Anaerobic Biodegradation Rates Research Articles

Meta-Analysis and Machine Learning Models for Anaerobic Biodegradation Rates of Organic Contaminants in Sediments and Sludge.

Anaerobic biodegradation rates (half-lives) of organic chemicals are pivotal for environmental risk assessment and remediation. Traditional experimental evaluation, constrained by prolonged, oxygen-free conditions, struggles to keep pace with emerging contaminants. Data-driven machine learning (ML) models serve as promising complements. However, reported quantitative structure-biodegradation relationships or ML models on anaerobic biodegradation are mostly based on small data sets (<100 records) and neglect experimental conditions, usually achieving compromised predictions. This work aimed to develop ML models for predicting the biodegradation half-lives of organic pollutants in anaerobic environments (i.e., sediment/soil and sludge). Focusing on important features of both chemicals and experimental conditions, we first curated two data sets, one for sediment/soil (SED) and the other for sludge (SLD), covering 978 records for 206 chemicals from the literature, and then conducted a meta-analysis. Next, we built a binary classification (half-life of 30 days as the cutoff) model with an accuracy of 81% and a regression model with R2 of 0.56 for SED based on LightGBM (80% and 0.31 for SLD based on Extra tree, respectively). The model interpretations underscored the significance of experimental conditions (e.g., temperature and inoculum dosage), as evidenced by their high feature importance, and the models were found to correctly capture the effects of chemical substructures, for example, branched structures and aromatic rings prolonged half-lives while methyl group and ortho-substitution on rings shortened half-lives. The applicability domains of the models were also defined, resulting in reasonable prediction for the half-lives of 41% (SED) or 67% (SLD) of over 4000 persistent, bioaccumulative, and toxic chemicals. Overall, this study pioneers ML models for predicting the anaerobic degradation half-lives, offering valuable support for future evaluation and implementation of chemical anaerobic biodegradation.

Burial and Denudation Alter Microbial Life at the Bottom of the Hypo‐Critical Zone

AbstractHow subsurface microbial life changed at the bottom of the kilometers‐deep (hypo) Critical Zone in response to evolving surface conditions over geologic time is an open question. This study investigates the burial and exhumation, biodegradation, and fluid circulation history of hydrocarbon reservoirs across the Colorado Plateau as a window into the hypo‐Critical Zone. Hydrocarbon reservoirs, in the Paradox and Uinta basins, were deeply buried starting ca. 100 to 60 Ma, reaching temperatures &gt;80–140°C, likely sterilizing microbial communities present since the deposition of sediments. High salinities associated with evaporites may have further limited microbial activity. Upward migration of hydrocarbons from shale source rocks into shallower reservoirs during maximum burial set the stage for microbial re‐introduction by creating organic‐rich “hot spots.” Denudation related to the incision of the Colorado River over the past few million years brought reservoirs closer to the surface under cooler temperatures, enhanced deep meteoric water circulation and flushing of saline fluids, and likely re‐inoculated more permeable sediments up to several km depth. Modern‐ to paleo‐hydrocarbon reservoirs show molecular and isotopic evidence of anaerobic oxidation of hydrocarbons coupled to bacterial sulfate reduction in areas with relatively high SO4‐fluxes. Anaerobic oil biodegradation rates are high enough to explain the removal of at least some portion of postulated “supergiant oil fields” across the Colorado Plateau by microbial activity over the past several million years. Results from this study help constrain the lower limits of the hypo‐Critical Zone and how it evolved over geologic time, in response to changing geologic, hydrologic, and biologic forcings.

