Comparison of modern drinking water network maintenance methods: Evaluation of removed deposits in the form of total suspended solids (TSS)

In e na ional Jou nal o En i onmen al Resea ch and Public Heal h A icle Compa ison o Mode n D inking Wa e Ne wo k Main enance Me hods: E alua ion o Remo ed Deposi s in he Fo m o To al Suspended Solids (TSS) Pe a Ju ek Vidlᡠo á* and Sil ie He iánko á   Ci a ion: Ju ek Vidlᡠo á, P.; He iánko á, S. Compa ison o Mode n D inking Wa e Ne wo k Main enance Me hods: E alua ion o Remo ed Deposi s in he Fo m o To al Suspended Solids (TSS). In . J. En i on. Res. Public Heal h 2021,18, 4311. h ps://doi.o g/10.3390/ ije ph18084311 Academic Edi o : Paul Tchounwou Recei ed: 12 Ma ch 2021 Accep ed: 15 Ap il 2021 Published: 19 Ap il 2021 Publishe ’s No e: MDPI s ays neu al wi h ega d o ju isdic ional claims in published maps and ins i u ional a il- ia ions. Copy igh : © 2021 by he au ho s. Licensee MDPI, Basel, Swi ze land. This a icle is an open access a icle dis ibu ed unde he e ms and condi ions o he C ea i e Commons A ibu ion (CC BY) license (h ps:// c ea i ecommons.o g/licenses/by/ 4.0/). Depa men o En i onmen al Enginee ing, Facul y o Mining and Geology, VSB-Technical Uni e si y o Os a a, 708 00 Os a a, Czech Republic; [email p o ec ed] *Co espondence: pe a. idla [email p o ec ed] Abs ac : Wa e pipe sedimen emo al should be implemen ed as an in eg al pa o wa e mains main enance in o de o s eadily supply consume s wi h d inking wa e o high quali y. Conside ing he numbe o di e en wa e pipe sedimen emo al me hods, he a icle aims o e alua e he cu en ly used me hods o emo e wa e pipe sedimen om he pipes o he d inking wa e dis ibu ion sys em. The e alua ion compa es he implemen a ion equi emen s o each me hod as well as he quali y and he quan i y o he emo ed p oduc s. The es ed me hods we e unidi ec ional lushing, Comp ex ® , and Ice Pigging ® . The esul s o he compa ison a e exp essed in e ms o o al suspended solids (TSS) eco e y, me als mass concen a ion and wa e consump ion. Since con amina ion can se le along he en i e su ace o he pipeline, i is mos app op ia e o ecalcula e he esul s pe uni a ea o he pipeline. The esul s poin a he ollowing e iciency he Comp ex ® me hod was he mos e icien in emo ing TSS, Ice Pigging ® was he nex and unidi ec ional lushing emo ed a negligible amoun o TSS compa ed o he o he wo me hods. The absolu e eco e y o TSS was 0.12–3.01 g · m −2 in unidi ec ional lushing o plas ic pipes, 1.58–8.54 g · m −2 in unidi ec ional lushing o me al pipes, 4.36–47.53 g · m −2 in Ice Pigging ® , and 5.19–69.23 g · m −2 in Comp ex ® . The composi ion o he sedimen was s ongly in luenced by pa icle o igin: Pipe ma e ial a ec ed he c ys alline phase o he sedimen and he wa e sou ce and he age o he pipe a ec ed he amo phous phase o he sedimen . The e o e, i was ound ha e alua ion o e iciency based on he amoun o TSS emo ed is only sui able o si es ha mee he same condi ions as pipe ma e ial, wa e sou ce and ideally he pipe age. I has u he been ound ha he Comp ex ® me hod can be ad an ageously used in eal condi ions o clean pipes wi h insu icien hyd aulic condi ions (such as wi h a high le el o inc us a ion), as he cleaning has low wa e low eloci y equi emen s. Keywo ds: d inking wa e dis ibu ion sys em (DWDS); unidi ec ional lushing; ai scou ing; Ice Pigging®; Comp ex®; o al suspended solids (TSS) 1. In oduc ion Supplying consume s wi h high-quali y d inking wa e is a challenging and complex p ocess. I places high demands on wa e p oduce s o ensu e p ope p o ec ion o wa e sou ces, i s ea men , accumula ion, and dis ibu ion o inal consume s [ 1 ]. The o al leng h o he d inking wa e ne wo k in Eu ope is 4,225,527 km [ 2 ]. This in as uc u e equi es main enance and in es men s o p o ide clean and wholesome wa e o all. The e o e, some o he basic p econdi ions o ensu e he supply o high-quali y d inking wa e o all consume s a e he p ope ope a ion o wa e in as uc u e, i s cons uc ion, enewal and main enance, in pa icula [2]. The enewal o he wa e supply ne wo k and he de elopmen o wa e supply ne - wo k moni o ing signi ican ly educe wa e losses in he wa e supply ne wo k. In ce ain EU membe s a es, he a e age daily demands (ADD) pe capi a a e dec easing (e.g., in he Czech Republic ADD has p ac ically hal ed since 1989 o da e; om 1.25 million m3·y−1 In . J. En i on. Res. Public Heal h 2021,18, 4311. h ps://doi.o g/10.3390/ije ph18084311 h ps://www.mdpi.com/jou nal/ije ph In . J. En i on. Res. Public Heal h 2021,18, 4311 2 o 16 o 585,000 m 3 .y −1 ) [ 3 ]. This has a posi i e e ec especially in e