Prospective environmental and economic assessment of solar-assisted thermal energy recovery from wastewater through a sequencing batch biofilter granular reactor

P ospec i e en i onmen al and economic assessmen o sola -assis ed he mal ene gy eco e y om was ewa e h ough a sequencing ba ch bio il e g anula eac o I an Muñoz a, *, F ancisco Po illo b, c, Sabina Rosiek b, c, F ancisco J. Ba lles b, c, Ja ie Ma ínez-Del-Río d, Iñaki Acasuso e, Valen ina Pie g ossi , Ma co De Sanc is , Sil ia Chimien i , Claudio Di Iaconi a 2.-0 LCA Consul an s, Rendsbu ggade 14, Room 2.345, 9000, Aalbo g, Denma k b Depa men o Chemis y and Physics, Uni e si y o Alme ía, 04120, Alme ía, Spain c CIESOL, Join Cen e o he Uni e si y o Alme ía -CIEMAT, 04120, Alme ía, Spain d Depa men o Economics and Business, Uni e si y o Alme ía, 04120, Alme ía, Spain e Hede a Helix I&B, A da. Pu xe a 1, Aban o y Zie bena, 48540, Bizkaia, Spain CNR e Wa e Resea ch Ins i u e, Via F. De Blasio 5, 70132, Ba i, I aly * Co esponding au ho . E-mail add ess: [email p o ec ed] (I. Muñoz). Abs ac The in eg a ion o an o -g id sola -assis ed hea pump (SHP) and a sequencing ba ch bio il e g anula eac o (SBBGR) o he mal ene gy eco e y om was ewa e was assessed by means o a p ospec i e li e cycle assessmen (LCA) and li e cycle cos ing (LCC), by heo e ically scaling up a pilo ins alla ion in Ba i, I aly, o a ull-scale uni designed o 5000 pe son-equi alen s. The LCA and LCC included all ac i i ies in he li e cycle o he SHP and was ewa e ea men plan (WWTP), namely cons uc ion, ope a ion and end-o -li e. The he mal ene gy p oduced by he SHP was assessed as supplying hea ing and cooling o an ai -condi ioning sys em, displacing a con en ional ai -sou ce hea pump powe ed by elec ici y om he g id. This in eg a ed sys em was compa ed o a e e ence si ua ion whe e was ewa e is ea ed in a con en ional WWTP applying ac i a ed sludge wi h no he mal ene gy eco e y sys em, showing clea en i onmen al bene i s in all impac indica o s, such as a 42% educ ion in g eenhouse-gas emissions and a cos educ ion o 53%. Se e al sensi i i y analyses con i med hese indings, wi h he excep ion o he p ice ebound e ec , which showed ha he lowe cos o he in eg a ed sys em could lead o o e u ning he en i onmen al bene i s. As a limi a ion o he s udy, he dis ibu ion o he supplied ai -condi ioning o mee a demand o -si e he WWTP p emises, such as in esiden ial buildings o ho els, was no included. The e o e, ou esul s cons i u e only a p elimina y posi i e ou come ha should be alida ed in a eal-li e applica ion. Keywo ds: Li e cycle assessmen (LCA) Li e cycle cos ing (LCC) Was ewa e -sou ce hea pump Sola - assis ed hea pump The mal ene gy eco e y 1. In oduc ion Was ewa e ea men cons i u es a subs an ial ene gy consume and sou ce o g eenhouse gas (GHG) emissions. Acco ding o Cao (2011), he p o ision o was ewa e ea men se ices ac- coun s o a ound 1% o a coun y's elec ici y consump ion. Also, was ewa e is esponsible o 4% and 2% o me hane and ni ous oxide emissions, espec i ely (USEPA, 2013). A he same ime, u ban was ewa e cons i u es a p omising low-g ade sou ce o he mal ene gy, as i is p oduced s eadily, in high olumes and wi h small empe a u e a ia ions; i is ypically wa me han he en i onmen du ing win e , bu colde in summe , making i sui - able o hea ing and cooling pu poses h ough hea pump sys ems (CWWA, 2009; F ijns e al., 2013; Megge s and Leibundgu , 2011). Tapping his esou ce o hea ing, en ila ion, and ai condi ioning (HVAC) in buildings is o pa icula in e es , gi en ha buildings accoun o a ound 40% o ene gy consump ion (EIA, 2018; Se ino e al., 2018) and ha ene gy consumed by HVAC sys ems is esponsible o he la ges sha e o a building's en i onmen al impac (Ochoa e al., 2005; Aliane e a . 