Biodegradation Kinetics Research Articles

Acidogenic fermentation of biowaste coupled with nitrogen recovery using selective membranes to produce a VFA-rich liquid with a high C/N ratio

This research focuses on the production of a liquid stream rich in volatile fatty acids (VFAs) and low ammoniacal nitrogen content (<0.1 g N/L) from biowaste. The liquid stream was obtained by combining (i) mixed culture acidogenic fermentation to maximise VFA production and (ii) gas-permeable membrane (GPM) contactor to recover ammoniacal nitrogen. Three batch fermentation tests of biowaste collected in a full-scale mechanical-biological treatment plant provided high and stable VFA concentrations (37–39 g CODVFA/L). VFAs represented 73–81 % of the soluble chemical oxygen demand (sCOD) concentration, with a predominance of acetic, propionic and butyric acids. A highly specialized microbial community was observed in all batch tests, with Bacteroidota and Firmicutes as predominant phyla (>90 % of relative abundance). The GPM contactor recovered more than 99 % of the ammoniacal nitrogen in the fermentation liquid without VFA losses. The suitability of the produced fermentation liquid with a high C/N ratio for downstream applications was evaluated using biomethane potential tests (BMP) at different total ammonium nitrogen (TAN) concentrations (0.76–3.15 g N/L) and circumneutral pH. Despite achieving similar ultimate methane yields (279–314 NmL CH4/g CODfeed), lower TAN concentrations in the biowaste fermentation liquid improved anaerobic biodegradation kinetics, enhancing its potential applicability for methane production.

Three-Dimensional Model for Bioventing: Mathematical Solution, Calibration and Validation

Bioventing is an established technique extensively employed in the remediation of soil contaminated with petroleum hydrocarbons. In this study, the objective was to develop an improved foundational bioventing model that characterizes gas flow in vadose zones where aqueous and non-aqueous phase liquid (NAPL) are present and immobile, accounting for interphase mass transfer and first order biodegradation kinetics. By incorporating a correlation for the biodegradation rate constant, which is a function of soil properties including initial population of petroleum degrader microorganisms in soil, sand content, clay content, water content, and soil organic matter content, this model offers the ability to integrate a specific biodegradation rate constant tailored to the soil properties for each site. The governing equations were solved using the finite volume method in OpenFOAM employing the “porousMultiphaseFoam v2107” (PMF) toolbox. The equation describing gas flow in unsaturated soil was solved using a mixed pressure-saturation method, where calculated values were employed to solve the component transport equations. Calibration was done against a set of experimental data for a meso-scale reactor considering contaminant volatilization rate as the pre-calibration parameter and the mass transfer coefficient between aqueous and NAPL phase as the main calibration parameter. The calibrated model then was validated by simulating a large-scale reactor. The modelling results showed an error of 2.9% for calibrated case and 4.7% error for validation case which present the fitness to the experimental data, proving that the enhanced bioventing model holds the potential to improve predictions of bioventing and facilitate the development of efficient strategies to remediate soil contaminated with petroleum hydrocarbons.

Role of biochar pyrolysis temperature on intracellular and extracellular biodegradation of biochar-adsorbed organic compounds

Immobilizing organic pollutants by adsorption of biochar in farmland soil is a cost-effective remediation method for contaminated soil. As the adsorption capacity of biochar is limited, biodegradation of biochar-adsorbed organic pollutants was a potential way to regenerate biochars and maintain the adsorption performance of biochars to lower the cost. It could be affected by the biochar pyrolysis temperature, but was not evaluated yet. In this study, biodegradation of adsorbed phenanthrene on a series of biochars with pyrolysis temperatures from 150 to 700 °C by Sphingobium yanoikuyae B1 was investigated using batch experiments of biodegradation kinetics at 30 °C, to explore the role of biochar pyrolysis temperature on biodegradation of biochar-adsorbed organic compounds. It was observed that 37.5–47.9% of adsorbed phenanthrene on moderate temperature-pyrolyzed biochars produced at 400 and 500 °C were biodegraded, less than that on high temperature-pyrolyzed biochars produced at ≥600 °C (48.8–60.8%) and low temperature-pyrolyzed biochars produced at ≤300 °C (63.4–92.5%). Phenanthrene adsorbed largely on the low temperature-pyrolyzed biochars by partition mechanism and thus is easily desorbed to water for a dominated intracellular biodegradation. On the high temperature-pyrolyzed biochars, phenanthrene is adsorbed largely by pore-filling mechanism and thus less desorbed to water for intracellular biodegradation. However, high temperature-pyrolyzed biochars can promote microbes to produce siderophore, H2O2 and thus release extracellular •OH for a dominated degradation of adsorbed phenanthrene by Fenton-like reaction. With the increase of biochar pyrolysis temperature, desorption and consequently the intracellular biodegradation of adsorbed phenanthrene on biochars decreased, while the secretion of siderophore and H2O2 by microbes on biochars increased to produce more extracellular •OH for degradation by Fenton-like reaction. The results could provide deep insights into the role of biochar pyrolysis temperature on biodegradation of biochar-adsorbed organic compounds, and optimize the selection of biochar with higher adsorption performance and easier regeneration for soil remediation.

