A biochemical methane potential of pig slurry

A ailable online a www.sciencedi ec .com ScienceDi ec Ene gy Repo s 8 (2022) 153–158 www.else ie .com/loca e/egy The 8 h In e na ional Con e ence on Ene gy and En i onmen Resea ch ICEER 2021, 13–17 Sep embe A biochemical me hane po en ial o pig slu y And eia D. San osa,∗, João R. Sil ab, Luis M. Cas oa,b,c, Rosa M. Quin a-Fe ei aa aCIEPQPF – Chemical Enginee ing P ocesses and Fo es P oduc s Resea ch Cen e , Depa men o Chemical Enginee ing, Facul y o Sciences and Technology, Uni e si y o Coimb a, Po ugal bIns i u o Poli écnico de Coimb a, Ins i u o Supe io de Engenha ia de Coimb a, Rua Ped o Nunes, Quin a da No a, 3030-199 Coimb a, Po ugal cIns i u o Poli écnico de Coimb a, Ins i u o de In es igação Aplicada, Labo a ó io SiSus, Rua Ped o Nunes, Quin a da No a, 3030-199 Coimb a, Po ugal Recei ed 20 Decembe 2021; accep ed 17 Janua y 2022 A ailable online xxxx Abs ac This s udy assesses he me hane p oduc ion po en ial o he Anae obic Diges ion o Pig Slu y, using wo di e en Subs a e o Inoculum Ra ios, 0.65, and 1, and i s compa ison wi h he heo e ical p edic ion. The Speci ic Biogas P oduc ion, he Speci ic Me hane P oduc ion, and he a e age me hane con en we e de e mined o bo h expe imen s and adjus ed o S anda d Tempe a u e (273.15 K) and P essu e (1 a m). The esul s eached in his s udy show ha he expe ience conduc ed wi h a SIR o 1 p oduced mo e olume o biogas, wi h highe me hane con en han he one wi h he lowe SIR. Wi h a SIR o 1.0, i was achie ed a SMP o 0.568 NL CH4/g VS wi h an a e age me hane con en o 83%. The Technical Diges ion Time was ound o be 12 days. By compa ing he expe imen al BMP wi h he es ima ed alue o 0.623 NL CH4/g VS, i was possible o conclude ha he es ima ed alue p esen ed a de ia ion o jus 2.96 % du ing he assay wi h a SIR o 1. © 2022 The Au ho (s). Published by Else ie L d. This is an open access a icle unde he CC BY license (h p://c ea i ecommons.o g/licenses/by/4.0/). Pee - e iew unde esponsibili y o he scien i ic commi ee o he 8 h In e na ional Con e ence on Ene gy and En i onmen Resea ch, ICEER, 2021. Keywo ds: Anae obic diges ion; Biochemical me hane po en ial; Ci cula economy; Me hane p oduc ion; Pig slu y; Theo e ical me hane p edic ion 1. In oduc ion Pig p oduc ion has been inc easing o e he las ew yea s in Eu opean Union due o he A ican Swine Fe e (ASF) sp ead in China and o he coun ies in sou h-eas e n Asia [1]. The o me con ibu es o inc easing en i onmen al issues on wa e , soil, and ai due o he high o ganic load p esen in pig manu e, p oducing bad smells and gases, and causing acidi ica ion and eu ophica ion o he soils. The manu e om pig a ming can be di ided in o (a) slu y, which is a mix u e o eces, u ine, and wa e , (b) solid manu e, composed o eces, and li e emaining om sc apping wi h cleaning wa e . The amoun o manu e p oduced depends on he numbe o pigs and hei g ow h s a e, as well as on he eed composi ion [2]. Due o i s simplici y, eliabili y, and en abili y, he ∗Co esponding au ho . E-mail add ess: [email p o ec ed] (A.D. San os). h ps://doi.o g/10.1016/j.egy .2022.01.127 2352-4847/© 2022 The Au ho (s). Published by Else ie L d. This is an open access a icle unde he CC BY license (h p://c ea i ecommons. o g/licenses/by/4.0/). Pee - e iew unde esponsibili y o he scien i ic commi ee o he 8 h In e na ional Con e ence on Ene gy and En i onmen Resea ch, ICEER, 2021. A.D. San os, J.R. Sil a, L.M. Cas o e al. Ene gy Repo s 8 (2022) 153–158 Anae obic Diges ion (AD) is