Integrated
watershed modeling is needed to couple water resource
recovery facilities (WRRFs) with agricultural management for holistic
watershed nutrient management. Surrogate modeling can facilitate model
coupling. This study applies artificial neural networks (ANNs) as
surrogate models for WRRF models to efficiently evaluate the long-term
treatment performance and cost under influent fluctuations. Specifically,
we first developed five WRRFs, including activated sludge, activated
sludge with chemical precipitation (ASCP), enhanced biological phosphorus
removal (EBPR), EBPR with acetate addition (EBPR-A), and EBPR with
struvite recovery (EBPR-S), in a high-fidelity simulation program
(GPS-X). The five WRRFs were based on an existing plant that treats
combined domestic and industrial wastewater. The ANNs have satisfactory
performance in capturing nonlinear biological behaviors for all five
WRRFs, even though the prediction performance (R-square)
slightly decreases as the model complexity increases. We advanced
ANNs application in WRRF models by simulating long-term (10-yr) performance
with monthly influent fluctuations using ANNs trained by simulation
data from steady-state models and evaluated their performance on Phosphorus
(P) and Nitrogen (N) removal. EBPR-S shows the most resilience, while
EBPR is more sensitive to influent characteristics impacted by stormwater
inflow. When comparing life cycle costs of N and P removal for each
layout over the 10-yr simulation period, EPBR-S is the most cost-effective
alternative, highlighting both the operational and cost benefits of
side-stream P recovery. By capturing both nonlinear behaviors of biological
treatment and operating costs with computationally lean ANNs, this
study provides a paradigm for integrating complex WRRF models within
integrated watershed modeling frameworks.