Microbial Growth Kinetics Research Articles

In vitro, modulation of the dominant intestinal microbiota in type 2 diabetics by controlling antimicrobial activity with the methanolic extract of Pistacia lentiscus L.

The intestinal microbiota has become known as the ‘second brain’ a complementary organ for most metabolic and defensive reactions. The study aims to investigate the potential of the methanolic extract of Pistacia lentiscus leaves to modulate the dominant flora in type 2 diabetic patients compared to healthy subjects, by controlling growth kinetics. Comparative study between the dominant flora of type two diabitics (DT2) and helthy subjects (HS) stools. Using fully sterilized experimental space and materials, the germs were isolated through an antimicrobial study, and their microbial growth kinetics, were analyzed both with and without phytotherapeutic treatment in vitro. This was carried out as part of a study into the effect of methanolic extract from the leaves of the Pistacia lentiscus L. plant harvested in north-west Algeria. The study found a decrease in the quantity of lactobacilli and streptococci in DT2 and an inverse relationship between enterobacteria and streptococci in all microbiotas. On the molecular side. The methanolic extract of P lentiscus leaves gave a super antimicrobial effect for E coli and Clostridium sp at concentrations below their Minimum Inhibitory Concentration (2 mg mL-1), compared with the other gram positives studied, lactobacillus and Streptococcus (4 mg mL-1). This beneficial action confirms the high antimicrobial effect of the methanolic extract of P lentiscus leaves with lower concentration for the quantitative restauration of intestinal microbiota, the intermediary between insoluno-resistance and metabolism. Pistacia lentiscus has the potential to modulate the dominant flora in type 2 diabetics, through its regulatory antimicrobial power.

Advanced temperature control in ethanol fermentation using a PSO-PID controller with split-range control strategy

Global energy demand is experiencing a notable surge due to growing energy security. Renewable energy sources, like ethanol, are becoming more viable. In the present study, the application of a PSO-PID (Particle Swarm Optimization – Proportional Integral Derivative) controller with a split-range control strategy was suggested for the regulation of temperature within the fermentation system. To optimize performance, a POS-PID controller with a split-range arrangement utilizing two control valves for hot and cold utilities was constructed. The study began by examining the open-loop dynamic response of the system to inlet temperature and concentration disturbances during ethanol production fermentation. Subsequently, a transfer function model was developed through linearization at the steady-state operating point. The split-range controller structure, implemented by optimizing the PSO-PID controller parameters using PSO, effectively demonstrated temperature control in simulations of a nonlinear model. In this investigation, the ethanol fermentation system was modeled as a CSTR using a modified Monod equation for microbial growth kinetics. Various dynamic behavioral disturbances were explored and verified in the model with plant data in this study. The simulation model results were validated through plant data. The proposed method showed superior closed-loop performance with respect to errors, with the actuators proving to be effective than other reported methods for temperature control.

Physicochemical, Dough Volume and Microbial Growth during Leavening of Cassava-heat Composite Dough

This study determined the impact of cassava inclusion on the physiochemical properties, dough volume, and microbial growth kinetics of cassava-wheat composite dough during leavening. A high-quality cassava flour (HQCF) proportions (10%, 20, 30%,40 and 50%) partially substituted the wheat flour for bread dough production were evaluated for pH, titratable acidity, dough volume, and microbial growth kinetics at 1-hour intervals. Overall, the dough volume progressively decreased with cassava inclusion which peaked at 84.00, 80.50, 74, 72.50, and 69.00 in 10%, 20%, 30%, 40%, and 50% cassava-wheat inclusion respectively during leavening. Cassava-wheat composite dough leavened with commercial yeast had the highest gas retention (85.50 cm3), followed by wheat dough co-fermented with amylolytic L. plantarum (AMz5), while cassava dough had the least (66.00 cm3). The 10% cassava-wheat composite dough had a dough volume comparable (p > 0.05) to the 100% wheat dough. The dynamics of dough-specific volume decreased with cassava inclusion in the order of 10% < 20% < 30% < 40% < 50%. The pH decreased from 4.75 to 3.60 in the wheat dough and from 5.30 to 4.50 in the composite dough during proofing. Moreover, the continuous growth of lactic acid bacteria decreased with cassava flour inclusion. Similarly, the baker’s yeast exhibited steady growth in the cassava-wheat composite dough with fermentation. This data indicates that using 10% or 20% cassava flour inclusion will provide dough with the leavening kinetics necessary for acceptable bread production.

