Utilisation of a packed-bed biofilm reactor for the determination of the potential of biofilm accumulation in water systems

Abstract

An experimental system has been developed that allows the monitoring of biofilm development on supports exposed to water of different characteristics. The system consists of a series of packed-bed reactors filled with glass beads, and by periodically removing biofilm attached to these beads for off-line analyses this provides a means for monitoring biofilm development. Despite its reduced dimensions (6.9 cm long and 1.58 cm in diameter), the experimental system used has a sampling surface of 90.3 cm² (including only the surface of the glass beads). This allows reproducible and representative samples to be taken from different water systems, providing a reliable and economic method for evaluating in situ the formation of biofilms from different environments. The set-up of the entire experimental system was constructed to meet the demands of field experiments in a well-defined hydrodynamic environment and to allow easy removal of samples for biomass quantification and microscopic observation. Data obtained using this device can be used as an indicator of the risk of biofilm formation in different water systems. This indicator, “the biofilm accumulation potential”, represents an effective and representative tool for the monitoring of biofilm development in an integrated antifouling strategy, in order to help keep biofouling, scaling and microbial risks under control. According to the experiments with the packed-bed reactors used with a high flow regime, the ratio TCN/HPC could provide an indication of the state of the biofilm, and lower ratios could indicate a higher biofilm accumulation potential.     

Biodegradation Kinetic Studies on Phenol in Internal Draft Tube (Inverse Fluidized Bed) Biofilm Reactor Using Pseudomonas fluorescens: Performance Evaluation of Biofilm and Biomass Characteristics

The bioremediation potential of Pseudomonas fluorescens was studied in an internal draft tube (inverse fluidized bed) biofilm reactor (IDTBR) under batch recirculation conditions using synthetic phenol of various concentrations (400, 600, 800, 1000, and 1200 mg/L). The performance of IDTBR was investigated and the characteristics of biomass and biofilm were determined by evaluating biofilm dry density and thickness, bioparticle density, suspended and attached biomass concentration, chemical oxygen demand, and phenol removal efficiency. Biodegradation kinetics had been studied for the suspended biomass culture and biofilm systems. Suspended biomass followed substrate inhibition kinetics, and the experimental data fitted well with the Haldane model. The correlation coefficient, R ², and root-mean-square error (RMSE) obtained for the Haldane model with respect to specific growth rate were .9389 and .00729, respectively, and with respect to specific phenol consumption rate were .9259 and .00972, respectively. It was also observed experimentally that biofilm overcame substrate inhibition effect and fitted the same to the Monod model (R ² = .9831, RMSE = .00884 for specific growth rate and R ² = .9686, RMSE = .00912 for specific phenol consumption rate).     

Fluidized bed biomethanation of acetic acid

Summary The kinetics of acetate biomethanation was studied in a high recycle ratio biological fluidized bed reactor behaving in practice as a completely mixed reactor. The active biofilm consisted of bacteria from a methane fermenter that after spontaneous immobilization on the bed particles (sand) were adapted to acetate as the only carbon source. The effects of temperature (13°, 20°, 25° and 35°C), substrate concentration (500, 1000 and 1500 mg chemical oxygen demand (COD) l^-1) and hydraulic retention time (1 to 8 h) on substrate consumption were studied. Maximum substrate consumption (as % COD reduction) amounted from 25% (13°C, 1500 mg COD l^-1) to 93% (35°C, 500 mg COD l^-1). At 35°C the concentration of attached biomass presented a weakly increase with reactor substrate concentration (from 3.10 g VS l^-1 to 4.54 g VS l^-1 for 32 and 1150 mg COD l^-1 respectively). On the other hand when reducing , a sharp incrase in biomass loss coefficient was observed showing that excess biofilm growth was continuously removed by shearing forces. Thus in the assayed conditions the attached biomass concentration was basically determined by the bed superficial velocity. Result show that diffusional resistances are negligible. Data are fairly well correlated by a variable order kinetic model. The apparent reaction order is a function of temperature and increases from 0.27 to 0.7 when temperature decreases from 35° C to 13°C.Nomenclature b Total biomass loss coefficient (T^-1) - J Flux of substrate removal into the biofilm surface (ML^-2 T^-1) - J _d Flux of substrate removed into the biofilm surface in deep conditions (ML^-2 T^-1) - k Maximum specific rate of substrate utilization (T^-1) - K Variable order kinetic constant (T^-1 M^n-1 L^3n-3) - K _s9 Hall saturation constant (ML^-3) - n Reaction order - q Feed flow rate (L³ T^-1) - S Substrate concentration (ML^-3) - Se Effluent substrate concentration (ML^-3) - So Influent substrate concentration (ML^-3) - Se_min Minimum substrate concentration able to sustain a steady-state biofilm (ML^-3) - T Temperature - t Time(T) - V Bed volume (L³) - VS Volatile solids (M) - VSS Volatile suspended solids - X Attached biomass concentration (ML^-3) - X _c Effluent volatile suspended solids (ML^-3) - Y Yield coefficient - Hydraulic retention time (T) This work forms part of a Doctoral Thesis of senior author     

