| Sažetak | U ovom doktorskom radu proučavan je i razvijen stabilan i u ciklusima ponovljiv proces anaerobne obrade pivske komine kao monosupstrata. U dostupnoj literaturi, ovakav proces do danas nije opisan, niti je instaliran u industrijskom mjerilu. Razlog tome je što pivska komina kao supstrat nije pogodna za anaerobnu obradu zbog visokog udjela dušika i lignoceluloznih materijala (lignina) u svom sastavu. Razgradnjom lignina nastaju intermedijarni produkti kao što je p-krezol koji inhibira anaerobne mikroorganizme, pa oni nisu učinkoviti pri anaerobnoj razgradnji pivske komine. Predloženi rad obuhvaća istraživanje anaerobne razgradnje pivske komine od bioplinskog potencijala do stabilnog dvostupnjevitog procesa, u kojemu je anaerobni proces proveden u reaktoru za anaerobnu razgradnju čvrstih tvari (SS-AD) (engl. SS-AD – Solid State Anaerobic Digestion) u kojem se pretežito odvija hidroliza i u reaktoru s granuliranom biomasom (GBR) (engl. GBR-Granular Biomass Reactor) u kojem se pretežito odvija proizvodnja bioplina. Dugoročno stabilan proces postignut je sa 80,4 % -tnom učinkovitošću razgradnje suhe tvari i prinosom bioplina od 107,1 L/kg sirove pivske komine. Doktorski rad je podijeljen na više dijelova, u kojima su proučavane mogućnosti uspješne anaerobne razgradnje pivske komine kao monosupstrata. U prvom dijelu proučavana je termokemijska hidroliza komine, pri čemu je zaključeno da se komina može dobro predobraditi termokemijskom hidrolizom i da se samom termokemijskom hidrolizom dobro razgradi lignocelulozna struktura komine. Prema dobivenim rezultima, pokazano je da se kiselinskom hidrolizom (HCl) kod pH = 2 i T = 140 °C u trajanju od 2 sata može ekstrahirati maksimalno 55 % TOC-a iz čvrste u kapljevitu fazu. U drugom dijelu rada određen je bioplinski potencijal pivske komine. Iz sirove komine je moguće dobiti 105 L/kg bioplina. Upotrebom komine koja je termokemijski predobrađena s kiselinom pri T = 70 °C moguće je proizvesti oko 115 L/kg, a s kominom obrađenom pri 140 °C moguće je proizvesti oko 120 L/kg bioplina, što potvrđuje bolju razgradnju predobrađene komine. U trećem dijelu proučavana je anaerobna razgradnja pivske komine u jednostupnjevitom procesu (SS-AD reaktor) i u dvostupnjevitim procesima. U dvostupnjevitom procesu je istraživan proces proizvodnje bioplina u dvije reaktorske konfiguracije. Prvi proces je istraživan u konfiguraciji dvaju reaktora i to sa SS-AD reaktorom u kojem je provedena hidroliza i reaktorom s granuliranom biomasom (GBR) koji je bio namjenjen za proizvodnju bioplina.
Drugi dvostupnjeviti proces je razvijan u konfiguraciji dvaju reaktora s miješanjem, prvog reaktora s klasičnom mokrom hidrolizom (SDR) i drugog, reaktora s granuliranom biomasom (GBR). Zaključeno je da pri provedbi jednostupnjevitog procesa nema bitnih razlika u prinosu bioplina između eksperimenata provedenih sa sirovom i predobrađenom kominom.
Postotak biorazgradivosti sirove komine je iznosio 62,0 %, a predobrađene komine 62,2 %.