2016; Ge e al., 2018). Cen alized sys ems o he mal ene gy eco e y om was e- wa e ha e been in place since he 1980's in Ge many, Swi ze land and Scandina ia (DWA, 2009), mainly ocused on eco e y om ea ed e luen s o WWTPs, whe eas eco e y wi hin sewe s o was ewa e ea men basins emains elusi e, mainly due o bio ouling o hea exchange s in con ac wi h un ea ed was ewa e (Chao e al., 2012; Liu e al., 2014). In his con ex , he no el sequencing ba ch bio il e g anula eac o (SBBGR) cons i u es a po en ial solu ion o his p oblem. The SBBGR is an a ached- biomass sys em ope a ing wi h a comple e sepa a ion o he biomass om he liquid phase, hus allowing o a eac o zone ee o suspended solids whe e a hea exchange can be placed (Di Iaconi e al., 2010, 2017; De Sanc is e al., 2017). Due o some addi ional ea u es o SBBGR biomass (i.e. long sludge age and concen a ion) i no only p e en s bio ouling o hea exchange s in he bio eac o , bu also a ou s he mal ene gy eco e y by maximising he con e sion o chemical ene gy s o ed in wa e pollu ion in o biochemical hea , as well as by wi hs anding was ewa e empe a u e changes (Pie g ossi e al., 2018). Coupling o a SBBGR wi h a sola -assis ed hea pump (SHP) has been ecen ly demons a ed a pilo - scale in Ba i, I aly (Pie g ossi e al., 2018). While he en i onmen al pe o mance o hese wo echnologies ha e been sepa a ely assessed in he pas by means o li e cycle assessmen (LCA) (Di Iaconi e al., 2017; Ba lles e al., 2010), he esul ing bene i s o o he wise om hei in eg a ion emain o be quan i ied. Fu he mo e, besides en i onmen al sus ainabili y, economic easibili y is also equi ed o a new echnology o ind i s way in o he ma ke and o his eason an e alua ion o li e cycle cos s (LCC) cons i u es an equally necessa y exe cise. In his a icle we p esen he esul s o a p ospec i e LCA and LCC applied o he in eg a ion o a SBBGR and SHP o HVAC pu poses, as desc ibed in Pie g ossi e al. (2018), conside ing i s implemen a ion a a la ge scale, namely in a hypo he ical WWTP designed o 5000 pe son-equi alen s (PE) in a Medi e anean con ex . 2. Ma e ial and me hods 2.1. Pilo plan desc ip ion The basis o he p ospec i e assessmen is a pilo plan ins alled in Ba i, whe e an exis ing SBBGR uni was upg aded wi h a SHP in Sep embe 2016 (Fig. 1). Below we p o ide a b ie desc ip ion o he ins alla ion. Fo de ailed desc ip ions on he SBBGR he eade is e e ed o Pie g ossi e al. (2018). Fig. 1. The THERBIOR pilo plan . The SBBGR p o o ype mainly consis s o wo columns wi h a o al olume o 300 L. One o such column cons i u es he bio il e (3200 mm in heigh and 220 mm in diame e ), which is packed wi h plas ic media whe e he biomass de elops and he biological deg ada ion akes place. The second compa men is known as he ae a o (273 mm in diame e and 3200 mm in heigh ). The eac o is ope a ed as a sequencing- ed ba ch p ocess, consis ing o h ee s ages: anae obic illing, ae obic eci cula ion be ween he wo columns and e en ually a wi hd awal phase. The ea men cycle akes 6 h in o al, a e which he e luen can be discha ged wi hou he need o a se ling ank. Du ing he eci cula ion phase, ai is p o ided by means o discon inuous 5-min blowing pe iods s a ing e e y 25 min. In addi ion, pu e oxygen is con inuously p o ided in o de o main ain a dissol ed oxygen concen a ion in he ae a o wi hin he 15e20 mg/L ange. The in luen ed o he eac o is eal u ban was ewa e om he local sewe in Ba i. The SHP is a sola -assis ed ully o -g id ene gy sys em capable o p oducing, eco e ing and s o ing he mal ene gy. I consis s o he main ollowing componen s: • A hea pump coupled o a i anium ubula hea exchange subme sed in he SBBGR uni , pa icula ly in he ae a o column. • A ecip oca ing comp esso wi h 