ms o sa ing wa e e- sou ces as he Ea h is cu en ly s uggling wi h a dec ease in he yield o unde g ound esou ces [ 4 ] o low in wa e cou ses [ 5 ] in many locali ies. Howe e , he wa e sa ings may ha e a nega i e impac on he wa e quali y due o i s longe esidence ime in he pipeline [ 6 ], [ 7 ], whe e he esul ing wa e quali y is al e ed in senso y and mic obiological pa ame e s (i.e., he e o ophic pla e coun ) [8,9]. All EU coun ies place high demands on he quali y o supplied d inking wa e , and wa e managemen companies ha e begun o alue consume s as aluable cus- ome s [ 10 ], [ 11 ]. The e o e, e o s ha e been inc easing o educe he occu ence o ad e se phenomena, such as u bid e en s in he wa e supply ne wo k, which he con- sume eels he mos . On he o he hand, he dis ibu ion sys em can ne e be ee om all pa icles o mic oo ganisms, being a complex se o chemical and biological eac an s [ 12 ]. Howe e , he p esence o sedimen s and mic oo ganisms can be educed signi ican ly by a co ec ly selec ed and equen main enance me hod o hei emo al [13]. The commonly-used me hods o dis ibu ion pipe cleaning [ 14 ] may be summa ized as pigging, Ice Pigging ® , ai scou ing (AS), and wa e lushing. Recen ly, Neu al Ou pu Discha ge Elimina ion Sys em (NO-DES) me hod has been in oduced, which unc ions as abo eg ound loops o dis ibu ion sys em be ween wo hyd an s using hoses and he wa e is ci cula ed wi hin he empo a y loop a scou ing eloci ies h ough he wa e main and il e s using pump moun ed on he uck [ 15 ]. The me hod mos au ho s ocus on is he so-called unidi ec ional lushing [ 12 , 16 – 22 ]. While he highes possible low a es o wa e in he pipeline a e achie ed, accumula ed sedimen o pa s o bio ilm a e emo ed om he pipe su ace [ 19 , 21 ]. The p inciple o his me hod is summa ized by [ 23 ] based on he knowledge o many au ho s. Recommended low eloci ies a e in he ange o = 1.0–1.6 m·s−1 [ 12 , 24 ]. These eloci ies a e su icien o he emo al o loose and cohesi e deposi s [19] and pa ly o ube cula ed pipes [24]. The wa e pipe can be clogged wi h ine sedimen a he bo om o he pipe o by chemical deposi s on he pipe walls, which can ill almos he en i e pipe diame e [ 25 ]. These sedimen s may be so , easily emo able o solid equi ing agg essi e cleaning me hods [ 7 , 18 ]. The e o e, a highe eloci y and highe shea s ess a e necessa y o clean he inne su ace o he pipe and i s adhe en ma e ial [ 12 , 24 ]. Howe e , his is o en p oblema ic when using he unidi ec ional lushing me hod in eal ope a ion condi ions, which is con i med by he esul s ob ained. Highe shea s ess can be achie ed by ai scou ing and Ice Pigging ® , each o hese me hods uses a di e en cleaning p inciple. Du ing ai scou ing comp essed ai is blown in o he pipe, oge he wi h a liquid, which inc eases he shea s ess a he pipe walls and scou s and lushes ou he sedimen om he pipe [ 12 ]. Ai scou ing has been mode nized o a so wa e-d i en impulse lushing which is ma ke ed unde ade names. Du ing Ice Pigging ® he ic ion a he pipe walls is 2–4 o de s o magni ude highe han a he same speed o a wa e s eam du ing lushing [ 26 ], because he ic ion is inc eased using wo-phase ice slu y in o m o a plug mo ing down he pipe and dislodging buil -up ma e ial [ 27 ]. Mos ly a mix u e o 5% ood sal and po able wa e is used in he p ocess [28,29]. In o ma ion abou he amoun and o igin o deposi s is use ul o p e en hei o - ma ion [ 19 ], he e o e au ho s e alua e he e iciency o emo al and composi ion o he deposi s. The majo i y o s udies ocus on unidi ec ional lushing [ 12 , 19 , 22 , 30 ]. Howe e , i has been ound ha limi ed knowledge exis s on he compa ison o he mode n me hods, such as Ice Pigging ® and ai scou ing, e en in e ms o ope a ional equi emen s o in e ms o e iciency. The exis ing s udies only compa ed unidi ec ional lushing o pigging [ 12 , 18 ] o examined hei e iciency in labo a o y condi ions [31]. The aim o he esea ch epo ed he e is o p o ide no el in o ma ion ega ding he e iciency o Ice Pigging ® and ai scou ing based on loose and adhe en deposi s emo al and o al wa e consump ion. The aim is o compa e wo comme cial me hods called Ice Pigging ® and so wa e-d i en impulse lushing Comp ex ® , and o con as he esul s wi h hese ob ained by unidi ec ional lushing. This new knowledge on sui able In . J. En i on. Res. Public Heal h 2021,18, 4311 3 o 16 ope a ion condi ions ob ained by es ing me hods in p ac ice can op imize he pe o mance o he dis ibu ion sys em cleaning. Ai scou ing is no in ol ed in gene al e alua ion because only one applica ion o AS was pe o med, and enough da a was no ob ained. Ai scou ing esul s a e in he main ex men ioned only o compa ison wi h he e ec i i y o so wa e-d i en p ocess Comp ex®. 