Maximum Specific Growth Rate Research Articles

Mathematical Modeling of Pilot Scale Olive Mill Wastewater Phytoremediation Units

A mechanistic state–space model has been developed to describe the dynamics of olive mill wastewater (OMW) treatment in phytoremediation pilot units with P. granatum L. and M. communis L. plants and to assess further the relative contribution of the plants in the overall OMW remediation process. Both phytoremediation and bioremediation processes have been considered in the model, i.e., phytodegradation, rhizodegradation, accumulation of hardly biodegradable organic matter on the root tissue of plants, microbial growth, maintenance and decay, and enzymatic decomposition of organics. Maximum specific microbial growth rates for bacteria and fungi were estimated within the range of 0.164–0.236 1/h. The specific rate for the decomposition of hardly biodegradable organics both by bacteria and fungi was within the range of 10.75–72.73 mg-substrate/g-biomass·h, whereas, particularly for the high-molecular-weight polyphenols, it was 1.02–18.25 mg-substrate/g-biomass·h. The values of the transpiration stream concentration factor were greater than 0.95 for both the non-phenolic and phenolic organics, which indicates almost passive uptake of OMW organics’ mixture by the plants. The corresponding factors for inorganic N and P were estimated as greater than unity, indicating active uptake. Overall, the model predicts the experimental data well when the organic concentration of OMW is high, and it predicts that phytoremediation processes contribute by more than 91% to the removal of OMW organics and nutrients, irrespective of the wastewater organic strength.

Effect of EPS production on the performance of membrane-based biofilm reactors

This study explored the effect of extracellular polymeric substance (EPS) production on the performance of membrane-based biofilm reactors. Changing EPS production was induced by eliminating one of the main EPS polysaccharides, i.e., Pel. The studies were carried out using a pure culture of either Pseudomonas aeruginosa or an isogenic P. aeruginosa mutant that was unable to produce the Pel polysaccharide. The biofilm cell density for both strains was compared to confirm the Pel deletion mutant decreased overall EPS production in a bioreactor system. When the Pel-deficient mutant was grown as a biofilm, its cell density, i.e., ratio of cells/(cells+EPS), was 74 % higher than the wild type, showing EPS production was reduced by eliminating pel production. The growth kinetics were determined for both strains. The Pel-deficient mutant had a maximum specific growth rate (μ^) that was 14% higher than the wild type. Next, the effects of EPS reduction on reactor performance were assessed for a membrane aerated biofilm reactor (MABR) and a membrane bioreactor (MBR). For the MABR, the organic removal with the Pel-deficient mutant was around 8% higher than for the wild type. For the MBR, the time to reach the fouling threshold was 65 % greater for the Pel-deficient mutant than for the wild type. These results suggest that amount of EPS production can have significant effects on bacterial growth kinetics and bacterial cell density, which in turn can affect the performance of the membrane-based biofilm reactors. In both cases, lower EPS production correlated with more efficient treatment processes.

Effect of different temperature regimes on remediation efficiency, photosynthetic performance and fatty acid profile of algal consortia

The present investigation was conducted to examine the adaptability potential of wastewater treated algal consortia (Consortia 1-Chlorococcum humicola and Tetradesmus sp; Consortia 2- Chlorococcum humicola, Scenedesmus vacuolatus and Tetradesmus sp) under temperature regime of 20°C and 40°C. The results exhibited that consortia 1 treated with 25 % wastewater showed highest remediation efficiency than consortia 2. However, maximum specific growth rate (0.064 ± 0.012) and biomass production (2010 ± 14.23 mg/L) was observed in wastewater (50 %) treated consortia 2. The results also revealed highest improvement in different photosynthetic parameters in consortia 1 at 20 °C and 40 °C. Additionally, enrichment of antioxidants and phenolic compounds at 40°C in consortia 1 was evident from FTIR spectroscopy. The results further showed that 40°C enhanced saturated fatty acid percentage (46.99%) in consortia 2. Overall, maximum growth, biomass production, photosynthetic performance and fatty acid profile of selected consortia reflected remarkable adaptability and tolerance towards thermal stress. Thus, employing consortia could serve as the competent bio-system to resolve wastewater complexity and concomitant bio-energy production under temperate and sub-tropical regions.

