Increase In Biofilm Thickness Research Articles

Effect of clays incorporation on properties of thermoplastic starch/clay composite bio-based polymer blends

In this study, thermoplastic starch (TPS) biofilms were developed using starch isolated from the seeds of Melicoccus bijugatus (huaya) and reinforced with bentonite clays at concentrations of 1%, 3%, and 5% by weight. Novelty of this research lies in utilizing a non-conventional starch source and enhancing properties of TPS through clay reinforcement. FTIR analysis verified bentonite’s nature of clays, while SEM analysis provided insights into morphology and agglomeration behavior. Key findings include a notable increase in biofilm thickness and elastic modulus with higher clay content. Specifically, tensile strength of biofilms improved from 2.5 MPa for pure TPS to 5.0 MPa with 5% clay reinforcement. The elastic modulus increased from 25 MPa (TPS) to 60 MPa (5% clay). Thermal stability also showed enhancement, with initial degradation temperature increasing from 110 °C for pure TPS to 130 °C for TPS with 5% clay. Water vapor permeability (WVP) tests demonstrated a decrease in WVP values from 4.11 × 10−10 g m−1 s−1 Pa−1 for pure TPS to 2.09 × 10−10 g m−1 s−1·Pa−1 for TPS with 5% clay, indicating a significant barrier effect due to clay dispersion. These results suggest that biofilms based on huaya starch and reinforced with bentonite clay have considerable potential for sustainable food packaging applications, offering enhanced mechanical and barrier properties.

Highly sensitive resistance spectroscopy technique for online monitoring of biofilm growth on metallic surfaces

Online techniques for monitoring biofilm formation and evolution are limited, especially as regards its application in flowing water systems. This is chiefly due to the absence of efficient non-destructive and non-invasive sensing methods. In this study, a sensitive electrical resistance spectroscopy technique is developed to monitor non-invasively and in real time the growth of biofilms over metallic surfaces inside water flow systems. To this aim, Pseudomonas fluorescens strain is used for biofilm development lasting 72 h in a laboratory-scale test channel of orthogonal cross section. Biofilm development corresponds to a progressively increasing coverage of the metallic surface area up to full coverage and a progressively increasing thickness. Biofilm development is registered by continuous recording of electrical impedance signals (time series). Proper configuration and tuning of the electronics promote the resistive contribution to the signal whereas careful grounding diminishes electrical interferences and yields superb sensing sensitivity. An increase of relative electrical resistance of around 15% is noticed in 72 h flow experiments which is attributed to both an increase of metallic surface area coverage and an increase of biofilm thickness. An independent estimation of these quantities using imaging tools and microscopy analysis, indicates that full coverage of the metallic surface occurs after only 48 h of the flow experiment, whereas biofilm thickness increases gradually along the entire 72 h of the experiment. Cross-examination of electrical signals with biofilm characteristics (metallic surface coverage and biofilm thickness) reveals that, qualitatively speaking, electrical signals are rather more sensitive to metallic surface coverage than biofilm thickness.

Long-term changes in thickness, live/dead bacterial ratio, and mineral content in biofilm on ceramic and stainless steel orthodontic attachments.

Fixed orthodontic appliances induce biofilm deposition, which harbors amicrobial population harmful to the periodontal health of the individual. The present study evaluated the changes in thickness, live/dead bacterial ratio, and mineral content in dental biofilm over 6months in patients with either stainless steel or ceramic orthodontic attachments. Eighty patients who require fixed orthodontic appliance treatment with first premolar extraction for correcting their malocclusion were selected and bonded with either stainless steel or ceramic orthodontic attachments on the buccal side. The attached buttons were retrieved at different periods-1week, 1month, 3months, and 6months. They were stained and visualized through confocal microscopy to detect biofilm thickness and the ratio of live/dead bacteria. X‑ray diffraction was used to identify the presence of calcium and phosphorous. Ceramic attachments showed agreater increase in biofilm thickness in comparison to stainless steel attachments except in the initial 1‑week evaluation. Ahigher live/dead bacterial ratio was observed in stainless steel attachments than in their ceramic counterparts at all four evaluation periods. Both stainless steel and ceramic surfaces exhibited the presence of mineral deposition (calcium and phosphorous) at all periods. More biofilm adhesion was observed over ceramic surfaces than over stainless steel orthodontic attachments. Stainless steel attachments exhibited biofilm with ahigher live/dead bacterial ratio than their ceramic counterparts at all evaluation periods. The presence of calcium and phosphorous in the adhered biofilm, pointing toward its calcification process, was identified.