The aerobic biofilm on naphthalene as the carbon source: Growth, biodegradability, and mass transfer-diffusion kinetics

Stable biofilm formation and substrate loss during mass transfer are key factors affecting the treatment efficiency of biofilm systems. In this research, a comprehensive study was conducted on the growth, biodegradability and mass transfer process of Ochrobactrum anthropi Na-B biofilm. The results showed that the biofilm mass increased at different rates before tending to stabilize under the optimal conditions. The growth process was divided into six phases and the biofilm which in logarithmic phase showed the highest microbial activity and the best degradation performance, the average removal of 30 mg/L naphthalene reached 61% after 24 h under pH= 7.0, T = 30 °C, and r = 100 rpm. With the growth and maturation of biofilm, microcolonies began to form on the membrane carrier surface and finally presented a dense, continuous and three-dimensional reticular biofilm structure. Furthermore, the mass transfer performance of biofilm declined with the growth of biofilm, the increase of initial naphthalene concentration and the decrease of temperature. The Mass Transfer-Diffusion kinetics of biofilm further indicated that in the range of 5–30 mg/L naphthalene concentration, the internal diffusion resistance in the biofilm was negligible and the mass transfer process of biofilm was mainly restricted by the external mass transfer resistance and biological reaction.

Isolation and characterization of distinctive pyrene-degrading bacteria from an uncontaminated soil.

Considerable efforts that isolate and characterize degrading bacteria for polycyclic aromatic hydrocarbons (PAHs) have focused on contaminated environments so far. Here we isolated three distinctive pyrene (PYR)-degrading bacteria from a paddy soil that was not contaminated with PAHs. These included a novel Bacillus sp. PyB-9 and efficient degraders, Shigella sp. PyB-6 and Agromyces sp. PyB-10. All three strains could utilize naphthalene, phenanthrene, anthracene, fluoranthene and PYR as sole carbon sources, and degraded PYR in a range of temperatures (27-37°C) and pH (5-8). Strains PyB-6 and PyB-10 almost completely degraded 50mgL-1 PYR within 15days, and 75.5% and 98.9% of 100mgL-1 PYR in 27days, respectively. The kinetics of PYR biodegradation was well represented by the Gompertz model. Ten and twelve PYR metabolites were identified in PYR degradation process by strains PyB-6 and PyB-10, respectively. Chemical analyses demonstrated that the degradation mechanisms of PYR were the same for strains PyB-6 and PyB-10 with initial dioxygenation mainly on C-4,5 positions of PYR. The degradation of 4,5-phenanthrenedicarboxylic acid was branched to 4-phenanthrenecarboxylic acid pathway and 5-hydroxy-4-phenanthrenecarboxylic acid pathway, both of which played important roles in PYR degradation by strains PyB-6 and PyB-10. To our knowledge, Shigella sp. and Agromyces sp. were found for the first time to possess the capability for PAHs degradation. These findings contributed to upgrading the bank of microbial resource and knowledge on PAH biodegradation.

Coupling pathway prediction and fluorescence spectroscopy to assess the impact of auxiliary substrates on micropollutant biodegradation.

