<p>Proizvodnja bioetanola iz među- i nusproizvoda procesa<br />prerade šećerne repe, može imati pozitivan uticaj na<br />regionalnu ekomomiju i socio-ekonomski razvoj u zemljama<br />sa razvijenom industrijom konzumnog šećera, kao što je<br />Srbija. Kao proizvodni mikroorganizam u proizvodnji<br />etanola u najvećoj meri se koristi kvasac Saccharomyces<br />cerevisiae. Primena imobilisanih ćelija kvasca u fermentaciji<br />podloga sa visokom sadržajem šećera (iznad 250 g/l), tzv.<br />VHG fermentacija, je često izučavana sa ciljem povećanja<br />efikasnosti proizvodnje etanola. U ovom radu su ćelije S.<br />cerevisiae imobilisane na različitim novim nosačima:<br />presovanim rezancima šećerne repe (PRŠR), suvim<br />rezancima šećerne repe (SRŠR), parenhimskom tkivu stabla<br />kukuruza (PTSK) u obliku diska, na kombinovanim<br />nosačima od PTSK u obliku diska obloženog Ca-alginatom(K1) i ispunjenog Ca-aglinatom (K2), na kuglicama Caalginata(AB) kao i na kombinovanim kuglicama od Caalginata i mliva PTSK (ABC). Imobilisane ćelije kvasca su primenjene za fermentaciju melase i gustog soka šećerne repe sa krajnjim ciljem da se racionalnim korišćenjem</p><p>među- i nusproizoda procesa prerade šećerne repe postigne<br />efikasna proizvodnja etanola uz smanjene troškove<br />proizvodnje kao, i uz smanjenje emisije otpadnih tokova.<br />U radu je ustanovljeno da su PRŠR, SRŠR i PTSK efikasni<br />nosači za imobilizaciju ćelija kvasca zahvaljujući prisustvu<br />pozitivno naelektrisanih funkcionalnih grupa, visokoj<br />poroznosti, hidrofilnosti, mehaničkoj čvrstini i stabilnosti.<br />Takođe ovi nosači štite kvasac od osmotskog stresa,<br />toksičnog dejstva etanola i inhibitora. Zahvaljujući<br />heterogenoj strukturi PRŠR, SRŠR i PTSK se mogu koristiti<br />kao efikasni adsorbenti za ćelije kvasca, kao i za uklanjanje<br />katjonskih i anjonskih komponenata u postupku prerade<br />otpadnih voda. Pored toga, utvđeno je da PTSK predstavlja<br />alternativni obnovljivi izvor hranljivih materija neophodnih<br />kvascu tokom fermentacije melase i gustog soka, a takođe<br />deluje i kao antipenušavac. Primenom ćelija kvasca<br />imobilisanih na SRŠR ostvarena je maksimalna<br />produktivnost etanola od 1,48 g/lh za melasu i 1,57 g/lh za<br />gusti sok, pri početnoj koncentraciji šećera u podlozi 180 g/l.<br />Primenom ćelija kvasca imobilisanih na PTSK u obliku<br />diska (visine oko 5 mm i prečnika oko 20 mm) postignuta je<br />produktivnost etanola 1,26 g/lh za melasu 1,42 g/lh za gusti<br />sok, pri početnoj koncentraciji šećera 150 g/l. Osnovni<br />nedostatak primene imobilisanih ćelija na SRŠR i PTSK u<br />alkoholnoj fermentaciji je lako ispiranje ćelija sa nosača.<br />Kombinovani nosači u obliku diska PTSK obloženog Ca alginatom<br />(K1) i ispunjenog Ca-aglinatom (K2) su<br />pripremljeni kako bi se sprečilo ispiranje ćelija kvasca.<br />Utvrđeno je da nosač K1 nije adekvatan za povećanje<br />efikasnosti imobilizacije. Imobilizacijom kvasca punjenjem<br />nosača K2 je povećana efikasnost imobilizacije ćelija kvasca<br />na PTSK, ali je usled velike zapremine i kompaktnosti<br />nosača K2 tokom fermentacije delimično otežan transport<br />supstrata i produkata kroz disk.<br />Melasa i gusti sok šećerne repe su veoma dobre sirovine za<br />proizvodnju etanola, usled visokog sadržaja fermentabilnih<br />šećera, koji slobodne i/ili imobiliane ćelije S. cerevisiae mogu<br />direktno koristiti za fermentaciju. Međutim, uzimajući u<br />obzir hemijski sastav ovih sirovina i ostvarene parametre</p><p>fermentacije, utvrđeno je da je gusti sok bolja sirovina za<br />proizvodnju etanola od melase, posebno u VHG uslovima.<br />Takođe je utvrđeno da se gusti sok može koristiti kao<br />sirovina za fermentaciju bez dodataka hranljivih materija.<br />Ustanovljeno je da su melase koje preostaju nakon osmotske<br />dehidratacije crvenog kupusa i mrkve veoma dobre sirovine<br />za proizvodnju etanola pri početnoj koncentraciji šećera u<br />podlozi do 150 g/l, ali nisu pogodne sirovine za VHG<br />fermentaciju pomoću slobodnih i imobilisanih ćelija u AB<br />kuglicama. Fermentacijom melase nakon osmotske<br />dehidratacije kupusa i mrkve početne koncentracije šećera<br />125 g/l, primenom ćelija kvasca imobilisanih u AB<br />kuglicama, ostvarena je najviša produktivnost etanola od<br />1,24 g/lh i 1,30 g/lh. Tokom fermentacije melase i gustog soka<br />primenom ćelija kvasca imobilisanih u AB kuglicama usled<br />izdvajanja CO2, dolazi do narušavanja strukture kuglica<br />pojavom poprečne pukotine koja kuglicu polimera deli na<br />dva približno jednaka dela.