Biodegradation Experiments Research Articles

Microbial degradation of polyethylene polymer: current paradigms, challenges, and future innovations.

Polyethylene (PE) is the second most commonly used plastic worldwide, mainly used to produce single-use items such as bags and bottles. Its significant resistance to natural biodegradation results in the accumulation of PE in landfills, leading to various ecological and toxicological consequences. Despite extensive research on the microbial degradation of PE, achieving complete biodegradation remains a challenge. Comparing experimental outcomes is complicated by the diverse array of microbes involved in PE biodegradation, variations in culture conditions, and differences in assessment tools. This review discusses the critical hurdles in PE biodegradation experiments, including the chemical complexity of PE substrates and the challenges of isolating effective microbes and forming stable consortia. The review also delves into the difficulties in accurately assessing microbial metabolic activity and understanding the biochemical pathways involved in PE degradation. Furthermore, it addresses the pressing issues of metabolic byproducts, slow degradation rates, scalability concerns, and the challenges in measuring biodegradation levels effectively. In addition to outlining the technical challenges associated with PE experiments, this review offers recommendations for future research directions to enhance PE biodegradation outcomes. Overcoming these challenges and implementing the proposed future strategies will improve the reliability, comparability, and practicality of current PE biodegradation experiments, ultimately contributing to better comprehension and management of PE waste in the environment.

Biobased and biodegradable polyester amides based on nylon 6,6 and polybutylene adipate via straightforward bulk polymerization

Aliphatic polyesters are generally known for their limited thermal and mechanical properties, but are prone to biodegradation. On the other hand, aliphatic polyamides, mainly represented by nylons, feature high thermal transition points and enhanced mechanical strength, but are usually classified as nonbiodegradable. In this work, the properties of the aliphatic polyester polybutylene adipate and nylon 6,6 were combined by synthesizing polyester amides. Relatively low- and high-molecular weight series, Mn¯ 7000 and 14400 g/mol, respectively, were synthesized via a straightforward bulk polymerization process by utilizing biobased starting materials: butanediol, adipic acid and nylon 6,6 salt. The amide-to-ester ratio was varied to analyze the influence of the amide content on the molecular structure, thermal properties, mechanical properties, hydrophilicity and biodegradability. Strong relationships between the amide content and the Tg, Tm, degree of crystallinity, and mechanical properties were observed. Water contact angle measurements revealed that all the polyester amides were hydrophilic. Finally, the biodegradation experiments demonstrated that all polyester amides are prone to biodegradation in activated sludge and that the amide content had a major influence on the biodegradation rate. This work supports the high potential of biobased polyester amides for applications in numerous fields due to their versatility in terms of polymeric properties and sustainable character.

Biostimulation of a novel native Bacillus strain capable of degrading gasoline

The contamination of soil with hydrocarbons is a significant ecological issue worldwide, posing a threat to the ecosystem. Therefore, it is crucial to develop environmentally friendly and effective techniques to eliminate pollutants using biological agents. This study aimed to isolate, characterize, and evaluate bacteria capable of degrading gasoline. Soil samples contaminated with gasoline were collected and diluted up to 10-10. Pure cultures were obtained by streaking dilutions of 10-7, 10-6, and 10-5 on nutrient agar. These pure cultures were then inoculated on a selective medium (Bushnell Haas minerals agar). The isolates were characterized based on their growth patterns using morphological characteristics, optical density measurement, and biochemical tests. As a result, five gasoline-degrading bacteria were identified as B. mojavensis and B. licheniformis. Two biodegradation experiments were conducted using low and high concentrations of gasoline (0.01/10 and 0.001/10 mL, respectively) over a period of 14 days. Furthermore, the bacterial strains were stimulated by adding nitrogen and phosphorus to evaluate their efficiency in degrading gasoline. The results showed that B. mojavensis has the potential to degrade gasoline more effectively than the other isolate. Additionally, the addition of nitrogen minerals enhanced the ability of this isolate to degrade gasoline. Conversely, the performance of B. licheniformis in degrading gasoline was improved with the addition of nitrogen and phosphorus. This study demonstrates the effectiveness of Gram-positive bacteria in gasoline degradation and highlights the potential of the genus B. mojavensis for in situ remediation of gasoline-contaminated soils.