Pressure drop increase by biofilm accumulation in spiral wound RO and NF membrane systems: role of substrate concentration,flow velocity,substrate load and flow direction

In an earlier study, it was shown that biofouling predominantly is a feed spacer channel problem. In this article, pressure drop development and biofilm accumulation in membrane fouling simulators have been studied without permeate production as a function of the process parameters substrate concentration, linear flow velocity, substrate load and flow direction. At the applied substrate concentration range, 100–400 μg l^?1 as acetate carbon, a higher concentration caused a faster and greater pressure drop increase and a greater accumulation of biomass. Within the range of linear flow velocities as applied in practice, a higher linear flow velocity resulted in a higher initial pressure drop in addition to a more rapid and greater pressure drop increase and biomass accumulation. Reduction of the linear flow velocity resulted in an instantaneous reduction of the pressure drop caused by the accumulated biomass, without changing the biofilm concentration. A higher substrate load (product of substrate concentration and flow velocity) was related to biomass accumulation. The effect of the same amount of accumulated biomass on the pressure drop increase was related to the linear flow velocity. A decrease of substrate load caused a gradual decline in time of both biomass concentration and pressure drop increase. It was concluded that the pressure drop increase over spiral wound reverse osmosis (RO) and nanofiltration (NF) membrane systems can be reduced by lowering both substrate load and linear flow velocity. There is a need for RO and NF systems with a low pressure drop increase irrespective of the biomass formation. Current efforts to control biofouling of spiral wound membranes focus in addition to pretreatment on membrane improvement. According to these authors, adaptation of the hydrodynamics, spacers and pressure vessel configuration offer promising alternatives. Additional approaches may be replacing heavily biofouled elements and flow direction reversal.     

Simplified Modeling of Simultaneous Reaction Kinetics of Carbon Oxidation and Nitrification in Biofilm Processes

Batch experiments with varying initial substrate concentrations and biomass volumes were performed in a three‐phase fluidized bed biofilm reactor treating simulated domestic wastewater to study the simultaneous carbon oxidation and nitrification in the biofilm process. A simplified mass balance equation for the biofilm was proposed and five different kinetic rate equations were used to match the actual data. The kinetic parameters were obtained by nonlinear regression analysis on a set of two differential equations representing the simultaneous carbon oxidation and nitrification. The competitive inhibition model incorporating the effects of total organic carbon (TOC) concentrations on nitrification rates was the best‐suited model based on the average r². In this model, oxygen concentration and its affinity constants were not included. Instead, it was assumed that the rate of carbon oxidation is independent of the NH₄⁺‐N, while nitrification is affected by TOC. The number of parameters was successfully minimized without reducing its ability to accurately predict the bulk concentration time course, which would reduce computational complexity and possibly enhance the availability for an actual wastewater treatment process.     