Iz sirove komine proizvedeno je 87,4 L/kg, a iz predobrađene 89,1 L/kg bioplina. Usporedbom ovih rezultata s rezultatima mjerenja bioplinskog potencijala može se zaključiti da je ostvareno 75 % vrijednosti bioplinskog potencijala sirovine. U dvostupnjevitom procesu (konfiguracija serijski povezanih SS-AD i GBR reaktora) razlika je očitija. Prilikom upotrebe sirove komine postignut je prinos bioplina 89,1 L/kg, a upotrebom predobrađene komine ova vrijednost iznosila je 103,2 L/kg. Postignuto je 63,5 % razgradnje suhe tvari sirove, a 73,6 % razgradnje suhe tvari predobrađene komine. Dvostupnjeviti proces proveden u reaktorima s miješanjem (konfiguracija serijski povezanih SDR i GBR reaktora), je još očitije prikazao razliku u razgradnji sirove i predobrađene komine. Razgradnjom sirove komine postignut je prinos bioplina od 106,4 L/kg, a kod predobrađene 105,5 L/ kg. Proces anaerobne razgradnje bio je značajno brži u slučaju kada je kao supstrat korištena predobrađena komina, jer je završio u periodu od 15 dana, što je dvostruko brže od 30 dana trajanja procesa kod sirove komine. Postotak razgradnje sirove komine u ovom slučaju iznosio je 83,1 %, dok je postotak razgradnje predobrađene komine iznosio 87,4 % suhe tvari. U ovom trećem dijelu rada pokazalo se, da je predobrada pozitivno utjecala na proces anaerobne razgradnje. Iz tog razloga u četvrtom dijelu doktorskog rada, istraživano je ponavljanje dvostupnjevitih procesa u ciklusima, pri čemu je upotrebljavana isključivo predobrađena komina. U ovom dijelu doktorskog rada, obzirom na pojavu intermedijarnih produkata kao inhibitora tijekom procesa i njihove akumulacije u reakcijskoj smjesi, istraživana je mogućnost izbjegavanja inhibicije procesa prilagodbom biomase. U tu svrhu u ciklusima su ponavljani dvostupnjeviti procesi razvijeni u prethodnom dijelu doktorskog rada (procesi u reaktorima bez miješanja i s miješanjem). Proces bez miješanja (konfiguracija serijski povezanih SS-AD i GBR reaktora) je bio vrlo uspješan u dogoročnom ponavljanju procesa u ciklusima. Uspješno je provođen 198 dana, što je ujedno i dokaz postizanja stabilnog procesa anaerobne obrade pivske komine kao monosupstrata, koji je unatoč inhibiciji s međuproduktima razgradnje lignocelulozne strukture supstrata, ponovljiv u ciklusima. Oko 100-og do 120-og dana provedbe procesa pojavile su se očekivane poteškoće s prilagodbom biomase na razgradnju intermedijarnih produkata, koje su uspješno savladane i proces je uspješno nastavljen. Dostignuta je razgradnja suhe tvari između 75,5 % i 80,4 % i prinos bioplina između 90,4 i 107 L/kg sirove pivske komine. Dvostupnjeviti proces u reaktorima s miješanjem (konfiguracija serijski povezanih SDR i GBR reaktora) je u prvom planu pokazao i bolju razgradivost supstrata. Postignuta je razgradnja suhe tvare između 88,6 % i 95,7 %, a proizvedeno je i više bioplina u odnosu na prethodni proces (između 83,1 L/kg i 119,8 L/kg sirove pivske komine), čime je gotovo dostignuta teoretska vrijednost bioplinskog potencijala. Međutim, problemi u kontinuiranoj provedbi procesa ustanovljeni su već oko 90-og dana trajanja procesa, kada se proces počeo usporavati. Intervencijom na proces oko 160-og dana, isti je spašen od zastoja, ali usporavanje se nastavilo do 290-og dana, kad je proces zaustavljen. Proces nije bio dovoljno stabilan za praktičnu primjenu i daljnji razvoj do industrijskog mjerila. Razlog za to je najvjerojatnije preintenzivno miješanje u reaktorima, uslijed čega su se u granuliranom reaktoru granule dezintegrirale, odnosno deaktivirale i nisu više bile u stanju uspješno razgrađivati intermedijarne fenolne produkte. U završnom dijelu rada analiziran je ostatak (digestat) anaerobne obrade komine za upotrebu u poljoprivredi kao gnojivo. Ostatak je zadovoljio sve parametre za upotrebu osim u pogledu izmjerene koncentracije antracena, koja je bila nešto povišena u odnosu na zakonski propisanu vrijednost. Pretpostavka je da bi sazrijevanjem ostatka (digestata) na isti način kako se ono odvija kod kompostiranja, bilo moguće zadovoljiti zahtjeve za njegovom upotrebom na poljoprivrednom zemljištu. Na taj način bi se krug upotrebe pivske komine kao monosupstrata zatvorio. Na temelju svega iznesenog, može se zaključiti da je proizvodnja bioplina iz pivske komine kao monosupstrata održiva i moguća. |
