Potential of Microalgal Biodiesel: Challenges and Applications

In the present scenario, rapid industrialization and urbanization have led to a dramatic increase in the levels of various hazardous pollutants in the environment, and this creates a serious threat to humankind. Today, most of the energy production comes from fossil fuel combustion, which is the key source of CO2 emissions. Research studies show that the utilization of microalgae could be the best option for the production of renewable and sustainable energy and for the mitigation of CO2 emission. Production of biofuels from microalgae can be classified as solid (biochar), liquid (bioethanol, biodiesel, bio-kerosene), and gaseous (biogas, bio-syngas, biohydrogen) fuels. Among these biofuels, biodiesel garners a lot of interest and attention because of its high accumulation of lipids (20–75%), which could be a potential alternative fuel for diesel engines. Algal lipids usually have a higher viscosity than petro-diesel; therefore, the transesterification process is required to decrease the viscosity of microalgal lipids before they can be combusted in the engines. However, microalgae are considered as a potential resource in the current biofuel industries; still, it fails at the commercial level. Thus, in this book chapter, we have discussed the microalgal biofuel production and the challenges behind and the future prospects

Use of Microalgae for Advanced Wastewater Treatment and Sustainable Bioenergy Generation

Given that sustainable energy production and advanced wastewater treatment for producing clean water are two major challenges faced by modern society, microalgae make a desirable treatment alternative by providing a renewable biomass feedstock for biofuel production, while treating wastewater as a growth medium. Microalgae have been known to be resilient to the toxic contaminants of highly concentrated organic wastewater (e.g., organic nitrogen, phosphorus, and salinity) and are excellent at sorbing heavy metals and emerging contaminants. Economic and environmental advantages associated with massive algae culturing in wastewater constitute a driving force to promote its utilization as a feedstock for biofuels. However, there are still many challenges to be resolved which have impeded the development of algal biofuel technology at a commercial scale. This review provides an overview of an integrated approach using microalgae for wastewater treatment, CO2 utilization, and biofuel production. The main goal of this article is to promote research in algae technologies by outlining critical needs along the integrated process train, including cultivation, harvesting, and biofuel production. Various aspects associated with design challenges of microalgae production are described and current developments in algae cultivation and pretreatment of algal biomass for biofuel production are also discussed. Furthermore, synergistic coupling of the use of microalgae for advanced wastewater treatment and biofuel production is highlighted in a sustainability context using life cycle analysis.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/140370/1/ees.2016.0132.pd

Microalgae cultivated in Swine Wastewater: Stimulation of Seed Growth and Biopesticide Potential

Humanity faces dramatic issues related to water scarcity and its contamination, as well as ex-cessive use of chemical fertilizers and pesticides, to increase agriculture efficiency. Eutrophication, contamination and soil infertility threatens agricultural sustainability and public health, as well as the earth’s ecosystems and biodiversity. Currently, microalgae are revealing themselves as promising on bioremediation of various wastewaters and as sustainable alternative on agriculture. This dissertation pretends to ally bioremediation to agriculture: the microalgae Chlorella proto-thecoides, Chlorella vulgaris, Scenedesmus obliquus e Synechocystis sp. were selected (after screen-ing) for swine wastewater treatment. The resulting biomass of the swine wastewater treatment was tested as germination/growth stimulation of tomato, watercress, cucumber, soy, barley and wheat seeds, and as biopesticide against Fusarium oxysporum. Regarding bioremediation, the four species reduced COD levels in 61-75%, total Kjeldahl nitro-gen in 70-80%, ammonia nitrogen in 93-97% and phosphorus between 94-100%, especially C. proto-thecoides and S. obliquus. In general, the limits imposed by Decree Law 236/98 of Portuguese legisla-tion for wastewater treatment were fulfilled and treated waters could be discharged or reused. The biochemical profiles of microalgae biomass presented protein contents between 34-47%, fatty acids (C12-C18) between 26-84%, and total sugars between 25-33%. The results for growth stimulation trials were positive for all microalgae depending on seed type and light conditions, Synechocystis sp. and C. vulgaris having the more relevant results. On biopesticide trials, Synechocystis sp. and S. obliquus obtained the best results as fungi growth inhibitors. In summary, S. obliquus and C. protothecoides were the most efficient in the wastewater treat-ment, S. obliquus and C. vulgaris, on germination/growth stimulation, and Synechocystis and S. obliquus, for biopesticide potential