Proof of concept: real-time viability and metabolic profiling of probiotics with isothermal microcalorimetry.

Isothermal microcalorimetry (IMC) is a potent analytical method for the real-time assessment of microbial metabolic activity, which serves as an indicator of microbial viability. This approach is highly relevant to the fields of probiotics and Live Biotherapeutic Products (LBPs), offering insights into microbial viability and growth kinetics. One important characteristic of IMC is its ability to measure microbial metabolic activity separately from cellular enumeration. This is particularly useful in situations where continuous tracking of bacterial activity is challenging. The focus on metabolic activity significantly benefits both probiotic research and industrial microbiology applications. IMC's versatility in handling different media matrices allows for the implementation of viability assessments under conditions that mirror those found in various industrial environments or biological models. In our study, we provide a proof of concept for the application of IMC in determining viability and growth dynamics and their correlation with bacterial count in probiotic organisms. Our findings reinforce the potential of IMC as a key method for process enhancement and accurate strain characterization within the probiotic sector. This supports the broader objective of refining the systematic approach and methods used during the development process, thereby providing detailed insights into probiotics and LBPs.

Production of red beetroot juice by different methods: Kinetics of microbial growth, sugar consumption, and acid production

As a fermentation method, the utilisation of starter culture is a common practice in industrial manufacturing, although spontaneous methods have been employed since ancient times. The objective of this study was to investigate the effect of different production methods on red beetroot juice (RBJ). For this purpose, as a starter culture, the probiotic Lactibasillus paracasei (Lc. paracasei) was inoculated into the RBJ samples after pasteurization. Also, the growth of cells, acid production, and substrate utilisation were monitored throughout the fermentation process of RBJ under two different methods of fermentation.The samples produced by the addition of Lc. paracasei demonstrated a slightly lower decrease in pH values in comparison to the samples obtained by the spontaneous method. The concentration of lactic acid (LA) and acetic acid (AA) at the end of fermentation reveals that Lc. paracasei exhibits a greater capacity for both LA and AA generation compared to the spontaneous method. The ratios of LA and AA molar concentrations of RBJ were determined to be 1.7 and 3.6 for the samples produced by adding Lc. paracasei and the spontaneous method, respectively. The samples produced by adding Lc. paracasei exhibited a greater consumption of sucrose. Both fermentation methods provide LAB counts exceeding 8 log CFU/mL at the end of fermentation.Time demonstrated a significant correlation with LA and AA in the method by adding Lc. paracasei (r = 0.942 and 0.745), respectively (p < 0.01). In both methods, it was demonstrated that while sucrose content decreased during the fermentation period, fructose and glucose content remained constant (p < 0.05).

Potency of Dimethyl Dicarbonate on the Microbial Inhibition Growth Kinetics, and Quality of Passion Fruit (Passiflora edulis) Juice during Refrigerated Storage.

