Determination of macronutrients in various digestates and synthetic fertilisers

Glavna produkta anaerobne razgradnje sta bioplin in presnovljen digestat, ki je bogat z makro in mikrohranili. Presnovljena biomasa je znana kot odlično gnojilo in je bolj homogena in bogata s hranili kot svež živalski gnoj. Možna je uporaba različnih surovin za izboljšanje učinkovitosti proizvajanja bioplina in večje vsebnosti hranil v presnovljeni biomasi. Raziskali smo kako substrati z različnimi vrstami dodanih snovi povečajo nastanek bioplina in obogatijo presnovljeno biomaso z dušikom, fosforjem in kalijem. Uporabljeni vzorci za analize so bili sestavljeni iz mešanice gnoja in inokuluma oz. iz mešanice gnoja, inokuluma ter dodanih različnih substratov (hranljivih surovin) kot so alge, odpadno olje, ostanki hrane, jedilni škrob in koruzna silaža. Med procesom anaerobne digestije smo spremljali volumen nastalega bioplina in vrednost pH digestata, s kivetnimi testi smo presnovljenemu digestatu merili vsebnost dušika in fosforja ter z atomsko emisijsko spektrometrijo določevali vsebnost kalija. Vsebnosti makrohranil (NPK) smo analizirali tudi v tekočih in trdnih umetnih gnojilih z znano sestavo ter primerjali dobljene vrednosti. Rezultati so pokazali, da so dodatki različnih hranljivih surovin povečali proizvodnjo bioplina glede na vzorce brez dodane hranljive snovi. Kot najboljša surovina se je izkazalo odpadno olje, sledijo mu koruzna silaža, jedilni škrob, ter ostanki hrane. Najmanj bioplina so proizvedle alge. Vrednost pH je celoten čas procesa ostajala v območju optimalnega intervala za metanogene bakterije. Rezultati analize NPK so pokazali, da je uporaba različnih surovin izboljšala vsebnost makrohranil. Najvišje vsebnosti kalija in dušika smo izmerili v vzorcih z dodanimi ostanki hrane in škrobom, najvišje vsebnosti fosforja pa pri vzorcih z dodanimi algami.The main products of anaerobic degradation are biogas and digestate rich in macro and micro-nutrients. The digested substrate is known as a valuable fertilizer and is more homogeneous and richer with nutrients than fresh manure. It is possible to use different raw materials to improve the efficiency of biogas production and to obtain higher nutrient content in digested substrates. During the diploma thesis it was investigated how substrates with different types of added substances increase the production of biogas and enrich the digested substrates with nitrogen, phosphorus and potassium. The samples used for the analyses were composed of a mixture of manure and inoculum or from a mixture of manure, inoculum and various substrates (nutrients) added, such as different types of algae, waste oil, food residues, edible starch and corn silage. During the anaerobic digestion process the volume of the resulting biogas and the pH of the digestate were monitored, and in the digestate nitrogen and phosphorus content were measured with the cuvette tests and potassium content with the atomic emission spectrometry. Macronutrients contents (NPK) were also analysed in liquid and solid synthetic fertilizers with known composition and the obtained values were compared with specified values. The results showed that the addition of various co-substrates increased the production of biogas compared to samples without added co-substrates. The best co-substrate showed to be waste oil, followed by corn silage, edible starch, and food residues. The smallest amounts of biogas were obtained from algae. The pH value throughout the process remained within the optimal range for methanogenic bacteria. The results of the NPK analysis showed that the use of various raw materials improved the content of macronutrients. The highest potassium and nitrogen contents were measured in samples with added food residues and starch, and the highest phosphorus content for samples with added algae