Model for predicting the performance of membrane bioadsorber reactor process in water treatment applications

This research focuses on the development of a mathematical model for performance prediction/simulation of the membrane bioadsorber reactor (MBR) process. The MBR process integrates biodegradation, adsorption and membrane filtration, for water or wastewater treatment and water reclamation. The model sub-processes include the following phenomenological aspects: (a) biological reaction in bulk liquid solution, (b) film transfer from bulk liquid phase to the biofilm, (c) diffusion with biological reaction inside biofilm, (d) adsorption equilibrium at the biofilm-adsorbent interface, and (e) diffusion within the adsorbent (powder activated carbon) particles. The model exhibited good simulative capability for three model organic compounds, namely, phenol, para-nitrophenol, and toluene, chosen based on their varying adsorption and biodegradation characteristics. A phenomenological approach was employed to examine the relative contributions of adsorption and biodegradation to contaminant removal, and to obtain insights into adsorbent bioregeneration. Therefore, simulation studies were conducted under three different scenarios: (a) adsorption and biodegradation in biofilm and liquid phase suspension are operative, conforming to the assumptions of the generalized model; (b) biodegradation is operative in biofilm as well as liquid phase suspension, but adsorption is absent; and (c) adsorption alone is operative without biodegradation. Sensitivity studies were preformed to investigate the dependence of process dynamics on model parameters pertaining to adsorption equilibrium and kinetics, liquid film transport, biofilm diffusion, biochemical reaction kinetics, influent concentration, and reactor flow conditions.     

Biofilter modeling for waste air treatment: Comparisons of inherent characteristics of biofilter models

The types of biofilter modeling may be primarily classified in accordance with whether a biofilm is differentiated from other phases in each model. It may be a secondary classification with regard to biofilter-modeling whether sorption volume and/or adsorption are adopted as reservoirs or not. Thirdly, biofilter models are classified as to whether adsorption is assumed to exist through gas phase and/or a biofilm. Among all the biofilter-models of previous investigators all model-components including gas phase, a biofilm, sorption volume and adsorption surface are considered only in the model of Lim. Since his model does not require a numerical solution but an algebraic solution to describe the concentration of organic pollutants in waste-air-streams along the height of a biofilter even under unsteady-state conditions, it satisfies the condition of simplicity that is one of the important model requirements. In spite of its simplicity, Lim's model predictions are fairly good to fit Hodge and Devinny’s experimental data.     

Mathematical modeling of granular activated carbon (GAC) biofiltration system

In this study, a mathematical model of a fixed bed Granular Activated Carbon (GAC) biofiltration system was developed to predict the organic removal efficiency of the filter. The model consists of bulk transportation, adsorption, utilization, and biodegradation of organics. The variation of the specific surface area due to biofilm growth and the effect of filter backwash were also included in the model. The intrapellet diffusion and the diffusion of substrate in the biofilm were described by linear driving force approximation (LDFA) method. Biodegradation of organics was described by Monod kinetics. Sips adsorption isotherm was used to analyze the initial adsorption equilibrium of the system. The model showed that the organic removal efficiency of the biofilter greatly depends on the parameters related to the biological activities such as the maximum rate of substrate utilization (k_max) and biomass yield (Y) coefficients. Parameters such as suspended cell concentration (X_s) and decay constant (K_d) had little effects on the model simulation results. The filter backwash also had no significant impact on the performance of the biofilter.     

Dynamics of a draft tube gas—liquid—solid fluidized bed bioreactor for phenol degradation

The transient response of a draft tube gas—liquid—solid fluidized bed biofilm reactor (DTFB) to a step increase in influent phenol concentration was experimentally investigated. A mathematical model, which considers the external mass transfer resistance, the simultaneous diffusion, reaction, and adsorption of phenol and oxygen inside the bioparticles, the dynamics of biofilm growth, and the time delay of microbial growth during the transient period, is proposed. The biofilm properties such as thickness and density are allowed to vary in the model with biofilm growth to simulate the real biofilm system. Simulation results predicted from the proposed model show reasonable agreement with the experimental data.     

