Microalgae hold a great potential to serve as feedstocks for biodiesel production. Tropical and subtropical zones have more solar energy than temperate areas for microalgal culturing. However, outdoor high irradiance results in high temperature in the culturing medium, which is damaging if not lethal to most known microalgal species. New microalgae with heat tolerance, high growth rates and high lipid contents are desirable to establish this industry. Four new green microalgae were isolated in southern Taiwan, located in the subtropical zone. All four species are members of the genus Desmodesmus in the family Senedesmaceae. Two of the four species survived at 45¢Jfor 24 hours, with 5 to 13% mortality rates caused by the heat. Lipid contents of two species reached over 50% in dry biomass under nitrogen starvation. Oil accumulation in tion. Oil accumulation in tion. Oil accumulation in tion. Oil accumulation in the four species positively correlates with their photosystem efficiencies during stress treatments (R2=0.90).

The present study developed a new ¡V typed Photobioreactor, ¡§ Automatically Temperature Controllable and Wave-Mixed Photobioreactor System, ATCWPS ¡§ . The main propose of the study is to reduce the energy consumption and production cost during the process of cultivation. It can be cut down the over-dependent of nature resource on the land and expand the ocean by using the advantage of the nature marine environment. The Photobioreactor based on baffled tanks is investigated and the effect of the displacement of the Photobioreactor induced by external waves on liquid sloshing is discussed. The vortices generated by baffles can mix the fluid in the Photobioreactor. The influence of water depths and baffle height can be utilized to develop the model of Photobioreactor by simulating the inner change of energy, and to decrease the temperature of Photobioreactor with the characteristic of seawater specific heat. The problem of non-averaged light in the system by optical fiber system of total internal refraction is also improved in this work. The result of the experiment made in the Shi-Hzuwan ( Bay ) aquaculture site shows the average temperature of algae liquid can be declined about 20%. The results of vibrating platform cultivation shows the baffled system can increase the energy of mixing micro-algae in the growing process. Optical fiber system of total internal refraction can enhance the light efficiency, and thus not only can improve the shading effect among algae, but speed up its growing rate. When the staggered baffles and the optical fiber system of total internal refraction are combined, the optimal result of the growth rate of algae can be obtained in this work.

High rate algal ponds (HRAPs) are an advanced pond that provide efficient and cost-effective wastewater treatment, as well as the ability to recover nutrients in the form of microalgal biomass. Microalgal photosynthesis, nutrient uptake and subsequent growth, coupled with aerobic bacteria degradation of organic compounds, are fundamental to the process of wastewater treatment in HRAPs, yet are often limited in these ponds and, in particular, microalgal photosynthesis is well below the reported theoretical maximum. Understanding how the physico-chemical environment affects microalgal performance is therefore critical to improved wastewater treatment and nutrient recovery, yet has been the subject to few studies to date. This research focused on the enhancement of microalgal photo-physiology, growth and nutrient removal efficiency (NRE) through modification to the physical and chemical environment in wastewater HRAPs. In this study, I first examined the seasonal dynamics of microalgal performance in full-scale wastewater HRAPs. While both retention-time corrected chlorophyll biomass and photosynthetic potential increased from winter to summer, the summer-time performance was considered to be constrained, as indicated by the decreased light absorption, light conversion efficiency and NRE. The physico-chemical environment in the full-scale HRAPs were characterised by high day-time pH, high light attenuation and long, straight channels with low turbulence. This led to questions regarding 1) effects of nutrient supply, in particular carbon and 2) the role of the HRAP light climate on microalgal performance. I addressed these questions using a series of experiments that involved either changing the nutrient concentration and its supply or by modifying the light environment, through changes in pond operational parameters including CO2 addition, influent dilution, pond depth, hydraulic retention time (HRT), mixing speed and frequency. The overall results from these experiments showed that carbon was the primary and light the secondary limiting factors of microalgal performance. These limitations negatively affected light absorption, photosynthesis, productivity and NRE. While each operational parameter tested impacted on microalgal performance, to some degree, CO2 addition had the greatest influence on light absorption, photosynthetic efficiency and productivity, while continuous mixing had the greatest effect on NRE. Adding CO2 increased light absorption by 110% and 128%, maximum rate of photosynthesis by 185% and 218% and microalgal biovolume by between 150 – 256% and 260 – 660% (species specific), when cultures were maintained at pH 8 and 6.5, respectively. Providing sufficient mixing to achieve continuous turbulence enhanced NRE by between 300 – 425% (species specific), increased biomass concentrations between 150% and 4000% (species specific) compared to intermittent and no mixing, respectively, and increased harvest-ability of colonial species. However, at present, both CO2 addition and mechanical mixing attract high capital and operational costs. Modification to these technologies would be required to meet the objectives of cost-effective wastewater treatment and biofuel production. A more immediate and cost-effective solution demonstrated in this study was the altering pond depth, influent concentration and HRT. Doubling pond depth from 200 to 400 mm increased both microalgal nutrient removal and photosynthetic efficiencies which led to areal productivity increasing by up to 200%. When increased pond depth was coupled with decreased HRT, light absorption and photosynthetic performance further increased due to decreased internal self-shading and improved pond light climate. For nutrients, high influent loads increased productivity, while moderate loads increased effluent water quality. Overall, this work demonstrated that optimising the chemical and physical environment of wastewater treatment HRAPs (CO2 addition to maintain pH at 6.5 – 7, 400 mm pond depth, continuous mixing with vertical speed of 200 mm s-1, moderate nutrient load (15- 30 g m-3) and moderate HRT (4 / 6 days summer / autumn) can enhance microalgal biomass productivity, nutrient recovery as well as improve effluent water quality, particularly during summer when growth can be constrained.