Novel synergistic metabolic processes for phenanthrene biodegradation by a nitrate-reducing phenanthrene-degrading culture and an anammox culture

The synergistic metabolism by anammox cultures and nitrate-reducers for anaerobic PAH biodegradation is largely unknown, including whether anammox culture and which kind of anammox bacterium can perform nitrogen metabolism in the anaerobic PAH biodegradation processes, the inhibitory effect of PAH on anammox activity and nitrite on PAH-degrading nitrate-reducers activity, and the synergistic metabolic processes. Herein, an anammox culture that can eliminate nitrite accumulation and decrease inorganic carbon emission during anaerobic phenanthrene (a model of PAH in this study) biodegradation, the synergistic mechanism for phenanthrene biodegradation by a nitrate-reducer and such anammox culture, and the inhibition effect of phenanthrene on such anammox culture and nitrite on a phenanthrene-degrading nitrate-reducer were newly discussed. The results showed that nitrite largely accumulated during anaerobic phenanthrene biodegradation (nitrate accumulation is a common phenomenon for the biodegradation of refractory matter, including PAHs, by nitrate-reducers) by a nitrate-reducer, PheN2, which mineralizes phenanthrene to inorganic carbon, and nitrite was verified as an inhibiting factor for further biodegradation. Anaerobic phenanthrene biodegradation rates and nitrite concentrations (0–7 mM) appeared to have a negative linear correlation. The anammox culture that mainly contained Candidatus Kuenenia was newly found to efficiently reduce nitrite accumulation and inorganic carbon emissions and significantly promote biodegradation efficiency by ∼1.94-fold. Our results showed that phenanthrene absorbed in and on anammox cells had a more direct relationship with the inhibitory effect on anammox activity than phenanthrene in the environment, and 15.2 mg/gVSS phenanthrene absorbed in and on the cells (4 mM concentration in the culture) showed nearly complete inhibition of anammox culture in this study. In addition, few (less than 2% abundance) anammox bacteria were found to be enough for the removal of nitrite produced from anaerobic phenanthrene biodegradation. In an ideal world, co-pollutants of ammonia, nitrate, phenanthrene, and nitrite could be converted to nitrogen gas and biomass by the synergistic metabolism of anammox cultures and nitrate reducers. Our study reveals a new synergistic process that may exist in our environments for PAH elimination by an anammox culture and a nitrate-reducer, which provides a new strategy for the bioremediation of PAH-polluted anoxic zones.

Slope stability analysis of a landfill subjected to leachate recirculation and aeration considering bio-hydro coupled processes

During the operation of landfills, leachate recirculation and aeration are widely applied to accelerate the waste stabilization process. However, these strategies may induce high pore pressures in waste, thereby affecting the stability of the landfill slope. Therefore, a three-dimensional numerical analysis for landfill slope stability during leachate recirculation and aeration is performed in this study using strength reduction method. The bio-hydro coupled processes of waste are simulated by a previously reported landfill coupled model programmed on the open-source platform OpenFOAM and then incorporated into the slope stability analysis. The results show that both increasing the injection pressure for leachate recirculation and maximum anaerobic biodegradation rate will reduce the factor of safety (FS) of the landfill slope maximally by 0.32 and 0.62, respectively, due to increased pore pressures. The ignorance of both waste biodegradation and gas flow will overestimate the slope stability of an anaerobic bioreactor landfill by about 20–50%, especially when the landfilled waste is easily degradable. The FS value of an aerobic bioreactor landfill slope will show a significant reduction (maximally by 53% in this study) when the aeration pressure exceeds a critical value and this value is termed as the safe aeration pressure. This study then proposes a relationship between the safe aeration pressure and the location of the air injection screen (i.e., the horizontal distance between the top of the injection screen and the slope surface) to avoid landfill slope failure during aeration. The findings of this study can provide insights for engineers to have a better understanding of the slope stability of a bioreactor landfill and to design and control the leachate recirculation and aeration systems in landfills.