| Sažetak (engleski) | The proposed doctoral dissertation studies and develops a stable and reproducible in cycles anaerobic treatment process of brewery spent grain as a mono substrate. According to the available literature data, this process has not yet been described, nor it has been implemented on an industrial scale. The main reason for this is because the brewery spent grain is not suitable as a substrate for anaerobic treatment due to its high nitrogen content and high content of lignocellulose materials (lignin). Intermediate products such as p-cresol are formed during lignin degradation which inhibit anaerobic microorganisms and makes them ineffective in the anaerobic degradation of the brewery spent grain. The dissertation includes gradual research of the anaerobic degradation of brewery spent grain from the biogas potential to a stable two-stage process, in which the anaerobic process was divided into a reactor for the anaerobic digestion of solids (SS-AD - Solid State Anaerobic Digestion reactor), in which hydrolysis mainly took place and into a reactor with granular biomass (GBR Granular Biomass Reactor) in which most of the biogas production took place. A long-term stable process has been achieved with the degradation of dry matter of 80.4 % and biogas yield of 107.1 L/kg of raw brewery spent grain. The dissertation is divided in several parts, in which the possibilities for successful anaerobic digestion of brewery spent grain as mono-substrate were studied. The thermo-chemical hydrolysis of the brewery spent grain was analysed in the first part of the dissertation, and it was concluded that the brewery spent grain can be successfully pretreated with thermo-chemical hydrolysis and that the thermo-chemical hydrolysis decomposes well the lignocellulosic structure of the brewery spent grain. The results showed that the acid (HCl) hydrolysis at pH = 2 and T = 140 °C for 2 hours can extract up to 55 % of the total organic carbon (TOC) from solid into liquid phase. The biogas potential of brewery spent grain was determined in the second part of the doctoral thesis. The results showed that it is possible to produce 105 L/kg, 115 L/kg and 120 L/kg of biogas from raw brewery spent grain, thermo-chemically pretreated brewery spent grain with an acid at T = 70 °C and 140 °C, respectively, which confirmed better degradation of pretreated brewery spent grain. In the third part of the doctoral thesis, the anaerobic degradation of the brewery spent grain was studied in one-stage (SS-AD reactor) and two-stage processes. The biogas production in the two-stage process was studied using two types of reactor configurations. The first type of reactor configuration consisted of two reactors, a SS-AD reactor in which hydrolysis took place and a GBR reactor which was used for the biogas production. The second type of two-stage reactor configuration consisted of two reactors with applied mixing, a reactor for the conventional wet hydrolysis (SDR – Solid Digestion Reactor) and a GBR reactor. It was concluded that there was no significant difference in the biogas yield from raw and pretreated brewery spent grain in the case of the one-stage process. The degradation of dry matter was 62,0 % and 62,2 % and the specific biogas production was 87,4 L/kg and 89,1 L/kg from raw and pretreated brewery spent grain, respectively. It can be concluded that approx. 75 % of the biogas potential of the raw substrate was achieved by comparing these results with the results obtained from the measurements of the biogas potential. The difference in the degradation of dry matter and specific biogas production between raw and pretreated brewery spent grain was noted during the study of the anaerobic degradation with the first type of the two-stage process (reactor configuration consisting of a SS-AD and GBR reactors connected in series) where the specific biogas production of 89,1 L/kg and 103,2 L/kg and the degradation of dry matter of 63,5 % and 73,6 % were obtained from raw and pretreated brewery spent grain, respectively. The difference in the degradation of dry matter between raw and pretreated brewery spent grain was