Microalgae: a robust “green bio-bridge” between energy and environment

Microalgae are a potential candidate for biofuel production and environmental treatment because of their specific characteristics (e.g. fast growth, carbon neutral, and rich lipid accumulations). However, several primary bottlenecks still exist in current technologies, including low biomass conversion efficiency, bio-invasion from the external environment, limited or costly nutrient sources, and high energy and capital input for harvest, and stalling its industrial progression. Coupling biofuel production with environmental treatment renders microalgae a more feasible feedstock. This review focuses on microalgae biotechnologies for both bioenergy generation and environmental treatment (e.g. CO2 sequestration and wastewater reclamation). Different intelligent technologies have been developed, especially during the last decade, to eliminate the bottlenecks, including mixotrophic/heterotrophic cultivation, immobilization, and co-cultivation. It has been realized that any single purpose for the cultivation of microalgae is not an economically feasible option. Combinations of applications in biorefineries are gradually reckoned to be necessary as it provides more economically feasible and environmentally sustainable operations. This presents microalgae as a special niche occupier linking the fields of energy and environmental sciences and technologies. The integrated application of microalgae is also proven by most of the life-cycle analysis studies. This study summarizes the latest development of primary microalgal biotechnologies in the two areas that will bring researchers a comprehensive view towards industrialization with an economic perspective

The Opportunity of Developing Microalgae Cultivation Techniques in Indonesia

The rate of population growth which is relatively rapidly increasing in Indonesia, will require increased fuel. The depletion of the availability of fossil fuels causes the search for the other natural resources needed to become a renewable energy source. One of the significant changes today is microalgae. The application of the algal aquaculture system has been widely applied in the world. The media used in cultivation also varies, one of which is wastewater. The composition of biodiesel energy in Indonesia is increasing and is starting to become the people's choice. Indonesia, which is rich in natural resources, especially the high biodiversity of microalgae, causes microalgae's potential use to be very high. Many studies report the explosion of algal participation in many parts of Indonesia. Research concerning the cultivation of microalgae has been widely successful in Indonesia. The use of microalgae is already available in the field with domestic water treatment applications. The conversion of microalgae into biodiesel also successfully met the requirements of SNI 04-7182-2006

Crescimento de microalgas em efluente de curtume : remoção de nutrientes, viabilidade de produção de biodiesel e utilização da biomassa residual