2. Me hodology 2.1. Selec ed Ne wo k Cha ac e is ics To add ess hese objec i es, ull-scale es s we e ca ied ou in es zones in he wa e dis ibu ion sys em o a 300,000-ci izen ci y, which consis s o 1064.8 km o pipes wi h he capaci y o 1.875 L · s −1 . Almos 16.5 km o he dis ibu ion sys em was moni o ed du ing he cleaning p ocesses applying Ice Pigging ® , Comp ex ® and unidi ec ional lushing. Ice Pigging ® was applied o 75% o in es iga ed pipes leng h, unidi ec ional lushing o 13% o in es iga ed pipes leng h, and Comp ex ® o 12% o in es iga ed pipes leng h. The a e age leng h o cleaned sec ion was o (a) Ice Pigging ® l IP = 1749.1 m; (b) Comp ex ® lCO = 363.3 m; (c) unidi ec ional lushing lUNI = 197.3 m. Acco ding o Macek and Šk ipko [ 16 ], i is possible o ca y ou unidi ec ional lushing up o pipe nominal diame e DN = 300 mm. Minimum ecommended speed [ 12 , 24 ] o his nominal diame e is equal o he ins an aneous low o Q = 63.6 L · s −1 . In he es ed ope a - ing condi ions, his low is o en limi ed by hyd odynamic p essu e and hyd an capaci y, he e o e i was possible o lush e ec i ely only sec ions up o DN = 150 mm . Comp ex ® me hod is capable o cleaning pipes o nominal diame e s up o DN = 1200 mm [ 32 ]. Candy e al. [ 33 ] s a e ha Ice Pigging ® can be applied o clean he diame e up o DN = 750 mm. Sec ions up o DN = 450 mm ha e been es ed unde eal ope a ing condi ions [ 33 ]. Based on his in o ma ion, pipes sui able o cleaning we e selec ed as ollows (a) pipes om DN = 80 mm o DN = 150 mm in unidi ec ional lushing; (b) pipes om DN = 100 mm o DN = 250 mm in Ice Pigging ® ; (c) pipes om DN = 80 mm o DN = 200 mm in Comp ex ® me hod. Tes ed locali ies we e named by code (Figu e 1), which cha ac e izes he selec ed me hod and basic p ope ies o he cleaned sec ion, such as pipe diame e (DN) and pipe ma e ial. The equency o he expe imen s was in luenced by he cos o he me hods being e alua ed. No cleaning in e en ions ha e been epo ed since he pipe was commissioned. In . J. En i on. Res. Public Heal h 2021, 18, x FOR PEER REVIEW 3 o 16 Pigging® and so wa e-d i en impulse lushing Comp ex®, and o con as he esul s wi h hese ob ained by unidi ec ional lushing. This new knowledge on sui able ope a ion con- di ions ob ained by es ing me hods in p ac ice can op imize he pe o mance o he dis- ibu ion sys em cleaning. Ai scou ing is no in ol ed in gene al e alua ion because only one applica ion o AS was pe o med, and enough da a was no ob ained. Ai scou ing esul s a e in he main ex men ioned only o compa ison wi h he e ec i i y o so wa e- d i en p ocess Comp ex®. 2. Me hodology 2.1. Selec ed Ne wo k Cha ac e is ics To add ess hese objec i es, ull-scale es s we e ca ied ou in es zones in he wa e dis ibu ion sys em o a 300,000-ci izen ci y, which consis s o 1064.8 km o pipes wi h he capaci y o 1.875 L·s−1. Almos 16.5 km o he dis ibu ion sys em was moni o ed du ing he cleaning p ocesses applying Ice Pigging®, Comp ex® and unidi ec ional lushing. Ice Pigging® was applied o 75% o in es iga ed pipes leng h, unidi ec ional lushing o 13% o in es iga ed pipes leng h, and Comp ex® o 12% o in es iga ed pipes leng h. The a - e age leng h o cleaned sec ion was o (a) Ice Pigging® lIP = 1749.1 m; (b) Comp ex® lCO = 363.3 m; (c) unidi ec ional lushing lUNI = 197.3 m. Acco ding o Macek and Šk ipko [16], i is possible o ca y ou unidi ec ional lush- ing up o pipe nominal diame e DN = 300 mm. Minimum ecommended speed [12,24] o his nominal diame e is equal o he ins an aneous low o Q = 63.6 L·s−1. In he es ed ope a ing condi ions, his low is o en limi ed by hyd odynamic p essu e and hyd an capaci y, he e o e i was possible o lush e ec i ely only sec ions up o DN = 150 mm. Comp ex® me hod is capable o cleaning pipes o nominal diame e s up o DN = 1200 mm [32]. Candy e al. [33] s a e ha Ice Pigging® can be applied o clean he diame e up o DN = 750 mm. Sec ions up o DN = 450 mm ha e been es ed unde eal ope a ing condi- ions [33]. Based on his in o ma ion, pipes sui able o cleaning we e selec ed as ollows (a) pipes om DN = 80 mm o DN = 150 mm in unidi ec ional lushing; (b) pipes om DN = 100 mm o DN = 250 mm in Ice Pigging®; (c) pipes om DN = 80 mm o DN = 200 mm in Comp ex® me hod. Tes ed locali ies we e named by code (Figu e 1), which cha ac e izes he selec ed me hod and basic p ope ies o he cleaned sec ion, such as pipe diame e (DN) and pipe ma e ial. The equency o he expe imen s was in luenced by he cos o he me hods being e alua ed. No cleaning in e en ions ha e been epo ed since he pipe was commissioned. Figu e 1. Code cha ac e izing he expe imen s’ nume ical o de and cleaning condi ions-used me hod, pipe nominal diame e and pipe ma e ial (in case o one cleaned sec ion is c ea ed by mo e ypes, e.g. a hyphen (-) di ides pa icula pipe nominal diame e s and a slash (/) di ides used ypes o pipe ma e ials). Figu e 1. Code cha ac e izing he expe imen s’ nume ical o de and cleaning condi ions-used me hod, pipe nominal diame e and pipe ma e ial (in case o one cleaned sec ion is c ea ed by mo e ypes, e.g. a hyphen (-) di ides pa icula pipe nominal diame e s and a slash (/) di ides used ypes o pipe ma e ials). 