Exploring the Viability of a Liquid-Permeable Membrane Biofilm Reactor

This study evaluated a novel biofilm reactor, the liquid-permeable membrane biofilm reactor, that supplies performance-enhancing chemicals directly to the base of a biofilm. The chemicals are supplied via a liquid-permeable membrane that serves as the biofilm support. Two studies were carried out. In the first, a denitrifying biofilm was established on the membrane, and then chlorate was added via the membrane to enhance the abundance of specialized (per)chlorate-reducing denitrifying bacteria. Approximately 98% denitrification was maintained throughout the experiment, but the addition of chlorate resulted in an increase in the relative abundance of putative (per)chlorate reducing bacteria by around 15%. In the second study, a nitrifying biofilm was first established, achieving approximately 70% ammonium removal. Then, a protozoan inhibitor (cycloheximide) was added via the membrane, resulting in an increase in biofilm thickness and an increase in ammonium removal to 93%. Biofilm image analysis identified the mass transport mechanism from membrane to biofilm as a combination of advection and diffusion. These studies demonstrate the viability and effectiveness using a liquid-permeable membrane to supply performance-enhancing chemicals to a biofilm growing on the membrane surface.

New quorum quenching bacteria for controlling biofilm thickness in the membrane aerated biofilm reactor

The uncontrolled increase of biofilm thickness on the membrane surface directly affects substrate diffusion rate, pollutant removal efficiency, and microbial ecology of the membrane aerated biofilm reactor (MABR). This study aimed to control the biofilm growth using a promising antifouling strategy called quorum quenching (QQ). For this purpose, new QQ bacteria (Bacillus methylotrophicus BT1, Klebsiella pneumoniae BT2, Lysinibacillus fusiformis BT3, and Achromobacter xylosoxidans BT4) were isolated and immobilized to control the biofilm thickness on the membrane fibers in MABR. The Bacillus methylotrophicus BT1 with the highest QQ activity disrupted bacterial communication among microorganisms, provided a relatively thin and dense biofilm thickness (250 µm), and exhibited the best MABR performance. The amount of EPS secreted by the microorganisms significantly decreased due to the increase in the QQ activities of the QQ bacteria. A significant COD removal performance improvement of 74.5% compared to the control-MABR was achieved by MABR containing BT1. Microbial analysis revealed a change in the microbial community structure of biofilms in the MABRs containing different QQ bacteria. In conclusion, the newly isolated QQ bacteria effectively could be controlled biofilm formation on the membrane fibers in MABR systems, and the results obtained can form the basis for larger-scale studies.

Influence of biofilm thickness on the removal of thirteen different organic micropollutants via a Membrane Aerated Biofilm Reactor (MABR)

The presence of organic micropollutants (OMPs) in natural water bodies has become an emerging concern due to their fast dissemination into natural water sources, high persistence, ubiquitous nature, and detrimental impact on the environment and human health. This study evaluated the Membrane Aerated Biofilm Reactor (MABR) efficiency in the removal of 13 OMPs commonly reported in water. Results demonstrated that OMPs removal is dependent on biofilm thickness and bacterial cell density, microbial community composition and physicochemical properties of OMPs. Effective removals of ammonium and organic carbon (COD, >50%), acetaminophen (70%) and triclosan (99%) were obtained even at early stages of biofilm development (thickness < 0.33 mm, 2.9 ×105 cell mL−1). An increase in biofilm thickness and cell density (1.02 mm, 2.2 ×106 cell mL−1) enhanced the system performance. MABR achieved over 90% removal of nonpolar, hydrophobic and hydrophilic OMPs and 22–69% removal of negatively charged and acidic OMPs. Relative abundances of Zoogloea, Aquabacterium, Leucobacter, Runella, and Paludilbaculum bacteria correlated with the removal of certain OMPs. In addition, MABR achieved up to 96% nitrification and 80% overall COD removal by the end of the experiment. The findings from this study demonstrated MABRs to be a feasible option to treat municipal wastewater polluted by OMPs.