This study aimed to investigate the effectiveness of dimethyl dicarbonate (DMDC) at various concentrations (0-250 ppm) in inhibiting the growth of Escherichia coli TISTR 117 and spoilage microbes in passion fruit juice (PFJ) and its impact on the physicochemical and antioxidant quality of the juice during refrigerated storage. The highest log reduction in the total viable count, yeast/molds and E. coli was attained in PFJ samples with 250 ppm of DMDC (p ≤ 0.05) added. Microbial growth inhibition by DMDC followed the first-order kinetic model with a coefficient of determination (R2) and inhibition constants (k) ranging from 0.98 to 0.99 and 0.022 to 0.042, respectively. DMDC at 0-250 ppm showed an insignificant effect on pH, °Brix, color (L*, a*, b*), ascorbic acid, total phenolic compound (TPC), total flavonoid content, and antioxidant activity (DPPH, FRAP) (p > 0.05). Control (untreated PFJ), DMDC-250 ppm, and pasteurized (15 s at 72 °C) samples were subjected to 27 days of cold storage at 4 °C. A decreasing trend in pH, total soluble solid, ascorbic acid content, DPPH and FRAP values were observed in all the samples during refrigerated storage. However, the DMDC-250 ppm sample showed a better prospect in physicochemical quality changes compared to the pasteurized and untreated control PFJ samples. ΔE values showed marked changes in the control sample than the DMDC-250 ppm and pasteurized samples at 27 days of storage. Additionally, the total viable count and yeast/mold count were augmented during storage, and an estimated shelf-life of the control, DMDC-250 ppm, and pasteurized samples was approximately 3, 24 and 18 days, respectively. In conclusion, DMDC at 250 ppm could ensure microbial safety without affecting the quality attributes of PFJ during 24 days of storage at 4 °C.

Kinetics of microbial cell growth, utilization of organic substrates and methane production in upflow anaerobic filters in two and three separated stages treating sanitary landfill leachates

AbstractThis paper deals with the kinetics of microbial cell growth, utilization of organic substrates and methane production in upflow anaerobic filters in two and three separated stages (UAF‐2SS and UAF‐3SS) treating sanitary landfill leachates, under three temperatures (20, 27, and 34°C), fed with volumetric organic loads (VOLs) for UAF‐2SS (1.8, 2.25, 2.76, 3.45, 3.71, 4.64 kgCOD (chemical oxygen demand)/m3/d) and UAF‐3SS (1.7, 2.25, 2.44, 2.6, 3.15, 3.45, 3.5, 4.57, 4.64, 6.31, 11.61, 14.18, 17.48 kgCOD/m3/d). Kinetic parameters were obtained at temperature (20–34°C), pH (8.8–9.1), each one of three stages within the UAF‐2SS and UAF‐3SS reactors containing methanogenic bacteria (Methanococcus sp., and Methanobacterium sp.) and Clostridium sp.: Maximum substrate utilization rate (rm,s) resulted in 102 mg COD/L/h, maximum microbial cell growth rate (μm) varied 102–103 CFU (colony forming units)/mL/h, methane (CH4) production rate (rm,CH4) tended to vary 100–101 mg CH4/d and the maximum production coefficient (Y) varied 0–102 CFU/mL/h/mgCOD/L/h.

Effects of type of substrate and dilution rate on fermentation in serial rumen mixed cultures.

Forages and concentrates have consistently distinct patterns of fermentation in the rumen, with forages producing more methane (CH4) per unit of digested organic matter (OM) and higher acetate to propionate ratio than concentrates. A mechanism based on the Monod function of microbial growth has been proposed to explain the distinct fermentation pattern of forages and concentrates, where greater dilution rates and lower pH associated with concentrate feeding increase dihydrogen (H2) concentration through increasing methanogens growth rate and decreasing methanogens theoretically maximal growth rate, respectively. Increased H2 concentration would in turn inhibit H2 production, decreasing methanogenesis, inhibit H2-producing pathways such as acetate production via pyruvate oxidative decarboxylation, and stimulate H2-incorporating pathways such as propionate production. We examined the hypothesis that equalizing dilution rates in serial rumen cultures would result in a similar fermentation profile of a high forage and a high concentrate substrate. Under a 2 × 3 factorial arrangement, a high forage and a high concentrate substrate were incubated at dilution rates of 0.14, 0.28, or 0.56 h-1 in eight transfers of serial rumen cultures. Each treatment was replicated thrice, and the experiment repeated in two different months. The high concentrate substrate accumulated considerably more H2 and formate and produced less CH4 than the high forage substrate. Methanogens were nearly washed-out with high concentrate and increased their initial numbers with high forage. The effect of dilution rate was minor in comparison to the effect of the type of substrate. Accumulation of H2 and formate with high concentrate inhibited acetate and probably H2 and formate production, and stimulated butyrate, rather than propionate, as an electron sink alternative to CH4. All three dilution rates are considered high and selected for rapidly growing bacteria. The archaeal community composition varied widely and inconsistently. Lactate accumulated with both substrates, likely favored by microbial growth kinetics rather than by H2 accumulation thermodynamically stimulating electron disposal from NADH into pyruvate reduction. In this study, the type of substrate had a major effect on rumen fermentation largely independent of dilution rate and pH.

