Aerobic Biodegradation Research Articles

Kinetic Modelling of Biodegradability Data of Commercial Polymers Obtained under Aerobic Composting Conditions

Methods to treat kinetic data for the biodegradation of different plastic materials are comparatively discussed. Different samples of commercial formulates were tested for aerobic biodegradation in compost, following the standard ISO14855. Starting from the raw data, the conversion vs. time entries were elaborated using relatively simple kinetic models, such as integrated kinetic equations of zero, first and second order, through the Wilkinson model, or using a Michaelis Menten approach, which was previously reported in the literature. The results were validated against the experimental data and allowed for computation of the time for half degradation of the substrate and, by extrapolation, estimation of the final biodegradation time for all the materials tested. In particular, the Michaelis Menten approach fails in describing all the reported kinetics as well the zeroth- and second-order kinetics. The biodegradation pattern of one sample was described in detail through a simple first-order kinetics. By contrast, other substrates followed a more complex pathway, with rapid partial degradation, subsequently slowing. Therefore, a more conservative kinetic interpolation was needed. The different possible patterns are discussed, with a guide to the application of the most suitable kinetic model.

Aerobic and Anaerobic Biodegradability of Organophosphates in Activated Sludge Derived From Kitchen Garbage Biomass and Agricultural Residues

Organophosphates (also known as organophosphate esters, OPEs) have in recent years been found to be significant pollutants in both aerobic and anaerobic activated sludge. Food waste, such as kitchen garbage and agricultural residues, can be used as co-substrates to treat the active sludge in sewage treatment plants (STPs). We investigated the biodegradability of nine OPEs derived from kitchen garbage biomass and agricultural residues under different conditions. Under anaerobic conditions, the rate of removal of triphenyl ester OPEs was significantly higher than that of chloride and alkyl OPEs. The addition of FeCl3 and Fe powder increased the rate of degradation of triphenyl ester OPEs, with a DT50 for triphenyl ester OPEs of 1.7–3.8 d for FeCl3 and 1.3–4.7 d for Fe powder, compared to a DT50 of 4.3–6.9 d for the blank control. Addition of an electron donor and a rhamnolipid increased the rate of removal of chlorinated OPEs, with DT50 values for tris(2-carboxyethyl)phosphine) (TCEP) and tris(1,3-dichloroisopropyl)phosphate (TDCPP) of 18.4 and 10.0 d, respectively, following addition of the electron donor, and 13.7 and 3.0 d, respectively, following addition of the rhamnolipid. However, addition of an electron donor, electron acceptor, surfactant, and Fe powder did not always increase the degradation of different kinds of OPEs, which was closely related to the structure of the OPEs. No treatment increased the removal of alkyl OPEs due to their low anaerobic degradability. Tween 80, a non-ionic surfactant, inhibited anaerobic degradation to some degree for all OPEs. Under aerobic conditions, alkyl OPEs were more easily degraded, chlorinated OPEs needed a long adaptation period to degrade and finally attain a 90% removal rate, while the rates of degradation of triphenyl ester OPEs were significantly affected by the concentration of sludge. Higher sludge concentrations help microorganisms to adapt and remove OPEs. This study provides new insights into methods for eliminating emerging pollutants using activated sludge cultured with kitchen garbage biomass and agricultural residues.

Biodegradation of Poly(Lactic Acid) Biocomposites under Controlled Composting Conditions and Freshwater Biotope.

The influence of additives such as natural-based plasticiser acetyl tributyl citrate (ATBC), CaCO3 and lignin-coated cellulose nanocrystals (L-CNC) on the biodegradation of polylactic acid (PLA) biocomposites was studied by monitoring microbial metabolic activity through respirometry. Ternary biocomposites and control samples were processed by a twin-screw extruder equipped with a flat film die. Commonly available compost was used for the determination of the ultimate aerobic biodegradability of PLA biocomposites under controlled composting conditions (ISO 14855-1). In addition, the hydro-degradability of prepared films in a freshwater biotope was analysed. To determine the efficiency of hydro-degradation, qualitative analyses (SEM, DSC, TGA and FTIR) were conducted. The results showed obvious differences in the degradation rate of PLA biocomposites. The application of ATBC at 10 wt.% loading increased the biodegradation rate of PLA. The addition of 10 wt.% of CaCO3 into the plasticised PLA matrix ensured an even higher degradation rate at aerobic thermophilic composting conditions. In such samples (PLA/ATBC/CaCO3), 94% biodegradation in 60 days was observed. In contrast, neat PLA exposed to the same conditions achieved only 16% biodegradation. Slightly inhibited microorganism activity was also observed for ternary PLA biocomposites containing L-CNC (1 wt.% loading). The results of qualitative analyses of degradation in a freshwater biotope confirmed increased biodegradation potential of ternary biocomposites containing both CaCO3 and ATBC. Significant differences in the chemical and structural compositions of PLA biocomposites were found in the evaluated period of three months.

