Liquid residence time distribution in a two‐compartment wastewater treatment bioreactor

Abstract

Residence time distribution (RTD) of liquid phase in a two‐compartment (packed‐bed/packed‐bed or packed‐bed/packing‐free) bioreactor for wastewater treatment was evaluated via a complex liquid flow structure. RTD in packed‐bed compartments was modelled using a modified axial dispersion‐exchange model with a liquid stream which bypasses the dynamic liquid region. The liquid in the dynamic region is dispersed in axial and transverse directions, whereas the stagnant region exchanges mass with the dynamic region, the two regions being in direct contact. RTD in packing‐free compartment was modelled as a continuous stirred‐tank reactor with ideal or non‐ideal mixing zone. Time‐domain analysis coupled with the phenomenological RTD model was used to identify the model parameters. The proposed RTD model offers the opportunity to quantify parameters as dynamic liquid fraction, dynamic liquid flow rate fraction, number of transfer units between dynamic and stagnant liquid regions, stagnant liquid holdup, which otherwise would have been difficult to estimate using other methods and which can affect the bioreactor performance. The proposed RTD model describes adequately the hydrodynamics of the two‐compartment packed‐bed bioreactor while the simulations unveil likely tendency of the RTD curves subject to different sets of model parameters.

Simulation of the inhibition of microbial sulfate reduction in a two-compartment upflow bioreactor subjected to molybdate injection

“…From this value, the average residence time remains constant. Similar behavior was observed when evaluating the effect of the number of transfer units for the case of a packed-bed bioreactor operated with horizontal flow [5,12]. Figure 5e shows the influence of the average residence time of the packed-free compartment (s 1 ) on the residence time distribution function E(t).…”

“…The mass balance for the system gives the governing equations for the tracer concentration in the mixture model with a mass exchange between dynamic and stagnant zones (packed-free) [19] and PDE model (packed-bed) which can be divided into dynamic and stagnant regions [6,12,20]:…”

“…where Q is the flow rate, and S is the cross section of the bed, e is the porosity of the bed and b d is the fraction of the reactor void volume in the dynamic zone or dynamic saturation), D d is the axial dispersion coefficient in the dynamic phase, k ma is the overall mass transfer coefficient at the interface dynamic-stagnant phase and u is the dynamic liquid fraction, Equations 3 and 4 are solved using the following initial and boundary conditions, which includes Danckwerts' conditions [6,12]:…”

“…Recently the hydrodynamics of a two-compartment bioreactor was described using a phenomenological model able to represent the mass exchange between active and stagnant zones, bypass and axial dispersion of the liquid [12]. This bioreactor has some similarity with the rector presented in this study; however, it is a two-compartment packing-free/packed-bed bioreactor instead of a packedbed/packing-free bioreactor.…”

Simulated Modelling, Design, and Performance Evaluation of a Pilot-Scale Trickling Filter System for Removal of Carbonaceous Pollutants from Domestic Wastewater

“…The TF system has numerous advantages in wastewater treatment compared to suspended growth systems, such as low space and operational requirements, cost effectiveness, being environmentally friendly, resistance to toxins and shock loads, operational compliance, increased retention time, enhanced biodegradation rate, and reduced sludge production due to a slower microbial growth rate. Moreover, TF systems also have the ability to regulate reaction rates according to the demand [17,18]. Furthermore, their large air-water interface can remove CO 2 , H 2 , N 2 , and other gases.…”