The self-treatment system of nature cannot handle man-caused high rate water pollution on its own, therefore cleaning in wastewater treatment plant (WWTP) is necessary to avoid eutrophication – excessive enrichment of nature by nutrients. Current technologies applied in WWTPs are old, outdating and highly energy demanding, especially biological treatment step generally requires large amount of energy for aeration of water. The alternative to current system could be microalgae treatment step, which would use green algae to consume pollutants present in the waste water, namely nitrogen, phosphorus and heavy metals. Via photosynthesis it could produce oxygen required for biological oxidation of organic matter. Furthermore carbon source is necessary for microalgal growth, this can be added to the water as CO2 produced in other industries and so decrease global greenhouse gas footprint. Co-digestion of microalgae with undigested wastewater sludge under mesophilic conditions can give a synergic effect for biogas production, therefore harvested and co-digested microalgae could contribute to positive energy balance of WWTP. Full-scale microalgae cultivation in WWTP can be achieved only when good grow is guaranteed. This is a result of many factors, particularly access to nutrients, light condition, water temperature, and pH. The goal of master’s thesis was to understand and evaluate main factors influencing algal growth using literature review, propose design of microalgae treatment step with artificial lights and evaluate energy balance, of wastewater treatment plants in Uppsala and Västerås with new design. The work proposed two different designs of microalgae treatment steps, modelled in Excel and applied to current state of municipal WWTP in Västerås and Uppsala with belonging satellite plants. The first design of microalgae activated photobioreactor (MAASPBR) aimed to replace current biological treatment step. This is possible in Västerås and Uppsala WWTPs if microalgae can consume 75% of total nitrogen (Ntot) and produce at least 13.5 and 2.4 tonne O2/day in Västerås and Uppsala respectively. The sensitivity analysis showed that minimal volumetric algal yield of 0.15 kg/m3 ,day and 0.25 kg/m3 ,day is required for Västerås and Uppsala respectively, when oxygen production rate of 1.92 kg O2/kg microalgae is assumed. Furthermore harvested and co-digested algae with sewage sludge contributes to significant increase of biogas production and negligible transportation energy increase. The second design of open algal pond for reject water (OAPRW) aims to cultivate microalgae on reject water with high concentration of nutrients, generated in sludge centrifuge. The model assumed high algal growth due to excessive amount of nutrients and increased water temperature to 24°C. Results show a possible 23% and 20% electricity saving on blowers in the biological treatment in Västerås and Uppsala respectively. Both models have positive impact on energy balance in all WWTPs, however MAASPBR has greater uncertainties, because this type of photobioreactor has not been tested unlike OAPRW which has been tested in pilot plant scale.

