenges, such as inco po a ing speci ica ions o wo o he
concep s ha ha e ecen ly gained a en ion: he ci cula economy and
he bioeconomy. The Eu opean bioeconomy has been launched o p o-
mo e s a egies and ini ia i es ocused on he deple ion o non-
enewable esou ces, he imp o emen o bio-based p ocesses and
echnological di e si ica ion and inno a ion, as well as o p omo ing
he implemen a ion o new p ac ices in he managemen o he p o-
duc ion and alue chain (Fische e al., 2024). Howe e , he p omo ion
o hese echnologies mus also go hand in hand wi h he accep ance and
en i onmen al awa eness o social communi ies (Mach e al., 2023). By
p omo ing a g een ansi ion, he Eu opean bioeconomy coope a es wi h
ci cula i y, which is based on p omo ing he c ea ion o closed-loop
sys ems by eusing, ecycling and eco e ing esou ces h oughou
hei li e cycle (Alhawa i e al., 2021; Ca ende -Ba es e al., 2013;
D’Ama o and Ko honen, 2021). This is why bo h concep s should be
conside ed when ce i ying hese echnologies.
Thus, bio-was e ma e ials could be used in alo iza ion p ocesses o
he gene a ion o ma ke able alue-added p oduc s o as in e media es
ha can be used as aw ma e ials o o he indus ial p ocesses
(Mahjoub and Domschei , 2020). Was ewa e , as pa o he wa e alue
chain, is also an example o biological was e wi h a mul i ude o alo-
iza ion possibili ies (i.e., om o ganic e ilize o ene gy and bio-
polyme s) (Ch ispim e al., 2021; Fe ei a e al., 2023; Lu zu e al.,
2021). In addi ion, eclaimed wa e could be one o hei co-p oduc s, a
esou ce o inc easing conce n in a eas su e ing wa e sca ci y (Foglia
e al., 2023). Al hough i is no a esou ce s ongly concen a ed (since i
is liquid) in eco e able componen s, i is a was e p oduced
con inuously om an h opogenic ac i i ies (supply is assu ed). How-
e e , he edesign o was ewa e ea men plan s o inco po a e aspec s
o ci cula economy, sus ainabili y and bioeconomy implies an ex a
e o as he acili ies become mul i unc ional (Ru í-Salís e al., 2022).
Howe e , ce i ica ion o end-o -li e p ocesses is no ully co e ed,
which hampe s he possibili ies o ce i ica ion o was ewa e man-
agemen (Maje e al., 2018). Al hough ce i ica ion schemes exis o
he wa e ea men sec o —such as he Alliance o Wa e S ewa dship
(AWS), IAMPO R&T, Eu opean Wa e S ewa dship (EWS), Sma
App o ed Wa e ma k, and Wa e S ewa dship Ve i ied (WAVE)— he
echnologies, p ocess s ages, and ope a ions o was ewa e ea men
plan s di e signi ican ly, which is essen ial o he de elopmen o he
basis o olun a y ce i ica ion in was ewa e (Alliance o Wa e
S ewa dship, 2024; Eu opean Wa e S ewa dship, 2024; In e na ional
Associa ion o Plumbing and Mechanical O icials, 2024; The Wa e
Council, 2024).
On he o he hand, while some ce i ica ion schemes a emp o
include wa e - ela ed c i e ia, hey do no add ess was ewa e ea men
and a e ins ead mo e sui ed o he ag o o es y sec o . Examples o hese
c i e ia a e iden i ica ion o wa e igh s, implemen a ion o a wa e
managemen plan, deple ion o wa e esou ces, wa e quali y and
p e en i e measu es o wa e pollu ion (Feh enbach, 2011). Howe e ,
he speci ica ions we e es ablished o a po en ial di ec impac wi hou
conside ing he indi ec impac s along he en i e alue chain. I is
he e o e u gen o c ea e and upda e he c i e ia ha mus be main-
ained by ce i ica ion sys ems in he was ewa e ea men sec o o a
company o be sus ainable and ci cula .
Based on his con ex , he ocus o his esea ch a icle is o p o ide a
me hodological amewo k o e alua ing was ewa e ea men ech-
nologies. This amewo k has been de eloped by iden i ying app op ia e
indica o s and equi emen s o be included in ce i ica ion schemes and
labels o e ec i ely assess he was ewa e sec o . The idea is o p o ide
use ul ini ial guidance o s akeholde s, esea che s and policy-make s
using in o ma ion ga he ed om Eu opean legisla ion and o he docu-
men s ele an o he sec o . In he sea ch o o mula ing a ce i ica ion
scheme, which would en ail s akeholde consul a ion and he c ea ion o
a con o mi y assessmen guide, his s udy is a i s s ep in iden i ying
gaps and possibili ies o he u u e c ea ion o an open access ce i i-
ca ion scheme. Rega ding he audi me hodology, an analysis o in-
dica o s om he li e a u e was conduc ed and subsequen ly co ela ed
wi h he equi emen s and c i e ia o he amewo k. Fu he mo e, o
assess he sui abili y and e ec i eness o he p oposed me hodological
amewo k, he design and ope a ion o wo la ge-scale was ewa e
ea men plan s we e conside ed as case s udies (Eu opean was ewa e
ea men plan s wi h a design capaci y o >100,000 popula ion
equi alen ).
2. Selec ion o documen s o be e iewed
A simul aneous wo-s ep in eg a ed p ocess has been ca ied ou o
he selec ion o he documen s om which he speci ica ions o e-
qui emen s o be me by was ewa e ea men plan s ha e been
collec ed. Fi s , a sys ema ic e iew o he o icial online da abase o
Eu opean Union law (EUR-Lex), which con ains, among o he s, legal
ac s, consolida ed ex s and in e na ional ag eemen s, was ca ied ou in
July 2024. Eu opean legal ac s a e subdi ided in o 15,8531 egula ions,
7749 di ec i es, 52,654 decisions, ecommenda ions and opinions,
which, wi h he excep ion o he las g oup, a e legally binding
(Eu opean Union, 2024). All o hem ha e been ca ego ized in o 21
domains. Conside ing ha he ope a ion o was ewa e ea men plan s
in ol es he compliance o e y di e se aspec s, he use o keywo ds was
no conside ed, and he ocus o he analysis was on Eu opean
Di ec i es.
The i s d a o selec ed di ec i es was conduc ed conside ing he
EUR-lex en y “Summa ies o he Eu opean Regula ions”. O he ypes o
documen s we e no conside ed o he sys ema ic e iew. Using he
Nomencla u e
ASC aquacul u e s ewa dship council
AWS alliance o wa e s ewa dship
BSCI business social compliance ini ia i e
EC Eu opean commission
EEA Eu opean en i onmen al agency
EU Eu opean union
EWS Eu opean wa e s ewa dship
FSC o es s ewa dship council
ISO in e na ional o ganiza ion o s anda diza ion
ISSC in e na ional sus ainabili y and ca bon ce i ica ion
MBBR mo ing bed bio ilm eac o s
MSC ma ine s ewa dship council
PEFC p og amme o he endo semen o o es ce i ica ion
RSB ound able on sus ainable bioma e ials
SBP sus ainable biomass p og am
UNE Una No ma Espa˜
nola
WAVE wa e s ewa dship e i ied
S. Es ´
e ez e al.
Wa e Resea ch 274 (2025) 123125
2
EUR-lex ad anced sea ch ool, he compila ion o di ec i es was pe -
o med by sea ching only o cu en legisla ion, excluding co igendum
and aking in o accoun he ele an legisla i e au ho i ies ( he Eu o-
pean Commission, he Eu opean Pa liamen and he EU Council). A o al
o 735 we e expo ed om he da abase, o which only 45 applied o he
was ewa e sec o .
The second s ep was he eading o he echnical documen a ion o
he wo case s udies used in his esea ch and he compila ion o he
applicable legisla ion. The o al numbe o di ec i es included o
analysis was 60, which means ha 15 could no be ound in he sys-
ema ic li e a u e e iew. The di ec i es o which in o ma ion has been
included in he speci ica ion amewo k a e shown in Table 1.
Addi ionally, o he 9 documen s we e also e alua ed despi e no
being he 60 di ec i es p e iously men ioned. The i s is a possible
u u e legisla i e ac , he p oposal o a Di ec i e o he Eu opean
Pa liamen and o he Council conce ning u ban was ewa e ea men
(COM/2022/541). The e is also one Regula ion ((EU) 2020/741 on
wa e euse) and wo Commission Delega ed Regula ions o he Eu o-
pean Pa liamen and o he Council ((EU) 2021/2139 and (EU) 2023/
2486 wi h he EU Taxonomy echnical c i e ia). Finally, i e ISO s an-
da ds ep esen a i e o a good managemen sys em we e chosen o
en i onmen (ISO 14,001:2015), quali y (ISO 9001:2015), ene gy (ISO
50,001:2018), economic (ISO 20,400:2017) and occupa ional heal h
(45,001:2018) issues. The possible lis o ISO di ec i es and s anda ds
(wi h some o he s no selec ed o he c i e ia amewo k) can be ound
in Supplemen a y Ma e ials B. I is impo an o emphasize ha only
he indica o s mos ele an o he ope a ion o was ewa e ea men
plan s a e conside ed, wi hou del ing in o speci ic de ails o he anal-
ysis (e.g., in luen and e luen composi ion) o equipmen
speci ica ions.