2.2. Fieldwo k P ocedu e, Moni o ing and Sampling Acco ding o V eebu g [ 12 ], Ellison [ 18 ], Ca iè e e al. [ 19 ], Ba beau e al. [ 22 ], Fann e al. [ 30 ] and Mille e al. [ 32 ], he e ec i eness o pipe cleaning me hods is o - en e alua ed as o al suspended solids emo al. Fo his pu pose, in-si u samples ( olume o 2 L each) we e collec ed and shipped o he labo a o y o analysis. In he case o unidi ec ional lushing and Comp ex ® , sampling was ca ied ou immedia ely a e he In . J. En i on. Res. Public Heal h 2021,18, 4311 4 o 16 s a o cleaning. In he case o Ice Pigging ® , he i s sample was aken a e a hyd aulic es (desc ibed by Fann e al. [ 32 ]) and u he samples a he momen as he on o he ice began o app oach, which in mos cases me one o he condi ions: (a) Tempe a u e d opped below 5 ◦ C; (b) conduc i i y began o ise abo e no mal le els in he a ea (up o K = 87.3 mS·cm−1). Quali a i e p ope ies o lushed wa e ( u bidi y, empe a u e) we e moni o ed on si e du ing he whole p ocess by digi al op ic senso : (a) METTLER TOLEDO InP o 8000 Se ies (880 nm wa eleng h, Back-sca e ed Ligh p inciple, Me le - Toledo, s. .o., P aha, Czech Republic) o Ice Pigging ® and (b) PONSEL ® (850 nm wa eleng h; Side-sca e ed Ligh p inciple, TECHNOAQUA, s. .o., DolníBˇ ežany, Czech Republic) o unidi ec ional lushing. In he case o Comp ex ® me hod, u bidi y was measu ed only by po able u bidime e Eu ech TN-100 (850 nm wa eleng h, Side-sca e ed Ligh p inciple, Fishe Scien i ic, spol. s .o., Pa dubice, Czech Republic), as he p esence o ai in he wa e impai s he accu acy o he con inuous measu emen . In all cases, he measu emen o u bidi y was complemen ed by measu ing o al i on by Fe o e ® me hod using Mul ipa ame e Po able Colo ime e HACH DR900 (HACH LANGE s. .o., P aha, Czech Republic). O he pa ame e s measu ed in-si u a e lis ed in Table 1below as pa ame e s measu ed on-si e du ing he whole p ocess using on-line senso s. Table 1. Pa ame e s o wa e moni o ed on-si e by on-line senso s. Me hod Ice Pigging®AS & Comp ex®Unidi ec ional Flushing Tempe a u e x x P essu e hyd os a ic/hyd odynamic x x x Tu bidi y x x Conduc i i y x Flow a e x x x 2.3. Cleaning Pa ame e s Unidi ec ional Flushing was ca ied ou a eloci ies anging om 0.42 o 2.76 m·s−1 o me al pipes, and 0.73 o 1.87 m · s −1 o plas ic pipes as a unc ion o pipe diame e and a ailable p essu e. Only 4 ou o 10 sec ions me he ecommended speeds [ 12 , 24 ] o pe o ming unidi ec ional lushing. Ai scou ing wi hou he possibili y o ai low adjus men was pe o med only a one loca ion as a es be o e Comp ex ® cleaning. The used comp esso was capable o c ea e maximum p essu e o 1 MPa and ai injec ion was con olled only by on al e closing. Ai pulses we e c ea ed while he inal wa e low eloci y was = 0.28 m · s −1 , while ai low could no be con olled. Se ope a ing pa ame e s o Comp ex ® cleaning me hod as a p essu e o indi idual pulses anged om 1.9 o 5.3 ba (190 kPa o 530 kPa), and he pulse leng h om 2 o 7 s. These pa ame e s we e a unc ion o egula hyd os a ic p essu e in cleaned pipe and pipe ma e ial. A o al o 179 o 537 pulses we e used. The olume o ice used o Ice Pigging ® is limi ed o 9 ons by ice manu ac u ing and s o age capaci y. This olume oge he wi h pipe diame e , ma e ial, low a e and ambien empe a u e in luence he o al leng h o pipe which can be cleaned a a ime [ 33 ]. The o al olume o ice used o Ice Pigging ® cleaning a ied 4–10 m 3 . Ice ac ion a ied om 75 o 85% (Mode o 80%). The cleaning pa ame e s, including he p ope ies o he cleaned pipes, a e summa- ized in Table 2. In cases whe e g oundwa e p edomina es o e su ace wa e (U > G) a speci ic g oundwa e -su ace wa e a io a ies acco ding o he ins an aneous wa e -use and i canno be accu a ely exp essed. In . J. En i on. Res. Public Heal h 2021,18, 4311 5 o 16 Table 2. P ope ies o he cleaned pipes and cleaning pa ame e s (NDA—no da a a ailable; DN—nominal diame e ; p—hyd odynamic p essu e; QA— low