活性炭生物转盘的制备及处理有机模拟废水

为了寻找一种质轻高效的新型生物转盘盘片材料,实验以活性炭作为生物膜附着的载体,聚丙烯塑料板为基体,采用化学氧化-铁离子覆盖技术制备了活性炭生物转盘盘片。使用该活性炭生物转盘处理有机模拟废水,以COD和NH3—N质量浓度变化为评价指标,借助微生物显微镜观察了挂膜期间微生物的生长过程。结果表明,该盘片具有独特的微生物吸附能力,微生物量达到2.60×109个/g,生物膜干质量为16.909 6 g/m2;在进水初始COD质量浓度为1 000 mg/L、NH3—N质量浓度为100 mg/L左右时,当HRT为12 h时,盘片的有机去除负荷为5.61 g/m2;当循环进水3 d时,COD和NH3—N去除率均在80%以上,该三级生物转盘反应器各级污染物去除率均较高,第1级去除效果最显著,处理后水质达到了国家污水综合排放标准(GB8978-96)的二级标准。     

Transient biofilter aerodynamics and clogging for VOC degradation

Removal of volatile organic compounds like toluene from waste gases with a biofilter can result in clogging of the reactor due to the formation of an excessive amount of biomass. Excessive biomass formation changes the bed's pore structure and leads to the progressive obstruction of the bed that is accompanied with a build-up in pressure drop and flow channeling. While the existing biofilter models appear to capture adequately the transport and reaction phenomena at the biofilm scale, they poorly address, or provide little insight about the connection between the aerodynamics, biological filtration (or clogging) and biokinetics at the bioreactor length scale. An attempt has been made with this contribution to fill in this gap by developing a unidirectional dynamic flow model based on the volume-average mass, momentum and species balance equations coupled with conventional diffusion/reaction equations describing apparent kinetics in the biofilm. Toluene biodegradation by biodegrading microbes immobilized on pelletized diatomaceous earth biological support media was chosen as a case study to illustrate the consequences of formation of excessive amounts of biomass. The simulation results were rationalized in terms of biofilm thickness, bed local porosity, gas-phase substrate residual concentration, and pressure drop rise in biological fixed-bed filters.     

ANAEROBIC BIOFILM REACTOR MODELING FOCUSED ON HYDRODYNAMICS

This work deals with an experimental and theoretical investigation of anaerobic biofilm reactors for treating wastewaters. Bioreactors are modeled as dynamic (gas-solid-liquid) three-phase systems. The anaerobic digestion model proposed by Angelidaki et al. (1999) was selected to describe the substrate degradation scheme and was applied to a biofilm system. The experimental setup consists of two mesophilic (36°±1°C) lab-scale anaerobic fluidized bed reactors (AFBRs) with sand as inert support for biofilm development. The experimental protocol is based on step-type disturbances applied on the inlet substrate concentration (glucose and acetate-based feeding) and on the feed flow rate considering the criterion of maximum efficiency. The predicted and measured responses of biological and hydrodynamic variables are investigated. Experimental data were used to estimate empirical values of biofilm detachment coefficients. Under the evaluated operating conditions, the proposed model for biofilm detachment rate, assumed as a first-order function of the energy dissipation parameter, is appropriate to represent the interaction between biofilm systems and fluidization characteristics in non-highly disturbed flow conditions. Model validation was carried out using the experimental data reported by Mussati et al. (2006). The results do not differ from those above. This seems to indicate that the proposed AFBR model is able to reproduce the main biological and hydrodynamic successes in the bioreactor.     

Microbial removal of alkanes from dilute gaseous waste streams: Mathematical modeling of advanced bioreactor systems

Many industries generate volatile organic compounds (VOCs) in dilute streams which must be removed before being released into the environment. Mathematical models for biological filters which can remediate waste streams are useful both as predictive tools and as a means to better understand the fundamental processes involved. Optimization of the system also necessitates a better understanding of the mechanisms by which biofilters work and can be approached through modeling and maximizing appropriate conditions for removal. In a trickle-bed bioreactor, VOCs (n-pentane and isobutane) were passed over a biofilm-coated packing which degraded the VOCs. Bacterial growth was controlled via liquid nutrient-limited media trickled through the reactor. Results from this trickle-bed system were analyzed by applying a simple mathematical model to accurately describe the processes which are believed to play important roles. The model was based on a two-step process: mass transfer in which the VOCs diffuse into the liquid biofilm, and kinetics by which VOCs are degraded by the biofilm. Modeling results revealed that both kinetic and mass transfer resistances were significant under typical operating conditions.     

