Biodegradation of catechol by free and immobilized cells of Achromobacter xylosoxidans strain 15DKVB isolated from paper and pulp industrial effluents

Optimized phenol degradation and lipid production by Rhodosporidium toruloides using response surface methodology and genetic algorithm-optimized artificial neural network

Oleaginous yeast can produce lipids while degrading phenol in wastewater treatment. In this study, a Plackett-Burman Design (PBD) was adopted to identify key factors of phenol degradation and lipid production using R toruloides 9564T. While temperature, inoculum size, and agitation were significant for both the processes (p < 0.05), pH and incubation were significant for lipid production, and phenol removal, respectively. Results from four factors (pH, temperature, inoculum size, and incubation period) central composite design (CCD) experiment were used to formulate quadratic and genetic algorithm-optimized ANN models. The reduced quadratic model for phenol degradation (R2: 0.993) and lipid production (R2: 0.958) were marginally inferior to ANN models (R2: 0.999, 0.982, respectively) on training sets. Multi-objective optimization with equal importance suggests phenol degradation between 106.4 and 108.76%, and lipid production of 0.864-0.903 g/L, by polynomial and ANN models. Complete phenol degradation (100%) and 3.35-fold increment (0.918 g/L) in lipid production were obtained at pH 6.07, inoculum size 14.68% v/v, at 29.5 °C in 92.17 h experimentally.

Kinetics of dye decolorization using heterogeneous catalytic system with immobilized Achromobacter xylosoxidans DDB6

Textile effluents containing toxic dyes must be treated effectively before discharge to prevent adverse environmental impacts. Traditional physical and chemical treatment methods are costly and generate secondary pollutants. In contrast, biological treatment is a more suitable, clean, versatile, eco-friendly, and cost-effective technique for treating textile effluent. It is well established that indigenous microbial populations present in effluents can effectively degrade toxic dyes. In this regard, Achromobacter xylosoxidans DDB6 was isolated from the effluent sample to decolorize crystal violet (CV), Coomassie brilliant blue (CBB), and alizarin red (AR) by 67.20%, 28.58%, and 20.41%, respectively. The growth parameters of A. xylosoxidans DDB6 in media supplemented with 100 ppm of various dyes were determined using the modified Gompertz growth model. The immobilized cells in calcium alginate beads showed apparent decolorization rate constant of 0.27, 0.18, and 0.13 h-1 for CV, CBB, and AR, respectively. The immobilized cells in a packed bed reactor with an optimum flow rate of 0.5 mL/min were used to treat 100 ppm of CV with a percentage decolorization of 79.47% after three cycles. Based on the findings, A. xylosoxidans DDB6 could be effectively used for decolorization of various dyes.

Genome-wide identification of resistance genes and response mechanism analysis of key gene knockout strain to catechol in Saccharomyces cerevisiae

Engineering Saccharomyces cerevisiae for biodegradation and transformation of industrial toxic substances such as catechol (CA) has received widespread attention, but the low tolerance of S. cerevisiae to CA has limited its development. The exploration and modification of genes or pathways related to CA tolerance in S. cerevisiae is an effective way to further improve the utilization efficiency of CA. This study identified 36 genes associated with CA tolerance in S. cerevisiae through genome-wide identification and bioinformatics analysis and the ERG6 knockout strain (ERG6Δ) is the most sensitive to CA. Based on the omics analysis of ERG6Δ under CA stress, it was found that ERG6 knockout affects pathways such as intrinsic component of membrane and pentose phosphate pathway. In addition, the study revealed that 29 genes related to the cell wall-membrane system were up-regulated by more than twice, NADPH and NADP+ were increased by 2.48 and 4.41 times respectively, and spermidine and spermine were increased by 2.85 and 2.14 times, respectively, in ERG6Δ. Overall, the response of cell wall-membrane system, the accumulation of spermidine and NADPH, as well as the increased levels of metabolites in pentose phosphate pathway are important findings in improving the CA resistance. This study provides a theoretical basis for improving the tolerance of strains to CA and reducing the damage caused by CA to the ecological environment and human health.

