Modelling a full scale membrane bioreactor using Activated Sludge Model No.1: challenges and solutions

Modeling, simulation and control of biological and chemical P-removal processes for membrane bioreactors (MBRs) from lab to full-scale applications: State of the art

Phosphorus (P) removal from the domestic wastewater is required to counter the eutrophication in receiving water bodies and is mandated by the regulatory frameworks in several countries with discharge limits within 1-2mgPL-1. Operating at higher sludge retention time (SRT) and higher biomass concentration than the conventional activated sludge process (CASP), membrane bioreactors (MBRs) are able to remove 70-98% phosphorus without addition of coagulant. In full-scale facilities, enhanced biological phosphorus removal (EBPR) is assisted by the addition of metal coagulant to ensure >95% P-removal. MBRs are successfully used for super-large-scale wastewater treatment facilities (capacity >100,000 m3d-1). This paper documents the knowledge of P-removal modeling from lab to full-scale submerged MBRs and assesses the existing mathematical models for P-removal from domestic wastewater. There are still limited studies involving integrated modeling of the MBRs (full/super large-scale), considering the complex interactions among biology, chemical addition, filtration, and fouling. This paper analyses the design configurations and the parameters affecting the biological and chemical P-removal in MBRs to understand the P-removal process sensitivity and their implications for the modeling studies. Furthermore, it thoroughly reviews the applications of bio-kinetic and chemical precipitation models to MBRs for assessing their effectiveness with default stoichiometric and kinetic parameters and the extent to which these parameters have been calibrated/adjusted to simulate the P-removal successfully. It also presents a brief overview and comparison of seven (7) chemical precipitation models, along with a quick comparison of commercially available simulators. In addition to advantages associated with chemical precipitation for P-removal, its role in changing the relative abundance of the microbial community responsible for P-removal and denitrification and the controversial role in fouling mitigation/increase are discussed. Lastly, it encompasses several coagulant dosing control systems and their applications in the pilot to full-scale facilities to save coagulants and optimize the P-removal performance.

Modeling of micropollutant removal in full-scale membrane bioreactors: calibration and operations to limit the emissions

Micropollutants are a major concern for aquatic organisms and human health. Membrane bioreactors (MBRs) are an efficient wastewater treatment and water reuse solution, but their micropollutant removal performances are still not fully determined. Modeling micropollutant behavior in MBRs could help better understand and optimize the removal process. Here we provide detailed explanation on a model of micropollutant removal in MBRs that predicts biodegradation and sorption rates. Parameters were calibrated following an iterative two-step procedure developed in this work and using data from two full-scale plants. The calibrated set of parameters was then used (i) to determine the influence of MBR operating conditions such as the duration of aerobic time and the sludge concentration in bioreactor, on micropollutant removal, and (ii) to better understand micropollutant behavior and removal performances in MBRs in response to sudden changes in operating conditions (rain event, F:M ratio). These predictive simulations showed that increasing sludge concentration in bioreactor can decrease effluent concentrations of most of the micropollutants studied by up to 15%, and increasing the duration of aerobic time decreases effluent concentrations of few organic micropollutants tested by up to 15%. Rain events and F:M ratio can increase effluent concentrations of six out of nine micropollutants tested by more than 15%.

Mathematical modelling of the internal circulation anaerobic reactor by Anaerobic Digestion Model No. 1, simultaneously combined with hydrodynamics

In this study, the hydrodynamic characteristic of a lab-scale internal circulation (IC) anaerobic reactor was investigated. We found that the gradual Increasing-Size Continuous Stirred-Tank Reactors (ISC) model is desirable to describe the hydraulic character of the reactor. As a generalized anaerobic digestion model, Anaerobic Digestion Model No.1 (ADM1) was combined simultaneously with the ISC model to simulate the effluent of the IC reactor. Both the stable running and overloading shock tests were carried out to validate the simulation. The mathematical simulation results agreed well with the experimental observation. This proposed model may be valuable to simulate the performance of the IC reactor effectively and to supply a useful tool to for designing and operating other anaerobic reactors.

Comparison of five wastewater COD fractionation methods for dynamic simulation of MBR systems

Five different wastewater COD fractionation methods were employed for simulating an experimental MBR wastewater treatment plant using WEST. The predictions of dynamic simulations using as input the data obtained according to each influent characterization methodology were compared with the results of the experimental system and differences between experimental and predicted values were analyzed in order to select the fractionation method which provides the best fitting and minimizes errors. Three of these methods were based on the determination of the biodegradable fractions using respirometric assays of real wastewater filtered through 0.45- and 0.22-μm pore size filters or adding a previous flocculation step before filtration. Moreover, a method based on physicochemical analyses and another one based on theoretical coefficients were also compared. Simulated system performance and effluent quality greatly depended upon the influent characterization and the proper model calibration. Thus the importance of selecting a suitable fractionation methodology is high, especially in MBR systems working at specific operational conditions that may alter COD fractions. In this study, MLSS in the bioreactors and sludge supernatant COD concentrations were better predicted when the influent characterization was based on respirometric methods. Both the method based on theoretical coefficients and the physicochemical method underestimated the particulate inert fraction and therefore, also the MLSS concentrations. Moreover, these results showed that for a correct effluent COD prediction in MBR systems, it is necessary to take into account that the membrane retained part of the soluble inert fraction.

Critical review of membrane bioreactor models--part 1: biokinetic and filtration models

Membrane bioreactor technology exists for a couple of decades, but has not yet overwhelmed the market due to some serious drawbacks of which operational cost due to fouling is the major contributor. Knowledge buildup and optimisation for such complex systems can significantly benefit from mathematical modelling. In this paper, the vast literature on modelling MBR biokinetics and filtration is critically reviewed. It was found that models cover the wide range of empirical to detailed mechanistic descriptions and have mainly been used for knowledge development and to a lesser extent for system optimisation/control. Moreover, studies are still predominantly performed at lab or pilot scale. Trends are discussed, knowledge gaps identified and interesting routes for further research suggested.

Modelling bioprocesses and membrane fouling in membrane bioreactor (MBR): a review towards finding an integrated model framework

The bioprocesses taking place in activated sludge wastewater treatment system itself are characterized by great complexity and yet incomplete understanding of some of the phenomena involved. The MBR technology inherent deficiencies for its simulation due to additional intrinsic complexities resulting from the interaction between concurrently occurring and dynamic biological processes with membrane filtration and the straightforward adoption of the activated sludge models' (ASM) frameworks or their modified variations. In this backdrop, this paper compiles a brief overview of the previous developments to the current state-of-the-art mathematical modelling approaches of the MBR system. With extended discussions on particular topics such as applications of modified ASMs to MBR modelling, ASM extensions incorporating soluble microbial products (SMP)/extracellular polymeric substances (EPS) concepts, this paper also provides a guide for different end-users of mathematical models of MBR systems.