Modelling the growth and ethanol production of Brettanomyces bruxellensis at different glucose concentrations

Aim: To study the effect of glucose concentrations on the growth by Brettanomyces bruxellensis yeast strain in batch experiments and develop a mathematical model for kinetic behaviour analysis of yeast growing in batch culture. Methods and Results: A Matlab algorithm was developed for the estimation of model parameters. Glucose fermentation by B. bruxellensis was studied by varying its concentration (5, 9·3, 13·8, 16·5, 17·6 and 21·4%). The increase in substrate concentration up to a certain limit was accompanied by an increase in ethanol and biomass production; at a substrate concentration of 50–138 g l^?1, the ethanol and biomass production were 24, 59 and 6·3, 11·4 g l^?1, respectively. However, an increase in glucose concentration to 165 g l^?1 led to a drastic decrease in product formation and substrate utilization. Conclusions: The model successfully simulated the batch kinetic observed in all cases. The confidence intervals were also estimated at each phase at a 0·95 probability level in a t‐Student distribution for f degrees of freedom. The maximum ethanol and biomass yields were obtained with an initial glucose concentration of 138 g l^?1. Significance and Impact of the Study: These experiments illustrate the importance of using a mathematical model applied to kinetic behaviour on glucose concentration by B. bruxellensis.     

The microbial community in a moving bed biotrickling filter operated to remove hydrogen sulfide from gas streams

The information available on the microbial communities responsible for pollutant degradation is increasingly accessible. Its use to optimize process design and operation is an important challenge in the field of effluent treatment research. Therefore, a prototype of a moving bed biotrickling filter (MBBTF) reactor was designed and, for the first time, operated at full-scale for the removal of sulfides desorbing from tannery industrial wastewater. The bacterial community operating in this innovative reactor was studied, and its composition and response to different operating conditions were characterized. A stable biomass, dominated by sulfur-oxidizing bacteria of the genus Acidithiobacillus was selected from inside the MBBTF reactor, and temperature, pH and bed rotation were shown to be the main factors driving the community structure. Moreover, data from different approaches indicated an uneven spatial distribution of biofilm inside the studied reactor, due to the combined effect of fluid dynamics and substrate gradients within the bed volume. Despite the high removal efficiency achieved by this innovative prototype (80% on average), the data suggested that the result could be improved by adopting solutions for a more stable and even biofilm distribution. It was shown that short frequent bed rotations, rather than long scattered rotations, ensured biomass stability. Furthermore, diversifying biofilm support media as a function of expected local pollutant concentrations should be considered. Data obtained from the bacterial community can therefore provide indications for possible further improvement of MBBTF reactor design and performance.     

Startup of anaerobic biofilm fluidized bed reactors on molasses and phenol under various conditions

Fluidized sand bed anaerobic biofilm reactors were operated in parallel to study the effects of inoculum, loading, residence time and carrier type on the startup dynamics for the degradation of molasses and phenol. Degradation rates generally depended most directly on concentrations rather than on other operating variables. Residence times did not appear to directly influence startup. Short residence times and high loadings gave the highest specific activities for both substrates. The type of inoculum was found to be most important for the molasses system, and inoculation on fresh carrier was found to be better than reinoculation. The two times higher specific biomass retention on Siran porous glass gave essentially the same degradation rates on a volume basis.List of Symbols L kg/h loading of reactor - M kg/kg biomass per carrier mass - Red. % reduction of feed concentration due to degradation - R kg/(m³ · h) reaction rate - S kg/m³ substrate concentration in reactor and effluent - S ₀ kg/m³ substrate concentration in feed - t h time     

The accumulation of fixed biomass increases the observed growth yield of a nitrifying biofilm

The observed growth yield (Y _obs) of a nitrifying biofilm metabolizing ammonia in a continuous flow reactor was constant below a fixed biomass concentration of 40–50 g COD-biomass cm^–2. Beyond this range, an increased Y _obs with the additional accumulation of fixed biomass could be due to a considerable accumulation of inactive materials within the nitrifying biofilm.     