Effect of lignocellulosic fiber composition on the aquatic biodegradation of wood pulps and the isolated cellulose, hemicellulose and lignin components: kinetic modelling of the biodegradation process

The importance of renewable and environmentally friendly wood pulp fibers as an input material for single-use products has grown significantly. However, discarded single-use materials are found in the environment as litter and are sometimes disposed of in wastewater. It is important that these materials are biodegradable and environmentally benign. Wood pulp is mainly comprised of lignocellulosic material, and its composition and structure can vary depending on raw materials and processing, ultimately impacting the biodegradability. In this research, the aquatic biodegradation of five kinds of wood pulp and six different samples of isolated lignocellulosic components (cellulose, hemicellulose, and lignin) have been explored in a consistent detailed manner for the first time, and the effects of chemical composition on the biodegradation discussed. Several lignocellulosic materials were characterized using compositional analysis and were subjected to aquatic biodegradation with bio-solids from a wastewater treatment plant as an inoculum to indicate the potential to biodegrade in the environment. Cellulose and hemicellulose were readily biodegraded over a course of one month. The lignin samples were not biodegradable under these conditions, and the lignin within fibers decreased the biodegradability of the other components of the lignocellulosic fibers. It was also determined that ash and extractives negatively affect the biodegradability. The aerobic aquatic biodegradation results are useful for product designers to select different lignocellulosic materials for applications and for environmental scientists to understand the fate of these fibers in the environment.

Reduction in lignin peroxidase activity revealed by effects of lignin content in urea crosslinked starch under aerobic biodegradation in soil

This study characterized the lignin peroxidase (LiP) activity of soil via an enzyme assay to determine the reaction rates and activation energies for 5 wt%, 10 wt%, 15 wt%, and 20 wt% lignin loads in urea crosslinked starch biocomposites. The results revealed that a mixed mode of LiP inhibition occurred after the soil was mixed with these biocomposites with different loads of lignin. Loading of lignin at 5 wt% and 10 wt% lignin resulted in higher values of catalytic activity of LiP: -39.58 and 49.14 µM h-1 g-1 soil, respectively. In comparison, with higher loading of lignin at 15 wt% and 20 wt%, decreases in the catalytic activity of LiP were found and were 28.72 to 37.25 µM h-1 g-1 soil, respectively. The activation energy of LiP increased approximately 1.11- to 1.22-fold when 15 and 20 wt% of lignin was loaded in biocomposites. Research findings established the possibility of unfavorable binding of the LiP to lignin with an increase in the load of lignin, possibly due to the complex structure of intact lignin and presence of inhibitory biodegradation products of lignin accumulates during lignin biodegradation in biocomposites. It was concluded that higher lignin contents (15 wt% and 20 wt%) were effective in reducing the activity of the soil LiP. Hence, higher lignin content possibly protects against losses of lignin, while acting as a filler in the formulation of biocomposites.

Demonstrating an ideal compostable plastic using biodegradability kinetics of poly(lactic acid) (PLA) based green biocomposite films under aerobic composting conditions