As microalgas são uma alternativa ecológica e economicamente viável para o tratamento de efluentes industriais, já que são capazes de assimilar compostos como nitrogênio, fósforo e carbono. Em consequência ao potencial para o tratamento de efluentes há a geração de biomassa que pode ser utilizada para a fabricação de produtos com valor agregado, como os biocombustíveis. Assim, neste trabalho, avaliou-se a viabilidade de crescimento e produção de biomassa microalgal em águas residuais de curtume, sem tratamento prévio e sem adição de nutrientes. Objetiva-se, com tais experimentos, verificar a capacidade de remoção de contaminantes deste efluente, bem como composição microalgal em proteínas, lipídios e carboidratos para subsequente utilização. Inicialmente, verificou-se a influência da intensidade luminosa e da concentração do efluente de curtume na produção da biomassa da Scenedesmus sp., e na remoção de poluentes tais como nitrogênio amoniacal, fósforo e demanda química de oxigênio pela microalga. A microalga foi cultivada em efluente bruto de curtume sem tratamento prévio, coletado diretamente da etapa de ribeira, sob diferentes concentrações (entre 20% e 100%) e intensidade luminosa (entre 80 e 200 μmol photons.m−2.s−1) com temperatura de 25 °C e aeração constante. Este estudo demonstrou que a concentração de efluente e a intensidade luminosa influenciaram positivamente na quantidade de biomassa produzida, bem como na remoção de nitrogênio amoniacal e fósforo e DQO. Em um segundo passo, cultivaram-se as microalgas Scenedesmus sp. e Chlorella sp. em fotobiorreatores airlift de 3 L, contendo diferentes concentrações de efluente bruto de ribeira de curtume (25%, 50% e 100%), sob intensidade luminosa de 200 μmol photons.m−2.s−1, à temperatura ambiente (25 °C), durante 20 dias. Nos cultivos com a microalga Scenedesmus sp. foi observada máxima concentração de biomassa de 1,75 g.L-1 e elevadas remoções de nitrogênio total - NT (91,68%), nitrogênio amoniacal - NH3-N (94,36%), fósforo - PO4-P (97,33%), carbono inorgânico - CI (93,56%) e demanda química de oxigênio - DQO (66,64%). Elevados teores de lipídios (27,14%) e carboidratos (34,17%) também foram verificados. Os resultados obtidos a partir dos cultivos com a Chlorella sp. apresentaram máxima concentração de 1,64 g.L-1. Além disso, foram observadas remoções de NT (91,59%), NH3-N (93,57%), PO4-P (98,10%), CI (89,46%), DQO (71,20%) e DBO (37,87%). Na composição da biomassa observou-se elevados teores de lipídios (25,46%) e carboidratos (36,36%). Na análise do perfil dos ácidos graxos, os biodieseis etílicos produzidos a partir dos lipídios das microalgas Scenedesmus sp. e Chlorella sp. apresentaram estabilidade oxidativa, devido ao grau de saturação. Assim estes estudos demonstraram que o processo combinado de tratamento de efluentes na conversão de biomassa de microalgas oferece muitos méritos ambientais com a produção de produtos de valor agregado, como o biodiesel. Neste estudo também investigou-se a recuperação da biomassa utilizando agentes coagulantes/floculantes inorgânicos (cloreto férrico e sulfato de alumínio) e taninos vegetais orgânicos (Tanfloc SL, Tanfloc SG e Tanfloc SH). Além disso, também foram analisados os efeitos das condições operacionais sobre o teor de lipídios nas microalgas e na composição de ácidos graxos do biodiesel produzido a partir dos lipídios. Verificou-se elevada eficiência de recuperação de biomassa de aproximadamente 98% para as microalgas Scenedesmus sp. e Chlorella sp. utilizando o tanino vegetal Tanfloc SH e ainda não foi observado alteração no conteúdo de ácidos graxos em FAEE com o uso do tanino floculante. A fim de maximizar a produção de energia obtida através das microalgas e reduzir os custos totais dos processos e do tratamento de resíduos, a biomassa residual gerada a partir da síntese do biodiesel foi utilizada como um adosorvente alternativo do corante Acid Blue 161 (AB-161) utilizado amplamente na indústria coureira. A biomassa foi caracterizada por técnicas analíticas de FTIR, MEV, BET, BJH e potencial zeta. As quantidades máximas de corante AB-161 adsorvido foram de 75,78 mg.g-1 a 25 °C e de 83,2 mg.g-1 a 40 °C. No tratamento de águas