achie ed; QR— low equi ed; WS—wa e sou ce; G—g oundwa e — U—unde g ound wa e ). Me hod Code DN Commissioning Ma e ial Leng h pQA QR WS mm Yea m ba L·s−1L·s−1 Unidi ec ional lushing 1UNI150PVC 150 1984 PVC 299.5 0.39 18.6 17.19 G 2UNI80PVC/PE 80 2000–2007 PVC-PE 279.8 0.15 6.3 5.41 G 3UNI80PE 80 2001 PE 122.9 0.28 9.4 4.30 G + U 4UNI100PVC 100 NDA PVC 199.2 0.41 6.6 8.01 U > G 5UNI100PE 100 2015 PE 134.2 0.05 5.8 6.36 U > G 6UNI100OC 100 1964 OC 93.5 0.06 4.5 7.85 U > G 7UNI80LT 80 1977 LT 135.9 0.04 3.1 5.02 U 8UNI80LT 80 1988 LT 250.5 0.28 13.9 5.02 G + U 9UNI100LT 100 1971 LT 314.2 0.07 3.8 7.85 U > G 10UNI80LT 80 1920 LT 143.5 0.07 2.1 5.02 U > G AS 12AS150LT 150 1985 LT 198.8 NDA 5.0 - G Comp ex® 11CO100PVC 100 1975 PVC 371.0 0.50 2.1 - G + U 12CO150LT 150 1985 LT 654.3 1.00 2.7 - G 13CO200LT 200 1970 LT 481.7 0.70 6.9 - U 14CO80LT 80 1977 LT 135.9 0.50 1.4 - U 15CO80LT 80 1953 LT 173.5 1.50 0.9 - G Ice Pigging® 16IP150- 250PVC/PE/OC 150, 250 1964–2001 PVC-PE-OC 1661.0 5.50 15.2 3.00 U 17IP250OC/LT 250 1964 OC-LT 1381.0 5.80 13.8 3.00 U 18IP150-200OC/LT 150, 200 1953–1966 OC-LT 633.0 NDA 3.00 G 19IP80- 150OC/LT/PE/PVC 80, 150 1953–1994 OC-LT-PE-PVC 1005.0 NDA 3.00 G 20IP150PVC/PE 150 1994–2008 PVC-PE 2052.0 3.80 14.2 3.00 G 21IP100-150PE 100, 150 2009–2012 PE 2327.0 2.80 11.5 3.00 G 22IP100-150PVC/PE 100, 150 1987–2016 PVC-PE 2638.0 0.50 8.8 3.00 U 23IP100-200PVC/PE 100, 200 1997–2011 PVC-PE 1495.0 0.60 7.5 3.00 G 24IP100-200LT/PVC 100, 200 1979 LT-PVC 687.0 0.40 14.5 3.00 G 25IP150-200LT/PVC 150, 200 1979 LT-PVC 323.0 NDA 14.5 3.00 G In . J. En i on. Res. Public Heal h 2021,18, 4311 6 o 16 2.4. De e mina ion o To al Wa e Consump ion As he wa e quali y was moni o ed du ing he whole cleaning p ocess, a e each- ing a u bidi y alue below 1 NTU, he mass concen a ion o o al i on was measu ed. The cleaning was comple ed when o al i on concen a ion me he equi emen s o Di- ec i e (EU) 2020/2184 o he Eu opean Pa liamen and o he Council o 16 Decembe 2020 on he quali y o wa e in ended o human consump ion. To each he p esc ibed limi s c(Fe) = 0.200 mg·L−1 , he selec ed cleaning me hod had o be combined wi h con- en ional lushing. The o al wa e consump ion was calcula ed as he o al olume o wa e consumed om he s a o he cleaning p ocess o i s end. The o al consump ion, he e o e, included he olume o wa e consumed o he ope a ion o he selec ed me hod and he olume o wa e consumed o con en ional lushing un il he d inking wa e quali y s anda ds we e eached. The e alua ion did no include possible loss in he e en o a ailu e and i s emo al, i his ailu e occu ed du ing cleaning. 2.5. Calcula ion o he To al Deposi s Remo ed as TSS The concen a ion o o al suspended solids (TSS) in collec ed samples we e de e - mined using il a ion h ough glass ibe il e s acco ding o Eu opean S anda d EN 872:2005. Con inuous moni o ing o u bidi y allowed o cons uc a cu e o dependence o he immedia e mass concen a ion o o al suspended solids on u bidi y and o calcula e missing alues o ob ain mo e accu a e esul s. The o al amoun o TSS in each expe imen was calcula ed using he sys em o mode n echnical compu ing Wol am Ma hema - ica [ 34 ] as a sum o de ini e in eg als o pa ial a eas unde a TSS concen a ion/consumed wa e olume cu e. The alues o he cumula i e olume o wa e consumed o lushing we e plo ed on he x-axis and on he y-axis he e we e plo ed he measu ed alues o TSS co esponding o he consumed amoun o wa e . A linea eg ession o he pa s be ween he indi idual measu emen poin s was pe o med and ound equa ions we e used o calcula e he de ini e in eg al. The equa ions hus di e ed o each locali y. 2.6. Solid Phase Composi ion The composi ion o solid phase was compa ed using Induc i ely coupled plasma op ical emission spec ome y (ICP-OES) EN ISO 11885:2009, powde X- ay di ac ion analysis (B uke AXS D8 Ad ance 2 Θ / Θ LynxEye, 40 KV/40 mA adia ion, emission line Cu-Kalpha, B uke EAS GmbH, Hanau, Ge many) and elec on mic oscopy using Quan a 650 FEG-Field Emission Scanning Elec on Mic oscope (FEI Czech Republic s. .o., B no, Czech Republic) a low- acuum-50 Pa, 1.4 nm @ 30 kV (SED). O ganic ma e in he solid phase o sedimen was es ima ed om he loss on igni ion (LOI 550 ) o he mass o measu ed o al suspended solids oxidized a 550 ± 5 ◦ C; = 1 h acco ding o ˇ CSN 75 7350:2008 Fu he on also as Vola ile suspended solids (VSS). 2.7. Liquid Phase Composi ion Colo , u bidi y, me als and suspended solids concen a ion we e analyzed in all he samples acco ding o he me hods o Induc i ely coupled plasma op ical emission spec ome y (ICP-OES) EN ISO 11885:2009, g a ime ic analysis EN 872:2005, spec opho- ome y EN ISO 6271:2015 and nephelome y ASTM D7726-11(2016)E1. 