4810 W e ige a ion capaci y. • Two sho - e m he mal la en ene gy ho and cold s o age uni s illed wi h phase-change ma e ials (PCM), ope a ing a 53 ◦C and 0 ◦C, espec i ely and wi h a capaci y o 0.3 m3 and 0.5 m3, espec i ely. • Ene gy dissipa ion de ices (condense and e apo a o ). • A oo op pho o ol aic plan wi h 5.1 kWp capaci y and 32 m2 module a ea, powe ing he en i e SHP sys em. The SHP is ully o -g id, wi h he excep ion o con ol and HVAC dis ibu ion de ices, which a e supplied om he g id in o de o ensu e 24-h ope a ion. F om a hyd aulic poin o iew, he sys em is composed o a ho wa e line and a cold wa e line. When su icien sola ene gy is a ailable, he SHP p oduces and s o es hea in he o m o PCM. Con e sely, he cold wa e line p oduces and s o es chilled wa e in he cold PCM ank. The SHP is used in a low- empe a u e ai -condi ioning sys em supplying a so-called expe imen al es labo a o y (ETL), a oom ha simula es demand on- si e. 2.2. LCA and LCC me hods LCA was ca ied ou wi h he ISO 14040 and 14044 s anda ds as main me hodological guidelines (ISO, 2006a; 2006b), and consequen ial modelling was used in he in en o y analysis, as de ined in Weidema (2003, 2009). The so wa e used o model he li e cycle was SimaP o e sion 8.5 (P e´, 2016). En i onmen al LCC was ca ied ou as desc ibed in Hunkele e al. (2008), ha is, accoun ing o in e nal cos s associa ed wi h he li e cycle o he p oduc ha a e co e ed by any one o mo e o he ac o s in he p oduc li e cycle. Bo h LCA and LCC we e aligned in e ms o unc ional uni , sys em bounda ies, e c. As highligh ed in he a icle i le, he o e all assessmen is p ospec i e in he sense ha 1) consequen ial modelling is used in he LCA and 2) he assessmen akes a s ep o wa d om i s ac ual pilo scale o a comme cial scale model. These wo me hodological aspec s allow o a mo e ealis ic depic ion o a po en ial deploymen o his echnology in he ma ke . 2.3. Goal and scena ios assessed The goal was o assess he expec ed li e-cycle en i onmen al and economic pe o mance o coupling a SHP o he mal ene gy eco e y om u ban was ewa e wi h a SBBGR uni , wi h he aim o p o iding cooling/hea ing o esiden ial buildings in a ou is ic Medi e anean egion. We call his he THERBIOR scena io. This is compa ed o a e e ence si ua ion o was ewa e ea men , in which u ban was ewa e is ea ed in a con en ional WWTP applying ac i a ed sludge (AS) and wi h no he mal ene gy eco e y sys em. Fig. 2 shows a concep ual low diag am o hese wo scena ios and he espec i e ac i i ies included in he s udy. Fig. 2. Flow diag am o he wo assessed scena ios: e e ence (le ) and THERBIOR ( igh ). AS: ac i a ed sludge; SHP: sola - assis ed hea pump 2.4. Geog aphical scope The case s udy conside s he implemen a ion o he p oposed concep in a hypo he ical WWTP loca ed in Ba i, whe e he pilo plan has been ins alled. This geog aphical se ing is assumed o ep esen a ypical Medi e anean loca ion. The a e age u ban was ewa e p oduc ion in his egion is app oxima ely 0.15 m3 pe pe son-equi alen (PE) and day. 2.5. Technological scope: was ewa e ea men and sludge disposal We conside he deploymen o his echnology in a WWTP designed o ea ing 5000 PE, o 750 m3/day. The decision o conside a highe scale han he ac ual expe imen al one is based on he ac ha esea ch scales such as lab- and pilo -scales a e no sui able o meaning ul en i onmen al (and economic) assessmen s (Munñoz e al., 2015; Ga anka e al., 2015; Piccinno e al.,2016). An impo an aspec linked o he size o he WWTP is he ac ha ou is ic a eas a e commonly subjec o subs an ial popula ion luc ua ions, wi h peaks in he summe season leading o simila luc ua ions in e ms o was ewa e p oduc ion. In o de o cope wi h hese peaks, WWTPs need o be designed o la ge capaci ies, esul