Analyzing the production, quality, and potential uses of solid recovered fuel from screening waste of municipal wastewater treatment plants

P ocess Sa e y and En i onmen al P o ec ion 172 (2023) 950–970 A ailable online 4 Ma ch 2023 0957-5820/© 2023 The Au ho (s). Published by Else ie L d on behal o Ins i u ion o Chemical Enginee s. 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/). Analyzing he p oduc ion, quali y, and po en ial uses o solid eco e ed uel om sc eening was e o municipal was ewa e ea men plan s Juan Jesús De la To e-Bayo a , Mon se a Zamo ano a , Juan C. To es-Rojo b , Miguel L. Rod íguez c , Jaime Ma ín-Pascual a , * a Depa men o Ci il Enginee ing. Uni e si y o G anada, G anada, Spain b Juan Ca los To es, Emasag a S.A., G anada, Spain c Depa men o Depa men o Applied Ma hema ics, Uni e si y o G anada, Spain ARTICLE INFO Keywo ds: Was ewa e sc eenings Solid eco e ed uel Was e o ene gy Ci cula economy Pelle Densi ica ion ABSTRACT O e ime, was ewa e managemen e ol es in o a ci cula model, p oducing ene gy and mo ing owa ds ze o was e. The usual sc eening was e ea men is he elimina ion, wi h no ene gy eco e y p ocesses. As an al e - na i e, he p oduc ion o solid eco e ed uel (SRF) om sc eening has been s udied, bo h non-densi ied and densi ied, in pelle o m. The densi ica ion was de eloped, aking as a iables he inpu mois u e and size o he die, ob aining 20 di e en samples. The op imum pelle izing condi ions a e an inpu mois u e con en o 10% and dies wi h a comp ession a io o 6/20, 6/24 and 8/32. SRF p ope ies ha e been e alua ed based on a quali y p oposal p esen ed in his pape , which has been de eloped gi en he lack o uni o mi y in he exis ing SRF s anda ds. The SRF p oduced complies wi h uel quali y equi emen s, such as lowe calo i ic alue, wi h alues be ween 13.37 and 25.65 MJ/kg; Cl and Hg con en , wi h maximums o 0.066% and 1.0 ×10 −5 mg/MJ, espec i ely; and ash con en , be ween 7.22% and 9.85%. Ene gy om was e plan s could be he des ina ion o all he SRF p oduced. I s use in cemen plan s and gasi ica ion p ocesses, mo e es ic i e han he p e ious one, would equi e manu ac u ing p ocesses wi h adequa e mois u e le els and die size. 1. In oduc ion The pu pose o a municipal was ewa e ea men plan (WWTP) is o educe he pollu an load o wa e a e use and be o e e u ning i o he na u al en i onmen . Di e en physical, chemical, and biological ea men s a e used. A i s inle , was ewa e con ains a la ge amoun o solid ma e ial o a ying na u e ha mus be emo ed o allow he subsequen ea men s ages. This solid ma e ial gene a es was e a a i al and du ing he p e- ea men s age. Among his was e is a ac- ion consis ing o a he e ogeneous mix u e o o ganic ma e , pape , sani a y was e, and plas ics, among o he s, classi ied unde EWC code 19 08 01, desc ibed as Sc eening. I is included in subchap e 19 08 Was es om was ewa e ea men plan s no speci ied in chap e 19 Was es om was e managemen acili ies, o -si e was ewa e ea men plan s, and om he p epa a ion o wa e in ended o human consump ion and wa e o indus ial use (Eu opeo, 2014). The ypical composi ion o sc eening was e epo ed in he li e a u e is cha ac e ized by he p edominance o sani a y ex iles, whose p esence has been p og essi ely inc easing o e he yea s wi h changes in socie y’s habi s (Wid and Ho an, 2016), going om 25% in 1996 (Clay e al., 1996) o an a e age alue o 50% oday (G ego e al., 2013). Howe e , pe cen ages o 87% ha e been epo ed (Le Hya ic e al., 2009). Pape and ege ables also ha e a signi ican p esence in was e, wi h di e ences depending on he ea men plan , a ying be- ween 1.3% and 13.1% by weigh (Le Hya ic e al., 2009). The company o ines, i.e., pa icles less han 20 mm in diame e ha a e e y di icul o sepa a e, a ies be ween 7.6 (Wid and Ho an, 2016) and 15.2% (Le Hya ic e al., 2009), and, inally, he se o plas ics, me als and non-biodeg adable ma e ials do no exceed alues be ween 3.1 (Wid and Ho an, 2016) and 9.7% (Le Hya ic e al., 2009). The amoun o his sc eening was e p oduced in WWTPs accoun s o abou 2% o he o al was e gene a ed du ing he p ocess (Le Hya ic e al., 2010), wi h alues in d y ma e anging om 0.08 kg/y .heq (Le Hya ic e al., 2010) o 1.1 kg/y .heq (Kaless e al., 2016). The amoun is a ec ed by ac o s such as ain all, as a me eo ological ac o (Canle and Pe e , 2004), he design o he p e- ea men and he sc een pas- sage span used (Le Hya ic e al., 2009), o he compac ion p ocess * Co espondence o: Se e o Ochoa S , no Fuen enue a Campus, 18071 G anada, Spain. E-mail add esses: [email p o ec ed] (J.J. De la To e-Bayo), [email p o ec ed] (M. Zamo ano), [email p o ec ed] (J.C. To es-Rojo), [email p o ec ed] (M.L. Rod íguez), [email p o ec ed] (J. Ma ín-Pascual). Con en s lis s a ailable a ScienceDi ec P ocess Sa e y and En i onmen al P o ec ion jou nal homepage: www.jou nals.else ie .com/p ocess-sa e y-and-en i onmen al-p o ec ion h ps://doi.o g/10.1016/j.psep.2023.02.083 Recei ed 4 No embe 2022; Recei ed in e ised o m 17 Feb ua y 2023; Accep ed 27 Feb ua y 2023 P ocess Sa e y and En i onmen al P o ec ion 172 (2023) 950–970 951 equen ly used o elimina e he amoun o wa e con ained, which in addi ion educes i s olume (Clay e al., 1996). The p oduc ion o sc eenings is low, o example, i compa ed o he gene a ion o o he ac ions p oduced in he pu i ica ion p ocess, such as sludge, which can each alues be ween 19 and 31 kg/y .heq in d y ma e (G anados, 2015). This low amoun has been he main eason why scien i ic esea ch on sc eenings has ecei ed li le in e es o da e, especially in e ms o inding an al e na i e o hei disposal in a land ill (G anados, 2015), he mos common des ina ion o his ype o was e (Wid and Ho an, 2018). This solu ion gene a es en i onmen al p ob- lems. I also in ol es a high cos in anspo ing he was e, gi en i s high mois u e con en . A he same ime, he e a e possible p oblems ega ding he admission o was e o a land ill due o i s o ganic ma e and mois u e con en (Cada id-Rod iguez and Ho an, 2012). On he o he hand, was e disposal by land illing is bound o disappea since, wi h he new es ic ions aised in Di ec i e 850/2018 (Eu opeo e al., 2018) in 2035, he amoun by weigh o municipal was e land illed will ha e o be educed o a maximum o 10% (MITECO, 2020). The ew pape s published on al e na i es o land illing in he sc eening ea - men o u ban was ewa e ea men plan s ha e mainly ocused on anae obic diges ion and co-diges ion o he same (Boni e al., 2021). S udies ha e been conduc ed o de e mine he me hane p oduc ion po en ial o sc eenings unde di e en condi ions, such as eac o ype, p esence o solids, and e en ion ime. Resul s ha e shown a po en ial ange o me hane p oduc ion om 0.19 (Le Hya ic e al., 2010) o 1.04 L CH 4 /g VS (Boni e al., 2021). A s udy abou using sc eenings was e o p oduce ee suga s o ob ain di e en p oduc s, including bioe hanol, was also ca ied ou (Balles e os e al., 2022). Fo all hese easons, WWTP managemen companies need o look o al e na i es o he cu en disposal o sc eening was es in land ills, hus con ibu ing o ci cula i y in hei ole as esou ce p oduce s. In ecen yea s, he conside a ion o his ype o acili y as a esou ce e- co e y ac o y has been gaining g ound, and i is now common o use e ms such as was ewa e esou ce eco e y acili ies (WRRFs) in he US o bio ac o ies in San iago de Chile (Donoso-B a o e al., 2020). Among he possible al e na i es o be conside ed is ene gy eco e y, which, h ough he bio uel p oduc ion (Sheha a e al., 2022), should play a ele an ole as an al e na i e o he use o ossil uels (Yan e al., 2021). E en mo e so and ine i ably, a e he impac on he global en- e gy sec o caused by COVID-19 and agg a a ed by Feb ua y 2022, when Russia in aded Uk aine, c ea ing