Growth of Dunaliella viridis in multiple cycles of reclaimed media after repeated high pH-induced flocculation and harvesting

Minimizing the use of water for growing microalgae is crucial for lowering the energy and costs of animal feed, food, and biofuel production from microalgae. Dunaliella spp., a haloterant species that can accumulate high intracellular levels of lipids, carotenoids, or glycerol can be harvested effectively using low-cost and scalable high pH-induced flocculation. However, the growth of Dunaliella spp. in reclaimed media after flocculation and the impact of recycling on the flocculation efficiency have not been explored. In this study, repeated cycles of growth of Dunaliella viridis in repeatedly reclaimed media from high pH-induced flocculation were studied by evaluating cell concentrations, cellular components, dissolved organic matter (DOM), and bacterial community shifts in the reclaimed media. In reclaimed media, D. viridis grew to the same concentrations of cells and intracellular components as fresh media—107 cells/mL with cellular composition of 3 % lipids, 40 % proteins, and 15 % carbohydrates—even though DOM accumulated and the dominant bacterial populations changed. There was a decrease in the maximum specific growth rate and flocculation efficiency from 0.72 d−1 to 0.45 d−1 and from 60 % to 48 %, respectively. This study shows the potential of repeated (at least five times) flocculation and reuse of media as a possible way of reducing the costs of water and nutrients with some tradeoffs in growth rate and flocculation efficiency.

Exploring the potential of thermophilic anaerobic co-digestion between agro-industrial waste and water hyacinth: operational performance, kinetic study and degradation pathway.

Anaerobic co-digestion (co-AD) of agro-industrial waste, namely, palm oil mill effluent (POME) and sugarcane vinasse (Vn), with water hyacinth (WH) as co-substrate was carried out in two separate Anaerobic Suspended Growth Closed Bioreactors (ASGCBs) under thermophilic (55°C) conditions. The highest chemical oxygen demand (COD) and soluble COD reduction in co-AD of POME-WH (78.61%, 78.86%) is slightly higher than co-AD of Vn-WH (75.75%, 78.24%). However, VFA reduction in co-AD of POME-WH (96.41%) is higher compared to co-AD of Vn-WH (85.94%). Subsequently, biogas production peaked at 13438mL/day values and 16122mL/day for co-AD of POME-WH and Vn-WH, respectively. However, the methane content was higher in the co-AD of POME-WH (72.04%) than in the co-AD of Vn-WH (69.86%). Growth yield (YG), maximum specific substrate utilization rate (rx,max) and maximum specific biomass growth rate (μmax) are higher in co-AD of POME-WH, as supported by the higher mixed liquor volatile suspended solids (MLVSS) and COD reduction efficiency compared to co-AD of Vn-WH. However, methane yield ([Formula: see text]) reported in the co-AD of POME-WH and Vn-WH are 0.2748 and 0.3112 L CH4/g CODreduction, respectively, which suggests that WH is a more suitable co-substrate for Vn compared to POME.

Research on the Mechanism of Ultrasound To Enhance the Biodegradation of Profenofos by Lactiplantibacillus plantarum

The effect and mechanism of ultrasound on the biodegradation of profenofos by Lactiplantibacillus plantarum were studied in this work. The results showed that ultrasound applied in the prelogarithmic phase of microbial growth would significantly enhance the biodegradation of profenofos (P < 0.05). The key ultrasonic parameters (ultrasonic intensity, pulse mode, and duration time) were optimized using the response surface methodology. The Holden model was used to describe the growth of L. plantarum and the biodegradation of profenofos. Under the optimal ultrasonic condition, the maximum specific growth rate of L. plantarum and the maximum specific degradation rate of profenofos were 2 and 1.7 times higher than those without sonication, respectively. The promotion of profenofos degradation by ultrasound comes from two aspects: one is the enhancement of phosphatase activity; the second is the improvement of cell membrane permeability, which accelerates the transport of nutrients, profenofos, and other metabolites through the cell membrane.