he mos common was ewa e ea men applied o manu e managemen . AD con e s o ganic ma e in o ene gy and educes pollu an gas emissions. Wi h his p ocedu e, i is also possible o con e he ag icul u e and o ganic by-p oduc s in o e ilize , uel, o elec ici y, inding a place in he ci cula economy and educing he en i onmen al impac [3]. Biochemical Me hane Po en ial (BMP) measu es he sample biodeg adabili y. The e o e, hese assays a e employed o unde s and and analyze pa ame e s such as pH, agi a ion, empe a u e, inoculum subs a e a io, among o he s, and he espec i e impac on he maximum me hane p oduc ion o a gi en subs a e [4]. Fo he BMP es s, a subs a e is mixed wi h an anae obic bac e ia cul u e, gene ally om an ac i e diges e . The mix u e is incuba ed unde mesophilic condi ions and con inuously mixed o e consecu i e days un il he achie ed me hane p oduc ion is lowe han 1% [5]. Du ing he incuba ion pe iod, he olume o biogas p oduced is measu ed as well as he me hane con en . Theo e ical me hods o p edic ing he BMP a e as and s aigh o wa d o implemen . Fo his, i is assumed ha he subs a e is comple ely deg aded [6]. Addi ionally, i is necessa y o add ess ha he accu acy o his me hod elies on he biodeg adable ac ion o he subs a e composi ion. The Speci ic Biogas P oduc ion (SBP) and he Speci ic Me hane P oduc ion (SMP) a e ools used o e alua e he BMP assay. The i s is desc ibed as he olume o biogas p oduced pe VS mass ed o he eac o and he second one is he olume o me hane p oduced pe VS mass ed o he eac o . When he SBP and he SMP ha e simila alues, he biogas p oduced has a high me hane concen a ion. The analysis o he SMP cu e o any BMP essay should desc ibe a simila beha io o o he SMP cu es o di e en subs a es [7]. The p ima y pu pose o his s udy is o de e mine he bes ope a ional condi ions o he AD o Pig Manu e (PM) a 8% concen a ion (on TS basis) o achie e maximum biogas p oduc ion. As a inal goal, he au ho s wan o add ess he easibili y o eusing he pig slu y was ewa e o p oduce ene gy while educing he o ganic ma e con en . To e alua e he Biochemical Me hane Po en ial (BMP) o he pig manu e, he wo selec ed Subs a e Inoculum Ra io (SIR) o he ba ch ope a ion we e 0.65 and 1. 2. Ma e ials and me hods 2.1. Subs a e and inoculum and expe imen al se up The subs a e used in his s udy was Pig Manu e (PM), collec ed om a pig a m placed in he cen al egion o Po ugal. Anae obic sludge om he anae obic diges e o a municipal was ewa e ea men plan was used as inoculum. The expe imen al p ocedu e was conduc ed in he AD Reac o loca ed a Ins i u o Supe io de Engenha ia de Coimb a, Po ugal. Fig. 1 p esen s a g aphic ep esen a ion o he AD Reac o used [8]. Fig. 1. Schema ic ep esen a ion o he labo a o y-scale anae obic diges e . I is cons uc ed in anspa en ac ylic and has 24.0 cm o diame e and 40.5 cm o o al heigh when he head ha e ains he biogas is down. The head o he AD eac o can mo e o accumula e he biogas p oduced. The head s o age can e ain a o al o 13.6 dm3. To assess i he inoculum had any me hane p oduc ion po en ial, be o e each essay, a blank es was pe o med, wi h he olume o he subs a e o be used being eplaced wi h dis illed wa e . 