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Biomass from semi-natural grassland for bioenergy

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Pisipilt

KuupƤev

2014

KƤttesaadav alates

Ajakirja pealkiri

Ajakirja ISSN

Kƶite pealkiri

Kirjastaja

Eesti MaaĆ¼likool

Abstrakt

One of the under-utilised potential agricultural sources of bioenergy feedstock is the herbaceous biomass obtained from semi-natural grasslands. For biodiversity maintenance, it is important that semi-natural grasslands are managed continuously using extensive methods (one cut per year and without seeding, fertilisation). However, many countries are facing great difficulties with consuming the biomass from these grasslands due to its low forage value. Therefore finding an alternative use of biomass from semi-natural grasslands has become a challenging option for bioenergy production. The main aim of the thesis is to evaluate the energy potential of herbaceous biomass from three Estonian semi-natural grassland types (alluvial meadow, dry to mesic meadow and wooded meadow) for bioenergy production. The share of different functional groups (grasses, legumes, sedges/rushes and other forbs), characteristics relevant for bioenergy production and factors that influence these parameters were examined. The biomass potential varies between semi-natural grassland types studied. In Estonian conditions the highest biomass yield can be obtained from alluvial meadows and this is the only type where the amount of biomass increases significantly from June to July. In alluvial meadows the largest proportion of biomass was contributed by sedges/rushes, in dry to mesic meadows the dominant functional group was grasses and other forbs group was prevalent in wooded meadows. The chemical composition and calorific value of biomass varies by functional groups. The highest cellulose concentration is in grasses and hemicellulose in sedges/rushes, while the concentration of lignin is the highest in legumes and other forbs. The average lignin and Ca concentration in biomass increases in time, but N concentration in biomass declines during summer. The highest Cl concentration is in grasses and the lowest in legumes, whilst the highest N and Ca concentration are in legumes. The other forbs group has the highest K, Mg and ash concentrations with the lowest calorific value and the sedges/rushes and legumes have lower ash content with higher calorific values. Biomass ensiling does not influence methane yield, but methane potential varies by functional groups. The feedstock-specific methane yield was the highest in grasses and sedges/rushes and the lowest in the other forbs. The highest energy potential can be obtained from alluvial meadows (>100 GJ ha-1) followed by dry to mesic meadows and wooded meadows. Theoretical energy yield through combustion is higher than that of methane production. Even with conservative assumptions about energy input (10 GJ ha-1), the energy yield from semi-natural grasslands, especially from alluvial meadows can be comparable with that of dedicated energy crops in boreal region. Alternative usage of the herbaceous biomass from semi-natural grasslands for bioenergy is a reasonable option for both sustainable management of semi-natural grasslands to achieve nature conservation goals and for embodying resource-efficiency principles.
KƤesoleva tƶƶ peamiseks eesmƤrgiks oli hinnata rohtse biomassi energeetilist potentsiaali bioenergia tootmiseks Eesti kolmel poolloodusliku rohumaa tĆ¼Ć¼bil (aru-, lammi- ja puisniit). Lisaks uuriti poollooduslike rohumaade biomassi funktsionaalsete gruppide koosseisu (kƵrrelised, liblikƵielised, tarnad/loalised ja muud rohundid) ja bioenergia tootmiseks olulisi omadusi ning neid mƵjutavaid tegureid. Uuritud poollooduslike rohumaade biomassi potentsiaal on vƤga varieeruv suurima keskmise saagikusega lamminiitudel, kus ainsa niidutĆ¼Ć¼bina biomassi kogus juunist juulini kasvas. Funktsionaalsete gruppide osakaal sƵltus rohumaa tĆ¼Ć¼bist. Suurim tarnade/loaliste osakaal biomassis oli lamminiitudel. KƵrrelised domineerisid aruniitudel ja muud rohundid puisniitudel. LiblikƵielisi esines kƵikidel poolloodusliku rohumaa tĆ¼Ć¼pidel, aga suurim osakaal biomassis oli aruniitudel. Funktsionaalsete gruppide biomass oli erineva keemilise koostise ja kĆ¼ttevƤƤrtusega. Kui tselluloosi ja hemitselluloosi sisaldus on kƵrgeim vastavalt kƵrrelistes ja tarnades/loalistes, siis kƵige suurema ligniini sisaldusega on liblikƵielised ja muud rohundid. Vastupidiselt rohtse biomassi keskmise ligniini sisalduse suurenemisele suve jooksul, langes biomassi keskmine N sisaldus, olles suurim liblikƵielistes. KƵigi funktsionaalsete gruppide biomassi S sisaldus oli sarnane, suurim Cl sisaldus leiti kƵrrelistes. Muud rohundid sisaldasid kƵige rohkem tuhka ja K ning koos liblikƵelistega ka Ca ja Mg. Biomassi keskmine Ca sisaldus suurenes suvekuude jooksul. KƵige madalam kĆ¼ttevƤƤrtus oli muudel rohunditel. Uurimistƶƶ kƤigus selgus, et rohtse biomassi sileerimine ei mƵjutanud metaani potentsiaali. Samas sƵltus see funktsionaalsest grupist - eksperimendi alguses oli metaani saagis suurim liblikƵielistel ja muudel rohunditel ning eksperimendi lƵpuks oli see suurim tarnadel/loalistel ja kƵrrelistel. Suurim teoreetiline energiapotentsiaal (>100 GJ ha-1) on lamminiitudel ning see on vƵrreldav bioenergiakultuurina kasvatatava hariliku pƤideroo energiapotentsiaaliga. Aruniitudel on see potentsiaal ligi kaks ja puisniitudel kolm korda vƤiksem. Energiasaagis pindalaĆ¼hiku kohta sƵltub biomassi kasutusviisist. Biogaasi tootmisel on see vƤhem kui 60% teoreetilisest potentsiaalist, mida oleks vƵimalik saada, kui seda biomassi absoluutselt kuivana pƵletada. Kui arvestada biomassi kƤttesaamise kuludeks ka kuni 10 GJ ha-1 on osade poollooduslike rohumaade majandamine energiakultuuridega energeetiliselt sama otstarbekas. Seega on poollooduslike rohumaade rohtse biomassi alternatiivne kasutamine bioenergia tootmiseks vƵimalik ja mƵistlik. See soodustaks pool-looduslike rohumaade kestlikku majandamist ja sƤilimist ning biomassi ressursside tƵhusat kasutamist.

Kirjeldus

MƤrksƵnad

rohumaad, biomass, biomassienergia, tootmine, Eesti, dissertatsioonid

Viide

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