Bioremediation of propylbenzenes by a novel marine microalga Rhinomonas reticulata S6A isolated from Daya Bay: acute toxicity, growth kinetics and biodegradation performance

This study investigated the degradation characteristics of propylbenzenes (PBZs, including isopropylbenzene and n-propylbenzene), with high leakage risks and ecological hazards, by a newly isolated marine microalga named Rhinomonas reticulata S6A which is a promising candidate for eco-friendly bioremediation from marine. About 72% and 56% of n-PBZ and i-PBZ can be degraded after 7 days in culture. The acute toxicity of n-PBZ (96h - EC50 = 2.38 mg/L) was higher than that of i-PBZ (96h - EC50 = 3.65 mg/L). The growth inhibition kinetics of this strain were consistent with the Edwards model (R2 = 0.998) and Aiba model (R2 = 0.999). The optimal concentrations for the degradation of n-PBZ and i-PBZ were calculated to be 2.42 mg/L and 2.78 mg/L, respectively. The degradation trends of PBZs conformed to the zero-order kinetic model, and k increased with initial concentrations. The moderate increase in inoculation density could accelerate the degradation of PBZs, with the maximum specific growth rates (r) of 1.116/d (n-PBZ) and 1.230/d (i-PBZ) at the initial inoculation density of 104 cells/mL, while over-inoculation (initial microalgae density more than 105 cells/mL) was not conducive to the degradation of the pollutants. There is not much data on the biodegradation of PBZs in the aquatic environment, so it would be worthwhile to try to apply the new microalgae to explore the fate of PBZs.

Production, characterization, and kinetic modeling of biosurfactant synthesis by Pseudomonas aeruginosa gi |KP 163922|: a mechanism perspective.

Kinetic studies and modeling of production parameters are essential for developing economical biosurfactant production processes. This study will provide a perspective on mechanistic reaction pathways to metabolize Waste Engine Oil (WEO). The results will provide relevant information on (i) WEO concentration above which growth inhibition occurs, (ii) chemical changes in WEO during biodegradation, and (iii) understanding of growth kinetics for the strain utilizing complex substrates. Laboratory scale experiments were conducted to study the kinetics and biodegradation potential of the strain Pseudomonas aeruginosa gi |KP 163922| over a range (0.5-8% (v/v)) of initial WEO concentration for 168h. The kinetic models, such as Monod, Powell, Edward, Luong, and Haldane, were evaluated by fitting the experimental results in respective model equations. An unprecedented characterization of the substrate before and after degradation is presented, along with biosurfactant characterization. The secretion of biosurfactant during the growth, validated by surface tension reduction (72.07 ± 1.14 to 29.32 ± 1.08 mN/m), facilitated the biodegradation of WEO to less harmful components. The strain showed an increase in maximum specific growth rate (µmax) from 0.0185 to 0.1415h-1 upto 49.92mg/L WEO concentration. Maximum WEO degradation was found to be ~ 94% gravimetrically. The Luong model (adj. R2 = 0.97) adapted the experimental data using a non-linear regression method. Biochemical, 1H NMR, and FTIR analysis of the produced biosurfactant revealed a mixture of mono- and di- rhamnolipid. The degradation compounds in WEO were identified using FTIR, 1H NMR, and GC-MS analysis to deduce the mechanism.

