Stirred Flow Chamber Research Articles

Aged polyamide microplastics enhance the adsorption of trimethoprim in soil environments

Microplastics (MPs) in the environment typically age. However, the influence of aged MPs on the adsorption of antibiotics in soil remains unknown. In this study, the adsorption behavior of trimethoprim (TMP) on soil and soil containing aged polyamide (PA) was investigated using batch and stirred flow chamber experiments. The adsorption of TMP on the tested soil with and without PA was fast, with the ka values ranging from 50.5 to 55.6 L (mg min)-1. The adsorption of TMP on aged PA was more than 20 times larger than that on the tested soil, which resulted in an "enrichment effect." Furthermore, aged PA altered the pH of the reaction system, thereby enhancing the adsorption of TMP. Consequently, the Kd values of TMP for soil, soil containing 5%, and 10% aged PA were 5.64, 12.38, and 23.65 L kg-1, respectively. The effect of aged PA on the adsorption of TMP on soil depended on pH values. However, TMP adsorption on soil containing 10% aged PA was constantly higher (p < 0.01) than that on soil with NaCl concentrations ranging from 0 to 50mmol L-1. These findings provide new insights into the effect of environmental MPs on the fate and transport of antibiotics in soil environments.

Phosphorus adsorption, availability, and potential loss characteristics in an Ultisol‐derived paddy soil chronosequence, using a stirred‐flow chamber study

AbstractThe adsorption characteristics, availability, and a loss risk of phosphorus (P) in paddy soil chronosequences had not been well established. In the present study, P adsorption characteristics of paddy soil chronosequence with 0, 7, 22, or 80 years of paddy cultivation history (PS0, PS7, PS22, and PS80, respectively) were identified by P adsorption isotherm, envelope, and stirred‐flow chamber (SFC) kinetics, along with the assessment of P availability and loss risks. Results indicated that P adsorption and desorption followed the same order of PS0 &gt; PS7 &gt; PS22 &gt; PS80. Pearson's correlation analysis revealed P adsorption capacity was significantly and positively correlated with the concentrations of both free iron (Fe) and aluminum (Al) (hydro)oxides (Fed and Ald, respectively), suggesting that the major P sorbents were Fed and Ald. Findings from SFC adsorption kinetics suggested that the kinetics of both P adsorption and desorption were biphasic, being fast in the first 100 min (75.11%–87.57% of P adsorbed and 79.00%–88.65% of P released), followed by a slow phase for the remaining 180 min. Bray‐P increased with the duration of rice cultivation and reached a maximum of 77.90 mg kg−1 at PS80, along with the highest P saturation degree and equilibrium phosphorus concentrations of 7.56% and 2.33 mg L−1, respectively. Hence, with an increasing duration of paddy cultivation, there was a less pronounced P sink function and a lower P availability, but a higher P loss risk, indicating that P availability in the younger and loss risk in the older Ultisol‐derived paddy soils deserve greater attention.

Adsorption-desorption kinetics and phosphorus loss standard curve in erosive weathered granite soil: Stirred flow chamber experiments

Weathered granite has a high soil adsorption rate and it is difficult to apply phosphate fertilizers. In order to effectively use phosphorus, it is very important to study the intensity and speed of soil retention and desorption of phosphorus. The purpose of this study is to evaluate the kinetics of adsorption and desorption in soils with different erodibility. We selected three weathered granite soils with hugely different erosions: topsoil layer (TL-Tillage layer), laterite layer (LL-Laterite layer) and sand layer (SL-Sand layer). Phosphorus adsorption and desorption experiments were successively carried out in the stirred flow reaction chamber, and the stirred flow experiment under unsaturated adsorption conditions was carried out for the first time. The maximum absorption capacity (qamax) and desorption capacity (qdmax) of phosphorus in TL soil was both greater than that in LL and SL soil. The adsorption process mainly occurs within the first 250 min of the reaction. The desorption ratio (Dr) in the TL soil is smaller than the LL and SL soil. The order of the fast reaction sites proportion (F) is SL > LL > TL in adsorption process and LL > SL > TL in desorption process. Seven key soil property indicators can fit qamax and qdmax values well. In the determination coefficient (R2) of the standard curve of phosphorus loss, SL soil is the larger than TL and LL. The qamax and Dr values measured in the stirred flow experiment are both larger than those in the batch experiment. Among the three soils, LL has the lowest adsorption capacity for P and the highest accessibility. The slow adsorption sites in TL account for the main part, and the adsorption in LL and SL mainly occurs at fast adsorption sites. Through the establishment of the phosphorus loss standard curve, the maximum phosphorus loss in the entire region can be predicted and calculated. This study can provide theoretical basis and reference for phosphorus management in similar soil types or physical geographical areas with severely eroded soils.