signi ican conce ns in he en- e gy supply (Es andabadi e al., 2022). The objec i e o solid eco e ed uel (SRF) p oduc ion is o dec ease he eliance on ossil uels in com- bus ion, gasi ica ion, and py olysis p ocesses (Nas ullah e al., 2014). By doing so, he densi ica ion o he inal p oduc no only lowe s he en i onmen al oo p in associa ed wi h managing was e (He ia achchi e al., 2019), bu also cu s he expenses o handling, anspo ing, and s o ing wood-based p oduc s along he supply chain (Whi ake and Shield, 2017). Fu he mo e, pelle izing in ag o-biowas e compos has he po en ial o educe he en i onmen al impac by o e 63% (Sa laki e al., 2021). The easibili y o he SRF p oduc ion and u iliza ion p o- cess mus be s udied in economic, social and en i onmen al e ms. Fo imp o ed decision-making, cos /bene i analyses ha e been de eloped o SRF om MSW o use in cemen plan s (Iaco idou e al., 2018) o gasi ica ion p ocesses (A ena e al., 2015). In he en i onmen al and social aspec s, an analysis wi h mo e a iables o he en i onmen al impac de i ed om he exposed p ocesses is necessa y (Aghbashlo e al., 2022). Li e Cycle Assessmen (LCA) is one o he mos use ul and es ablished me hodologies (Fe a i e al., 2021) being a powe ul compu e ized ool ha , in he case o SRF, analyzes impac s de i ed om i s p oduc ion (G osso e al., 2016) and use (B eckel e al., 2013). In his sense and conce ning al e na i es o cu en disposal o he sc eening was e, e en hough i s composi ion is simila o ha o municipal was e (Dong e al., 2010), no s udies ha e been epo ed ha analyse he possible use o WWTP sc eenings o ene gy eco e y h ough he p oduc ion o SRF. Thus, among he was es ha Sa c e al (Sa c e al., 2014). conside sui able o SRF p oduc ion, as he mos commonly used, a e ejec s om biological ea men o municipal was e (Jęd czak and Suchowska-Kisielewicz, 2018) and cons uc ion and demoli ion by-p oduc s (Nas ullah e al., 2015a) wi h EWC codes 19 12 12 and 17 09 04, espec i ely. Sc eening was es (EWC code 19 08 01) do no appea among hem. Howe e , ISO 21640:2021 (AENOR, 2021a), which in 2021 upda ed he speci ica ions and classes o EWCs, al eady conside s "solid was e om u ban was ewa e ea men " as a possible o igin. The p esen wo ks aim o s udy he u iliza ion o sc eening was e om WWTPs o p oduce non-densi ied and densi ied SRF as an al e - na i e o i s p oblema ic disposal in land ills. The de e mina ion o he p ope ies o he SRF gene a ed, and he e alua ion o i s quali y has been de eloped based on an exhaus i e s udy o he exis ing egula ions on SRF and densi ied bio uels o e alua ing he easibili y o using SRF as an al e na i e o ossil uels in combus ion o gasi ica ion p ocesses. To he bes o ou unde s anding, his is he i s ime ha solid uel p oduc ion om his was e has been e alua ed. 2. Ma e ials and me hods The wo k de eloped o achie e his se o objec i es includes he ollowing ou s ages (Fig. 1) which a e desc ibed in he ollowing sec- ions: (i) p oduc ion o SRF a a labo a o y scale; (ii) basis o es ab- lishing he quali y o he SRF p oduced; (iii) de e mina ion o he quali y o he SRF; (i ) de e mina ion o he po en ial uses o he SRF. 2.1. SRF p oduc ion a a labo a o y scale In his s udy, labo a o y-scale p oduc ion o SRF om sc eenings has been ca ied ou . Bo h non-densi ied and densi ied SRF we e p oduced. Fo his pu pose, he p oduc ion p ocess shown in Fig. 1, desc ibed below, was ollowed. 2.1.1. Collec ion o ma e ial The sc eenings used came om he Bio ac o ía Su o G anada (Spain). To wo k wi h he mos ep esen a i e ma e ial possible, se e al samples we e aken. Speci ically, 16 samples o app oxima ely 8 kg we e aken om he ou pu o he sc een compac o . Two pieces pe week, h oughou Oc obe and No embe 2021, we e collec ed on andom Nomencla u e SRF Solid eco e ed uel. WWTP Was ewa e ea men plan . EWC Eu opean was e ca alogue. WRRF Was ewa e esou ce eco e y acili y. Dd Diame e o pelle izing die. Lc Comp ession leng h o pelle izing die. Dd/Lc Comp ession a io o pelle izing die. MSW Municipal solid was e. LHV Lowe hea ing alue. N.S. No speci ied. E W Ene gy om was e plan s. Dp Pelle diame e . Lp Pelle leng h. DP Pelle densi y. BD Bulk densi y. DU Pelle mois u e. Mp Pelle mois u e. M Non-densi ied SRF mois u e. HD Ha dness. NR No ecommended. J.J. De la To e-Bayo e al. P ocess Sa e y and En i onmen al P o ec ion 172 (2023) 950–970 952 days o he week and du ing day ime and nigh - ime hou s (Fig. 2a). 2.1.2. D ying and cleaning Once each sample was ecei ed in he labo a o y, i was d ied. Fo his pu pose, he sample was sp ead on me al ays, and a e 24 h in an o en a 105 ◦C, i was mixed o be in oduced again in he o en a he same empe a u e o ano he 24 h. Once d y, he undesi able ac ions ha could a ec he p ocess, especially hose o an ine na u e, we e emo ed and p epa ed o c ushing (Fig. 2b). 2.1.3. Sh edding The d y was e was sh edded using a Viking GE450 ga den bio- sh edde wi h a powe o 2500 W (Fig. 2e), which yielded he non- densi ied SRF, shown in Fig. 2c, cha ac e ized by a ligh ma ix and a co ony appea ance, due o he high con en o sani a y ex iles. 2.1.4. S o age A po ion o he SRF p oduced was s o ed a oom empe a u e o cha ac e iza ion. The es was used o he p oduc ion o densi ied SRF. 2.1.5. Densi ica ion Finally, o p oduce he densi ied SRF, non-densi ied SRF was qua - e ed o ob ain a homogeneous sample and pelle ized using a la die ype p ess, KAHL 14–175, wi h a d i e powe o 3 kW and a eed capaci y o 50 kg/h (Fig. 2 ). The pelle izing p ocess is subjec o inpu a iables including pa icle size, mois u e, he diame e and comp es- sion leng h o he die, empe a u e (Ga cia-Ma a e e al., 2015), and he p esence o addi i es (Said e al., 2015). A e p elimina y es s, and because o he low densi y o he esidue due o he con en o sani a y ex iles, wo k was ca ied ou a in ensi ies lowe han 7 A and em- pe a u es ha did no exceed 29 ◦C. Likewise, he homogenei y in he pa icle size o he sample was no conside ed a a iable. The e o e, h ee ope a ing a iables we e conside ed o he pelle izing p ocess: mois u e o he inle s eam and he die`s diame e and comp ession leng h. In he case o mois u e, s udies o he pelle iza ion o ejec s om biological and mechanical ea men o municipal was e we e aken as a e e ence, wi h maximum mois u e pe cen ages o 45% (Za a i and Kianmeh , 2014), which allowed es ablishing ou ope a ion alues, 10%, 20%, 30% and 40%. These alues we e achie ed by sp aying he d y sample, ob ained a e he d ying and sh edding p ocesses, wi h wa e un il eaching he alues equi ed o each es , aking in o ac- coun o his pu pose he mois u e alue o he s o ed non-densi ied SRF, ob ained in i s cha ac e iza ion a he ime o i s use. In e ms o diame e (Dd) and comp ession leng h (Lc) o he pelle izing dies, which de e mines hei comp ession a io (Dd/Lc), i e a ailable dies we e used wi h diame e s o 6 o 8 mm and comp ession leng hs o 16, 20-, 24-, 32- o 48-mm. Table 1 shows he designa ion and cha ac e is ics o he i e dies used. Finally, o lowe p oduc ion cos s, and gi en ha Fig. 1. S udy phases o Solid Reco e ed Fuel (SRF). J.J. De la To e-Bayo e al. P ocess Sa e y and En i onmen al P o ec ion 172 (2023) 950–970 953 s udies o pelle p oduc ion om u ban was e showed he possibili y o manu ac u ing hem wi hou he need o add addi i es (Rezaei e al., 2020), i was decided no o use addi i es o he densi ica ion o he ma e ial. As a esul , 20 pelle samples we e ob ained, whose designa- ions a e gi en in Table 1, which we e s o ed a oom empe a u e o . 