Some bacteria can degrade organic micropollutants (OMPs) as primary carbon sources. Due to typically low OMP concentrations, these bacteria may benefit from supplemental assimilation of natural substrates present in the pool of dissolved organic matter (DOM). The biodegradability of such auxiliary substrates and the impacts on OMP removal are tightly linked to biotransformation pathways. Here, we aimed to elucidate the biodegradability and effect of different DOM constituents for the carbofuran degrader Novosphingobium sp. KN65.2, using a novel approach that combines pathway prediction, laboratory experiments,and fluorescence spectroscopy. Pathway prediction suggested that ring hydroxylation reactions catalysed by Rieske-type dioxygenases and flavin-dependent monooxygenases determine the transformability of the 11 aromatic compounds used as model DOM constituents. Our approach further identified two groups with distinct transformation mechanisms amongst the four growth-supporting compounds selected for mixed substrate biodegradation experiments with the pesticide carbofuran (Group 1: 4-hydroxybenzoic acid, 4-hydroxybenzaldehyde; Group 2: p-coumaric acid, ferulic acid). Carbofuran biodegradation kinetics were stable in the presence of both Group 1 and Group 2 auxiliary substrates. However, Group 2 substrates would be preferable for bioremediation processes, as they showed constant biodegradation kinetics under different experimental conditions (pre-growing KN65.2 on carbofuran vs. DOM constituent). Furthermore, Group 2 substrates were utilisable by KN65.2 in the presence of a competitor (Pseudomonas fluorescens sp. P17). Our study thus presents a simple and cost-efficient approach that reveals mechanistic insights into OMP-DOM biodegradation.

Kinetics of anaerobic biodegradation of synthetic dairy wastewater pretreated with lactase

Kinetics of anaerobic biodegradation of synthetic dairy wastewater pretreated with lactase

Isolation, and characterization of Cladosporium alboflavescens for Acetaminophen biodegradation

One of the pharmaceutical micropollutants with a detrimental effect on the environment is paracetamol. Mycoremediation of the pollutants is a widely accepted concept based on cost and eco-friendly nature. Fungi isolated from pharmaceutical industry effluent have been used to target the biodegradation of paracetamol. The fungus’s internal transcribed spacer (ITS 1) sequencing matched that of Cladosporium alboflavescens (GenBank accession number OQ977005) by 99.81%. The strain demonstrated 89% biodegradation of paracetamol (1000 ppm) after 96 hours of incubation with 4-aminophenol as the predominant biodegradative metabolite, according to the spectrophotometric and high-performance liquid chromatographic analysis. The half-life of 1.44 days and simple first order kinetics were proposed by the Computer Assisted Kinetic Evaluation (CAKE) tool used to examinethe biodegradation kinetics.&#x0D; Key words: Acetaminophen, 4-aminophenol, Cladosporium, Mycoremediation

Dynamical analysis of a chemostat model for 4-chlorophenol and sodium salicylate mixture biodegradation

We consider a mathematical continuous-time model for biodegradation of 4-chlorophenol and sodium salicylate mixture by the microbial strain Pseudomonas putida in a chemostat. The model is described by a system of three nonlinear ordinary differential equations and is proposed for the first time in the paper [Y.-H. Lin, B.-H. Ho, Biodegradation kinetics of phenol and 4-chlorophenol in the presence of sodium salicylate in batch and chemostat systems, Processes, 10:694, 2022], where the model is only quantitatively verified. This paper provides a detailed analysis of the system dynamics. Some important basic properties of the model solutions like existence, uniqueness and uniform boundedness of positive solutions are established. Computation of equilibrium points and study of their local asymptotic stability and bifurcations in dependence of the dilution rate as a key model parameter are also presented. Thereby, particular intervals for the dilution rate are found, where one or three interior (with positive components) equilibrium points do exist and possess different types of local asymptotic stability/instability. Hopf bifurcations are detected leading to the occurrence of stable limit cycles around some interior equilibrium points. A transcritical bifurcation also exists and implies stability exchange between an interior and the boundary (washout) equilibrium. The results are illustrated by lots of numerical examples.

Study on the Biodegradation Kinetics of Bioplastic Obtained from Tapioca Starch

Study on the Biodegradation Kinetics of Bioplastic Obtained from Tapioca Starch

Long-term in vivo degradation and biocompatibility of degradable pHEMA hydrogels containing graphene oxide