ing in subop imal use o he in as uc u e o he mos pa o he yea . In ou s udy we assume ha he WWTP is o e sized by a ac o o 50%. This esul s in an ac ual capaci y o 3333 PE, which equals 500 m3/day o 182,500 m3/yea . In bo h scena ios he WWTPs need o discha ge a ea ed e luen complying wi h he Eu opean Di ec i e 91/271/EEC conce ning u ban was ewa e ea men . The AS plan conside ed as e e ence includes he ollowing uni ope a ions: mechanical p e- ea men , p ima y se ling, biological ea men wi h ni ogen emo al, seconda y se ling, sand il a ion and disin ec ion. Excess sludge is subjec o ae obic es abiliza ion and dewa e ing. The SBBGR WWTP in ol es subs an ially less uni ope a ions, namely only mechanical p e- ea men and biological ea men in he SBBGR uni (ae a o -bio il e ). Excess sludge does no equi e a s abiliza ion p ocess in his case, bu only dewa e ing. Conce ning nu ien (ni ogen and phospho us) emo al, his is in p inciple no equi ed by cu en legisla ion gi en he size o he assessed WWTPs, howe e o ni ogen we see in he Eu opean En i on- men Agency's WATERBASE da abase (EEA, 2016) ha 37% o plan s in I aly designed o 5000 PE do ea u e ni ogen emo al and o his eason we decided o include i o he e e ence AS plan . On he o he hand, chemical phospho us emo al is less common in hese plan s, wi h only 13% o hem ea u ing his ope a ion; o his eason, i is no included in ou model. In he case o he SBBGR, bo h ni ogen and (biological) phospho us emo al a e conside ed, based on p e ious expe imen al esul s wi h his pilo plan (De Sanc is e al., 2017). Sludge disposal in he wo scena ios is assumed o be h ough incine a ion. This is based on an analysis o sludge disposal ends in Eu ope, using Eu os a da a (see SM). This analysis shows ha om ou main disposal op ions (use in ag icul u e, land illing, incine a ion and compos ing), only incine a ion and compos ing show a g ow h end o e ime, wi h his end being mo e han h ee imes highe o incine a ion compa ed o compos ing. 2.6. Technological scope: sola -assis ed hea pump Simila size conside a ions apply o he SHP as hose discussed o he WWTPs. The SHP ins alla ion a he pilo plan , coupled o a SBBGR ea ing 269 L was ewa e /day, does no p ope ly e lec he expec ed size and numbe o componen s o coupling wi h a WWTP ea ing 500 m3/day. In o de o o e come his limi a ion, we ca ied ou a heo e ical scale-up o he pilo SHP, by e- dimensioning he indi idual equipmen and/o inc easing he numbe o uni s. This p ocess was done in de ail o he mos impo an componen s such as pho o ol aic plan , anks, comp esso , e c. Also, equipmen conside ed o be pa o he pilo plan only o esea ch pu poses was disca ded in he ull-scale design. The esul ing SHP model had a capaci y o 244 kW hea - ing and 160 kW cooling, powe ed by 1225 m2 o pho o ol aic modules. 2.7. Technological scope: subs i u ed g id powe -d i en hea pump The hea ing and cooling se ice ul illed by he implemen a ion o he p oposed concep is assumed o subs i u e hea ing and cooling supplied by an ai -sou ce hea pump d i en by elec ici y om he g id, ha ing he same hea ing and cooling capaci y as he SHP. This is in acco dance wi h a simila s udy (Ba lles e al., 2010) e alua ing a sola HVAC sys em in Alme ía, Spain, wi h e y simila clima ic condi ions o Ba i. The choice o a single hea pump o e e.g. a combined hea pump ( o cooling) and a boile ( o hea ing) can be jus i ied based on he ac ha gi en he ela i ely mild win e s in he Medi e anean egion, he ins alla ion o wo di e en sys ems is no jus i ied, as he hea pump can deli e bo h unc ions. A su ey in Spain (IDAE, 2016) shows ha in he Medi- e anean egions o he coun y hea pumps a e mo e commonly used o esiden ial and comme cial uses compa ed o he No he n A lan ic egions, wi h colde clima e, whe e lowe cooling and highe hea ing equi emen s a e ound. As o he ype o hea pump, his same su ey in Spain shows ha ai -sou ce hea pumps domina e bo h in e ms o ins alled uni s (78% o o al) and ins alled capaci y (71% o o al) o e wa e -sou ce and geo he mal hea pumps. 