Soil Slurry Systems Research Articles

Electrochemical Framework for Dynamic Tracking of Soil Organic Matter (SOM)

Soil Health parameters serve as excellent surrogate measures towards assessing environmental quality and understanding effects of climate change mitigation via carbon sequestration. Soil health monitoring in the near past has been highly qualitative and speculative with more recent advancements still trying to fill the void of determining a holistic soil profile through phantom based measurements. In fields and crop-circles, testing methods to perform in-situ profiling however from one lab is likely to vary with another and hence results are not universally compatible. Additionally, these normalized techniques ideally involve empirical approaches, extensive sample preparation which adds on to a temporal factor along with equipment for extraction and subsequently-analysis. Even with the upcoming research breakthroughs in non-destructive approaches like spectroscopy and tomography-based models, there is a barrier in-terms of equipment complexity and availability as well as high costs and high logistical overhead.There are a wide number of redox systems present in soil that exist in reduced state under ideal conditions (submerged). While Carbon monitoring would be highly beneficial in the field, an overall sense of the organic matter nutrients present in soil denoted as soil organic matter understanding would offer a wholistic manner of surveying soil and environmental health. In this work, faradaic and non-faradaic measurements are utilized to determine threshold changes in soil electrochemical activity due to presence of various electroactive substances present in the matrix. First, a galvanostatic approach using the chronopotentiometry modality was applied to a soil slurry system- ‘test’ sample to which different levels (w/v %) of the following amendments were added to see how the effective charge modulation can be visualized. Utilizing this experimental framework as preliminary information- A hypothesized mechanism of interaction between the RTIL (Room Temperature Ionic-Liquid) modified electrode and the OM functional moieties based on hydrogen bonding and pi-pi interactions captured using charge-based (chronocoulometry) and interfacial mapping-based (electrochemical impedance spectroscopy) method is utilized to design and test a first-of-a-kind electrochemical soil organic matter (SOM) sensor. Figure 1. Chronopotentiometric characterization of soil organic matter using an RTIL modified electrode. Figure 1

Bacterial community and physiological characteristics of octylphenol polyethoxylate biodegradation in soil slurries

Octylphenol polyethoxylate (OPEO) surfactants are widely used as commercial cleaning products and agricultural pesticides. Sewage effluents containing high levels of OPEOs are often discharged into soil–slurry systems. OPEOs have been identified as endocrine-disrupting compounds and are a threat to organisms present in ecological systems. Several studies have previously investigated methods to degrade OPEOs; however, clarifications regarding the impact on environmental ecology and bacterial physiological changes are required. This study aimed to evaluate the changes in bacterial community and physiological characteristics that occur during OPEO biodegradation in terms of abiotic factors. The results show that adsorption of OPEO on soil can be described using the Freundlich adsorption isotherm. The rates of OPEO biodegradation in different environmental matrices were compared and the results are as follows: aqueous system > clay–slurry system > natural soil–slurry system, all of which can be identified by their distinct community-level physiological profiles (CLPPs). OPEO biodegradation is always faster in the monomer state than in the micelle state. Bacterial numbers are maintained at high level and range from 107 to 108 CFU/mL; Pseudomonas spp. is dominant and likely plays an important role in OPEO biodegradation. Fluctuations in the utilisation of carboxylic acid groups were found. The enzymatic activity of esterases was significant, ranging from 12.5–54.1%. Phosphatase activity in the soil slurries ranged from 2.1–45.8%. The responses in terms of physiological characteristics indicate the soil ecology state during OPEO biodegradation.

Bisulfite reduction of soil iron for the reductive degradation of trichloroethylene

This study explored the potential reactivities of various reductants in inducing subsurface TCE degradation in natural soils. It was found that bisulfite (HSO3−) exhibited the ability to induce reduction in soil iron minerals, and increase the degradation of TCE in the soil slurry system; however, no TCE degradation occurred in the aqueous system. The role of TCE degradation by soil constituents, such as major soil mineral elements, Fe and humic acid (HA) on HSO3−, was examined in aqueous phase. It was seen that by themselves, the presence of Fe3+, HA, Fe2O3, FeOOH, and Fe3O4 did not result in substantial TCE removals. However, the presence of HSO3− can significantly induce iron reduction, producing a reducing condition that can result in complete TCE degradation. Furthermore, the reductive pathway was identified as the dominant degradation route via electron scavenging with periodate ion. To demonstrate the applicability of HSO3− reduction enhancement, a HSO3−/TCE mixed solution was flushed through a soil column, with gradually increased HSO3− concentrations, at a fixed flow rate, and also with varied flushing rates at a fixed HSO3− concentration. Based on our study, a 10 mM HSO3− solution may be effective for some environmental sites; however, each site requires specific evaluation based on contaminant concentrations and subsurface conditions.