2.2. Basis o es ablishing he quali y o he SRF p oduced The quali y o he SRF p oduced was es ablished based on he clas- si ica ion o he se o p ope ies ha cha ac e ize i . These cha ac e - is ics a e ela ed. On one hand, is i s use as uel, as well as i s inal use, ega dless o i s p esen a ion in densi ied o m o no , aking in o ac- coun economic, echnical, and en i onmen al aspec s. On he o he hand, in he case o densi ied SRF, i is necessa y o conside o he p ope ies di ec ly ela ed o i s densi ied o m and which a ec i s s o age, anspo , and eeding in he he mochemical p ocesses in which i can be used. Gi en he di e si y o exis ing e e ence s anda ds, as well as he absence o speci ic s anda ds o classi y pelle s gene a ed om sc eening o simila was es (e.g., municipal solid was e), i was decided o de elop ou p oposal o o ganize he iden i ied p ope ies based on a se o exis ing s anda ds which we e used o de e mine he op imal condi ions o p oduce densi ied SRF in he o m o pelle s. Fo his pu pose, he ollowing s ages we e ollowed Fig. 1: (i) e iew o he a ailable s an- da ds; (ii) selec ion o p ope ies o he cha ac e iza ion o he p o- duced SRF; (iii) p oposal o p ope ies classi ica ion. These s ages a e desc ibed below. 2.2.1. Re iew o a ailable s anda ds In he i s place, he e iew o s anda ds applicable o manu ac u ed Fig. 2. Non-densi ied and densi ied Solid Reco e ed Fuel (SRF) p oduc ion p ocess. a) Was e a e collec ion. b) D y was e. c) Non-densi ied SRF. d) Densi ied SRF. e) Bio sh edde Viking GE450. ) KAHL 14–175 Pelle ize . J.J. De la To e-Bayo e al. P ocess Sa e y and En i onmen al P o ec ion 172 (2023) 950–970 954 SRF included hose p ope ies ha e alua e i s quali y as a uel. Fo densi ied uel, his was comple ed wi h a se o p ope ies o assess he quali y o he densi ied o m as pelle s. Table 2 and Table 3 lis he s anda ds used as a e e ence o e alua e he quali y o he SRF p oduced as uel and pelle s, espec i ely, indica ing end uses, ca ego ies, and equi emen s conce ning hei p ope ies. 2.2.2. Selec ion o p ope ies o he cha ac e iza ion o he p oduced SRF Based on he e iew o a ailable s anda ds, he p ope ies conside ed o cha ac e ize he p oduced SRF we e selec ed and a e shown in Table 4, including he s anda ds analy ical me hods. In he non-densi ied SRF, he ollowing we e selec ed: LHV, Cl con- en , Hg con en , ash, and mois u e. The i s h ee, which ha e g ea ele ance om an economic, echnical, and en i onmen al poin o iew, we e selec ed because hey a e included in ISO 21640:2021 (AENOR, 2021a). Mois u e and ash con en , al hough no limi ed o ISO 21640:2021 (AENOR, 2021a), we e inco po a ed because hey a e p esen in mos o he s anda ds included in he ISO/TR 21916:2021 epo (ISO/TC 300, 2021). The epo men ioned abo e consis s o an ex ensi e s udy on he quali y o SRFs based on a li e a u e e iew and consul a ions wi h p oduce s, concluding ha in 99% o he exposed cases, he mois u e and ash con en o he SRFs p oduced is e alua ed. On he o he hand, o he p ope ies inco po a ed in some o he s an- da ds (Table 2), such as pa icle size and densi y, we e conside ed o li le ele ance o his wo k since, in addi ion o being p esen in only h ee o he ele en s anda ds e iewed, he p oduc ob ained, as indi- ca ed abo e, is di icul o b eak down in o pa icles. Finally, he con en o o he hea y me als, in addi ion o Hg, was no conside ed due o he na u e o he was e ob ained. In he case o densi ied SRF, a o al o ele en p ope ies we e used, i e o hem we e included in he cha ac e iza ion o non-densi ied SRF and six addi ional ones a e ela ed o he condi ioning o SRF in pelle o m, including diame e , leng h, pelle densi y, bulk densi y, du abili y, and ha dness. Diame e and leng h a e p esen in all s anda ds; bulk densi y and du abili y a e in all bu one, and pelle densi y is in hal o he e ised s anda ds. Finally, ha dness was included, despi e no being included in any o he s anda ds e iewed (Ga cía-Ma a e e al., 2011), because i is a p ope y linked o pelle handling and s o age (Said e al., 2015), and i has been ex ensi ely analysed in nume ous s udies such as o e ac ion analysis (Hayki i-Acma and Yaman, 2022) o he e ec o addi i es in pelle s (Nu sani e al., 2020), including manusc ip s ha ocus on he ela ion o ha dness o o he uel pa ame e s (Su yawan Table 1 Denomina ion o pelle samples p oduced. J.J. De la To e-Bayo e al. P ocess Sa e y and En i onmen al P o ec ion 172 (2023) 950–970 955 e al., 2022). As a esul o he abo e analysis, Table 5 and Table 6 show he s anda ds, p ope ies, and he included alues applied o he SRF wi hou densi ica ion and SRF pelle s, espec i ely. The e e ence uni s we e aken om ISO 21640 (AENOR, 2021a). I was necessa y o con e uni s o some s anda ds. In he case o Hg con en , and gi en he impossibili y o uni con e sion, i was decided o include he wo uni s ha appea in he s anda ds. On he o he hand, i was obse ed ha he e e ence alues used o mois u e con en o non-densi ied and densi ied SRF a e di e en ; his is because mois u e, unlike LHV, and ash, Cl, and Hg con en s, is a p ope y ha a ec s he logis ics o SRF, so i was e alua ed based on he pelle s anda ds, in addi ion o being condi ioned by he manu ac u ing p ocess. Finally, ha dness was ana- lysed as a ele an p ope y o SRF, bu i does no appea in any s an- da d. So, i was compa ed, based on he li e a u e which conside s i a pe inen pa ame e in pelle quali y. 2.2.3. P oposed classi ica ion o p ope ies Gi en he absence o an SRF p ope y classi ica ion applicable o he speci ic case o he was e unde conside a ion and based on he alues es ablished in he s anda ds analysed o he selec ed p ope ies (Table 4), a p oposal will be p epa ed o lead o a classi ica ion ha includes ou ca ego ies, acco ding o he le els indica ed below: •Class 1 (C1). I will co espond o he ange o op imum alues o he p ope y unde conside a ion and includes hose alues me in 100% o he s anda ds selec ed o his s udy. •Class 2 (C2). I will co espond o a e age quali y alues o he p ope y unde conside a ion and includes a ange ha me a leas 50% o he s anda ds selec ed o his s udy wi hou eaching 100%. •Class 3 (C3). I will co espond o low-quali y alues o he p ope y unde conside a ion and includes a ange ha me a leas 25% o he s anda ds selec ed o his s udy wi hou eaching 50%. •No ecommended (NR). Finally, i he alue o p ope y esul s in quali y ou side he limi s o be es ablished in he indica ed classes, i will be conside ed unsui able o no ecommended, co esponding o alues included in less han 25% o he consul ing s anda ds. 2.3. De e mina ion o he quali y o he SRF p oduced To de e mine he quali y o he SRF p oduced, he analy ical me hods lis ed in Table 6 we e applied. Each de e mina ion was pe - o med in iplica e o ob ain an a e age alue. In he case o densi ied SRF, o de e mine he mos sui able p oduc ion condi ions, he co e- la ion be ween he independen a iables (ini ial humidi y, comp ession leng h, and die diame e ) and pelle p ope ies was s udied (Table 4) using R (V. 4.1.1), a ee p og amming en i onmen and language wi h a ocus on s a is ical analysis. Table 2 Quali y o Solid Reco e ed Fuel (SRF) as uel. Re e ence s anda ds. S anda d Applica ion a ea Final use Classes Included p ope ies LHV a Cl Hg Mois u e Ash Pa icle size/ densi y Hea y me al ISO 21640:2021 Solid eco e ed uels — Speci ica ions and classes ( AENOR, 2021a). In e na ional N.S. b ✓ ✓ ✓ ✓ UNI 9903–1:2004 Non mine al e use de i ed uels - Speci ica ions and classi ica ion (En e Nazionale I aliano di Uni icazione UNI, 2004). I aly Cemen plan s, E W ✓ ✓ ✓ ✓ ✓ ✓ ✓ A ˆ e ´ e du 23 mai 2016 ela i ` a la p ´ epa a ion des combus ibles solides de ´ e cup´ e a ion en ue de leu u ilisa ion dans des ins alla ions ele an de la ub ique 2971 de la nomencla u e des ins alla ions class´ ees pou la p o ec ion de l′en i onnemen ( L′´ ene gie e de la me Minis ` e e de l′en i onnemen , 2016). F ance E W c ✓ ✓ ✓ ✓ RAL-GZ 724 (2008) Quali y and es ins uc ions Solid Reco e ed Fuels (Gü egemeinscha Sekund¨ a b enns o e und und und, G.P. ü S. e. V, 2008). Ge many Cemen plan s, lime kilns, E W ✓ ✓ ✓ ✓ ✓ ✓ ✓ WRAP. A classi ica ion scheme o de ine he quali y o was e de i ed uels (Was e and Resou ces Ac ion P og amme, 2013). Uni ed Kingdom E W ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ No. 389/2002 in he Incine a ion Was e, BGBI ( BMLFUW, 2002). Aus ia Cemen plan , E W, Co- incine a ion ✓ ✓ ✓ ✓ ✓ ✓ Limi alues se by au ho i ies o indi idual pe mi s o cemen plan s in Spain (Scho ch e al., 2013). Spain Cemen plan s ✓ ✓ ✓ Limi alues se by au ho i ies o indi idual pe mi s o cemen plan s in Belgium (Scho ch e al., 2013). Belgium Cemen plan s ✓ ✓ ✓ SFS 5875 (2000) Solid Reco e ed Fuel - Quali y Con ol Sys em (Gene al Indus y Fede a ion, 2008). Finland Incine a ion, Co- incine a ion ✓ ✓ ✓ ✓ Guidelines on Usage o Re use De i ed Fuel in Va ious Indus ies. D a o July 2018 (Heal h e al., 2018). India Cemen plan s ✓ ✓ ✓ ✓ ✓ ✓ Ac on he P omo ion o Sa ing and Recycling o Resou ces En o cemen Regula ion (Addendum 7) ( R. o Ko ea, 2002) Sou h Ko ea N.S. ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ a LHV: Lowe hea ing alue. b N.S.: No speci ied. c E W: Ene gy om was e plan s J.J. De la To e-Bayo e al. P ocess Sa e y and En i onmen al P o ec ion 172 (2023) 950–970 956 2.4. De e mina ion o he po en ial uses o he p oduced SRF Finally, aking ISO/TR 21916:2021 (ISO/TC 300, 2021) as a e e - ence, h ee po en ial uses will be conside ed o he SRF p oduced: cemen plan s, powe plan s, and gasi ica ion. The minimum and maximum alues o be aken as e e ence es ablished o he SRF p ope ies conside ed in he p e ious epo (LHV, Cl con en , Hg con- en , ash, and mois u e) a e shown in Table 7. 3. Resul s and discussion The non-densi ied and densi ied SRF we e p oduced a a labo a o y scale acco ding o he desc ibed p ocedu e. Then we p oceeded o es ablish he basis o de ining he classi ica ion o i s p ope ies, based on which samples we e cha ac e ized and classi ied, and hei po en ial use was ound. The esul s ob ained a e p esen ed, analysed, and dis- cussed below. 3.1. P oposed classi ica ion o SRF p ope ies Taking in o accoun he c i e ia es ablished in he me hodology desc ibed abo e and he p ope ies and alues included in he e ised s anda ds (Table 5 and Table 6), a classi ica ion p oposal o hese p ope ies was p epa ed, es ablishing limi alues o he di e en classes de ined (Class 1, Class 3, Class 3, and No ecommended). Fig. 3 and Fig. 4 show he p oposed anges, wi h he limi alues es ablished o each class and p ope ies conside ed o he non-densi ied and densi ied SRF. 3.2. SRF cha ac e iza ion Once he SRF was manu ac u ed, i was cha ac e ized by de e - mining he p ope ies and analy ical me hods shown in Table 4. Resul s a e shown in Table 8 and Table 9, which show he alues ob ained o each p ope y and i s class acco ding o he p oposed classi ica ion. The esul s a e p esen ed and discussed below. 3.2.1. Cha ac e is ics o he non-densi ied SRF The alues de e mined o he p ope ies o he non-densi ied SRF samples and hei classi ica ion a e shown in Table 8. Fo cla i y, a colou code, including g een, yellow, o ange, and ed, was used o classes C1, C2, C3, and NR, espec i ely. Sh edding he esidue a he labo a o y le el equi ed e y high d ying o ob ain an SRF wi h 4.5% mois u e, which canno be conside ed a ealis ic op ion a an indus ial scale. To comple e he s udy, esul s a e included based on mois u e le els co esponding o he limi s es ablished o his p ope y o each p oposed class (20%, 25%, and 35%). The esul s ob ained a e discussed below. 3.2.1.1. Lowe hea ing alue. De ined as he economic pa ame e wi hin he equi emen s o cha ac e iza ion as SRF (Ma ignon, 2020), his is a s anda d ha measu es he o al ene gy con en p oduced as hea when a subs ance is bu ned (E im e al., 2022). The esul s o SRF p oduced a a labo a o y scale (Table 8) p esen ed a alue o 22.93 MJ/kg o a mois u e con en o 4.5%. This alue dec eases wi h inc easing he mois u e con en o 13.37 MJ/kg o 35% wa e con en . The LHV, on a d y basis, was 24.29 MJ/kg, highe han ha e e enced o SRF gene a ed om was e ea men plan ejec s o incine a ion o Table 3 Quali y o Solid Reco e ed Fuel (SRF) as pelle . Re e ence s anda ds. S anda d Applica ion a ea Ex ac ion Final Use Classes Included p ope ies Dp a Lp b PD c BD d DU e Mp Ash LHV g Chemical elemen s ISO 17225:2021 Biocombus ibles s´ olidos. Especi icaciones y clases de combus ibles (AENOR, 2021b) In e na ional Wood o he baceous biomass Comme cial and esiden ial applica ions. Indus ial. ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ O NORM M7135 (O NORM M, 7135, 2002) Aus ia Wood o he baceous biomass Indus ial ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ DIN 51731 and DIN PLUS ( No m, 2002) Ge many Wood o he baceous biomass Speci ic boile s o pelle s. Indus ial ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ Ag o and Ag oþ(Na a e al., 2012) F ance Ag icul u al o igin Incine a ion, boile s o u naces. ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ SS187120 Sweden N.S. N.S. h ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ Pele Fuel Ins i u e S anda ds (SS20 Pele Fuel Ins i u e S anda ds, 1871, 2014) Uni ed S a es o Ame ica Wood N.S. ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ NY/T 1878–2010 (R.K.L. o R. E. Minis y o Ag icul u e, 2010) China Wood o he baceous biomass N.S. ✓ ✓ ✓ ✓ ✓ JAS S anda ds o Wood Pelle s o Non-Indus ial Use (F. and F. Minis y o Ag icul u e, 2021) Japan Wood Non indus ial ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ a Dp: Pelle diame e . b Lp: Pelle leng h. c PD: Pelle densi y. d BD: Bulk densi y. e DU: Du abili y. Mp: Pelle mois u e. g LHV: Lowe hea ing alue. h N.S.: No speci ied J.J. De la To e-Bayo e al. P ocess Sa e y and En i onmen al P o ec ion 172 (2023) 950–970 957 co-incine a ion, wi h alues anging om 20.06 MJ/kg (Mon ejo e al., 2011) o 22.13 MJ/kg (Edo-Alc´ on e al., 2016). The esul s ob ained place he SRF p oduced in class C1 o h ee o he ou samples, wi h class C2 co esponding o he sample co esponding o 35% mois u e. 3.2.1.2. Cl con en . F om he combus ion poin o iew, low Cl con en educes ad e se e ec s such as co osion, slagging, and ouling in boile s (Ro e e al., 2011). In addi ion, a s udy on he emission o nano- pa icles by con en ional and ad anced echnology no ed ha he lowe p esence o Cl sugges ing p edomina ely biodeg adable sal s, bu no oxic me als (Panessa-wa en e al., 2022). The Cl pe cen age was de e mined d yly, so i s con en does no a y wi h humidi y, eaching a alue o 0.031% (Table 8). The alues ob ained a e lowe han hose e e enced in he case o samples gene a ed om u ban was e in he s udies o Mon an´ e e al (Mon ane e al., 2013)., Nas ullah (Nas ullah e al., 2015b), and Velis (Velis e al., 2012) who ob ained simila alues, speci ically 0.65%, 0.60%, and 0.69% espec i ely. The highe Cl con- en e e enced in he s udies abo e is mo i a ed by he mo e signi ican p esence o igid plas ics such as PVC (Rada and Ragazzi, 2014; Ma e al., 2008). These plas ics a e p ac ically non-exis en in he SRF p oduced, wi h a majo p esence o sani a y ex iles which, e en hough hey include plas ics in hei composi ion, a e mainly composed o syn he ic ib es (Ma ques e al., 2020). Wi h he alue ob ained, he Cl con en complies wi h he equi emen s o class C1 (Table 8). 