Developing biocompatible, non-fouling and biodegradable hydrogels for blood-contacting devices remains a demanding challenge. Such materials should promote natural healing, prevent clotting, and undergo controlled degradation. This study evaluates the biocompatibility and biodegradation of degradable poly(2-hydroxyethyl methacrylate) (d-pHEMA) hydrogels with or without reinforcement with oxidized few-layer graphene (d-pHEMA/M5ox) in a long term implantation in rats, assessing non-desired side-effects (irritation, chronic toxicity, immune response).Subcutaneous implantation over 6 months revealed degradation of both hydrogels, despite slower for d-pHEMA/M5ox, with degradation products found in intracellular vesicles. No inflammation nor infection at implantation areas were observed, and no histopathological findings were detected in parenchymal organs. Immunohistochemistry confirmed d-pHEMA and d-pHEMA/M5ox highly anti-adhesiveness. Gene expression of macrophages markers revealed presence of both M1 and M2 macrophages at all timepoints. M1/M2 profile after 6 months reveals an anti-inflammatory environment, suggesting no chronic inflammation, as also demonstrated by cytokines (IL-α, TNF-α and IL-10) analysis.Overall, modification of pHEMA towards a degradable material was successfully achieved without evoking a loss of its inherent properties, specially its anti-adhesiveness and biocompatibility. Therefore, these hydrogels hold potential as blank-slate for further modifications that promote cellular adhesion/proliferation for tissue engineering applications, namely for designing blood contacting devices with different load bearing requirements. Statement of significanceBiocompatibility, tunable biodegradation kinetics, and suitable immune response with lack of chronic toxicity and irritation, are key features in degradable blood contact devices that demand long-term exposure. We herein evaluate the 6-month in vivo performance of a degradable and hemocompatible anti-adhesive hydrogel based in pHEMA, and its mechanically reinforced formulation with few-layer graphene oxide. This subcutaneous implantation in a rat model, shows gradual degradation with progressive changes in material morphology, and no evidence of local inflammation in surrounding tissue, neither signs of inflammation or adverse reactions in systemic organs, suggesting biocompatibility of degradation products.Such hydrogels exhibit great potential as a blank slate for tissue engineering applications, including for blood contact, where cues for specific cells can be incorporated.

Deep insights into biodegradability mechanism and growth cycle adaptability of polylactic acid/hyperbranched cellulose nanocrystal composite mulch

The widespread use of petroleum-based plastic mulch in agriculture has accelerated white and microplastic pollution while posing a severe agroecological challenge due to its difficulty in decomposing in the natural environment. However, endowing mulch film with degradability and growth cycle adaptation remains elusive due to the inherent non-degradability of petroleum-based plastics severely hindering its applications. This work reports polylactic acids hyperbranched composite mulch (PCP) and measured biodegradation behavior under burial soil, seawater, and ultraviolet (UV) aging to understand the biodegradation kinetics and to increase their sustainability in the agriculture field. Due to high interfacial interactions between polymer and nanofiler, the resultant PCP mulch significantly enhances crystallization ability, hydrophilicity, and mechanical properties. PCP mulch can be scalable-manufactured to exhibit modulated degradation performance under varying degradation conditions and periods while concurrently enhancing crop growth (wheat). Thus, such mulch with excellent performance can reduce labor costs and the environmental impact of waste mulch disposal to replace traditional mulch for sustainable agricultural production.

Simultaneous biodegradation kinetics of 1,4-dioxane and ethane.

Biodegradation of 1,4-Dioxane at environmentally relevant concentrations usually requires the addition of a primary electron-donor substrate to sustain biomass growth. Ethane is a promising substrate, since it is available as a degradation product of 1,4-Dioxane's common co-contaminants. This study reports kinetic parameters for ethane biodegradation and co-oxidations of ethane and 1,4-Dioxane. Based on experiments combined with mathematical modeling, we found that ethane promoted 1,4-Dioxane biodegradation when the initial mass ratio of ethane:1,4-Dioxane was < 9:1mg COD/mg COD, while it inhibited 1,4-Dioxane degradation when the ratio was > 9:1. A model-independent estimator was used for kinetic-parameter estimation, and all parameter values for 1,4-Dioxane were consistent with literature-reported ranges. Estimated parameters support competitive inhibition between ethane as the primary substrate and 1,4-Dioxane as the secondary substrate. The results also support that bacteria that co-oxidize ethane and 1,4-Dioxane had a competitive advantage over bacteria that can use only one of the two substrates. The minimum concentration of ethane to sustain ethane-oxidizing bacteria and ethane and 1,4-Dioxane-co-oxidizing bacteria was 0.09mg COD/L, which is approximately 20-fold lower than the minimum concentration reported for propane, another common substrate used to promote 1,4-Dioxane biodegradation. The minimum 1,4-Dioxane concentration required to sustain steady-state biomass with 1,4-Dioxane as the sole primary substrate was 1.3mg COD/L. As 1,4-Dioxane concentrations at most groundwater sites are less than 0.18mg COD/L, providing ethane as a primary substrate is vital to support biomass growth and consequently enable 1,4-Dioxane bioremediation.

