Substrate interactions and kinetics study of phenolic compounds biodegradation by Pseudomonas sp. cbp1-3

An alternative approach to biokinetic modelling for phenol pollutant degradation and microbial growth using Genetic Programming

Biokinetic models can optimise pollutant degradation and enhance microbial growth processes, aiding to protect ecosystem protection. Traditional biokinetic approaches (such as Monod, Haldane, etc.) can be challenging, as they require detailed knowledge of the organism's metabolism and the ability to solve numerous kinetic differential equations based on the principles of micro, molecular biology and biochemistry (first engineering principles) which can lead to discrepancies between predicted and actual degradation rates. More recently, data-driven machine-learning techniques have emerged as a promising alternative for modelling microbial systems. A few machine learning models (such as ANN, SVM, RF, DT, XG BOOST, etc.) have been used recently for modelling phenol degradation, but they lack the robustness of generating mathematical models. This gap is addressed in this study using Genetic Programming (GP) as the modelling approach for modelling the phenol degradation. This study utilises the microalgae Acutodesmus Obliquus, finding that phenol degradation of 98% required 216 hours. Both the traditional kinetic approach and the Genetic Programming (GP) approach were used to determine the specific growth rate (µmax) and saturation constant (Ks). It is noted that without any a priori information on the form of the mathematical mode, GP can evolve a model which closely fits the Monod kinetics, thus demonstrating that data-driven models can bring out the first engineering principles on which biokinetic models are dependent or framed in a most swift and effective way. Performance was assessed using root mean square error (RMSE) and correlation coefficient (R), with the GP model showing superior predictive accuracy.

Phenol Degradation Performance in Batch and Continuous Reactors with Immobilized Cells of Pseudomonas putida

Phenol is a highly persistent environmental pollutant and is toxic to living organisms. The main objective of this study is to observe the phenol degradation performance by free and immobilized Pseudomonas putida (P. putida) in batch and continuous reactors, respectively. Batch experiments were evaluated to determine the maximum specific growth rate, saturation constant, inhibition constant, and cell yield. These kinetic parameters were used as the input values for the continuous-flow immobilized cells model. The immobilized cells model was validated by experimental results obtained from an immobilized cells continuous reactor. The model-predicted and experimental results showed good agreement for phenol effluent concentration in the continuous mode. In the steady-state condition, high phenol removal was achieved under various hydraulic retention times. The corresponding removal of phenol ranged from 93.3 to 95.9%, while the hydraulic retention times were maintained at 3.1–10.5 h. Furthermore, polyvinyl alcohol-immobilized cells with nanoscale particles were also prepared. The polyvinyl alcohol-immobilized P. putida cells with nanoscale Fe3O4 enhanced the ability of phenol degradation. The experimental results revealed that immobilized cells with nano-Fe3O4 had the highest phenol degradation performance at a low salinity of 1%. However, the advantage of the addition of nano-Fe3O4 was insignificant for phenol degradation at a higher salinity of 5%. The approaches of the batch and continuous column tests were practical in the treatment of actual phenol-containing wastewater.

Stability Analysis of a Chemostat Model for Phenol and Sodium Salicylate Mixture Biodegradation

In this paper we consider a mathematical continuous-time model for biodegradation of phenol in the presence of sodium salicylate in a chemostat. The model is described by a system of three nonlinear ordinary differential equations. Based on the dynamical systems theory we provide mathematical investigations of the model including local and global analysis of the solutions. The local analysis consist in computation of two equilibrium points—one interior and one boundary (washout) equilibrium—in dependance of the dilution rate as a key model parameter. The local asymptotic stability of the equilibria is also presented. The global analysis of the model solutions comprises proving existence, uniqueness and uniform boundedness of positive solutions, as well as global asymptotic stabilizability of the dynamics. The theoretical investigations are illustrated by some numerical examples. The results in this study can be used in practice as a tool to control and optimize the chemostat performance of simultaneous biodegradation of mixed substrates in wastewater.