3. De ini ion o he ce i ica ion amewo k
The amewo k p oposed o his esea ch is s uc u ed in di e en
le els: pilla s, p inciples, c i e ia and equi emen s. The i s s ep was
he de ini ion o each o he a o emen ioned le els. This is because hei
meaning is nowadays subjec o a ce ain deg ee o subjec i i y among
documen s, as discussed in Col e e al. (1995), BOPP (2012), Ri chie
e al. (2000) and UNE-EN 16,751:2016.
The mos de ailed o speci ic le el o he amewo k a e he e-
qui emen s, which a e he speci ica ions ha o ganiza ions mus mee in
o de o comply wi h he equi emen s o acc edi a ion o , i his is no
possible, a leas o comply wi h legisla ion. Thus, hey de ine he ype o
ac ion o be aken o pe o m well in e ms o sus ainabili y o ci cu-
la i y. These equi emen s we e ga he ed om he documen a ion
al eady p esen ed in Sec ion 2.
Supplemen a y Ma e ials B show he ela ionship be ween each o
he equi emen s wi h he a icles o sec ions ound wi hin each di ec-
i e o documen . They ha e all been g ouped acco ding o he aspi a-
ional goal o be me and hus de ine objec i es o he company. These
g oups a e called c i e ia. C i e ia can be u he classi ied in o p inci-
ples, which a e laws ha p o ide a a ionale o ac ion o highe pu -
poses (i.e., p ese a ion o habi a s o app op ia e use o esou ces).
Finally, p inciples a e in ended o gi e ep esen a ion o di e en key
hema ic a eas o in e es (sus ainabili y o ci cula i y). Fig. 1 is a ep-
esen a ion o he di e en le els o he amewo k, oge he wi hin
hei de ini ions and he numbe ound o each o hem.
Tables 2 and 3 show he pilla s, p inciples and c i e ia wi h he
numbe o equi emen s and a code o each o hem. The code has been
de ined in ou le els, acco ding o he amewo k s uc u e le els. The
i s wo o h ee le e s e e o he pilla . ES is o en i onmen al sus-
ainabili y; SES is o socioeconomic sus ainabili y and CI is o ci cu-
la i y. The numbe s sepa a ed by do s a e necessa y o iden i y he
p inciples, c i e ia and equi emen s. Fo example, he code ES 01.01.01
indica es ha he i s equi emen o he i s c i e ion and i s p in-
ciple as shown in Tables 2, 3and Supplemen a y Ma e ials B has been
ci ed.
As shown in Tables 2 and 3, he speci ica ion amewo k has been
buil on a o al o 102 equi emen s dis ibu ed be ween en i onmen al
sus ainabili y (~49 %), socio-economic sus ainabili y (~38 %) and
ci cula i y (~13 %). The numbe o p inciples is 9, while he numbe o
c i e ia is 26. The c i e ia wi h he highes numbe o equi emen s a e
socio-economic and e e o he sa e y o he ope a ion. In e ms o
c i e ia, he maximum numbe is in he en i onmen al pilla and be-
longs o he p inciple e e ing o he conse a ion and managemen o
ecosys ems.
4. Da ase o a ailable indica o s
An audi me hodology consis s o p ocedu es ha esul in he
compila ion o e idence abou he o ganiza ion’s pe o mance in ela-
ion o he equi emen s o he amewo k (shown in Sec ion 3)
Table 1
Di ec i es unde conside a ion o he p oposed amewo k o he me hodology classi ied pe decades and a eas o p o ec ion.
A ea o p o ec ion Di ec i e code
Be o e-1990 1990–2000 2000–2010 2010–2020 2020-Now
Ai quali y –92/62/EEC 2003/87/EC, 2008/50/EC 2010/75/
EU
2015/1127/EU, 2015/1480/
EU 2016/2284/EU
2024/299/EU
Ene gy – – – 2018/2001/EU, 2018/2002/
EU 2018/844/EU
2023/1791/EU,
2023/2413/EU 2024/
1405/EU
En i onmen al
Assessmen
– – 2001/42/EC, 2003/35/EC and 2009/
147/EC
– –
Na u e conse a ion –92/43/EEC 97/62/EC – – -
Noise 70/157/EEC, 81/
334/EEC 84/424/
EEC
92/97/EEC, 96/20/EC,
1999/101/EC2000/14/EC
2002/49/EC 2007/34/EC 2015/996/EU 2020/367/EU -
P e en ion and
con ol
– – 2004/35/EC – –
Residues and
con amina ed soils
86/278/EEC 1999/31/EC 2008/98/EC 2018/851/EU -
Sa e y – – – 2012/18/EU 2014/34/EU -
Technical aspec s 89/491/EEC – – 2011/92/EU 2014/30/EU –
Wa e and coas –91/271/EEC, 91/676/EEC
2000/60/EC
2006/7/EC, 2006/118/EC, 2007/60/
EC, 2008/56/EC, 2008/105/EC 2009/
90/EC
2013/39/EU, 2014/101/EU,
2014/80/EU 2020/2184/EU
-
Wo k condi ions 89/391/EEC 91/322/EEC, 1999/92/EC
2000/39/EC
2006/54/EC –2022/2041/EU 2024/
1500/EU
S. Es ´
e ez e al.
Wa e Resea ch 274 (2025) 123125
3
(Mi oneasa and Codin˘
a, 2013). The na u e o hese p ocedu es is based
on analysis, inspec ion, obse a ion, inqui y, calcula ion and ep o-
duc ion. No mally, he audi o selec s he mos app op ia e p ocedu e o
educe he isk o e o o judgmen o an accep able le el (Xiao e al.,
2020). Indica o s, as quan i a i e, quali a i e o bina y me ics, can be
used o e i y he eliabili y and he accessibili y o he in o ma ion
p o ided by o ganiza ions. In addi ion, hey can be used by an ex e nal
audi o o quali y compliance wi h equi emen s and c i e ia. The e o e,
i is o i al impo ance ha he diagnosis is ca ied ou wi h well
selec ed indica o s.
The e o e, once he speci ica ion amewo k has been de ined, a
subsequen s ep is o iden i y he mos sui able indica o s o each o he
equi emen s. In o de o know he possibili ies o in eg a ing indica o s
in o he amewo k, i is i s necessa y o iden i y iable indica o s ha
can be used o was ewa e ea men plan s. Fo his eason, a scien i ic
and g ey li e a u e e iew was conduc ed. This ype o e iew was
Fig. 1. S uc u e o he speci ica ion amewo k applicable o ce i ica ion schemes in he was ewa e sec o .
Table 2
P esen a ion o he speci ica ion amewo k in e ms o pilla , p inciples and c i e ia o he en i onmen al pilla o sus ainabili y.
Pilla P inciples Desc ip ion o he p inciples C i e ia Code o he
equi emen s
Numbe o
equi emen s
ES: En i onmen al
sus ainabili y
Conse a ion and
p ese a ion o habi a
di e si y
This p inciple looks o he p o ec ion o
habi a s and di e si y. I is conside ing bo h he
conse a ion o bio ic and abio ic ac o s.
The o ganiza ion shall conside
limi a ions ega ding he ope a ion in
sensi i e o p o ec ed a eas
ES
01.01.01–06
6
   The o ganiza ion shall p ese e he
biological di e si y o species and
es ic s he use o gene ically modi ied
in asi e species
ES
01.02.01–03
3
Conse a ion and
managemen o he
unc ions o he
ecosys em
This p inciple encompasses all he objec i es o
he company o p ese e he unc ions o soil,
wa e and ai wi h he con ol o he
con amina ion. Bo h di ec and indi ec impac s
a e conside ed.