3.2.1.3. Hg con en . The Hg con en ep esen s he en i onmen al ac- o o he SRF, measu ing he possible oxici y caused by i s combus ion (Iaco idou e al., 2018). I s cha ac e iza ion is pe o med on a we basis, p o iding con en s o labo a o y-p oduced SRF ha anged be ween 1.0 ×10 −5 and 5.9 ×10 −6 mg/MJ (Table 8) o samples SD-35 and SD-4.5, espec i ely. These alues a e lowe han he 6.9 ×10 −3 mg/MJ epo ed by Ranie i e al (Ranie i e al., 2017). o SRF p oduced om municipal was e. I he a e age Hg con en is w i en conce ning he mass o he SRF made, esul s o 1.3 ×10 −4 mg/kg a e ob ained. This is lowe han he 9.0 ×10 −2 mg/kg ound in he li e a u e (Ramos Casado e al., 2016). The Hg con en would gi e he SRF gene a ed om sc eening class C1 (Table 8) in any o he samples p oduced. 3.2.1.4. Ash con en . De e mina ion o he amoun o ash quan i ies he amoun o ine ma e ials p esen in he SRF, which in his s udy was 9.4% in all samples (Table 8) since i is de e mined on a d y basis. I his alue is compa ed wi h ha epo ed in s udies o SRF p oduced om ejec s coming om u ban was e, i is obse ed ha hey a e highe , as Table 4 P ope ies analyzed o de e mine he quali y o he manu ac u ed Solid Reco - e ed Fuel (SRF). SRF ype P ope ies Uni S anda d analy ical me hod Densi ied SRF Non- densi ied SRF Lowe Hea ing Value (LHV) MJ/ kg UNE-EN 15400:2011 ( AENOR, 2011a) Cl Con en % UNE-EN ISO 10304–1:2009 (AENOR, 2009) Hg Con en mg/ MJ UNE-EN 15411:2012 ( AENOR, 2012a) Ash Con en % UNE-EN 15403:2011 ( AENOR, UNE-EN 3, 1540, 2011) Mois u e (M, o non densi ied SRF). (Mp, o densi ied SRF) % UNE-EN 15414–3:2011 ( AENOR, 2011b) Pelle Diame e (Dp) mm UNE-EN 16127:2012 ( AENOR, 2012a) Pelle Leng h (Lp) mm UNE-EN 16127:2012 ( AENOR, 2012a) Pelle Densi y (PD) kg/ m 3 UNE-EN 15150:2012 ( AENOR, 2012b) Bulk Densi y (BD) kg/ m 3 UNE-EN 15103:2010 ( AENOR, 2010a) Du abili y (DU) % UNE-EN 15210–1:2010 ( AENOR, 2010b) Ha dness (HD) kg De e mina ion made by using a manual ha dness es e (Amandus Khal mod. 21465) ( Ga cia-Ma a e e al., 2015) Table 5 S anda ds and ecommended alues o he uel p ope ies o Solid eco e ed uel (SRF) a . S anda d LHV b Cl Hg Ash M c MJ/kg % mg/MJ mg/ kg % % 1 ISO 21640:2021 Solid eco e ed uels — Speci ica ions and classes (AENOR, 2021a). ≥3 ≥25 ≤3 ≤0.2 ≤0.15 ≤0.02 2 UNI 9903–1:2004 Non mine al e use de i ed uels - Speci ica ions and classi ica ion (En e Nazionale I aliano di Uni icazione UNI, 2004). ≥15 ≥25 ≤1 ≤3 ≤20 ≤15 ≤25 ≤15 3 A ˆ e ´ e du 23 mai 2016 ela i ` a la p ´ epa a ion des combus ibles solides de ´ e cup´ e a ion en ue de leu u ilisa ion dans des ins alla ions ele an de la ub ique 2971 de la nomencla u e des ins alla ions class´ ees pou la p o ec ion de l′en i onnemen (L′´ ene gie e de la me Minis ` e e de l′en i onnemen , 2016). ≥12 ≤1.5 ≤3 4 RAL-GZ 724 (2008) Quali y and es ins uc ions Solid Reco e ed Fuels (Gü egemeinscha Sekund¨ a b enns o e und und und, G.P. ü S. e. V, 2008). ≥13 ≥27 ≤1 ≤0.7 ≤1 ≤0.5 ≤20 ≤9 ≤35 ≤12.5 5 WRAP. A classi ica ion scheme o de ine he quali y o was e de i ed uels (Was e and Resou ces Ac ion P og amme, 2013). ≥6.5 ≥25 ≤0.8 ≤0.2 ≤0.12 ≤0.04 ≤50 ≤10 ≤40 ≤10 6 No. 389/2002 in he Incine a ion Was e, BGBI (BMLFUW, 2002). ≥11 ≥25 ≤1.5 ≤0.8 ≤0.075 ≤35 ≤10 7 Limi alues se by au ho i ies o indi idual pe mi s o cemen plan s in Spain (Scho ch e al., 2013). ≤2 ≤10 8 Limi alues se by au ho i ies o indi idual pe mi s o cemen plan s in Belgium (Scho ch e al., 2013). ≤2 ≤5 9 SFS 5875 (2000) Solid Reco e ed Fuel - Quali y Con ol Sys em (Gene al Indus y Fede a ion, 2008). ≤1.5 ≤0.15 ≤0.5 ≤0.1 10 Guidelines on Usage o Re use De i ed Fuel in Va ious Indus ies. D a o July 2018 (Heal h e al., 2018). ≥12.5 ≥18.5 ≤1 ≤0.5 ≤15 ≤10 ≤20 ≤10 11 Ac on he P omo ion o Sa ing and Recycling o Resou ces En o cemen Regula ion (Addendum 7) (R. o Ko ea, 2002) ≥12.5 ≥27.2 ≤2 ≤0.3 ≤1.2 ≤0.6 ≤20 ≤4 ≤25 ≤10 a The cells wi h se e al alues show ha he s anda d es ablishes di e en classes, so he es ablished limi s a e included. b LHV: Lowe hea ing alue. c M: Mois u e o non-densi ied SRF J.J. De la To e-Bayo e al. P ocess Sa e y and En i onmen al P o ec ion 172 (2023) 950–970 958 in he case o Velis (Velis e al., 2012) o Dunnu (Dunnu e al., 2010) whose ash pe cen age was 17.3% and 15.79%, espec i ely. The ash con en ob ained allows classi ying his p ope y in he SRF p oduced, class C1 o all samples (Table 8). 3.2.1.5. Mois u e. The low mois u e con en o he SRF allows consid- e able ene gy cos sa ings (Mohammed e al., 2017), as i is di ec ly ela ed o ene gy alue and anspo a ion (Hilbe e al., 2007). Due o he need o lowe he mois u e con en as much as possible o acili a e he sh edding p ocess, he mois u e con en o he SRF p oduced om sc eening was 4.5% (Table 8), a ela i ely low alue compa ed o o he s udies. S udies o SRF made om u ban was e ha e e e enced mois- u es o be ween 15 (Nas ullah e al., 2015b) and 25% (Rada and Ragazzi, 2014). This implies ha , on an indus ial scale, i could be p oduced wi h highe mois u e alues, hus educing p oduc ion cos s, aking as a e e ence he limi s conside ed o his p ope y, i.e., 20%, 25%, and 35%. Conside ing all o he abo e in he analysis o he di e en p ope ies ha ha e been included in he cha ac e iza ion o he non-densi ied SRF, i can be concluded ha all he samples p oduced would comply wi h he es ablished limi s, and none o hem would be classi ied as no ecom- mended. On he o he hand, he samples p oduced wi h lowe mois u e alues (4.5% and 20%) would ha e all hei p ope ies classi ied as C1, i. e., hey would allow ob aining he uel wi h he highes quali y. In he case o mois u e alues o 25%, o he p oduc ion o SRF, only his p ope y would be a ec ed, and i would be classi ied in a lowe ca e- go y, C2. Finally, he p oduc ion o SRF om sc eening wi h 35% mois u e, classi ied as C3, would also sligh ly educe i s quali y due o he e ec o mois u e on i s LHV, which would be classi ied as C2. 3.2.2. Cha ac e is ics o he densi ied SRF The alues and classi ica ion o each o he p ope ies analysed o he 20 pelle samples manu ac u ed, he co ela ion wi h he p ocess inpu a iables, and he compa ison o he esul s ob ained om o he s udies a e p esen ed below. A e age alues and s anda d de ia ion ob ained o he p ope ies de e mined o samples a e shown in Table 9, and hei classi ica ion acco ding o he colou code is desc ibed. Fig. 5 shows he co ela ion be ween he inpu a iables (mois u e, diame e , and comp ession leng h) and he chemical (LHV, Cl, Hg, and ash con en s), physical (mois u e, diame e , leng h and densi y o he pelle s, and bulk densi y), and mechanical (ha dness and du abili y) p ope ies o he pelle s p oduced; he co ela ion coe icien s a e shown also. When an inc ease in one accompanies an inc ease in he alue o ano he one o he a iables, i will be conside ed a posi i e o di ec co ela ion, ep esen ed in Fig. 5 wi h a ange o blue colou s. Con e sely, i a dec ease in one a iable accompanies an inc ease in ano he , he co ela ion is nega i e o in e se, ep esen ed in a ange o ed colou s. A co ela ion coe icien o 1 implies a pe ec and posi i e co ela ion. On he con a y, he alue −1.00 implies an ideal and nega i e co ela ion, and inally, he alue 0 means ha he e is no Table 6 S anda ds and ecommended alues o Solid Reco e ed Fuel (SRF) pelle p ope ies a . S anda d Mp b Dp c Lp d PD e BD DU g % mm mm kg/m 3 kg/m 3 % 1 ISO 17225:2021 Biocombus ibles s´ olidos. Especi icaciones y clases de combus ibles (AENOR, 2021b) ≤10 ≤12 ≤15 ≥6 ≤25 ≥3.15 ≤50 ≥550 ≤750 ≥96.0 ≥97.7 2 O NORM M7135 (O NORM M, 7135, 2002) ≤10 ≥4 ≤10 ≥20 ≤50 ≥1120 ≥540 ≥97.7 3 DIN 51731 and DIN PLUS (No m, 2002) ≤10 ≤12 ≥4 ≤10 ≥20 ≤50 ≥1000 ≥540 ≥97.7 4 Ag o and Ag o+(Na a e al., 2012) ≤11 ≤15 ≥6 ≤8 ≥10 ≤30 ≥1200 ≤1400 ≥580 ≥92 5 SS187120 ≤10 ≤12 ≤25 ≥3.15 ≤40 ≥500 ≥98.5 ≥99.2 6 Pele Fuel Ins i u e S anda ds (SS20 Pele Fuel Ins i u e S anda ds, 1871, 2014) ≤8 ≤10 ≥5.84 ≤7.25 ≥3.15 ≤38.1 ≥609 ≤737 ≥95 7 NY/T 1878–2010 (R.K.L. o R.E. Minis y o Ag icul u e, 2010) ≤13 ≤25 ≥3.15 ≤40 ≥1000 8 JAS S anda ds o Wood Pelle s o Non-Indus ial Use (F. and F. Minis y o Ag icul