Optimization of biotic and abiotic factors liable for biodegradation of chlorpyrifos and their modeling using neural network approaches

Chlorpyrifos has a substantial risk to human health besides biodiversity. In the present study, a previously isolated bacterial strain Enterobacter sp. SWLC2 has been used to investigate its biodegradation potential in different soil-slurries systems and to optimize culture conditions to achieve enhanced biodegradation of chlorpyrifos. The optimization results indicate that the maximum (87%) spiked-chlorpyrifos biodegradation occurred in a sandy loam soil-slurry system in aeration mode after 18 days of incubation at the optimal temperature (35 °C) and pH (7). The effect of sources of carbon/nitrogen (organic sugars, organic acids, and amino acids, etc.) on the biodegradation of chlorpyrifos has been investigated and their optimal values are estimated. The neural networks have been designed to find the optimal values of earlier factors in the predictive modeling of degradation of chlorpyrifos.

The Performance of Slurry Phase Reactors on the Treatment of Polycyclic Aromatic Hydrocarbons from Soils

The contaminated Kaynaklar soil containing high level of diesel (100,000 mg/kg dw) was treated in slurry systems with solid-to-liquid ratios (S/L) of 1/5, 1/10, and 1/20 to describe the performance of physical treatment. The soil microbial mass was inhibited by using mercury chloride and autoclaving prior to the diesel spiking in order to eliminate any bacterial degradation of non-aqueous phase liquids (NAPLs) and has been treated in the reactor systems for 8 h. The removal performance of PAHs in soil slurry systems was evaluated according to the number of benzene rings: 3, 4, and 5and 6 ring PAHs. The experimental results showed that PAH treatment efficiency sharply decreases in slurry soils with increasing number of benzene rings; maximum treatment efficiencies in soil were 82%, 56%, and 42% for 3 ring (ACY), 4 ring (PY), and 5 and 6 ring (BbF) PAHs, respectively. In addition, a significant correlation between the PAH removal efficiencies and their vapor pressures has found. The impact of solid-to-liquid ratio on slurry system performance was found negligible; therefore, higher solid-to-liquid ratios are recommendable to be applied on the contaminated sites to remove high concentrations of PAHs from soil for reducing the investment and operational costs. The soil used in this study has relatively large specific surface area and considerable amount of clay. The removal performance of slurry systems may be elevated with sandy soils containing high concentrations of PAHs, where can be faced at the seashores due to the off shore oil spills.

Evaluation of enhanced bioremediation for soils contaminated with used lubricating oil in soil slurry system

Evaluation of enhanced bioremediation for soils contaminated with used lubricating oil in soil slurry system

Significant Effect of Evaporation Process on the Reaction of Sulfamethoxazole with Manganese Oxide.

Soil in the vadose zone is an important sink for antibiotics. However, previous studies have examined only the degradation of antibiotics in soil slurry systems, which were largely different from real-world unsaturated soil environments. Whether the same transformation mechanisms apply to unsaturated soil systems has been a question. Here, the degradation of sulfamethoxazole (SMX) by manganese dioxide (γ-MnO2) in both suspension systems and evaporation processes were examined. Results show that the slow degradation of SMX in the suspension system can be significantly promoted as the water gradually evaporates. SMX degraded differently in evaporation as compared to suspension systems because of the quenching effect of generated Mn2+. Transformation products of SMX in both systems also showed different toxicity toward Escherichia coli because of different evolutions of intermediates. This study has strong implications for the assessment and prediction of the transformation and fate of antibiotics in natural soil environments.