The o ganiza ion shall p e en indi ec
wa e con amina ion h ough soil
quali y p ese a ion
ES
02.01.01–04
4
   The o ganiza ion shall ha e con ol
o e i s wa e - ela ed discha ges o e
he en i onmen
ES
02.02.01–07
7
   The o ganiza ion shall ha e s a egies
o minimize di ec emissions causing
clima e change
ES
02.03.01–05
5
   The o ganiza ion shall p ese e he
unc ions o he soil o u u e uses
ES
02.04.01–02
2
   The o ganiza ion shall p ese e he
unc ions o he ai o u u e uses
ES
02.05.01–02
2
   The o ganiza ion shall p o ide
su eillance o he ecosys em unc ions
ES
02.06.01–06
6
   The o ganiza ion shall p e en he
emissions o physical o igin (i.e., noise,
elec omagne ism, odou …)
ES
02.07.01–05
5
Sus ainable use o
esou ces o p e en
deple ion
Inpu lows should be measu ed o ensu e ha
he cu en demand can be me h ough he ime
o ope a ion
The o ganiza ion shall ha e limi a ions
on he use o ene gy
ES 03.01.01 1
   The o ganiza ion shall ha e limi a ions
on he use o chemicals
ES
03.02.01–02
2
   The o ganiza ion shall ha e limi a ions
on he use o wa e
ES
03.03.01–02
2
Was e managemen Non-p oduc ou pu s should be aced o ensu e
ha hey a e managed p ope ly
The o ganiza ion shall cha ac e ize he
was e gene a ed
ES
04.01.01–03
3
   The o ganiza ion shall ensu e he
aceabili y o was e
ES
04.02.01–02
2
S. Es ´
e ez e al.
Wa e Resea ch 274 (2025) 123125
4
selec ed conside ing ha his s udy has e y open sea ch ields (in-
dica o s and was ewa e ea men ) (Snyde , 2019). The compila ion o
he indica o s ound is shown in Supplemen a y Ma e ials A, whe e
hey ha e been g ouped in o h ee da a se s acco ding o hei p ima y
goal.
- The i s da ase includes 106 echnical and sus ainabili y indica o s
o desc ibe quan i a i ely a was ewa e ea men plan (p ocess-
based sys em bounda ies).
- The second da ase compiles 61 echnical and sus ainabili y in-
dica o s o sewe cons uc ion, ope a ion and main enance.
- The hi d da ase has 32 indica o s o ci cula i y.
In addi ion o he name, o mula and pa ame e s o hei calcula-
ion, each o he indica o s was classi ied o o ganized by a eas o p o-
ec ion. Fig. 2 shows he ep esen a i eness o each o he p o ec ion
a eas o each o he da ase s. I should be no ed ha he igu e is shown
only o aspec s wi hin he economic, en i onmen al and social pilla s o
sus ainabili y and ci cula i y. Technical pe o mance indica o s a e no
shown in he g aph, bu a e desc ibed in Supplemen a y Ma e ials A.
Conside ing ha legisla i e ac ions seek he implemen a ion o
measu es ha socie y o indus y mus comply wi h, he hi d ci cula i y
da ase collec s consis en ci cula i y indica o s speci ic o he sec o .
These ypes o indica o s we e selec ed o measu e he en i onmen al,
economic and social pe o mance o ci cula economy s a egies
implemen ed wi hin he Eu opean Union ha impac sus ainabili y
(Ren ew e al., 2024; Saidani e al., 2019). No in insic ci cula i y in-
dica o s applicable o was ewa e ea men ha measu e he success o
he implemen a ion o ci cula i y p inciples we e inco po a ed. This is
because ci cula i y p inciples and c i e ia a e s ill a a non-sec o al le el,
as exempli ied by he Eu opean G een Deal, he Ca alogue o Bes
P ac ices in Ci cula Economy, he Ca ego isa ion sys em o he ci cula
economy and he EEA (Eu opean En i onmen Agency) Repo 2/2016
(Eu opean Commission, 2020; Eu opean En i onmen Agency, 2016;
Minis e io pa a la T ansici´
on Ecol´
ogica y el Re o Demog ´
a ico, 2021;
The Eu opean G een Deal, 2019).
5. Sc eening o indica o s
To ensu e e i ica ion o he equi emen s, i is necessa y, as a i s
s ep, o associa e and selec he da abase indica o s desc ibed in Sec ion
4wi h he speci ica ion amewo k (shown in Table 4). Fo his pu pose,
all indica o s we e co ela ed wi h hose aspec s ha could be quan i-
ied. Indica o s o hose aspec s ha we e quali a i e we e also p o-
posed, as shown in Supplemen a y Ma e ials B. Since hey could no be
es ima ed, hey we e no e i ied in he amewo k o his esea ch.
Once chosen, a mul i a ia e analysis was pe o med o impu e missing
alues. In o he wo ds, each indica o was s udied o he iden i ica ion
o he pa ame e s on which da a should be collec ed. Also, in connec ion
wi h his analysis, sys em bounda ies and case s udy p ocesses we e
in es iga ed. Impo an da a we e collec ed in e ms o capaci y, p ocess
uni s, ope a ing limi a ions, and chemical and ene gy consump ion.
6. Applica ion o case s udies
The c ea ion o he p ocess in en o ies o he calcula ion and es ing
o he indica ion was pe o med using wo case s udies, A and B,
ep esen a i e o cen alized Spanish was ewa e ea men plan s. P i-
ma y da a we e aken mainly om acili y ope a ion and p ojec con-
s uc ion epo s, bu seconda y da a om models o mass-ene gy
balances we e also used when p ima y da a we e no a ailable. Figs. 3
and 4 show he p ocess low diag ams o case s udies A and B.
Case s udy A is a acili y ha se es 260,000 inhabi an s and ea s
domes ic was ewa e om i e adjacen u ban a eas. As in any ypical
Table 3
P esen a ion o he speci ica ion amewo k in e ms o pilla , p inciples and c i e ia o he socio-economic pilla o sus ainabili y and ci cula i y.
Pilla P inciples Desc ip ion o he p inciples C i e ia Code o he
equi emen s
Numbe o
equi emen s
SES: Socio-
economic
sus ainabili y
Sys em hinking, alue
c ea ion and business
models
This p inciple indica es ha e o s should be made o
inc ease he unc ionali y and pe o mance o
esou ces and a comp ehension o he in e ac ion o
he di e en economic ac o s in ol ed.
The o ganiza ion shall ob ain
p o i s om he p oduc ion o
esou ces
SES
01.01.01–05
5
   The o ganiza ion shall ha e
good inancial managemen
SES 01.02.01 1
   The o ganiza ion shall es ima e
and egis e i s ope a ional and
cons uc ion cos s
SES
01.03.01–04
4
   The o ganiza ion shall be
awa e o he social wel a e
p o ided
SES
01.04.01–02
2
Sa e y and labou
condi ions
This p inciple aims a he sa e and heal hy ope a ion o
he acili ies
The o ganiza ion shall ensu e
ha he wa e is sa e o human
consump ion
SES 02.01.01 1
   The o ganiza ion shall ensu e
minimum wo king condi ions
SES
02.02.01–05
5
   The o ganiza ion shall ha e
plans o ensu e ha he
acili ies ope a e sa ely
SES
02.03.01–14
14
   The o ganiza ion shall ha e
es ic ions o p ese e human
heal h
SES 02.04.01 1
T anspa ency o
in o ma ion
The goal o his p inciple is o ensu e ha documen s
a e sha ed wi h he in e es ed pa ies
The o ganiza ion shall ensu e
ha he company makes
documen a ion a ailable
SES
03.01.01–06
6
CI: Ci cula i y A ailabili y o esou ces
by keeping hem a he
highes alue
This p inciple ies o educe he dependence on i gin
esou ces and he inpu equi emen s
The o ganiza ion shall p oduce
ci cula p oduc s om esidual
ma e ials
CI 01.01.01–03 3
   The o ganiza ion shall make
use o enewable ma e ials
CI 01.02.01–07 7
Con ibu e o he
esilience and
egene a ion
This p inciple p omo es he esilience o ma e ials
h ough hei ecycling and euse in he p oduc ion
p ocess o alue chain
The o ganiza ion shall apply
he ules o he R´s in ci cula
economy
CI 02.01.01–03 3
S. Es ´
e ez e al.
Wa e Resea ch 274 (2025) 123125
5

la ge-scale was ewa e ea men plan , he ea men scheme consis s
mainly o ou s ages (p e ea men , p ima y, seconda y, e ia y and
sludge ea men ). P e ea men ocuses on he emo al o ine and
coa se solids, as well as g ease and g i . A h ee-line g i ing and
deg easing p ocess wi h he in oduc ion o ai wi h subme sible ae a-
o s is used. The solid esidues emo ed om he sc eens a e comp essed
be o e being s o ed and expo ed o -si e o ea men . The sands and
g ains a e hen pumped o a sand classi ie and su ace sc ape s o
educe he wa e con en be o e being s o ed.
Du ing p ima y ea men , chemical coagula ion- loccula ion wi h
i on chlo ide and polyelec oly e is used, while a 4-line ea men ain
(one anoxic chambe and h ee sequen ial ae obic chambe s) o mo ing
bed bio ilm eac o s (MBBR) has been ins alled o o ganic ma e
deg ada ion and ni i ica ion-deni i ica ion. A e he MBBR, he
e luen is ed o an Ac i lo®Tu bo cla i ie ha pe o ms seconda y
coagula ion, loccula ion and lamina se ling wi h mic osand. Finally,
he e is a e ia y ea men wi h ul a iole disin ec ion. A e his
s age, he ea ed was ewa e is discha ged o he sea wi h a ansma ine
pumping s a ion.
