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

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.