Keeping in view the bio-extraction potential of microalgae along with biomass pro­duction, such integrated systems that use microalgae for treating waste water and producing oil for biodiesel and chemical products are gaining interests globally. It has demonstrated that dual-use of microalgae cultivation for waste water treatment coupled with biofuel generation is an attractive option for reducing energy, fertil­izer, and freshwater costs of production along with reduced GHG emissions (Pittman et al. 2011; Park et al. 2011; Menger-Krug et al. 2012). A group of researchers have claimed that microalgae-mediated CO2 fixation coupled with biofuel production is more sustainable if we integrate biomass production with wastewater treatment (Kumar et al. 2010). Actually, cultivation of microalgae consumes more fertilizers as compared to the most common oleaginous plants. For instance, N-fertilizer consumption in the range of 0.29-0.37 kg kg-1 oil is reported, which is higher than that for Jatropha and palm oil where 0.24-0.048 kg of fertilizer is required per kg oil production, respectively (Lam and Lee 2012). So, use of waste water enriched with nutrients will undoubtedly decrease the cost of production.

Moreover, although microalgae grow in an aquatic medium yet they require less water than terrestrial oleaginous crops while making use of saline, brackish, and/or coastal seawater (Kliphuis et al. 2010; Rodolfi et al. 2009). This allows the production of algal biomass without competing for valuable resources such as arable land, land­scapes, and freshwater. The microalgae Nannochloropsis sp., Dunaniella salina, Chlorella sp., and Etraselmis sp. were found suitable for a multiple-product algae crop. The tropical and sub-tropical microalgae display a variety of fatty acid profiles making algal biomass production more attractive to obtain oil-based bio-products, including biodiesel and omega-3 fatty acids (Lim et al. 2012). Conclusively, a biore­finery approach (integration of waste water treatment and algal biomass production) for microalgae would make the process economically feasible but challenges remain there regarding the efficient harvesting and extraction processes for some species.