2.8. Func ional uni The unc ion o he sys em unde s udy is es ablished as p o iding ea men o u ban was ewa e . The THERBIOR scena io, howe e , p o ides an addi ional unc ion, namely he eco e y o he mal ene gy o be used o cooling/hea ing. This addi ional unc ion is deal wi h in he LCA and LCC by means o subs i u ion. The unc ional uni and e e ence low used in he s udy is he ea men o 1 m3 o u ban was ewa e wi h he ollowing composi ion, ob ained om he WWTP a Pu ignano (Sou he n I aly): 937 mg chemical oxygen demand (COD)/L, 93 mg o al ni- ogen (TN)/L, 625 mg suspended solids (SS)/L and 10 mg o al phospho us (TP)/L. 2.9. Limi a ions We can highligh wo main limi a ions in ou assessmen , one ela ed o ene gy use and he o he ela ed o was ewa e ea men . F om he ene gy poin o iew, he pu pose o ou esea ch p ojec was o assess he po en ial o he mal ene gy eco e y om was ewa e h ough he inno a i e SHP. In he pilo plan he eco e ed ene gy is used o p o ide hea ing and cooling o he simula ed ETL a ached o he plan . In a ull-scale deploymen o his echnology, howe e , he hea ing and cooling demand could be loca ed ou side o he WWTP p emises, in ho els, esidences o o ice buildings. In ou s udy we do no include he anspo o he p oduced ene gy o a hypo he ical building o -si e. We ins ead quan i y he se ice as i i was supplied on-si e (no dis ibu ion ne wo k, no losses). F om he was ewa e ea men side, a ele an aspec ha could be add essed is he a e and po en ial oxici y impac s o hea y me als and o ganic mic opollu an s p esen in he aw was ewa e and how hese di e when a SBBGR is used ins ead o ac i a ed sludge. Un o una ely, in his s udy we lacked in o ma ion on he co esponding pe o mance o SBBGR s. ac i a ed sludge wi h ega d o hese pollu an s. The concen a ion o some hea y me als and o ganic mic opollu an s in SBBGR in luen and e luen was measu ed du ing a p e ious s udy on was ewa e euse in ag icul u e (De Sanc is e al., 2017). Mos o he selec ed mic o- pollu an s we e no de ec ed in he was ewa e used in ha s udy. In he in en o y analysis we do no quan i y emissions o ai , wa e o soil om hese pollu an s in was ewa e . 2.10. Impac assessmen me hod The me hod used o impac assessmen in he LCA s udy is S epwise 2006, e sion 1.5. The me hod is desc ibed and documen ed in Annex II in Weidema e al. (2007) and in Weidema (2009). S epwise is capable o p o iding esul s a he le el o midpoin s (cha ac e iza ion) and endpoin s (damage). A he endpoin le el, each impac ca ego y is exp essed in mone a y uni s (Eu o), measu ing en i onmen al damage. In o al, S ep- wise2006 includes a o al o 16 impac ca ego ies commonly used in LCA, howe e , gi en he lack o da a a he in en o y le el on he p esence and a e o mic opollu an s in was ewa e , we decided o exclude eshwa e eco oxici y om he se o en i onmen al impac ca ego ies assessed. 2.11. Da a collec ion o li e cycle assessmen The li e cycle model was buil using he consequen ial lib a y a ailable in ecoin en .3.2 (Ecoin en , 2018) as backg ound da a- base, whe eas a a ie y o p ima y da a sou ces we e used in he in en o y analysis. In his sec ion we ou line he main sou ces and assump ions, whe eas a summa ised mass and ene gy balance is p o ided in Fig. 3 o he wo scena ios (excluding sludge disposal, capi al equipmen and he backg ound sys em). Fo comple e and de ailed in en o y ables he eade is e e ed o he SM. Fig. 3. Summa ised mass and ene gy balance o he wo assessed scena ios du