Biodegradation of bioplastics under aerobic and anaerobic aqueous conditions: Kinetics, carbon fate and particle size effect

The biodegradation of PHB, PHBV, PBS, PBAT, PCL, PLA, and a PLA-PCL blend was compared under aerobic and anaerobic aqueous conditions assessing biodegradation kinetics, extent, carbon fate and particle size influence (in the range of 100–1000 µm). Under standard test conditions, PHB and PBHV were biodegraded anaerobically (83.9 ± 1.3% and 81.2 ± 1.7%, respectively) in 77 days or aerobically (83.0 ± 1.6% and 87.4 ± 7.5%) in 117 days, while PCL was only biodegraded (77.6 ± 2.4%) aerobically in 177 days. Apparent biomass growth accounted for 10 to 30.5% of the total initial carbon depending on the bioplastic and condition. Maximum aerobic and anaerobic biodegradation rates were improved up to 331 and 405%, respectively, at the lowest particle size tested (100–250 µm). This study highlights the usefulness of analysing biodegradation kinetics and carbon fate to improve both the development and testing of biodegradable materials, and waste treatments in the context of a circular bioeconomy.

Anaerobic phenanthrene biodegradation with four kinds of electron acceptors enriched from the same mixed inoculum and exploration of metabolic pathways

Polycyclic aromatic hydrocarbons (PAHs) are widespread and persistent contaminants worldwide, especially in environments devoid of molecular oxygen. For lack of molecular oxygen, researchers enhanced anaerobic zones PAHs biodegradation by adding sulfate, bicarbonate, nitrate, and iron. However, microbial community reports of them were limited, and information of metabolites was poor except two-ring PAH, naphthalene. Here, we reported on four phenanthrene-degrading enrichment cultures with sulfate, bicarbonate, nitrate, and iron as electron acceptors from the same initial inoculum. The high-to-low order of the anaerobic phenanthrene biodegradation rate was the nitrate-reducing conditions>sulfate-reducing conditions>methanogenic conditions>iron-reducing conditions. The dominant bacteria populations were Desulfobacteraceae, Anaerolinaceae, and Thermodesulfobiaceae under sulfate-reducing conditions; Moraxellaceae, Clostridiaceae, and Comamonadaceae under methanogenic conditions; Rhodobacteraceae, Planococcaceae, and Xanthomonadaceae under nitrate-reducing conditions; and Geobacteraceae, Carnobacteriaceae, and Anaerolinaceae under iron-reducing conditions, respectively. Principal component analysis (PCA) indicated that bacteria populations of longtime enriched cultures with four electron acceptors all obtained significant changes from original inoculum, and bacterial communities were similar under nitrate-reducing and iron-reducing conditions. Archaea accounted for a high percentage under iron-reducing and methanogenic conditions, and Methanosarcinaceae and Methanobacteriaceae, as well as Methanobacteriaceae, were the dominant archaea populations under iron-reducing and methanogenic conditions. The key steps of phenanthrene biodegradation under four reducing conditions were carboxylation, further ring system reduction, and ring cleavage.

Effect of influent pH on hydrolytic acidification performance and bacterial community structure in EGSB for pretreating crotonaldehyde manufacture wastewater after ozonation.

The objective of this work was to evaluate the effect of influent pH on the hydrolytic acidification (HA) performance and microbial community structure in an expanded granular sludge bed (EGSB) pretreating crotonaldehyde manufacture wastewater (CMW) after ozonation. The results showed that higher chemical oxygen demand (COD) removal rate (40.1%) and acidification degree (27.6%) were obtained at pH 8.0 than those at pH 6.0 and pH 4.0. The concentration of extractable extracellular polymeric substance (EPS) in the sludge gradually decreased with the pH decreasing from 8.0 to 4.0. A similar change was also observed for the concentration of total volatile fatty acids (TVFA) in the effluent. The optimal detoxification efficiency by the HA process was obtained at pH 8.0, with higher removal efficiency (all higher than 90%) of the main toxic pollutants (crotonaldehyde, 5-formyl-6-methyl-4,5-dihydropyran, etc.) and higher anaerobic biodegradation rate (44.5%) in biochemical methane potential (BMP) assay. Among the predominant genera, the Acinetobacter and Pseudomonas were possibly related to biodegradation of pollutants, since their higher relative abundance also coincided with the better performance of the HA process at pH 8.0.