Phosphorus-nitrogen-containing flame-retardant plasticizers derived from L-lactic acid for poly (lactic acid) improved toughness, flame retardancy and crystallization

Designing highly-effective and environmentally friendly biobased flame-retardant plasticizers for polylactic acid (PLA) remains a formidable challenge. In this study, we synthesized four novel phosphorus-nitrogen-containing L-lactic acid-based flame-retardant plasticizers with adjustable chemical structures and phosphorus content, designated as NPDL-Cn, where ’n’ corresponds to the alkyl groups numbers in the alkylamine chain (with n = 4, 6, 8, and 10). Incorporating NPDL-Cn into the PLA matrix offered a twofold benefit, significantly enhancing both the flame retardancy and toughness of PLA. Remarkably, as incorporating 20 phr NPDL-Cn, the resulting blends all achieved UL-94 V-0 grade, and their limiting oxygen index reached about 30.8 %, 29.5 %, 28.3 % and 27.2 %, respectively. A comprehensive analysis of the volatile gases and char layer generated during combustion showed that the flame-retardant mechanism of NPDL-Cn in PLA significantly influenced both the condensed-phase and gas-phase behavior. Meanwhile, NPDL-Cn effectively overcame the brittleness and rigidity of PLA, thus realizing the enhancement of its toughness. In particular, as compared to a mere 3.7 % and 1.7 MJ/m3 for neat PLA, when the methylene numbers of NPDL-Cn were 4, the elongation at break and tensile toughness of the PLA/NPDL-C4 exhibited a substantial increase to 180.1 % and 43.4 MJ/m3, respectively, due to the best interfacial tension of NPDL-C4 with PLA matrix. Additionally, while the tensile strength of neat PLA is notably high at 50.7 MPa, the introduction of PLA/NPDL-C4 results in a significant decrease to 26.3 MPa. Interestingly, biodegradation experiments showed that NPDL-C4 was decomposed into non-toxic and harmless small molecules. This study presents a method for constructing toughened and flame-retardant PLA blends by modulating the alkyl chain length of flame-retardant plasticizers and elucidating their structure–property relationships.

ATR-FTIR characterisation of daily-use plastics mycodegradation

Synthetic polymers, such as plastics, have permeated all aspects of modern life, and nowadays plastic pollution is a major environmental problem. Mycodegradation of these polymers could represent part of the solution to this problem since it calls on a broad toolbox of enzymes and applies non-enzymatic mechanisms to degrade and deteriorate recalcitrant materials. However, not enough is known about this ability for most of the representatives of the fungal kingdom. Another bottleneck is the harmonisation of technologies to analyse plastic degradation. This work involved the design of a biodegradation experiment, where the potential of four fungi representative of Dikarya and Penicillia (Funalia floccosa, Trametes versicolor, Pycnoporus cinnabarinus and Penicillium oxalicum) were tested on their ability to deteriorate the six most used plastics based on gravimetry and attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR). The following correlation between changes in the band signals and the loss of mass after treatment was determined using polyethylene terephthalate, polypropylene, polyethylene, poly vinyl chloride, high density polyethylene, low density polyethylene and nylon. After treatment, the decrease in absorbance of the characteristic bands of the plastics was taken as an indication of the degradation of the corresponding bonds/functionalities. The four fungi used could transform CH, CH2, CH3, CO, CO, CN, NH and CCl bonds. The best result was obtained using the fungus F. floccosa with 90-day treatments for high density polyethylene (∼ 62.0 %), low density polyethylene (∼ 23.6 %) and nylon (∼ 35.6 %). Therefore, mycodegradation could open up new doors in the fight against plastic pollution.