A synchronous photoautotrophic-heterotrophic biofilm cultivation mode for Chlorella vulgaris biomass and lipid simultaneous accumulation

Microalgae biofilm was a porous structure formed by the accumulation of microalgae cells. The cells in upper layer of biofilm could receive light for photosynthetic growth and meanwhile removed the inorganic nitrogen and phosphorus etc. From wastewater to cleaner biomass. While with the increase of biofilm thickness, light could not reach the underlayer, forming a natural dark area in the bottom of the biofilm for microalgae heterotrophic growth. The naturally formed synchronous photoautotrophic-heterotrophic microalgae growth environment realized the synchronization of biofilm growth and lipid enrichment. The transmission of metabolic gases made the biofilm loose and porous (120.18% increase on the biofilm porosity), which provided more channels for the transmission of nutrients. Due to the synchronous heterotrophic enrichment in the bottom layer of biofilm, the maximum growth rate of biomass cultivated under synchronous photoautotrophic-heterotrophic biofilm was 3.04 times higher than that of photo-autotrophic biofilm and lipid yield increased by 2.22 times. The proportion of photosynthetic autotrophy of cells in the biofilm increased with the increase of light intensity which made an increase of 33.45% in the growth rate of biofilm but with a price of 43.88% reducing in the lipid content. While, the increase of heterotrophic proportion in the biofilm realized the simultaneous enhancement of biomass density and lipid content. The biomass productivity increased to 55.81 g m−2 d−1 and the lipid content increased to 46.79% at the same time. Thus, it solved the contradictory between the growth of microalgae and the accumulation of lipid, and provided a new idea for the application of changing wastewater resources to clean biofuel. It would have an important significant to the development of low-carbon renewable and clean energy.

Biofuel generation from high-fat effluent in a biofilm reactor with backwash

ABSTRACT The performance of an up-flow 0.5 m high and 0.076 m diameter fixed-film bioreactor treating lipid-rich synthetic wastewater has been investigated under the present study. The initial porosity of the filter bed using immobilised microorganisms were on the support matrices has been measured to be 0.67. Excess biomass accumulation on the support leads to an increase in biofilm thickness with time. The filter bed has been regenerated by backwashing after the stipulated time to regain its efficiency in terms of COD removal through the revival of the contact surface. A mathematical model has been developed to predict the loss of contact area and decrease in the porosity of bed with operation time. The backwashing time has been correlated to the inlet concentration of substrate. Methanogens like Methanococcus sp. and Methanosarcina sp. are detected in the mixed anaerobic consortia and favourable growth condition for methanogens in the reactor leads to a maximum cumulative methane production at the exit of the reactor estimated to be 785 ml CH4 (STP)/(g VSS added). The originality of the present research lies in investigating erucic acid-rich wastewater in a bioreactor with backwash and proposing an integration of this bioconversion with syngas-based 2G-Biorefinery.