This study demonstrates the kinetics of aerobic biodegradation of melt-extruded poly(lactic acid) (PLA) based biocomposite films by online monitoring of CO2 using gas chromatography technique following ASTM International D 5338–15 protocol. Biodegradation studies of PLA and its biocomposites were carried out in the presence of compost microbes, without the addition of any external inoculum. The first-order kinetics model was modified by incorporating a linear lag phase for each test sample. Bacterial identification by 16S rRNA gene sequencing showed Bacillus flexus as one of the microbes responsible for biodegradation of the exposed films at thermophilic temperatures. Neat PLA (NPLA) and PLA/Chitosan composite films were found to evolve high amounts of C–CO2 (carbon-to-carbon dioxide). C–CO2 conversion was found to be very low in PLA/cellulose nanocrystals and PLA/gum arabic biocomposites, expressing the presence of only 4% and 6% slowly hydrolysable carbon, respectively, as compared to NPLA and PLA/chitosan samples. The CCO2 evolution rate was the highest for PLA/chitosan sample at 1.13 day−1. Experimental data of all the test samples showed a good fit (R2 ~ 99.99) with the kinetic model. Morphological analysis by FESEM confirmed the erosion of polymer during composting.

A review paper on aerobic and anaerobic biodegradation

Biodegradation, whether aerobic or anaerobic, is a method for cleaving large molecules from a mosaic of chemicals and materials in a series of steps, with some of the smaller molecules being valorized as a pollution abatement strategy and a source of energy through biogas generation. Biogas may be made from virtually any kind of biomass, including main agricultural sectors and different organic waste streams, which can be used as a sustainable energy source. Animal dung that has not been properly handled or managed is a significant cause of pollution in the air and water. Some of the most serious concerns include nutrient leakage, particularly of nitrogen and phosphorus, as well as ammonia evaporation and microbial contamination. the animal manufacturing is responsible for 18 percent of total CO2 equivalent emissions and 37 percent of atmospheric methane, which has 23 times the global temperature potential of CO2. Furthermore, the global animal production sector is responsible for 65 percent of human activity nitrous oxide and 64 percent of anthropogenic ammonia emissions.

Enhanced biodegradation of 17α-ethinylestradiol by rhamnolipids in sediment/water systems

Environmental context The steroid hormone 17α-ethinylestradiol (EE2) has been established as a highly estrogenic substance, which potentially causes serious harm to environmental health. Rhamnolipids are a widely researched glycolipid used for the degradation of organic pollutants. Therefore, this study focused on the change of biodegradation of EE2 affected by rhamnolipids in sediment/water systems, showing increased and more rapid degradation. Abstract Rhamnolipids can enhance the remediation of hydrophobic organic pollutants in the environment. However, the rhamnolipid-associated biodegradation of hormones has rarely been investigated. In this study, aerobic biodegradation shake-flask experiments were conducted to investigate biosurfactant-associated biodegradation of 17α-ethinylestradiol (EE2) in sediment/water systems and to assess how the biodegradation rate is influenced by rhamnolipids produced by Pseudomonas aeruginosa MIG-N146. Results showed that EE2 biodegradability is significantly increased with increasing rhamnolipid concentration. An improved pseudo-first-order kinetic equation was established to simulate enhanced EE2 biodegradation at varying rhamnolipid concentrations. The biodegradation rate (k) initially increased marginally, and then increased rapidly with rhamnolipid concentrations exceeding the effective critical micelle concentration. The degree of enhancement of organic biodegradation was mainly affected by organic mass transfer, owing to rhamnolipidic micellar solubilisation, and by rhamnolipids acting as a primary substrate to stimulate the microbial consortium. Analysis results through various techniques indicated the formation of three main types of metabolic intermediates, with diverse polarity and biodegradability characteristics, in the process of EE2 biodegradation. Thus, it was concluded that the presence of rhamnolipids did not negatively affect the processes of EE2 biotransformation by indigenous microorganisms in the original sediment/water systems. This study presents an effective potential application of rhamnolipidic surfactants for enhancement of EE2 biodegradation in sediment/water systems.

Application of the Principal Component Analysis (PCA) to aerobic biodegradation process