As o he sludge line, he solids emo ed wi h he wa e line ech-
nologies a e subjec ed o hickening and/o s abiliza ion p ocesses
(anae obic diges ion). The case s udy desc ibed he e is cha ac e ized by
a seg ega ion o he sludge s eam, since solids om p ima y and sec-
onda y ea men a e no mixed oge he . Thus, all sludge om he
p ima y ea men has been alo ized as biogas unde anae obic con-
di ions, bu he seconda y sludge is only pa ially ea ed wi hin he
diges ion s age. The e luen om he anae obic eac o is hickened ( o
a leas 20 % d yness) and subsequen ly s o ed. The concen a ion o he
seconda y sludge is also a p econdi ion o i s anspo o an au ho ized
ex e nal manage (minimum d yness o 18 %). Subsequen dewa e ing
and hickening o he sludge also akes place.
Case s udy B was designed o 800,000 inhabi an s-equi alen . P e-
ea men is based on la ge pa icle pi s, au oma ic la ge pa icle
sc eening, ine solids sc eening, was e anspo and compac ion,
Fig. 2. Rep esen a i eness o he a eas o p o ec ion o sus ainabili y (a) and ci cula i y (b) indica o s o he da ase s o be accoun ed o he ce i ica-
ion amewo k.
S. Es ´
e ez e al.
Wa e Resea ch 274 (2025) 123125
6
Table 4
Co ela ion be ween he equi emen s o he speci ica ion amewo k and quan i a i e indica o s om he was ewa e ea men da ase . The equa ions o he in-
dica o s a e shown in Supplemen a y Ma e ials A.
Code o he
equi emen s
Indica o (uni ) Pa ame e s used Uni s o he
pa ame e
Th esholds o he indica o Re s.
ES 02.01.01 I1. Sewage sludge quali y
indica o (Dimensionless)
F
2
O
3
mass in he sewage sludge
ash
kg/d The e a e no h esholds o he indica o o o he
compounds used o es ima e.
P eisne e al.
(2022)
  Al
2
O
3
oxides mass in sewage
sludge ash
kg/d  
  MgO mass in sewage sludge ash kg/d  
  P
2
O
5
mass in sewage sludge ash kg/d  
  Fe mass in sewage sludge ash kg/d  
  Al mass in sewage sludge ash kg/d  
  CaO mass in sewage sludge ash kg/d  
ES 02.01.02 I2. Eu ophica ion ne
en i onmen al impac
(Dimensionless)
Po en ial o eu ophica ion
p oduced by he discha ge o
was ewa e wi hou p e ious
ea men
kg PO
4
−3
eq/
d
The indica o alues below he uni mean ha he
WWTP is unde pe o ming wi h espec o he
heo e ical emo al capaci y while alues o e he uni
indica e a pe o mance abo e he legisla ion s anda ds.
Lo enzo-Toja
e al. (2016)
  Po en ial o eu ophica ion
indi ec ly coming om he
p ocess ea men
kg PO
4
−3
eq/
d
 
  Po en ial o eu ophica ion
caused by he discha ge o he
e luen
kg PO
4
−3
eq/
d
 
  Po en ial o eu ophica ion
caused by he discha ge o he
e luen de e mined by law
kg PO
4
−3
eq/
d
 
ES 02.01.04 I3. Sludge disposed (non-
u ilized) (%)
Volume ic low a e o sludge
disposed
m
3
/d The es ic ions a e a iable and depend on he coun y
and egions whe e he was ewa e ea men plan s a e
ins alled. The e could be limi a ions o sludge disposal
in land ills. In some cases, only he sludges ha could
no be alo ised would be admissible o land ill
disposal.
Ma os e al.
(2003)
  Volume ic low a e o sludge
p oduced
m
3
/d  
ES 02.02.04 I4. In e mi en o e low
discha ge olume pe
capaci y (%)
O e low discha ge caused by
e en s (i.e., hea y ains)
m
3
/d An o e low educ ion plan should be in place bu he e
a e no h esholds es ablished.
Kang e al.
(2020)
  A e age ope a ional ea men
capaci y by design
m
3
/d  
ES 02.02.06 I5. O ganic ma e
emo al e iciency (%)
Chemical oxygen demand
concen a ion in he in luen
mg/L The minimum pe cen age o educ ion is 70–90 % o
biological oxygen demand, 75 % o chemical oxygen
demand, 90 % o o al solids o acili ies wi h
>10,000 habi an s equi alen , 70 % o o al solids o
acili ies be ween 2000 and 10,000 habi an s
equi alen .
P eisne e al.
(2022)
Council di ec i e
91/271/EEC
  Chemical oxygen demand
concen a ion in he e luen
mg/L  
  A e age ope a ional ea men
capaci y
m
3
/d  
Code o he
equi emen s
Indica o (uni ) Pa ame e s used Uni s o he
pa ame e
Th esholds o he indica o Re s.
ES 02.02.06 I6. Ni ogen emo al
e iciency (%)
Ni ogen concen a ion in he in luen mg/L The minimum pe cen age o educ ion is 70–80
% o o al ni ogen.
P eisne e al.
(2022)
Council
di ec i e
91/271/EEC
  Ni ogen concen a ion in he e luen mg/L  
ES 02.02.06 I7. Phospho us emo al
e iciency (%)
Phospho us concen a ion in he in luen mg/L The minimum pe cen age o educ ion is 80 %
o o al phospho us.
P eisne e al.
(2022)
Council
di ec i e
91/271/EEC
  Phospho us concen a ion in he e luen mg/L  
ES 02.02.07 I8. Reduc ion o low o
was ewa e gene a ed
(Dimensionless)
Concen a ion o o al suspended solids in he
e luen
mg/L The con aminan s o he was ewa e e luen s
should ha e concen a ions below 25 mg/L o
biological oxygen demand, 125 mg/L o
chemical oxygen demand, 35 mg/L o o al
solids in acili ies wi h >10,000 habi an s
equi alen , 60 mg/L o o al solids o
acili ies be ween 2000 and 10,000 habi an s
equi alen , 2 mg/L o o al phospho us in
acili ies be ween 10,000–100,000 and 1 mg/L
o acili ies la ge han 100,000 habi an s
equi alen , 15 mg/L o o al ni ogen o
acili ies be ween 10,000–100,000 and 10 mg/
Kisele e al.
(2019)
Council
di ec i e
91/271/EEC
(con inued on nex page)
S. Es ´
e ez e al.
Wa e Resea ch 274 (2025) 123125
7
Table 4 (con inued)
Code o he
equi emen s
Indica o (uni ) Pa ame e s used Uni s o he
pa ame e
Th esholds o he indica o Re s.
L o acili ies >10,000 habi an s equi alen .
Fo he indica o , he esul is 1 when he a io
be ween he measu ed and he legisla i e
alues o he p e iously ci ed pa ame e is
lowe o 1.
  Concen a ion o biodeg adable oxygen
demand in he e luen
mg/L  
  Concen a ion o chemical oxygen demand in
he e luen
mg/L  
  Concen a ion o Kjeldahl ni ogen in he
e luen
mg/L  
  Concen a ion o phospho us in he e luen mg/L  
  Concen a ion o ni a es in he e luen mg/L  
ES 02.03.02 I9. Global wa ming
po en ial (kg CO
2
eq./m
3
kg CO
2
eq./habi an )
This indica o needs mass balances a ound
he sys em bounda ies. Fo a was ewa e
ea men plan should include a leas :
composi ion and low a e o he was ewa e
e luen , composi ion and low a es o ai
di ec emissions, mass and ype o chemicals
consumed, quan i y o ene gy (bo h hea and
elec ici y) and composi ion and low a e o
was es, sludges and p oduc s.
kg CO
2
eq./
m
3
kg CO
2
eq./
habi an
Th esholds ha e s ill no been es ablished by
law. Examples o es ima ions o la ge scale
cen alized was ewa e ea men plan s: (1)
Ranie i e al. (2024) calcula ed he g eenhouse
gases o 183 was ewa e ea men plan s wi h
compensa ion measu es. Thei esul s
indica ed an a e age ca bon oo p in o 1.22
kg CO
2
eq/m
3
. (2) Pa a icini e al. (2022)
p oposed a ange o emissions o WWTPs
be ween 50 and 125 kg CO
2
eq/pe son
equi alen /y. (3) Lo enzo-Toja e al. (2015)
s udied 113 Spanish WWTPs. The a e age
ca bon oo p in was 0.45 kg CO
2
eq/m
3
.
Cossio e al.
(2020)
Ranie i e al.
(2024)
Pa a icini e al.
(2022)
Lo enzo-Toja
e al. (2015)
Code o he
equi emen s
Indica o (uni ) Pa ame e s used Uni s o he
pa ame e
Th esholds o he indica o Re s.
