The increase in atmospheric CO 2 concentration and the release of nutrients from wastewater treatment plants (WWTPs) are environmental issues linked to several impacts on ecosystems. Numerous technologies have been employed to resolves these issues, nonetheless, the cost and sustainability are still a concern. Recently, the use of microalgae appears as a cost-effective and sustainable solution because they can effectively uptake CO 2 and nutrients resulting in biomass production that can be processed into valuable products. In this study single (Spirulina platensis (SP.PL) and mixed indigenous microalgae (MIMA) strains were employed, over a 20-month period, for simultaneous removal of CO 2 from flue gases and nutrient from wastewater under ambient conditions of solar irradiation and temperature. The study was performed at a pilot scale photo-bioreactor and the effect of feed CO 2 gas concentration in the range (2.5-20%) on microalgae growth and biomass production, carbon dioxide bio-fixation rate, and the removal of nutrients and organic matters from wastewater was assessed. The MIMA culture performed significantly better than the monoculture, especially with respect to growth and CO 2 bio-fixation, during the mild season; against this, the performance was comparable during the hot season. Optimum performance was observed at 10% CO 2 feed gas concentration, though MIMA was more temperature and CO 2 concentration sensitive. MIMA also provided greater removal of COD and nutrients (~83% and >99%) than SP.PL under all conditions studied. The high biomass productivities and carbon bio-fixation rates (0.796-0.950 g dw .L −1 .d −1 and 0.542-1.075 g C .L −1 .d −1 contribute to the economic sustainability of microalgae as CO 2 removal process. Consideration of operational energy revealed that there is a significant energy benefit from cooling to sustain the highest productivities on the basis of operating energy alone, particularly if the indigenous culture is used.

A technoeconomic assessment (TEA) has been conducted of the feasibility of large-scale application of microalgal culture technology (MCT) to the combined mitigation of CO2 emissions from flue gases and nutrient discharges from wastewater in the Arabian Gulf. The assessment has incorporated the selection of the algal species and MCT technologies, the extent of nutrient removal, and the biomass/biofuel production rate. The cost benefit of the abatement of pollutants (in the form of CO2 and nutrient discharges) was included by assigning appropriate credits to these contributions. The overall economic viability was quantified as the break-even selling price (BESP) of the generated biocrude, taken to be the price at which the product must sell to cover the operating expenditure (OPEX). Based on available information and optimal operational conditions, the BESP was calculated as being $0.544 per kg biomass, equating to $0.9 L-1 for the extracted biocrude, the credited items contributing ~14% of this figure. The BESP was found to be most sensitive to the algal growth rate µ, the BESP changing by ±24% in response to a ±20% change in µ. Whilst the terms of reference of the study are limited to OPEX contributors, the potential for sustainability associated with the innately reliably high levels of natural light in the Gulf region appear to provide auspicious circumstances for large-scale implementation of MCT. For emerging economies with a comparable climate but without a mineral oil-based economy a greater financial benefit from the proposed scheme would arise.