residuais de curtumes reais, os resultados mostram que a utilização da biomassa residual (após extração dos lipídios) como adsorvente, reduziu significativamente a concentração de corante (76,65%), carbono orgânico total - COT (50,78%) e nitrogênio total - TN (19,80%).Microalgae are an ecologically and economically viable alternative for the industrial wastewater treatment, since they are able to assimilate compounds such as nitrogen, phosphorus and carbon. As a consequence of the potential for the treatment of wastewater, there is the generation of biomass that can be used for the production of value-added products, such as biofuels. Thus, in this work, it was evaluated the viability of growth and production of microalgal biomass in tannery wastewater, without previous treatment and without addition of nutrients. The objective of these experiments was to verify the bioremediation capacity to remove contaminants from this effluent, as well as microalgal composition for subsequent use. The influence of light intensity and concentration of tannery effluent on Scenedesmus sp. biomass production, as well as the removal of pollutants such as ammoniacal nitrogen, phosphorus and chemical oxygen demand from the microalga were verified. The microalga was cultivated in raw wastewater from untreated tannery collected directly from the beamhouse stage under different concentrations (between 20% and 100%) and light intensity (between 80 and 200 μmol photons.m−2.s−1) with a temperature of 25°C and constant aeration. In a second step, the microalgae Scenedesmus sp. and Chlorella sp. were grown in 3 L airlift photobiororators, containing different concentrations of raw tannery wastewater (25%, 50% and 100%), under light intensity of 200 μmol photons.m−2.s−1, at temperature (25°C) for 20 days. In the cultures with the Scenedesmus sp. microalgae, a maximum biomass concentration of 1.75 g.L-1 and high removals of total nitrogen (NT) (91.68%), NH3-N (94.36%), phosphorus - PO4-P (97,33%), inorganic carbon - CI (93,56%) and chemical oxygen demand - COD (66,64%). High levels of lipids (27.14%) and carbohydrates (34.17%) were also observed. The results obtained from the cultures with Chlorella sp. presented a maximum concentration of 1.64 g L-1. In addition, NT (91.59%), NH3-N (93.57%), PO4-P (98.10%), CI (89.46%), COD (71.20%), and BOD (37.87%) removals were observed. The composition of the biomass showed high levels of lipids (25.46%) and carbohydrates (36.36%). In the analysis of the fatty acid profile, the ethylic biodiesel produced from the lipids of the microalgae Scenedesmus sp. and Chlorella sp. presented oxidative stability due to the degree of saturation. Thus these studies have shown that the combined process of effluent treatment in the conversion of microalgae biomass offers many environmental merits with the production of value-added products, such as biodiesel. This study also investigated biomass recovery using inorganic coagulants / flocculants (ferric chloride and aluminum sulfate) and organic vegetable tannins (Tanfloc SL, Tanfloc SG and Tanfloc SH). In addition, the effects of operating conditions on lipid content in microalgae and on the fatty acid composition of biodiesel produced from lipids were also analyzed. There was a high biomass recovery efficiency of approximately 98% for the microalgae Scenedesmus sp. and Chlorella sp. using Tanfloc SH and it was not observed any alteration in fatty acid content in FAEE with the use of flocculent tannin. In order to maximize energy production through microalgae and reduce the total costs of waste treatment processes and treatment, the residual biomass generated from the biodiesel synthesis was used as an alternative adder of the Acid Blue 161 dye (AB-161) widely used in the hull industry. Biomass was characterized by analytical techniques of FTIR, MEV, BET, BJH and zeta potential. The maximum amounts of adsorbed AB-161 dye were 75.78 mg.g -1 at 25 °C and 83.2 mg.g -1 at 40 °C. The results showed that the use of residual biomass (after lipid extraction) as adsorbent significantly reduced the concentration of dye (76.65%), total organic carbon (TOC) (50.78%) and total nitrogen - TN (19.80%)