Microbial Primer: Bacterial growth kinetics.

tGrowth of microorganisms and interpretation of growth data are core skills required by microbiologists. While science moves forward, it is of paramount importance that essential skills are not lost. The bacterial growth curve and the information that can gleaned from it is of great value to all of microbiology, whether this be a simple growth experiment, comparison of mutant strains or the establishment of conditions for a large-scale multi-omics experiment. Increasingly, the basics of plotting and interpreting growth curves and growth data are being overlooked. This primer article serves as a refresher for microbiologists on the fundamentals of microbial growth kinetics.

Electromagnetic fields effects on microbial growth in cocoa fermentation: A controlled experimental approach using established growth models

Understanding the effects of electromagnetic fields is crucial in the fermentation of cocoa beans, since through precise control of fermentation conditions the sensory and nutritional properties of cocoa beans could be improved. This study aimed to evaluate the effect of oscillating magnetic fields (OMF) on the kinetic growth of the core microbial communities of the Collections Castro Naranjal (CCN 51) cocoa bean. The data was obtained by three different models: Gompertz, Baranyi, and Logistic. The cocoa beans were subjected to different OMF strengths ranging from 0 mT to 80 mT for 1 h using the Helmholtz coil electromagnetic device. The viable microbial populations of lactic acid bacteria (LAB), acetic acid bacteria (AAB), and yeast (Y) were quantified using the colony-forming unit (CFU) counting method. The logistic model appropriately described the growth of LAB and Y under magnetic field exposure. Whereas the Baranyi model was suitable for describing AAB growth. The microbial populations in cocoa beans exposed to magnetic fields showed lower (maximum specific growth rate (μmax), values than untreated controls, with AAB exhibiting the highest average growth rate value at 5 mT and Y having the lowest average maximum growth rate value at 80 mT. The lower maximum specific growth rates and longer lag phases when exposed to magnetic fields compared to controls demonstrate the influence of magnetic fields on microbial growth kinetics.

Fermentation of Plant-Based Feeds with Lactobacillus acidophilus Improves the Survival and Intestinal Health of Juvenile Nile Tilapia (Oreochromis niloticus) Reared in a Biofloc System.

This study evaluated the effect of fermentation with Lactobacillus acidophilus on the biochemical and nutritional compositions of a plant-based diet and its effects on the productive performance and intestinal health of juvenile Nile tilapia (Oreochromis niloticus) reared in a biofloc technology (BFT) system. The in vitro kinetics of feed fermentation were studied to determine the L. acidophilus growth and acidification curve through counting the colony-forming units (CFUs) mL-1 and measuring the pH. Physicochemical and bromatological analyses of the feed were also performed. Based on the microbial growth kinetics results, vegetable-based Nile tilapia feeds fermented for 6 (FPB6) and 18 (FPB18) h were evaluated for 60 days. Fermented diets were compared with a positive control diet containing fishmeal (CFM) and a negative control diet without animal protein (CPB). Fermentation with L. acidophilus increased lactic acid bacteria (LAB) count and the soluble protein concentration of the plant-based feed, as well as decreasing the pH (p < 0.05). FPB treatments improved fish survival compared with CPB (p < 0.05). Fermentation increased feed intake but worsened feed efficiency (p < 0.05). The use of fermented feeds increased the LAB count and reduced pathogenic bacteria both in the BFT system's water and in the animals' intestines (p < 0.05). Fermented plant-based feeds showed greater villi (FPB6; FPB18) and higher goblet cell (FPB6) counts relative to the non-fermented plant-based feed, which may indicate improved intestinal health. The results obtained in this study are promising and show the sustainable potential of using fermented plant-based feeds in fish feeding rather than animal protein and, in particular, fishmeal.