even more pronounced during the study of the anaerobic degradation with the two-stage process with mixing (reactor configuration consisting of a SDR and GBR reactors connected in series). During the anaerobic degradation the specific biogas production was 106,4 L/kg and 105,5 L/kg from raw and pretreated brewery spent grain, respectively. The anaerobic degradation process was considerably faster when the pretreated brewery spent grain was used as substrate because the process ended in 15 days, which was twice as fast in comparison to a 30 days duration of the process with the raw brewery spent grain. With this reactor configuration the obtained degradation of dry matter was 83,1 % and 87,4 % from raw and pretreated brewery spent grain, respectively. During this third part of the doctoral thesis it was shown that pretreatment had a positive effect on the anaerobic degradation process. For this reason, in the fourth part of the doctoral thesis only the pretreated brewery spent grain was used during the research of the repetition of the two-stage processes in multiple cycles. Due to the formation of intermediate products which acted as inhibitors to the anaerobic degradation process and due to their accumulation in the reaction mixture, the possibility of avoiding the occurence of inhibition of the process by adapting the biomass was investigated in this part of the dissertation. For this purpose the two-stage processes developed in the previous part of the doctoral thesis (processes in reactors with and without mixing) were repeated in several cycles. The process without mixing (reactor configuration consisting of a SS-AD and GBR reactors connected in series) has been very successful in long-term process repetition in cycles. It was conducted successfully for 198 days which is the the proof of achieving a stable anaerobic treatment process of brewery spent grain as a mono-substrate, which was repeatable in cycles despite inhibition. Between days 100 and 120 of the process, the expected difficulties in biomass adjustment for the degradation of intermediate products occurred, which were successfully overcame, and the process continued successfully. The dry matter degradation was between 75,5 % and 80,4 %, and the specific biogas production was between 90,4 L/kg and 107,0 L/kg of raw brewery spent grain. At the forefront, the two-stage process with mixing (reactor configuration consisting of a SDR and GBR reactors connected in series) achieved even better degradability. The degradation of dry matter was between 88,6 % and 95,7 % and the specific biogas production was higher in comparison to the previous process and it amounted between 83,1 L/kg and 119,8 L/kg of raw brewery spent grain, which was almost the theoretical biogas potential of the substrate. However, the problems with the continuous implementation of the process have been identified at approx. 90th day of the process, when the process began to slow down. Intervening on the process at approx. 160th day omitted a colapse, but the slowing down of the process continued untill the 290th day, when the process was stopped. The process didn't show sufficient stability for practical implementation and further development to the industrial scale. The reason for that was the use of too intensive mixing which caused the disintegration and deactivation of the granules in the GBR and the microorganisms were not able to adapt and successfully degrade the intermediate phenolic compounds. In the final part of the doctoral thesis the residue after the anaerobic treatment of brewery spent grain (the digestate) was analyzed for use in agriculture as fertilizer. The digestate met all parameters for use as fertilizer, except for anthracene where the legal limit was slightly exceeded. It's assumed that by further maturation of the residue (digestate), in an equal way as in the process of composting, the residue could meet all the legal requirements for the use on agricultural land. In this way, it would be possible to close the cycle of usage of the brewery spent grain as mono-substrate. Based on all presented data, it can be concluded that the biogas production from brewery spent grain as mono-substrate is possible and sustainable. |