Exploitation of microalgal biomass as an alternative source to bioethanol production

The use of natural sources in economic activities can aid in the resource saving and recycling and reuse of wastes, contributing for a more sustainable world by providing clean technologies in the industrial and agricultural sector in both developed and developing countries. In general, increased and improved global strategies for energy safety, security and mitigation of CO2 emissions from energy production processes are required, especially those aimed at maximizing the energy efficiency by expanding the use of clean energy. This means using fuels that are able to implement the carbon cycle without changing the atmospheric balance (renewable fuels), by developing energy resources in CO2 reduced/neutral systems (Brennan and Owende, 2011; Moraes et al., 2017). The expansion of biofuels production and use is an important issue since it plays primary role in reducing global the climate change. But, in order to insert a new source/technology in the market, several factors are involved such as industrial aspects and economic feasibility, legal restrictions and incentives, international trade, land use, raw material availability and management techniques. At present, ethanol is the main biofuel produced worldwide. Between 2007 and 2015 bioethanol throughput practically doubled, reaching 25 billion gallons per year, even though after 2010 the production was stagnant (AFDC, 2016). This is the result of a number of reasons, to cite: - high dependency on the first-generation crops which need a lot of arable land and compete directly with food/feed production; - need for a complete validation of the lignocellulosic ethanol industry due to unsuitability of the large-scale process because of corrosion problems (mainly in the pretreatment), cost of enzymes, difficult/inhibition of the fermentation step; - difficulty to utilize all lignocellulosic fractions, according to a biorefinery approach, because each biomass has its biological complexity and the related lignocellulosic content/arrangement/recalcitrance changes significantly; - Lacking of investments/incentives (mainly, governmental) after the decrease of petroleum prices occurred at the end of 2014. In fact, based on the type of biomass, bioethanol production is classified as first (raw material saccharine or starch-based – sugarcane and corn); second (lignocellulosic materials); third (microalgal/macroalgal biomass) and fourth (genetically modified cyanobacteria) generation. Sugar cane ensures the lowest bioethanol production costs. In spite of its significant advantage, it is not a viable option for all the regions of the planet owing to climatic and soil limitations (Belincanta et al., 2016). Consequently, countries of the northern hemisphere have been incessantly looking for new technological routes that permit the efficient production of biofuels while respecting environmental and economic sustainability issues, and ‘new’ generations of biomass-to-ethanol processes are proposed. In addition, countries as Brazil have their sugarcane cultivation saturated, i.e., there is no new extensions of arable land to expand significantly the Brazilian ethanol industry. Low production costs are the advantage of first generation bioethanol, with the exception of corn-based one, which has a well-established and economically sustainable technology, while second generation still requires more investigations to become economically competitive, with pretreatment and hydrolysis processes needing to be more effective and largely scalable (Gupta and Verna, 2015). On the other hand, micro and macroalgae have not reached a maturity for designing and operating industrial scale plants yet. Therefore, in the case of third and fourth generation bioethanol, further studies are required to develop a competitive and consolidated technology, taking into account also issues other than technological ones. In third generation bioethanol, microalgae and/or macroalgae biomass are used, which do not have lignin in their cellular structure, and are cultivated with higher growth rates when compared to higher plants. As for this biomass, a suitable process is not available yet, and the related costs cannot be properly estimated. Researchers are currently trying for microalgae: to optimize microalgal productivity and cultivation conditions, as this represents the highest production costs, considering that hydrolysis and fermentation are instead easier compared with lignocellulosics and macroalgae (Jonh et al., 2011; Wei et al., 2013; Hong et al., 2014). Thanks to their high growth rate, and relatively simple biochemical composition (partitioned among carbohydrates, lipids and proteins), microalgae are acknowledged as very promising feedstock for