Mathematical modeling of bioethanol production from sweet sorghum juice under high gravity fermentation: Applicability of Monod-based, logistic, modified Gompertz and Weibull models

BackgroundMathematical modeling of a fermentation process is crucial in understanding and predicting dynamics of the process, which can be used in process improvement, design and control. The present study aimed to develop Monod-based kinetic models to describe cell growth, substrate consumption and ethanol production by Saccharomyces cerevisiae NP 01 under high gravity (HG) fermentation of sweet sorghum juice (SSJ). ResultsThe fermentation using an initial total sugar (TS) concentration of 240 g/L resulted in 113.3 g/L of ethanol production, with 90.9% TS consumption and a fermentation efficiency of 94.4%. Growth of the yeast in terms of specific growth rate was found to be inhibited at a threshold TS concentration of 65 g/L, and the maximum specific growth rate, Monod constant and inhibition constant were 0.45 1/h, 19.5 g/L and 0.002 L/(g·h), respectively. Monod-based models incorporating substrate and product inhibition terms showed high applicability to describe the changes of cell, TS and ethanol concentrations, based on the values of bias factor, accuracy factor, coefficient of determination and root mean square error. ConclusionsThe Monod-based models fitted the data equally well as compared with the logistic, modified Gompertz, and Weibull models, despite estimating the value of different kinetic parameters. These results demonstrated that all the models tested were applicable in modeling HG ethanol fermentation.How to cite: Salakkam A, Phukoetphim N, Laopaiboon P, et al. Mathematical modeling of bioethanol production from sweet sorghum juice under high gravity fermentation: Applicability of Monod-based, logistic, modified Gompertz and Weibull models. Electron J Biotechnol 2023;64. https://doi.org/10.1016/j.ejbt.2023.03.004.

Fermentation Kinetics of Gluten-Free Breads: The Effect of Carob Fraction and Water Content.

In this study, gluten-free doughs with rice flour, substituted by 15% fractions of different carob seed flours, were prepared by varying their water content. The coarse carob fraction A (median particle size of flour, D50: 258.55 μm) was rich in fibers, fraction B (D50: 174.73 μm) was rich in protein, C (D50: 126.37 μm) was rich in germ protein, and fraction D (D50: 80.36 μm) was a mix, reconstituted from the other fractions and pulverized using a jet mill. Τhe experimental data of the dough's volume over time were fitted to the Gompertz model for each carob fraction and water content. The calculated parameters of the model were the maximum relative volume expansion ratio (a), the maximum specific volume growth rate (μ), and the time lag of the leavening process (tlag). Gompertz's equation adequately described the individual experimental curves. In the next step, a composite model was applied for each carob fraction where the parameters a and tlag were expressed as quadratic functions of water content levels (W), while μ was linearly dependent on W. Each carob fraction presented an optimum water content level for which dough height was maximized and time lag was minimized. Optimized dough volume could be predicted by the composite model; it was shifted to lower values as finer carob flour was used. In respect to baked products, softer breads were produced using finer carob flour and porosity values were higher at optimum water content levels. The investigated fermentation kinetics' models provide significant information about the role of water and carob flour on gluten-free dough development and bread volume expansion.

Strain Screening and Conditions Optimization in Microalgae-Based Monosodium Glutamate Wastewater (MSGW) Treatment

The wastewater generated from monosodium glutamate production displays distinctive features of elevated salinity, organic content, as well as nitrogen and phosphorus concentrations, and its indiscriminate disposal poses a significant threat to water quality and can cause detrimental impacts on aquatic ecosystems. The application of microalgae for monosodium glutamate wastewater (MSGW) treatment can result in simultaneous wastewater purification and biomass recovery. In this study, the algae species capable of thriving in diluted MSGW were screened, and the wastewater composition and growth conditions were optimized to obtain high algal biomass and nutrient removal rate. Among the tested species, Chlorella sp. FACHB-30 demonstrated superior potential for MSGW treatment and achieved a maximum specific growth rate of 0.28 d−1 and the highest COD removal rate of 61.50% over a 20-day cultivation period with trace metals supplementation in the wastewater. Moreover, the cultivation of Chlorella sp. FACHB-30 yielded considerable reductions in total phosphate (69.09%), total nitrogen (26.93%), and NH4+-N (51.91%) levels in the wastewater. The optimum conditions for achieving maximum algal density and highest nutrient removal were determined as light intensity of 150 μmol m−2s−1, inoculation concentration of 1 × 105 cells mL−1, and an iron concentration of 10−5 mol L−1. Finally, under the optimized conditions, the removal rates of total phosphate, total nitrogen, NH4+-N, and COD were determined to be 87.60%, 68.05%, 75.89%, and 77.96%, respectively. The findings of this study highlight the potential for enhancing the nutrient removal efficiency of microalgae-based MSGW treatment through the implementation of a combined approach that involves the selection of tolerant strains, optimization of cultivation conditions, and refinement of wastewater composition.