CFD study of the hydrodynamics and biofilm growth effect of an anaerobic inverse fluidized bed reactor operating in the laminar regime

The unsteady laminar flow of an inverse fluidized bed reactor was addressed in this study using computational fluid dynamics (CFD). Three-dimensional (3D) and two-dimensional (2D) simulations were carried out using the Eulerian-Eulerian approach with the Syamlal O'Brien and Gidaspow models for modeling the drag between the solid and liquid phases. Reported data of solids expansion and bed porosity were used to validate the simulations. Results show that 2D simulations can satisfactorily reproduce experimental data of fluidized bed reactors, which are essentially equal to those obtained on 3D simulations. The model of Syamlal O'Brien was found to be in better agreement with experiments than that of Gidaspow. It is shown that commonly used correlations for predicting bed porosity fail to provide a reasonable overall description of the evaluated operating conditions. The flow patterns for both phases in the bed section exhibit chaotic recirculation zones with high values of shear stress, and after this, the flow quickly becomes fully developed. The effect of biofilm thickness increase on bed porosity, under similar apparent densities of colonized particles reported for this system, is analyzed. Biofilm growth generates a decrease in the Archimedes number (i.e., decreases the buoyancy of particles) and an increase in the particle Reynolds numbers (Rep), affecting significantly the final porosity of the bed. However, this effect vanishes for Rep < 0.25. Results from this work can be used to develop scale‐up criteria and to establish safe operating conditions (e.g., maximum liquid velocity and biofilm thickness) to avoid loss of support particles.

Biofilm and microbiome response of attached growth nitrification systems across incremental decreases to low temperatures

The study investigates low temperature attached growth rates and nitrifying biofilm, biomass, and microbiome responses down to 1 °C. Two moving bed biofilm reactors (MBBR) were acclimatized from 10 °C to 1 °C by incremental decreases in temperatures. A non-linear decline in nitrification with decreasing temperatures was recorded with a kinetic threshold temperature delineated between 4 °C and 2 °C, at which a significant decline in efficiency of 22.47% occurred. An increase in biofilm thickness of 25.47% occurs between 10 °C and 4 °C, followed by lesser increases of 6.55% and 9.60% at 2 °C and 1 °C. Biofilm density decreases between 10 °C and 1 °C. An increase in embedded viable cells of 24.01% occurs between 10 °C and 4 °C, followed by lesser non-statistically relevant increases at 2 °C and 1 °C. No statistically significant change in the number of estimated species is observed; however, β-diversity analysis indicates greater microbial community shifts above the kinetic threshold followed by lesser shifts between 2 °C and 1 °C. Nitrosomanadacea and Nitrosopira are the ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) families in the biofilm with relative abundances of 3.43 ± 0.51% and 0.94 ± 0.44% respectively at 10 °C. A change in NOB relative abundance occurred between the temperatures of 10 °C and 1 °C, decreasing to 0.19 ± 0.10% above the kinetic threshold. The estimation of nitrifiers per carrier in the bioreactors, based on biofilm thickness, biomass viability and relative abundances shows an increase of 30.2% in AOB/carrier above the kinetic threshold temperature (> 4 °C) followed by lesser increases down to 1 °C.

Anammox attachment and biofilm development on surface-modified carriers with planktonic- and biofilm-based inoculation

This study investigates the kinetics, attachment, biofilm development and anammox bacteria enrichment of a novel detached anammox biofilm inoculation method on non-modified virgin MBBR carriers and pre-seeded denitrifying carriers. The study compares these results to the more common use of attached anammox carriers for anammox MBBR inoculation. The anammox bacteria specific attachment-growth rates for virgin carriers inoculated with detached anammox biofilm mass were 38.1% greater for the first 25 days, leading to approximately 30% less time required to achieve complete biofilm coverage than those measured in attached biofilm carrier inoculated systems during the attachment and early biofilm growth stages. The biofilm thickness increase rate was also 52.3% higher for virgin carriers with detached biofilm inoculum. Further, inoculation using pre-seeded denitrifying carriers compared to virgin carriers demonstrated a 13.8% preferential increase in anammox bacteria specific attachment-growth rate and a corresponding 47.2% higher NH4+-N removal rate at the time of biofilm maturation.