154 A.D. San os, J.R. Sil a, L.M. Cas o e al. Ene gy Repo s 8 (2022) 153–158 2.2. Analy ical me hods Chemical Oxygen Demand (COD) o al (COD ) and soluble (CODs) was de e mined by he 5220 D me hod es ablished in he S anda d Me hods (Closed Re lux). The To al Solids (TS), Vola ile Solids (VS), To al Suspend Solids (TSS), and Vola ile Suspend Solids (VSS) we e calcula ed using he 2540 B, D, and E in he S anda d Me hod [9]. The Me hane con en was e alua ed using he Abso p ion o CO2in he alkaline liquid me hod p oposed by Abdel-Hadi [10]. The measu ed biogas and me hane olumes we e adjus ed o S anda d Tempe a u e (273.15 K) and P essu e (1 a m). The elemen a y molecula analysis was conduc ed on he equipmen Fisons Ins umen s model EA1108 o de e mine he amoun o Ca bon (C), Oxygen (O), Hyd ogen (H), Ni ogen (N), and Sul u (S) ha is p esen in he PM. 2.3. The Biochemical Me hane Po en ial (BMP) In his s udy, besides he expe imen al de e mina ion o he BMP, he Elemen a y Composi ion (EC), Chemical Composi ion, and Chemical Oxygen Demand o biomass we e applied o es ima e he heo e ical BMP o he subs a e. 2.3.1. Elemen al composi ion The Buswell o mula, Eq. (1), allows es ima ing heo e ical BMP. Wi h his equa ion, i is equi ed o know he chemical composi ion o he subs a e [6]. CaHbOc+(a−b 4−c 2)H2O→(a 2+b 8−c 4)CH4 +(a 2−b 8+c 4)CO2(1) Eq. (1) was modi ied by Boyle [11] o include he ni ogen and he sul u , o ob ain he amoun o ammonia and hyd ogen sul ide p oduced du ing he AD p ocess, Eq. (2). CaHbOcNdSe+(a−b 4−c 2+3d 4+e 2)H2O→(a 2+b 8−c 4−3d 8−e 4)CH4 +(a 2−b 8+c 4+3d 8+e 4)CO2+dNH3+eH2(2) Eq. (3) allows es ima ing he heo e ical me hane po en ial acco ding o Achinas and Eu e ink [12]. BM P h EC (NL CH4/V S) =22.4×(a 2+b 8−c 4−3d 8−e 4) 12.017a+1.0079b+15.999c+14.0067d+32.065e(3) 2.3.2. Chemical Oxygen Demand and subs a e biodeg adabili y Niel a e al. [5] p oposed Eq. (4) ha allows es ima ing he maximum me hane po en ial using he mass o Vola ile Solids (V Sadded) and he COD concen a ion o subs a e. The au ho s assumed ha he in eg al oxida ion o he subs a e CaHbOcconsumes 64 g o oxygen pe each mole o he es ima ed o med me hane calcula ed om Eq. (1). BM P h C O D (NL CH4/g V S)=nCH4×R×T P×V Sadded ,whe e nCH4=C O D 64 (g mol )(4) The subs a e biodeg adabili y can be calcula ed acco ding o Eq. (5) [13]: Biodeg adabili y (%)=Cumula i e me hane yield (lCH4/g V S) Theo e ical me hane yield (lCH4/g V S)×100 (5) 155 A.D. San os, J.R. Sil a, L.M. Cas o e al. Ene gy Repo s 8 (2022) 153–158 3. Resul s and discussion The expe imen al BMP assay was pe o med wi h wo di e en SIR, 0.65 and 1.0, BMP1 and BMP2, espec i ely. Fo bo h assays, he ini ial and inal condi ions o he eac o sludge, as well as he biogas p oduc ion and me hane con en , we e e alua ed. The cha ac e iza ion o he inoculum and he subs a e used in he BMP assay a e p esen ed in Table 1. Be o e each expe imen , a blank assay was pe o med, and he biogas p oduc ion associa ed wi h he sludge was emo ed. Table 1. Cha ac e iza ion o he subs a e and he inoculum used in he BMP assay in e ms o COD , CODs, TS, VS, TSS, VSS, TC, and TN. Pa ame e [g/L] COD CODsTS VS TSS VSS TC TN Inoculum 40.62 2.278 29.48 17.32 23.08 11.77 1.195 0.725 Subs a e 7.391 2.182 3.657 2.732 2.225 1.815 0.716 0.183 3.1. Expe imen al biochemical me hane po en ial Fo he i s BMP assay (BMP1), he SIR was se a 0.65, o a wo king eac o olume o 8.6 L. In he second BMP assay (BMP2), a SIR o 1 and a wo king olume o 14.25 L we e used. The empe a u e was main ained a 36 ±1◦C and he s i ing a 8 pm. Fig. 2 shows he biogas p oduc ion du ing he BMP es s o bo h assays. The biogas p oduc ion and me hane con en we e assessed e e y day, excep weekends. Fig. 2. Biogas and me hane olume p oduced (NL) o (a) BMP1 and (b) BMP2. On day one, BMP1 biogas p oduc ion eached a maximum ou pu o 1.60 NL ep esen ing 1.39 