Medium composition and aeration to high (R,R)-2,3-butanediol and acetoin production by Paenibacillus polymyxa in fed-batch mode.

Concerning the potential application of the optically active isomer (R,R)-2,3-butanediol, and its production by a non-pathogenic bacterium Paenibacillus polymyxa ATCC 842, the present study evaluated the use of a commercial crude yeast extract Nucel®, as an organic nitrogen and vitamin source, at different medium composition and two airflows (0.2 or 0.5 vvm). The medium formulated (M4) with crude yeast extract carried out with the airflow of 0.2 vvm (experiment R6) allowed for a reduction in the cultivation time and kept the dissolved oxygen values at low levels until the total glucose consumption. Thus, the experiment R6 led to a fermentation yield of 41% superior when compared to the standard medium (experiment R1), which was conducted at airflow of 0.5 vvm. The maximum specific growth rate at R6 (0.42h-1) was lower than R1 (0.60h-1), however, the final cell concentration was not affected. Moreover, this condition (medium formulated-M4 and low airflow-0.2 vvm) was a great alternative to produce (R,R)-2,3-BD at fed-batch mode, resulting in 30g.L-1 of the isomer at 24h of cultivation, representing the main product in the broth (77%) and with a fermentation yield of 80%. These results showed that both medium composition and oxygen supply have an important role to produce 2,3-BD by P. polymyxa.

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.

Inverse problems for a model of biofilm growth

Abstract A bacterial biofilm is an aggregate of micro-organisms growing fixed onto a solid surface, rather than floating freely in a liquid. Biofilms play a major role in various practical situations such as surgical infections and water treatment. We consider a non-linear partial differential equation (PDE) model of biofilm growth subject to initial and Dirichlet boundary conditions, and the inverse coefficient problem of recovering the unknown parameters in the model from extra measurements of quantities related to the biofilm and substrate. By addressing and analysing this inverse problem, we provide reliable and robust reconstructions of the primary physical quantities of interest represented by the diffusion coefficients of substrate and biofilm, the biomass spreading parameters, the maximum specific consumption and growth rates, the biofilm decay rate and the half saturation constant. We give particular attention to the constant coefficients involved in the leading-part non-linearity, and present a uniqueness proof and some numerical results. In the course of the numerical investigation, we have identified extra data information that enables improving the reconstruction of the eight-parameter set of physical quantities associated to the model of biofilm growth.

The best location for the application of static magnetic fields based on biokinetic coefficients in complete-mix activated sludge process

The use of the kinetic coefficients for the mathematical expression of the biochemical processes and the relationship between the effective parameters is importance. Change of the biokinetic coefficients in the complete-mix activated sludge processes were calculated for 1 month operation of the activated sludge model (ASM) in a Lab-scale in three series. 15 mT intensity of static magnetic fields (SMFs) applied on the aeration reactor (ASM 1), clarifier reactor (ASM 2) and, sludge returning systems (ASM 3) for 1 h, daily. During the operation of the systems, five basic biokinetic coefficients such as maximum specific substrate utilization rate (k), heterotrophic half-saturation substrate concentration (Ks), decay coefficient (kd), yield coefficient (Y) and, maximum specific microbial growth rate (μmax) were determined. The rate of k (g COD/g Cells.d) in ASM 1 was 2.69% and, 22.79% higher than ASM 2 and, ASM 3. The value of Ks (mg COD/L) was 54.44 and, 71.13 (mg/L) lower than the ASM 2 and, ASM 3. The rate of kd ASM 1, ASM 2 and, ASM 3 was 0.070, 0.054 and, 0.516 (d−1). The value of Y (kg VSS/kg COD) in ASM 1 was 0.58% and, 0.48% lower than ASM 2 and, ASM 3. The rate of μmax (d−1) in ASM 1 was 0.197, this value for ASM 2 and ASM 3 were 0.324 and 0.309 (d−1). Related to the biokinetic coefficients analyses the best location for the application of 15 mT SMFs was the aeration reactor, where the present of oxygen, substrate and, SMFs have the greatest impact on the positive changes of these coefficients.