Impact of bioaugmentation of soil with n-hexadecane-degrading bacteria and phosphorus source on the rate of biodegradation in a soil-slurry system

<p>In recent years, n-hexadecane, a component of diesel petroleum hydrocarbons, is frequently detected as the contaminant in many soils and water resources. The main aims of this study were focused on the feasibility of using the biodegradation for the removal of n-hexadecane from the soil-slurry system, by assessing the effects of phosphorus sources on biodegradation rate and determining the optimal conditions of the process. This study was carried out using an experimental method at the laboratory scale. The Taguchi method was used to optimize variables and their levels using the Qualitek-4 (w32b) software. We investigated the effects of initial concentration of n-hexadecane as the sole source of carbon (1-80 g/kg of soil), the role of phosphorus sources, at the concentration ranges from 10 to 600 g per Kg of soil, released by different bacterial species (Acinetobacter radioresistens, Pseudomonas aeruginosa, Bacillus subtilis, and the bacterial consortium) at the incubation time between 0 and 30 days. The optimum values of the response variables were predicted through signal-to-noise ratio (S/N). Results indicated that Bacillus subtilis were more effective in n-hexadecane degradation compared to the others (42%). Optimization process by Taguchi method suggested that the optimal conditions for the removal of n-hexadecane in a soil-slurry system are as follows: the initial n-hexadecane concentration as sole source of carbon in soil, Na2HPO4.12H2O as phosphorus source at the concentration of 300 mg per kg of soil and, finally, level of significance for the study parameters were 74.31, 6.48 and 8.51, respectively. In conclusion, bioaugmentation of soil with n-hexadecane-degrading bacteria providing an adequate supply of phosphorus source may enhance the biodegradation rate in a polluted soil.</p>

Gas-liquid oxygen transfer in aerated and agitated slurry systems with high solid volume fractions

Oxygen transfer can be a limiting step in aerobic biodegradation processes. Therefore, this process has been widely investigated for wastewater treatment, but only few research works have been done on soil slurry systems. This study focuses on the gas-liquid oxygen mass transfer in clay slurry conditions in an aerated and agitated reactor using a marine propeller. Conversely to most studies on oxygen transfer, pneumatic power input is not negligible compared to mechanical power input. Clay presence has a negative impact on the oxygen transfer. However, the effect of agitation and aeration on this process remains unaffected at the clay concentrations tested. Three different phases explaining the depletion in the oxygen transfer rate are hypothesized. A model to predict the oxygen transfer coefficient in slurry reactors, including the three operational parameters tested within their respective ranges, is proposed.

Effect of culturing temperatures on cadmium phytotoxicity alleviation by biochar.

Biochar produced from rice straw at 400°C (RS400) was prepared to determine its alleviating effect on Cd phytotoxicity to wheat seedlings under different cultivation temperatures and pH. A hydroponic system (pH4.3) and a loam soil slurry system were designed to respectively simulate acidic and neutral soil condition, and cultivation at increasing temperatures (20, 25, and 30°C) were performed to evaluate the greenhouse effect. The root and shoot elongation and the Cd concentration in root and solution were measured; furthermore, batch experiments for Cd adsorption were undertaken. An increasing inhibition of the root by Cd addition was observed at increasing temperatures. The inhibition rate was 50.50 and 20.80% in hydroponic system and slurry system at 25°C, respectively; however, the corresponding inhibition rates of root were significantly decreased to 25.5 and 3.5% with addition of RS400. This is mainly attributed to the reduction of Cd migration into the roots by RS400, which decreased Cd bioavailability. The mechanism behind the reduced Cd bioavailability is attributed to the Cd adsorption and the strong buffering capacity of acidity by RS400. Therefore, biochar could be a potential amendment for the remediation of Cd-contaminated soil even at increasing culturing temperatures.

