Optimizing airflow rate and carbon source dosage strategies for wastewater treatment plant: Toward carbon emission reduction and enhanced nitrogen removal

The current operational strategies of Wastewater Treatment Plants (WWTPs) rely heavily on manual experience, which poses challenges in simultaneously achieving carbon emission reduction targets and improving effluent quality. To address this issue, this study proposed the carbon source dosage and airflow rate adjustment strategies based on the carbon-nitrogen and gas-water ratios, respectively, with the aim of reducing the effluent total nitrogen concentration (TNeff). Additionally, the Indirect Carbon Emission Intensity (ICEI) and Total Carbon Emission Intensity (TCEI) were calculated as carbon emission evaluation indicators. As a trial-and-error tool, the GRU-LSTM prediction model was developed to predict real-time TNeff, providing a reference for strategy development. Using a full-scale WWTP as a case study, results showed that TNeff decreased by 1.71 mg/L on average under the proposed strategies, with fluctuations reduced from 1.32 mg/L to 0.98 mg/L. At the same time, ICEI decreased by 4.18 %. The GRU-LSTM prediction model achieved R-2 values of 0.94, demonstrating its effectiveness in predicting real-time TNeff accurately. The results illustrated that dynamic operation strategies can simultaneously achieve carbon emission reduction and improved nitrogen removal. The finding could provide evidence-based decision support for WWTPs to optimize nitrogen removal and carbon emission.