Degradation of lignocellulosic biomass by fungi Pleurotus ostreatus before the solid state anaerobic digestion

Omejeni viri, visoke cene in okoljski vpliv fosilnih goriv narekujejo razvoj alternativnih virov energije, med katere spada tudi proizvodnja energije iz lignocelulozne biomase. Lignocelulozna biomasa (LB) kmetijskih, vrtnih in gozdarskih ostankov se v veliki količini kopiči na regionalnem zbirnem centru za ravnanje z odpadki, kjer jo uporabijo v procesu kompostiranja. Z našo nalogo smo raziskali možnosti proizvodnje bioplina iz lokalno zbrane LB. S tem namenom smo optimirali in nadgradili proces anaerobne fermentacije LB za pridobitev biometana, obnovljivega vira energije. Izdelali smo pilotni sistem šaržnih reaktorjev s strnjenim slojem in križnim pretakanjem izcedne vode, z namenom simulacije procesa na ustrezni velikosti glede na vstopno biomaso. Pri izvedbi eksperimentov v reaktorjih na pilotnem merilu, smo glavni poudarek namenili študiji vpliva pretakanja izcedne vode med reaktorji na proizvodnjo bioplina. Rezultati tovrstnih poskusov so pokazali, da je pretakanje izcedne vode med reaktorji ključnega pomena za stabilnost procesa in povečano proizvodnjo bioplina. Raziskave kažejo, da je proizvodnjo bioplina iz LB možno povečati z učinkovito predobdelavo. Nadgradnjo procesa anaerobne fermentacije smo izvedli z biološko predobdelavo LB. In sicer smo glivo P.ostreatus gojili direktno na LB, v nadaljevanju smo za razgradnjo LB uporabili le encime glive. V laboratorijskem sistemu AMPTS smo določili biometanski potencial LB in LB preraščeni z glivo. Postopek predobdelave LB, pri katerem smo glivo gojili direktno na vzorcih LB, se je izkazal za neučinkovitega, saj je bil biometanski potencial vzorcev preraščenih z glivo mnogo nižji od biometanskega potenciala LB, ki ni bil izpostavljen nobeni predobdelavi. Naše raziskave smo nato nadaljevali v smeri gojenja glive na trdnem gojišču, sestavljenem iz pšeničnih otrobov in lignocelulozne biomase, in nato pridobivanja hidrolitičnih in oksidativnih encimov. Iz rezultatov encimskih aktivnosti smo ugotovili, da je gliva P. ostreatus, proizvedla celulitične encime v manjših količinah, medtem ko so bile lakaze, ki razgrajujejo ligninske komponente, proizvedene v velikih količinah. Glede na to, da veljajo lakaze tudi za širše industrijsko zanimive encime, smo z optimizacijo po Taguchi metodi raziskovali vpliv sestave gojišča na produktivnost lakaz. Optimizacija gojišča s Taguchi ortogonalno matriko L18 (21 × 37) se je izkazala za uspešno metodo, s katero smo pridobili podatke za sestavo gojišča na katerem izloči gliva P. ostreatus največ lakaz. Za primerjavo učinkovitosti razgradnje LB z encimskim ekstraktom, pridobljenim iz gojišč P. ostreatus, smo uporabili dva komercialna encima. Rezultati so pokazali, da je bil encimski ekstrakt učinkovit pri razgradnji LB, kakor tudi pri razgradnji trdnega ostanka po fermentaciji.The limited resources, high cost and the environmental impact of fossil fuels require the development of alternative energy sources, which include energy production from lignocellulosic biomass (LB). LB from agricultural, garden and forestry residues has been accumulated in large quantities at a regional collection centre for waste management, where it is used in the composting process. In our study, we discussed the possibility of biogas production from locally collected LB. In this purpose, we optimized and upgraded the anaerobic digestion process of LB for biomethane production, a renewable energy source. We have made our system of batch reactors with fluidized bed and leachate recirculating system, and we followed the principle of cost effectiveness production of reactors system. In carrying out the experiments in the reactors system on a pilot scale, the emphasis has been given to the study of leachate recirculation impact between reactors on the biogas production. The results of these experiments showed the crucial importance of leachate recirculation between reactors on the process stability and increased biogas production. Researchers have shown that the production of biogas from the LB can be enhanced by an effective pre-treatment. We have upgraded our anaerobic digestion process with LB biological pre-treatment. Biological pre-treatment has been carried out with P. ostreatus cultivation directly on LB samples and in the continuation of pre-treatment study only the enzymes from P. ostreatus have been used. Biomethane potential has been determined by laboratory AMPTS system for LB and pretreated LB, respectively. Pre-treatment process with direct fungi cultivation on LB has been proved as ineffective since the biomethane potential of these samples has been much lower than the biomethane potential of LB, which has not been treated with any pre-treatment. We continued our research in the field of fungi cultivation on solid state culture medium composed of wheat bran and LB with the aim of hydrolytic and oxidative enzymes production. From the results of enzyme activities, we found out that P. ostreatus has been, in our case, poor cellulolytic enzymes producer, but on the contrary lacases, known as enzymes for lignin degradation, have been produced in large quantities. According to the possibility of laccase application at industrial scale, we have been carried out optimization of culture medium for laccase production with Taguchi method. Optimization of culture medium with Taguchi orthogonal array L18 (21 × 37) has been proved as a successful method for obtaining the data of culture medium composition, which served as medium for maximum laccase production of P. ostreatus. To compare the efficiency of LB degradation of enzyme extract obtained from P. ostreatus cultivation, we have been used two commercial enzymes. The results showed an efficiency of enzyme extract in the LB and digestate degradation, respectively