BTEX- and naphthalene-degrading bacterium Microbacterium esteraromaticum strain SBS1-7 isolated from estuarine sediment

In this study, a non-pathogenic, BTEX-degrading Microbacterium esteraromaticum SBS1-7 was isolated from estuarine sediment in Thailand via an enrichment technique. M. esteraromaticum SBS1-7 was able to degrade all six BTEX components, in both liquid medium and soil slurry system, when BTEX was supplied as an individual component or a mixture. It exhibited a high level of tolerance towards a wide range of hydrocarbons and also utilized alkanes and naphthalene. Detection of metabolites produced during BTEX and naphthalene degradation revealed highly extensive biodegradation pathways used by M. esteraromaticum SBS1-7. Toluene was metabolized via activities of both monooxygenase (toluene 4-monooxygenase or T4MO) and dioxygenases (toluene dioxygenase or TDO and naphthalene 1,2-dioxygenase or NDO). Benzene was metabolized via phenol, possibly by an activity of T4MO. Ethylbenzene was converted into styrene and 1-phenethyl alcohol by a well-documented activity of NDO. Dioxidation of ethylbenzene, possibly by ethylbenzene dioxygenase or EBDO, was also found. All xylene isomers were converted into their corresponding alcohols via an activity of NDO while naphthalene was metabolized via dioxidation reaction by the same enzyme. This study is, by far, the first direct evidence of BTEX biodegradation by a non-pathogenic, rhizosphere bacterium M. esteraromaticum.

Bacterial mineralization of phenanthrene on thermally activated palygorskite: A 14C radiotracer study.

Clay-bacterial interaction can significantly influence the biodegradation of organic contaminants in the environment. A moderate heat treatment of palygorskite could alter the physicochemical properties of the clay mineral and thus support the growth and function of polycyclic aromatic hydrocarbon (PAH)-degrading bacteria. By using 14C-labelled phenanthrene and a model bacterium Burkholderia sartisoli, we studied the mineralization of phenanthrene on the surface of a moderately heat-treated (up to 400°C) palygorskite. The heat treatment at 400°C induced a reduction of binding sites (e.g., by the elimination of organic matter and/or channel shrinkage) in the palygorskite and thus imparted a weaker sequestration of phenanthrene on its surface and within the pores. As a result, a supplement with the thermally modified palygorskite (400°C) significantly increased (20-30%; p<0.05) the biomineralization of total phenanthrene in a simulated soil slurry system. These results are highly promising to develop a clay mineral based technology for the bioremediation of PAH contaminants in water and soil environments.

Screening Nonionic Surfactants for Enhanced Biodegradation of Polycyclic Aromatic Hydrocarbons Remaining in Soil After Conventional Biological Treatment.

A total of five nonionic surfactants (Brij 30, Span 20, Ecosurf EH-3, polyoxyethylene sorbitol hexaoleate, and R-95 rhamnolipid) were evaluated for their ability to enhance PAH desorption and biodegradation in contaminated soil after treatment in an aerobic bioreactor. Surfactant doses corresponded to aqueous-phase concentrations below the critical micelle concentration in the soil-slurry system. The effect of surfactant amendment on soil (geno)toxicity was also evaluated for Brij 30, Span 20, and POESH using the DT40 B-lymphocyte cell line and two of its DNA-repair-deficient mutants. Compared to the results from no-surfactant controls, incubation of the bioreactor-treated soil with all surfactants increased PAH desorption, and all except R-95 substantially increased PAH biodegradation. POESH had the greatest effect, removing 50% of total measured PAHs. Brij 30, Span 20, and POESH were particularly effective at enhancing biodegradation of four- and five-ring PAHs, including five of the seven carcinogenic PAHs, with removals up to 80%. Surfactant amendment also significantly enhanced the removal of alkyl-PAHs. Most treatments significantly increased soil toxicity. Only the no-surfactant control and Brij 30 at the optimum dose significantly decreased soil genotoxicity, as evaluated with either mutant cell line. Overall, these findings have implications for the feasibility of bioremediation to achieve cleanup levels for PAHs in soil.

Degradation of soil-adsorbed DDT and its residues by NZVI addition

Interaction of NZVI with DDTr in soil-slurry system.

