Controlling Mainstream PdNA Through Advanced Aeration Control Strategies at Nine North American Facilities

Introduction The widespread adoption of partial denitrification-anammox (PdNA) technology depends not on proving its benefits-which include 60% carbon savings, 25% aeration reduction, and 30-50% capacity increases-but on demonstrating reliable control strategies across diverse configurations. This combination of resource efficiency and capacity enhancement positions PdNA as both an operational optimization and capital avoidance strategy. While the water sector has implemented conventional nitrification-denitrification control successfully, PdNA introduces unique challenges: maintaining precise ammonia-to-NOx (AvN) ratios, coordinating carbon dosing, and managing anammox biomass retention at reduced solids retention times. This research addresses these challenges through a multi-site demonstration spanning nine facilities across North America. Unlike previous single-implementation studies, this effort evaluates control strategies across pre-anoxic, post-anoxic, and tertiary PdNA configurations simultaneously. The work builds upon successful implementations including HRSD's York River plant, where automated AvN control has enabled stable operation at nearly half the original design SRT while maintaining stringent effluent limits. Central to this effort is developing comprehensive process models using BioTwin (BioWin's real-time platform) to implement distinct mathematical frameworks for anammox kinetics, biofilm dynamics, and real-time monitoring. The modeling extends beyond steady-state design by incorporating dynamic control algorithms that reproduce transient behavior under diurnal loads, seasonal temperature fluctuations, and influent perturbations. Five controller approaches were evaluated through 30-day simulations, spanning a tuning complexity spectrum: from simple timer-based intermittent aeration requiring minimal calibration, through single-parameter ABAC, to multi-variable AvN and STAR strategies requiring systematic sensitivity analysis for setpoints and cascade loop optimization. Methodological Approach This research employs systematic validation using full-scale operational data to establish transferable control frameworks. HRSD's York River facility serves as primary calibration site, with five years of data supporting control strategy development. Parallel efforts at WSSC's Seneca sidestream pilot test ABAC with intermittent aeration in an integrated N/DN configuration, evaluating aerobic fraction control under different process constraints. Results and Discussion The modeling effort successfully replicated York River's transition from conventional operation to PdNA, achieving calibration R² values >0.85 for MLSS (2000-2600 mg/L), aerobic SRT (4-6 days), and effluent TIN (<3 mg/L). Models captured the operational shift where aerobic SRT was decoupled from total SRT through intermittent aeration, maintaining 7-8 days total SRT while reducing aerobic SRT by 40-50%-directly translating to capacity increases. Five control approaches were evaluated across the tuning complexity spectrum: Timer-based intermittent aeration: Fixed aerobic/anoxic cycles requiring minimal tuning 1.ABAC: Continuous aeration with DO setpoint adjusted based on ammonia concentration only 2.STAR Control: Intermittent aeration using dual-parameter control with ammonia and NOx monitoring, creating aerobic/anoxic cycles 3.AvN Control: Modified STAR optimized for anammox with equal slopes and zero intercept 4.AvN with carbon trim: Cascade configuration adding feedforward-feedback carbon dosing to AvN control Results indicate that controller selection should be driven by effluent TIN requirements and existing infrastructure rather than pursuing maximum complexity. Facilities targeting TIN <3 mg/L benefit from AvN control with carbon trim, while those with moderate limits (>5 mg/L) achieve comparable results using simpler ABAC or timer-based approaches. The critical finding: ammonia-only instrumentation paired with intermittent aeration delivers 70-80% of the benefits achievable with full NOx monitoring, substantially lowering the barrier to entry for utilities considering PdNA adoption. Conclusion This research provides configuration-specific guidance for PdNA control implementation. For post-polishing systems, AvN control with tight setpoint management (0.4-0.6) maximizes anammox activity. For integrated systems, ABAC with aerobic fraction control delivers robust performance while reducing instrumentation requirements. The framework developed enables utilities to select control strategies matched to their TIN limits, automation capabilities, and operational constraints, rather than defaulting to complex approaches that may exceed facility needs or staff capacity.