Supplementing air with CO2 stripped from recirculating aquaculture improves growth of two green microalgae in aquaculture wastewater

To improve sustainability and to implement the principles of circular economy in aquaculture, we tested the possibility to boost the capture of nitrate by two green microalgal species from recirculating aquaculture system's (RAS) wastewater by supplementing air with carbon dioxide stripped from a RAS. Carbon dioxide addition increased cell densities of Monoraphidium griffithii and Haematococcus pluvialis in photobioreactors during 9-day growing periods. However, growth rates and nitrate uptake rates were only improved for M. griffithii. Addition of CO2 decreased pH of the medium with M. griffithii which likely also affected positively on algal growth and nutrient uptake. These laboratory scale experiments suggest that microalgal cultivation to produce valuable biomass could be connected to a RAS to decrease nitrate and CO2 emissions from aquaculture.

Automated summary

In order to enhance sustainability and implement circular economy principles in aquaculture, we investigated the potential of using carbon dioxide from a recirculating aquaculture system (RAS) to promote the capture of nitrate by two green microalgal species from RAS wastewater. Addition of carbon dioxide increased cell densities of Monoraphidium griffithii and Haematococcus pluvialis in photobioreactors, but only M. griffithii showed improved growth and nitrate uptake rates. The addition of CO2 also decreased the pH of the medium with M. griffithii, which likely had a positive effect on algal growth and nutrient uptake. These experiments suggest that microalgal cultivation connected to a RAS could reduce nitrate and CO2 emissions in aquaculture.