ES 02.03.03 I10. Spills and/o leakages o
chemicals, by-p oduc s and
was ewa e (kg/10
6
m
3
)
Gas chemicals
acciden ally eleased o
he a mosphe e
kg/d Th esholds we e no iden i ied o his indica o . The
expec ed esul should indica e ha any kind o spill o
p oduced
Quad os e al.
(2010)
  A e age ope a ional
ea men capaci y
m
3
/d  
Es 02.04.01 I.11 Pollu an con en indica o
om sewage sludge
(Dimensionless)
Concen a ion o
cadmium in he sludge
mg/kg The limi ing alues o hea y me als in sludge o be use
in ag icul u e in mg/kg a e: 20–40 o cadmium,
1000–1750 o coppe , 300–400 o nickel, 750–1200
o lead, 2500–4000 o zinc and 16–25 o me cu y.
P eisne e al.
(2022)
Council di ec i e
86/278/EEC
  Concen a ion o coppe
in he sludge
mg/kg  
  Concen a ion o
ch omium in he sludge
mg/kg  
  Concen a ion o
phospho us pen oxide in
he sludge
mg/kg  
  Concen a ion o
me cu y in he sludge
mg/kg  
  Concen a ion o nickel
in he sludge
mg/kg  
  Concen a ion o lead in
he sludge
mg/kg  
  Concen a ion o zinc in
he sludge
mg/kg  
ES 02.04.02 I12. Cu en land alua ion
(
€
/m
3
)
Value o he land whe e
he WWTP is loca ed
€
These cos s a e dependen on he coun y and egion. A
ma ke analysis is needed bu he e a e no h esholds
associa ed.
Quad os e al.
(2010)
  A e age ope a ional
ea men capaci y
m
3
 
ES 02.07.02 I13. Noise le els a ec ing he
popula ion (Dimensionless)
Noise le el du ing he
day- ime
dBA The pe missible sound o each ype equipmen can be
ound on a icle 12 o Di ec i e 2000/14/EC
Colli igna elli
e al. (2022)
Di ec i e
2000/14/EC
  Noise le el du ing he
e ening- ime
dBA  
  Noise le el du ing he
nigh - ime
dBA  
ES 02.07.05 I14. Odo emission po en ial
(Dimensionless)
Maximum chemical
oxygen demand
concen a ion
mg/L Nowadays, he e a e no legisla i e h esholds o odo
emissions.
an Schaik e al.
(2021)
  In luen chemical
oxygen demand
concen a ion
mg/L  
  Odou emission a e pe
ype o ea men uni
mg/L  
S. Es ´
e ez e al.
Wa e Resea ch 274 (2025) 123125
8
Code o he
equi emen s
Indica o (uni ) Pa ame e s used Uni s o he
pa ame e
Th esholds o he indica o Re s.
ES 03.01.01 I15. Ene gy consump ion
pe low a e (kWh/m
3
o
kWh/habi an )
Ene gy consumed by he
acili y du ing i s ope a ion
kWh/d Fo was ewa e ea men in as uc u e (acco ding o
legisla ion), he consump ion should be below 35 kWh/
habi an s equi alen o acili ies below 10,000; 25
kWh/habi an s equi alen o acili ies be ween 10,000
and 100,000 and 20 kWh/habi an s equi alen o
acili ies abo e 100,000.
He e al. (2019) p o ided a ange o ene gy
consump ion in WWTPs o 0.1–1.2 kWh/m
3
which is
compa able wi h he esul s o Toja e al. (2016)
(0.185–0.785 kWh/m
3
)
COM/2022/541 indica es ha ene gy neu ali y in
was ewa e ea men plan s should be achie ed by
2040 o all acili ies abo e 10,000 habi an s
equi alen .
Cassidy e al.
(2020)
Di ec i e (EU)
2023/1791
COM/2022/541
Di ec i e
2010/75/EU
He e al. (2019)
Toja e al. (2016)
  A e age ope a ional
ea men capaci y
m
3
/d o
habi an
 
ES 03.02.01 I16. Consump ion o
chemicals (% o kg/m
3
)
Flow a e o acids and/o
bases consumed du ing
p ocess ope a ion
m
3
/d o kg/d The consump ion o chemicals should be p og essi ely
minimized bu he e a e no legisla i e h esholds.
Quad os e al.
(2010)
  A e age ope a ional
ea men capaci y
m
3
/d  
ES 03.03.02 I17. F eshwa e
consump ion (%)
Flow a e o eshwa e (o
po able wa e ) consumed
du ing he p ocess
ope a ion
m
3
/d Tempo a y h esholds could be imposed by egional
go e nmen s du ing wa e sca ci y seasons based on
he se e i y o he d ough s. The e o e, he esul s o
his indica o should be minimized.
Quad os e al.
(2010)
  A e age ope a ional
ea men capaci y
m
3
/d  
ES 04.01.01 I18. Sedimen s om sewe s
and anks (m
3
/habi an ⋅d
o kg/habi an ⋅d)
Flow a e o sedimen s
collec ed om sewe s and
anks
m
3
/d o kg/d Al hough he indica o makes e e ence o he
p oduc ion o g i s, no h eshold can be imposed. The
indica o should be minimized.
Ma os e al. (2003)
  Habi an equi alen s se ed
by he acili y
Dimensionless  
ES 04.01.01 I19. Solid was e om
sc eenings and g i
chambe s
(m
3
/habi an ⋅d o kg/
habi an ⋅d)
Flow a es om o
sc eenings and g i
chambe s
m
3
/d o kg/d Same commen as desc ibed o he p e ious indica o
(also ela ed o equi emen ES 04.01.01)
Ma os e al. (2003)
  Habi an equi alen s se ed
by he acili y
Dimensionless  
ES 04.02.01 I20. Sludge des ina ion
(kg/d)
Mass low a e used in
ma e ial eco e y
kg/d Same h esholds han o he indica o associa ed o he
equi emen ES 02.01.04
Colli igna elli
e al. (2021)
  Mass low a e used in
ene gy eco e y
kg/d  
Code o he
equi emen s
Indica o (uni ) Pa ame e s used Uni s o he
pa ame e
Th esholds o he indica o Re s.
SES
01.01.01–02
I21. Re enues om he
selling o e ilize s (
€
/d)
Mass low a e o
eco e ed phospho us
kg/d In e ms o p o i abili y he maximum ideal alue is achie ed
when all he phospho us and ni ogen o he was ewa e
in luen has been eco e ed. Apa om he quali y o ma ke
limi a ions ha he company may ound in he
comme cializa ion o he e ilize s, he e a e no h esholds o
his indica o .
Smol and
Koneczna
(2021)
  Mass low a e o
eco e ed ni ogen
kg/d  
  A e age selling p ice o
phospho us
€
/kg  
  A e age selling p ice o
ni ogen
€
/kg  
SES 01.01.03 I22. Re enues om he
selling o p oduced
elec ici y (
€
/d)
Elec ici y p oduc ion
om he diges e
kWh/d The limi a ion o he elec ici y p oduc ion is heo e ical
me hane yield (0.35 Nm
3
me hane/kg chemical oxygen
demand) and he e iciency o he hea and powe uni (o
o he ).
Smol and
Koneczna
(2021)
  A e age coun y
elec ici y p ice
€
/kWh  
SES 01.01.05 I23. Reuse o was ewa e
(Dimensionless)
Mass low a e o
eco e ed phospho us
kg/d This indica o ep esen s a a io o a oided cos s conside ing
he managemen o ni ogen and phospho us as e ilize s
compa ed o hei emo al o p e en en i onmen al impac s
and damages. The maximum alue is 1, esul ha indica es
ha all he emo ed ni ogen and phospho us om he
was ewa e in luen has been eco e ed. The e a e no
minimum h esholds, bu low (specially <0.5) alues shows
ha he acili y ad oca es mo e o he emo al han o he
eco e y.
Kayal e al.
(2019)
  Mass low a e o emo ed
phospho us
kg/d  
(con inued on nex page)
S. Es ´
e ez e al.
Wa e Resea ch 274 (2025) 123125
9
Fig. 5. Fi s page o he eques o m o da a collec ion o pe o m a ci cula i y and sus ainabili y analysis wi h indica o s.
S. Es ´
e ez e al.
Wa e Resea ch 274 (2025) 123125
16

equi emen s o he amewo k.
To be e unde s and hei applicabili y, he indica o s calcula ed in
he case s udies we e classi ied acco ding o hei objec i es and he ype
o in o ma ion hey p o ide o imp o ing was ewa e ea men plan s.
Table 6 o ganizes hese indica o s based on hei use ulness—whe he
hey con ibu e o he o e all enhancemen o he acili y o suppo he
moni o ing o p ocess inpu s and ou pu s. Fu he mo e, he indica o s
we e ca ego ized by he na u e and ime ame o he in o ma ion hey
p o ide.