Mathematical modeling of biofilm‐covered granular activated carbon: a review

This paper reviewed the mass‐transfer of the target substance in the biofilm‐covered granular activated carbon (BGAC) system. Representative hypotheses and equations related to developing the mathematical models for a BGAC reactor were discussed in terms of granular activated carbon (GAC) phase, biofilm phase and bulk solution, respectively. It should be noted that discrete phenomena such as biofilm detachment due to erosion or sloughing were not considered for the modeling system. Recent advances on this topic were thoroughly updated, as well as those models proposed in past decades. It appears that a general BGAC model has not been available so far, and further efforts are required to obtain models more approaching of the physical mechanism of this complicate system. Copyright © 2012 Society of Chemical Industry     

Study of the adsorption of phenol by two soils based on kinetic and isotherm modeling analyses

Various natural adsorbents, which have been in used for removal of pollutants, in general, and phenol, in particular, are mostly directed towards improving the adsorption capacity of the adsorbents by various pretreatments (chemical, thermal or biological), which necessarily lead to increase in the cost as well as in the level of difficulties in regeneration/disposal of the adsorbent. The present studies, on the other hand, are aimed towards evaluating the feasibility of using two common soils as potential low-cost adsorbents for the removal of phenol from its aqueous solution, in their natural forms (i.e., without any pretreatment). Accordingly, experiments were carried out (in batch mode) for optimization of the adsorption parameters (such as pH, contact time, equilibrium time and adsorbent dosage), for varying initial phenol concentrations. The results showed that the maximum phenol adsorption capacity was found at pH ~6, under a constant temperature of 30 ± 2 °C (at 6-hour equilibrium period). Several kinetic models (viz. Lagergren first-order, pseudo-second-order, Elovich and intra-particle diffusion) as well as isotherm models (Langmuir, Freundlich, Redlich and Peterson and Sip) were applied to the experimental data. The pseudo-second-order model was found to be the most suitable model describing the adsorption of phenol by two soils (which indicated this adsorption as a chemisorption process). On analysis of equilibrium isotherms for the adsorption of phenol by two soils, Redlich-Peterson and Sip isotherms were found to be the best representative for phenol-sorption on two selected, soil adsorbents.     

生物膜数学建模的发展

生物膜普遍存在于自然与工业环境中。探讨生物膜的结构对研究生物膜的形成机理至关重要。而数学模型是模拟生物膜结构的一种有效工具。文章重点阐述了一维连续介质模型、扩散限制凝聚(DLA)模型、离散-连续介质耦合模型、多项流体模型四类模型在生物质生长和扩散、基质传递和耗散的生物膜结构中的研究进展与实验中的新发现。     

Strong resistance of poly (ethylene glycol) based L‐tyrosine polyurethanes to protein adsorption and cell adhesion

Biofouling that involves protein adsorption, cell and bacteria adhesion, and biofilm formation between a surface and biological entities is a great challenge for biomedical and industry applications. In this work, L ‐tyrosine‐derived polyurethanes (L ‐polyurethane) with different molecular weights of poly(ethylene glycol) (PEG) were synthesized, characterized and coated on gold surfaces using spin‐coating. The non‐fouling activity of different L ‐polyurethane films was evaluated by protein adsorption and cell adhesion. Surface plasmon resonance and cell assay results demonstrate that the PEG content in these L ‐polyurethanes contributes excellent resistance to protein adsorption and cell attachments. This work provides alternative and effective biomaterials for potential applications in blood‐contacting devices. Copyright © 2011 Society of Chemical Industry     

挂膜方式对曝气生物滤池的影响

对新型接种挂膜与逐渐增加流量的自然挂膜两种方式进行了比较和分析。结果表明，挂膜后期前者的COD去除率可达90．36％，NH3-N去除率可达70．14％，后者则为87．69％和34．67％。前者生物膜生长情况好于后者，生物膜的成熟期缩短了4d；采用两级反应柱可以增加曝气生物滤池对NH3-N的去除效果。     

Biofilm growth pattern in honeycomb monolith packings: Effect of shear rate and substrate transport limitations