Η αύξηση των ενεργειακών απαιτήσεων όπως και η έλλειψη ορυκτών καυσίμων καθιστούν αναγκαία τη χρήση εναλλακτικών πηγών ενέγειας. Τα μικροφύκη αποτελούν μία από τις πλέον υποσχόμενες εναλλακτικές πηγές ενέργειας. Το στάδιο της συλλογής της βιομάζας από τις καλλιέργειες μικροφυκών είναι το πιο περίπλοκο και αυτό με το πιο υψηλό κόστος, το οποίο αναφέρεται ότι αποτελεί έως και το 20-30% του συνολικού κόστους παραγωγής βιομάζας. Αυτός είναι και ο κύριος λόγος που εστιάστηκε η συγκεκριμένη εργασία στο κομμάτι της συλλογής με την χρήση κροκιδωτικών και μαγνητικών υλικών για την καθίζηση της βιομάζας, προκειμένου αυτή να συλεχθεί και να επεξεργασθεί περαιτέρω. Στη παρούσα εργασία πραγματοποιήθηκε καλλιέργεια δύο ειδών μικροφυκών σε εργαστηριακής κλίμακας αντιδραστήρες. Συγκεκριμένα εξετάστηκε ένα φύκος του γλυκού νερού, Scenedesmus rubescens και ένα φύκος αλμυρού νερού, Dunaliella tertiolecta και στη συνέχεια, με τις καλλιέργειες των δύο φυκών πραγματοποιήθηκαν πειράματα για την συλλογή τους. Από τις εργαστηριακές μετρήσεις που διεξάχθηκαν προσδιορίστηκαν οι εξής παράγοντες: τα αιωρούμενα και πτητικά αιωρούμενα στερεά, η οπτική πυκνότητα και η θολερότητα των καλλιεργειών, η χλωροφύλλη, το pH, τα ανιόντα όπως και η περιεκτικότητα των φυκών σε λιπίδια. Όλα τα πειράματα διεξήχθηκαν υπό ελεγχόμενες συνθήκες. Επίσης σε τακτά χρονικά διαστήματα έγινε μικροσκοπική εξέταση σε οπτικό μικροσκόπιο και ηλεκτονικό μικροσκόπιο σάρωσης. Εν συνεχεία, χρησιμοποιήθηκαν οι καλλιέργειες για να πραγματοποιηθούν πειράματα συλλογής της βιομάζας με τη χρήση κοινών κροκιδωτικών (άλατα Fe3+ και Al3+) και μαγνητικών μικροσωματιδίων. Συγκεκριμένα έγιναν 27 πειράματα jar-test και 24 πειράματα με τη χρήση μαγνητικών υλικών. Στο κεφάλαιο 1 και 2 γίνεται αναφορά στα μικροφύκη και τις μεθόδους των διεργασιών συλλογής αυτών, καθώς και στα βιοκαύσιμα. Στη συνέχεια, στο 3ο κεφάλαιο γίνεται περιγραφή των πειραματικών διατάξεων, των εργαστηριακών μετρήσεων και σκοπτική περιγραφή της πειραματικής διαδικασίας που ακολουθήθηκε. Στο 4ο κεφάλαιο παρουσιάζονται τα πειραματικά αποτελέσματα των εργαστηριακών και των πειραματικών μετρήσεων. Στο 5ο κεφάλαιο γίνεται σύγκριση των αποτελεσμάτων της παρούσης εργασίας με αποτελέσματα που έχουν ευρεθεί σε άλλες παρόμοιες μελέτες στη βιβλιογραφία. Τέλος, στο 6ο κεφάλαιο, ακολουθούν τα συμπεράσματα που προέκυψαν από τα πειραματικά αποτελέσματα της παρούσας εργασίας. Απο τη μελέτη που πραγματοποιήθηκε συμπαιρένεται οτι η χρήση κροκιδωτικών και μαγνητικών υλικών είναι κατάλληλες και αποδοτικές για τη συλλογή βιομάζας των μικροφυκών, vi με ποσοστό αφαίρεσης της βιομάζας έως και 95%. Σε αντίθεση με τη μέθοδο της καθίζησης, στην οποία το ποσοστό αφαίρεσης εξαρτάται κυρίως απο το είδος και τη μορφολογία του κάθε μικροφύκους. / --

Fossil fuels are not sustainable due to their worldwide depletion and greenhouse gas (GHG) emissions. Transportation biofuels produced from microalgae are sustainable if GHG emissions are lower than fossil fuels and the sources for materials used during production are sustainable. Four areas were evaluated to address these concerns. First, a study of peer reviewed life-cycle analyses (LCAs) was performed. The purpose of this evaluation was to determine which processing choices during cultivation have the most impacts. Data from nine authors was converted to similar units, and a new LCA was performed to evaluate the impacts. Overall GHG emissions per kg of algae cultivation ranged from 0.1 - 4.4 kg CO₂ eq. / kg algae, with the most of the emissions coming from fertilizer contributions. The second topic evaluated was the GHG emissions from experimental dewatering technologies. The five experimental technology emissions, for acoustic harvesting, membrane filtration, flocculation, electrocoagulation and flocculation plus belt filtration, were compared to a modeled dissolved air flotation technology and a fossil fuel source. For a functional unit of one MJ of renewable diesel (RD), membrane filtration had the lowest GHG emissions at 40.8 g CO₂(eq)/MJ RD. Dissolved air flotation was the highest scenario at 51.9 g CO₂(eq)/MJ RD. All technologies were lower than gasoline at 90.7 g CO₂(eq)/MJ gasoline. The third topic evaluated was the GHG emissions from the materials used for plant construction. A LCA was performed for the infrastructure materials and compared to results from the fuel-cycle. Plastic from pond liners had the largest contribution to GHG emissions for the baseline case. Increasing productivity and lipid content both decreased infrastructure emissions. The final topic evaluated was the sustainability of nitrogen, phosphorus and potassium used for microalgae growth. Results show that the surplus of world fertilizers cannot sustain large scale algae production in the United States. Technology choices that can recycle nutrients lower the overall requirement. Alternative sources of nutrients, like concentrated animal feeding operations, can provide enough nutrients for large scale production of algae.