On one hand, some indica o s need o be analyzed be o e he con-
s uc ion o he acili y ( e e ed o as ex-an e indica o s in Table 6),
while o he s a e ele an du ing ope a ion. Among he la e , ce ain
indica o s a e s a ic, whe eas o he s equi e con inuous e alua ion o e
ime. S a ic indica o s can also be subdi ided in o hose conside ing
legisla i e h esholds and hose p o iding in o ma ion on he acili y.
The classi ica ion o indica o s in Table 6 highligh s a c i ical inding:
he need o de elop h esholds and alida ion ools o ensu e he sui -
abili y o he acili y du ing he planning and cons uc ion phases.
7.4. Mo ing owa ds a mo e comp ehensi e was ewa e ea men sys em
7.4.1. Imp o emen o he ce i ica ion amewo k: a compa ison
Volun a y s anda diza ion aims o p o ide uni ied and logical p o-
cedu es o speci ica ions o acili a e he implemen a ion o ac ions ha
esul in imp o emen s compa ed o common p ac ices. Depending on
i s na u e, his s anda diza ion can be classi ied in o s anda ds, ce i i-
ca ion, acc edi a ion, and labels. While s anda ds communica e docu-
men ed ag eemen s o echnical speci ica ions on p oduc s (no
necessa ily ollowing manda o y egula ions), managemen sys ems,
and p ocesses, ce i ica ion in ol es p ocedu es o ensu e con o mi y
wi h mul iple s anda ds along he supply chain.
Based on he p e ious de ini ions, he amewo k p esen ed in Sec-
ion 3 could be conside ed a guideline o was ewa e sec o assessmen ,
conside ing he equi emen s o Eu opean legisla ion while ollowing a
s uc u e commonly used in ce i ica ion schemes. In his ega d, anal-
ogous e minology has been conside ed (e.g., o analyzing he deg ee o
compliance wi h ce i ica ion schemes such as he Round able on Sus-
ainable Bioma e ials o RSB, which uses e ms like "shall" o de ine
manda o y equi emen s, "should" o ecommenda ions, "may" o
op ional implemen a ions, and "can" o possibili ies and capabili ies).
Speci ically, he e m "shall" is used, as all he equi emen s in he p o-
posed amewo k s em om legisla ion and, he e o e, mus be s ic ly
complied wi h.
Mo eo e , he amewo k has been designed o po en ially co e , in
he u u e and wi h he necessa y adap a ions, all six s ages o he en i e
wa e cycle: (1) wa e cap u e o supply di e en ac o s (e.g., commu-
ni ies o indus ies) and ea men , (2) wa e s o age and dis ibu ion
(al eady co e ed by some ce i ica ion schemes such as AWS), (3)
was ewa e collec ion and sewage ne wo ks, (4) was ewa e ea men ,
(5) by-p oduc s comme cializa ion, and (6) solid was e ea men and
eco e y. Al hough he inal s ages a e no pa o he u ban wa e cycle,
hey should be included unde a ci cula economy app oach, ocusing on
he eco e y o esou ces om was ewa e and he alo iza ion o he
was es p oduced.
Rega ding he s uc u e o he p oposed amewo k o he ope a ion
o was ewa e ea men acili ies, i s cons uc ion was inspi ed by
exis ing ce i ica ion schemes om o he bio-based sec o s (i.e., o es y,
ag icul u e and ishe ies), bu inc easing he obus ness by de ining
mo e han wo o h ee le els o classi ica ion. Fo example, FSC is
cons i u ed by 10 p inciples (de ined as essen ial ule o elemen ) and
ela ed 57 c i e ia (a means o judging) (Ma ias e al., 2024); RSB has 12
p inciples ha desc ibe he bes legal, social, en i onmen al and man-
agemen p ac ices, 40 c i e ia and 165 explici c i e ia (RSB, 2023); SBP
is cons i u ed by 2 p inciples, 16 c i e ia and 38 indica o s (SBP, 2015);
MSC s anda d has 28 pe o mance indica o s, unde he h ee p inciples
(Pie ucci e al., 2022); ASC Salmon s anda ds ha e 8 p inciples and a se
o 32 c i e ia (ASC, 2024). The Be e Biomass ce i ica ion scheme is
cons i u ed o 9 p inciples, 25 c i e ia and 14 indica o s, and i is
highligh ed ha o his scheme he de ini ion o he p inciple and in-
dica o is aligned wi h he ISO 13,065. Am o i BSCI is a wo-laye ce -
i ica ion scheme which is no s uc u ed in o p inciples and c i e ia bu
a he in pe o mance a eas (a o al o 13) and equi emen s (am o i
BSCI, 2022). PEFC, on he o he hand, is de ined by objec i es and e-
qui emen s (known as quan i a i e o quali a i e pa ame e s desc ibing
he di e en subjec s o be e alua ed) (PEFC, 2021).
Compa ed o he p e iously p esen ed ce i ica ion schemes, he
p oposed amewo k in his manusc ip ep esen s a signi ican
ad ancemen by in eg a ing i e dis inc laye s, as well as de ining
h esholds (a ailable in Supplemen a y Ma e ial B): pilla s, p inciples,
c i e ia, equi emen s, and indica o s. In his way, he p inciples we e
classi ied based on hei abili y o ul ill he sus ainabili y pilla s and
ci cula i y. Addi ionally, he e is a clea dis inc ion be ween c i e ia,
equi emen s, indica o s, and h esholds, which enhances usabili y and
comp ehension. Mo eo e , he p oposed amewo k also conside s he
assessmen o quan i a i e indica o s, a he han ocusing solely on
quali a i e ones, which is he mos common app oach in he a o e-
men ioned ce i ica ion schemes. This is conside ed a signi ican s ep
owa d achie ing g ea e accu acy and anspa ency in he de elopmen
o audi ing p ocesses (Halalisan e al., 2023).
7.4.2. Da a gaps and ou es o esea ch on indica o s
Some gaps we e iden i ied h ough he c ea ion and s udy o he
amewo k. Fi s , he e a e no su icien quan i a i e legisla i e
h esholds (also as shown in Table 6) o all en i onmen al, economic o
social aspec s lis ed in he equi emen s. The e o e, measu ing he pe -
o mance o was ewa e ea men plan s should be done p ima ily by
compa ison wi h p ede ined baselines o e alua e he po en ial and
willingness o acili ies o imp o e. Fo such a eason, a he han
imposing immedia e compliance, u u e legisla ion and s anda ds
should se dynamic a ge s o be me o e ime. The p oposal and use o
h esholds will allow he moni o ing o a ge s and he iden i ica ion o
planned ad hoc go e nmen in es men s in was ewa e ea men plan s
o a oid de ia ions. Mo eo e , he de elopmen o policies should ocus
on de ining good p ac ices and es ablishing app op ia e ope a ional
anges o acili ies based on di e en scales and echnologies. Finally,
he e should also be speci ic legisla ion o he manu ac u ed p oduc s,
aking in o accoun hei quali y, sa e y o use, and pe missible
applica ions.
In addi ion o p oposing b oade h esholds o he sec o , he e
should be an upda e in he de elopmen o sus ainabili y indica o s.
Cu en ly, he e is a gap be ween he ex ensi e lis o indica o s in he
li e a u e and he da a ha can be egula ly collec ed in was ewa e
ea men plan s. Some examples could be ene gy consump ion pe
equipmen , was ewa e ea men cha ac e iza ion o he egion adja-
cen o he acili y, sewe sizing, and eco ding di e en aspec s ela ed
o eme gency e en s (i.e., medical ca e needed, main enance, sa e y
audi , blockages and looding, among o he s).
In addi ion o he di e si y o da a and he di icul ies encoun e ed in
collec ing i , he legisla ion moni o s he beha io o companies and
indi iduals wi hou using speci ic quan i a i e speci ica ions. On he
o he hand, cu en ce i ica ion schemes look o documen s o eco ds
o ensu e compliance wi h he p ede ined c i e ia and gua an ee he
quali y o he se ices p o ided. The e o e, he cu en assessmen
p ocedu es make i di icul o implemen digi ized da a sys ems and
o he ac ions o in eg a e company moni o ing wi h a i icial
in elligence.
Finally, he e is a lack o guidelines o a common s anda dized
me hodology applicable o plan ope a o s and sus ainabili y (o ci cu-
la i y) assessmen p o essionals o da a collec ion ha can be unde -
s ood simul aneously by bo h. This is especially impo an when a mul i-
c i e ia analysis is needed since di e en depa men s o he company
migh be in ol ed du ing da a ga he ing and ime can be sa ed.
S. Es ´
e ez e al.
Wa e Resea ch 274 (2025) 123125
17
Table 6
Classi ica ion o he calcula ed (in he case s udies) indica o s o he amewo k conside ing i s objec i es, ime ames and na u e o in o ma ion.