Biodegradation Kinetics of Phenol and 4-Chlorophenol in the Presence of Sodium Salicylate in Batch and Chemostat Systems

The biodegradation of phenol, sodium salicylate (SA), and 4-chlorophenol (4-CP) by Pseudomonas putida (P. putida) was evaluated by batch and chemostat experiments in single and binary substrate systems. The Haldane kinetics model for cell growth was chosen to describe the batch kinetic behavior to determine kinetic parameters in the single or binary substrates system. In the single phenol and SA system, the kinetic constants of μm,P = 0.423 h−1, μm,A = 0.247 h−1, KS,P = 48.1 mg/L, KS,A = 71.7 mg/L, KI,P = 272.5 mg/L, and KI,A = 3178.2 mg/L were evaluated. Experimental results indicate that SA was degraded more rapidly by P. putida cells compared to phenol because SA has a much larger KI value than phenol, which makes the cells less sensitive to substrate inhibition even though the μm,P value is larger compared to μm,A. The ratio of inhibition of phenol degradation due to the presence of SA (IA1) to the inhibition of SA degradation due to the presence of phenol (IA2) is 2.3, indicating that SA has a higher uncompetitive inhibition on phenol biodegradation compared to that of phenol on SA biodegradation in the binary substrate system. In the ternary substrate system, the time required for the complete degradation of SA and phenol was 14 and 11.5 d and an approximately 90% removal efficiency for 4-CP was achieved within 14 d. In the chemostat system, the removal rates of phenol and SA were 96.6 and 97.0%, while those of SA and 4-CP were 91.4% and 95.2%, respectively. The model prediction agreed satisfactorily with the experimental results of the chemostat system.

Identification and Characterization of Peruvian Native Bacterial Strains as Bioremediation of Hg-Polluted Water and Soils Due to Artisanal and Small-Scale Gold Mining in the Secocha Annex, Arequipa

The water and soils pollution due to mercury emissions from mining industries represents a serious environmental problem and continuous risk to human health. Although many strategies have been designed for the recovery or elimination of this metal from environmental sources, microbial bioremediation has proven to be the most effective and environmentally friendly strategy and thus control heavy metal contamination. The main objective of this work, using native bacterial strains obtained from contaminated soils of the Peruvian region of Secocha, was to identify which of these strains would have growth capacity on mercury substrates to evaluate their adsorption behavior and mercury removal capacity. Through a DNA analysis (99.78% similarity) and atomic absorption spectrometry, the Gram-positive bacterium Zhihengliuella alba sp. T2.2 was identified as the strain with the highest mercury removal capacity from culture solutions with an initial mercury concentration of 162 mg·L−1. The removal capacity reached values close to 39.5% in a period of incubation time of 45 days, with maximum elimination efficiency in the first 48 h. These results are encouraging and show that this native strain may be the key to the bioremediation of water and soils contaminated with mercury.

Kinetics of Cometabolic Transformation of 4-chlorophenol and Phenol Degradation by Pseudomonas putida Cells in Batch and Biofilm Reactors

The biodegradation kinetics of 4-chlorophenol (4-CP) and phenol and microbial growth of Pseudomonas putida (P. putida) cells were estimated in batch and biofilm reactors. The kinetic parameters of cells on phenol were determined using the Haldane formula. The maximum specific growth rate of P. putida on phenol, the half-saturation constant of phenol and the self-inhibition constant of phenol were 0.512 h−1, 78.38 mg/L and 228.5 mg/L, respectively. The yield growth of cells on phenol (YP) was 0.618 mg phenol/mg cell. The batch experimental results for the specific transformation rate of 4-CP by resting P. putida cells were fitted with Haldane kinetics to evaluate the maximum specific utilization rate of 4-CP, half-saturation constant of 4-CP, and self-inhibition constant of 4-CP, which were 0.246 h−1, 1.048 mg/L and 53.40 mg/L, respectively. The negative specific growth rates of cells on 4-CP obtained were fitted using a kinetic equation to investigate the true transformation capacity and first-order endogenous decay coefficient, which were 4.34 mg 4-CP/mg cell and 5.99 × 10−3 h−1, respectively. The competitive inhibition coefficients of phenol to 4-CP transformation and 4-CP to phenol degradation were 6.75 and 9.27 mg/L, respectively; therefore, phenol had a higher competitive inhibition of 4-CP transformation than the converse. The predicted model examining cometabolic transformation of 4-CP and phenol degradation showed good agreement with the experimental observations. The removal efficiencies for phenol and 4-CP were 94.56–98.45% and 96.09–98.85%, respectively, for steady-state performance.