u e, 2021) ≤10 ≥6 ≤8 ≥3.15 ≤40 ≥600 ≥96.5 a The cells wi h se e al alues show ha he s anda d es ablishes di e en classes, so he es ablished limi s a e included. b Mp: Pelle mois u e c Dp: Pelle diame e . d Lp: Pelle leng h. e PD: Pelle densi y. BD: Bulk densi y. g DU: Du abili y. Table 7 Maximum and minimum alues e e enced o he use o he Solid Reco e ed Fuel (SRF). Uses P ope ies LHV a (MJ/kg) Cl (%) Hg (mg/MJ) Ash (%) M b o Mp c (%) Cemen plan s 15.6–32.4 0.05–3.89 N.S. d 5.27–30.60 1.4–35.0 E W e 13.24–32.98 0.10–1.16 0.001–0.209 7.40–23.60 3.8–34.1 Gasi ica ion 15.4–25 0.26–0.65 0.02–0.04 6.30–21.20 2.5–15.0 a LHV: Lowe hea ing alue. b M: Mois u e o non-densi ied SRF. c Mp: Pelle mois u e. d N.S.: No speci ied e E W: Ene gy om was e plan . J.J. De la To e-Bayo e al. P ocess Sa e y and En i onmen al P o ec ion 172 (2023) 950–970 965 diame e dies p edomina es, al hough some s udies wi h la ge di- ame e s o 16, 18, and 20 mm ha e also been e e enced (Jewia z e al., 2020). The alues ob ained in he case o leng h ha e shown la ge a i- abili y, wi h a minimum o 17.79 mm (P-30-D8L32) and a maximum o 36.80 mm (P-20-D8L16), as shown in Table 9. Also, he e was a weak posi i e co ela ion wi h die diame e , a weak nega i e co ela ion wi h comp ession leng h, wi h a co ela ion coe icien o −0.33, and close o mode a ely nega i e, wi h a coe icien o −0.4, in he case o inpu mois u e (Fig. 5). The e ec o inle mois u e is highe , as shown in Table 9, in he case o pelle s manu ac u ed wi h a diame e o 8 mm. Al hough, in some cases, hey a e highe , he leng h alues ob ained could be conside ed simila o hose o o he s udies, wi h alues ha ha e a ied be ween 20 (Wang e al., 2018) and 24 mm (Nu sani e al., 2020). The esul s ob ained o he p ope ies ha de ine he size o he pelle s made i possible o classi y hem in o se e al o he es ablished classes. By diame e (Table 9), six o he samples would be classi ied as class C1, all o hem p oduced by 6 mm diame e dies, while he emaining 14, co esponding o pelle s manu ac u ed wi h 8 mm diame e dies, would be included in class C2. Rega ding he leng h (Table 9), 16 o he 20 samples co espond o Class C1, while he emaining ou all in o Class C2. Wi h he M1, M2 and M5 dies, pelle s classi ied as Class C1 we e p oduced. In he case o he M3 and M4 dies, Class C2 pelle s we e p oduced wi h 10% and 20% and 30% and 40% mois u e con en , espec i ely. 3.2.2.7. Pelle densi y. Pelle densi y is a undamen al pa ame e because low-densi y pelle s a e mo e easily b oken and decomposed (Ga cia-Ma a e e al., 2015; Leh ikangas, 2001). Acco ding o he li e a u e e iewed, he use o high-densi y bio uels gene ally imp o es combus ion (Jewia z e al., 2020), gasi ica ion (Nixon e al., 2013), and py olysis p ocesses (Chen e al., 2014), al hough he e a e s udies ha a gue ha a e y high pelle densi y could gene a e combus ion p ob- lems (Ta aso e al., 2013). Table 9 and Fig. 6 show he densi y alues o he manu ac u ed pelle s, which a ied be ween 522.61 and 1198.03 kg/m 3 o samples P- 40-M4 and P-10-M1, obse ing he e ec ha mois u e has on he p o- duc ion p ocess. In ac , Fig. 5 shows a high in e se co ela ion be ween pelle densi y and mois u e o he inpu s eam, wi h a co ela ion co- e icien o −0.88 (Fig. 5). Also, in he case o he a iables ela ed o pelle die cha ac e is ics, an in e se co ela ion is obse ed in bo h cases, bu i is e y weak in he case o comp ession leng h and weak o die diame e , wi h co ela ion coe icien s o −0.06 and −0.38, espec i ely (Fig. 5). Compa ing hese esul s wi h hose e e enced in o he s udies, i becomes clea ha hey a e compa able o hose o o he s udies in he case o pelle s p oduced wi h low eed s eam humidi y alues (10% and 20%). Thus, Ramos Casado (Ramos Casado e al., 2016) p oduced pelle s om he ejec s o mechanical biological ea men plan s o municipal was e, eaching a densi y o 1050 kg/m 3 . A e o e ac ion o such was e, Ma e al (Ma e al., 2022). p oduced pelle s wi h densi ies ha a ied be ween 994.78 and 1208.86 kg/m 3 , depending on he o e- ac ion and pelle iza ion empe a u e. Meanwhile, mix u es o di e en was e ac ions p esen in MSW we e pelle ized, eaching alues ha a ied be ween 1040 and 1199.5 kg/m 3 . The minimum alue co e- sponded o he composi ion wi h a lowe pe cen age o pape (Rezaei e al., 2020). Finally, s udies o densi ica ion o sewage sludge mixed wi h biomass allowed ob aining pelle s wi h densi ies anging om 851.2 o 1270.3 kg/m 3 (Jiang e al., 2014). Wi h inc easing inle s eam mois u e up o 30% and 40%, pelle densi y alues we e educed o alues below he minimum alue e e enced by Jiang e al (Jiang e al., 2014). o sewage sludge wi h biomass. The pelle densi y esul s ob ained allowed classi ying his p ope y in he di e en es ablished classes (Fig. 6), wi h a p edominance ( ou een o he wen y samples analysed, 75%) o hose being classi ied as no ecommended. Fu he mo e, none o he samples p oduced was classi ied as class C1, only one as C2 (pelle ed a 10% mois u e), and i e as C3 (pelle ed a 10% and 20% mois u e). The low-densi y alues a e explained by he use o e e ence alues o es ablish he classi ica ion based on s anda ds applicable o ag icul u al was e, which usually epo highe alues such as 1327 kg/m 3 o oli e wood (Ga cia-Ma a- e e al., 2015), 1260 kg/m 3 o ice s aw (Said e al., 2015), o 1198 kg/m 3 o pelle s p oduced om al al a (Sa ke e al., 2015). Howe e , he composi ion o he ini ial sc eening is cha ac e ized by he high p esence o low-densi y ac ions (52.1% o sani a y ex iles and 11.7% pape and ca dboa d). These alues could be inc eased by adding a binde , as epo ed in he s udy by Nu sani e al (Nu sani e al., 2020). which p oduced pelle s wi h a densi y be ween 988 −1009 kg/ m 3 om u ban was e. 3.2.2.8. Bulk densi y. Some o he p oblems de i ed om he low bulk densi y o SRF is he need o high s o age olumes, inc eased ans- po a ion cos s, as well as di icul ies in eeding (Lomas Es eban e al., 2001), hence he impo ance o he analysis o his p ope y, which in his s udy eached alues be ween 301.07 and 517.53 kg/m 3 o samples P-40-D8L16 and P-10-D8L32 (Table 9), espec i ely. The e ec o inle s eam mois u e was obse ed (Fig. 6). This ansla es in o a s ong in- e se co ela ion be ween bulk densi y and inle s eam mois u e, wi h a co ela ion coe icien o −0.89 (Fig. 5). In he case o comp ession leng h and die diame e , he obse ed co ela ions we e weakly posi i e and e y weakly nega i e, wi h co ela ion coe icien alues o 0.26 and −0.07, espec i ely (Fig. 5). Compa ing hese alues wi h hose ob ained in o he MSW pelle - izing s udies, i becomes clea ha hey a e compa able o hose e e - enced in o he s udies o hose p oduced wi h low eed s eam mois u es (10% and 20%). MSW pelle izing s udies show bulk densi ies ha a ied be ween 383.9 (Nu sani e al., 2020) and 540 kg/m 3 (Ramos Casado e al., 2016). In ano he s udy, Ri e a (Ri e a, 2018) epo ed alues be ween 420 and 510 kg/m 3 . The esul s o his p ope y, shown in Table 9, allow he samples o be classi ied in o he es ablished classes. None o he samples p oduced was classi ied as class C1 and C2 o his p ope y. Th ee o hem, co - esponding o an inle s eam mois u e con en o 10%, we e classi ied as C3, while he emaining 17 (85% o he samples p oduced) eached bulk densi ies below 500 kg/m 3 , and he e o e, we e classi ied as no ec- ommended. Again, he low-densi y alues a e explained by he p esence o low-densi y ac ions in he was e and he use o e e ence alues o es ablish he classi ica ion based on s anda ds applicable o ag icul u al was e, which usually epo highe alues. In ac , in he case o pelle s p oduced om a ious biomasses, acco ding o a e iew, he densi y alues we e ound o be highe han 600 kg/m 3 (Mi anda e al., 2015a). These alues we e epo ed o pelle s om oli e pomace wi h 780 kg/m 3 (Mi anda e al., 2012) and oak and Sco s pine wood wi h 678 (Mi anda e al., 2009) and 675 kg/m 3 ( Filbakk e al., 2011 ) , espec i ely, o whea s aw wi h a bulk densi y o 620 kg/m 3 (Ve ma e al., 2012). The alues o bulk densi y could be inc eased by adding a binde , as epo ed in some s udies ce i ying ha binde s s eng hen he cohesion be ween pa icles and inc ease he densi y, bo h pa icle and bulk (Ju e al., 2020; ZDANOWICZ and CHOJNACKI, 2017). 