Kinetics of biotransformation of chlorpyrifos in aqueous and soil slurry environments

The attenuation of chlorpyrifos (CPF) by the enriched indigenous soil microorganism was studied in 15 d aerobic and 60 d anaerobic batch experiments in aqueous and soil slurry (1:3 w/w) media. At the end of the batch experiments, 2.78 ± 0.11 μM of CPF was degraded by 82% in aerobic and 66% in anaerobic aqueous environments, while 12.4 ± 0.5 μM of CPF was degraded by 48% in aerobic and 31% in anaerobic soil slurries. The reduced degradation in the soil slurries was due to the significantly (2–10 times) slower rate of degradation of soil phase CPF compared with its degradation rate in water. The pathways of degradation of CPF were identified, including a partial anaerobic degradation pathway that is constructed for the first time. The simulation of the various conversions in the degradation pathways using first order kinetics was used to analyze relative persistence of metabolites. The common metabolite 3,5,6-trichloro-2-pyridinol (TCP) accumulated (increased monotonically during the period of experiments) in aerobic soil slurry and in anaerobic aqueous as well as soil slurry systems but did not accumulate in aerobic aqueous system. The most toxic compound in the pathway, chlorpyrifos oxon (CPFO) was not detected in anaerobic environment. In aerobic environment, CPFO was short lived in aqueous medium, but accumulated slowly in the soils.

The reductive degradation of 1,1,1-trichloroethane by Fe(0) in a soil slurry system

Most studies on the treatment of chlorinated contaminants by Fe(0) focus on aqueous system tests. However, few is known about the effectiveness of these tests for degrading chlorinated contaminants such as 1,1,1-trichloroethane (TCA) in soil. In this work, the reductive degradation performance of 1,1,1-TCA by Fe(0) was thoroughly investigated in a soil slurry system. The effects of various factors including acid-washed iron, the initial 1,1,1-TCA concentration, Fe(0) dosage, slurry pH, and common constituents in groundwater and soil such as Cl(-), HCO3 (-), SO4 (2-), and NO3 (-) anions and humic acid (HA) were evaluated. The experimental results showed that 1,1,1-TCA could be effectively degraded in 12 h for an initial Fe(0) dosage of 10 g L(-1) and a soil/water mass ratio of 1:5. The soil slurry experiments showed two-stage degradation kinetics: a slow reaction in the first stage and a fast reductive degradation of 1,1,1-TCA in the second stage. The reductive degradation of 1,1,1-TCA was expedited as the mass concentration of Fe(0) increased. In addition, high pHs adversely affected the degradation of 1,1,1-TCA over a pH range of 5.4-8.0 and the reductive degradation efficiency decreased with increasing slurry pH. The initial 1,1,1-TCA concentration and the presence of Cl(-) and SO4(2-) anions had negligible effects. HCO3(-) anions had a accelerative effect on 1,1,1-TCA removal, and both NO3(-) and HA had inhibitory effects. A Cl(-) mass balance showed that the amount of Cl(-) ions released into the soil slurry system during the 1,1,1-TCA degradation increased with increasing reaction time, suggesting that the main degradation mechanism of 1,1,1-TCA by Fe(0) in a soil slurry system was reductive dechlorination with 1,1-DCA as the main intermediate. In conclusion, this study provides a theoretical basis for the practical application of the remediation of contaminated sites containing chlorinated solvent.

Bioremediation of Phenanthrene by Mycoplana sp. MVMB2 Isolated from Contaminated Soil

AbstractThe effect of nutrient and surfactant addition on the biodegradation of phenanthrene was studied in a batch scale soil–slurry system using isolated Mycoplana sp. MVMB2strain. The study was conducted using an artificially phenanthrene spiked and as well as contaminated soil from petrochemical industrial site. Maximum phenanthrene degradation and subsequent high microbial growth were observed at optimum pH (pH 6) and C/N/P ratio (100:20:3). To investigate maximum substrate degradation potential of Mycoplana sp. MVMB2, very high concentrations of phenanthrene (50–200 mg/kg soil) were used. The organism was capable of degrading &gt;60% for a concentration below 20 mg/kg soil and &gt;40% for concentrations up to 200 mg/kg within 8 days. Further the influence of five different surfactants namely Span 80, Tween 20, Triton X‐100, cetyl trimethyl ammonium bromide, and sodium dodecyl sulfate were tested at their critical micelle concentration (CMC) levels for phenanthrene degradation in the soil. The addition of surfactant enhanced the biodegradation and a maximum of 84.49% was obtained for Triton X‐100. Complete phenanthrene degradation by Mycoplana sp. MVMB2 was observed at 3 CMC concentration of Triton X‐100. The optimized parameters obtained were used for the degradation of phenanthrene present in the contaminated soil and 98.6% biodegradation was obtained. Thus, the results obtained in the study suggested that biodegradation of phenanthrene by Mycoplana sp. MVMB2 appeared to be feasible to remediate phenanthrene rich contaminated sites.