The Principal Component Analysis (PCA) is a method widely used to process experimental data. The PCA aims to reduce the dimensionality of a data set composed of many interrelated variables, preserving the variation as much as possible. This can be achieved by transforming the data set to a new one, containing the principal components (PCs), which are uncorrelated, and which maximize the variance of the original data. In this study, the PCA was applied to experimental tests on aerobic bioremediation of soil polluted with diesel oil. Twelve microcosms (200 g of soil) were prepared, polluted with commercial diesel oil (70 g/kg of dry soil), and hydrated with a mineral salt solution suitable to stimulate the indigenous bacteria. The aerobic process for diesel oil degradation was studied changing two operative parameters, namely, water content (u%) and carbon to nitrogen ratio (C/N). Three values of water content (u% = 8%, 12% and 15% by weight) and four of carbon to nitrogen ratio (C/N = 60, 120, 180 and 300) were tested. The microcosms were monitored for 30 days by the measurements of these parameters: 1) the CO2 production, to evaluate the microbial respiration, 2) the fluorescein production, to check the microbial activity, and 3) the diesel oil concentration, to assess the pollutant degradation and calculate the removal efficiency. The Principal Component Analysis was done considering the water content values as variables and the carbon to nitrogen ones as systems to be analyzed. By a linear transformation, two principal components were achieved, namely PC1 and PC2. There sults for the CO2 production, fluorescein production, and diesel oil removal efficiency were used, and overall variances always over 94% were obtained. The results showed that two microcosms stood out from the others, namely:-the microcosm with u% = 12% b.w. and C/N = 180,sinceit gave the highest amount of CO2 and fluorescein;- the microcosm with u% = 8% b.w. and C/N = 120,due to the highest diesel oil removal efficiency.

Evaluation of the aerobic and anaerobic degradation of an industrial effluent from vegetable tannery processing of leather on batch reactors

<p>In this study, the aerobic and anaerobic biodegradability of the industrial wastewater from the vegetable tanning process were evaluated. Water from a food wastewater treatment system was used as seed inoculum for the aerobic process and mature granular methanogenic sludge from a brewery industrial wastewater plant was used for the anaerobic process. The water from the tanning industry had a biological to chemical oxygen demand ratio of 33% with values of total chemical oxygen demand (COD) in the range of 342000 mg O2/L and total dissolved solids of 506595 mg/L. The assay of the tannery effluent under aerobic conditions resulted in a decrease of COD of 39.2% and a degradation of tannins lower than 12% after 26 days, while the anaerobic degradation showed a COD reduction of 65% with a 39% of degradation of tannins. The production of methane and Volatile Fatty Acids, during the anaerobic treatment, suggests a potential adaptation of biological organisms present in the mature anaerobic granular methanogenic sludge.</p>

Comparison of treatability of four different chlorophenol-containing wastewater by pyrite-Fenton process combined with aerobic biodegradation: Role of sludge acclimation

Aerobic biodegradation combined with pyrite-Fenton process was used for the treatment of wastewater containing different chlorophenols (4-CP, 2,3-DCP, 2,4-DCP, 2,4,6-TCP). Fenton degradation using pyrite as the low cost iron catalyst was used as a pre-treatment step to lower the toxicity of CPs prior to aerobic biodegradation. Synthetic wastewater spiked directly with either 100 mg/L CPs or pyrite-Fenton pre-treated CPs was fed to the batch bioreactors inoculated with unacclimated or acclimated activated sludge using glucose as the C-source. The results show that the CP biodegradation under aerobic conditions was highly dependent on the type of CP treated. Except for 2,4-DCP, all other CPs investigated caused severe sludge toxicity, and thus significantly hindered glucose degradation by unacclimated sludge. The CP toxicity decreased in the order of: 2,4,6-TCP > 2,3-DCP > 4-CP > 2,4-DCP. The toxic effect was explained through an interaction of CPs with the lipid fraction of cell membrane. While the pyrite-Fenton pre-treatment improved the COD removal efficiency using unacclimated sludge, the sCOD removal efficiency was still less than the control reactor operated with no CP addition. With sludge acclimation, however, the sCOD removal efficiencies increased, and approached 74% for 2,4-DCP, 61% for 4-CP, 56% for 2,4,6-TCP and 46% for 2,3-DCP, suggesting an enhanced biomass tolerance to CP toxicity. On the other hand, the sludge acclimation combined with pyrite Fenton pre-treatment provided the best bioreactor performance for all CPs with the sCOD removal efficiencies reaching 81% for 2,4,6-TCP, 78% for 2,4-DCP, 73% for 4-CP and 62% for 2,3-DCP. This suggests that the dechlorination of CPs with Fenton process, in conjunction with sludge acclimation, not only reduced the sludge toxicity, but also enhanced the bioavailability of CP-containing wastewater for microorganisms, especially for highly chlorinated toxic CPs such as 2,4,6-TCP. Overall, the findings highlight the need for sludge acclimation for effective treatment of chlorophenol-containing wastewater by a combined pyrite-Fenton and aerobic biodegradation system.