bioethanol production (Chen et al., 2013). Main aspects needing to be developed in this respect are: carbohydrate cultivation (productivity), hydrolysis and ethanolic fermentation and nutrient recycling/recovery from residual medium/biomass. With regard to the open issues recalled above, the aim of this research project has been to address and study how to improve the knowledge and discuss the real potentiality of microalgal biomass as a feedstock for an effective bioethanol production, from a perspective of biomass/carbohydrate productivity (microalgal cultivation) and bioconversion process (hydrolysis and fermentation) in a context of a biorefinery concept. In fact, experimental values about fermentation applications from microalgae are not expanded yet in literature. The topics addressed by this thesis are organized and subdivided in twelve chapters as follows. In Chapter 1, a literature survey to collect and discuss the available information about bioethanol from photosynthetic microorganisms, and to delimit the main lacks to be developed, is done. Chapter 2 shows a basic analysis of an ethanol biorefinery scheme aimed to include microalgal biomass, discussing the main bottlenecks and the processes which must be developed to adequately evaluate the potentiality of this type of biomass for industrial fermentation proposes. Chapter 3 treats specifically of the carbohydrate-rich biomass cultivation from microalgae utilizing nutritional and environmental techniques. Operation mode of microalgae cultivation is discussed as well, and the importance to consider semi-continuous and continuous processes is shown, because batch mode is extensively used but less efficient. Chapter 4 develops a design procedure of a two-unit system composed by a reactor and settler, discussing the influence of operating variables and their limiting values. Specifically, recycle ratio and purge flow rate concepts and effects are extensively studied. In Chapter 5, the carbohydrate cultivation with Synechococcus PCC 7002 is optimized with respect to the carbon source and pH, because a stable pH (greatly influenced by the carbon source) is necessary for this strain and organic buffers exhibit toxicity. An inorganic buffer study (CO2-bicarbonate) is developed and detailed. Chapter 6 shows S. PCC 7002 treating urban wastewater to remove chemical oxygen demand, nitrogen and phosphorous content, thus ensuring a double gain: environmental enhancement and valorization of cyanobacterial biomass. In Chapter 7, continuous cultivation of Chlorella vulgaris in flat-plate photobioreactors to improve carbohydrate productivity is assessed and evaluated using nitrogen limitation as a combination between nitrogen concentration inlet, light intensity and residence time under constant light intensity. Chapter 8 demonstrates that a similar approach used for the continuous cultivation of C. vulgaris is applicable also to Scenedesmus obliquus. Additionally, it is proved that under outdoor conditions (seasonal regime of illumination – summer and winter), a high carbohydrate content can be produced as well. In Chapter 9, the kinetics regarding acidic hydrolysis to biomass solubilization and sugars depolymerization is studied with Chlorella vulgaris biomass. An n order kinetics for biomass solubilization and m order for acid concentration is applied for biomass solubilization, providing values of reaction order and activation energy for microalgae. In addition, a saccharification model based on the Michaelis-Menten model is proposed and validated. Chapter 10 demonstrates how the kinetics considerations determined in the previous chapter can be efficiently applied with the concept of severity factor – CSF (combination between time, temperature and acid concentration). A literature discussion about some assumptions so far considered and the importance to know the biomass nature to determine a coherent range of CSF is provided. Chapter 11 reports ultrasonication as an effective pretreatment method to improve enzyme accessibility and promote a high rate of hydrolysis from Scenedesmus obliquus biomass. Pretreatment time, ultrasonication intensity and biomass concentration are specifically studied in order to minimize the energy consumption since the bottleneck of the pretreatment method is a high energy dissipation. In Chapter 12, ethanolic fermentation is addressed with acidic and enzymatic hydrolysates. A systematic optimization of inoculum concentration and consortium between Saccharomyces cerevisiae and Pichia stipitis is determined. Then, the influence of salinity/matrix characteristics was evaluated to understand possible interferences during fermentation process and exhibited lower biochemical yields than the control conditions. Thus, further fermentations experiments are necessary

