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Microalgae have the intrinsic ability to harness energy from sunlight and photosynthetically valorize CO2 into fuel molecules, which can further be converted to biodiesel. They have a unique profile of fatty acids comprising of a mixture of saturated and unsaturated fatty acids. Microalgae have adapted to grow in various nutritional environments due to their metabolic versatility and resilience. Cultivation systems are of major importance for upscaling and generating large amounts of biomass with fuel properties. Novel photobioreactor designs have recently been explored for integration with urban infrastructure by fusion of principles of urban ecology and environmental sustainability. High throughput techniques for estimation of biodiesel quality have made analysis simpler and more reliable. For economical production of biomass, integrating biodiesel production with industrial flue gases and wastewater treatment is considered a viable strategy in algal cultivation. This chapter sheds light on the current state of art in algal cultivation for biomass and enhancing the lipid profile towards biodiesel production thus reducing carbon footprints.

Short-chain (volatile) fatty acids (C2–C4; SCFA) generated during biohydrogen process via anaerobic fermentation is an unrecognized treasure with multifaceted applications in the synthesis of biofuels and bioproducts. These carboxylic fatty acids are often abundantly available in dark fermentation effluents as raw materials. They are undervalued due to their disposal in wastewaters and side streams of biological hydrogen production by dark fermentation. Research community is now realizing the enormous potential of these short-chain carboxylic acids as low-cost alternatives to chemical fertilizers and carbon substrates. SCFAs exist as amenable feedstock for a wide range of bioprocesses, viz., biohydrogen, bioelectricity, bioplastics, and algal cultivation. Prevalence of microbial community structure during dark fermentation plays an important role in efficient utilization of SCFAs or conversion into different products based on the fatty acid composition. Biological and electrogenic interventions can help in chain elongation of SCFA to medium-chain fatty acids enabling huge innovation potential for SCFA utilization. In the present chapter, current state of the art in applications of SCFAs as economical feedstock for various bioprocesses was evaluated. From a bioeconomy perspective, it is crucial to integrate bioprocesses where side-streams generated from one process act as feedstock for other process resulting in an intricate network of multilevel processes in a biorefinery approach.

Mixotrophic and heterotrophic cultivation modes were studied for enhancing the biomass and lipid productivities using light and carbon as critical factors. The adaptability of the newly isolated Chlorella sp towards transition from mixotrophic to heterotrophic cultivation mode was evaluated. Organic carbon illustrated higher affinity towards both biomass and lipid productivities. Specific changes in fatty acid profile were observed with respect to trophic condition. Maximum biomass productivity (4.21 g/l) and relatively higher lipid productivity (107.3 g/kg of DCW) was observed with mixotrophic (MXG) condition while heterotrophic mode showed higher lipid content (28.9%). Higher carbohydrate content (94.3 mg/g DCW) was observed in mixotrophic mode and maximum protein content (450 mg/g DCW) was obtained with heterotrophic condition. The synergism between total lipid content, fatty acid composition and biomass productivities during trophic transition was critically evaluated. The transition between the trophic modes have given deeper insights into the metabolic partitioning of carbon in photosynthetic and respiratory pathways during synthesis of biodiesel precursors. Mining of bio-based products from microalgae can create more sustainable economies and integrated approach will add paybacks to process signifying algal based biorefinery model.

Considerable interest in the development of biobased polymers is being garnered due to their diverse applications and biodegradability. In this communication, bioplastics (as polyhydroxyalkanoates) production using wastewater as a substrate was studied by varying the reactor microenvironment (aerobic and microaerophilic) and operating pH (6, 7 and 8). Redox reactions occurring in the mixed culture during polyhydroxyalkanoates production were investigated. Maximum polyhydroxyalkanoates production in terms of dry cell weight (%) was observed in microaerophilic operation (56%), compared to aerobic (34%) operation. Neutral pH showed better polyhydroxyalkanoates synthesis (56%) than basic (44%) and acidic (28%) redox microenvironments. Neutral pH operation documented higher dehydrogenase enzyme activity, reduction currents, substrate degradation than acidic and alkaline pH at microaerophilic environment that correlated well with higher polyhydroxyalkanoates production. Biopolymer composition showed the presence of co-polymer, poly-(3-hydroxybutyrate-co-3-hydroxyvalerate). Fluorescence in situ hybridization analysis revealed the presence of phylum Proteobacteria, Acidobacteria and Firmicutes in mixed culture which are known for polyhydroxyalkanoate production. This study illustrated that efficient utilization of wastewater for bioplastics production at optimum conditions can be viewed as viable solution for tackling the problems of increasing waste advocating the concept of ‘waste to wealth’.

Critical influence of different short chain fatty acids as organic carbon source, during growth (GP) and nutrient stress lipogenic phase (NSLP) was investigated on biomass and lipid productivity, in mixotrophic fed-batch microalgae cultivation. Nutrient deprivation induced physiological stress stimulated highest lipid productivity with acetate (total/neutral lipids, 35/17) with saturation index of 80.53% by the end of NSLP followed by butyrate (12/7%; 78%). Biomass growth followed the order of acetate (2.23 g/l) >butyrate (0.99 g/l) >propionate (0.77 g/l). VFA removal (as COD) was maximum with acetate (87%) followed by butyrate (55.09%) and propionate (10.60%). Palmitic acid was the most dominant fatty acid found in the fatty acid composition of all variants and butyrate fed system yielded a maximum of 44% palmitic acid. Protein profiling illustrated prominence of acetyl CoA-synthetase activity in acetate system. Thus, fatty acids provide a promising alternative feedstock for biodiesel production with integrated microalgae-biorefinery.