Development of a Microalgal (Chlorella)-Bacterial (Paracoccus) Symbiotic System for Pyridine Biodegradation under Photosynthetic Oxygenation

Aerobic pyridine biodegradation, which has been proven to be efficient, was often limited by serious air pollution caused by high pyridine volatilization under traditional bubble aeration. In this ...

Ready Biodegradability Ring Testing of 4-Isopropylphenol in Different Laboratories for Critical Evaluation of a Biodegradable Reference Substance.

Ready biodegradability is a key property for studying the environmental and ecological risks posed by chemicals, and a reference substance is used to check the reliability of the test results. Traditional reference substances such as aniline, sodium benzoate, and ammonium acetate rapidly degrade even in test systems without inoculum. In this study, 4-isopropylphenol was investigated as a reference candidate. Aerobic biodegradation of 4-isopropylphenol was studied using different methods, and repeatability tests were performed in multiple laboratories. 4-Isopropylphenol met the ready biodegradability passing level in a closed bottle test (OECD 301D) and manometric respirometry test (OECD 301F). No obvious toxicity was found in activated sludge respiration inhibition and biodegradable toxicity control tests. The results of 301F tests performed in 15 Chinese laboratories were compared using statistical robustness analyses and Z-scores. The robust average 28-d biodegradability rate for 4-isopropylphenol was 80.3%, and the relative standard deviation was 9.20%. The data from the 15 laboratories consistently indicated that 4-isopropylphenol was readily biodegradable, except for an "unsatisfactory" outlier result from 1 laboratory. The degradation kinetics of 4-isopropylphenol were derived from a logistic model, which had a good fit for the degradation curve. The biodegradation lag phase was 2.3 d (range 2-5 d), and the pass level was attained at 6.5 d on average (range 2-9 d), which met the 10-d window requirement. The biodegradation rate at 28 d was 75.3% (range 64.0%-95.1%). The ready biodegradability of 4-isopropylphenol indicates that it will be more appropriate as a reference chemical than other reference compounds used for investigating the biodegradability of chemicals. Integr Environ Assess Manag 2021;17:562-572. © 2020 SETAC.

Aerobic degradation of nonhalogenated organophosphate flame esters (OPEs) by enriched cultures from sludge: Kinetics, pathways, bacterial community evolution, and toxicity evaluation

The degradation by bacteria has been considered the main process for eliminating nonhalogenated organophosphate esters (OPEs) from wastewater treatment plants (WWTPs), but limited research has reported the biodegradation processes and clarified the microbial-mediated mechanisms for nonhalogenated OPE degradation in WWTPs. The aim of this study was to monitor the biodegradation of the most common nonhalogenated OPEs, namely, tris(2-butoxyethyl) phosphate (TBOEP), tris (n-butyl) phosphate (TNBP) and trisphenyl phosphate (TPHP), under aerobic conditions by sludge cultures from a conventional sewage plant. The microbial cultures were enriched separately with each OPE from activated sludge cultures, and the presence of glucose significantly enhanced degradation of the OPEs during the enrichment. The removal ratios for the three OPEs reached 29.3–89.9% after 5 cycles (25 days) of cultivation, and the first-order degradation kinetics followed the order of TPHP > TBOEP > TNBP, with their half-lives ranging between 12.8 and 99.0 h. Pathways of hydrolysis, hydroxylation, methoxylation, and substitution were confirmed for the aerobic biodegradation of these nonhalogenated OPEs, but only di-alkyl phosphates (DAPs) largely accumulated in culture medium as the most predominant transformation products. Phylotypes in Klebsiella were significantly more abundant during OPE biodegradation than in the initial sludge, which indicated that these microorganisms are associated with the biodegradation of nonhalogenated OPEs in sludge culture. Biodegradation of all investigated nonhalogenated OPEs was associated with a significant reduction in the residual toxicity to Vibrio fischeri, indicating a rather positive ecotoxicological outcome of the aerobic biotransformation processes achieved by the enriched sludge culture.