Potential application of monolith reactors in a biological process was investigated experimentally. A possible problem when using monolith reactors in biological applications is clogging due to biofilm formation. An interesting phenomenon is the pattern in which biofilms develop inside the monolith channels. Rather unexpectedly at a first glance, it was repeatedly observed that biofilm formation started in the middle of a side of the square-section monolith channels, instead of colonizing first the low-shear areas in the corners. To explain this biofilm formation pattern, a two-dimensional mechanistic model based on substrate diffusion and consumption accompanied by microbial growth and detachment was developed in this study. Simulation results suggest that the unexpected biofilm patterns are generated by the balance between biofilm growth and biofilm detachment due to shear stress induced erosion. In the early stages, the biofilm growth in the corners is strongly limited by the external resistance to substrate transfer. As time passes and the biofilm grows in thickness, mechanical forces due to passing gas bubbles will lead to a more regular biofilm shape, including the channel corners.     

Modeling biological nutrient removal in a liquid–solid circulating fluidized bed bioreactor

BACKGROUND: Both laboratory‐scale and pilot‐scale liquid–solid circulating fluidized bed (LSCFB) bioreactors have demonstrated excellent biological nutrient removal (BNR) from municipal wastewater. In this study, a model for the LSCFB for biological nutrient removal has been developed, calibrated, and validated using pilot‐scale experimental results. RESULTS: An efficient reactor arrangement predicted anoxic–anaerobic and aerobic biofilm thicknesses of 150–400 and 70–175 µm in the riser and downer, respectively. Furthermore, distribution of chemical oxygen demand (COD), NH₄‐N, NO_X‐N, and dissolved oxygen in the biofilm, as well as nutrients removed in the aerobic and anoxic zones, reflect nitrification, denitrification and enhanced biological phosphorus removal in the LSCFB. The model predicted both anoxic effluent and final effluent COD, SCOD, SBOD, NH₄‐N, NO₃‐N, TKN, TN, PO₄‐P, and TP were within the 95% confidence intervals of the experimental data. Model‐predicted simultaneous nitrification/denitrification occurring in the aerobic downer. CONCLUSION: This model developed for LSCFB using the AQUIFAS biofilm diffusion model successfully evaluated the process performance. It is an efficient tool for further research, design, and optimization of the fixed film bioreactor. Copyright © 2010 Society of Chemical Industry     

Liquid Phase Adsorption of Phenol and Chloroform by Activated Charcoal

The adsorption equilibria of phenol and chloroform from aqueous solutions on four different particle sizes of activated charcoal were examined at different initial concentrations of the adsorbates. The experimental data were analyzed using the Langmuir and Freundlich isotherm models. Both models fit the adsorption data for phenol. The Freundlich model more accurately fits the adsorption data for chloroform than the Langmuir model. The sorption kinetics for phenol was studied using pseudo‐first‐order and second‐order kinetic models. The adsorption data better fit the second‐order model. The results of the study show that activated charcoal can be used as potential adsorbent for phenol and chloroform in drinking water.     

Treatment of ampicillin‐loaded wastewater by combined adsorption and biodegradation

BACKGROUND: This study investigated the treatment of ampicillin (AMP)‐loaded wastewater in airlift reactors where biofilms were developed on granular activated carbon (GAC). A series of batch experiments were thus carried out in order to differentiate potentials of adsorption and biodegradation which would jointly contribute to the AMP removal. RESULTS: Results showed that almost all influent AMP was removed in two reactors supplemented with 4 and 8 mg L^?1 AMP, respectively. Batch experiments revealed that the percentage of the AMP removed through biodegradation increased along with the development of biofilms on GAC. For the mature biofilm‐covered GAC, adsorption accounted for about 60% of the observed AMP removal, whereas the other 40% could be attributed to biodegradation. Possible degraders of AMP were also identified, such as Acinetobacter sp., Flavobacterium sp., Pseudoxanthomonas sp., Delftia sp. and Sphingobium sp. CONCLUSION: The airlift biofilm reactor with GAC as carrier would be a feasible technology for treating AMP‐loaded wastewater due to the joint action of adsorption and biodegradation of AMP by the biofilm‐covered GAC. Copyright © 2010 Society of Chemical Industry