Removal of dissolved organic carbon and nutrients from urban wastewaters by Galdieria sulphuraria: Laboratory to field scale demonstration

Previous laboratory studies have demonstrated the ability of microalgae Galdieria sulphuraria (G. sulphuraria) in removing organic carbon and nutrients from filtered primary-settled urban wastewater via mixotrophic metabolism. An advantage of mixotrophic cultivation of G. sulphuraria over heterotrophic conditions is higher biomass yield that can potentially translate into higher energy recovery from the biomass. This study recorded a yield of 0.63 g biomass/g glucose under mixotrophic conditions while that under heterotrophic conditions was 0.42 g biomass/g glucose. These laboratory studies were extended to cultivate G. sulphuraria under field conditions in a 700 L photobioreactor (PBR) fed with primary-settled wastewater. Biomass growth and removal of dissolved organic carbon and nutrients in this PBR under batch mode were monitored over a range of influent and operating conditions. This field study confirmed that G. sulphuraria was able to grow well in primary-settled wastewater and reduce organic carbon (measured as BOD₅), ammoniacal nitrogen, and phosphate levels to below the respective discharge standards; corresponding 3-day removal efficiencies ranged 46–72%; 63–89%; and 71–95%.