Real-time biomonitoring of oxygen uptake rate and biochemical oxygen demand using a novel optical biogas respirometric system

In response to the ever-increasing need for monitoring-based process control of wastewater treatment plants, an online applicable respirometer shows great promise for real-time measurement of oxygen uptake rate (OUR) and biochemical oxygen demand (BOD) measurements as a surrogate of the biodegradability of wastewater. Here, we have developed a photosensor-assisted real-time respirometric system equipped with bubble counting sensors for accurate measurement of microbial oxygen consumption in a bottle. This system can measure OUR and BOD in a bottle equipped with a tube containing NaOH solution to absorb carbon dioxide and supplied with continuous atmospheric oxygen to the bottle, which reliably supplies non-limiting dissolved oxygen (DO) for aerobic biodegradation even at high organic loads. These technical improvements allow a sensitive and rapid analytical tool offering real-time profiles of oxygen uptake rate as well as BOD measurements with an extended measurable range (0–420 mg O2/L), enabling significant reduction or elimination of dilution steps. The respirometric system was used to elucidate the biodegradable kinetics of domestic and swine wastewaters as a function of the type and concentration of organic matters, depending on source characteristics including rapidly or slowly oxidizable organic substances by bacteria. Compared with conventional and manometric BOD methods, our method is reliable and accurate.

Anaerobic and aerobic biodegradation of soil-extracted dissolved organic matter from the water-level-fluctuation zone of the Three Gorges Reservoir region, China

The biodegradation of dissolved organic matter (DOM) in natural environments is determined by its molecular composition and reactivity. Redox oscillations are common in the water-level-fluctuation zone (WLFZ) of the Three Gorges Reservoir (TGR). As a consequence, the soil DOM released is degraded under both anaerobic and aerobic conditions. The DOM compounds available for degradation under contrasting redox conditions and the resulting DOM composition still need to be elucidated. By combining laboratory experiments with an in-depth characterization of DOM optical properties, we show that different pathways controlled the depletion and enrichment of the DOM optical components under different oxygen regimes. In particular, 28-day dark biodegradation assays showed that up to 39.5 ± 4% DOM was degraded under anaerobic conditions, while 55.5 ± 6% DOM was biodegraded under aerobic conditions. Aerobic biodegradation resulted in a higher aromaticity and degree of humification of the DOM compared to anaerobic degradation. The specific UV absorbance at a wavelength of 254 (SUVA254) and biological index (BIX) could be used to track DOM biodegradation under anaerobic conditions. Under aerobic conditions, the SUVA254, BIX and concentration of coloured DOM (CDOM, reflected by a (355)) could track DOM biodegradation, and significant amounts of CDOM could be aerobically biodegraded.

Direct aerobic NSZD of a basalt vadose zone LNAPL source in Hawaii

In recent years, a number of methods have been used to measure the biodegradation of petroleum light non-aqueous phase liquids (LNAPL) at petroleum release sites, a process known as natural source zone depletion (NSZD). Most commonly, NSZD rates have been measured at sites with unconsolidated geology and relatively shallow groundwater (<50 ft. bgs, <15 m bgs). For this study, we have used two methods (1. carbon dioxide flux measured using carbon traps and 2. heat flux based on subsurface temperature gradients) to measure NSZD rates at a petroleum release site in Hawaii with basalt geology and deep groundwater (>300 ft. bgs, >100 m bgs). Both methods documented the occurrence of NSZD at the facility and the two methods yield estimates of the NSZD rate that agreed within a factor of 2 (4600 to 7400 gal/yr; 17,000 to 28,000 L/yr for the flux method and 8600 to 13,000 gal/yr; 33,000 to 49,000 L/yr for the temperature method). Soil gas samples collected directly above the water table and at shallower depths within the vadose zone indicated aerobic conditions throughout the vadose zone (oxygen >13%) and no detectable methane. These results indicate that NSZD occurs at this site through the direct aerobic biodegradation of LNAPL rather than the two-step process of anaerobic methanogenesis followed by methane oxidation at a shallow depth interval documented at other sites.