Biodegradability of polyethylene: Challenges and future perspectives

Polyethylene (PE) is the second most abundant plastic worldwide due to its broad application in manufacturing disposable materials such as bags and bottles. Since it is highly resistant to natural biodegradation, it can accumulate in landfills, causing various ecological and toxicological consequences. Even though microbial degradation of PE has been extensively investigated, complete biodegradation of PE has yet to be achieved, and comparisons of PE biodegradation experiment findings are not practical. This may be due to the wide variety of PE substances used, and a wide variety of culture conditions, and many of the published findings still need key chemistry of PE materials, as well as basic biochemistry and microbiology. This review highlights the need for standardization in PE biodegradation studies and defining key biochemical terms. It aims to identify deficiencies and challenges in PE degradation experiments, enhancing future research for scientific and technological advancement. This review provides a biochemically based definition of PE biodegradation and summarizes microorganisms responsible for PE biodegradation. We also caution readers about the chemical makeup and structure of the PE, as well as the approaches utilized in microbes’ isolation. This review defines the fundamental elements required to conduct an effective PE biodegradation investigation.

Microbial Degradation of Polyester Microfibers Using Indigenously Isolated Bacterial Strain Exiguobacterium Sp.

ABSTRACTSynthetic microfibers are emerging environmental microplastic pollutants released from different industrial and domestic sources. The present investigation describes the isolation of potential bacterial strains from microplastic‐contaminated sites of Bhubaneswar city of Odisha, India. Four morphologically distinct bacterial strains were isolated using 2% polyethylene glycol (PEG) supplemented nutrient agar (NA) medium and were screened for their polymer tolerance ability by growing them on 2%–8% PEG. A single microorganism capable of growing on 8% PEG was selected for biodegradation experiment. Through 16S rRNA sequencing, the selected bacterial strain was identified as Exiguobacterium sp. with gene bank accession number ON318396. The microbial strain's microfiber biodegradation ability was assessed in a laboratory setting over a period of 28 ± 2 days, utilizing optimized conditions with an initial pH of 7, 2 mL inoculum volume, an incubation temperature of 30°C ± 2°C, and 150 rpm, using 2 g of polyester microfiber. In optimum conditions, the weight loss of the treated sample with the selected microbial strain was 19.2%. The polyester degradation was confirmed through scanning electron microscopic images viewing the degradation of the polyester microfiber surfaces. Variation in functional groups confirmed through Fourier transform infrared spectrophotometry. Detection of carbonyl (C═O) group stretching band at 1711 cm−1 through ATR‐FTIR analysis in the treated sample confirmed the polymer biodegradation. The potential isolate can efficiently degrade polyester and, in the future, can be employed as a promising solution for the sustainable treatment of synthetic microfiber pollution.

Overload of dissolved organic matter (DOM) in riparian infiltration zone increasing the pollution risk of naphthalene, insight from the competitive inhibition of naphthalene biodegradation by DOM.

Riparian infiltration zones are crucial for maintaining water quality by reducing the aqueous concentrations of polycyclic aromatic hydrocarbons (PAHs) through adsorption and biodegradation within the aquatic ecosystem. Dissolved organic matter (DOM) are ubiquitous in riparian infiltration zones where they extensively engage in the adsorption and biodegradation of PAHs, thereby influencing PAHs natural attenuation potential within riparian infiltration zones. Few studies have explored the natural attenuation mechanisms of PAHs influenced by DOM in riparian infiltration zones. In this study, the natural attenuation mechanisms of naphthalene (a typical PAHs component), under the influence of DOM, were explored, based on a case riverside source area. Analysis of microbial community structures, and the electron acceptor (e.g., Fe(III), DO/NO3-, SO42-)/electron donor (naphthalene and DOM) concentration changes within the riparian infiltration zone revealed a competitive inhibition relationship between DOM and naphthalene during microbial metabolism. Biodegradation experiments showed that when the concentration of DOM is higher than 4.0 mg·L-1, it inhibits the biodegradation of naphthalene. DOM competitively inhibits the biodegradation of naphthalene through the following mechanisms: (i) triggering microbial antioxidative defense mechanisms, diminishing the available resources for microbial participation in naphthalene degradation; (ii) altering microbial community structure; (iii) modulating microbial EPS composition, reducing the efficiency of microorganisms in utilizing carbon sources; and (iv) inhibiting the expression levels of downstream genes involved in naphthalene degradation. The competitive inhibition constants of DOM with concentrations of 1.0, 2.0, 4.0, 8.0, and 16.0 mg·L-1 on naphthalene biodegradation are -2.0 × 10-3, -5.0 × 10-3,1.0 × 10-3, 4.0 × 10-4, and 1.0 × 10-4, respectively. These findings enhance understanding of PAHs attenuation in riparian infiltration zone, providing a basis for assessing and managing PAHs pollution risks during riparian extraction.