3. Resul s and Discussion Th ee calcula ion app oaches we e used o e alua e he amoun o emo ed sedimen in he o m o TSS. The o al amoun o TSS om one speci ic sec ion cleaning, which was de e mined by in eg a ion o he a ea unde a TSS concen a ion/consumed wa e olume cu e, was ecalcula ed o a uni o leng h, a uni o olume and a uni o a ea o he cleaned pipe. All he esul s a e summa ized in Table 3and di ided acco ding o implemen ed cleaning me hod and he chosen e alua ion app oach. As he esul s ob ained om unidi ec ional lushing showed a dependence on he pipe ma e ial and su icien da a In . J. En i on. Res. Public Heal h 2021,18, 4311 7 o 16 we e ob ained, his me hod o cleaning is in Table 3di ided in o wo sec ions UF o plas ic pipes and UF o me al pipes. Fo each cleaning me hod, an a e age and a median a e lis ed. The esul s a e commen ed on in he ollowing subsec ions. Table 3. Summa y o o al sedimen s eco e y as TSS pe uni leng h, uni olume and uni a ea and wa e consump ion o es ed me hods including a e age and median. (UNI—Unidi ec ional lushing; AS—Ai scou ing; Reco e y 1—To al TSS calcula ed pe leng h o he pipe; Reco e y 2—To al TSS calcula ed pe he inne olume o he pipe; Reco e y 3—To al TSS calcula ed pe he inne a ea o he pipe; * es ima ed wa e consump ion). Me hod Code Reco e y 1 Reco e y 2 Reco e y 3 Wa e Consump ion-Pipe Volume Ra io g·m−1g·m−3g·m−2 UNI o plas ic pipes 1UNI150PVC 0.14 8.0 0.29 13.7 2UNI80PVC/PE 0.15 29.0 0.59 4.5 3UNI80PE 0.72 143.0 2.86 6.0 4UNI100PVC 0.95 120.0 3.01 2.2 5UNI100PE 0.04 5.0 0.12 1.6 A e age 0.40 61.0 1.37 5.6 Median 0.15 29.0 0.59 4.5 UNI o me al pipes 6UNI100OC 2.03 258.0 6.46 3.9 7UNI80LT 0.76 151.0 3.01 9.9 8UNI80LT 2.15 427.0 8.54 4.6 9UNI100LT 0.50 63.0 1.58 1.4 10UNI80LT 0.74 148.0 2.96 4.1 A e age 1.23 209.4 4.51 4.78 Median 0.76 151.0 3.01 4.10 AS 12AS150LT 1.82 103.0 3.86 6.0 Comp ex® 11CO100PVC 1.63 208.0 5.19 4.0 12CO150LT 5.20 294.0 11.04 2.9 13CO200LT 10.37 330.0 16.50 4.9 14CO80LT 5.83 1160.0 23.21–50.31 13.1–25.3 * 15CO80LT 17.40 3612.0 69.23 9.2 A e age 8.09 1120.8 27.70 6.9 Median 5.83 330.0 16.50 4.9 Ice Pigging® 16IP150- 250PVC/PE/OC 25.27 1065.0 47.53 4.9 17IP250OC/LT 14.46 295.0 18.41 4.6 18IP150- 200OC/LT No da a a ailable 2.5 19IP80- 150OC/LT/PE/PVC No da a a ailable 2.2 20IP150PVC/PE 6.07 344.0 12.89 1.8 21IP100-150PE 1.77 130.0 4.36 3.9 22IP100- 150PVC/PE 9.86 677.0 23.39 2.6 23IP100- 200PVC/PE 18.91 965.0 39.58 2.4 24IP100- 200LT/PVC 15.90 736.0 31.10 4.3 25IP150- 200LT/PVC No da a a ailable 3.1 A e age 13.18 601.7 25.32 3.2 Median 14.46 677.0 23.39 2.6 In . J. En i on. Res. Public Heal h 2021,18, 4311 8 o 16 3.1. To al Sedimen s Remo ed as TSS To al amoun o emo ed impu i ies in he o m o TSS de e mined by in eg a ion was ecalcula ed pe (a) uni leng h, (b) uni olume and (c) uni a ea o he cleaned pipeline. The esul s di e depending on he chosen e alua ion me hod. In case o (a) he mos impu i ies we e emo ed as ollows: Ice Pigging ® (60%), Comp ex ® (36%) and unidi ec ional lushing (4%). In case o (b) he mos impu i ies we e emo ed by Comp ex ® (60%), Ice Pigging ® (33%) and unidi ec ional lushing (7%), and in case o (c) he mos impu i ies we e emo ed by Comp ex ® (50%), Ice Pigging ® (45%) and unidi ec ional lushing (5%). The pe cen age was calcula ed as he a io o he amoun o TSS emo ed by he selec ed me hod o he o al amoun o TSS emo ed by all me hods always ela ed o a dimension uni . See also Figu e 2. In . J. En i on. Res. Public Heal h 2021, 18, x FOR PEER REVIEW 8 o 16 3.1. To al Sedimen s Remo ed as TSS To al amoun o emo ed impu i ies in he o m o TSS de e mined by in eg a ion was ecalcula ed pe (a) uni leng h, (b) uni olume and (c) uni a ea o he cleaned pipe- line. The esul s di e depending on he chosen e alua ion me hod. In case o (a) he mos impu i ies we e emo ed as ollows: Ice Pigging® (60%), Comp ex® (36%) and unidi ec- ional lushing (4%). In case o (b) he mos impu i ies we e emo ed by Comp ex® (60%), Ice Pigging® (33%) and unidi ec ional lushing (7%), and in case o (c) he mos impu i ies we e emo ed by Comp ex® (50%), Ice Pigging® (45%) and unidi ec ional lushing (5%). The pe cen age was calcula ed as he a io o he amoun o TSS emo ed by he selec ed me hod o he o al amoun o TSS emo ed by all me hods always ela ed o a dimension uni . See also Figu e 2. Figu e 2. E ec i eness o me hods depending on he chosen e alua ion p ocedu e pe (a) uni leng h, (b) uni olume and (c) uni a ea o he cleaned pipe: The pe cen age was calcula ed as he a io o he amoun o TSS emo ed