Effect of ferrolysis and organic matter accumulation on chromate adsorption characteristics of an Oxisol-derived paddy soil

How paddy cultivation influences the adsorption isotherms, envelopes, and the kinetics of hexavalent chromate (Cr(VI)) on Fe (hydro)oxide-rich paddy soil, as well as the mechanisms involved, remain largely unaddressed. To this end, the Cr(VI) adsorption characteristics on a paddy soil, in comparison with its parent upland Oxisol, were studied. The results showed that Cr(VI) adsorption capacities (Qmad) were higher in the surface Oxisol than in the same layer of paddy soil. The Qmad increased by 18.0% and 41.3% after removal of soil organic matter (SOM) from the surface Oxisol and paddy soil layers, respectively, indicating that Cr(VI) adsorption was considerably inhibited by SOM. The adsorption and desorption isotherms demonstrated that non-electrostatic adsorption was mainly responsible for Cr(VI) adsorption, accounting for 59.37%–83.42% of Cr(VI) adsorption capacities. The negative shift of the zeta potential–pH curves with Cr(VI) loading further corroborated the finding that non-electrostatic adsorption is largely responsible for Cr(VI) retention. Cr(VI) adsorption at equilibrium, obtained by the stirred flow chamber technique, and the free Fe (hydro)oxides (Fed) contents were in the same order, suggesting that Fed are the main adsorbents for Cr(VI). Therefore, paddy cultivation has had a profound impact on the electrochemical properties of the Oxisol and on subsequent Cr(VI) adsorption characteristics.

Adsorption-desorption of doxycycline in agricultural soils: Batch and stirred-flow-chamber experiments

With the aim of obtaining information about the environmental fate and dynamics of the antibiotic doxycycline (DC) when it reaches soil, adsorption and desorption processes were studied for this compound in 20 agricultural soils, by means of batch-type and stirred-flow-chamber experiments. The results indicate that the studied soils adsorbed high amounts of DC, with adsorption percentages >91% in all cases. In addition, adsorption results were satisfactorily modeled, with good fittings to the Langmuir and Freundlich equations, with the values for Langmuir's maximum adsorption capacity (qmax) varying between 14,692 and 26,141 μmol kg−1 (average 17,816), and between 1,906 and 13,120 Ln μmol1−n kg−1 (average 6,969) for the Freundlich affinity coefficient, which are very high. The soil variables most related to the adsorption of the antibiotic were linked to organic matter (specifically, soil organic carbon–SOC– and soil nitrogen -N- contents), and to the clay fraction, as well as to cation exchange capacity, being the soils with a greater content in these variables those that presented a greater adsorption. FTIR results shown that DC adsorption mechanisms were based on interactions such as hydrogen bonds and π-π interactions between the antibiotic and soils. Desorption was very low, reaching values between 1 and 2% in batch experiments, and between 5 and 15% in stirred flow chamber experiments, which indicates a strong hysteresis affecting adsorption and desorption processes. This fact can be considered positively, as these soils could retain DC very strongly, thus reducing risks to human and ecological health.

Factors influencing adsorption and desorption of trimethoprim on marine sediments: mechanisms and kinetics

Adsorption-desorption behavior of ionic antibiotics in natural aquatic environment is complex, especially in coastal or estuary area where influencing factors such as pH and salinity usually varied in a wide range. In this study, batch-type and stirred flow chamber (SFC) experiments were carried out to simulate the sorption-desorption behavior of trimethoprim (TMP) in seawater-sediment system. Equilibrium and kinetic modeling were carried out to determine the rate and extent of TMP sorption on two marine sediments with different properties. Sediment BHB (K d , 6.40Lkg-1) has a greater sorption capacity compared with sediment LZB (K d , 3.40Lkg-1), which is related to the higher content of organic carbon and clay of sediment BHB. Adsorption of TMP varied in the pH range of 6.9 to 8.1 with maximum adsorption at pH 7.4. Increasing salinity and presence of phosphate and nitrate led to decreased TMP sorption. Attenuated total reflection Fourier transform infrared (ATR-FTIR) analysis demonstrated the formation of hydrogen bond between TMP and marine sediments. Adsorption of TMP on marine sediments was a non-equilibrium process that can be described with second-order kinetic model. Our analysis suggested that chemical non-equilibrium was the rate controlling process and intraparticle diffusion was also involved in TMP adsorption. A moderate desorption percentage (16.4-22.8% for LZB and 32.5-42.0%for BHB) was observed. Overall, the results showed that environmental factors and time-dependent processes need to be considered in modeling the fate and transport of TMP in coastal/estuarine waters.