Micro-wave induced pyrolysis of low density polyethylene (LDPE) and biodegradation of resulting wax in soil and by defined microbial consortia is closing the loop towards LDPE upcycling

Plastic has become essential in daily life, replacing traditional materials like glass and wood due to its flexibility, durability, strength, and cost-effectiveness. However, the global plastic production surged to nearly 400 million tons in 2020, causing significant environmental accumulation. Polyethylene (PE), a ubiquitous polymer, poses recycling challenges due to its stability and widespread use in layered products, contributing to long-term pollution. This study focuses on PE degradation challenges, advocating for integrated chemical and biological treatments. Chemical methods like pyrolysis show promise but aren't fully eco-friendly. Microwave-induced pyrolysis emerges as a viable alternative, offering faster, targeted heating with lower energy consumption. Using microwave-absorbent materials such as silicon carbide, this method efficiently breaks down even challenging low-density PE (LDPE), yielding wax products of 68–91 % yield, with reduced molecular weight suitable for further biological degradation. Biodegradation experiments demonstrated over 95 % degradation by defined microbial consortia and considerable degradation in soil without bioaugmentation. The Rhodococcus consortium showed exceptional potential, degrading 90 % of LDPE-wax as a carbon source within 28 days, particularly strain CHBE-144 achieving 98 % degradation in just 14 days. Genomic analysis revealed enzymes crucial for alkane and plastic breakdown, with strains capable of producing biosurfactants, suggesting up-cycling potential for PE-derived materials into value-added products. Integrating microwave-induced pyrolysis with microbial biodegradation offers a promising pathway for managing PE waste sustainably, potentially reducing environmental impact while creating valuable resources from plastic waste. Further research is warranted to optimize these processes and scale them for practical application in waste management and resource recovery efforts globally.

Determination of biodegradation performance for fabricated by MEW Chitosan/PCL composite stents with in vitro tests

Today, biodegradable implants have begun to become a serious alternative to permanent implant groups. Especially the development of polymer material technology can be an alternative to metallic medical instruments. An innovative manufacturing method for the fabricated of these polymeric implants is melt electrowriting (MEW). This innovative method, which emerged as a result of studies on the production quality of additive manufacturing technology, is used in products with smaller and more complex geometries, such as stents. It is anticipated that this method, which is particularly convenient for patient-specific implant models, will have an important place in the implant production market in the future. Within the framework of this perspective, in this study, a study was conducted on the polycarbolactone group using the MEW method. In order to improve the biodegradability character, biodegradability experiments of chitosan-doped stents were conducted in vitro. The degradation character of the samples subjected to immersion corrosion in two different media for 1, 7, 14 and 21 days was examined based on residual mass. It has been determined that chitosan reinforcement has a buffering effect and plays a retarding role on the degradation time.

A biodegradable multifunctional pectin–montmorillonite fertilizer coating: Controlled-release, water-retention and soil-cementation

Coated fertilizers have been widely used to improve fertility in barren land. However, improving soil structure and water-retention capacity is also essential for arid and semi-arid areas with sandy soils to promote crop growth. Most currently available coated fertilizers rarely meet these requirements, limiting their application scope. Therefore, this study “tailored” pectin–montmorillonite (PM) multifunctional coatings for arid areas, featuring intercalation reactions and nanoscale entanglement between pectin and montmorillonite via hydrogen bonding and electrostatic and van der Waals forces. Notably, PM coatings have demonstrated an effective “relay” model of action. First, the PM-50 coating could act as a “shield” to protect urea pills, increasing the mechanical strength (82.12 %). Second, this coating prolonged the release longevity of urea (<0.5 h to 15 days). Further, the remaining coating performed a water-retention function. Subsequently, the degraded coating improved the soil properties. Thus, this coating facilitated the growth of wheat seedlings in a simulated arid environment. Moreover, the cytotoxicity test, life cycle assessment, and soil biodegradation experiment showed that the PM coating exhibited minimal environmental impact. Overall, the “relay” model of PM coating overcomes the application limitations of traditional coated fertilizers and provides a sustainable strategy for developing coating materials in soil degradation areas.