by he selec ed me hod o he o al amoun o TSS emo ed by h ee me hods (IP−Ice Pigging®; UNI−Unidi ec ional lushing; CO−Com- p ex®). In he case o uni leng h (a) he smalles amoun o emo ed TSS was gained du ing unidi ec ional lushing. Unidi ec ional lushing o plas ic pipes emo ed 0.04–0.95 g·m−1 and unidi ec ional lushing o me al pipes emo ed 0.50–2.15 g·m−1. The o al amoun pe uni leng h depended on he ma e ial o he cleaned pipe and i s age, he pa ame e s in- luencing hyd aulic condi ions. Comp ex® emo ed 1.63–17.40 g·m−1 (an a e age o 8.09 g·m−1 TSS o 5 applica ions) and Ice Pigging® emo ed 1.77–25.27 g·m−1 (an a e age o 13.18 g·m−1 TSS o 7 applica ions). Fo compa ison, V eebu g [12], Ca iè e e al. [19] and Ba - beau e al. [22] ob ained by unidi ec ional lushing esul s o emo ed impu i ies in o m o TSS om 0.1 o 0.4 g·m−1 and Mille e al. [35] using Ice Pigging® om 0.1 o 58 g·m−1. Howe e , compa isons based on uni leng h a e possible o make only o pipes o iden- ical nominal diame e s. The e o e, his e alua ion app oach is no sui able in he case o di e en pipe nominal diame e s and may dis o he esul s. In case o uni olume (b) amoun o emo ed TSS pe uni olume, he leas impu- i ies we e emo ed by unidi ec ional lushing o plas ic pipes, namely 8.0–143.0 g·m−3 (61.0 g·m−3 o TSS in a e age) and unidi ec ional lushing o me al pipes 63.0–427.0 g·m−3 (209.4 g·m−3 o TSS in a e age). Comp ex® emo ed 208.0–3612.0 g·m−3 (1120.8 g·m−3 o TSS on a e age) and Ice Pigging® emo ed 130.0–1065.0 g·m−3 (601.71 g·m−3 o TSS on a e age). Resea che s do no use his exp ession o esul s e y o en, and no compa able da a we e ound. In he case o uni a ea (c), which is he mos app op ia e me hod o esul exp ession as deposi s can se le o e he en i e pipe su ace [12]. The ollowing esul s we e Figu e 2. E ec i eness o me hods depending on he chosen e alua ion p ocedu e pe ( a ) uni leng h, ( b ) uni olume and ( c ) uni a ea o he cleaned pipe: The pe cen age was calcula ed as he a io o he amoun o TSS emo ed by he selec ed me hod o he o al amoun o TSS emo ed by h ee me hods (IP − Ice Pigging ® ; UNI − Unidi ec ional lushing; CO−Comp ex®). In he case o uni leng h (a) he smalles amoun o emo ed TSS was gained du ing unidi ec ional lushing. Unidi ec ional lushing o plas ic pipes emo ed 0.04–0.95 g · m −1 and unidi ec ional lushing o me al pipes emo ed 0.50–2.15 g · m −1 . The o al amoun pe uni leng h depended on he ma e ial o he cleaned pipe and i s age, he pa ame e s in luencing hyd aulic condi ions. Comp ex ® emo ed 1.63–17.40 g · m −1 (an a e age o 8.09 g · m −1 TSS o 5 applica ions) and Ice Pigging ® emo ed 1.77–25.27 g · m −1 (an a e age o 13.18 g · m −1 TSS o 7 applica ions). Fo compa ison, V eebu g [ 12 ], Ca iè e e al. [ 19 ] and Ba beau e al. [ 22 ] ob ained by unidi ec ional lushing esul s o emo ed impu i ies in o m o TSS om 0.1 o 0.4 g · m −1 and Mille e al. [ 35 ] using Ice Pigging ® om 0.1 o 58 g·m−1 . Howe e , compa isons based on uni leng h a e possible o make only o pipes o iden ical nominal diame e s. The e o e, his e alua ion app oach is no sui able in he case o di e en pipe nominal diame e s and may dis o he esul s. In case o uni olume (b) amoun o emo ed TSS pe uni olume, he leas impu- i ies we e emo ed by unidi ec ional lushing o plas ic pipes, namely 8.0–143.0 g · m −3 ( 61.0 g·m−3 o TSS in a e age) and unidi ec ional lushing o me al pipes 63.0–427.0 g · m −3 (209.4 g · m −3 o TSS in a e age). Comp ex ® emo ed 208.0–3612.0 g · m −3 (1120.8 g · m −3 o TSS on a e age) and Ice Pigging ® emo ed 130.0–1065.0 g · m −3 (601.71 g · m −3 o TSS on a e age). Resea che s do no use his exp ession o esul s e y o en, and no compa able da a we e ound. In he case o uni a ea (c), which is he mos app op ia e me hod o esul exp ession as deposi s can se le o e he en i e pipe su ace [ 12 ]. The ollowing esul s we e achie ed: unidi ec ional lushing o plas ic pipes emo ed 0.12–3.01 g/m 2 (an a e age o 1.37 g · m −2 In . J. En i on. Res. Public Heal h 2021,18, 4311 9 o 16 TSS o 5 applica ions), 1.58–8.546 g · m −2 om he me al pipes (an a e age o 4.51 g · m −2 TSS o 5 applica ions). Comp ex ® emo ed 5.19–69.23 g · m −2 (an a e age o 25.03 g · m −2 TSS o 5 applica ions), and Ice Pigging ® emo ed 4.36–47.53 g · m −2 (an a e age o 25.32 g · m −2 TSS o 7 applica ions). The amoun s o sedimen emo ed a ied only in he mul iples o ens o hund eds based on he chosen me hod. The 100–1000 imes g ea e e iciency has no been achie ed as is s a ed by Mille e al. [ 35 ]. Despi e he ac , ha he equi ed low a es in he pipeline we e no eached in he case o unidi ec ional lushing o me al