INFLUENCE OF DIGESTATE CONCENTRATION IN NUTRIENT SOLUTION TO THE YIELD AND THE QUALITY OF WATER LENS FOR THE PURPOSE OF BIOGAS PRODUCTION

Vodena leća je široko rasprostranjena vrsta sitnih slobodno plivajućih kritosjemenjača, čiji je tipičan predstavnik velika vodena leća (Spirodela polyrhiza). Česta je na vodenim površinama kontinentalne Hrvatske, razmnožava se vegetativno i spolno te vrlo brzo povećava biomasu, pa je dobra sirovina za proizvodnju bioplina. Primarni cilj istraživanja je utvrditi mogućnosti kontinuiranog uzgoja velike vodene leće na različitim koncentracijama digestata s ciljem proizvodnje bioplina. Sekundarni cilj je utvrditi zavisnost između različitih koncentracija digestata korištenih za proizvodnju zelene mase vodene leće te kvantitete i kvalitete bioplina dobivenog kroz postupak anaerobne digestije pri termofilnim uvjetima. Pokusima su potvrđene postavljene hipoteze da će koncentracija digestata u hranjivoj otopini utjecati na prinos zelene mase različitih vodenih leća, da se vodene leće mogu kontinuirano uzgajati na otopini digestata i da koncentracija digestata utječe na proizvodnju bioplina i metana. Vodene leće se smatraju poželjnom sirovinom za proizvodnju bioplina, jer usvajaju nitrate iz poljoprivredne proizvodnje, koji zagađuju okoliš, te zbog svoje sposobnosti rasta u eutrofnim uvjetima. Uzgoj ovih biljaka i proizvodnja bioplina vjerojatno bi smanjili iskorištavanje obradivih površina za uzgoj različitih energetskih biljaka te pridonijeti zaštiti okolišaDuckweeds are a widespread species of small free-floating angiosperms, whose typical representative is the large duckweed (Spirodela polyrhiza). It is common on the water surfaces of continental Croatia, reproduces vegetatively and sexually and increases biomass very quickly, so it is a good raw material for biogas production. The primary goal of the research is to determine the possibilities of continuous cultivation of large duckweed at different concentrations of digestate with the aim of biogas production. The secondary goal is to determine the relationship between different concentrations of digestate used for the production of green mass of duckweed and the quantity and quality of biogas obtained through the process of anaerobic digestion under thermophilic conditions. Experiments have confirmed the hypotheses that the concentration of digestate in the nutrient solution will affect the green mass yield of different duckweeds, that duckweeds can be continuously cultivated in digestate solution and that the concentration of digestate affects biogas and methane production. Duckweeds are considered a desirable raw material for biogas production because they absorb nitrates from agricultural production, which pollute the environment, and because of their ability to grow in eutrophic conditions. The cultivation of these plants and the production of biogas would probably reduce the utilization of arable land for the cultivation of various energy plants and contribute to environmental protectio