Evaluation of Microbial Degradation of Thermoplastic and Thermosetting Polymers by Environmental Isolates

In this study, a microbial–enzymatic strategy was pursued to address the challenge of degrading thermoplastic and thermosetting polymers. Environmental microorganisms were isolated, and their enzymatic activities were assessed using colorimetric assays to evaluate their potential for producing enzymes capable of degrading these polymers. Microorganisms demonstrating higher positivity in the enzymatic assays were selected for a 30-day biodegradation experiment, in which epoxy resins, polyethylene terephthalate, or polystyrene served as the sole carbon source. The effectiveness of biodegradation was assessed through the ATR-FTIR analysis of the chemical composition and the SEM examination of surface characteristics before and after degradation. The results indicated that thermoplastic compounds were more susceptible to microbial degradation, exhibiting greater changes in absorbance. In particular, PET treated with Stenotrophomonas sp. showed the most significant efficacy, achieving a 60.18% reduction in the area under the curve with a standard error of ± 3.42 when analyzed by FTIR spectroscopy. Significant alterations in surface morphology were noticed in thermoplastic compounds. In contrast, thermosetting compounds demonstrated lower reactivity, as evidenced by the absence of band shifts in FTIR spectra and minor changes in bond absorbance and surface morphology.

The Ability of the Indigenous Bacteria Chromobacterium haemolyticum strain W15 to Degrade Chromium (Cr) and Lead (Pb) in Liquid Coal Waste

The use of coal as a raw material for power plants has a good economic impact, but it also has a detrimental environmental impact, particularly due to the presence of Cr and Pb, heavy metals with bioaccumulation and biomagnification qualities. Efforts to control Pb and Cr in liquid coal waste can be achieved by bioremediation. The goal of this study is to screen indigenous bacteria, identify, and test biodegradation on the best bacteria capable of degrading Cr and Pb. Bacterial screening is done experimentally in the lab. Bacterial identification is done using morphological, biochemical, and molecular genetic methods. Using atomic absorption spectroscopy to validate Cr and Pb biodegradation research. Biodegradation experiments revealed that the efficacy of indigenous bacteria reduced Pb by 216% (0.238 ppm to 0.11 ppm) and Cr by 195% (0.34 ppm to 0.174 ppm). The findings of biochemical, morphological, and molecular genetic studies revealed that the top bacterial strains were up to 96% related. using Chromobacterium haemolyticum strain W15. Chromobacterium haemolyticum strain X, an indigenous bacteria capable of degrading Cr and Pb, was successfully isolated from liquid waste.

Investigating functional mechanisms in the Co-biodegradation of lignite and guar gum under the influence of salinity

The biodegradation of guar gum by microorganisms sourced from coalbeds can result in low-temperature gel breaking, thereby reducing reservoir damage. However, limited attention has been given to the influence of salinity on the synergistic biodegradation of coal and guar gum. In this study, biodegradation experiments of guar gum and lignite were conducted under varying salinity conditions. The primary objective was to investigate the controlling effects and mechanisms of salinity on the synergistic biodegradation of lignite and guar gum. The findings revealed that salinity had an inhibitory effect on the biomethane production from the co-degradation of lignite and guar gum. The biomethane production declined with increasing salinity levels, decreasing from 120.9 mL to 47.3 mL. Even under 20 g/L salt stress conditions, bacteria in coalbeds could effectively break the gel and the viscosity decreased to levels below 5 mPa s. As salinity increased, the removal rate of soluble chemical oxygen demand (SCOD) decreased from 55.63% to 31.17%, and volatile fatty acids (VFAs) accumulated in the digestion system. High salt environment reduces the intensity of each fluorescence peak. Alterations in salinity led to changes in microbial community structure and diversity. Under salt stress, there was an increased relative abundance of Proteiniphilum and Methanobacterium, ensuring the continuity of anaerobic digestion. Hydrogentrophic methanogens exhibited higher salt tolerance compared to acetoclastic methanogens. These findings provide experimental evidence supporting the use of guar gum fracturing fluid in coalbeds with varying salinity levels.

