Forecasting nitrous oxide emissions from a full-scale wastewater treatment plant using LSTM-based deep learning models

Abstract

• LSTM-based deep learning models trained on long-term data from a full-scale WWTP. • Deep learning models evaluated to forecast N 2 O emissions up to 6 hours ahead. • Best model achieved R 2 of 0.59-0.98 for prediction horizons spanning 0.5-6.0 hours. • Model performance declined as the prediction horizon increased. • Hybrid deep learning-biokinetic models could improve accuracy and robustness. Nitrous oxide (N 2 O) emissions from wastewater treatment plants (WWTPs) exhibit significant seasonal variability, making accurate predictions with conventional biokinetic models difficult due to complex and poorly understood biochemical processes. This study addresses these challenges by exploring data-driven alternatives, using long short-term memory (LSTM) based encoder-decoder models as basis. The models were developed for future integration into a model predictive control framework, aiming to reduce N 2 O emissions by forecasting these over varying prediction horizons. The models were trained on 12 months and tested on 3 months of data from a full-scale WWTP in Amsterdam West, the Netherlands. The dataset encompasses seasonal peaks in N 2 O emissions typical for winter and spring months. The best performing model, featuring a 256-256 LSTM architecture, achieved the highest accuracy with test R 2 values up to 0.98 across prediction horizons spanning 0.5 to 6.0 hours ahead. Feature importance analysis identified past N 2 O emissions, influent flowrate, NH 4 + , NO x , and dissolved oxygen (DO) in the aerobic tank as most significant inputs. The observed decreasing influence of historical N 2 O emissions over extended prediction horizons highlights the importance and significance of process variables for the model's performance. The model's ability to accurately forecast short-term N 2 O emissions and capture immediate trends highlights its potential for operational use in controlling emissions in WWTPs. Further research incorporating diverse datasets and biochemical process inputs related to microbial activities in the N 2 O production pathways could improve the model's accuracy for longer forecasting horizons. These findings advocate for hybridising deep learning models with biokinetic and mechanistic insights to enhance prediction accuracy and interpretability.

Topics & Concepts