Economic benefits of carbon source selection for polyphosphate-accumulating organisms in enhanced biological phosphorus removal.

Despite the wide application of enhanced biological phosphorus removal (EBPR) in wastewater treatment plants (WWTPs), the economic and environmental benefit of carbon source selection remains poorly understood. To address this problem, metabolic modeling and carbon flux analysis were performed to evaluate the optimized polyphosphate-accumulating organism (PAO)-carbon source combinations, in terms of phosphorus (P) removal efficiency, cost, CO2 emission, and O2 demand. Three groups of representative PAOs (Ca. Accumulibacter, Microlunatus phosphovorus, and Tetrasphaera) and six carbon sources (acetate, lactate, succinate, aspartate, glutamate, glucose) were assessed, focusing on carbon flux/allocation to intracellular polymer synthesis, CO2 emission, and biomass production. Significant difference was observed among PAOs and carbon sources. Microlunatus phosphovorus with glucose achieved the highest P removal efficiency with low CO2 emission and O2 demand, outperforming Ca. Accumulibacter with any single carbon source. Tetrasphaera showed poor carbon efficiency due to their tendency to fermentation. For Ca. Accumulibacter, lactate emerges as the most economical carbon source, achieving high P removal and low CO2 emission; succinate offered a workable substitute with an emission penalty; acetate showed low CO2 emission but the highest O2 demand and high cost, making it less favorable under energy- or cost-constrained conditions. In contrast, amino acids such as aspartate and glutamate were the least cost-effective, reflecting by their high costs and decarboxylation-related CO2 emission. These findings provide a mechanistic and model-based approach for carbon source selection in EBPR systems, offering new insights into more sustainable, cost-effective, and environmentally friendly carbon management strategies.