Microalgae are inexhaustible feedstock for synthesis of biodiesel rich in polyunsaturated fatty acids (PUFA) and valuable bioactive compounds. Their cultivation is critical in sustaining the global economy in terms of human consumption of food and fuel. When compared to autotrophic cultivation, heterotrophic systems are more suitable for producing high cell densities of microalgae for accumulation of large quantities of lipids (triacylglycerols) which can be converted into biodiesel. Consorted efforts are made in this communication to converge recent literature on heterotrophic cultivation systems with simultaneous wastewater treatment and algal oil production. Challenges faced during large scale production and limiting factors which hinder the microalgae growth are enumerated. A strategic deployment of integrated closed loop biorefinery concept with multi-product recovery is proposed to exploit the full potential of algal systems. Sustainable algae cultivation is essential to produce biofuels leading to green future.

Microalgae are solar-driven cellular biofactories that convert carbon dioxide into various cellular biocomponents such as pigment, proteins, lipids, polysaccharides, and vitamins through light-induced electron transport. Carotenoids are class of nonnitrogenous colored terpenoids pigments that are universally produced in two major types, hydrocarbon class (carotenes) and oxygenated class (xanthophylls) with a strong antioxidant property. Microalgae-based carotenoid production is garnering interest in the recent times due to the ease of scalable cultivation in diverse conditions with good productivity in short durations. Several microalgal species like Dunaliella salina (β-carotene), Haematococcus pluvialis , and Chlorella zofingiensis (astaxanthin) have showed good carotenoid production ability. Carotenoids have multiple applications in the food, pharmaceutical, nutraceutical, healthcare, and cosmetic industrial sector owing to their high commercial value. The chapter tends to provide an overview of carotenogenesis from microalgae.

Microalgae are responsible for more than half of the world’s primary production of oxygen. They are the simplest and most abundant form of plant life on the earth (Energy from algae (Technical Summary. Scott Maden, 2010). These photosynthetic organisms are categorized under third generation biofuels and are known to have high oil and biomass yields, can be cultivated with wastewater, do not need arable land for cultivation, do not compete with common food resources and very efficiently use water and nutrients for growth (Hannon et al., Biofuels 1:763–784, 2010). There are various routes of metabolism which microalgae have adopted for their growth and survival viz., autotrophic, heterotrophic and mixotrophic. They are capable of shifting their metabolism in response to changes in the environmental conditions (Devi et al., J Renew Energy 43:276–283, 2012). Algal cultivation for biodiesel production is considered more amenable a technology than the cultivation of oil crops (Chisti, Biotechnol Adv 25:294–306, 2007) because the yields of algae-derived oils are much higher (Abou-Shanab et al., J Power Energy Eng 1:4–6, 2010). Autotrophically algae gain energy through light by fixing atmospheric CO2 (Devi and Venkata Mohan, Bioresour Technol 112:116–123, 2012). However, low biomass yields, requirement of cultivation systems with large surface area and shallow depth for better access of light are some of the disadvantages associated with autotrophic mode of nutrition. In the absence of light, the photosynthetic process gets suppressed and algae gain energy from alternative organic processes using heterotrophic pathways that convert sugar into lipids (Perez-Garcia et al., J Phycol 46:800–812, 2010). This pathway leads to significantly denser biomass, facilitating greater lipid yields.

The role of operating temperature as a physical stress factor for enhancing lipid induction during microalgae cultivation with domestic wastewater was evaluated. Experiments were designed with dual mode microalgae cultivation viz., growth phase (GP) and temperature induced stress phase (25 °C, 30 °C and 35 °C). GP showed enhancement in biomass growth and carbohydrate accumulation while stress phase (SP) operation at 30 °C showed noticeable improvement in lipid productivities (total/neutral lipid, 24.5/10.2%). Maximum carbohydrate utilization was observed during SP at 30 °C operation (57.8%) compared to 25 °C (50.6%) and 35 °C (26.9%) correlating well with the lipid synthesis. Interestingly the neutral lipid content documented five-fold increment illustrating feasibility towards good biodiesel properties. Biodiesel profile at 30 °C temperature is well supported by higher saturated fatty acids (SFA) to unsaturated fatty acids (USFA) ratio. GP operation showed good COD and nutrient removal concomitant to the biomass growth.

Critical role of organic carbon supplementation on the lipid synthesis during growth and nutrient deprived stress phase was investigated in present study. Mixotrophic cultivation showed relatively higher biomass productivity at lower carbon loading condition (500 mg COD/l). Nutrient deprivation induced physiological stress and glucose supplementation with 2000 mg COD/l supported higher lipid accumulation (26%). Glucose supplementation in mixotrophic growth phase showed distinct influence on biomass growth whereas glucose supplementation in nutrient starvation resulted in higher lipid storage. Compositional variation in FAME profile was observed with respect to saturated fatty acids when operated with increasing glucose concentrations. Mixotrophic mode of cultivation showed remarkable benefits of nutrient removal and organic carbon supplementation influenced greatly on biodiesel production which can be easily scaled up to pilot plant and large scale production facilities.

In this paper a compact circularly polarized antenna is proposed to operate in X-band spectrum. The F-shaped monopole element is used as the radiating structure and the closed coplanar-waveguide ground is used on a FR4 substrate. The proposed feeding mechanism with asymmetric ground planes and the three rectangular strips connected to the feed line. The proposed antenna operates with a -10dB reflection coefficient bandwidth from 9.3 GHz to 13 GHz and the circular polarized performance is attained from 9.8 GHz – 11.2 GHz with axial ratio less than 3dB (AR < 3dB). The antenna gain in the boresight direction is found to be achieved as 4.34dB and radiates with a maximum efficiency of 90% which is suited for amateur radio applications in X-band spectrum based vehicular communications.