The role of quorum sensing and the effect of environmental conditions on biofilm formation by strains of Vibrio vulnificus

Abstract

It has been suggested that Vibrio vulnificus attaches to plankton and algae and is found in large numbers in the environment. Factors affecting attachment, biofilm formation and morphology of V. vulnificus have not been thoroughly investigated. This study evaluated the role of quorum sensing (QS) and environmental conditions on biofilm development of V. vulnificus. It was found that biofilm development by V. vulnificus was affected by nutrient and glucose concentration, but not by NaCl concentration or temperature under the conditions used here. Moreover, biofilm development of a QS mutant strain proceeded rapidly and sloughing occurred earlier than for the isogenic parent strain. There was a significant loss of viability for the QS mutant biofilm early in development. Hence, it is hypothesised that factors regulated by the QS system play a role in proper biofilm development and maintenance of V. vulnificus. Furthermore, it is shown that biofilm development varied among isolates.     

The Use of Cellulase in Inhibiting Biofilm Formation from Organisms Commonly Found on Medical Implants

A study was made of the use of cellulase to inhibit biofilm formation by a pathogenic bacterium commonly found in medical implants. A Pseudomonas aeruginosa biofilm was grown on glass slides in a parallel flow chamber for 4 d with glucose as the nutrient source. Biofilm development was assessed by measuring the colony forming units (CFU) and biomass areal density. Biofilm was grown at pH 5 and 7 in the presence of three different cellulase concentrations, 9.4, 37.6 and 75.2 units ml^{m 1}. In addition, a control study using deactivated cellulase was performed. The results show that cellulase is effective in partially inhibiting biomass and CFU formation by P. aeruginosa on glass surfaces. The effect of cellulase depended on concentration and was more effective at pH 5 than pH 7. The experiment was further extended by investigating the effect of cellulase on the apparent molecular weight of purified P. aeruginosa exopolysaccharides (EPS). The observation of EPS using size exclusion chromatography showed a decrease in apparent molecular weight when incubated with enzyme. An increase in the amount of reducing sugar with time when the purified EPS were incubated with enzyme also supports the hypothesis that cellulase degrades the EPS of P. aeruginosa. While cellulase does not provide total inhibition of biofilm formation, it is possible that the enzyme could be used in combination with other treatments or in combinations with other enzymes to increase effectiveness.     

Model of steady-state-biofilm kinetics

A steady-state biofilm is defined as one that has neither net growth nor decay over time. The model, developed for steady-state-biofilm kinetics with a single substrate, couples the flux of substrate into a biofilm to the mass (or thickness) of biofilm that would exist at steady-state for a given bulk substrate concentration. Based on kinetic and energetic constraints, this model predicts for a single substrate that a steady-state bulk concentration, S_min, exists below which a steady-state biofilm cannot exist. Thus, in the absence of adsorption of bacteria from the bulk water and for substrate concentration below S_min, substrate flux and biofilm thickness are zero. Equations are provided for calculating the steady-state substrate flux and biofilm thickness for S greater than S_min. An example is provided to demonstrate the use of the steadystate model.     

A simple structured model for biomass and extracellular enzyme production with recombinant Saccharomyces cerevisiae YPB-G

A simple structured model is proposed for simulating batch cultivation data on growth, substrate utilization, and heterologous enzyme production of recombinant Saccharomyces cerevisiae YPB-G. The enzyme is a fusion protein displaying α-amylase and glucoamylase activities. Cell growth is modulated mainly by intracellular substrate and ethanol concentrations. Intracellular substrate concentration is evaluated by means of the extracellular substrate and biomass concentrations. Extracellular α-amylase and glucoamylase activities are taken to depend on biomass concentration. The nine parameters of the proposed model are determined using nonlinear estimation techniques, and the model is validated against experiments not used in parameter determination. The model developed simulates glucose consumption, cell mass, α-amylase and glucoamylase production in a batch system. Simulation and experimental results are found to be in good agreement. Journal of Industrial Microbiology & Biotechnology (2002) 29, 111–116 doi:10.1038/sj.jim.7000281 Received 07 January 2002/ Accepted in revised form 22 May 2002     

Influence of glucose,fructose and sucrose as carbon sources on kinetics and stoichiometry of lysine production by <Emphasis Type="Italic">Corynebacterium glutamicum</Emphasis>

