Integrated CO₂ capture, wastewater treatment and biofuel production by microalgae culturing - A review

Algae have recently received growing attention given its prospects as a source of renewable energy and its potential for CO₂ capture. Algae culture is of increasing value given that: (i) algae can be cultivated on non-agricultural land using wastewater, (ii) algae can provide a high yield on a per unit of light irradiated area, (iii) algae growth requires CO₂ and nutrients that can be obtained from wastewater and fossil fuel combustion and (iv) algae contains high oil and starch making possible the production of high quality biodiesel. Thus, algae culture can contribute to CO₂ fixation, wastewater treatment and can be a source of bioenergy. This article presents a critical review, focusing on various microalgae species that consume CO₂ and nutrients from wastewater, and provide high quality biofuel. In this respect, a number of relevant topics are discussed in this review: (a) the media for algae culture, (b) the photobioreactor, (c) the associated wastewater treatment processes, (d) the CO₂ capture mechanism and (e) microalgal harvesting. This review also considers various aspects of the biomass processing such as (a) lipid extraction, (b) thermodynamics of the produced biomass conversion, (c) biomass gasification, (d) biodiesel production, (e) catalysts, (f) reaction pathways/mechanisms and (g) reaction kinetics.