Dissolved organic phosphorus bioremediation from food-waste centrate using microalgae

Dissolved organic phosphorus (DOP) accounts for a substantial proportion of the total phosphorus remaining in the wastewater discharge and remains a concern for the receiving environment. This study assessed the potential of wastewater microalgae for the bioremediation of DOP from anaerobically digested food-waste centrate. For high DOP to low DIP ratio, the microalgal consortia was able to remove over 98% of DOP and 95% of total dissolved phosphorus. However, under a 1:1 ratio of DOP to DIP, the microalgal consortia was only able to remove 5% of the organic phosphorus and 76% of total dissolved phosphorus. All five main microalgal species were capable of producing alkaline phosphatase to some degree, the enzyme responsible for hydrolysing the phosphorus. For the dominant species Desmodesmus communis, total phosphatase activity reduced from 46.0 ± 2.3 mmol L^-1 h^-1 in axenic cultures to only 6.3 ± 0.7 mmol L^-1 h^-1 in presence of its microbiome. This resulted in a reduction in biomass from 209 ± 13 g m^-3 to 73 ± 5 g m^-3. For Tetradesmus dimorphus, alkaline phosphatase increased from 6.5 ± 0.3 mmol L^-1 h^-1 in the axenic culture to 169.8 ± 40.1 mmol L^-1 h^-1 in presence of both its microbiome and centrate-sourced bacteria but had little impact on biomass production. DOP removal rates across all five species, in all treatments ranged from 17 to 91%. With the exception of D. communis, the nutrient removal efficiency of DOP per unit biomass suggested luxury uptake of phosphorus into the microalgal cell. For wastewaters with low inorganic and moderate to high organic phosphorus microalgal-based wastewater treatment systems may offer a cost-effective mechanism for the removal and recovery of dissolved organic phosphorus from wastewater. Further research on refining organic phosphorus bioremediation in a range of wastewater types, particularly at pilot and full-scale, is needed.