NL CH4. F om his poin o wa d, he biogas p oduc ion dec eased un il day 10, wi h biogas p oduc ion ceasing wi h he expe imen being s opped on day 20. Rega ding he BMP2, he biogas p oduc ion s a ed slowe han o BMP1, eaching he maximum biogas p oduc ion on day 4 wi h 1.99 NL wi h a CH4o 1.75 NL. A e day ou , biogas p oduc ion dec eased un il day 18, p oducing jus abou he same olume e e y day un il day 24. On day 25, he biogas p oduc ion s ops, and he expe imen was e mina ed on day 30. Fig. 3 ep esen s he cumula i e me hane p oduc ion du ing he BMP1 and BMP2. Fig. 3. Cumula i e biogas and me hane p oduc ion (NL) o (a) BMP1 and (b) BMP2. Fo BMP1, he cumula i e biogas and me hane p oduc ion eached hei maximum on day 9, wi h 7.39 NL and 5.93 NL, espec i ely. On he o he hand, BMP2 eached he cumula i e biogas and me hane p oduc ion a day 25, wi h 19.06 NL and 16.03 NL, espec i ely. I is possible o unde s and ha he inc emen om BMP1 o BMP2 was conside able, 61.2% o he o al biogas p oduc ion and 63.0% o he o al me hane p oduc ion. Compa ing he esul s o bo h es s, BMP2 p oduced be e esul s han BMP1. Fo he i s assay, he SBP was 0.410 NL/g VS and he SMP o 0.329 NL CH4/g VS. The a e age me hane con en du ing he assay was 79.0 ±3.2%. In BMP2, i was possible o achie e an SBP o 0.675 NL/g VS, and SMP o 0.568 NL CH4/g VS. 156 A.D. San os, J.R. Sil a, L.M. Cas o e al. Ene gy Repo s 8 (2022) 153–158 The a e age me hane con en du ing his assay was 82.8 ±3.2%. The e o e, he pe cen age o me hane p oduced on BMP2 was, on a e age, 3.8% highe since he a io o subs a e o inoculum was highe han in BMP1. Ano he aspec wo h men ioning is he echnical diges ion ime (TDT), de ined as he ime equi ed o each 80%–90% o o al biogas p oduc ion [14]. This a iable is c ucial o make he scale-up o he anae obic diges e s because i can be assumed as he Hyd aulic Re en ion Time (HRT) o he p oposed condi ions and unde con inuous ope a ion. Fo he second expe imen , he TDT was eached be ween days 12 and 16, when 77.9% and 91% o he o al biogas p oduc ion was achie ed. In he i s expe imen , he TDT is be ween days 5 and 7, when 76.6% and 89.6% o he o al biogas was p oduced. Ka le e al. [15] used a SIR o 0.5 and a VS concen a ion o 2.5 g VS/L had achie ed an SBP o 0.394 NL/g VS and an SMP o 0.325 NL CH4/g VS. Using he same SIR and inc easing he VS concen a ion o 3.5 g VS/L, Ka le and Chen [14], eached SBP o 0.495 NL/g VS and an SMP o 0.323 NL CH4/g VS. When compa ing he esul s ob ained in bo h pape s, i can be seen ha he inc ease o he VS concen a ion imp o ed he biogas p oduc ion, bu he me hane con en dec eased om 82.6% o 63.5%. Sun e al. [16] execu ed a BMP assay in 500 ml lasks wi h a wo king olume o 400 mL, wi h a VS concen a ion o 10 g VS/Land a SIR o 0.5 a 36 ◦C. The subs a e had a concen a ion o 5.1% on TS basis. An expe imen al me hane yield o 0.308 NL CH4/gVS and a p edic ed me hane yield o 0.479 NL CH4/gVS we e achie ed, which a e lowe han he ones ob ained in his pape o bo h cases wi h SIR 0.65 and 1. Zhang e al. [17] used a SIR o 1.5 and a subs a e concen a ion o 40 gVS/L. The ini ial pH was adjus ed o 7.0 ±0.1, and he empe a u e inside he diges e s was main ained a 37 ±1◦C. The du a ion o he expe imen was dependen on he biogas o ma ion. In hei expe imen s, hey achie ed 0.359 NL CH4/gVS. The p esen ed esul s indica e ha a SI o 1 p oduces he bes esul s when compa ed o SI o 0.5, 0.65, and 1.5. Howe e , i is necessa y o keep in mind ha he ype o eac o , sludge, inoculum, and o he expe imen al condi ions a e di e en . 