Retention of quaternary ammonium herbicides by acid vineyard soils with different organic matter and Cu contents

Adsorption and desorption of quaternary ammonium herbicides (paraquat, diquat, and difenzoquat) has been studied in four acid vineyard soils with a range of organic matter and copper contents, in order to assess the influence of copper on herbicide adsorption. Adsorption at equilibrium has been studied in batch experiments, and kinetics have been studied in a stirred flow chamber. Adsorption and desorption kinetics were well described by the pseudo-first-order model. The retention capacity for the pesticides by the four soils, based on the results of the batch experiments, followed the sequence: paraquat>diquat>difenzoquat. The different adsorption capacities of each soil were not related to pH, clay or organic matter contents, as could be expected, but rather to copper contents. The results show that, in vineyard soils with these characteristics, competition with Cu for adsorption sites is an important factor in quaternary ammonium herbicides retention.

Heavy metals fractionation and desorption in pine bark amended mine soils

The European Community Bureau of Reference method (BCR) was used for evaluating the effects of pine bark amendment (0, 24 and 48 g kg−1) and ageing (1 and 30 days) on Cd, Cu, Ni, Pb and Zn fractionation, on samples from an acid mine soil. In addition, the stirred flow chamber technique was applied for analyzing heavy metals desorption from the unamended and pine bark amended mine soil. When the unamended soil were not subjected to ageing, the added heavy metals were mainly accumulated as soluble fraction (>90% for Cd, Ni and Zn; 71% for Cu; and 45% for Pb). Pine bark amendment and ageing had little effect on Cd, Ni and Zn fractionation, whereas important changes were detected for Cu and Pb in response to both pine bark amendment and ageing (decrease in the soluble fractions, and increase in less mobile fractions). Desorption experiments showed that both pine bark amendment and ageing decreased heavy metals release from the mine soil. The results of this study indicate that pine bark amendment could be used to increase heavy metals retention (especially in the case of Cu and Pb) in acid mine soils, thus reducing the risks of metal transfer to uncontaminated environmental zones.

Adsorption-desorption of oxytetracycline on marine sediments: Kinetics and influencing factors

To reveal the kinetics and mechanisms of antibiotic adsorption/desorption processes, batch and stirred flow chamber (SFC) experiments were carried out with oxytetracycline (OTC) on two marine sediments. The OTC adsorption capacities of the marine sediments were relatively weak and related to their organic carbon (OC) and contents of fine particles. Sorption isotherms of OTC on marine sediment can be well described by both the Langmuir and Freundlich models. Langmuir adsorption maxima (qmax) and Freundlich distribution coefficients (Kf) increased with the decrease of salinity and pH, which indicated the importance of variable charged sites on sediment surfaces. A second order kinetic model successfully described adsorption and desorption kinetics of OTC and well reproduced the concentration change during stop-flow. The adsorption kinetic rates (ka) for OTC under different experimental conditions ranged from 2.00 × 10−4 to 1.97 × 10−3 L (mg min)−1. Results of SFC experiments indicated that diffusive mass transfer was the dominant mechanism of the time-dependent adsorption of OTC and its release from marine sediment was mildly hysteretic. The high desorption percentage (43–75% for LZB and 58–75% for BHB) implied that binding strength of OTC on two marine sediments was weak. In conclusion, marine sediment characteristics and environmental factors such as salinity, pH, and flow rate are critical factors determine extent of OTC sorption on marine sediment and need to be incorporated in modeling fate and transport of OTC in marine environment.