Microalgae have now been widely considered as a promising bio-energy feedstock. The current microalgae harvesting methods used, such as centrifugation, sedimentation and flocculation, have been shown to be effective but are costly, representing between 35 % to 50 % of the total production cost. The aims of this study were: (1) to investigate the effectiveness of two electrocoagulation processes, electroflocculation and electroflotation, as algae pre-harvesting processes; and (2) to design, test and optimize a cost-effective and efficient filtration-based harvesting mechanism for micrioalgae. The principal results of the study showed that: (1) The mean final concentration for electroflocculation of 17.94 gL⁻¹ significantly exceeded (p = 0.0416) that for electroflotation of 9.51 gL⁻¹, indicating electroflocculation to be the more effective process; (2) Microscope images of the algae showed that, for the level of power applied (1 A, 40 V max), electrocoagulation did not appear to have produced any effect on the algae that was significantly different from that by centrifugation and that neither method appeared to have caused any significant cell wall damage or rupture; (3) The most effective configuration for the harvester prototype -- resulting in higher throughput rate (0.303 gh⁻¹), higher efficiency (233.33 gL⁻¹), as well as a lower energy consumption (143.46 kWhm⁻³) -- corresponded with higher concentration of the incoming biomass (21.5 gL⁻¹), lower belt velocity (0.05 ms⁻¹), higher inclination angle (25°) and lower pressure (0 Psi); and (4) The total energy consumption for the harvester prototype, when combined with a preceding pre-harvesting process, of 4.95 kWhm⁻³ was comparable to those reported by others for filtration-based harvesting. The new efficient harvesting mechanism proposed showed significant potential in successfully reducing algae production cost and make biofuels from microalgae economically feasible in the mid to long term in view of the prototype having achieved high output biomass concentration, low energy consumption per unit volume, high throughput rate, and facility of implementation.

In this literature review the characteristics of two free-floating macrophytes, water hyacinth   (Eichhornia crassipes) and duckweed (Lemna sp.), and two microalgae, Chlorella and Scenedesmus, have been examined regarding their suitability as efficient nutrient removers in the treatment of wastewater with high levels of nutrients and suspended solids from a biogas plant in Loudden. The needs required for the plants to be able to grow in wastewater and the amounts of biomass they can produce have also been studied. The results show that Chlorella is capable of a very high uptake of nutrients in photobioreactors with high nutrient loadings. With an ammonia uptake maximum value at 10900mg/m2/d Chlorella outshines the other organisms in this study. The test organism that performed the closest to Chlorella in terms of nitrogen uptake was water hyacinth with an uptake about 1602mg/m2/d. One factor affecting nutrient uptake in a positive way is the growth rate. Free-floating macrophytes produce more biomass than algae do, and water hyacinth have been shown to be the most productive. It is important to conduct a regular harvest of the plants if a high production should be maintained. High quantity of biomass per unit area can inhibit the growth, and algae are more sensitive to this than the macrophytes often suffering from self-shading when the density is too high. The high level of nutrients in the wastewater prevents growth and dilution is required to achieve any growth at all. Therefore, conventional treatment methods might prove to be a better option.

During nutrient-replete growth of microalgae, new photosynthate is allocated toward three different biochemical pools: light harvesting compounds, the biosynthetic apparatus and energy storage. The mechanisms governing allocation of photosynthate between the energy storage compounds carbohydrate and lipid are not well understood. For biofuel production, it is desirable to identify conditions and algal strains that allocate maximum amounts of photosynthate to lipid. This thesis assessed the allocation of photosynthate toward the energy storage pool, and to lipid vs. carbohydrate, at two light levels and during ongoing nitrogen-starvation, for two diatoms and two chlorophytes. Nitrogen-starvation resulted in an increase in the photosynthate allocated toward energy storage, however the magnitude of change was determined by a combination of species and light level. Of the four species studied, the diatom Chaetoceros muelleri, grown in high light, accumulated lipid during N-starvation at a relatively high rate, making it a good candidate for biofuel production.

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