Use of crude glycerol for biogas production

Proizvodnja biodizla z leti strmo narašča. Glavni stranski produkt pri proizvodnji biodizla je surovi glicerol, ki predstavlja kar desetino produktov. Ker se z naraščanjem proizvodnje biodizla veča tudi količina nastalega surovega glicerola, se zaloge le-tega hitro kopičijo. Prečiščen glicerol se uporablja v farmacevtski, kozmetični in prehrambeni industriji, vendar je čiščenje drago, zato bi bilo dobro najti alternativno uporabo za surovi glicerol. Namen našega dela je preizkus in analiza vpliva dodatka surovega glicerola k biomasi za proizvodnjo bioplina. Zanima nas obnašanje glicerola kot ko-substrata ter razlika v prostornini in sestavi dobljenega bioplina. Opravili smo eksperimenta z blatom iz čistilnih naprav ter s perutninskim inokulumom, slamnato steljo in silažo, substratom pa smo dodali še pufer za stabilizacijo pH vrednosti. Rezultati kažejo, da glicerol pozitivno vpliva na količino in sestavo nastalega bioplina. V obeh poskusih nam je večja količina dodanega surovega glicerola prinesla več bioplina. Ugotovili smo, da lahko s primerno količino dodanega surovega glicerola volumen produkta celo podvojimo. V diplomskem delu prikazujemo tudi ekonomsko analizo procesa s perutninskim gnojem, ki prikazuje izračun stroškov, ki jih ima bioplinarna za nakup in prevoz surovin, ki jih potrebuje za proizvodnjo določene količine bioplina. Zaradi nihanja cene glicerola so rezultati prikazani za različne cene le-tega. Vse naše ocene dajejo pozitiven rezultat, torej nižje stroške. Glicerol poveča ekonomičnost procesa, saj so stroški potrebnega glicerola v primerjavi s silažo vsaj prepolovljeni, razen tega pa z uporabo surovega glicerola odstranimo odpadke, medtem ko je uporaba silaže moralno sporna, ker se silaža uporablja v prehrani živine.The production of biodiesel is rising every year. Main by-product in the production is crude glycerol, which represents about ten percent of the products. Since with more produced biodiesel we also get more crude glycerol, there comes to quick stockpiling. Pure glycerol is used in pharmaceutical and cosmetic industryhowever, the purification is expensive. Therefore there is a need to find alternative use for crude glycerol. The purpose of diploma work is an experimental analysis of impact of crude glycerol addition to biomass for biogas production. The impact of glycerol as a co-substrate is studied in terms of the differences in volumes and compositions of produced biogas. Experiments are performed with sewage sludge and with poultry inoculum, poultry bedding and corn silage. Buffer is also added to substrates to stabilize pH value. Results show that glycerol positively influences the volume and composition of produced biogas. In both experiments more biogas was produced from substrates that contained crude glycerol. Results also show that with suitable quantity of added crude glycerol the volume of the product could even be doubled. In diploma work also economic analysis is performed for the experiment with poultry manure, which shows the calculation of expenses that the biogas plant has for the purchase and transport of the substrates, required to produce certain amounts of biogas. Calculations are made for different prices of crude glycerol. All variants give positive results, namely lower cost. Glycerol significantly increases the economics of the process – expenses for the glycerol are at least halved compared to those for the corn silage. Besides lower expenses, glycerol also has a positive impact on the environment due to reduced waste of crude glycerol, while usage of silage is ethically controversial as silage could be used as a livestock feed