Adsorption and desorption kinetics and phosphorus hysteresis in highly weathered soil by stirred flow chamber experiments

Soils with a high weathering degree present great difficulties for management of phosphorus (P) fertilization due to their high adsorption rates. The magnitude and velocity of the P retention phenomena in these soils is still poorly understood and has great importance to effective management of soil phosphorus. The objective of this study was to evaluate the adsorption and desorption kinetics and phosphorus adsorption irreversibility (hysteresis) in highly weathered soils. For this purpose, we selected four soils: Xanthic Ferralsol-1 (FR-1), Xanthic Ferralsol-2 (FR-2), Rhodic Ferralsol (FR-3) and Hortic Anthrosol “Terra Preta de Índio” (AT). Adsorption followed by desorption experiments in Stirred flow chamber were performed. From obtained data, parameters related to P kinetics were estimated, considering the presence of two types of adsorption and desorption sites (fast and slow), estimating also the hysteresis index. It was observed that FR-2 and FR-3 showed higher P adsorption and most of the adsorbed P was at first 100min of evaluation. Furthermore, in FR-1, FR-2 and FR-3, approximately half of adsorption occurred by rapid sites (F which is the fraction of fast sites ranging from 0.45 to 0.55), while AT adsorption was lower (qmax=48.95mgkg−1) and occurred slower (F=0.33). In FR-2 and FR-3, between 71 and 72% of adsorbed P was not desorbed, while in AT, only 11% of P was irreversibly adsorbed. The P kinetics in highly weathered soils proved to be a process governed by the fast sites on adsorption and slow sites on desorption, resulting in high levels of hysteresis.

Changes in Cd, Cu, Ni, Pb and Zn Fractionation and Liberation Due to Mussel Shell Amendment on a Mine Soil

AbstractMining activities are related to relevant environmental pollution issues that should be controlled. We used sequential extractions to fractionate Cd, Cu, Ni, Pb and Zn retained on unamended or mussel shell‐amended mine soil samples, all of them treated with a mixture of the five heavy metals (total metal concentration of 1·57 mmol L−1), after 1, 7 and 30 days of incubation. In addition, we used the stirred flow chamber technique to study the release of each of the five heavy metals from these different unamended and shell‐amended soil samples. The results indicate that the shell amendment caused a decrease in the most soluble fraction, while increasing the most recalcitrant (least mobile) fraction. With equivalent implications, the stirred flow chamber experiments showed that mussel shell amendment was associated to a decrease in heavy metal release and increased retention. The highest mussel shell dose and incubation time caused the most relevant changes in pH values and thus in metal retention, also indicating the importance of pH modifications in the mechanism of retention acting in the amended samples. In view of these results, the use of mussel shell amendment can be encouraged to increase heavy metal retention in acid mine soils, in order to minimise risks of environmental pollution. Copyright © 2016 John Wiley &amp; Sons, Ltd.

Competitive adsorption/desorption of tetracycline, oxytetracycline and chlortetracycline on two acid soils: Stirred flow chamber experiments

The objective of this work was to study the competitive adsorption/desorption of tetracycline (TC), oxytetracycline (OTC) and chlortetracycline (CTC) on two acid soils. We used the stirred flow chamber technique to obtain experimental data on rapid kinetic processes affecting the retention/release of the antibiotics. Both adsorption and desorption were higher on soil 1 (which showed the highest carbon, clay and Al and Fe oxides content) than on soil 2. Moreover, hysteresis affected the adsorption/desorption processes. Experimental data were fitted to a pseudo-first order equation, resulting qamax (adsorption maximum) values that were higher for soil 1 than for soil 2, and indicating that CTC competed with TC more intensely than OTC in soil 1. Regarding soil 2, the values corresponding to the adsorption kinetics constants (ka) and desorption kinetics constants for fast sites (kd1), followed a trend inverse to qamax and qdmax respectively. In conclusion, competition affected adsorption/desorption kinetics for the three antibiotics assayed, and thus retention/release and subsequent transport processes in soil and water environments.

Kinetics of tetracycline, oxytetracycline, and chlortetracycline adsorption and desorption on two acid soils.

The purpose of this work was to quantify retention/release of tetracycline, oxytetracycline, and chlortetracycline on two soils, paying attention to sorption kinetics and to implications of the adsorption/desorption processes on transfer of these pollutants to the various environmental compartments. We used the stirred flow chamber (SFC) procedure to achieve this goal. All three antibiotics showed high affinity for both soils, with greater adsorption intensity for soil 1, the one with the highest organic matter and Al and Fe oxides contents. Desorption was always <15%, exhibiting strong hysteresis in the adsorption/desorption processes. Adsorption was adequately modeled using a pseudo first-order equation with just one type of adsorption sites, whereas desorption was better adjusted considering both fast and slow sorption sites. The adsorption maximum (qmax) followed the sequence tetracycline > oxytetracycline > chlortetracycline in soil 1, with similar values for the three antibiotics and the sequence tetracycline > chlortetracycline > oxytetracycline in soil 2. The desorption sequences were oxytetracycline > tetracycline > chlortetracycline in soil 1 and oxytetracycline > chlortetracycline > tetracycline in soil 2. In conclusion, the SFC technique has yielded new kinetic data regarding tetracycline, oxytetracycline, and chlortetracycline adsorption/desorption on soils, indicating that it can be used to shed further light on the retention and transport processes affecting antibiotics on soils and other media, thus increasing knowledge on the behavior and evolution of these pharmaceutical residues in the environment.