Ultrasound Driven Biofilm Removal for Stable Power Generation in Microbial Fuel Cell

Anodic biofilm plays a crucial role in bioelectrochemical system to make it sustainable for long-term performance. However, the accumulation of dead cells over time within the anode biofilm can be particularly detrimental for current generation. In this study, the effect of ultrasound on anode biofilm thickness was investigated in microbial fuel cells (MFCs). Ultrasonic treatment was employed for different durations to evaluate its ability to control the thickness of the biofilm to maintain stable power generation. Cell viability count and field emission scanning electron microscopy (FESEM) analysis of the biofilms over time showed that the number of dead cells increased with the increase of biofilm thickness, and eventually exceeded the number of live cells by many-fold. Electrochemical impedance spectroscopy (EIS) analysis indicated that the high polarization resistance appeared due to the dead layer formation, and thus the catalytic efficiency was reduced in MFCs. The stable power generation was achiev...

Meso and micro-scale response of post carbon removal nitrifying MBBR biofilm across carrier type and loading

This study investigates the effects of three specific moving bed biofilm reactor (MBBR) carrier types and two surface area loading rates on biofilm thickness, morphology and bacterial community structure of post carbon removal nitrifying MBBR systems along with the effects of carrier type and loading on ammonia removal rates and effluent solids settleability. The meso and micro analyses show that the AOB kinetics vary based on loading condition, but irrespective of carrier type. The meso-scale response to increases in loading was shown to be an increase in biofilm thickness with higher surface area carriers being more inclined to develop and maintain thicker biofilms. The pore spaces of these higher surface area to volume carriers also demonstrated the potential to become clogged at higher loading conditions. Although the biofilm thickness increased during higher loading conditions, the relative percentages of both the embedded viable and non-viable cells at high and conventional loading conditions remained stable; indicating that the reduced ammonia removal kinetics observed during carrier clogging events is likely due to the observed reduction in the surface area of the attached biofilm. Microbial community analyses demonstrated that the dominant ammonia oxidizing bacteria for all carriers is Nitrosomonas while the dominant nitrite oxidizing bacteria is Nitrospira. The research showed that filamentous species were abundant under high loading conditions, which likely resulted in the observed reduction in effluent solids settleability at high loading conditions as opposed to conventional loading conditions. Although the settleability of the effluent solids was correlated to increases in abundances of filamentous organisms in the biofilm, analyzed using next generation sequencing, the ammonia removal rate was not shown to be directly correlated to specific meso or micro-scale characteristics. Instead post carbon removal MBBR ammonia removal kinetics were shown to be related to the viable AOB cell coverage of the carriers; which was calculated by normalizing the surface area removal rate by the biofilm thickness, the bacterial percent abundance of ammonia oxidizing bacteria and the percentage of viable cells.

Cadmium Modulates Biofilm Formation by Staphylococcus epidermidis

The aim of the study was to evaluate the effect of cadmium exposure on Staphylococcus epidermidis (ATCC 35984) biofilm formation. Bacteria were cultured in the absence or presence of different concentrations (0–50 µM) of cadmium. Biofilm formation and bacterial viability were assessed. Quantitative Real Time-PCR (qRT-PCR) was used to determine the mRNA expression of molecular markers of S. epidermidis biofilm formation and dispersion. S. epidermidis biofilm formation was stimulated (p < 0.001) by 1.56 and 3.13 µM cadmium. Confocal laser scanning microscopy (CLSM) analysis confirmed an increase in biofilm thickness (23 and 22 µm, versus 17.8 µm in the controls) after exposure to 1.56 or 3.13 µM cadmium, respectively. qRT-PCR was performed showing the up-regulation of atlE, embp, aap, icaA and icaB after exposure to 3.13 µM cadmium. Taken together, these findings show that cadmium at low, sub-toxic concentrations acts as inducer of S. epidermidis biofilm formation.