3.2. Theo e ical biochemical me hane po en ial An elemen a y molecula analysis was conduc ed o de e mine he amoun o Ca bon (C), Oxygen (O), Hyd ogen (H), Ni ogen (N), and Sul u (S) ha is p esen in he PM. The composi ion is p esen ed in Table 2 Table 2. Composi ion o he subs a e in % (m/m) o each elemen . Elemen C H O N S % (m/m) 41.7 5.18 22.4 1.84 0.0100 The heo e ical maximum me hane po en ial was p edic ed by applying Eqs. (4) and (5), wi h he ob ained alues p esen ed in Table 3, as well as he pe cen age o biodeg adabili y o he subs a e and he de ia ion be ween he heo e ical and expe imen al BMP. Analyzing Table 3, i is possible o conclude ha he BMP2 consumes highe amoun s o subs a e when compa ed wi h BMP1. This leads o a conclusion ha using a SIR o 1 he AD’s pe o mance will be op imized, he maximum me hane ha i is possible o achie e om his subs a e will be a ained. Table 3. Theo e ical p edic ion o he BMP h ough he EC and COD, biodeg adabili y, and de ia ion. Pa ame e BM P h EC BM P h C O D BMP1 BMP2 N L CH4/g VS 0.623 0.947 0.329 0.568 Biodeg adabili y (%) 52.8 91.1 De ia ion o BM P h EC (%) 67.5 2.96 4. Conclusions The BMP is shown o be a e y use ul ool o selec ope a ional condi ions o imp o e biogas p oduc ion du ing he anae obic diges ion p ocess. Compa ing he esul s o bo h assays, he BMP2, in which a highe SIR was used (1.0), p oduced be e esul s han BMP1 (SIR 0.65). I was egis e ed an inc ease o 60.6% o he SBP, and he SMP imp o ed by abou 62.7% wi h he a e age me hane con en inc easing om 79.0 o 82.8%. The echnical diges ion ime was ound o be 5–7 days o he i s assay and 12–16 days o he second one. These numbe s can be a e e ence o HRT o u u e wo k wi h simila condi ions. The esul s ob ained in BMP2 we e much close o he heo e ical p edic ions o BMP, indica ing ha wi h a SIR o 1.0 he amoun o subs a e added o he diges e was enough o achie e a me hane p oduc ion close o he heo e ically a ainable alue. 157 A.D. San os, J.R. Sil a, L.M. Cas o e al. Ene gy Repo s 8 (2022) 153–158 CRediT au ho ship con ibu ion s a emen And eia D. San os: In es iga ion, Da a cu a ion, Concep ualiza ion, Fo mal analysis, Valida ion, W i ing – o iginal d a . Jo˜ ao R. Sil a: Da a cu a ion, W i ing – e iew & edi ing. Luis M. Cas o: Concep ualiza ion, Supe ision, Valida ion, W i ing – e iew & edi ing. Rosa M. Quin a-Fe ei a: Concep ualiza ion, Supe ision, W i ing – e iew & edi ing, P ojec adminis a ion, Funding acquisi ion. Decla a ion o compe ing in e es The au ho s decla e ha hey ha e no known compe ing inancial in e es s o pe sonal ela ionships ha could ha e appea ed o in luence he wo k epo ed in his pape . Acknowledgmen s Au ho s g a e ully acknowledge o P oyec o 0340 SYMBIOSIS 3 E, co inanciado po el FEDER a a ´ es del P og ama INTERREG V A Espa˜ na – Po ugal (POCTEP). Funding INTERREG V A Espanha Po ugal (POCTEP) 007 Re e ences [1] Eu opean Comission. Sho - e m ou look o EU ag icul u al ma ke s in 2019 and 2020 au umn 2019 Edi ion N◦25 39. 2020. [2] Mache e JB, Chabo RG. A e iew o pigge y manu e managemen : gene ally, ac oss wes e n, Asian and a ican coun ies. Bo swana J Ag ic Appl Sci 2020;14:17–27. h p://dx.doi.o g/10.37106/bojaas.2020.17. [3] Secco C, Luz LM, da Pinhei o E, de F ancisco AC, Puglie i FN, Pieka ski CM, F ei e FMCS. Ci cula economy in he pig a ming chain: P oposing a model o measu emen . J Clean P od 2020;260:121003. h p://dx.doi.o g/10.1016/j.jclep o.2020.121003. 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