Soil Batch Experiments Research Articles

Nitrate and Dissolved Organic Carbon Release in Sandy Soils at Different Liquid/Solid Ratios Amended with Graphene and Classical Soil Improvers

This study emphasizes the importance of employing parallel batch tests with different liquid/solid (L/S) ratios to assess their dissolution mechanisms. Changes in physicochemical parameters (electrical conductivity, pH, and oxidation-reduction potential), as well as the sorption/desorption of dissolved organic carbon (DOC) and nitrate (NO3−) due to graphene addition in a calcareous sandy soil (CS) and in a siliciclastic riverine sandy soil (SS) were assessed via batch experiments at different L/S ratios. Graphene’s production is growing at a great pace, so it’s important to test methods to reuse graphene wastes. The results of soil batch experiments mixed with graphene were compared with classical soil improvers (compost, biochar, and zeolites). The batches were performed using the saturation soil extraction method with deionized water as a proxy of rainwater. The contact time was 48 h. At the end of the experiment, water samples were collected to be analyzed for NO3−, DOC, DIC, Ca, and Mg. Graphene did not alter the physiochemical parameters of both soils. Moreover, its addition did not trigger any NO3− increase respect to control and to other improvers. Biochar increased EC and pH beyond recommended limits for most crops’ growth in both soils. As expected, compost addition produced the highest NO3− release.

Effects of composting and carbon based materials on carbon and nitrogen loss in the arable land utilization of cow manure and corn stalks

Recycling organic wastes to arable land as fertilizers has been recognized as a sustainable utilization to reduce environmental pollution. Techniques used for the treatment of organic wastes determine their nutrient contents and thus fertilizer efficiency for agricultural applications. The current study investigated the influences of composting and carbon based materials (biochar and woody peat), on carbon and nitrogen loss in the process of agricultural wastes utilization in the soil batch experiments. The results indicated composting process significantly strengthened the organic matter mineralization, increased the carbon loss rates from 33.46-38.96% to 60.54–86.15% and the nitrogen loss rates from 5.01-22.22% to 48.64–58.16%, dominant lost as carbon dioxide (CO2) and ammonia (NH3) emissions. Addition of carbon based materials could effectively reduce the carbon and nitrogen loss during both composting and soil incubation process. When the composted organic wastes were used in the soil batch experiments, woody peat was more effective to reduce nitrogen loss, while biochar was more effective to control carbon loss. When organic wastes were directly fertilized to soil, biochar could effectively reduce nitrogen loss. These results suggested that fertilizing raw agricultural wastes to with carbon based materials could reduce carbon and nitrogen losses, and increased the nutrient bioavailability in soil in comparison with their farmland application after composting.

Experimental evaluation of CO2 percolation effects on subsurface soil microbiota

Carbon dioxide is an increasing greenhouse gas; its capture and sequestration seems a promising alternative to mitigate global warming, providing all physical, chemical and biological aspects of subsurface gas sequestration are understood. Possible leaks may change soil balance, impacting ecosystems and, consequently, human and animal health. Few data are available on the effects of augmented CO2 concentrations in soil and studies are required to define the role of biological systems and response mechanisms, and to identify CO2 bioindicators for post-injection monitoring. This study was conducted with soil from the Atlantic forest zone, in two scales: unstructured soil batch experiments, in aerobic and CO2 atmosphere, and column microcosms with unstructured and structured soil under CO2 percolation. Microbial metabolic profiles, protein synthesis and degradation activity, soils moisture, available carbon and pH were assessed. In all assays, microbial activity tended to drop with prolonged exposure to CO2. In batch and structured soils, augmented activity, biomass, species richness, besides altered metabolic profiles, all seemed linked to increased CO2. In unstructured column soil a slower pace of response was explained by low initial activity. No significant change in soil moisture was detected and stable pH indicated absence of carbonate precipitation. In conclusion, augmented CO2 changes microbiota composition, enhancing the activity of favoured anaerobic species, which could change ecosystem functions.

Sorption and degradation of 17β-estradiol-17-sulfate in sterilized soil–water systems

To identify abiotic processes that govern the fate of a sulfate conjugated estrogen, 17β-estradiol-17-sulfate (E2-17S), soil batch experiments were conducted to investigate the dissipation, sorption, and degradation of radiolabeled E2-17S under sterilized conditions. The aqueous dissipation half-lives (DT50) for E2-17S ranged from 2.5 to 9.3h for the topsoil of high organic carbon (OC) content (1.29%), but E2-17S remained at ∼80% of applied dose in the low OC (0.26%) subsoil by 14d. The non-linear sorption isotherms indicated limited sorption of E2-17S, and the concentration-dependent log KOC values were 2.20 and 2.45 for the topsoil and subsoil, respectively. Additionally, two types of hydroxyl E2-17S (OH-E2-17S and diOH-E2-17S) were found as major metabolites in the aqueous phase, which represented 9–25% and 6–7% of applied dose for the topsoil and subsoil at 14d, respectively. Free estrogens, 17β-estradiol (E2) and estrone (E1), were detected from the sorbed phase of the soil–water systems.