Enhanced biodegradation kinetics in the copper-polluted sediment through bioaugmentation with water spinach and peanut husk-derived biochar

Stenotrophomonas maltophilia is a copper-tolerant bacterium that is used for improving the resilience and efficacy of microorganisms engaged in degrading substrate under high copper contamination. Examination of reaction kinetics indicates that the original consortia, Stenotrophomonas maltophilia and the mixed culture, follow a first-order reaction. The Michaelis-Menten model suggests that elevated copper concentrations exert stress on the original bacterial population and Stenotrophomonas maltophilia. However, when a mixed culture is employed during the bioaugmentation process, it brings about an enhancement in microbial resistance and performance. This study demonstrates that the poor performance of indigenous bacteria in media that are highly contaminated with copper can be improved by adding exogenous copper-tolerant bacteria. Furthermore, poor mass transfer in sediments can be improved by adding plants and biochar. This strategic addition serves a dual purpose: it increases the affinity of the substrate for sediments characterized by poor mass transfer and alleviates the inhibitory effects induced by copper. In addition, high percentages of Firmicutes, Bacteroidetes, and Euryarchaeota within the biochar matrix were verified to expedite the substrate biodegradation process even at high copper concentrations. The findings in this work provide an important basis for the future design of in situ bioremediation systems for heavy metal-contaminated sites.

Transformation of Benzene Derivatives in Acidic Conditions by the Fungus Hormoconis Resinae – Reductive, Oxidative, or Both?

Hormoconis resinae (or Cladosporium resinae), colloquially known as the kerosene fungus, is predominantly found in fuel tanks (Rafin and Veignie 2018). Its occurrence in fuel tanks was first reported in early 1960s. Since then, it has been considered as a serious threat by the petroleum industry for bio-deteriorating fuel quality, corroding storage tanks, and clogging pumps and filters (Sheridan et al. 1971). This fungus flourishes well in the presence of water and can thrive at a wider pH range (2-10), than most commonly studied bacteria, with optimum towards the acidic end (Rafin and Veignie 2018). As a biosafety level 1 organism (ATCC 2021) with wide natural prevalence, H. resinae is both safe to study and apply in the field. Thus, it can be utilized for developing bioremediation processes suitable for petroleum-contaminated sites. Contamination of groundwater sources by fuel pollutants has been an important public health concern for decades (Mitra and Roy 2011). Several components of fuel are known to be toxic even at low concentrations with deleterious health effects including teratogenicity and carcinogenicity (ATSDR 1995). Past research has mainly focussed on the degradation of n-alkanes, a major component of fuel, by H. resinae which used the n-alkanes as sole carbon and energy sources (Rafin and Veignie 2018). Benzene derivatives like toluene, benzaldehyde, benzoic acid are also often found as fuel pollutants. Though some studies have investigated the effects of benzene derivatives on the survival and growth of H. resinae (Cofone et al. 1973, Oh et al. 2001, Qi et al. 2002), not much work has been done on their biodegradation (Kato et al. 1990). Previous study showed a reductive transformation of benzoate to benzaldehyde, benzyl alcohol, and 1-phenyl-l,2-propanediol (Kato et al. 1990). More work was needed to study the further transformation of these products. Thus, the current study focussed on the transformation of benzaldehyde and benzyl alcohol in acidic conditions by H. resinae ATCC 34066. The main objectives were to study the effects of: culture media, glucose, and oxygen enrichment on the fungal growth in the presence of these benzene derivatives and their biodegradation kinetics and pathways. culture media, glucose, and oxygen enrichment on the fungal growth in the presence of these benzene derivatives and their biodegradation kinetics and pathways. Some experiments were also conducted with toluene as the contaminant. H. resinae was not able to transform toluene (1-200 ppm) at all, though it was able to grow on it in the presence of 1% glucose. The fungus was able to transform benzaldehyde (≤550 ppm) to benzyl alcohol (reductive) and benzoic acid (oxidative). Many monoaromatics such as catechol, resorcinol, hydroxybenzoic acids and aliphatic compounds such as fumaric acid, levulinic acid were also detected as the oxidation products of benzaldehyde by high-resolution liquid chromatography-mass spectrometry. The presence of glucose slowed down benzaldehyde transformation but increased the benzyl alcohol formation relative to benzoic acid, probably due to the further slower transformation of benzyl alcohol. Oxygen enrichment enhanced the benzaldehyde transformation. Glucose was a preferred culturing media as fungus grown on potato dextrose agar (PDA) showed a 5-week lag phase for benzaldehyde transformation. However, this PDA-cultured fungus, after growing on benzaldehyde, did not exhibit a lag phase and started benzaldehyde transformation immediately. Transformation of benzyl alcohol, as target contaminant, was slower and incomplete in the presence of glucose. Benzyl alcohol was transformed mainly to benzoic acid via an oxidative pathway. In summary, this study has shown that H. resinae can transform the benzene derivatives via both oxidative and reductive pathways. Moreover, H. resinae can use these compounds as sole carbon and energy sources.