Classi ica ion g oups Indica o s wi h legisla i e h esholds Indica o s o be e alua ed o e ime In o ma i e indica o s o quali y Indica o s o ex-
an e
implemen a ion
Rela ed
o
inpu s
In luen s – – – –
Chemicals –I16: The p og essi e educ ion o he
consump ion o chemicals is a symp om
o no el echnology implemen a ion and
p ocess op imiza ion.
I17: F eshwa e dec ease shows how he
acili y eclaims mo e e luen
was ewa e o i s ac i i ies, and i is also
ela ed o a lowe need o chemical
dilu ion.
– –
Ene gy I15: EU Taxonomy impu es
h esholds o ene gy demand based
on p ocess capaci y
I15: Ene gy neu ali y mus be achie ed
by 2040.
I37: The goal o any WWTP should be o
achie e ene gy-sel -su iciency.
I38: The acili y should look o he
maximiza ion o ene gy demand ha is
enewable.
I38: When he ene gy is aken om he
coun y g id, he indica o in o ms how
he WWTP enewabili y is dependen om
he p og ess in e ms o sus ainabili y o
he coun y o ope a ion.
–
Rela ed
o
ou pu s
Was es and
sludge
I11: The sludge should be o good
quali y in e ms o hea y me als.
I18 and I19: The esidues gene a ed by
he acili y should be educed h ough
he implemen a ion o in-si u
echnologies o alo iza ion.
I1: The sludge should be o a good quali y
(in e ms o composi ion) compa ed o i s
e ilize powe o be able o be used in
ag icul u e.
I3: The indica o shows whe he he sludge
is alo ized.
I20. The alo iza ion op ions o he sludge
should be aceable and indica ed by he
acili y.
I44: The sludge quan i y can be maximized
(i he e a e eco e y op ions a ailable) o
minimized (i ea ed o an ex e nal
manage ) in acco dance wi h he p io i ies
and echnologies o he acili y.
I46: This indica o in o ms abou he sha e
o sludge coming om anae obic diges ion.
–
P oduc s –I21 and I22: To measu e he e enues
om he p oduc ion o e ilize s and
elec ici y is impo an in WWTPs
looking o a ansi ion o a ci cula
economy.
I45: An imp o emen in he p oduc ion
o biogas om sludge is a consequence o
a echnology modi ica ion, eac o and
p ocess op imiza ion.
I41 and I42: The quali y o he e ilize s
ob ained in he WWTP should be
compa ed wi h con en ional mine al
e ilize s.
I43: This indica o in o ms abou he
amoun o bio e ilize s p oduced om
sewage sludge. I is no a ansi o y
indica o because he sludge can be
alo ized by o he op ions.
–
E luen s I5, I6 and I7: The o ganic ma e ,
ni ogen and phospho us emo al
e iciency should be below he
h esholds indica ed by he Council
di ec i e 91/271/EEC
I24: To measu e he bene i s om he
eclama ion o was ewa e is impo an
in a ansi ion o ci cula economy.
I39 and I40: The phospho us and
ni ogen eco e y e iciencies should be
inc eased o align wi h ci cula economy
s a egies.
I8: The indica o shows i he acili y
complies wi h he Council di ec i e 91/
271/EEC in e ms o e luen emissions.
I24: The bene i s om he eclama ion o
was ewa e a e quan i a i e in o ma ion o
inco po a e in economic epo s.
I36: This indica o in o ms abou he use in
ag icul u e o eclaimed wa e .
–
Classi ica ion
g oups
Indica o s wi h
legisla i e
h esholds
Indica o s o be e alua ed o e ime In o ma i e indica o s o quali y Indica o s o ex-an e
implemen a ion
Rela ed o
o e all
moni o ing
–I9: The e a e s ill no h esholds o global wa ming
po en ial in was ewa e ea men plan s and hus an
ini ial baseline scena io should be de ined.
I25: This in o ma ion in o ms abou he minimiza ion
o cos s and maximiza ion o bene i s ( om he
implemen a ion o alo iza ion o eco e y
measu es). The alue o he indica o can be
inc eased up o he esul s achie ed unde op imal
heo e ical ope a ion.
I26: The cos s o he acili y should be minimized
o e ime.
I27: The WWTP ope a ion should educe he
en i onmen al cos s h oughou he implemen a ion
o con inuous measu es in he p ocess.
I28: The e should be a ansi ional inc emen o he
emo al o pollu an s om he in luen and he
eclama ion o he e luen .
I2: The indica o shows he
no malized eu ophica ion
po en ial o he acili y conside ing
indi ec impac s.
I23: The indica o in o ms abou he
deg ee o eco e y o he acili y
compa ed o he emo al o
nu ien s.
I12: The p ice o he land o he
cons uc ion o he WWTP should be
conside ed in he selec ion o he
loca ion.

S. Es ´
e ez e al.
Wa e Resea ch 274 (2025) 123125
18
7.4.3. Unce ain ies o scale in was ewa e ea men plan s
The amewo k is b oadly applicable o was ewa e ea men plan s
o all scales, wi h excep ions pe aining o speci ic en i onmen al and
socio-economic sus ainabili y equi emen s ha a e unique o ce ain
acili y capaci ies.
The socio-economic pilla is gene ally less a ec ed han he en i-
onmen al pilla . Among he socio-economic c i e ia, SES 02.03 (“The
o ganiza ion has plans o ensu e ha he acili ies ope a e sa ely”) is he only
one wi h speci ic ema ks o small-scale plan s. App oxima ely 10 o he
14 equi emen s unde his c i e ion a e in luenced by Di ec i e 2012/
18/EU (Se eso III), which add esses he con ol o majo -acciden haz-
a ds in ol ing dange ous subs ances. This Eu opean egula ion applies
o acili ies ha s o e a leas one o he 48 subs ances lis ed in Annex I,
and only when he quan i y o a subs ance exceeds he de ined h eshold
ha ca ego izes he acili y as an uppe - ie es ablishmen . Conse-
quen ly, small-scale acili ies a e o en no classi ied as uppe - ie es-
ablishmen s, and equi emen s ela ed o his di ec i e may no be
applicable. Fu he de ails abou he speci ic equi emen s can be ound
in Supplemen a y Ma e ials B.
Rega ding he en i onmen al pilla , h ee p inciples a e applied
di e en ly depending on he scale o he acili y. One such p inciple is ES
02 o “Conse a ion and managemen o he unc ions o he ecosys em”.
Hal o i s six equi emen s a e in luenced by Di ec i e 2000/14/EC,
which pe ains o noise emissions in he en i onmen caused by ou doo
equipmen . Speci ically, compliance wi h he CE label and he indica ion
o he gua an eed sound powe le el depend on equipmen size, which
in u n is linked o he capaci y o he acili y. Beyond noise con ol, he
“iden i ica ion o measu es o he pe o mance o an en i onmen al impac
assessmen o achie e and main ain a good en i onmen al s a us” (ES
02.06.04) also di e s be ween small and la ge acili ies. Acco ding o
Annex I o Di ec i e (EU) 2011/92, an en i onmen al impac assessmen
is manda o y only o was ewa e ea men plan s wi h a capaci y
exceeding 150,000 popula ion equi alen s.
Rega ding ene gy demand, c i e ia ES 03.01 (“The o ganiza ion has
limi a ions on he use o ene gy”), h ee documen s speci y limi a ions o
scale: Di ec i e (EU) 2018/2021, COM/2022/541 and EU Taxonomy.
Di ec i e (EU) 2018/2001 p omo es he use o ene gy om enewable
sou ces, emphasizing he possibili y o go e nmen s o p o ide eed-in
a i s o small acili ies p oducing elec ici y. While Di ec i e (EU)
2018/2001 does no speci y a h eshold, COM/2022/541 o e s mo e
de ailed guidance, highligh ing he equi emen o was ewa e ea -
men plan s (WWTPs) se ing popula ions o >10,000 equi alen in-
habi an s o achie e ca bon neu ali y by 2040. Addi ionally, he EU
axonomy de ines ene gy consump ion h esholds based on acili y ca-
paci ies: 35 kWh pe inhabi an equi alen o acili ies se ing ewe
han 10,000 inhabi an s, 25 kWh pe inhabi an equi alen o capac-
i ies be ween 10,000 and 100,000, and 20 kWh pe inhabi an equi a-
len o capaci ies abo e 100,000.
On he o he hand, wi h espec o he le el o ea men , COM/
2022/541 iden i ies he ollowing equi emen s: (1) all u ban was e-
wa e ea men plan s wi h a capaci y o 100,000 popula ion equi a-
len s o mo e mus p o ide qua e na y ea men (ES 02.02.06), (2)
agglome a ions o be ween 10,000–100,000 popula ion equi alen
should apply qua e na y ea men in a eas iden i ied as sensi i e o
pollu ion om mic o-pollu an s (ES 02.02.06), (3) in eg a ed u ban
managemen plans a e manda o y o agglome a ions wi h 100,000 o
mo e (ES 02.06.05), (4) such plans a e also equi ed o agglome a ions
be ween 10,000 and 100,000 popula ion equi alen s i s o mwa e
o e low and u ban uno pose isks o he en i onmen o human
heal h (ES 02.06.05) and (5) a minimum annual numbe o samples o
all he le els o ea men should be de eloped.
