Mikrolevien viljely hiilidioksidin sitomiseksi voimalaitosten savukaasuista

Microalgae are a diverse group of unicellular, photosynthetic organisms that fix carbon dioxide (CO2) efficiently and hence produce biomass rapidly which are utilized as raw material for e.g. bioenergy production. This master's thesis concerns the potential of cultivating microalgae for fixing CO2 from power plant flue gases, which are among the major sources of CO2 emissions. The topic is approached from the point of view of microbiology, by analysing the growth characteristics and requirements of microalgae enabling industrial-scale cultivation on the one hand, and imposing challenges on the other. The main benefits of microalgae are related to their high photosynthetic efficiency compared with multicellular plants, the ability to utilize high-concentration CO2 sources, and simple growth requirements. The prominent challenges are related to the provision of light and gas transfer in dense cultivations, as well as maintaining stable growth conditions. On this basis, a review to the possibilities and limitations of algal cultivation and bioenergy production process is provided. The key factor in the successful process development is to enable maximal growth by eliminating the challenges in a sustainable and economically feasible fashion. Potential limitations specifically related to flue gases are assessed in more detail. According to previous studies algal growth could be reduced due to the presence of potentially toxic compounds in the flue gas, especially nitrogen oxides and sulphur oxides, as well as pH decrease resulting from an oversupply of CO2. In this thesis, growth of four microalgal species was examined in a laboratory-scale batch-mode comparative cultivation experiment with pure CO2 and actual flue gas, in which gas supply was adjusted according to the carbon uptake capacity of the microalgae. The growth was observed with maximal fluorescence and optical density measurements, and the final biomass concentrations were determined. No significant differences in the growth were observed between the experiments, except for one of the species that had decreased growth during flue gas cultivation. These results suggests that cultivation of microalgae with flue gas as a carbon is feasible -at least when CO2 is provided according to the carbon demand of microalgae -but also that species selection is to be considered as an essential part of the production process optimization. Furthermore, there were indications that microalgae might be able to utilize flue gas nitrogen and sulphur as nutrients. The result encourage conducting further experiments on a larger scale and continuous cultivation mode, as well as for further assessment of economic profitability and ecological sustainability of microalgal cultivation.Mikrolevät ovat yksisoluisia ja yhteyttäviä organismeja, jotka sitovat tehokkaasti hiilidioksidia. Ne ovat näin ollen nopeakasvuisia eli tuottavat runsaasti biomassaa, jota voidaan hyödyntää esimerkiksi bioenergian raaka-aineena. Tämä diplomityö tarkastelee mikrolevien viljelyä hiilidioksidin sitomiseksi voimalaitosten savukaasuista, jotka ovat merkittävimpiä hiilidioksidipäästöjen lähteitä. Aihetta tarkastellaan mikrobiologian näkökulmasta analysoimalla mikrolevien kasvuominaisuuksia ja -vaatimuksia, jotka yhtäältä mahdollistavat ja toisaalta rajoittavat teollisen mittakaavan mikroleväviljelyä. Mikrolevien merkittävimpiin hyötyihin lukeutuvat monisoluisiin kasveihin nähden korkea yhteyttämistehokkuus, kyky hyödyntää korkeita hiilidioksidipitoisuuksia, sekä yksinkertaiset kasvuvaatimukset. Keskeisiä haasteita ovat riittävän valonsaannin ja kaasujenvaihdon turvaaminen tiheissä viljelmissä, sekä kasvuolosuhteiden ylläpitäminen vakaina. Naiden tarkastelujen pohjalta luodaan katsaus mikrolevien kasvatuksen ja leväpohjaisen energiantuotantoprosessin mahdollisuuksiin ja rajoituksiin. Avaintekijänä prosessisuunnittelussa on kasvun maksimointi ja kasvuun liittyvien ongelmien minimointi siten, että kokonaisuus on ympäristön kannalta kestävä ja taloudellisesti kannattava. Myös savukaasujen käyttöön mikrolevien hiilenlähteenä liittyy mahdollisesti rajoitteita. Tutkimuskirjallisuuden mukaan savukaasujen jotkin yhdisteet, erityisesti typen ja rikin oksidit, saattavat olla myrkyllisiä mikroleville. Myös hiilidioksidin ylitarjonta levien hiilensitomiskykyyn nähden voi hidastaa levien kasvua pH:n laskiessa kasvatusliuoksessa. Diplomityön kokeellisessa osassa neljää levälajia kasvatettiin laboratoriomittakaavan panoskasvatuskokeissa, joista ensimmäisessä käytettiin puhdasta hiilidioksidia ja toisessa savukaasua. Kaasusyöttö säädettiin levien hiilentarpeen mukaan, levien kasvua seurattiin fluoresenssi- ja optisen tiheyden mittauksilla, ja lopuksi määritettiin biomassan loppukonsentraatiot. Testattujen mikrolevien kasvussa ei havaittu merkittäviä eroja kokeiden välillä, lukuun ottamatta yhtä levälajia joka kasvoi hitaammin savukaasukasvatuksen aikana. Tulosten perusteella mikrolevien kasvatus savukaasujen avulla on mahdollista, ainakin kun hiilidioksidin syöttö tapahtuu levien hiilentarpeen mukaan, mutta levälajin valinta on keskeinen osa kasvatusprosessin optimointia. Lisäksi kokeet antoivat joitain viitteitä siitä, että levät saattoivat hyödyntää savukaasujen typpeä ja rikkiä ravinnon lähteinä. Tulosten perusteella voidaan suositella sekä jatkotutkimuskokeita suuremmassa mittakaavassa ja jatkuvakestoisella kasvatuksella, että mikroleväviljelyn ekologisen kestävyyden ja taloudellisen kannattavuuden selvittämistä

