Dimensioning of Synechococcus elongatus PCC 7492 cultivation photobioreactor for valorization of wastewater resources

In compliance with circular economy and sustainability principles, novel wastewater treatment processes based on microalgae and/or cyanobacteria cultivation should be developed and applied. The lack of fundamental design and operational parameters hinders upscaling and implementation of such phototrophic wastewater treatment processes. In this regard, the present study sheds light on the dimensioning of a Synechococcus elongatus PCC 7492 (S7942) cultivation photobioreactor for nitrogen removal from different salinity wastewaters and for biomass-derived added value products. To attain photobioreactor dimensioning, S7942 & PRIME;s cell productivity, nitrates removal rate and specific nitrates utilization rates were calculated based on experimental data under non-favorable growth conditions of limited lighting (5 to 30 mu mol m(-2) s(-1)). Chlorophyll a and phycocyanin concentrations, as well as biomass nitrogen content were measured to assess nitrogen assimilation in relation to salinity. Under conditions of limited lighting, S7942 & PRIME;s cell productivity ranged from 43.7 to 20.0 mgVSS L-1 d(-1). Increasing salinity up to the obtained threshold value of 450 mmolNaCl L-1, specific nitrogen utilization rate ranged from 0.140 to 0.286 mgNO(3)_N mgVSS(-1). The resulting photobioreactor volume is 10 to 20 times larger compared to an activated sludge denitrification reactor, thus does not hinder the application of the proposed process. Given an optimal cell productivity obtained by applying light intensity of 150 mu mol m(-2) s(-1), photobioreactor volume can be at the same order of magnitude (1.5 to 4 times larger). In contrast to activated sludge denitrification reactors, the volume of S7942 photobioreactor remains relatively constant regardless of the wastewater salinity. The study promotes the implementation of phototrophic wastewater treatment processes contributing to GHGs emission mitigation, resources recovery, as well as added value products and green energy obtainment.