Process Simulation and Optimization of Biodiesel Production from Algae Biomass

There is need to further examine optimization of biodiesel production from renewable sources. In this study, we report the optimization of biodiesel produced from microalgae biomass using the CHEMCAD process simulator. Results show that the overall molar flow and energy was calculated to be 7.010kmoles/h and -4936.5MJ/h respectively. And also the liquid viscosity of the microalgae oil is greater than that of the biodiesel produced

Development of a novel membrane bioreactor for cost-effective wastewater treatment and microalgae harvesting

The rapid depletion of fossil fuels has raised increasing attention worldwide, and initiated intensive research for sustainable alternatives for energy production. Among these, biodiesel from microalgae has appeared as one of the most promising candidate due to their ability to accumulate large amount of lipids. Indeed, microalgae can achieve a productivity up to 25 higher than other crop sources without need of cultivatable soil, therefore without competing with food production. In the meantime, microalgae have also shown promising results for the treatment of various kind of wastewaters. However, the cultivation of microalgae for energy production suffers from the large costs of harvesting and dewatering of biomass, prior to lipid extraction and biofuel production, which accounts for up to 50% of operating costs. Therefore, the search for cost-effective methods of harvesting and dewatering of microalgae biomass has become necessary to optimize their usage. This study investigates forward osmosis (FO) for the dewatering of microalgae biomass and its implementation within a photobioreactor used for wastewater treatment. FO is a cost-effective filtration process based on the differences of osmotic pressure across a semi-permeable membrane. The use of FO for microalgae dewatering is of high interest, given the high fouling ability of microalgae biomass and the low fouling promises of FO. First, the feasibility of using FO for microalgae dewatering was assessed, focusing on better understanding the fouling mechanisms involved. The filtration performances have been investigated under various operating parameters. It has been found that when Ca2+-containing draw solutions were used, microalgae responded to the back diffusion of calcium ions by an extensive excretion of carbohydrates, accelerating the formation of algal flocs, thus enhancing the rate and extent of flux decline and reducing the algae dewatering efficiency. However, most of the fouling was reversible by simple hydraulic flushing. In addition, substantial adsorption of algal biomass was observed on the feed spacer. Also, Scenedesmus obliquus and Chlamydomonas reinhardtii, with fructose and abundant glucose and mannose in its cell wall, showed strong response to the back diffusion of calcium ions which encouraged S. obliquus to produce more extracellular carbohydrates and formed a stable gel network between algal biomass and extracellular carbohydrates, leading to algae aggregation and severe loss in both water flux and algae biomass during FO dewatering with Ca2+-containing draw solution. Among the species investigated, Chlorella vulgaris without fructose was the most suitable microalgae species to be dewatered by FO with a high algae recovery and negligible flux decline regardless of which draw solution was applied. These findings improve mechanical understanding of FO membrane fouling by microalgae; have significant implications for the algae species selection; and are critical for the development and optimization of FO dewatering processes. Finally, the implementation of FO dewatering with continuous microalgae biomass production and synthetic wastewater treatment was investigated. Two systems (External FO ; Immersed FO) have been studied and compared in order to provide insights on the advantages and disadvantages of each system. Constant parameters have been set identical for both systems: operation time; photobioreactor; hydraulic retention time; biomass production; FO permeate volume. The results reveals that the wastewater treatment efficiency (nutrients removal), as well as the production of biomass were greater with the immersed system due to a greater microalgae growth. However, these may not be sustainable in a long term operation of the immersed system. The external FO system was found better in terms of salinity build-up and FO dewatering performances. Overall, an external FO dewatering is recommended due to its better flexibility and sustainability

