Resource recovery technologies are often evaluated against their own primary performance metric in isolation, without assessing simultaneous consequences across the full plant operational space. This study evaluates temperature-phased anaerobic digestion (TPAD)-derived internal carbon recovery at a full-scale water resource recovery facility (WRRF) and assesses the simultaneous impacts on nitrogen compliance, energy demand, clarifier stability, and biogas recovery across the full operational space. A pilot-scale TPAD system (thermophilic, 55°C; mesophilic, 38°C) was operated for 121 days on primary sludge. Fermentate quality was characterized through physicochemical and respirometric assays. A plant-wide mass balance and calibrated dynamic simulation model assessed trade-offs among fermentate dosing rate, solids retention time (SRT), and seasonal temperature. TPAD achieved effective volatile fatty acid (VFA) accumulation while preserving total methane yields equivalent to single-stage mesophilic digestion, confirming that resource and energy recovery are not mutually exclusive. Plant-wide simulations identified the minimum fermentate dosing requirements and SRT thresholds for nitrogen compliance under cold-weather conditions, quantifying the associated energy costs and clarifier stability boundaries. Temporal variability in fermentate quality was identified as a key implementation challenge with direct consequences for plant energy balance. The resulting decision maps constitute a site-adaptable framework for carbon-limited WRRFs implementing circular carbon management, demonstrating that resource recovery interventions must be evaluated across the full plant key performance indicator (KPI) space to support informed utility decision-making.
Borzooei et al. (2026) studied this question.