Antifungal activity of Annona crassiflora Mart. dichloromethane fraction against strains of C. albicans.

Products derived from medicinal plants with antimicrobial activity are considered a promising alternative in the treatment of fungal infections. In this perspective, this study proposed to evaluate the antifungal activity of the dichloromethane fraction of Annona crassiflora Mart. against C. albicans strains. Tests were carried out to determine Minimum Inhibitory Concentration (MIC), Minimum Fungicide Concentration (MFC), microbial growth kinetics, fungal cell wall and membrane mechanisms of action, antifungal biofilm activity, and cytotoxic effects on human erythrocytes. The extract presented MIC and MFC values that ranged from 256 µg/mL to 1,024 µg/mL, with fungicidal activity in the microbial growth kinetics assay. The mechanism of action did not occur through damage to the cell wall or via binding to ergosterol in the membrane, though the fraction presents activity against biofilm and is not cytotoxic in human erythrocytes. The dichloromethane fraction of Annona crassiflora Mart. presented antifungal activity and reduced biofilm growth, without toxicity against human erythrocytes; however, further studies are needed to define its mechanism of action.

Comparison of SYBR® Green qPCR assay and plate count method to describe growth of Weissella viridescens and Leuconostoc mesenteroides in pure and mixed cultivation

The current study was conducted to statistically compare the SYBR® Green quantitative polymerase chain reaction (qPCR) assay and the conventional plate counting (PC) method to construct growth curves of a cocktail of Weissella viridescens in pure culture under different isothermal storage conditions (4, 8, 14, and 30 °C) and in mixed culture with Leuconostoc mesenteroides at 8 °C. The efficiency and specificity of the qPCR standard curves were confirmed, and both methods were adequate to quantify the growth kinetics of W. viridescens at all isothermal temperatures, demonstrating a good correlation and agreement. The efficiencies of the standard curves varied between 98% and 102%. The SYBR® Green qPCR assay was also able to differentiate the growth curves of W. viridescens and L. mesenteroides in the mixed culture at 8 °C. Additionally, the SYBR® Green qPCR method was considered a faster and more sensitive alternative to construct growth curves under different isothermal conditions and differentiate morphologically similar lactic acid bacteria. Overall, the results suggest that the SYBR® Green qPCR method is a reliable and efficient tool to study microbial growth kinetics in pure and mixed cultures.

Machine learning approach for microbial growth kinetics analysis of acetic acid-producing bacteria isolated from organic waste

This study proposes novel hybrid methodology that combines machine learning (ML) techniques with experimental strategies to analyse microbial growth-kinetics of acetic acid-producing bacteria isolated from fruit waste. This work employs ML algorithms to create different models such as multivariate linear regression (MLR), partial least square regression (PLSR), Kernel ridge regression (KRR), support vector regression (SVR), Gradient boosting regression (GBR) that captures time-dependent patterns of bacterial growth dynamics. Experiments for microbial growth kinetic analysis were conducted on best isolate of acid producing bacteria with different glucose concentrations (1–5 %) at predefined operating conditions. It is found significant growth rate (µ) was obtained at 4 % and 5 % concentration of glucose from experimental work. 0.0588 h−1 and 0.0571 h−1 are the specific growth rate obtained at 4 % and 5 % glucose concentration respectively. Proposed ML models employed to predict growth rate kinetics theoretically at varied glucose concentrations. Comparative results indicate that GBR model exhibits superior performance in predicting growth kinetics than other models. GBR model fits the experimental results approximately with lower RMSE (0.004) than other models. This enables more accurate representation of growth patterns that is difficult to discernible through conventional analytical methods. This approach will help to understand growth kinetics of acetic acid-producing bacteria for resource recovery, wastewater treatment, and bioremediation.