Role of algal biofilm in improving the performance of free surface, up-flow constructed wetland

The role of algal biofilm in a pilot-scale, free-surface, up-flow constructed wetland (CW), was studied for its effect on chemical oxygen demand (COD), ammonia and phosphate removal during three seasons-autumn, winter and early spring. Effect of hydraulic retention time (HRT) was also investigated in presence and absence of algal biofilm. Principal Component Analysis was used to identify the independent factors governing the performance of CW. The study showed algal biofilm significantly improved nutrient removal, especially phosphate. Ammonia removal varied with HRT, biofilm and ambient temperature. Increase in biofilm thickness affected ammonia removal efficiency adversely. Algal biofilm-assisted COD removal compensated for reduced macrophyte density during winter. Two-way ANOVA test and the coefficients of dependent factors derived through multiple linear regression model confirmed role of algal biofilm in improving nutrient removal in CW. The study suggests that algal biofilm can be a green solution for bio-augmenting COD and nutrient removal in CW.

Species and material considerations in the formation and development of microalgal biofilms

The development of microalgal biofilms has received very limited study despite its relevance in the design of photobioreactors where film growth may be advantageous for biomass separation or disadvantageous in fouling surfaces. Here, the effects of species selection, species control, and substrate properties on biofilms of Scenedesmus obliquus and Chlorella vulgaris were investigated. Experiments were conducted in batch culture and in continuous culture modes in a flow cell. Cell growth was monitored using confocal laser scanning microscopy and gravimetrically. Species selection and species control had significant effects on biofilm development. On non-sterile wastewater, C. vulgaris shifted from primarily planktonic (23.7% attachment) to primarily sessile (79.8% attachment) growth. The biofilms that developed in non-sterile conditions were thicker (52 ± 19 μm) than those grown in sterile conditions (7 ± 6 μm). By contrast, S. obliquus attained similar thicknesses (54 ± 31 and 53 ± 38 μm) in both sterile and non-sterile conditions. Neither species was able to dominate a non-sterile biofilm. The effect of substrate surface properties was minimal. Both species grew films of similar thickness (approximately 30 μm for S. obliquus, < 10 μm for C. vulgaris) on materials ranging from hydrophilic (glass) to hydrophobic (polytetrafluoroethylene). Surface roughness created by micropatterning the surface with 10 μm grooves did not translate into long-term increases in biofilm thickness. The results indicate that species selection and control are more important than surface properties in the development of microalgal biofilms.

Biofilm formation on materials commonly used in household drinking water systems

Biofilms are surface-associated bacterial communities that predominate in natural and pathogenic ecosystems. Their formation in drinking water systems creates potential risks for consumers’ health. Herein we tested biofilm formation on materials commonly used for indoor household drinking water systems (copper, PVC and stainless steel) simulating an average family water usage. Water parameters were determined by standardized methods while biofilm formation was assessed by epifluorescent and laser scanning confocal microscopy, for determining the numbers of attached cells, biofilm thickness, colony size and average colony surface. Results showed a very fast colonization on all materials used, of log 6–7 cm−2 cells disposed on a single layer on copper and PVC. On stainless steel, beginning on the 24th experimental day, there were observed multiple layers of cells and a rapid increase of biofilm thickness. The lowest overall number of attached cells was found on copper. Microorganism colonization and biofilm formation is possible and quite fast on an indoor water system connected to a chlorinated water network. From the tested materials, the greatest risk to consumer health comes from biofilm formation on stainless steel parts which are used in the very large majority of residences.

Effect of bioclogging in porous media on complex conductivity signatures

Flow through sand columns inoculated with Pseudomonas aeruginosa were used to investigate the effect of bioclogging on the complex conductivity and flow and transport properties. Complex conductivity (0.1–1000 Hz), the bulk hydraulic conductivity (K), volumetric flow rate (Q), dispersivity (D), and microbial cell concentrations were monitored over time. Environmental scanning electron microscope images of the sands were obtained at the end of the experiment. Bioclogging resulting from increases in microbial cell concentration and the production of exopolymeric substances (EPS) had a large impact on the imaginary conductivity (σ″), K, Q, D, and porosity (Φ). Changes in electrical and transport properties developed in three stages: an initial stage 1 with no significant changes in all measured parameters (Days 1–8), which we attribute to the reversible and irreversible attachment of microbial cells to the sand. In stage 2a (Days 9–16), bioclogging caused by the growth of biomass either as microcolonies filling pore throats and/or as uniform covering on the sand surfaces resulted in maximum decrease in Q and K, but with only moderate increases in σ″. In stage 2b (Days 17–24), significant production of EPS substances and increase in biofilm thickness resulted in a higher rate of increase in σ″ compared to stage 2a. In stage 3 (Days 25–32), biofilm growth reached a quasi steady state and insignificant changes are observed in all measured parameters. The results of this study suggest that σ″ can provide complimentary information in the assessment of bioclogging in porous media.