Optimization of phenanthrene biodegradation process by isolated bacterial strain Rhodococcus sp. using response surface methodology

This research aimed to assess the biodegradation potential of phenanthrene in a simulated aqueous solution using an isolated bacterial strain, Rhodococcus sp., with the assistance of a Box-Behnken design matrix. To gauge the impact of key operational factors, pH (6.0 to 9.0), temperature (20 to 40°C), initial phenanthrene concentration (50 to 100 ppm) and incubation time (7 to 21 days), the Response Surface Methodology (RSM) was employed to design the biodegradation experiment. The experimental findings highlighted incubation time as the most influential variable followed by initial phenanthrene concentration, pH and temperature via Box-Behnken Design (BBD) matrix. To determine the maximum phenanthrene biodegradation, the Desirability Function Methodology (DFM) was applied. Within the designated parameter ranges, the highest phenanthrene biodegradation (70.0%) was observed at pH 7.3, temperature of 30°C and an initial phenanthrene concentration of 70 ppm on the 19th day of incubation. The model's fitness was thoroughly validated, with a correlation coefficient (R²) of 0.9899 and a "Prob&gt;F" value below 0.0500, affirming its suitability for optimization purposes. This study underscores the utility of the RSM in optimizing operational variables, ultimately resulting in significant time and cost savings for experimentation.

Recyclable and biodegradable bio-based polyurethane elastomers with exceptional mechanically properties

Bio-based polyurethanes (BPUs) have garnered significant attention due to their sustainable nature and potential to replace conventional petroleum-based PUs. This study delves into the synthesis, characterization, and application of a novel BPU variant, BPUPEG, derived from A-B-A triblock polyols. DSC tests highlighted the crystallization properties of the PEG block within BPUPEG, setting it apart from other BPU samples. Structural insights were further obtained from POM and WAXS tests, revealing the nanocrystalline structures and differences among the BPU samples. Mechanical testing showcased BPUPEGs superior fracture stress and strain, emphasizing its enhanced mechanical properties. Biodegradation experiments were conducted, underscoring the environmentally benign nature of all BPUs, with BPUPEG demonstrating a slower hydrolysis rate attributed to its PEG crystalline phase. Importantly, BPUPEGs degradation byproducts were ascertained to be non-toxic, emphasizing its eco-friendly attributes. The study also explored BPUPEGs recyclability, confirming its potential for multiple reuse cycles without degradation in mechanical properties. In conclusion, BPUPEG emerges as a sustainable, high-performance BPU, holding promise for diverse applications in the future, aligning with global sustainability and carbon reduction goals.

Fungal removal of cyanotoxins in constructed wetlands: The forgotten degraders

Harmful cyanobacterial blooms have increased globally, releasing hazardous cyanotoxins that threaten the safety of water resources. Constructed wetlands (CWs) are a nature-based and low-cost solution to purify and remove cyanotoxins from water. However, bio-mechanistic understanding of the biotransformation processes expected to drive cyanotoxin removal in such systems is poor, and primarily focused on bacteria. Thus, the present study aimed at exploring the fungal contribution to microcystin-LR and cylindrospermopsin biodegradation in CWs. Based on CW mesocosms, two experimental approaches were taken: a) amplicon sequencing studies were conducted to investigate the involvement of the fungal community; and b) CW fungal isolates were tested for their microcystin-LR and cylindrospermopsin degradation capabilities. The data uncovered effects of seasonality (spring or summer), cyanotoxin exposure, vegetation (unplanted, Juncus effusus or Phragmites australis) and substratum (sand or gravel) on the fungal community structure. Additionally, the arbuscular mycorrhizal fungus Rhizophagus and the endophyte Myrmecridium showed positive correlations with cyanotoxin removal. Fungal isolates revealed microcystin-LR-removal potentials of approximately 25 % in in vitro biodegradation experiments, while the extracellular chemical fingerprint of the cultures suggested a potential intracellular metabolization. The results from this study may help us understand the fungal contribution to cyanotoxin removal, as well as their ecology in CWs.