Batch cultivations of l-lysine-producing Corynebacterium glutamicum ATCC 21253 were carried out on the different carbon sources, glucose, sucrose and fructose. The time profiles of substrate and product concentrations were evaluated to compare kinetics and stoichiometry of lysine production. The lysine yield (mol C/mol C) on glucose was 8% higher than on sucrose and 30% higher than on fructose. The highest final biomass concentration of 5.0 g/l was obtained on glucose, whereas fructose and sucrose yielded 20% less biomass. Compared to glucose, fructose resulted in significantly higher respiration rates, a higher substrate uptake rate but a lower lysine production rate during the cultivation process. This was probably due to a higher tricarboxylic cycle activity combined with a lower activity of the pentose phosphate pathway. On sucrose, specific rates and yields differed significantly from those on fructose and glucose. Transport and metabolism of sucrose, therefore, are not a simple superposition of its building blocks, glucose and fructose. Journal of Industrial Microbiology & Biotechnology (2002) 28, 338–343 DOI: 10.1038/sj/jim/7000252 Received 28 November 2001/ Accepted in revised form 06 March 2002     

The Role of the Liquid Phase in the Degradation of Toluene and m‐Cresol within a Biofilm Trickle‐Bed Reactor

The degradation of toluene and m‐cresol in a biofilm trickle‐bed reactor was experimentally and theoretically investigated. Degradation is the result of the cooperation between suspended and immobilized microorganisms in the trickling film and the biofilm. The role of the trickling film is that of a barrier for mass transfer to the biofilm or that of an additional reaction space. This is the result of physical availability of pollutants to the liquid phase as well as co‐substrate degradation of inherent biomass. An instationary reactor balance model is presented. In addition to this the change in wetting behavior of carrier surface due to biofilm formation is discussed. A partial wetting of biofilm surface by rivulets of the trickling film is proposed. The model was verified by experimental data. The different reactor operation modes denoted as biofilm regime versus trickling film regime for the chosen pollutant system were expressed in terms of dimensionless reactions and transfer numbers. It is shown that the volumetric reaction rates for toluene in a trickling film regime reaches values twice as high as that of a biofilm regime due to the presence of the second substrate m‐cresol. The limiting step in both cases is the mass transfer of oxygen to bacteria in the biofilm or trickling film.     

Efficacy of silver-releasing rubber for the prevention of Pseudomonas aeruginosa biofilm formation in water

Abstract

The aim of the present study was to evaluate the efficacy of Elastoguard? silver-releasing rubber in preventing Pseudomonas aeruginosa biofilm formation in water. Biofilm formation by P. aeruginosa under various conditions in an in vitro model system was compared for silver-releasing and conventional rubber. Under most conditions tested, the numbers of sessile cells attached to silver-releasing rubber were considerably lower with reference to conventional rubber, although the effect diminished with increasing volumes. The release of silver also resulted in a decrease in planktonic cells. By exposing both materials simultaneously to conditions for biofilm growth, it became obvious that the antibiofilm effect was due to a reduction in the number of planktonic cells, rather than to contact-dependent killing of sessile cells. The data demonstrate that the use of silver-releasing rubber reduces P. aeruginosa biofilm in water and reduces the number of planktonic cells present in the surrounding solution.     

Evaluation of growth yield of Spirulina (Arthrospira) sp. in photoautotrophic, heterotrophic and mixotrophic cultures

In microbial cultures, both cellular growth rate and yield (defined as the degree of substrate conversion into the biomass) are important. Although effect of culture conditions on growth kinetics has been well documented for various microbial strains, there is almost no literature concerning the effect of environmental conditions on growth equilibrium, expressed as biomass yield coefficients from substrate. The present paper discusses the effect of culture conditions: irradiance (physical substrate) and glucose concentration (chemical substrate) on biomass yield coefficients from two chemical substrates: glucose and nitrate-nitrogen in photoautotrophic, heterotrophic and mixotrophic culture of blue-green alga Spirulina (Arthrospira) sp. The efficiency of substrates incorporation into the biomass can be precisely determined only if the elemental composition of the biomass is known. The experimental results showed that culture conditions had a substantial influence on biomass yield coefficients (biomass yield from glucose and nitrate-nitrogen). It was found that, the increase of irradiance favoured increase of biomass yield coefficient from both, glucose and nitrate-nitrogen. However, in the case of yield from nitrogen in mixotrophic culture, the effect was opposite. The effect of glucose concentration was different: the higher the initial glucose concentration, the lower the biomass yield coefficients from chemical substrates.     