3.2.2.9. Du abili y. Du abili y is an essen ial pa ame e conce ning anspo a ion and logis ics (Jewia z e al., 2020). I can be conside ed a e e ence p ope y o SRF pelle condi ioning (Said e al., 2015). High du abili y is synonymous wi h high-quali y (Za a i and Kianmeh , 2014) as i a oids he gene a ion o ine pa icles ha could inc ease pollu an emissions and e en heal h isks (Mi anda e al., 2015b). Table 9 and Fig. 6 show he du abili y alues o he manu ac u ed pelle s, which anged om 62.63% o 99.76%, o samples P-40-D8L32 and P-10–48, espec i ely. Fig. 5 shows a s ong in e se co ela ion be ween J.J. De la To e-Bayo e al. P ocess Sa e y and En i onmen al P o ec ion 172 (2023) 950–970 966 du abili y and inle s eam mois u e, wi h a coe icien o −0.60. The e ec o die diame e and comp ession leng h is no signi ican , wi h obse ed co ela ion coe icien alues o −0.22 and −0.09, espec- i ely (Fig. 5), also implying an in e se co ela ion bu in his case weak and e y weak. The analyses o du abili y alues ob ained in o he s udies o densi ied SRF p oduc ion om MSW show simila alues, such as hose ob ained om MSW ejec s wi h du abili y o 96.8% (Ramos Casado e al., 2016). In a wo k whe e wa e con en was analysed as a a iable, 93.10% and 98.72% du abili ies we e ob ained wi h inpu s eam mois u e alues o 30% and 15%, espec i ely (Rezaei e al., 2020). Conside ing pelle izing empe a u e as a a iable, he maximum du a- bili y (96%) was eached a 120 ◦C (Jewia z e al., 2020). Highe du abili y alues ha e been ound in he case o o e ied biodeg adable p oduc s om MSW, wi h 99.67% (Ma e al., 2022) and up o 99% imp o ing he pelle by adding 6% binde (Nu sani e al., 2020). The pelle s p oduced om ubbe wood and was e de i a i e mix u es p e- sen ed high du abili y le els (98.27–99.07%) (Laosena e al., 2022). The du abili y esul s conce ning he inpu a iables (Fig. 6) allow placing he samples in he es ablished classes, p edominan ly class C2, which includes 50% o hem, ollowed by C3 wi h ou samples, and C1 wi h 3. Finally, only 3 o he samples p oduced we e conside ed no ecommended, wi h alues lowe han 92%, all o hese co esponded o inle cu en humidi y alues o 40%. 3.2.2.10. Ha dness. As men ioned in he me hodology, he impo ance o his p ope y lies in handling and s o age, as well as in he combus ion p ocess i sel , whe e adequa e ha dness is equi ed o a oid c ushing and de o ming he pelle s (Said e al., 2015; Gilbe e al., 2009), which causes di icul ies in he boile ope a ion due o occasional blocking o he sc ew con eyo , ega dless o he he mal boile load (Ga cia-- Ma a e e al., 2014). The esul s ob ained o his p ope y in he SRFs sc eening co e a b oad spec um o alues, wi h a minimum o 3.33 kg and a maximum o 20 kg o samples P-40-D8L32 and P-10-D8L48, espec i ely (Table 9). Rega ding he ela ionship o his p ope y wi h he inpu a iables, a s ong in e se co ela ion was obse ed be ween ha dness and inpu mois u e, wi h a co ela ion coe icien o −0.3, which is also e iden in Fig. 5. The co ela ion was also ha m ul in he case o diame e , al hough ela i ely weak (−0.24), while o comp ession leng h, i is also so bu posi i e (0.16) (Fig. 5). I he esul s a e compa ed wi h o he s udies, he maximum alues a e simila . Howe e , he minimum alue is much lowe . Thus, in a s udy de eloped o imp o e he p ope ies o pelle s om municipal was e by hyd o he mal ea men , ha dness alues be ween 7.37 and 13.34 kg we e ob ained (Phasee and A eep ase , 2018). In he case o he pelle s p oduced by Rezaei (Rezaei e al., 2020), he ha dness a ied be ween 11.11 and 17.13 kg o wa e con en s o 15% and 30% espec i ely. The addi ion o binde in he pelle manu ac u ing p ocess inc eased he ha dness up o 17.68–21.37 kg (Nu sani e al., 2020). In any case, i was obse ed ha o mois u e below 30%, SRF ha dness alues can be simila o hose ound in he li e a u e. No classes ha e been es ablished in his case because he p ope y is no con empla ed in he e e ence s anda ds. Howe e , he alues ob- ained a e below hose ecommended in s udies o biomass pelle s such as wood (A shadi e al., 2008) and he baceous o ag icul u al esidues (Ca oll and Finnan, 2012; Zamo ano e al., 2011), whose op imum ha dness, acco ding o he li e a u e, would be 22 kg (Said e al., 2015). Taking in o accoun he classi ica ions o he p ope ies conside ed o es ablish he quali y o he densi ied SRF in pelle o m, shown in Table 9 wi h he colou code, i is obse ed ha only 3 o he 20 samples p o- duced comply wi h he limi s es ablished o all o he p ope ies, spe- ci ically samples P-10-D6L20, P-10-D6L24, and P-10-D8L32. In he es o he samples, some o he p ope ies we e no ecommendable, so he quali y o he pelle s would no be sui able acco ding o he classi ica ion p oposal. On he o he hand, o all he samples, i was obse ed ha he speci ic p ope ies conduci e o e alua ing he quali y o SRF as uel each classes C1 and C2. Mois u e, pelle densi y, and bulk densi y a e he ones ha each alues wi h a lowe a e (C3), no e en ecommendable in mos o he densi y de e mina ions. This esul is explained by he use o s anda ds o pelle s p oduced om ag icul u al esidues, wi h highe densi y han sc eening esidue, which has a lowe densi y due o i s high con en o sani a y ex iles. Fo his eason, i is conside ed ha he p oposal o quali y s anda ds in he u u e should conside his aspec , as well as he inco po a ion o ha dness, which is no inco po a ed in he cu en s anda ds o o he ypes o was e since i is iewed as a p ope y o be included in u u e pelle quali y s anda ds. On he o he hand, conce ning he ope a ing a iables o he pelle izing p ocess o his esidue, he mos a ou able esul s we e ob ained wi h 10% mois u e in he inle s eam, which would imply he need o subjec he sc eening esidue, cha ac e ized by high mois u e, o an in ense d ying p ocess, which would mean highe p oduc ion cos s. Rega ding he dies, he mos sui able op ion would be he 6 mm inle diame e . Wi h he wo comp ession leng hs es ed (20 and 24 mm), his 6 mm die makes i possible o ob ain con enien pelle s (classes C1, C2, o C3). I is also possible o p oduce pelle s wi h a la ge diame e , 8 mm, wi h a comp ession a io o 8/32. 3.3. De e mina ion o SRF uses The esul s o he p ope ies p oduced om sc eening bo h densi ied and non-densi ied SRF we e compa ed wi h he e e ence anges shown in Table 7 o i s uses in cemen plan s, powe plan s, and gasi ica ion, esul ing in he deg ee o compliance by p ope ies shown o e all in Table 10. Fi s ly, i can be seen ha he Cl, Hg, and ash con en o he SRF manu ac u ed was limi ing o any o he uses analysed, while LHV limi s i s applica ion in cemen wo ks and LHV and mois u e o gasi ica ion. On he o he hand, i was obse ed ha he applica ion o manu- ac u ed SRF in plan s o p oduce ene gy om was e does no pose any limi a ion. In he case o cemen plan s, he possibili y o applica ion is high, since h ee o he ou and i een o he wen y samples o non- densi ied and densi ied SRF, espec i ely, comply wi h all he es ab- lished limi s, which ep esen s 75% o he same. In bo h cases, he limi ing p ope y was he LHV, which shows he di icul y o using SRF p oduced a humidi y alues abo e 35%. Finally, gasi ica ion u ned ou o be he applica ion wi h he lowes numbe o samples sui able o use, wi h only one o he i e applicable non-densi ied SRF samples and six o he wen y in he case o densi ied, ep esen ing 25% and 30%, espec i ely. In his case, he applicabili y is limi ed o SRF p oduced a humidi y alues below 20%. The mois u e con en o he manu ac u ed SRF was he mos limi ing p ope y since 17 samples did no mee he equi emen s. These co esponded o he samples o non-densi ied SRF manu ac u ed wi h a mois u e con en o 35% and o all he samples o densi ied SRF p oduced wi h mois u e con en equal o o highe han 20%, excep in he case o one ha used a longe comp ession leng h (P- 20-D8L48), which ailed wi h mois u e con en alues equal o o highe han 30%. In he case o LHV, gi en i s ela ionship wi h humidi y, six samples we e added o he non-compliance lis , one in non-densi ied SRF and i e in densi ied SRF. These cases also co esponded wi h samples o SRF manu ac u ed wi h humidi y alues equal o o highe han 35%. 