Chemically Recyclable and Biodegradable Vulcanized Rubber.

The cross-linked nature of vulcanized rubbers as used in tire and many other applications prohibits an effective closed-loop mechanical or chemical recycling. Moreover, vulcanization significantly retards the material's biodegradation. Here, we report a recyclable and biodegradable rubber that is generated by the vulcanization of amorphous, unsaturated polyesters. The elastic material can be broken down via solvolysis into the underlying monomers. After removal of the vulcanized repeat units, the saturated monomers, constituting the major share of the material, can be recovered in overall recycling rates exceeding 90%. Respirometric biodegradation experiments by 13CO2 tracking under environmental conditions via the polyesters' diol monomer indicated depolymerization and partial mineralization of the vulcanized polyester rubbers.

Concentration and compositional controls on degradation of permafrost‐derived dissolved organic matter on the Qinghai–Tibetan Plateau

AbstractUnderstanding the fate of permafrost‐derived dissolved organic matter (DOM) is critical for unraveling its role in carbon cycling. However, it remains unclear whether the high lability of permafrost‐derived DOM can be attributed to intrinsic chemical properties or elevated carbon concentrations. We investigated the dynamics of permafrost DOM from the Qinghai–Tibetan Plateau using both biodegradation and photodegradation experiments. Biodegradation and photodegradation of permafrost‐derived DOM exhibited distinct qualitative preferences for specific chemical groups (i.e., peptide‐like and aromatics, respectively). Notably, reducing the initial concentration of dissolved organic carbon (DOC) by half and a quarter resulted in shifts in biodegradable DOC content from 11.2% to 11.5% and 8.5%, respectively, accompanied by a corresponding decrease in the biodegradation rate from 0.11 to 0.06 and 0.03. This insight highlights the importance of recognizing the interplay between DOM quality and concentration and bears broader significance for our understanding of the fate of permafrost‐derived DOM in natural ecosystems.

Enzymatic Bioregeneration of Activated Carbon by Laccase

Activated carbon is widely used in combination with biological treatment systems for the treatment of organic compounds, which are refractory or toxic in conventional biological treatment systems. In these systems, compounds adsorbed on activated carbon may desorb within time due to a concentration gradient between adsorbent and the bulk liquid caused by the biodegradation of substrates in the liquid phase by microorganisms. The desorbed compounds are further biodegraded by microorganisms. This mechanism is called bioregeneration of activated carbon. Previous studies showed that bioregeneration percentages could be higher than the concentration gradient-driven desorbability. This was attributed to exoenzymatic bioregeneration occurring due to the activity of extracellular enzymes secreted by microorganisms in these systems. These extracellular enzymes can diffuse into the activated carbon pores where they can react with the previously adsorbed compounds resulting in their desorption from the carbon surface and degradation. However, the effect of extracellular enzymes on bioregeneration was not conclusively proven in any of the literature studies on bioregeneration because extracellular enzymes were not directly used for the purpose of bioregeneration. In this study, enzymatic bioregeneration of activated carbon was investigated by directly using an extracellular enzyme, laccase, which is known from the literature to catalyze the oxidation reactions of phenolic substances and is commercially available in its pure form. Therefore phenol, 2-nitrophenol, and bisphenol-A were used as the target compounds. For this purpose, batch adsorption, abiotic desorption, enzymatic degradation and enzymatic bioregeneration experiments were performed using two different activated carbon types; thermally and chemically activated ones. The results showed that there was a significant difference between the total enzymatic bioregeneration efficiencies and abiotic desorption efficiencies for each phenolic compound depending on the activated carbon type. Thereby, exoenzymatic bioregeneration has been quantitatively shown for the first time in the literature.