Energy analysis of algae-to-biofuel production chains integrated with a combined heat and power plant

This study examines the energy and mass balances of algae cultivation and different post-processing pathways. Flue gases and excess heat from a combined heat and power (CHP) plant are used in algae cultivation, with nutrients from municipal wastewater. In the studied pathways, algae are cultivated in open ponds and photobioreactors with or without artificial lighting. Algal mass is used for methane, biodiesel or ethanol production, or it is combusted in a boiler. Results show that in most process pathways energy output exceeds the energy consumption in processing, and the energy returns are approximately twice as large as the electricity input. A large fraction of input energy is low-temperature heat, while the products have a higher value. Energy outputs from different pathways are similar, but heat and electricity consumption in processing vary significantly. Supercritical water gasification pathway is identified as a possible future option, whereas lipid extraction pathways are suggested to be the most likely candidates for industrial scale operations.Peer reviewe

Hyvästit kertakäyttöisille take away -pakkauksille? Neljä näkökulmaa toimivaan panttipakkaukseen

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CO2 from industrial off-gases for algae cultivation

In this work, technical solutions for capturing CO2 from CO2-containing off-gases from industry for feeding an algal cultivation were qualitatively evaluated. Also, cultivation of algae using both vent gases from a sour gas processing plant and flue gases from a coal-fired combined heat and power (CHP) plant was studied. The most promising methods for CO2 capture seem to be those that absorb CO2 directly into the cultivation media by using separate bubbling carbonation columns, both for open ponds and closed photobioreactors. This lowers the energy requirements in comparison to flue gas injection and also enables the remainder of the flue gas to be led out through the existing flue gas stack. The low capacity of water to dissolve CO2 can be improved by addition of alkaline salts. The growth of two green algae, one diatom, and one cyanobacterium was examined in a laboratory-scale, batch-mode comparative cultivation experiment, using both pure CO2 and flue gas from a coal-fired CHP plant. No significant statistical differences in the growth were observed between the experiments except for the cyanobacterium, which had a decreased growth during flue gas cultivation. Microalgae suitable for cultivation using vent gases from a sour gas processing plant were screened by employing a 20 L photobioreactor. Based on these experiments, a certain mixture of microalgae exhibited rapid growth and better tolerance towards in terms of time taken to reach pH 7. A small-scale CO2 capture and cultivation pilot was set up using a 0.3 m3 CO2 absorption column for absorbing CO2 from vent gas in connection to a 0.2 m3 raceway pond. The produced algae was harvested and sent for anaerobic digestion studies. The experiments were successful, with a microalgae yield of 18 g/m2/day achieved, which on anaerobic digestion yielded about 0.4 m3 CH4/kg volatile solids fed

Lameness detection in dairy cows: Part 1. How to distinguish between non-lame and lame cows based on differences in locomotion or behavior?

Due to its detrimental effect on cow welfare, health and production, lameness in dairy cows has received quite some attention in the last decades. Not only in terms of prevention and treatment of lameness but also in terms of detection, as early treatment might help decreasing the number of severely lame cows in the herds as well as decreasing the direct and indirect costs associated with lameness cases. Generally, lame cows are detected by the herdsman, hoof trimmer or veterinarian based on abnormal locomotion, abnormal behavior or the presence of hoof lesions during routine trimming. In scientific literature, several guidelines are proposed to detect lame cows based on visual interpretation of the locomotion of individual cows, i.e. locomotion scoring systems. Moreover, research and the industry focus on automating such observations to support the farmer in finding the lame cows in their herds, but until now, such automated systems are rarely being used in commercial herds. This review starts with the description of normal locomotion of cows in order to also define ‘abnormal’ locomotion caused by lameness. Cow locomotion (gait and posture) and behavioral features that change when a cow becomes lame are described and linked to the existing visual scoring systems. In addition, the lack of information of normal cow gait and a clear description of ‘abnormal’ gait are discussed. Finally, the different set-ups used during locomotion scoring and their influence on the resulting locomotion score is evaluated.status: publishe