Biostimulation enhanced the biotic degradation of hexabromocyclododecane in sediments

The aim of this study was to investigate biodegradation of γ-hexabromocyclododecane (γ-HBCDD) under conditions mimicking three bioremediation strategies: (i) biostimulation: addition of sodium formate and ethanol to stimulate biodegradation as the carbon source and electron donor, respectively; (ii) bioaugmentation: addition of an enrichment culture of Dehalobium chlorocoercia strain DF-1; and (iii) natural attenuation: no amendments. To differentiate between biotic and abiotic mechanisms affecting γ-HBCDD degradation, four control microcosms were set up as sterile, negative, abiotic, and contaminant control. Sediment microcosms were prepared in 20-mL bottles and operated as duplicate sacrificial reactors with a sediment-to-liquid ratio of 3 g wet solid:3.5 mL liquid. Total incubation time was 36 days with sampling every 4 days, except the last day. γ-HBCDD contents of sediments were extracted using ultrasonication and analyzed using GC-MS. Four control microcosms were used to observe the effect of (i) microbial activity (sterilization with mercuric chloride and autoclaving), i.e., sterile; (ii) microbial culture without DF-1 cells, i.e., negative control; (iii) sediments, where kaolinite is used instead of sediments, i.e., abiotic control; and (iv) γ-HBCDD, where no analyte is added, i.e., contaminant control. Biostimulation showed the highest γ-HBCDD biodegradation rate (k = 0.0542 day−1) and enhanced biodegradation compared to natural attenuation (k = 0.0155 day−1). Bioaugmentation (k = 0.0123 day−1) with DF-1 strain showed a sharp decrease at the beginning, but could not maintain this trend afterwards. Paired comparison of microcosms yielded no statistically significant difference between bioaugmentation and natural attenuation; hence, DF-1 strain did not improve degradation when compared to natural attenuation. This was also substantiated by observations from the negative control set. Sterile and abiotic control sets showed no significant concentration change in time. Consequently, adsorption was not considered as a significant mechanism acting on γ-HBCDD concentration change in our sediment microcosms. Thus, γ-HBCDD decrease observed in bioremediation microcosms was attributed to microbial activity. We reported effective analyte degradation with biostimulation. This was the first study to test bioaugmentation for HBCDD degradation, but we observed no enhancement of degradation with the DF-1 strain tested. Previous studies observed HBCDD reduction in their sterilized controls, hence reported total biotic and abiotic degradation rate. In this study, comparative evaluation of three test and four control microcosms enabled identification of only anaerobic biodegradation rates for γ-HBCDD, providing useful information for bioremediation of contaminated sites.

Anaerobic biodegradation of pyrene by Klebsiella sp. LZ6 and its proposed metabolic pathway

ABSTRACTPyrene is one of the polycyclic aromatic hydrocarbons, which are a potential threat to ecosystems due to their mutagenicity, carcinogenicity, and teratogenicity. In this study, several bacteria were isolated from oil contaminated sludge and their capacity to biodegrade pyrene was investigated. Of these bacteria, the monoculture strain LZ6 showed the highest pyrene anaerobic biodegradation rate of 33% after 30 days when the initial concentration was 50 mg/L, and was identified as Klebsiella sp. LZ6 by morphological observation, the GENIII technology of Biolog, and 16S rDNA gene sequence analysis. The influence of various culture parameters on the biodegradation of pyrene were evaluated, and Klebsiella sp. LZ6 all showed the high degradation rate at an inoculum of 10–20% (v/v), pH 6.0–8.4, temperature 30–38°C, and initial pyrene concentration of 50–150 mg/L. The intermediate metabolites of the anaerobic biodegradation were analyzed by GC-MS. Several metabolites were identified, such as pyrene, 4,5-dihydro-, phenanthrene, dibenzo-p-dioxin, and 4-hydroxycinnamate acid. The anaerobic metabolic pathway for the degradation of pyrene was inferred by the products. It seems that pyrene was first reduced to pyrene,4,5-dihydro- by the adding of two hydrogen atoms, and then the carbon–carbon bond cleavage at saturated carbon atoms generated phenanthrene.