Pine bark as bio-adsorbent for Cd, Cu, Ni, Pb and Zn: Batch-type and stirred flow chamber experiments

The objective of this work was to determine the retention of five metals on pine bark using stirred flow and batch-type experiments. Resulting from batch-type kinetic experiments, adsorption was rapid, with no significant differences for the various contact times. Adsorption was between 98 and 99% for Pb2+, 83–84% for Cu2+, 78–84% for Cd2+, 77–83% for Zn2+, and 70–75% for Ni2+, and it was faster for low concentrations, with Pb suffering the highest retention, followed by Cu, Cd, Ni and Zn. The fitting to the Freundlich and Langmuir models was satisfactory. Desorption increased in parallel to the added concentrations, with Pb always showing the lowest levels. Stirred flow chamber experiments showed strong hysteresis for Pb and Cu, sorption being mostly irreversible. The differences affecting the studied heavy metals are mainly due to different affinity for the adsorption sites. Pine bark can be used to effectively remove Pb and Cu from polluted environments.

Influence of mussel shell on As and Cr competitive and non-competitive sorption–desorption kinetics in a mine soil: stirred flow chamber experiments

ObjectiveThe objective of this work was to study the effects of amending a pyrite-derived mine soil with mussel shell (MS) on As and Cr adsorption/desorption. MethodsThe methodological approach consisted in using stirred flow chamber experiments to elucidate competitive and non-competitive As and Cr adsorption/desorption kinetics, both in un-amended and MS-amended mine soil samples. ResultsThe results of the experiments indicate that, in non-competitive trials, the MS amendment caused no effect on Cr adsorption, but increased As adsorption, which would be due to the formation of Ca-mediated cationic bridges between As and functional groups present in the negatively-charged soil colloids; whereas, in competitive trials, the MS amendment caused an increase in adsorption for both As and Cr. Additionally, desorption was low for both amended and non-amended soil, showing curves that correspond to fast and slow binding sites, thus differing from adsorption, which were characterized by presenting one-slope curves. ConclusionIn conclusion, MS amendment could be used to increase As and Cr adsorption when both pollutants are present in pyrite-derived mine soils, or to increase As adsorption when this element is present in the mine soil in the absence of Cr, but the MS amendment could not give further Cr adsorption in this medium when As is not present. PracticeThese conclusions could be made effective in pyrite-derived mine soil environments. ImplicationThe achievements of this study could be useful to diminish As and Cr pollution in these environments.

Metalaxyl mobility in acid soils: evaluation using different methods

In the present work, different methods were tested to evaluate the adsorption and desorption of metalaxyl in two acid soils with different organic carbon and clay contents. The three methods (batch, stirred flow chamber and column) that were examined produced similar findings when the two soils were compared: (a) the metalaxyl adsorption capacity was higher in the soil with higher organic matter and clay content, and (b) the soil with the lower organic matter and clay contents provided higher adsorption rate constants. In the two soils tested, the metalaxyl adsorbed in the soil was highly reversible. When only one soil was considered, the different methods yielded different results. The metalaxyl adsorption and its rate were higher with the stirred flow chamber than in the column experiments, and in the column experiments, the total metalaxyl adsorption and the rate of adsorption were higher than in the batch experiments. The percentages of metalaxyl desorbed from the soil were similar in the stirred flow chamber and column experiments, but in the batch experiments, the percentages were significantly lower. In the stirred flow chamber experiments, the desorption processes were faster than the adsorption processes, while in the column experiments, the adsorption and desorption processes exhibited similar rates.

Mercury removal using ground and calcined mussel shell

We determined mercury retention on calcined and ground mussel shell, in presence and absence of phosphate, using batch and stirred flow chamber experiments. In batch experiments the calcined shell exhibited higher Hg adsorption, with good fitting to Freundlich equation (R2: 0.925–0.978); the presence of phosphate increased Hg adsorption; mercury desorption was 13% or lower, diminishing up to 2% under the presence of phosphates. In stirred flow chamber experiments calcined shell retained more Hg than ground shells (6300 vs. 4000–5200 μmol/kg); Hg retention increased an additional 40% on calcined shell and up to an additional 70% on ground shells when phosphates were present; mercury desorption was quite similar in all shell types (20%–34%), increasing up to 49%–60% in ground shells when phosphates were present. The higher Hg adsorption on calcined shell would be related to its calcite and dolomite concentrations; mercury-phosphate interactions would cause the increase in Hg retention when phosphates are present. Data on Hg desorption suggest that Hg retention was not easily reversible after batch experiments, increasing in the stirred flow chamber due to convective flow. Calcined and ground mussel shells could be recycled removing Hg from water, with the presence of phosphates in solution improving efficacy.