Effects of liquid swine manure on dissipation of 17β-estradiol in soil

17β-estradiol (E2), a natural estrogenic hormone, degrades within hours and bind strongly to soils and sediments; however, estrogens are frequently detected in the environment at concentrations that impact water quality. Colloidal (COC) and dissolved (DOC) organic carbon may enhance the persistence and mobility of E2. Soil batch experiments were used to identify the persistence and sorption of radiolabeled E2 dissolved in solutions of (i) COC/DOC derived from liquid swine manure and (ii) CaCl2. Estradiol disappeared from the aqueous phase before 7d in the CaCl2 solution, yet persisted throughout the duration of the 14d experiment in the liquid manure solution. There was also concomitant formation of estrone (E1; a metabolite of E2) as E2 dissipated in sterile batch experiments, which was attributed to abiotic oxidation. The liquid manure solution appeared to interact with the estrogen and/or oxidation reaction sites, reducing E2 degradation. Furthermore, the liquid manure solution reduced E2/E1 binding to the soil surface resulting in more E2/E1 in the aqueous layer compared to the CaCl2 solution. Ultrafiltration results of liquid manure indicated that ∼1/3 of E2 was associated with COC, which may be responsible for the reduced degradation and sorption of E2 in the liquid manure solution.

Zinc and lead transfer in a contaminated roadside soil: Experimental study and modeling

The application of a surface complexation model to simulate the sorption of metals on single sorbents is very well investigated, but very little is known regarding the use of surface complexation modeling to simulate the metal mobility in contaminated roadside soils. The overall objective of this study was to examine whether the use of the surface complexation model (SCM) could correctly describe the migration of zinc and lead in roadside soil under various physicochemical conditions. The release and transport of Zn and Pb was studied by means of batch reactors and saturated chromatography columns. Soil batch experiments were conducted to evaluate the effects of pH variation and ionic strength on the metal mobility from soil. Elution of Pb and Zn was examined in column experiments by using acetic acid at pH5 and EDTA at pH7. The modeling work has focused on the development of a SCM using MINTEQ2 database incorporated in PHREEQC-2 to describe the interactions between trace metals and the main mineral soil components (quartz, iron and aluminum oxides). In this study, it was found that the SCM was able to simulate the mobility of metals from soil by assuming one mononuclear surface reaction between one solution species (Me 2+) and one type of site on the surface of soil dominant sorbents.

Kinetics of Trichloroethylene Cometabolism and Toluene Biodegradation: Model Application to Soil Batch Experiments

AbstractTrichloroethylene (TCE) biodegradation in soil under aerobic conditions requires the presence of another compound, such as toluene, to support growth of microbial populations and enzyme induction. The biodegradation kinetics of TCE and toluene were examined by conducting three groups of experiments in soil: toluene only, toluene combined with low TCE concentrations, and toluene with TCE concentrations similar to or higher than toluene. The biodegradation of TCE and toluene and their interrelationships were modeled using a combination of several biodegradation functions. In the model, the pollutants were described as existing in the solid, liquid, and gas phases of soil, with biodegradation occurring only in the liquid phase. The distribution of the chemicals between the solid and liquid phase was described by a linear sorption isotherm, whereas liquid‐vapor partitioning was described by Henry's law. Results from 12 experiments with toluene only could be described by a single set of kinetic parameters. The same set of parameters could describe toluene degradation in 10 experiments where low TCE concentrations were present. From these 10 experiments a set of parameters describing TCE cometabolism induced by toluene also was obtained. The complete set of parameters was used to describe the biodegradation of both compounds in 15 additional experiments, where significant TCE toxicity and inhibition effects were expected. Toluene parameters were similar to values reported for pure culture systems. Parameters describing the interaction of TCE with toluene and biomass were different from reported values for pure cultures, suggesting that the presence of soil may have affected the cometabolic ability of the indigenous soil microbial populations.

Coupling transport and biodegradation of toluene and trichloroethylene in unsaturated soils

Trichloroethylene (TCE), a common groundwater pollutant generally resistant to aerobic biodegradation, can be cometabolized in the presence of another compound such as toluene. The coupled transport and biodegradation of TCE and toluene was investigated and modeled in laboratory soil columns. Toluene biodegradation was linked to microbial growth using Monod kinetics, while TCE degradation was described using Michaelis‐Menten kinetics modified to account for changing enzyme levels. Biodegradation of TCE was modeled as a mass fraction of the toluene degradation rate. Both growth and decay were incorporated into the equations to model microbial population dynamics. With the exception of the initial biomass, a single set of parameters to describe both degradation functions was obtained from independent soil batch experiments. Physical parameters were obtained from sterile soil columns. The initial biomass declined from the inlet to the outlet side of the chamber. Toluene was fully degraded in the soil column with the majority occurring closest to the inlet chamber. A substantial amount of TCE was not degraded because it diffused faster and was transformed at a lower rate than toluene.

Water-soluble organic matter in forest soils

By applying a modified gel permeation technique, the molecular-size distribution (MSD) and complexing properties of water-soluble organic matter (WSOM), isolated from the Ah horizon under stands with either Douglas-fir, European beech or Scots pine were established. Both with respect to MSD and complexing properties, the dissolved organic matter was highly similar. WSOM was comprised of compounds apparently high in molecular weight (>1 kDa) and with a complexing capacity of 1.0±0.1 μmol mg−1 carbon as determined for Cu(II) at pH 5.5 and 0.01 M ionic strength. The effect of WSOM on the partitioning of cations between soil solid phase and soil solution was evaluated in several soil batch experiments using loamy sand or sandy soil material. Although a large part of WSOM was sorbed to the soil matrix, Al, Cu, Fe and Pb were solubilized in considerable amounts by complexation. The Mn concentration in the soil solution was also significantly increased but this probably resulted from a redox reaction, with certain constituents of WSOM serving as electron donor. With a decrease in soil pH, cation mobilization by WSOM was significantly lower as a result of increased sorption and a decrease in complexing capacity of the soluble organics. Application of several low MW aliphatic and phenolic acids gave results similar to the results obtained with WSOM.