Yield and production cost of Chlorella sp. culture in a Fibonacci-type photobioreactor

In this research work, the performance of a Fibonacci-type photobioreactor scaled to 2500L to produce Chlorella sp. .is presented. The results show that this photobioreactor design kept the Chlorella culture at its optimal temperature, pH and dissolved oxygen levels. Despite the fact of being a closed reactor, the temperature was kept below 30 °C while the dissolved oxygen was maintained below 200 % Sat. under outdoor conditions at which the mean daily solar radiation ranged from 139 to 450 µE/m2s. Under these conditions, a maximum specific growth rate of 0.31 day−1, a biomass concentration of 1.9 g/L, and volumetric biomass productivity of 0.37 g/L day were achieved. The Fibonacci-type tubular photobioreactor presented here offers substantial advances compared to classic tubular photobioreactors, as it has proven to be flexible in its geometric design and it can adapt its parameters to the photosynthetic needs of the microalgae to ensure maximum efficiency, thus making it an alternative to conventional tubular systems. In addition, it is feasible to consider industrial production, since its costs have been estimated as 27.4 €/kg, at an annual production scale of 37 tons.

SYNERGISTIC EFFECTS OF NITROGEN DEPRIVATION AND HIGH IRRADIANCE TO ENHANCE BIOMASS AND LIPID PRODUCTION IN NANNOCHLOROPSIS

Nannochloropsis, due to its high lipid content, small size and growth rate, can be exploited for the production of biofuel and other value-added products. This study analyzed synergistic responses of high irradiance and nitrogen deprivation on Nannochloropsis cells to enhance biomass and lipid production. The growth of Nannochloropsis was first optimized under different irradiance 50, 100, 150, 200 and 250 μmol photons m-2 s-1. The maximum specific growth rate (0.25 day-1) and dry weight (0.67 g L-1) were obtained (p&lt;0.05) at photosynthetically active radiation (PAR) of 200 µmol photons m-2 s-1, further increase in light intensity decreased the growth rate and dry weight up to 0.2 day-1 and 0.41g L-1, respectively. The stress of high light for a short period increased the lipid content by 51.1% and decreased the protein content by 35.2% over the control values. In the second phase of the study, the combined stress of high light intensity of 200 µmol photons m-2 s-1 PAR and nitrate depletion (50%, 75%, 100% N-) were studied and observed significant (p&lt;0.05) increase in lipid content from 21.3±1.4% to 43.2±1.56% DCW and decrease in protein from 30.7±1.3% to 16.3±1.2% DCW, respectively. The highest lipid productivity (140 mg L-1 d-1) had been observed in a culture grown at 75% N- starved cells (p&lt;0.05). However, the further increase of nitrate deprivation to 100% decreased the lipid productivity to 107 mg L-1 d-1. Maximum accumulations of TG (19.6% DCW) were observed on 6 days (early stationary phase) in a 100% nitrogen deprived medium, although significant accumulation was observed on 4 days and 6 days of nitrate reduction.