Improving the efficiencies of photoautotrophic biofuel production: from biomass to biocatalysts

The rising effects of climate change and global problems of resource scarcity and environmental pollution require a change in paradigm towards sustainable energy and chemicals production. Photosynthetic microbes, including cyanobacteria and green algae, are promising raw materials for future production platforms which have high aerial productivity and don’t compete with food and feed. They are also well suited to act as chassis for the direct and continuous production of targeted fuels and chemicals, thus functioning as true biocatalysts. However, efficiencies of photoautotrophic production system need improvement before a successful shift to these platforms. The overall aim of this thesis is to improve efficiencies of photoautotrophic production platforms. To meet this aim, I have studied two approaches: (i) Integrative biomass-based production; and (ii) Direct biofuel/chemical production. The first approach involved the integration of wastewater treatment with biofuel production, using native Finnish microalgae. Screening revealed the native alga UHCC0027 as a suitable candidate for efficient nutrient removal and lipid accumulation. At pilot scale, UHCC0027 demonstrated robust nutrient removal performance in real wastewater of both high and low organic loading and at different temperatures, including a cold temperature relevant to Nordic conditions. Nutrient balances (C:N and N:P) were important in biomass accumulation and nutrient removal performance. Whilst Fatty acid methyl ester (FAME) profiles did not meet requirements of unblended fuel standards, workarounds such as hydrogenation may succeed in future. The second approach involved the immobilization of cyanobacterial and green algal cells in a novel tunable immobilization material, TEMPO oxidized cellulose nanofibrils (TEMPO CNF). This transfers the capabilities of current suspension photosynthetic cell factories to a solid-state that restricts loss of energy to biomass accumulation and enables photosynthetic cells to operate as long-living true catalysts for bioproduction. Three different construction methods were used: (i) a pure TEMPO CNF hydrogel; (ii) a Ca2+-stabilized TEMPO CNF hydrogel; and (iii) a polyvinyl alcohol (PVA) crosslinked solid TEMPO CNF film. Important outcomes were the considerably higher hydrogen yields of TEMPO CNF immobilized Chlamydomonas reinhardtii (compared to alginate controls) and the recovery and efficient hydrogen production of Anabaena sp. PCC7120 ΔhupL cells after drying. Drying was required for stable film formation and presents an opportunity for scaffold-free films in future. Overall, this thesis presents work demonstrating promising optimizations for improving efficiencies of microalgal wastewater treatment and biofuel (chemicals) production. Additionally, the novel employment of TEMPO CNF immobilization matrix for photobiological hydrogen production is an important step to addressing porosity and mechanical stability limitations of current immobilization techniques.Yhä kasvavat ilmastonmuutoksen, resurssiniukkuuden ja ympäristön saastumisen aiheuttamat haitat vaativat uutta kestävämpää tapaa energian ja kemikaalien tuotantoon. Yhteyttävät mikrobit, jotka sisältävät syanobakteerit ja viherlevät, ovat lupaavia lähtöaineita niiden tuotantoon, koska niiden tuotto pinta-alaa kohden on suuri, eikä niiden kasvatus kilpaile ruuantuotannon kanssa. Lisäksi ne soveltuvat haluttujen polttoaineiden ja kemikaalien tuotantoon eräänlaisina biokatalyytteinä, jolloin solu tuottaisi näitä lopputuotteita ilman erillistä jalostusvaihetta. Kuitenkin tarvitaan vielä merkittäviä parannuksia tuottotehokkuuteen, jotta näiden biokatalyyttien teollinen käyttö tulisi kannattavaksi. Väitöskirjan aiheena on tehostaa yhteyttävien mikrobien tehokkuutta eri sovelluksissa. Tämän tavoitteen saavuttamiseksi työssä tutkittiin kahta eri lähestymistapaa: (i) yhdistetty biomassapohjainen tuotanto ja (ii) suora biopolttoaine-/kemikaalituotanto. Ensimmäisessä lähestymistavassa sovellettiin yhdistettyä jätevedenpuhdistusta ja biopolttoaineiden tuotantoa hyödyntäen suomalaisia mikroleväkantoja. Leväkantojen seulonnassa UHCC0027 levälaji osoittautui lupaavaksi ravinteiden kerääjäksi. Lisäksi se oli tehokas rasvapitoisuuden keräämisessä. Pilotti-mittakaavassa se osoitti tehokasta ravinteiden sitomista oikeassa jätevedessä useissa eri olosuhteissa (mm. korkea ja matala orgaanisen aineen pitoisuus ja eri lämpötilat). Ravinteiden suhteilla (C:N ja N:P) oli tärkeä rooli biomassan kasvussa ja ravinteiden sitomisnopeudessa. Rasvahappojen metyyliesterien profiilit eivät täyttäneet sekoittamattoman biodieselin vaatimuksia, mikä voidaan välttää esimerkiksi hydrogenoimalla rasvahapot. Toinen lähestymistapa oli syanobakteerien ja viherleväsolujen immobilisointi TEMPO-hapetettuihin selluloosa nanofibrilleihin (TEMPO CNF), mikä tehtiin ensimmäistä kertaa tämän väitöskirjatyön puitteissa. Immobilisointi mahdollistaa useimmiten käytettyjen liuosmaisten kasvatusten siirtämisen kiinteään matriisiin. Tämä puolestaan tehostaa solujen energiatehokkuutta lopputuotteiden suuntaan, kun solujen jakaantuminen saadaan pysäytettyä. Lisäksi immobilisointi säilyttää fotosynteettisten solujen biokatalyyttisen aktiivisuuden pidempään. Tässä lähestymistavassa käytettiin kolmea eri metodia: (i) puhdas TEMPO CNF hydrogeeli; (ii) Ca2+-ioneilla stabilisoitu TEMPO CNF hydrogeeli; ja (iii) polyvinyylialkoholilla (PVA) ristisilloitettu kiinteä TEMPO CNF filmi. Tärkeimpiä tuloksia olivat TEMPO CNF immobilisoitujen Chlamydomonas reinhardtii viherlevien korkeampi vedyntuotto (verrattuna alginaatti verrokkiin) ja Anabaena sp. PCC7120 ΔhupL solujen tehokas vedyntuotto kuivausvaiheen jälkeen. Kuivausvaihe tarvittiin jäykän ja vahvan filmin aikaansaamiseksi. Yhteenvetona voidaan todeta, että tämä väitöskirjatyö osoitti lupaavia tapoja mikrolevillä tehtävän jätevedenpuhdistuksen ja biopolttoaineiden tuotannon tehostamiseksi. Lisäksi ensikertaa mikroleväsolujen immobilisointiin käytetyllä TEMPO CNF nanoselluloosalla on monia ominaisuuksia, kuten huokoisuus ja mekaaninen vahvuus, jotka parantavat biokatalyyttien tuottotehokkuutt