I is also wo h men ioning he Council Di ec i e 91/271/EEC, he
oldes egula ion conce ning u ban was ewa e ea men , as i es ab-
lishes s anda ds o e luen composi ion and he minimum echnologies
o be implemen ed based on ea men capaci y equi emen s. A icle 4
speci ies he minimum capaci y o plan s o inco po a e seconda y
ea men , while Annex I ou lines he numbe o samples equi ed based
on plan capaci y and he concen a ion o o al suspended solids. The
minimum pe cen age o educ ion o his compound is 90 % in acili ies
se ing >10,000 popula ion equi alen s and 70 % in acili ies se ing
be ween 2000 and 10,000 popula ion equi alen s. Conside ing hese
aspec s, he di ec i e add esses equi emen s ela ed o discha ge poin s
(ES 02.02.03), sensi i e a eas (ES 01.01.04), and e luen composi ions
(ES 02.02.06 and ES 02.02.07).
7.4.4. The ci cula economy: he up ising needs in was ewa e ea men
ce i ica ion
An impo an opic o add ess in he discussion o he amewo k is
ci cula i y. A e iew o he was ewa e - ela ed di ec i es sugges s ha
cu en egula ions p ima ily ocus on educing dependence on i gin
esou ces and p omo ing esou ce esilience (e.g., ex ending esou ce
li e). Howe e , hey do no comp ehensi ely add ess ci cula economy
p inciples. This app oach aligns wi h he p ac ices obse ed in mos
ecognized ce i ica ion s anda ds. Fo ins ance, ce i ica ions such as
ISCC, ASC, Be e Biomass, BSCI, and UEBT emphasize p ope was e
managemen p ac ices, including was e seg ega ion by ype, minimizing
he use o non- enewable ene gy and wa e , and implemen ing docu-
men ed plans o was e educ ion, euse, and ecycling. The no able
excep ion is he C adle- o-C adle® ce i ica ion scheme, which in-
co po a es ci cula economy p inciples bu only a he p oduc le el.
This na ow ocus can p o ide an incomple e pe spec i e on ci cula i y.
The e o e, he e is a p essing need o ad ance bo h quan i a i e and
quali a i e analyses o li e cycle and ci cula i y app oaches. Such ad-
ancemen s aim o enhance he alidi y and anspa ency o assessmen s
ac oss alue chains.
In his con ex , in eg a ing he ISO 59,004 s anda d in o ce i ica ion
schemes and legisla i e amewo ks could o e a p elimina y solu ion.
This in eg a ion would suppo indus ial symbiosis and p omo e he
closu e o esou ce loops, all while main aining p oduc quali y and
imp o ing social indica o s. I is essen ial, he e o e, o conside his
b oade con ex when de eloping s a egies o in eg a ing ci cula ac-
ions in o was ewa e ea men plan s, ac oss all scales and echnolo-
gies. Doing so could con ibu e o c ea ing a mo e obus and cohesi e
was ewa e ea men sec o , suppo ed by guidelines simila o hose o
Bes A ailable Techniques.
8. Conclusions and u u e ou look
While en i onmen al p oduc ce i ica ion has a s ong backg ound
o sec o s such as ag icul u e, o es y, ex iles and cons uc ion, his is
no he case o he was ewa e sec o . The e o e, a s ep o wa d was
aken in his esea ch wi h he objec i e o laying he g oundwo k o an
end-o -li e ce i ica ion scheme o his sec o . Sys ema ic and
comp ehensi e-c i ical li e a u e e iews we e conduc ed o ga he in-
o ma ion om di ec i es and scien i ic and o he documen s wi h he
objec i e o c ea ing a amewo k o equi emen s and da a se s wi h
sus ainabili y and ci cula i y indica o s. Each piece o in o ma ion was
combined o de e mine whe he he quan i a i e indica o s collec ed
we e su icien o indica e whe he he equi emen s we e me . Since he
indica o s equi e da a o hei es ima ion, wo case s udies we e used
o e i y he easibili y o using hem o alida e he amewo k and
p o ide guidelines o imp o e he ope a ion o any was ewa e ea -
men plan . Conside ing ha he da a needed o es ima e he indica o s
do no ma ch he da a ha can be p o ided by he was ewa e ea men
acili ies, a ac shee was p o ided o suppo companies in da a
collec ion.
As desc ibed in his manusc ip , he p esen ed amewo k can be
used as a p elude o quan i a i e e i ica ion o compliance wi h
legisla ion, imp o ing communica ion be ween was ewa e ea men
ope a o s and me hodology de elope s, and es ablishing a baseline o
gap iden i ica ion. In addi ion o his, he p oposed amewo k could
also be use ul o ad ance he digi iza ion o he ce i ica ion p ocess wi h
S. Es ´
e ez e al.
Wa e Resea ch 274 (2025) 123125
19
he inco po a ion o indica o s ha can be au oma ically es ima ed and
e i ied.
The esul s o his esea ch demons a ed ha he cu en amewo k
o he was ewa e amewo k is no capable o add essing wi h a
comple e quan i a i e con o mi y assessmen model. The e o e, u u e
wo k should ocus on c ea ing quan i a i e h esholds and indica o s o
some o he equi emen s ha a e now add essed quali a i ely. In
addi ion o his, mo e e o and money should be in es ed o he
ans o ma ion o he p esen ed legisla ion-based amewo k in o an
ope a ional ce i ica ion scheme wi h ea u es compa able o hose
al eady exis ing in he ma ke . Examples o ac ions could be he c ea ion
o a e i ica ion guide o quali a i e equi emen s ha can be used by
audi o s; inco po a ion o equi emen s ha go beyond legisla ion wi h
he use o ini ia i es, epo s and scien i ic li e a u e; alignmen o
was ewa e sec o equi emen s wi h o he bio-based sec o s; s eng h-
ening aceabili y c i e ia, as was ewa e ea men plan s will also ha e
o ce i y hei p oduc s; s akeholde in ol emen ; and he c ea ion o a
eliable sco e o he indica o sys em ha accoun s o digi aliza ion,
keeping he economic cos s ela ed o ce i ica ion low.
CRediT au ho ship con ibu ion s a emen
So ía Es ´
e ez: W i ing – o iginal d a , Visualiza ion, Me hodology,
In es iga ion, Fo mal analysis. Ana A ias: W i ing – o iginal d a ,
Visualiza ion, Me hodology, In es iga ion, Fo mal analysis. Gume -
sindo Feijoo: W i ing – e iew & edi ing, Valida ion, Supe ision.
Ma ía Te esa Mo ei a: W i ing – e iew & edi ing, Valida ion,
Supe ision.
Decla a ion o compe ing in e es
The au ho s decla e he ollowing inancial in e es s/pe sonal e-
la ionships which may be conside ed as po en ial compe ing in e es s:
So ia Es e ez Ri adulla epo s inancial suppo was p o ided by
Spanish Minis y o Science, Inno a ion and Uni e si ies. Ana A ias
Cal o epo s inancial suppo was p o ided by Galician Go e nmen .
So ia Es e ez Ri adulla epo s inancial suppo was p o ided by
HORIZON
–
CL6–2021-ZEROPOLLUTION-01. So ia Es e ez Ri adulla
epo s inancial suppo was p o ided by Galicia Go e nmen . I he e
a e o he au ho s, hey decla e ha hey ha e no known compe ing
inancial in e es s o pe sonal ela ionships ha could ha e appea ed o
in luence he wo k epo ed in his pape .
Acknowledgmen s
This esea ch has been suppo ed by he BIORECER (No 101060684)
p ojec , unded by he Eu opean Commission HORIZON
–
CL6–2021-
ZEROPOLLUTION-01, and also by Inno augas (2022-CP060), which
ecei ed suppo om he Xun a de Galicia Go e nmen . A. A ias also
hanks he Galician Go e nmen o inancial suppo (G an e e ence
ED481B-2023–072). S. Es ´
e ez also hanks o he Spanish Minis y o
Science, Inno a ion and Uni e si ies o inancial suppo (G an e e -
ence PRE2020–092074). A. A ias, S. Es ´
e ez, G. Feijoo, and M.T. Mo -
ei a, au ho s belong o he Galician Compe i i e Resea ch G oup (GRC
ED431C 2021/37) and o he C oss-disciplina y Resea ch in En i on-
men al Technologies (CRETUS Resea ch Cen e , ED431G 2023/12).
Supplemen a y ma e ials
Supplemen a y ma e ial associa ed wi h his a icle can be ound in
he online e sion a doi:10.1016/j.wa es.2025.123125.
Da a a ailabili y
Da a will be made a ailable on eques .
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