A critical review on environmental risk and toxic hazards of refractory pollutants discharged in chlorolignin waste of pulp and paper mills and their remediation approaches for environmental safety

Agro-based pulp and paper mills (PPMs) inevitably produce numerous refractory pollutants in their wastewater, including chlorolignin, chlorophenols, chlorocatechols, chloroguaiacol, cyanide, furan, dioxins, and other organic compounds, as well as various heavy metals, such as nickel (Ni), zinc (Zn), chromium (Cr), iron (Fe), lead (Pb), arsenic (As), etc. These pollutants pose significant threats to aquatic and terrestrial life due to their cytogenotoxicity, mutagenicity, impact on sexual organs, hormonal interference, endocrine disruption, and allergenic response. Consequently, it is crucial to reclaim pulp paper mill wastewater (PPMW) with high loads of refractory pollutants through effective and environmentally sustainable practices to minimize the presence of these chemicals and ensure environmental safety. However, there is currently no comprehensive published review providing up-to-date knowledge on the fate of refractory pollutants from PPMW in soil and aquatic environments, along with valuable insights into the associated health hazards and remediation methods. This critical review aims to shed light on the potential adverse effects of refractory pollutants from PPMW on natural ecosystems and living organisms. It explores existing effective treatment technologies for remediating these pollutants from wastewater, highlighting the advantages and disadvantages of each approach, all in pursuit of environmental safety. Special emphasis is placed on emerging technologies used to decontaminate wastewater discharged from PPMs, ensuring the preservation of the environment. Additionally, this review addresses the major challenges and proposes future research directions for the proper disposal of PPMW. It serves as a comprehensive source of knowledge on the environmental toxicity and risks associated with refractory pollutants in PPMW, making it a valuable reference for policymakers and researchers when selecting appropriate technologies for remediation. The scientific community, concerned with mitigating the widespread risks posed by refractory pollutants from PPMs, is expected to take a keen interest in this review.

Genomic Analysis and Stability Evaluation of the Phenol-Degrading Bacterium Acinetobacter sp. DW-1 During Water Treatment

Phenol is a toxic organic molecule that is widely detected in the natural environment, even in drinking water sources. Biological methods were considered to be a good tool for phenol removal, especially microbial immobilized technology. However, research on the “seed” bacteria along with microbial community analysis in oligotrophic environment such as drinking water system has not been addressed. In this study, Acinetobacter sp. DW-1 with high phenol degradation ability had been isolated from a drinking water biofilter was used as seeded bacteria to treat phenol micro-polluted drinking water source. Meanwhile, the whole genome of strain DW-1 was sequenced using nanopore technology. The genomic analysis suggests that Acinetobacter sp. DW-1 could utilize phenol via the β-ketoadipate pathway, including the catechol and protocatechuate branches. Subsequently, a bio-enhanced polyhedral hollow polypropylene sphere (BEPHPS) filter was constructed to investigate the stability of the seeded bacteria during the water treatment process. The denatured gradient gel electrophoresis (DGGE) profile and the quantification of phenol hydroxylase gene results indicate that when the BEPHPS filter was operated for 56 days, Acinetobacter sp. was still a persistent and competitive bacterium in the treatment group. In addition, 16S rRNA gene amplicon sequencing results indicate that Acinetobacter sp., as well as Pseudomonas sp., Nitrospira sp., Rubrivivax sp. were the predominant bacteria in the treatment group, which were different from that in the CK group. This study provides a better understanding of the mechanisms of phenol degradation by Acinetobacter sp. DW-1 at the gene level, and provides new insights into the stability of seeded bacteria and its effects on microbial ecology during drinking water treatment.

Impact of electrical stimulation modes on the degradation of refractory phenolics and the analysis of microbial communities in an anaerobic-aerobic-coupled upflow bioelectrochemical reactor

An electrically stimulated anaerobic-aerobic coupled system was developed to improve the biodegradation of refractory phenolics. Expected 4-nitrophenol, 2, 4-dinitrophenol, and COD removals in the system with aerobic cathodic and anaerobic anodic chambers were approximately 53.7%, 45.4%, 22.3% (intermittent mode) and 37.9%, 19.8%, 17.3% (continuous mode) higher than that in the control system (26.0 ± 6.4%, 30.7 ± 7.1%, 49.8 ± 3.0%). 2, 4-dichlorophenol removal in the system with aerobic anodic and anaerobic cathodic chambers was approximately 28.5% higher than that in the control system (71.4 ± 5.7%). The contribution of the aerobic cathodic/anodic chambers to the removal of phenolic compounds was higher than that of the anaerobic cathodic/anodic chambers. The species related to phenolic biodegradation (Rhodococcus, Achromobacter, PSB-M-3, and Sphingobium) were enriched in the cathodic and anodic chambers of the system. These results showed that intermittent electrical stimulation could be a potential alternative for the efficient degradation of refractory phenolics.