<br />Kako bi se sprečila degradacija Ca-alginata tokom<br />fermentacije pripremljen je novi kombinovani nosač od Caalginata<br />i mliva PTSK (ABC). Dodatkom samlevenog PTSK<br />sa mikrostrukturom pčeljinjeg saća u Ca-alginat je povećana<br />poroznost kuglica čime je omogućen efikasniji prenos mase<br />supstrata i produkata, povećana je raspoloživa površina za<br />adsorpciju i rast ćelija kvasca kao i čvrstina i stabilost<br />kuglica. Poređenjem parametara fermentacije, utvrđeno je<br />da su ćelije kvasca imobilisane na ABC kuglicama efikasniji<br />biokatalizator u poređenju sa slobodnim ćelijama kvasca,<br />kao i u poređenju sa ćelijama imobilisanim u AB kuglicama.<br />Dodatkom samlevenog PTSK u podlogu ili u Ca-alginat<br />povećava se sadržaj etanola i metanola, smanjuje se sadržaj<br />kiselina i acetaldehida u sirovom destilatu, dok se sadržaj<br />viših alkohola, estara i furfurala ne menja značajno. Ćelije<br />kvasca imobilisane u kombinovanim ABC kuglicama se<br />mogu uspešno primeniti za pet ponovljenih fermentacija<br />gustog soka pri standardnim (NG) i uslovima visoke<br />koncentracije šećera (VHG) pri čemu se može postići<br />produktivnost etanola 1,92-2,30 g/lh. Primenom imobilisanih<br />ćelija kvasca u kombinovanim ABC kuglicama u<br />kontinualnoj VHG fermentaciji gustog soka, početne<br />koncentracije šećera 300 g/l, ostvaren je stabilan<br />fermentacioni sistem tokom 15 dana, pri čemu je<br />produktivnost etanola iznosila 3,29 do 4,66 g/lh.</p> / <p>Bioethanol production from intermediate and byproducts<br />of sugar beet processing has a beneficial scope<br />in view of the socio-economic development and regional<br />economy in countries with developed sugar industry,<br />such as Serbia. Saccharomyces cerevisiae strain is the<br />most widely used ethanol producing microorganism. To<br />increase the efficiency of ethanol production, many<br />process improvements including immobilized cells<br />application and fermentation of very high gravity (VHG)<br />media with initial sugar over 250 g/l, have been studied.<br />In the present work yeast S. cerevisiae was immobilized<br />onto different new carriers: pressed sugar beet pulp<br />(PSBP), dried sugar beet pulp (DSBP), maize stem<br />ground tissue (MSGT) disks, MSGT discs coated with<br />Ca-alginate (K1) and MSGT discs filled with Ca-alginate<br />(K2), Ca-alginate beads (AB) and combined beads made</p><p>of Ca-alginate and maize stem ground tissue meal (ABC).<br />Immobilized yeast cells were used for ethanol<br />fermentation of molasses and thick juice with purposes to<br />obtain efficient ethanol production, to lower high<br />operating costs and to achieve the zero-waste goal<br />through a rational use of by-products of sugar beet<br />processing.<br />In the present work it was found that PSBP, DSBP and<br />MSGT are efficient carriers for yeast cell immobilization<br />due to the presence of positively charged binding sites,<br />high porosity and hidrophylicity, good mechanical<br />strength and stability, while functioned as a fortification<br />against osmotic stress, toxins and inhibitors. It was also<br />found that due to the heterogeneous structure the PSBP,<br />DSBP and MSGT are promising adsorbents for the<br />removal of cationic and anionic compounds from<br />aqueous solutions in the waste water treatment. Besides,<br />it is found that the MSGT can be used as an alternative<br />nutrient source for yeast cells and as an anti foaming<br />agent. A maximum ethanol productivity of 1.48 g/lh and<br />1.57 g/lh was achieved in the fermentation of molasses<br />and thick juice (initial sugar of 180 g/l) using yeast<br />immobilized on DSBP. The highest values of ethanol<br />productivity, obtained in the case of using yeast<br />immobilized on MSGT discs as biocatalyst, for molasses<br />and thick juice (initial sugar of 150 g/l) fermentation<br />were 1.26 g/lh and 1.42 g/lh. The main disadvantage of<br />using DSBP and MSGT supported biocatalyst is intensive<br />leakage of yeast cells during the fermentation. In order to<br />prevent yeast leakage combined carriers in the form of<br />MSGT discs coated with Ca-alginate (K1) and MSGT<br />discs filled with Ca-alginate (K2) were prepared. The K1<br />carrier was found to be unsuccessful for improving yeast<br />immobilization efficiency, while the application K2<br />carrier improved yeast immobilization efficiency during<br />the fermentation. However, due to the large volume and<br />compactness of the K2 carrier substrate and product<br />mass transfer limitation were observed during the<br />fermentation.<br />The sugar beet molasses and thick juice are very good<br />raw materials for ethanol production due to high content<br />of fermentable sugars, which can be directly used for<br />fermentation by free and/or immobilized S. cerevisiae<br />cells without any modification. However, taking into</p><p>consideration quality of these raw materials and obtained<br />fermentation parameters, sugar beet thick juice was<br />found to be more suitable raw material for ethanol<br />fermentation, compared to molasses, particularly in the<br />VHG fermentation process and can be used without any<br />nutrient supplementation. Similarly, it was found that<br />molasses left after the osmotic dehydratation of red<br />cabbage (M1) and carrots (M2) are excellent raw<br />materials for ethanol fermentation of media with initial<br />sugar concentration up to 150 g/l, while they are not<br />convenient for VHG fermentation by free or immobilized<br />yeast cells in AB carrier. Maximum ethanol productivity<br />obtained at the end of fermentation of molasses M1 and<br />M2 by immobilized yeast in AB carrier was 1.24 g/lh and<br />1.30 g/lh, respectively. The release of CO2 during the<br />fermentation of molasses and thick juice by yeast cells<br />immobilized in the AB, lead to breakage of polymer<br />beads on two halves.<br />In order to prevent AB disruption, a new combined yeast<br />carrier (ABC) was developed by the addition of MSGT<br />meal into the Ca-alginate. It was found that the addition<br />of MSGT meal, with honeycomb microstructure,<br />provided large surface area for yeast cell attachment and<br />biofilm growth, and also increased alginate matrix<br />porosity, enabling better mass transfer characteristic,<br />better physical strength and stability of beads. The<br />highest values of fermentation parameters were obtained<br />in the fermentation system with yeast immobilized on<br />ABC carrier in comparison with free yeast cells and yeast<br />immobilized on AB carrier. The Ca-alginate and medium<br />supplementation with MSGT meal significantly increased<br />ethanol and methanol content, decreased acetaldehyde<br />and acetic acid content of the distillate, but did not affect<br />fusel alcohol, ester and furfural content of the distillate.<br />Repeated batch normal gravity (NG) and very high<br />gravity (VHG) ethanol fermentation of thick juice by<br />yeast immobilized on ABC carrier was successfully<br />carried out for at least five successive cycles without any<br />significant decrease in ethanol productivity which was in<br />the range 1.92-2.30 g/lh. Continuous VHG ethanol<br />fermentation of thick juice (initial sugar of 300 g/l) using<br />yeast immobilized on ABC was stable for at least 15 days<br />while achieved ethanol productivity was 3.29-4.66 g/lh.</p>
| Identifer | oai:union.ndltd.org:uns.ac.rs/oai:CRISUNS:(BISIS)82712 |
| Date | 07 September 2012 |
| Creators | Vučurović Vesna |
| Contributors | Razmovski Radojka, Markov Siniša, Mojović Ljiljana |
| Publisher | Univerzitet u Novom Sadu, Tehnološki fakultet Novi Sad, University of Novi Sad, Faculty of Technology at Novi Sad |
| Source Sets | University of Novi Sad |
| Language | Serbian |
| Detected Language | Unknown |
| Type | PhD thesis |
| Format | application/pdf |
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