Biosorption and biodegradation of phenanthrene and pyrene in sterilized and unsterilized soil slurry systems stimulated by Phanerochaete chrysosporium

To assess the “bioaccessible” pool of mycelia-bound polycyclic aromatic hydrocarbons (PAHs) and to quantify its biodegradation kinetics in soil, a soil-slurry system containing mycelial pellets of Phanerochaete chrysosporium as a separable biophase was set up. In sterilized and unsterilized soil-slurry, the distribution and dissipation of phenanthrene and pyrene in soil, fungal body of P. chrysosporium and water were independently quantified over the incubation periods. Biosorption and biodegradation contributions to bio-dissipation of dissolved- and sorbed-PAHs were identified. The biodegradation kinetics of PAHs by allochthonous P. chrysosporium and soil wild microorganisms was higher than those predicted by a coupled desorption–biodegradation model, suggesting both allochthonous and wild microorganisms could access sorbed-PAHs. The obvious hysteresis of PAHs in soil reduced their biodegradation, while the biosorbed-PAHs in P. chrysosporium body as an interim pool exhibited reversibly desorption and were almost exhausted via biodegradation. Both biosorption and direct biodegradation of PAHs in soil slurry were stimulated by allochthonous P. chrysosporium. After 90-day incubation, the respective biodegradation percentages for phenanthrene and pyrene were 63.8% and 51.9% in the unsterilized soil without allochthonous microorganisms, and then increased to 94.9% and 90.6% when amended with live P. chrysosporium. These indicate that allochthonous and wild microorganisms may synergistically attack sorbed-PAHs.

HYDROCARBON DEGRADING MICROFLORA IN A TROPICAL FUEL-CONTAMINATED AQUIFER: ASSESSING THE FEASIBILITY OF PAH BIOREMEDIATION

An aquifer located within a petroleum processing plant in Moin, Costa Rica, suffers hydrocarbon pollution. This study aimed to determine the ability of indigenous microorganisms from this site to degrade polycyclic aromatic hydrocarbons (PAHs) to evaluate the feasibility of an eventual bioremediation process. Aerobic conditions were found in the aquifer, while microbial analyses of the groundwater indicated the presence of important hydrocarbon-degrading populations. Sixteen PAH-degrading strains were isolated with the ability to grow on naphthalene (5 strains), phenanthrene (3), fluorene (6) and pyrene (2). Most of the identified isolates belonged to the genus Pseudomonas, although, Comamonas, Sphingomonas Stenotrophomonas and Delftia were also found. A mixture of selected strains was evaluated by its performance of PAH degradation in soil-slurry systems, where efficiency of removal was naphthalene > fluorene > phenanthrene > pyrene. This study is an initial approach to evaluate the feasibility of applying a bioremediation process in the contaminated site.

Adsorption Isotherms for Naphthalene on Clay and Silt Soil Fractions: A Comparison of Linear and Nonlinear Methods

Polycyclic aromatic hydrocarbons occur naturally in petroleum oil and coal and the burning of fuel and the activities of paper mills also release these compounds to the environment. Batch experimental adsorption study for both soil fractions was conducted in a soil slurry system at ambient temperature, using &lt;0.02mm particle sizes. Comparison was made of the linear least-squares method and a trial-and-error nonlinear method of some widely used isotherm models for the adsorption of naphthalene on clay and silt fractions. The experimental results were fitted to the Langmuir, Freundlich, Radke-Prausnitz, Sips, Temkin and Redlich-Peterson isotherms to obtain their characteristic parameters of each model. The coefficient of determination obtained from the different models using the linear method showed that Freundlich isotherm had the highest values for both clay and silt soil fractions with values of 0.843 and 0.897 respectively. The equilibrium data did not fit the Langmuir isotherm with values of 0.287 and 0.021 for clay and silt soil respectively. Using the nonlinear method the equilibrium data gave good fit for Radke-Prausnitz, Sips, Temkin and Redlich-Peterson isotherms. Sips isotherm gave the best fit for silt soil with the r2 value of 0.9779 and this was followed by Temkin isotherm for clay soil with the value of 0.9673.