Microalgal flocculation: Global research progress and prospects for algal biorefinery.

Microalgal research has made significant progress due to versatile and high-value industrial applications of microalgal biomass or its derivatives. However, to explore their full potential and to achieve commercial robustness, microalgal biorefinery needs cost-effective technologies to produce, harvest, and process the microalgal biomass on large scale as higher production and harvesting cost is one of the key hindrances in the commercialization of algae-based products. Among several other algal biomass harvesting technologies, self-flocculation seems to be an attractive, low-cost, and eco-friendly harvesting technology. This review covers various flocculation-based methods that have been employed to harvest microalgal biomass with a special emphasis on self-flocculation in microalgae. Moreover, genetic engineering approaches to induce self-flocculation in non-flocculating microalgae along with the factors affecting self-flocculation and recent research trends have also been discussed. It is concluded that self-flocculation is the most desired approach for the energy- and environment-efficient harvesting of microalgal biomass. However, its poorly understood genetic basis needs to be deciphered through detailed studies to harness its potential for the algal biorefinery.

Impact of wastewater cultivation on pollutant removal, biomass production, metabolite biosynthesis, and carbon dioxide fixation of newly isolated cyanobacteria in a multiproduct biorefinery paradigm.

The impact of wastewater cultivation was studied on pollutant removal, biomass production, and biosynthesis of high-value metabolites by newly isolated cyanobacteria namely Acaryochloris marina BERC03, Oscillatoria sp. BERC04, and Pleurocapsa sp. BERC06. During cultivation in urabn wastewater, its pH used to adjust from pH 8.0 to 11, offering contamination-free cultivation, and flotation-based easy harvesting. Besides, wastewater cultivation improved biomass production by 1.3-fold when compared to control along with 3.54-4.2 gL-1 of CO2 fixation, concomitantly removing suspended organic matter, total nitrogen, and phosphorus by 100%, 53%, and 88%, respectively. Biomass accumulated 26-36% carbohydrates, 15-28% proteins, 38-43% lipids, and 6.3-9.5% phycobilins, where phycobilin yield was improved by 1.6-fold when compared to control. Lipids extracted from the pigment-free biomass were trans-esterified to biodiesel where pigment extraction showed no negative impact on quality of the biodiesel. These strains demonstrated the potential to become feedstock of an integrated biorefinery using urban wastewater as low-cost growth media.