Reverse osmosis is a widely used technology in wastewater treatment water purification, water reclamation and reuse. A major concern is production of brine concentrates containing high levels of ammonia or nitrogen. This work addresses biological denitrification of brine concentrates in anaerobic fluidized bed reactor (AFBR) systems. Previous publications (Ersever et al., 2007a, 2007b) described the first phase: process development, feasibility evaluation, and reaction optimization. This paper describes the second phase involving process modeling for performance prediction, simulation, and design with upscaling implications. Laboratory scale studies provided data for AFBR process evaluation and model verification under different conditions, including media characteristics, hydraulic residence Limes, and influent nitrate levels. Model simulations facilitated process design and upscaling, and further projected that among different parameters the Monod yield coefficient and maximum specific growth rate significantly influenced process dynamics. Transient state dynamics provided insight into process induction and acclimation besides process recovery after upsets. (C) 2013 Elsevier Lid. All rights reserved.