Mesophilic anaerobic biodegradation test and analysis of eubacteria and archaea involved in anaerobic biodegradation of four specified biodegradable polyesters

The anaerobic biodegradability of four bioplastics powders (125–250 μm), polycaprolactone (PCL), poly(lactic acid) (PLA), polyhydroxybutyrate (PHB) and poly(butylene succinate) (PBS), were compared at 37 °C under aquatic conditions using our previously reported evaluation system (the modified ISO 13975 method). The bioplastics were ranked PHB >> PLA > PCL in terms of anaerobic biodegradation rate. The biodegradability of PHB, PLA, and PCL was 90% in 9 days, 29% and 49% in 277 days, and 3% and 22% in 277 days, respectively. PBS could not be anaerobically biodegraded by the sludge used in this study. The eubacteria and archaea participating in anaerobic bioplastic biodegradation were detected using the RT-PCR DGGE method. Some eubacteria participating in anaerobic biodegradation of PCL and PLA were of unique character. Eubacteria involved in anaerobic biodegradation of PHB were 98% homologous with Arcobacter thereius, Clostridium sp, and Clostridium sp, respectively. The eubacteria involved in the anaerobic biodegradation of PLA were 100% identical to Xanthomonadaceae bacterium and Mesorhizobium sp.; however, the other three bacterium were poorly related (<95% similarity) to any of the cultured-bacterium or database sequences. Anaerobic biodegradation of PCL was conducted by eubacterium with 98% similarity to A thereius, and by five organisms with poor similarity (≤95%) to any of the cultured-bacterium or database sequences. Archaea involved in anaerobic biodegradation of PLA and PCL were 97% and 95% identical to Methanosaeta concilii and Methanobacterium petrolearium. Only faint bands were observed in the RT-PCR DGGE profile of the archaea generated during PHB anaerobic biodegradation.

Anaerobic biodegradation of high-molecular-weight polycyclic aromatic hydrocarbons by a facultative anaerobe Pseudomonas sp. JP1.

Polycyclic aromatic hydrocarbons (PAHs) are harmful persistent organic pollutants, while the high-molecular-weight (HMW) PAHs are even more detrimental to the environment and human health. However, microbial anaerobic degradation of HMW PAHs has rarely been reported. One facultative anaerobe Pseudomonas sp. JP1 was isolated from Shantou Bay, Shantou, China, which could degrade a variety of HMW PAHs. After 40 days cultivation with strain JP1, anaerobic biodegradation rate of benzo[a]pyrene (BaP), fluoranthene, and phenanthrene was 30, 47, and 5 %, respectively. Consumption of nitrate as the electron acceptor was confirmed by N-(1-naphthyl) ethylenediamine spectrophotometry. Supplementation of sodium sulfite, maltose, or glycine, and in a salinity of 0-20 ‰ significantly stimulated anaerobic degradation of BaP. Lastly, the anaerobic degradation metabolites of BaP by strain JP1 were investigated using GC/MS, and the degradation pathway was proposed. This study is helpful for further studies on the mechanism of anaerobic biodegradation of PAHs.