pipes, a la ge amoun o sedimen pe 1 m 2 was emo ed om he me al pipes han om he plas ic pipes. The la ge amoun o sedimen pe 1 m 2 was also emo ed by Comp ex ® me hod in me al pipes. The same obse a ion was no alid o Ice Pigging me hod ® , as he e we e o en ope a ional complica ions wi h he dosing o ice in o he wa e supply sys em when cleaning me al pipes, which can ha e a signi ican e ec on he cleaning p ocess and o al eco e y o impu i ies. Nex , he esul s can be compa ed wi h he esea ch epo ed by Fann e al. [ 30 ] who p esen he esul s o Ice Pigging ® and unidi ec ional lushing cleaning me hod o asbes os cemen pipes DN = 150–400 mm, Mille e al. [ 35 ] who p esen he esul s o Ice Pigging o cas i on pipes DN = 200 mm, and Ba beau e al. [ 22 ] in es iga ing unidi ec ional lushing o pipes o DN = 200 mm o cemen -lined duc ile i on and unlined g ey cas i on. The esul s a y conside ably: 2.91–28.85 g · m −2 o asbes os cemen pipes, 90.498 g · m −2 and 23.13 g · m −2 o cas i on pipes, and 0.41 o g ey cas i on and 0.64 g · m −2 o cemen -lined duc ile i on. The esul s may di e due o di e en samples’ olumes, sampling in e als o cleaning e mina ion poin s. A commonly used limi o ending he cleaning is by achie ing a u bidi y alue ≤ 5 NTU [ 17 , 19 ]. Di e en pipe age, which has a di ec e ec on he condi ion o he pipeline, can ha e a g ea e ec (Figu e 3). The compa ison abo e con i ms he indings o Ba beau e al. [ 22 ] ha deposi accumula ion (and i s eco e y) is highly si e-speci ic. In . J. En i on. Res. Public Heal h 2021, 18, x FOR PEER REVIEW 10 o 16 chosen moni o ed pa ame e ( u bidi y X o al i on) and he alue [15,39], when cleaning is comple ed. In he case o Ice pigging consump ion may also be in luenced i he o al wa e consump ion includes wa e consumed o he necessa y hyd aulic es . These da a a e no usually lis ed-see [30,37]. Figu e 3. To al suspended solids and wa e consump ion ( ed- amed columns indica e inc us ed sec ions, o 18IP150- 200OC/LT, 19IP80-150OC/LT/PE/PVC and 25IP150-200LT/PVC-da a is no a ailable). 3.3. Maximum Impu i ies Concen a ion Rega dless o he chosen cleaning me hod, he e was always a sha p inc ease in measu ed alues o obse ed chemical pa ame e s (i on, manganese and aluminum mass concen a ion, colo and u bidi y) when he equi ed hyd aulic condi ions (o he on o he ice) we e eached. All he es ed me hods equally show a g adual dec ease in he concen a ion o emo ed impu i ies un il he momen when all pa ame e s me he e- qui emen s o Di ec i e (EU) 2020/2184 and he cleaning was inished. Howe e , he ime needed o emo e he la ges po ion o impu i ies di e ed (Figu e 4). The e o e, he achie ed maximum alues o TSS, colo , u bidi y and me als’ mass concen a ion also di e . The highes alues o measu ed pa ame e s we e achie ed using Ice Pigging ® when emo ed pa icles a e abso bed he mos in on o he ice me hod (TSS = 924–8100 mg·L −1 ; colo > 4000 mg·L −1 P ; u bidi y > 7500 ZF( ); ρ(Fe) = 65.7–627 mg·L −1 ; ρ(Mn) = 3.06–329 mg·L −1 ; ρ (Al) = 32.1–274 mg·L −1 ). While in Comp ex ® (TSS = 478–1200 mg·L −1 ; colo = 480– 2100 mg·L −1 P ; u bidi y = 66–2300 ZF( ); ρ(Fe) = 62.1–285 mg·L −1 ; ρ(Mn) = 1.06–67.7 mg·L −1 ; ρ(Al) = 1.15–22.9 mg·L −1 ) and unidi ec ional lushing (TSS = 6.4–450 mg·L −1 ; colo = 190– 1600 mg·L −1 P ; u bidi y = 35–950 ZF( ); ρ (Fe) = 0.573–138 mg·L −1 ; ρ(Mn) = 0.098–91.6 mg·L −1 ; ρ(Al) = 0.181–5.02 mg·L −1 ) pa icles a e g adually en ained by he wa e s eam, shea s ess in luences he esul s. Since samples aken du ing Comp ex ® had a cha ac e o a mixed sample gi en by a single block o wa e , he e o e he maximum measu ed concen a ions o indi idual pa ame e s p obably do no co espond o he absolu e max- ima ha we e eached du ing cleaning and may be unde es ima ed. The measu ed esul s hus showed ha colo , u bidi y o concen a ion indica o s a e no sui able o compa - ing he me hods be ween one o he , as h ee es ed me hods showed a di e en Figu e 3. To al suspended solids and wa e consump ion ( ed- amed columns indica e inc us ed sec ions, o 18IP150- 200OC/LT, 19IP80-150OC/LT/PE/PVC and 25IP150-200LT/PVC-da a is no a ailable). In . J. En i on. Res. Public Heal h 2021,18, 4311 16 o 16 27. Sunny, I.; Husband, S.; D ake, N.; McKenzie, K.; Boxall, J. Quan i y and quali y bene i s o in-se ice in asi e cleaning o unk mains. D ink. Wa e Eng. Sci. 2017,10, 45–52. [C ossRe ] 28. Foch o á, L.; Ru a , L. Ice Pigging: ˇ Ciš ˇeníPo ubíLedo ou Tˇ íš í. 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Applica ion o unidi ec ional lushing in wa e dis ibu ion pipes. J. Wa e Supply Res. Technol. 2011,60, 40–50. [C ossRe ]