4. Conclusions and u he pe spec i es Ene gy eco e y om he sc eening was e would be a de ini i e s ep owa ds achie ing he ze o was e objec i e in was ewa e ea men , a oiding he economic and en i onmen al cos s de i ed om land ill disposal. The ollowing is a summa y o he mos ele an conclusions ob ained ela ing o he objec i es se ou in he s udy. In ela ion o he p oposed classi ica ion o he SRF p oduced, based J.J. De la To e-Bayo e al. P ocess Sa e y and En i onmen al P o ec ion 172 (2023) 950–970 967 on exis ing egula ions on he quali y o SRF as a uel, and on hose ela ing o he quali y o he pelle acco ding o i s mechanical p ope ies. •The p oposed classi ica ion o he p ope ies ha a ec he quali y o non-densi ied SRF is a e e ence amewo k o be conside ed o u u e quali y s anda ds since i b ings oge he he di e si y o exis ing s anda ds and can be used as a common amewo k. •Due o i s bene i s in handling and use, he in e es in densi ica ion, in he o m o pelle s, o SRF om sou ces such as municipal solid was e o sc eening was e equi es he de elopmen o quali y s an- da ds, depending on i s uses, which a e cu en ly non-exis en . In his sense, he p oposed classi ica ion o he p ope ies ha a ec he quali y o densi ied SRF is a ame o e e ence o be aken in o ac- coun o u u e quali y s anda ds ha can be based on he cu en s anda ds o ag icul u al and o es y was e o simila was e. Howe e , i will be necessa y o uniquely analyse alues ha limi p ope ies linked o he cha ac e is ics o hese was es de i ed om hei composi ion and he inco po a ion o ha dness alues due o hei e ec s on he handling and use o he pelle s. The p oduc ion o SRF a labo a o y scale equi ed some condi- ions, mainly o he expe imen al design o densi ied SRF. The inpu mois u e con en o densi ica ion a ied be ween 10% and 40%, and he comp ession a ios o he ma ices used we e 6/20, 6/24, 8/16, 8/32 and 8/48. In ligh o he esul s, i can be concluded: •The p oduc ion o SRF, bo h densi ied and non-densi ied, is a iable op ion o sc eening was e ha mee s he equi emen s o he Eu- opean s anda d ISO 21640:2021. •In he case o he p oduc ion o he non-densi ied SRF, aking in o accoun he classi ica ion p oposed o he p ope ies selec ed o de e mine i s quali y, i would be desi able o p oduce i om sc eening esidues wi h a maximum o 20% mois u e; i is possible o do so up o mois u e con en o 35%, e en i he e is a loss in i s LHV. •In he case o he p oduc ion o densi ied SRF in he o m o pelle s, aking in o accoun he classi ica ion p oposed o he p ope ies selec ed o de e mine i s quali y, i would be desi able o p oduce i wi h a esidual mois u e con en o 10%, using a die wi h a 6 mm inle diame e wi h comp ession leng hs o 20 o 24 mm, o a la ge diame e , 8 mm, wi h a comp ession a io o 8/32. •The mois u e con en o he esidue used o he p oduc ion o SRF is he a iable ha will condi ion he p ocess he mos since i is necessa y o educe i o alues o 35% in he case o non-densi ied and 10% o he manu ac u e o pelle s, which could a ec he economic iabili y o he p oduc . In ela ion o he uses o he SRF p oduced: •The Cl, Hg, and ash con en o he SRF manu ac u ed did no limi any o he uses analysed, while he LHV limi s i s applica ion in cemen wo ks, and LHV and mois u e we e limi ing in he case o gasi ica ion. •The use o he SRF p oduced is no limi ed in he case o powe plan s. Cemen plan s would equi e p oduc ion p ocesses wi h hu- midi y alues below 35%, bo h o non-densi ied and densi ied SRF. The majo limi a ion o SRF use is obse ed in i s applica ion o gasi ica ion. Non-densi ied SRF could be used when manu ac u ed wi h humidi y alues lowe han 35%, educing his limi o alues lowe han 20% in he case o densi ied SRF o samples densi ied wi h a high comp ession a io die (8/48). The p esen s udy p o ides e idence o he po en ial o gene a e SRF om sc eening was e. This inding se es as a s a ing poin o scaling up he p ocess and assessing he echnical, economic, and en i onmen al iabili y o indus ial-le el p oduc ion. Au ho con ibu ions The au ho s con ibu ed equally o his wo k. All au ho s ha e ead and ag eed o he published e sion o he manusc ip . Table 10 Compa a i e p ope ies o Solid Reco e ed Fuel (SRF) p oduced o use in cemen , was e o ene gy, and gasi ica ion plan s. SRF ype Samples Uses Cemen plan s Ene gy om was e plan s Gasi ica ion LHV a Cl Hg Ash M b Sui able LHV Cl Hg Ash M Sui able LHV Cl Hg Ash M Sui able Non densi ied SRF ND-4.5 ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ND-20 ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ⊗ ⊗ ND-25 ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ⊗ ⊗ ND-35 ⊗✓ ✓ ✓ ✓ ⊗✓ ✓ ✓ ✓ ✓ ✓ ⊗✓ ✓ ✓ ⊗ ⊗ Densi ied SRF P-10-D6L20 ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ P-20- D6L20 ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ⊗ ⊗ P-30- D6L20 ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ⊗ ⊗ P-40- D6L20 ⊗✓ ✓ ✓ ✓ ⊗✓ ✓ ✓ ✓ ✓ ✓ ⊗✓ ✓ ✓ ⊗ ⊗ P-10- D6L24 ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ P-20- D6L24 ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ⊗ ⊗ P-30- D6L24 ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ⊗ ⊗ P-40- D6L24 ⊗✓ ✓ ✓ ✓ ⊗✓ ✓ ✓ ✓ ✓ ✓ ⊗✓ ✓ ✓ ⊗ ⊗ P-10- D8L16 ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ P-20- D8L16 ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ⊗ ⊗ P-30- D8L16 ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ⊗ ⊗ P-40- D8L16 ⊗✓ ✓ ✓ ✓ ⊗✓ ✓ ✓ ✓ ✓ ✓ ⊗✓ ✓ ✓ ⊗ ⊗ P-10- D8L32 ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ P-20- D8L32 ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ⊗ ⊗ P-30- D8L32 ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ⊗ ⊗ P-40- D8L32 ⊗✓ ✓ ✓ ✓ ⊗✓ ✓ ✓ ✓ ✓ ✓ ⊗✓ ✓ ✓ ⊗ ⊗ P-10- D8L48 ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ P-20- D8L48 ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ P-30- D8L48 ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ⊗ ⊗ P-40- D8L48 ⊗✓ ✓ ✓ ✓ ⊗✓ ✓ ✓ ✓ ✓ ✓ ⊗✓ ✓ ✓ ⊗ ⊗ a LHV: Lowe hea ing alue. b M: Mois u e. J.J. De la To e-Bayo e al. P ocess Sa e y and En i onmen al P o ec ion 172 (2023) 950–970 968 Funding This s udy was made possible hanks o unding om EMASAGRA by means o an ag eemen wi h e e ence numbe 4325. The company has ac i ely collabo a ed on he exis ing p oblem’s concep ual amewo k and he expe imen s’ de elopmen . Funding o open access cha ge: Uni e si y o G anada / CBUA. 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: Juan Jesus de la To e Bayo epo s inancial suppo was p o ided by Emasag a. Acknowledgmen s The au ho s app ecia e he suppo o he esea ch g oup TEP-968 (Technologies o Ci cula Economy) o he Uni e si y o G anada and o Emasag a. Re e ences AENOR, UNE-EN ISO 10304–1:2009. Calidad del agua: De e minaci´ on de aniones disuel o po c oma og a ía de iones en ase líquida. 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