ing he ope a ion li e cycle phase: e e ence (le ) and THERBIOR ( igh ). * 0.14 kWh is he elec ici y consump ion o SHP and all pe iphe al componen s such as ci cula ion pumps and an-coil uni . Cons uc ion o a con en ional WWTP designed o ea ing 750 m3/day was es ima ed wi h a linea eg ession using exis ing in en o ies o WWTPs o di e en capaci ies in Swi ze land, a ailable in he ecoin en da abase. These same da a we e he basis o he SBBGR WWTP cons uc ion, o which no da a we e ound. We ook he assump ion ha in as uc u e ma e ial inpu s a e p opo ional o in es men cos s, meaning ha he lowe in es - men cos o a SBBGR WWTP (see 2.12) leads o a p opo ional in as uc u e ma e ial educ ion. WWTP ope a ion included in- pu s o elec ici y, sodium hypochlo i e o disin ec ion, poly- elec oly e o sludge dewa e ing, sodium hyd oxide o sand il e cleaning and sand eplacemen s o his il e . All ma e ial inpu s we e quan i ied based on li e a u e (see SM) wi h he excep ion o elec ici y consump ion, which was aken om he WWTP a Pu ignano. This plan has ecen ly been pa ially upg aded o a SBBGR ea men , allowing us o ge accu a e da a o bo h con en ional (ac i a ed sludge) and SBBGR ea men . A de ailed heo e ical mass balance was es ablished o he WWTPs, based on he in luen and e luen composi ion, using WW LCI, a li e cycle in en o y model o chemicals discha ged in was ewa e (Muñoz e al., 2016; Kalba e al., 2017). Wi h his model we es ima ed di ec emissions om he WWTP o ai (CO2, N2O), o wa e (NO3, NH4, TP) as well as sludge p oduc ion, which esul ed in 0.51 kg d y mass/m3 o he con en ional WWTP a e ae obic diges ion and 0.14 kg d y mass/m3 o he SBBGR WWTP. WW LCI was also used o model wo addi ional p ocesses. Fi s ly, emissions o CO2 and N2O esul ing om he ul ima e deg ada ion in he aqua ic en i onmen o o ganics and nu ien s in he ea ed e luen . Secondly, o model sludge disposal by incine a ion, which in ol es anspo o dewa e ed sludge, d ying o a con en o 90% d y mass and combus ion wi h ene gy eco e y (see SM o de ails). The in en o y o cons uc ion o he SHP, based on a heo e ical scale-up o he pilo , was accomplished by i s compiling a de ailed bill o ma e ials o his pilo , which esul ed in 1.7 onnes o equipmen . In he scale-up we enla ged, changed and adap ed all his equipmen , esul ing in a SHP embedding 56 onnes o equipmen , including a 190 kWp pho o ol aic plan wi h 1225 m2 module a ea. In o de o annualize he consump ion o equipmen , se ice li es in yea s we e de ined o each ype o componen , anging om 7 yea s o elec onics o 30 yea s o s uc u al elemen s. One o he di icul ies aced o build his in en o y lies in he cu en lack o da a se s in ecoin en o ep esen some o he machine y and equipmen ins alled in he SHP. In he SM we epo in de ail how we adap ed and linked ou da a o he ecoin en da abase. The ope a ion o he SHP includes some g id elec ici y needed o keep he hea ing/cooling dis ibu ion unning du ing he nigh , bu mo e impo an ly, he amoun o hea ing/cooling p oduced and eco e ed by his sys em, exp essed in MJ. This consis s o wo con ibu ions: he sola -powe ed hea pump i sel and he he mal ene gy eco e y om was ewa e . The i s con ibu ion is quan i ied conside ing he SHP hea ing and cooling capaci y, o 244 kW and 160 kW, espec i ely and an end- use hea ing and cooling demand o 632 h/yea and 864 h/yea , espec i ely o a Medi e anean loca ion (Ba lles e al., 2010). Conce ning he mal ene gy eco e y om was ewa e , as desc ibed in Pie g ossi e al. (2018), i was ound ha a subs an ial sha e o he eco e ed he mal ene gy was sensible hea om sola adia ion, i.e. hea ing o he SBBGR columns by di ec exposu e o sunligh , as hey a e placed abo e g ound (see Fig. 1). Howe e , in a ull-scale SBBGR uni he anks would