Aerobic aquatic biodegradation of bio-based and biodegradable polymers: Kinetic modeling and key factors for biodegradability

With the increasing concern about plastic waste, numerous efforts have been made to find substitutes for existing non-biodegradable synthetic polymers. Bio-based and/or purported petroleum-based biodegradable polymers are considered probable plastic replacement candidates. However, the durability of non-biodegradable plastic is a key feature of plastics. Thus, a balance must be achieved between biodegradation and environmental material stability. The objective of this study is to determine the impact of crystallinity, molecular chemistry, and hydrophilicity on the rate of aquatic biodegradation of biobased plastic materials. In the present study, twelve bio-based/purported biodegradable materials were investigated under aerobic aquatic biodegradation conditions for 56 days by tracking oxygen consumption. Crystallinity, hydrophobicity, chemistry, and chemical structure were varied to understand potential means for controlling the rate of biodegradation. The biodegradation kinetics were analyzed and discussed, relating to the characteristics of polymers. Polyvinyl alcohol (PVA), Chitosan, Rayon, Polyhydroxy-butyrate-co-valerate (PHBV), PHBH, and Polybutylene succinate (PBS) showed the biodegradation extents over 70% at 56 days. Cellulose acetates (CAs) and Polylactic acid (PLA) showed biodegradation extent lower than 20%. The chemistry of the polymer backbone chain, substituent structure, and degree of substitution were the dominant factors affecting biodegradation. The crystallinity of the polyesters had a negative correlation with the initial biodegradation rate and the ultimate biodegradation of polyesters, and the hydrophobicity of the polymers delayed the initiation of biodegradation. The aerobic aquatic biodegradation results related to the polymer characteristics are useful for product designers and environmental scientists to understand the fate of these polymeric materials in the environment.

KINETIC ASSESSMENT OF BIODEGRADABILITY IN GEL-FORMING SOIL CONDITIONERS BASED ON BOD ANALYSIS

Biodegradation is one of the main factors limiting the efficiency and service life of gel-forming soil conditioners. The study quantifies this process using laboratory analysis of biological oxygen uptake (BOD) in innovative composite superabsorbents with an acrylic polymer matrix, amphiphilic agents (humates, peat) and silver ions as an inhibitor of biological activity. A simple kinetic model of BOD is proposed to standardize the analysis and calculation of the half-life of polymers after their incubation in precision VELP respirometers (Italy). The half-life of hydrogels swollen in distilled water (1:100) at a temperature of 30°C varied in the range from 0,8±0,2 to 2,4±1,6 years. The addition of an aqueous extract from compost sharply enhances biodegradation and reduces the half-life of hydrogels up to 40–60 days. Doses of 0,1–1% silver in a polymer matrix or 10-100 ppm in swollen hydrogels increase their half-life by 5–20 times. The new methodological approach makes it possible to fully automatically evaluate the biodegradation of gel–forming polymers in laboratory conditions, however, for stable materials with a half-life of more than 2,5–3 years, the accuracy of manometric BOD analyzers is insufficient for a statistically reliable assessment of the kinetics of biodegradation even in long (120 days) incubation experiments.