Thermophilic anaerobic biodegradation test and analysis of eubacteria involved in anaerobic biodegradation of four specified biodegradable polyesters

The anaerobic biodegradability of 4 bioplastics powders (125–250 μm), polycaprolactone (PCL), poly(lactic acid) (PLA), polyhydroxybutyrate (PHB) and poly(butylene succinate) (PBS), were compared at 55 °C under aquatic conditions using our evaluation system reported previously, (the modified ISO 13975 method). In order of increasing anaerobic biodegradation rate, the bioplastics were ranked PHB > PCL > PLA. The biodegradability of PHB, PCL, and PLA was 90% in 14 days, 80% in 50 days, and 75% in 75 days, respectively. PBS could not be anaerobically biodegraded by the sludge used in this study. The eubacteria participating in anaerobic bioplastic biodegradation were detected using modern polymerase chain reaction techniques that distinguish metabolically active cells from resting, dormant, or starved cells. Some of the eubacteria participating in anaerobic biodegradation of PHB, PCL, and PLA were of unique character. Organisms involved in anaerobic biodegradation of PHB were 97, 100, and 98% identical to Peptococcaceae bacterium Ri50, Bacteroides plebeius, and Catenibacterium mitsuokai, respectively. The organism involved in the anaerobic biodegradation of PCL, however, was poorly related (<95% similarity) to any of the cultured-bacterium database sequences. Anaerobic biodegradation of PLA was undertaken by an organism with 100% identity to Ureibacillus sp., and by three organisms with poor similarity (≤95%) to any database sequence. Bacillus infernus, Propionibacterium sp., and two unidentified species were implicated in the anaerobic biodegradation of all three biodegradable plastics.

Effect of biostimulants on 2,4,6-trinitrotoluene (TNT) degradation and bacterial community composition in contaminated aquifer sediment enrichments

2,4,6-Trinitrotoluene (TNT) is a toxic and persistent explosive compound occurring as a contaminant at numerous sites worldwide. Knowledge of the microbial dynamics driving TNT biodegradation is limited, particularly in native aquifer sediments where it poses a threat to water resources. The purpose of this study was to quantify the effect of organic amendments on anaerobic TNT biodegradation rate and pathway in an enrichment culture obtained from historically contaminated aquifer sediment and to compare the bacterial community dynamics. TNT readily biodegraded in all microcosms, with the highest biodegradation rate obtained under the lactate amended condition followed by ethanol amended and naturally occurring organic matter (extracted from site sediment) amended conditions. Although a reductive pathway of TNT degradation was observed across all conditions, denaturing gradient gel electrophoresis (DGGE) analysis revealed distinct bacterial community compositions. In all microcosms, Gram-negative γ- or β-Proteobacteria and Gram-positive Negativicutes or Clostridia were observed. A Pseudomonas sp. in particular was observed to be stimulated under all conditions. According to non-metric multidimensional scaling analysis of DGGE profiles, the microcosm communities were most similar to heavily TNT-contaminated field site sediment, relative to moderately and uncontaminated sediments, suggesting that TNT contamination itself is a major driver of microbial community structure. Overall these results provide a new line of evidence of the key bacteria driving TNT degradation in aquifer sediments and their dynamics in response to organic carbon amendment, supporting this approach as a promising technology for stimulating in situ TNT bioremediation in the subsurface.

Anaerobic Biodegradation of Poly (Lactic Acid) Film in Anaerobic Sludge

The anaerobic biodegradation rates of four different sizes of poly (lactic acid) (PLA) films (thickness 25 μm) in anaerobic sludge at 55 °C were examined. The anaerobic biodegradation rates of small pieces of PLA film were slower than for large pieces of PLA film. We also examined whether PLA film could also be used as a reference material in the anaerobic biodegradation test in addition to PLA powder. The anaerobic biodegradation rate of PLA film became slower with lower activity sludge, but the rate of decrease was gradual, and the anaerobic biodegradation rate of PLA film was faster than the PLA powder (125–250 μm). The anaerobic biodegradation rate of the PLA powder (125–250 μm) reflected the plastic anaerobic biodegradation activity of the sludge more accurately than the thin PLA film (thickness 25 μm). Consequently, PLA powder (125–250 μm) is more suitable than thin PLA film (thickness < 25 μm) for use as a reference material to assess the plastic anaerobic biodegradation activity of the sludge in an anaerobic biodegradation test at 55 °C.

