Cyanobacteria pigment production in wastewater treated for heavy metal removal

Abstract

Cyanobacterial pigments have an evolving market demand as natural colorants with numerous health benefits and diversified applications. Nevertheless, scaling up cyanobacterial pigment production to meet the market demand is economically unsustainable due to the high upstream processing costs, notably associated with the supply of nutrients during cyanobacteria cultivation. Thus, utilization of wastewater as alternative nutrient sources for cultivation is a potential method to enhance the economic viability and sustainability of pigment production. In wastewater-integrated cyanobacteria cultivation, nutrients are assimilated to produce biomass simultaneous to bioremediation. Nonetheless, the toxic heavy metals present in wastewater may accumulate in cyanobacteria and adversely affect biomass valorization. Therefore, the use of suitable heavy metal removal techniques is essential prior to integration of wastewater with the upstream process of cyanobacterial pigment production in view of improving product safety. Accordingly, the current review discusses primary literature on pigment biosynthesis and heavy metal accumulation in cyanobacteria cultured in wastewater and details physicochemical, electrochemical, and biological treatment methods available for heavy metal removal from wastewater prior to cyanobacteria cultivation. The suitability of heavy metal removal methods is analyzed with respect to various technical and economic aspects, including selective heavy metal removal, minimizing nutrient loss, and incremental capital/operating costs. Moreover, future perspectives in the research domain are discussed, with emphasis on the requirement for techno-economic assessments, life cycle analysis, product safety assessment, and public perception. Thus, the current review comprehensively analyses strategies for heavy metal removal from wastewater prior to its integration with the upstream process of cyanobacterial pigment production.