be ins ead placed on he g ound (simila ly o con en ional ac i a ed sludge anks), and he e o e he hea ing con ibu ion om sunligh would no occu . A de ailed ene gy balance o he SBBGR eac o e ealed ha in a e age, app oxima ely 50% o he eco e ed ene gy is due o sola exposu e o he eac o (Po illo, 2017). In ou scale-up calcula ions we excluded his con ibu ion and quan i ied he eco e able he mal ene gy as 13.8 MJ pe m3 was ewa e , and he ac ually eco e ed ene gy as 4.6 MJ/m3, gi en ha he SHP can only ope a e du ing dayligh (8 h/day). Conside ing he wo con ibu ions (SHP and was ewa e ), he o al he mal ene gy eco e ed is 10.4 MJ/m3. The in en o y o he subs i u ed ai -sou ce hea pump was quan i ied based on a mi o design o he up-scaled SHP whe e he pho o ol aic sys em was emo ed and powe om he g id was ins ead conside ed. Finally, elec ici y p oduc ion in I aly, which supplies all he abo e ac i i ies, was modelled conside ing only lexible supplie s in he pe iod 2012e2020, esul ing in a g id mix con aining 88% enewably-sou ced elec ici y (see SM o de ails). 2.12. Da a collec ion o li e cycle cos ing Cos s assessed included in es men and ope a ion, whe eas decommissioning cos s we e neglec ed (Muñoz, 2006). In es men cos s we e annualized using he so-called capi al eco e y ac o (CRF), as a unc ion o se ice li e in yea s and in e es a e. The la e was aken as 1%, which co esponds o he GDP-weigh ed Eu o a ea en-yea so e eign bond yield, acco ding o he Eu o- pean Cen al Bank a he beginning o 2018 (ECB, 2018). As in he p e ious sec ion, below we only p o ide a summa y o he main da a sou ces and assump ions, whe eas de ailed cos calcula ions a e a ailable in he SM. In es men cos s o a con en ional and SBBGR WWTP we e es ablished as 350V and 224V pe PE, espec i ely, based on in- o ma ion supplied by he in eg a ed wa e se ices ope a o in he Apulia egion, which ope a es he Pu ignano WWTP upg aded o SBBGR. In es men cos o he up-scaled SHP was es ima ed close o 906,000 V, based on he o al equipmen cos plus ins alla ion, enginee ing cos s, e c. The CRF o hese in es men s was calcula ed assuming a se ice li e o 30 yea s o he WWTP and 20 yea s o he SHP. Ope a ion cos s o he WWTP included elec ici y cos s, o he ope a ion cos s and sludge disposal. Elec ici y cos s o I alian indus ial consume s was ob ained om EUROSTAT (2018) as 0.185 V/kWh. O he ope a ion cos s we e es ima ed as 3% o he in es men cos , annually (COWI, 2010), and sludge disposal cos s included anspo and incine a ion cos s, es ima ed o I aly as 203 V pe onne in we weigh , based on Diaz e al. (2015) and UN- Habi a (2008). Ope a ion cos s o he SHP included g id elec ici y consump ion o equipmen unning 24 h and main enance cos s. The la e we e es ima ed as 3% o he in es men cos s, annually. This is he a e age alue ob ained om a s udy on li e cycle cos s o HVAC sys ems (Wu and Clemen s-C oome, 2007). The subs i u ed ai -sou ce hea pump cos s we e quan i ied ollowing a simila app oach as in he SHP. In es men cos s we e es ima ed as 167,600V wi h a se ice li e o 15 yea s. Ope a ion cos s included elec ici y and main enance, aking he same app oach as in he SHP. In his case, he g id elec ici y consump ion is 0.144 kWh pe MJ hea ing/cooling. O e all, he uni a y cos o his pump esul s in 0.043V pe MJ hea ing/cooling. 