Anaerobic biodegradation of phenol in wastewater treatment: achievements and limits

Anaerobic biodegradation of toxic compounds found in industrial wastewater is an attractive solution allowing the recovery of energy and resources but it is still challenging due to the low kinetics making the anaerobic process not competitive against the aerobic one. In this review, we summarise the present state of knowledge on the anaerobic biodegradation process for phenol, a typical target compound employed in toxicity studies on industrial wastewater treatment. The objective of this article is to provide an overview on the microbiological and technological aspects of anaerobic phenol degradation and on the research needs to fill the gaps still hindering the diffusion of the anaerobic process. The first part is focused on the microbiology and extensively presents and characterises phenol-degrading bacteria and biodegradation pathways. In the second part, dedicated to process feasibility, anaerobic and aerobic biodegradation kinetics are analysed and compared, and strategies to enhance process performance, i.e. advanced technologies, bioaugmentation, and biostimulation, are critically analysed and discussed. The final section provides a summary of the research needs. Literature data analysis shows the feasibility of anaerobic phenol biodegradation at laboratory and pilot scale, but there is still a consistent gap between achieved aerobic and anaerobic performance. This is why current research demand is mainly related to the development and optimisation of powerful technologies and effective operation strategies able to enhance the competitiveness of the anaerobic process. Research efforts are strongly justified because the anaerobic process is a step forward to a more sustainable approach in wastewater treatment.Key points• Review of phenol-degraders bacteria and biodegradation pathways.• Anaerobic phenol biodegradation kinetics for metabolic and co-metabolic processes.• Microbial and technological strategies to enhance process performance.

Global Stability Analysis of a Bioreactor Model for Phenol and Cresol Mixture Degradation

We propose a mathematical model for phenol and p-cresol mixture degradation in a continuously stirred bioreactor. The model is described by three nonlinear ordinary differential equations. The novel idea in the model design is the biomass specific growth rate, known as sum kinetics with interaction parameters (SKIP) and involving inhibition effects. We determine the equilibrium points of the model and study their local asymptotic stability and bifurcations with respect to a practically important parameter. Existence and uniqueness of positive solutions are proved. Global stabilizability of the model dynamics towards equilibrium points is established. The dynamic behavior of the solutions is demonstrated on some numerical examples.

Experimental and kinetic study on the cometabolic biodegradation of phenol and 4-chlorophenol by psychrotrophic Pseudomonas putida LY1

This study investigated the kinetics of phenol and 4-chlorophenol (4-CP) biodegradation by a cold-adapted bacteria, Pseudomonas putida LY1, isolated from Songhua River sediment. The results showed that P. putida LY1 cannot grow on 4-CP as a sole carbon source. P. putida LY1 had the potential to cometabolic biodegrade phenol and 4-CP in a wide range of temperature (varying from 5 to 35 °C) with the optimal temperature around 25 °C. Mixture of phenol and 4-CP were completely removed at two 4-CP concentrations (15 and 40 mg/L) over a wide range of phenol (20-400 mg/L) concentrations, whereby the ratio of 4-CP/biomass (S 2/X) was lower than 0.03. The kinetic models of cometabolic biodegradation of phenol and 4-CP were proposed, considering the growth and nongrowth substrate inhibition. These models successfully simulate the processes of cometabolic degradation of phenol and 4-CP.