Bioproduct Potential of Outdoor Cultures of Tolypothrix sp.: Effect of Carbon Dioxide and Metal-Rich Wastewater

Chinnathambi Velu; Samuel Cirés; Diane L Brinkman; Kirsten Heimann

doi:10.3389/fbioe.2020.00051

Bioproduct Potential of Outdoor Cultures of Tolypothrix sp.: Effect of Carbon Dioxide and Metal-Rich Wastewater

Front Bioeng Biotechnol. 2020 Feb 11:8:51. doi: 10.3389/fbioe.2020.00051. eCollection 2020.

Authors

Chinnathambi Velu¹, Samuel Cirés^{1

2}, Diane L Brinkman³, Kirsten Heimann^{1

4}

Affiliations

¹ North Queensland Algal Identification Facility, Aquaculture, College of Science and Engineering, James Cook University, Townsville, QLD, Australia.
² Departamento de Biología, Universidad Autónoma de Madrid, Madrid, Spain.
³ Australian Institute of Marine Science (AIMS), Townsville, QLD, Australia.
⁴ Centre for Marine Bioproducts Development (CMBD), College of Medicine and Public Health, Flinders University, Bedford Park, SA, Australia.

Abstract

Rising CO₂ levels, associated climatic instability, freshwater scarcity and diminishing arable land exacerbate the challenge to maintain food security for the fast growing human population. Although coal-fired power plants generate large amounts of CO₂ emissions and wastewater, containing environmentally unsafe concentrations of metals, they ensure energy security. Nitrogen (N₂)-fixation by cyanobacteria eliminate nitrogen fertilization costs, making them promising candidates for remediation of waste CO₂ and metals from macronutrient-poor ash dam water and the biomass is suitable for phycocyanin and biofertilizer product development. Here, the effects of CO₂ and metal mixtures on growth, bioproduct and metal removal potential were investigated for the self-flocculating, N₂-fixing freshwater cyanobacterium Tolypothrix sp. Tolypothrix sp. was grown outdoors in simulated ash dam wastewater (SADW) in 500 L vertical bag suspension cultures and as biofilms in modified algal-turf scrubbers. The cultivation systems were aerated with air containing either 15% CO₂ (v/v) or not. CO₂-fertilization resulted in ∼1.25- and 1.45-fold higher biomass productivities and ∼40 and 27% increased phycocyanin and phycoerythrin contents for biofilm and suspension cultures, respectively. CO₂ had no effect on removal of Al, As, Cu, Fe, Sr, and Zn, while Mo removal increased by 37% in both systems. In contrast, Ni removal was reduced in biofilm systems, while Se removal increased by 73% in suspension cultures. Based on biomass yields and biochemical data obtained, net present value (NPV) and sensitivities analyses used four bioproduct scenarios: (1) phycocyanin sole product, (2) biofertilizer sole product, (3) 50% phycocyanin and 50% biofertilizer, and (4) 100% phycocyanin and 100% biofertilizer (residual biomass) for power station co-located and not co-located 10 ha facilities over a 20-year period. Economic feasibility for the production of food-grade phycocyanin either as a sole product or with co-production of biofertilizer was demonstrated for CO₂-enriched vertical and raceway suspension cultures raised without nitrogen-fertilization and co-location with power stations significantly increased profit margins.

Keywords: biofertilizer; biorefinery; bioremediation; coal-fired power; economics; metals; nitrogen-fixing cyanobacteria; phycobiliproteins.