A tailored permeable reactive bio-barrier for in situ groundwater remediation: removal of 3-chlorophenol as a case study

ABSTRACT The present study explored bacterial aerobic biodegradation of reduced carbon-contaminants (RCC) in a pilot system mimicking remediation of a saturated aquifer in a permeable reactive biobarrier (PRBB). Bioaugmentation was performed with a pure culture of Pseudomonas putida macro-encapsulated in a cellulose-acetate porous envelope and integrated transversely to the flow trajectory of the fluid in the biobarrier and compared with controls without capsules. The macro-encapsulation technique applied allowed the incorporation of a built-in nutrient core for the slow release of macronutrients, i.e. N, P, instead of exogenous nutrients supply. 3-Chlorophenol (3CP) at a concentration range of 350–500 mg/L was chosen as an RCC model compound. The findings indicate efficient 3CP biodegradation during the PRBB operation with a similar degree of transformation (76 ± 2% and 72 ± 2%) and mineralization (55 ± 4% vs. 49 ± 3%) for exogenous and built-in nutrients supply, respectively. The extent of dechlorination in both cases (54 ± 10% vs. 40 ± 2%, respectively) followed mineralization rather than transformation, suggesting that Cl− release took place in late transformation stages. Negligible decontamination was observed in the control system without bioaugmentation. Concluding, tailored PRBB with macro-capsules incorporating a built-in nutrient core to support bacterial growth presents a significant environmental advantage controlling excess nutrients release required in bioremediation of oligotrophic systems.

Nitrate-assisted biodegradation of polycyclic aromatic hydrocarbons (PAHs) in the water-level-fluctuation zone of the three Gorges Reservoir, China: Insights from in situ microbial interaction analyses and a microcosmic experiment.

An increase in polycyclic aromatic hydrocarbon (PAH) pollution poses significant challenges to human and ecosystem health in the Three Gorges Reservoir (TGR) of the Yangtze River. Based on the combination of PAH analysis with qPCR and high-throughput sequencing of bacteria, 32 topsoil samples collected from 16 sites along the TGR were used to investigate the distribution and biodegradation pathways of PAHs in the water-level-fluctuation zone (WLFZ). The results indicated that the concentrations of PAHs were 43.8-228.2 and 30.8-206.3ng/g soil (dry weight) under the high- and low-water-level (HWL and LWL) conditions, respectively. The PAH concentration in urban areas was higher than that in rural areas. Under both the HWL and LWL conditions, the abundance of the bamA gene, a biomarker of anaerobic PAH biodegradation, was significantly higher than that of the ring-hydroxylating-dioxygenase (RHD) gene, a biomarker of aerobic PAH biodegradation. The abundance of the bamA gene was significantly positively correlated with PAHs (R2=0.8), and the biodegradation percentage of PAHs incubated anaerobically was greater than that in the aerobically incubated microcosm experiments. These data implicated a key role of the anaerobic pathway in PAH biodegradation. Co-occurrence network analysis suggested that anaerobic Anaerolineaceae, Dechloromonas, Bacteroidetes_vadin HA17 and Geobacter were key participants in the biodegradation of PAHs. The diversity analysis of functional bacteria based on the bamA gene and microcosm experiments further demonstrated that nitrate was the primary electron acceptor for PAH biodegradation. These findings provide a new perspective on the mechanism of PAH biodegradation in the TGR and knowledge that can be used to develop strategies for environmental management.

Design method of a modified layered aerobic waste landfill divided by coarse material.

To overcome the weaknesses of traditional landfills, a modified aerobic landfill concept with intermediate covers of coarse material between waste layers functioning as facilities of drainage and aeration has been proposed recently. In this study, a one-dimensional coupled model, including aerobic biodegradation, oxygen diffusion, and advection, is proposed to describe oxygen distribution in this new type of landfill. Homotopy analysis method and perturbation method are applied to solve this model at passive aeration and active aeration, respectively. The model has six input variables, that is, oxygen diffusion coefficient, gas permeability, maximum oxygen consumption rate, layer thickness of waste, and injection pressure and extraction pressure. A combination of their typical values gives rise to over 700,000 scenarios which can be calculated by the proposed solution. The coupled effect of the above variables on oxygen migration is quantitatively investigated, followed by an estimation formula of the minimum oxygen concentration in waste layer. The maximum waste layer thickness is defined as a function of other variables for a given aeration target of oxygen volume concentration larger than 5%. A generalized design method of waste layer thickness, injection pressure, and extraction pressure is then developed for the newly proposed modified layered aerobic landfill, which can promote its popularization and application.