The Influence of Lactiplantibacillus plantarum and Oenococcus oeni Starters on the Volatile and Sensory Properties of Black Raspberry Wine.

Malolactic fermentation (MLF) by different lactic acid bacteria has a significantly influence on the aromatic and sensory properties of wines. In this study, four strains including two Oenococcus oeni (commercial O-Mega and native DS04) and two Lactiplantibacillus plantarum (commercial NoVA and native NV27) were tested for their performances over MLF and effects on the basic composition, volatile components and sensory property of black raspberry wine. Results of microbial growth kinetics showed Lactiplantibacillus strains had higher fermentation efficiency than Oenococcus. The volatile compounds were determined by GC-IMS; NoVA and NV27 had higher production of volatile esters, and DS04 synthesized more amounts of acetate esters and several alcohols. In terms of sensory evaluation, NV27 and DS04 showed great aroma properties due to the enhanced fruity and sweet aroma. Furthermore, PLS was used for the establishment of the relationship between volatiles and sensory odors and sensory data interpretation.

Main Challenges Expected from the Impact of Climate Change on Microbial Biodiversity of Table Olives: Current Status and Trends.

Climate change is a global emergency that is affecting agriculture in Mediterranean countries, notably the production and the characteristics of the final products. This is the case of olive cultivars, a source of olive oil and table olives. Table olives are the most important fermented vegetables in the Mediterranean area, whose world production exceeds 3 million tons/year. Lactic acid bacteria and yeast are the main microorganisms responsible for the fermentation of this product. The microbial diversity and population dynamics during the fermentation process are influenced by several factors, such as the content of sugars and phenols, all of which together influence the quality and safety of the table olives. The composition of fruits is in turn influenced by environmental conditions, such as rainfall, temperature, radiation, and the concentration of minerals in the soil, among others. In this review, we discuss the effect of climate change on the microbial diversity of table olives, with special emphasis on Spanish and Portuguese cultivars. The alterations expected to occur in climate change scenario(s) include changes in the microbial populations, their succession, diversity, and growth kinetics, which may impact the safety and quality of the table olives. Mitigation and adaptation measures are proposed to safeguard the authenticity and sensorial features of this valuable fermented food while ensuring food safety requirements.

Automatically showing microbial growth kinetics with a high-performance microbial growth analyzer

It is difficult to show microbial growth kinetics online when they grow in complex matrices. We presented a novel strategy to address this challenge by developing a high-performance microbial growth analyzer (HPMGA), which employed a unique 32-channel capacitively coupled contactless conductivity detector as a sensing element and fixed with a CellStatz software. It was capable of online showing accurate and repeatable growth curves of well-dispersed and bad-dispersed microbes, whether they grew in homogeneous simple culture broth or heterogeneous complex matrices. Moreover, it could automatically report key growth kinetics parameters. In comparison to optical density (OD), plate counting and broth microdilution (BMD) methods, we demonstrated its practicability in five scenarios: 1) the illustration of the growth, growth rate, and acceleration curves of Escherichia coli (E. coli); 2) the antimicrobial susceptibility testing (AST) of Oxacillin against Staphylococcus aureus (S. aureus); 3) the determination of Ag nanoparticle toxicity on Providencia rettgeri (P. rettgeri); 4) the characterization of milk fermentation; and 5) the enumeration of viable pathogenic Vibrio in shrimp body. Results highlighted that the HPMGA method had the advantages of universality and effectivity. This technology would significantly facilitate the routine analysis of microbial growth in many fields (biology, medicine, clinic, life, food, environment, and ecology), paving an avenue for microbiologists to achieve research goals that have been inhibited for years due to a lack of practical analytical methods.