A pulsing device for packed-bed bioreactors: II. Application to alcoholic fermentation

When the immobilized cells are employed in packed-bed bioreactors several problems appear. To overcome these drawbacks, a new bioreactor based on the use of pulsed systems was developed [1]. In this work, we study the glucose fermentation by immobilized Saccharomyces cerevisiae in a packed-bed bioreactor. A comparative study was then carried out for continuous fermentation in two packed-bed bioreactors, one of them with pulsed flow. The determination of the axial dispersion coefficients indicates that by introducing the pulsation, the hydraulic behaviour is closer to the plug flow model. In both cases, the residence time tested varied from 0.8 to 2.6 h. A higher ethanol concentration and productivity (increases up to 16%) were achieved with the pulsated reactors. The volumes occupied by the CO₂ were 5.22% and 9.45% for fermentation with/without pulsation respectively. An activity test of the particles from the different sections revealed that the concentration and viability of bioparticles from the two bioreactors are similar. From the results we conclude that the improvements of the process are attributable to a mechanical effect rather than to physiological changes of microorganisms.List of Symbols D m²/s dispersion coefficient - K _is l/g inhibition substrate constant - K _ip l/g inhibition ethanol constant - K _s g/l Apparent affinity constant - P g/l ethanol concentration - q _p g/(gh) specific ethanol productivity - Q _p g/(lh) overall ethanol productivity - q _s g/(gh) specific glucose consumption rate - Q _s g/(lh) glucose consumption rate - S g/l residual glucose concentration - S(in0) g/l initial glucose concentration - V _max g/(lh) maximum rate - Y _p/s g/g yield in product     

Evaluation of phenol diffusivity through Pseudomonas putida biofilms: application to the study of mass velocity distribution in a biofilter

Phenol diffusivity through Pseudomonas putida biofilms with thickness ranging from about 9?10^-6 to 90?10^-6?m has been evaluated in order to carry out a kinetic study on phenol aerobic degradation in a biofilter. An average effective diffusivity of 8.92.10^-12?m²?s^-1 has been calculated at 20?°C, with no appreciable dependence on biofilm thickness. This value, that is only 0.6% of that calculated in water at the same temperature, has been used to carry out a comparison between diffusion, convection and bioreaction mass velocities along the biofilter fed with air streams contaminated with different levels of phenol. Although diffusion through the biofilm is the limiting step at local level, biomass grows so abundantly within the support pores at high residence time that the most superficial active layers of biofilm are enough to transform nearly completely the substrate fed. At low residence time, on the contrary, the system is not able to face an evident situation of substrate overloading. Deodorization tests have also been carried out varying the support porosity, the superficial gas flow rate, and the starting phenol concentration in the polluted gaseous stream. This study could provide a general tool to model fixed-bed columns.     

Evaluation of steady-state-biofilm kinetics

Laboratory-scale biofilm reactors were used to evaluate a model of the kinetics of steady-state biofilm and the concept that there is a minimum concentration, S_min, below which no steady-state activity can occur. With acetate as the ratelimiting substrate, the steady-state concept of S_min was verified for naturally grown biofilms. Substrate removal and biofilm thickness declined rapidly as the substrate concentration approached S_min, which was 0.66 mg/liter for acetate. Using independently derived kinetic parameters, the model of steady-state-biofilm kinetics successfully predicted substrate utilization and biofilm thickness without the need for fitting factors. The results imply that organic materials may persist in water and wastewater, in part, because they are too low in concentration to supply sufficient energy to sustain the microorganisms.