Due to the many problems associated with the implementation of second-genera­tion biofuels, initiatives are now undertaken to research third-generation biofuels that mainly make use of algal biomass as the feedstock (John et al. 2011). Algal

• Simple and well-known

production methods:

Produced directly from food crops by extracting the oils for use in biodiesel or producing bioethanol through fermentation

• Scalable to smaller production

capacities

• Experience with commercial

production and use in many countries

• Well-recognized feedstocks:

Wheat and sugar are the most widely used feedstock for bioethanol while oil seed rape for use in biodiesel

• Fungibihty with existing

petroleunr-based fuels

• Major issue is ‘fuel versus food’

• Produce negative net energy gains Releasing more carbon in their

production than their feedstock’s capture in their growth

• High-cost feedstocks lead to high-cost

production

• Low land-use efficiency

• Produces sustainable energy but

also can capture and store CCb

• Biomass materials, which have

absorbed CO2 while growing, are converted into fuel using the same processes as second-generation biofuels

• Require nretabohcally engineering

nricroalgae that can capture CCb and synthesize biofuels at the same time

• Technically very cumbersome and

commercially not viable

biomass is derived from both micro — and macroalgae and contains high amount of lipids. Such biomass has high potential as biodiesel precursors as they con­tain up to 70 % of oil on dry-weight basis (Demirbas 2011). However, it should be noted that all species of microalgae are not suitable for biodiesel production. Microalgae require low maintenance and are able to grow in wastewaters, non­potable water or water unsuitable for agricultural purpose, and even in sea water (Alp and Cirak 2012). The biomass can double in less than a day, and its produc­tion can be combined with CO2 from petroleum industries. The main limitation of microalgae-based biofuels is the requirement of large areas for their cultivation or costly photo-bioreactors. Moreover, such large units need to be located near the production unit, which is not feasible in many instances. The major decisions to be taken for setting up a microalgae-based biofuel production facility involve selec­tion of open or closed system and batch or continuous mode of operation. Algal biomass can be easily cultivated in open-culture systems such as lakes and ponds and in closed-culture systems like photo-bioreactors. However, both open-culture and closed-culture systems have their own merits and demerits. The closed-culture systems can be operated in either batch or continuous mode. Although continu­ous mode of operation seems convenient, it suffers from contamination and dif­ficulty in controlling the non-growth-related products. Among the macroalgae, the Laminaria spp. and Ulva spp. are the most important ones from the energy per­spective. On the other hand, there are at least 30,000 known species of microalgae. In brief, the supply chain of algae-derived biofuels includes biomass generation, harvesting, pretreatment, downstream processing, and market.