Simulation-based process optimization of full-scale advanced wastewater treatment systems using powdered activated carbon

This study extends a previously developed competitive modeling approach for predicting the adsorption of organic micropollutants (OMPs) on powdered activated carbon (PAC) in full-scale advanced wastewater treatment. The approach incorporates adsorption analysis for organic matter fractionation, assumes pseudo-first order kinetics and differentiates between fresh and partially loaded PAC through fraction segregation. Validation through full-scale measurement campaigns reveals successful model predictions of OMP removal, underestimating, however, diclofenac removals by 15-20%. Based on model testing, the impact of excess PAC return to the biological stage enhanced OMP removal, reaching up to 15% improvement for benzotriazole, carbamazepine and metoprolol, but no evident improvement of diclofenac removal. Intermittent PAC dosing revealed rapid process response, where organic matter concentration increased within 2 h after PAC cut-off. The simulation-based study demonstrated that during rain events, the overall OMP removal efficiency in the entire wastewater treatment plant was reduced by approximately 50% due to a shift of OMP concentration and a shortened hydraulic retention time in the biological and adsorption stages. Testing of various PAC dosing strategies revealed potential PAC savings of 10-15% compared to inflow-proportional dosing by using predefined OMP removal grades or maximum allowable effluent OMP concentrations as criteria for PAC dosing.