Elucidation of associations of ash-forming matter in woody biomass residues using on-line chemical fractionation

This article reports the application of on-line dynamic chemical fractionation using a stirred-flow chamber for fast characterization of ash-forming metals, namely, K, Ca, Na and Mg, and Al as well in woody biomass residues (bark and twigs) and laboratory ashed bark. The chemical fractionation procedure is harnessed to discriminate with minimal operational maintenance those target species associated to the water-soluble, the exchangeable and the acid-soluble fractions as a result of their varying occurrence in the biofuels by resorting subsequently to chemicals of increasing leachability. The final goal is to assist in the evaluation of actual pools of ash-forming elements in industrial boilers.The proposed technique is able to handle up to 1.0g of woody biofuels and provide, as opposed to conventional fuel characterization, relevant insight into the amount of leachable elements under worst case scenarios, and real-time quantification of potentially reactive species beside insight into the leaching kinetics of target elements. Screening results can be obtained in less than 3h instead of more than one week in the batchwise counterpart methods.For elucidation of metal–biomass/ash associations and investigation of the actual selectivity of extractants, a novel approach has been undertaken by resorting to dynamic fractionation assays in combination with scanning electron microscopy with energy dispersive X-ray fluorescence spectrometry (SEM–EDX) and X-ray diffraction (RXD) assays.

Effect of Carbonates and Organic Matter in Retention and Release of Nickel by a Central Italy Soil

To improve the prediction and management of problems associated with toxicity in nickel (Ni)-contaminated soils, a better understanding of their sorptive and desorptive behavior is required. In this research, the sorptive and desorptive behavior of Ni in a clay loam soil (Fluventic Xerochrept), typical of central Italy, was measured using a stirred-flow reactor where the desorption products are continuously removed from solution. In addition, the effects of the presence of carbonates (calcite) and organic matter on Ni adsorption and desorption by the soil were investigated. For this purpose, samples obtained depriving the whole soil (S) of carbonates (S-C) and, successively, organic matter (S-C-OM) or only organic matter (S-OM) were prepared. In the samples containing carbonates, Ni adsorption was characterized by a fast initial reaction in which all the Ni added to the stirred-flow chamber was sorbed; following this, a slower and incomplete sorption occurred. This Ni adsorption process was totally nonreversible. This behavior enables hypothesizing the formation of a complex Ni calcite that can be considered to be mainly responsible for Ni sorption in calcareous soils. When the pH of the whole soil was lowered, depriving the soil of carbonates, its Ni sorptive capacity was significantly reduced and the Ni sorption process became partially reversible. The removal of organic matter decreased both the adsorbed and the desorbed Ni percentage only in the soil samples previously deprived of carbonates.

Comparison of batch, stirred flow chamber, and column experiments to study adsorption, desorption and transport of carbofuran within two acidic soils

Different methods (batch, column and stirred flow chamber experiments) used for adsorption and desorption of carbofuran studies were compared. All tested methods showed that the carbofuran adsorption was higher in the soil with the higher organic matter content, whereas the opposite behaviour was observed for the percentage of carbofuran desorbed. However, different methods have revealed some discrepancies in carbofuran adsorption/desorption kinetics. Although batch method showed interesting data on equilibrium experiments, such as a low heterogeneity for the carbofuran adsorption sites independent of soil organic matter content, it had some disadvantages for carbofuran adsorption/desorption kinetic studies. The disadvantages were related with the excessive limitations of this method on kinetics, i.e., no difference could be detected between different soils. However, with column and stirred flow chamber methods the carbofuran adsorption/desorption kinetics of different soils could be compared. Moreover, the absolute values of carbofuran adsorption/desorption and its rate were higher in the stirred flow chamber than in the batch and column experiments. Using stirred flow chamber experiments the carbofuran desorption was significantly faster than its adsorption, whereas carbofuran using column experiments they were similar. These discrepancies should be considered when the results obtained only with one method is discussed.