8 / 2023-12-16 03:02:14

Development of Hybrid and Coupled Models for Designing Upflow Anaerobic Filters through Multiple Separate Stages in the Removal of Organic Matter from Sanitary Landfill Leachates

Design, modelling, filters in two separated stages, filters in three separated stages, validation.

In this paper, three novelties are presented, type of reactor, hybrid and coupled models for the design of UAF-MSS (Upflow Anaerobic Filter – Multiple Separated Stages) reactors, and the kinetic coefficients for UAF-MSS performance in the COD (Chemical Oxygen Demand) removal from leachates of sanitary landfills. The formulation, calibration and validation of mathematical structures of hybrid models and five coupled models were proposed for UAF-2SS and UAF-3SS reactors. Hybrid models were based on the law of mass conservation, with the organic matter transformation component within the UAF-2SS and UAF-3SS reactors, being estimated from  empirical equations that have been tested in aerobic culture reactors, adapted to experimental factors, including among these, those under a non-stationary - advective conditions based on Velz's Law, Phelps's Law and Monod’s equation. Coupled models combined components of molecular transport by biosorption and molecular diffusion processes, with adaptations of Stack’s equation and Fick's Law, as well as transformation of organic substrates by biomass, whose kinetic coefficients contributed to explain the fraction, in which, the processes of mobility and biochemical transformation of the organic matter were occurring in the biomass within bioreactors. The kinetic parameter associated to the maximum substrate utilization rate (SUR) resulted in approximated mean value varying in the order of 10⁰ and 10¹ d^-1 for UAF-MSS.  Biosorption coefficient  values varied in the order of 10^-3 to 10^-1 m³ kg^-1 d (0.1 – 100 L kg^-1 d) for fixed biofilm bioreactors, indicating that, at any given time, the majority of the contaminant molecules were bioavailable in surface water and less likely to be adsorbed to the sediment. In consequence, COD was showing trend to be dissolved in water and in less proportion sorbed on biofilm. Molecular diffusion coefficient (D_M), D_MV and D_MH varied between 10^-1 and 10² m² s^-1. The transport and transformation rate of substrate were significantly different between the vertical and horizontal motion. It was found that the number of stages or phases of the novel biological filters influenced the COD removal. COD removal efficiencies were increased between 1.3 and 3.5 times from UAF-2SS reactor to UAF-3SS reactor. Hybrid and coupled models, the best performance in the approximation of measured values in the ratio to the predicted results of models were the equations for UAF-2SS reactor and UAF-3SS reactor, whose coupled models consisted of a combination of transport process model (sorption-desorption and molecular diffusion) and transformation models based on the substrate utilization rate by the microorganisms.