Bioengineered Graphene Oxide Microcomposites Containing Metabolically Versatile Paracoccus sp. MKU1 for Enhanced Catechol Degradation

Paracoccus sp. MKU1, a metabolically versatile bacterium that encompasses diverse metabolic pathways in its genome for the degradation of aromatic compounds, was investigated for catechol bioremediation here for the first time to our knowledge. Paracoccus sp. MKU1 degraded catechol at an optimal pH of 7.5 and a temperature of 37 °C, wherein 100 mg/L catechol was completely mineralized in 96 h but required 192 h for complete mineralization of 500 mg/L catechol. While investigating the molecular mechanisms of its degradation potential, it was unveiled that Paracoccus sp. MKU1 employed both the ortho and meta pathways by inducing the expression of catechol 1,2-dioxygenase (C12O) and catechol 2,3-dioxygenase (C23O), respectively. C23O expression at transcriptional levels was significantly more abundant than C12O, which indicated that catechol degradation was primarily mediated by extradiol cleavage by MKU1. Furthermore, poly(MAA-co-BMA)-GO (PGO) microcomposites containing Paracoccus sp. MKU1 were synthesized, which degraded catechol (100 mg/L) completely within 48 h with excellent recycling performance for three cycles. Thus, PGO@Paracoccus microcomposites proved to be efficient in catechol degradation at not only faster rates but also with excellent recycling performances than free cells. These findings accomplish that Paracoccus sp. MKU1 could serve as a potential tool for bioremediation of catechol-polluted industrial wastewater and soil.

Immobilization of Rhodopseudomonas palustris P1 on glass pumice to improve the removal of NH4 + -N and NO2 - -N from aquaculture pond water

We conducted this research in order to investigate the potential of a new material called glass pumice for use as a microorganism immobilization carrier to improve aquaculture pond water quality. The pH adjustment capacity and the Rhodopseudomonas palustris P1 cell adsorption capacity of glass pumice were measured. The immobilized Rps. palustris P1 and the free sample were compared to determine which had an enhanced NH₄ ⁺ -N and NO₂ ^- -N removal efficiency. The results showed that glass pumice significantly affected the pH of the acid solution (P < 0.05); the pH increased from 3.0 ± 0.08 to 7.21 ± 0.13 in 12 H. Rps. palustris P1 adsorption to glass pumice was rapid and reached equilibrium within 60 Min. The Langmuir adsorption parameter data showed that glass pumice had a higher affinity for Rps. palustris P1 than SiO₂ powder, with an adsorption capacity of 4.02 × 10⁸  cells g^-1 . The maximum NH₄ ⁺ -N and NO₂ ^- -N removal rates by immobilized Rps. palustris P1 were 134.82 ± 0.67% and 93.68 ± 0.14% higher than those of nonimmobilized P1, respectively. Based on the above results, we propose that glass pumice is potential as a microorganism carrier material in aquaculture water treatment.

Performance and kinetics of triclocarban removal by entrapped Pseudomonas fluorescens strain MC46

This study investigated removal of triclocarban (TCC) from contaminated wastewater by Pseudomonas fluorescens strain MC46 entrapped in barium alginate. Appropriate entrapped cell preparation conditions (cell-to-entrapment material ratio and cell loading) for removing TCC were examined. The highest TCC removal by the entrapped and free cell systems at the initial TCC concentration of 10 mg/L was 72 and 45%, respectively. TCC was degraded to less toxic compounds. Self-substrate inhibition was found at TCC concentration of 30 mg/L. The kinetics of TCC removal by entrapped and free cells fitted well with Edwards model. Scanning and transmission electron microscopic observations revealed that entrapment matrices reduced TCC-microbe contact, which lessened TCC inhibition. A live/dead cell assay also confirmed reduced microbial cell damage in the entrapped cell system compared to the free cell system. This study reveals the potential of entrapment technology to improve antibiotic removal from the environment.

Assessment of pesticides removal using two-stage Integrated Aerobic Treatment Plant (IATP) by Bacillus sp. isolated from agricultural field

The biodegradation of synthetic wastewater containing Atrazine, Malathion and Parathion was studied in two stage Integrated Aerobic Treatment Plant using Bacillus sp. (consortia) isolated from agricultural field. The influent stream containing these pesticides with initial COD of 1232mg/L were fed to first reactor and treated effluent of first reactor was fed to second reactor. The maximum removal of pesticides in IATP was found to be greater than 90%. The various process parameters such as pH, DO, Redox potential and BOD₅/COD were monitored during the treatment. The degradation of pesticides and its metabolites in the treated effluent were confirmed by GC-MS. Kinetic parameters such as first order rate constant (K_obs), cell yield (Y_X/C) and decay coefficients (K_dp) were evaluated and found to be 0.00425 per hr, 0.696mg of COD/mg MLSS and 0.0010 per hr respectively. This integrated process was found more effective than physico-chemical treatment of pesticides.