Aerobic biodegradation of trichloromethane by Stenotrophomonas sp. GYH and its biodegradation mechanism analysis

A new strain, Stenotrophomonas maltophilia GYH, used trichloromethane (TCM) as the only carbon source for its growth was isolated. This strain was the first reported bacterium with TCM aerobic degradation ability. The initial TCM concentration of 8.93 mg·L-1 resulted in a degradation efficiency of 100% and a mineralization efficiency of 52% under the role of the strain. Based on the carbon balance and chlorine balance, the strain GYH could convert about 40 μg organic C contained by TCM to 20.4 μg inorganic C and 19.4 μg C by biomass, along with the complete dechlorination of TCM in 84 h. The maximum specific growth and biodegradation rates were 0.078 and 0.018 h-1, respectively. Two TCM-degrading genes were cloned and successfully expressed in the constructed strains, with 66.45% and 23.61% dechlorination efficiency. In combination with gas and ion chromatography detection and genetic analysis, an aerobic biodegradation pathway of TCM was proposed. TCM was finally converted to CO2, Cl-, and biomass under the aerobic degradation of the GYH. Such results supply fundamental knowledge for future research to effectively explain the molecular mechanism of TCM aerobic biodegradation and expand the potential industrial application of TCM biodegradation in polluted environments.

Modeling the Growth of Six Listeria monocytogenes Strains in Smoked Salmon Pâté

In this study, the growth of six L. monocytogenes strains isolated from different fish products was quantified and modeled in smoked salmon pâté at a temperature ranging from 2 to 20 °C. The experimental data obtained for each strain was fitted to the primary growth model of Baranyi and Roberts to estimate the following kinetic parameters: lag phase (λ), maximum specific growth rate (μmax), and maximum cell density (Nmax). Then, the effect of storage temperature on the obtained μmax values was modeled by the Ratkowsky secondary model. In general, the six L. monocytogenes strains showed rapid growth in salmon pâté at all storage temperatures, with a relatively short lag phase λ, even at 2 °C. The growth behavior among the tested strains was similar at the same storage temperature, although significant differences were found for the parameters λ and μmax. Besides, the growth variations among the strains did not follow a regular pattern. The estimated secondary model parameter Tmin ranged from -4.25 to -3.19 °C. This study provides accurate predictive models for the growth of L. monocytogenes in fish pâtés that can be used in shelf life and microbial risk assessment studies. In addition, the models generated in this work can be implemented in predictive modeling tools and repositories that can be reliably and easily used by the fish industry and end-users to establish measures aimed at controlling the growth of L. monocytogenes in fish-based pâtés.

Bio-augmentation effect of Achromobacter sp. strain JWJ-09 on quinoline and real coking wastewater under methanol co-metabolism

Quinoline is a refractory substance found in industrial wastewater. The biodegradation of quinoline by the novel Achromobacter sp. strain JWJ-09 in an inorganic salt medium was investigated over a wide range of initial quinoline concentrations (100–700 mg·l−1), with methanol as the co-metabolic substrate. Nearly complete degradation of 300 mg·l−1 quinoline was achieved at 32 h accompanied by bacterial growth when 100 mg·l−1 methanol was added to the quinoline-containing solution. Strain JWJ-09 showed strong quinoline degradability. Quinoline degradation was demonstrated through the 8-hydroxycoumarin metabolic pathway. The cell growth kinetics was evaluated by using the Haldane model. Both the maximum specific growth rate (μmax = 0.67 h−1) and the substrate inhibition coefficient (Ki = 795.02 mg·l−1) were higher than those observed by other researchers. This indicated that strain JWJ-09 grew faster and could tolerate higher quinoline concentrations. Furthermore, under methanol co-metabolizing, strain JWJ-09 together with the activated sludge was used to treat the real coking wastewater, quinolone could be degraded in only 24 h and TOC (total organic carbon) removal efficiency reached 90.75 %. High-throughput sequencing analysis showed that the biological enhancement effect of strain JWJ-09 and methanol was obvious, which could increase the abundance of the dominant bacteria in the activated sludge. The results confirmed that strain JWJ-09 could be used to treat the quinoline-containing wastewater.