I såväl Brasilien som runt om i världen finns stora mängder organiskt avfall som skulle kunna utnyttjas på ett bättre sätt. Många potentiella substrat för biogasproduktion deponeras, eldas upp eller komposteras utan att den energi som skulle kunna utvinnas vid denna process tas tillvara. Detta examensarbete inriktade sig på att i laboratorium undersöka potentialen för biogasproduktion från några av dessa avfallsprodukter. Från biodieselproduktion, vilket är en snabbt växande industri i Brasilien, fås exempelvis 1 kg av restprodukten råglycerol per 9 kg producerad biodiesel. Detta är en restprodukt som man i dagsläget letar efter fler tillämpningar för och biogasproduktion har visat sig vara en möjlighet. Biogas har som förnybart bränsle dessutom ökat i attraktivitet under de senaste åren som ett alternativ till fossila bränslen. Syftet med undersökningen var att se om en liten mängd tillsatt råglycerol, eller glycerin som det också kallas, till en redan pågående rötningsprocess kunde öka den totala mängden producerad biogas från huvudsubstratet i fråga. Under arbetets gång utfördes två separata laboratorietester på olika typer av substrat. Det ena var slakteriavfall från ett kycklingslakteri och det andra var ett rötslam från en avfallshanteringsanläggning där industriellt avfall behandlas i bassänger med anaerobisk rötning. Dessa två substrat representerade två mycket olika mikrobiologiska processer där den ena var en ganska ostabil, nystartad process medan den andra var mycket stabil och etablerad. Resultaten från testerna visar att den ostabila processen inte alls klarade påfrestningen som det tillsatta glycerinet innebar, samtidigt som den stabila klarade sig mycket bra. Därför är en av slutsatserna som dras av arbetet att stor försiktighet måste tas när glycerin ska fasas in i en pågående rötningsprocess. Testerna visar dock att en satsvis tillsats av glycerin till rötslammet från avfallshanteringsanläggningen Ecocitrus skulle kunna öka biogasproduktionen från denna anläggning markant, vilket är ett intressant resultat då de står nära en investering i en riktig biogasanläggning. En tillsats av 6,0 eller 9,0 vol.% glycerin till en sådan anläggning har potential att fördubbla biogasproduktionen, samtidigt som metanhalten hålls på en godtagbar nivå. / In both Brazil and around the world, there are large amounts of organic waste that could be exploited in a better way. Many potential substrates for biogas production is deposited in land fillings, burned or composted, without taking advantage of the energy that could be extracted in this process. This thesis focuses on the potential for biogas production from some of these waste products. From biodiesel production for example, which is a rapidly growing industry in Brazil, 1 kg of the waste product crude glycerol is obtained per every 9 kg of produced biodiesel. This is a waste product that is beginning to be in a need for more applications, and biogas production has proven to be a possible application. Biogas as a renewable fuel has furthermore increased in attractiveness in the latest years, as an alternative to fossil fuels. The purpose of this study was to see if a small amount of added crude glycerol, also known as glycerine, to an ongoing digestion process could increase the total amount of biogas produced from the main substrate in question. During the test period, two separate laboratory tests were carried out on various types of substrates. One was the waste from a chicken slaughterhouse and the other was sludge from a waste treatment plant where industrial waste is being treated in pools with anaerobic digestion. These two substrates represented two very different microbiological processes of which one was a quite unstable, recently started process, while the second one was very stable and established. The results of the tests show that the unstable process could not manage the stress that the glycerine meant for the microorganisms, while the stable managed to handle it very well. One of the conclusions drawn from the work is that great care must be taken when glycerine is added to an ongoing anaerobic digestion process. The tests show that a batch addition of glycerin to the substrate from the waste treatment plant Ecocitrus could increase the biogas production from this plant considerably. This is an interesting result since this company is close to an investment in a real biogas plant. An addition of 6.0 or 9.0 vol.% glycerine to such a plant has the potential to double the biogas production, while methane concentration is still kept on an acceptable level.

The increased use of fossil fuels during the last centuries has caused elevated levels of carbon dioxide in the atmosphere. There is significant evidence that this is the cause of global warming. To mitigate the global warming, measures has to be taken to use renewable fuels and make processes more efficient. Catalytic gasification and downstream upgrading of synthesis gas is a promising technology for biofuel production, where previous research in black liquor gasification is currently expanding into a wider fuel feedstock. This work focuses on co-gasification of black liquor and by-products from other biofuel production technologies. The interesting by-products were crude glycerol from biodiesel production and spruce fermentation residue from ethanol production. The main goals were to study if the fuels can mix homogeneously and study the char reactivity. CO2 char gasification for mixtures of black liquor and glycerol or fermentation residue respectively was studied using thermogravimetric analysis (TGA) for four temperatures between 750°C and 900°C. The results show that glycerol can be mixed in all proportions with black liquor and indicate that the char reactivity is unchanged. The sustained char reactivity for blends is attributed to the volatility of glycerol. The fermentation residue does not produce a homogeneous mixture with black liquor and the char is less reactive. More studies should be performed to further elucidate the validity of the results.