RNA analysis of anaerobic sludge during anaerobic biodegradation of cellulose and poly(lactic acid) by RT-PCR–DGGE

Here, we apply a method to evaluate the anaerobic biodegradability of bioplastics, such as polycaprolactone and poly(lactic acid) (PLA), in aquatic (slurry) conditions at 55 °C. Previous reports have suggested that some of the microorganisms participating in the anaerobic biodegradation of cellulose and PLA differ. However, polymerase chain reaction–denaturing gradient gel electrophoresis (PCR–DGGE) analysis was ineffective at detecting the microorganisms involved in the anaerobic biodegradation of cellulose and PLA. In this study, reverse transcription-PCR–DGGE analysis was employed instead. New DGGE bands appeared during the anaerobic biodegradation of cellulose and PLA, and some of these DGGE bands differed between the anaerobic biodegradation of cellulose and PLA, indicating that some of the microorganisms involved in these two processes differed. These results and those of our previous study therefore show that it is necessary to describe, not the anaerobic biodegradation rate of cellulose, as generally used at present, but the anaerobic biodegradation rate of plastic in the plastic anaerobic biodegradation test, to evaluate the sludge condition containing plastic anaerobic biodegradation activity in the sludge used in the anaerobic biodegradation test of plastics at 55 °C.

Biodegradation and seasonal variations in septage characteristics

Composite samples of septage discharging at the Khirbit As-Samra municipal wastewater treatment plant were analyzed during the period from February to the end of October 2007. Septage showed difference in concentrations of pollutants between summer and winter. The average total chemical oxygen demand (COD) of 6,425 mg/L during summer was 2.16 times greater than that in winter, which is 2,969 mg/L. The total biochemical oxygen demand (5 d) represented 45% of total COD in both winter and summer. Anaerobic biodegradability was 75% after 81 d of digestion at 35°C with a biodegradation rate constant (k) of 0.024 d⁻¹, which was lower compared with 0.103 d⁻¹ calculated for wastewater with domestic origin in Jordan. Aerobic biodegradability for septage was 48%-COD basis-after 7 d of digestion at 35°C. The lower anaerobic biodegradation rate of septage compared with that of raw wastewater of domestic origin suggested that septage could have a negative effect on the performance of a domestic wastewater treatment plant if septage discharges are not taken into account in the original design of the treatment plant.

Anaerobic biodegradation tests and gas emissions from subsurface flow constructed wetlands

Anaerobic tests with gravel from horizontal subsurface flow constructed wetlands (SSF) used for the treatment of urban wastewater were developed in order to evaluate the anaerobic biodegradability of their effluents. Two types of assays were conducted. The reactors used for the first type were glass vials of 45 mL, that were used for only one measurement, requiring starting experiments with a number of reactors equal to the measurements to be made. For the second type of experiments multiple measurements were done in the same reactors, by using flasks of 2.2 L. The COD of the SSF effluents used for the tests ranged from 60 to 130 mg/L. The evolution of CO 2 in the headspace of the reactors was used as indicator of anaerobic biodegradation rates. CO 2 mass emission rates ranged from 0.005 to 0.015 μmol/mL day. CH 4 generation was not detected in the tests in relation with the refractory properties of the effluent organic matter of the studied SSF. In situ measurement of CO 2 and CH 4 emissions from the gravel of the SSF ranged from 0.106 to 0.464 and from 0.039 to 0.107 mmol/m 2 h, respectively. Several CO 2 fluxes measured in the field were quite consistent with the emissions observed in the laboratory. The developed tests can help to understand the performance of SSF and improve their operation.