3. Resul s and discussion 3.1. Li e cycle impac assessmen Table 1 shows he li e cycle impac assessmen esul s o he wo scena ios, a bo h midpoin and endpoin le el. While a midpoin each indica o has i s own speci ic uni s, a endpoin le el hey a e all exp essed in mone a y uni s. A midpoin le el we can see ha he THERBIOR scena io shows lowe en i onmen al impac in all 15 indica o s, wi h a educ ion in impac anging om 19% in mine al ex ac ion o 93% in ozone laye deple ion. In na u e occupa ion, he THERBIOR scena io p esen s a nega i e sco e, meaning a ne bene icial e ec on his indica o . The inclusion o esul s a endpoin le el is use ul o iden i y hose impac indica o s whe e he sys em has he highes con ibu ion o en i onmen al damages. I can be seen in Table 1 ha in ou case s udy his co esponds o global wa ming, espi a o y ino ganics and eshwa e eu ophica ion, wi h he i s one o hese h ee ha ing he highes magni ude. Table 1. Li e cycle impac assessmen esul s a midpoin and endpoin le el pe m3 was ewa e . Impac ca ego y Midpoin Endpoin Uni Re e ence THERBIOR Uni Re e ence THERBIOR Human oxici y, ca cinogens kg C 2 H 3 Cl-eq in o ai 0.023 0.011 V 0.006 0.003 Human oxici y, non-ca cinogens kg C 2 H 3 Cl-eq in o ai 0.042 0.015 V 0.011 0.004 Respi a o y ino ganics kg PM 2.5 -eq 0.00086 0.00035 V 0.058 0.024 Ionizing adia ion Bq Ca bon-14 in o ai 0.60 — 0.19 V 1.2E-05 —3.8E-06 Ozone laye deple ion kg CFC11-eq 7.5E-08 5.0E-09 V 7.7E-06 5.2E-07 Eco oxici y, e es ial kg ie hylene glycol-eq in o soil 5.5 3.1 V 1.2E-04 1.7E-04 Na u e occupa ion m 2 ag . land 0.037 — 0.001 V 0.0045 — 0.0001 Global wa ming kg CO 2 -eq 0.82 0.47 V 0.068 0.039 Acidi ica ion m 2 unp o ec ed ecosys em 0.044 0.015 V 0.0003 0.0001 Eu ophica ion, aqua ic kg NO 3 -eq 0.33 0.21 V 0.033 0.021 Eu ophica ion, e es ial m 2 unp o ec ed ecosys em 0.11 0.03 V 0.0014 0.0004 Respi a o y o ganics Pe son$ppm$h 0.00059 0.00023 V 1.5E-04 6.0E-05 Pho ochemical ozone, ege a ion m 2 $ppm$hou 6.8 2.4 V 0.0025 0.0009 Non- enewable ene gy Megajoule 8.9 2.5 V 0 0 Mine al ex ac ion Megajoule 0.12 0.10 V 5.0E-04 4.0E-04 Fig. 4 shows a con ibu ion analysis o he global wa ming indica o , exp essing GHG emissions in CO2-eq. I mus be s essed ha biogenic CO2 emissions om he deg ada ion o o ganic ma e in was ewa e a e conside ed o be clima e-neu al in ou analysis. The g aph shows ha GHG emissions a e especially lowe o he THERBIOR scena io in wo aspec s: sludge disposal and hea pump subs i u ion. Wi h ega d o sludge disposal, he e is a clea ad an age o he SBBGR due o i s subs an ially lowe sludge p oduc ion. This means less anspo , less uel equi emen s o d y sludge p io o incine a ion, and less incine a ion emissions. O e all, GHG emissions ela ed o sludge disposal a e educed by a ac o ou . Conce ning hea pump subs i u ion, his is shown wi h a nega i e sign in he g aph, meaning ha 0.27 kg CO2-eq a e a oided pe m3 was ewa e . These emissions a e ela ed o he (a oided) p oduc ion, ope a ion and end o li e o a con en ional hea pump powe ed by he g id. The e is no such sa ing in he e e ence scena io, as he e is no he mal ene gy p oduc ion in ha case. O e all, in he THERBIOR scena io he SHP leads o a o al emission o e he li e cycle (cons uc ion, ope a ion, end o li e) o 0.16 kg CO2-eq/m3, bu his is mo e han compensa ed by he a o emen ioned sa ing o 0.27 kg CO2-eq/m3. I is also wo h men ioning ha he THERBIOR scena io also in ol es a GHG educ ion du ing WWTP cons uc ion, howe e his esul is subjec o unce ain y, as we ha e assumed ha in as uc u e impac s a e di ec ly linked o in es men cos s. I seems easonable hough ha he much simple layou o a SBBGR WWTP should in ol e, o some ex en , a lowe need o cons uc ion ma e ials such as conc e e and ein o ced s eel, among o he s. F amewo k. In e na ional S anda d O ganiza ion (ISO), Gene e. ISO, 2006b. ISO 14044 En i onmen al Managemen - Li e Cycle Assessmen e Requi emen s and Guidelines. In e na ional S anda d O ganiza ion (ISO), Gene e. Kalba , P., Mun~oz, I., Bi k ed, M., 2017. WW LCI 2: a second-gene a ion li e cycle in en o y model o chemicals discha ged o was ewa e sys ems. Sci. 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