High-throughput and specific detection of microorganisms by intelligent modular fluorescent photoelectric microbe detector

Food safety has emerged as a major global issue. Detecting foodborne pathogenic microorganisms and controlling them is vital to guard against foodborne diseases caused by microorganisms. However, the current detection methods need to meet the demand for real-time detection on the spot after a simple operation. Considering unresolved challenges, we developed an Intelligent Modular Fluorescent Photoelectric Microbe (IMFP) system containing a special detection reagent. This IMFP system can automatically monitor microbial growth in which the photoelectric detection, temperature control, fluorescent probe, and bioinformatics screen are integrated into one platform and employed to detect pathogenic microorganisms. Moreover, a specific culture medium was also developed, which matched the system platform for Coliform bacteria and Salmonella typhi. The developed IMFP system could attain a limit of detection (LOD) of about 1 CFU/mL for both bacteria, while the selectivity could reach 99%. In addition, the IMFP system was applied to detect 256 bacterial samples simultaneously. This platform reflects the high-throughput needs of fields for microbial identification and related requirements, such as the development of pathogenic microbial diagnostic reagents, antibacterial sterilization performance tests, and microbial growth kinetics. The IMFP system also confirmed the other merits, such as high sensitivity, high-throughput, and operation simplicity compared to conventional methods, and it has a high potential as a tool for application in the health and food security fields.

Coupled model for microbial growth and phase mass transfer in pressurized batch reactors in the context of underground hydrogen storage.

A rising interest in a strong hydrogen economy as a part of the future net-zero economy results in an increasing necessity to store hydrogen as a raw material or an energy carrier. Experience and studies show that storing hydrogen in deep underground sites could enable microbial conversion of hydrogen. To predict and examine the loss of hydrogen, laboratory studies, and analysis are essential. A growth model is required to interpret batch or chemostat experiments. With this model, the parameters of microbial growth, and the conversion of hydrogen can be specified. This study presents experiments with methanogens and a hydrogen/carbon dioxide gas mixture performed in batch reactors. Further, the microbial growth was modeled by a double Monod model with hydrogen and carbon dioxide as the limiting substrates. As the amount of carbon dioxide dissolved in the water phase can not be neglected, both phases were considered in the proposed model. The mass-transfer rate between the gas and water phase was implemented by a linear relation including the concentrations in both phases and the mass-transfer coefficient. With the resulting coupled model, it was possible to match the pressure behavior in the reactor and conclude the microbial growth kinetics. Two types of methanogenic species were tested to validate the model. The mass transfer coefficient proves to impact the growth behavior in porous media. The mathematical model and experimental data are necessary to determine the growth rate and yield coefficient.

Investigating the effect of electrosprayed alginate/PVA beads size on the microbial growth kinetics: Phenol biodegradation through immobilized activated sludge

The presence of cyclic organic compounds, including phenol, in the wastewater of many industries has made phenol removal an important issue. Meanwhile, the biological methods of removing phenol have attracted the attention of researchers in recent years. Recently, the use of immobilized microbial cells is proposed as a new approach in industrial wastewater treatment. In this research, the aim is to study the effect of immobilized beads size on the phenol biodegradation efficiency and specific microbial growth rate. For this purpose, electrospray technique was used to immobilize activated sludge in hybrid matrix of alginate and polyvinyl alcohol (PVA). The fabricated alginate/PVA beads were characterized using Fourier transform infrared spectroscopy (FTIR). Evaluation of the results related to the free and immobilized cell systems in the shake flask experiments showed that at low phenol concentrations the immobilized cell system had the same performance as the free cell system, while the immobilized cell system at higher concentrations had a better performance in removing phenol so that at a concentration of 2000 mg/L, removal percentage has increased from 15% to 25–34%. On the other hand, in this survey, the kinetic behavior of activated sludge was in good agreement with Haldane's equation. Moreover, the maximum specific growth rate was measured 0.033 and 0.041 (h−1) beside 544 and 636 mg/L substrate inhibition constant, for free and immobilized cell systems, respectively. This result shows that the phenol biodegradation has been improved by using the cell immobilization technique especially with applying the smaller beads, which is due to improved mass transfer and microbial cell protection from harsh environments.