Energy generation from bioelectrochemical techniques: Concepts, reactor configurations and modeling approaches

The process industries play a significant role in boosting the economy of any nation. However, poor management in several industries has been posing worrisome threats to an environment that was previously immaculate. As a result, the untreated waste and wastewater discarded by many industries contain abundant organic matter and other toxic chemicals. It is more likely that they disrupt the proper functioning of the water bodies by perturbing the sustenance of many species of flora and fauna occupying the different trophic levels. The simultaneous threats to human health and the environment, as well as the global energy problem, have encouraged a number of nations to work on the development of renewable energy sources. Hence, bioelectrochemical systems (BESs) have attracted the attention of several stakeholders throughout the world on many counts. The bioelectricity generated from BESs has been recognized as a clean fuel. Besides, this technology has advantages such as the direct conversion of substrate to electricity, and efficient operation at ambient and even low temperatures. An overview of the BESs, its important operating parameters, bioremediation of industrial waste and wastewaters, biodegradation kinetics, and artificial neural network (ANN) modeling to describe substrate removal/elimination and energy production of the BESs are discussed. When considering the potential for use in the industrial sector, certain technical issues of BES design and the principal microorganisms/biocatalysts involved in the degradation of waste are also highlighted in this review.

Linking the source, molecular composition, and reactivity of dissolved organic matter in major rivers across the pearl river delta

Dissolved organic matter (DOM) constitutes a substantial portion of the global carbon cycle and serves as the largest reservoir of reactive carbon on Earth. Studying DOM's sources, molecular compositions, and reactivity is central to understanding the fate and environmental effects of organic carbon, yet, links between DOM composition and reactivity remain to be established. In this study, stable carbon isotopic composition and ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) were combined with degradation experiments to comprehensively study DOM's properties in the major rivers across the Pearl River Delta (PRD) in South China. The increasing δ13C-DOC along the Pearl River at the PRD suggests that terrestrial DOM from upstream was gradually diluted by local processes. Although affected by different interaction patterns of multiple sources, a major component of DOM, enriched in CHO and lignins, is molecularly indistinguishable in different rivers (molecular Bray-Curtis dissimilarity of 15%–31%). The photo-degradation removed 34% (PDOC%) of initial DOM within 14 days, twice that by biodegradation (BDOC%). In contrast to earlier research, the distinctive integration of molecular characterization with DOM degradation kinetics indicates that both regional (common shared molecules) and local (partial shared and unique molecules) derived DOM play a collective role in governing the bio-degradation kinetics of DOM, while the photo-degradation kinetics of DOM are barely correlated to molecular composition. The thorough investigation of DOM molecular composition and its correlation with bulk DOM properties in the PRD region, though requiring further investigation into its mechanisms, offers valuable insights into the role of riverine DOM in coastal hypoxia and the global carbon cycle.

Indene, indane and naphthalene in a mixture with BTEX affect aerobic compound biodegradation kinetics and indigenous microbial community development

BTEX (benzene, toluene, ethylbenzene, xylene) are common pollutants often found in former gasworks sites together with some other contaminants like indene, indane and naphthalene (Ie, Ia, N). This study aimed to evaluate the inhibitory or stimulative substrate interactions between BTEX, and Ie, Ia, N during aerobic biodegradation. For this, batch bottles, containing originally anaerobic subsurface sediments, groundwater and indigenous microorganisms from a contaminated former gasworks site, were spiked with various substrate combinations (BTEX, BTEXIe, BTEXIa, BTEXN, BTEXIeIa, BTEXIeN, BTEXIaN, BTEXIeIaN). Subsequently concentrations were monitored over time. For the BTEXIeIaN mixture, initial concentrations were between 1 and 5 mg L-1, and all compounds were completely degraded by the microbial consortia within 39 days of incubation. The experimental data were fitted to a first order kinetic degradation model for interpretation of inhibition/stimulation between the compounds. Results showed that indene, indane, and naphthalene inhibited the degradation of benzene, toluene, ethylbenzene, o-xylene, with benzene being the most affected. M/p-xylene is the only compound whose biodegradation is stimulated by the presence of indene and indane (individually or mixed) but inhibited by the presence of naphthalene. 16S rRNA amplicon sequencing revealed differentiation in the microbial communities within the batches with different substrate mixtures, especially within the two microbial groups Micrococcaceae and Commamonaceae. Indene had more effect on the BTEX microbial community than indane or naphthalene and the presence of indene increased the relative abundance of Micrococcaceae family. In conclusion, co-presence of various pollutants leads to differentiation in degradation processes as well as in microbial community development. This sheds some light on the underlying reasons for that organic compounds present in mixtures in the subsurface of former gasworks sites are either recalcitrant or subjective towards biodegradation, and this understanding helps to further improve the bioremediation of such sites.