Depth-related influences on biodegradation rates of phenanthrene in polluted marine sediments of Puget Sound, WA

A whole-core injection method was used to determine depth-related rates of microbial mineralization of 14C-phenanthrene added to both contaminated and clean marine sediments of Puget Sound, WA. For 26-day incubations under micro-aerobic conditions, conversions of 14C-phenanthrene to 14CO 2 in heavily PAH-contaminated sediments from two sites in Eagle Harbor were much higher (up to 30%) than those in clean sediments from nearby Blakely Harbor (<3%). The averaged 14C-phenanthrene degradation rates in the surface sediment horizons (0–3 cm) were more rapid (2–3 times) than in the deeper sediment horizons examined (>6 cm), especially in the most PAH polluted EH9 site. Differences in mineralization were associated with properties of the sediments as a function of sediment depth, including grain-size distribution, PAH concentration, total organic matter and total bacterial abundance. When strictly anaerobic incubations (in N 2/H 2/CO 2 atmosphere) were used, the phenanthrene biodegradation rates at all sediment depths were two times slower than under micro-aerobic conditions, with methanogenesis observed after 24 days. The main rate-limiting factor for phenanthrene degradation under anaerobic conditions appeared to be the availability of suitable electron acceptors. Addition of calcium sulfate enhanced the first order rate coefficient ( k 1 increased from 0.003 to 0.006 day −1), whereas addition of soluble nitrate, even at very low concentration (<0.5 mM), inhibited mineralization. Long-term storage of heavily polluted Eagle Harbor sediment as intact cores under micro-aerobic conditions also appeared to enhance anaerobic biodegradation rates ( k 1 up to 0.11 day −1).

Intrinsic bioremediation of diesel-contaminated cold groundwater in bedrock

In 1982 diesel fuel migrated from a well lease site into underlying fractured bedrock contaminating the groundwater-bearing zone approximately 30 m below ground surface. Historical contaminant concentrations, geochemical indicators, and microbiological data were analysed to evaluate natural attenuation, specifically intrinsic bioremediation. Evidence of microbial activity was provided by most probable number (MPN) and commercial biological activity reaction tests (BART™). Laboratory microcosms using groundwater from the site were incubated under aerobic and anaerobic conditions with electron acceptor and nutrient amendment to assess microbial activity. Aerobic biodegradation rates were determined by measuring mineralization of 14C-dodecane. Nutrient amendment combined with a higher temperature (28 °C) increased the first-order aerobic biodegradation rate to 0.0066 d–1 from 0.0002 d–1 at 10 °C. Anaerobic biodegradation rates were calculated from depletion of total extractable hydrocarbons (TEH) over 717 d at 10 °C. Nutrient addition increased the anaerobic first-order biodegradation rate to 0.0016 from 0.0005 d–1. Data from these laboratory microcosms indicate that the current slow rates of intrinsic bioremediation may be enhanced with nutrient addition. Key words: intrinsic bioremediation, natural attenuation, groundwater, diesel fuel, hydrocarbon biodegradation, anaerobic hydrocarbon biodegradation, biological activity reaction test (BART™).

Use of Potassium Formate in Road Winter Deicing Can Reduce Groundwater Deterioration

We present here an aquifer scale study on the fate of potassium formate, an alternative, weakly corrosive deicing agent in soil and subsurfaces. Potassium formate was used to deice a stretch of a highway in Finland. The fate of the formate was examined by monitoring the groundwater chemistry in the underlying aquifer of which a conceptual model was constructed. In addition, we determined aerobic and anaerobic biodegradation rates of formate at low temperatures (-2 to +6 degrees C) in soil microcosms. Our results show that the formate did not enter the saturated zone through the thin vadose zone; thus, no undesirable changes in the groundwater chemistry were observed. Furthermore, the conceptual model explained the distribution of chloride in the aquifer used in deicing for the past 30 years. We recorded mineralization potential up to 97% and up to 17% within 24 h under aerobic and anaerobic conditions, respectively, in the soil and subsurface samples obtained from the site. This demonstrates that biodegradation in the topsoil layers was responsible for the removal of the formate. We conclude that the use of potassium formate can potentially help diminish the negative impacts of road winter deicing on groundwater without jeopardizing traffic safety.