(18b) Mathematical Modeling of Hybrid Adsorption and Biological Treatment Systems (HABiTs) for Enhanced Nitrogen Removal

The discharge of excess nutrients, in particular nitrogen (N) and phosphorus (P), to surface water bodies and groundwater systems can have deleterious environmental impacts.  One such environmental impact is associated with eutrophication, which can significantly degrade water quality and exacerbate the problem of harmful algae blooms  in surface water systems. Common sources of excess nutrients include domestic and industrial wastewater treatment facilities, agricultural runoff, stormwater runoff, and atmospheric deposition. Biological nitrogen removal (BNR) is one of the most common methods for treating various waste streams. BNR utilizes biologically mediated nitrification and denitrification processes for converting NH₄⁺ to NO₃^- (nitrification) and subsequently NO₃^- to N₂ (denitrification). However, there are challenges associated with BNR, such as the inhibitory effect of high NH₃concentrations on the rate of nitrification and issues associated with transient loadings in onsite wastewater treatment systems (OWTs). Hybrid Adsorption Biological Treatment Systems (HABiTS) are a novel approach to address the challenges in BNR systems by utilizing an ion exchange (IX) medium that also serves as a biofilm carrier. The enhanced design and optimization of HABiTS require appropriate tools for describing and predicting nitrogen fate and transport in these systems. In this research mathematical and numerical models of HABiTS were developed to describe the physico-chemical and biological processes in batch and packed bed reactors. The utility of the models is that they facilitate the optimal design of bioreactors for OWT and treatment of high strength wastewaters.

Results from numerical models of two different HABiTS will be presented:1) a batch system with the zeolitic material, chabazite, used in combination with nitrifying bacteria for high ammonia (NH₄⁺) strength wastewater treatment, 2) a packed bed reactor with the zeolite, clinoptilolite, under dynamic loading conditions for treatment of wastewater from onsite systems. A homogenous surface diffusion model (HSDM) combined with a model of biological nitrification was developed to predict the temporal variations of NH₄⁺ and Na⁺ concentrations in the batch system. The results show good correspondence to experimental data from IX kinetic and bioregeneration studies of the batch reactor. A multi-scale approach that combines the HSDM with the transport of NH₄⁺ by advection and dispersion through the packed bed, and biologically mediated nitrification is currently being developed to predict the performance the second system. The model describes the NH₄⁺ behavior under dynamic loading conditions typically observed in OWTs, where nitrogen is adsorbed by an IX material during high loading periods and slowly released during low loading periods to provide a conducive environment for BNR.