Dissolved oxygen as a factor influencing nitrogen removal rates in a one-stage system with partial nitritation and Anammox process

A biofilm system with Kaldnes biofilm carrier was used in these studies to cultivate bacteria responsible for both partial nitritation and Anammox processes. Due to co-existence of oxygen and oxygen-free zones within the biofilm depth, both processes can occur in a single reactor. Oxygen that inhibits the Anammox process is consumed in the outer layer of the biofilm and in this way Anammox bacteria are protected from oxygen. The impact of oxygen concentration on nitrogen removal rates was investigated in the pilot plant (2.1 m3), supplied with reject water from the Himmerfjärden Waste Water Treatment Plant. The results of batch tests showed that the highest nitrogen removal rates were obtained for a dissolved oxygen (DO) concentration around 3 g O2 m(-3) At a DO concentration of 4 g O2 m(-3), an increase of nitrite and nitrate nitrogen concentrations in the batch reactor were observed. The average nitrogen removal rate in the pilot plant during a whole operating period oscillated around 1.3 g N m(-2)d(-1) (0.3 +/- 0.1 kg N m(-3)d(-1)) at the average dissolved oxygen concentration of 2.3 g O2 m(-3). The maximum value of a nitrogen removal rate amounted to 1.9 g N m(-2)d(-1) (0.47 kg N m(-3)d(-1)) and was observed for a DO concentration equal to 2.5 g O2 m(-3). It was observed that increase of biofilm thickness during the operational period, had no influence on nitrogen removal rates in the pilot plant.

An investigation of biphasic growth kinetics for Phanerochaete chrysosporium (BKMF-1767) immobilised in a membrane gradostat reactor using flow-cells

A novel membrane gradostat reactor (MGR) was patented in 1999. This MGR is used for the continuous production of secondary metabolites, such as lignin peroxidase and manganese peroxidase, from an immobilised biofilm of Phanerochaete chrysosporium, in response to nitrogen starvation. Extensive research has been done previously on the biochemistry and the enzymatic activities of this fungus, but very little information is available on this fungus’ growth kinetics and nutrient consumption, within a continuously operated MGR system. It was the purpose of this study to identify the biofilm growth phases and to quantify the growth kinetics and nutrient consumption of an immobilised biofilm of P. chrysosporium (BKMF-1767) using single-capillary flow-cell MGR's, operated under different spore concentrations and airflow rates. Biofilm thickness increased with an increase in both spore concentration and airflow rate. Biphasic growth (first and second exponential growth phases, separated by a short intermediate lag phase) was demonstrated. For the first exponential growth phase, the biofilm thickness increase rate ( k f) ranged between 0.07 and 0.1 h −1 and for the second exponential growth phase the growth slowed down to between 0.015 and 0.05 h −1. The ammonium depletion of 96–99% corresponded to the time of the intermediate lag phase. At the end of the first exponential growth phase, the glucose depletion was approximately 13%, compared to 24% during the second exponential growth phase. For this system, the intermediate lag phase occurred in response to the ammonium depletion and not glucose depletion. The fungal growth was accompanied by pH acidification, attributed to NH 4 +/H + exchange, only up to the time of ammonium depletion. The determination of the biofilm thickness increase rate, k f, for biphasic growth, in relation to glucose and ammonium consumption, for within a MGR system, was not previously reported.