Soil Washing Research Articles

Development of a potassium-based soil washing solution using response surface methodology for efficient removal of cesium contamination in soil

The overuse of chelating soil washing agents for removal of heavy metal can release soil nutrients and negatively affect organisms. Therefore, developing novel washing agents that can overcome these shortcomings is necessary. In this study, we tested potassium as a main solute of novel washing agent for cesium-contaminated field soil, owing to the physicochemical similarities between potassium and cesium. Response surface methodology was combined with a four-factor, three-level Box–Behnken design to determine the superlative washing conditions of the potassium-based solution for the removal of cesium from the soil. The parameters that were considered were the following: potassium concentration, liquid-to-soil ratio, washing time, and pH. Twenty-seven sets of experiments were conducted using the Box–Behnken design, and a second-order polynomial regression equation model was obtained from the results. Analysis of variance proved the significance and goodness of fit of the derived model. Three-dimensional response surface plots displayed the results of each parameter and their reciprocal interactions. The washing conditions that achieved the highest cesium removal efficiency (81.3%) in field soil contaminated at 1.47 mg/kg were determined to be the following: a potassium concentration of 1 M, a liquid-to-soil ratio of 20, washing time of 2 h, and a pH of 2.

Tween 80 assisted washing ciprofloxacin-contaminated soil, and recycled it using active chlorines

Active chlorines (ACs) can selectively oxidize contaminants with benzene rings to recycle surfactants, which greatly facilitates the resource cycle. This paper firstly utilized Tween 80 to assist in ex-situ washing the ciprofloxacin (CI) contaminated soil, including the solubilization experiment, shake washing and soil column washing, all of which showed that 2 g/L of Tween 80 (TW 80) was the most effective in removing CI. Then electrochemically treated the collected soil washing effluent (SWE) at 10 V with an electrolyte of 20 mM NaCl + 10 mM Na2SO4; Pre-experiments screened the range of electrode spacing, pH and temperature, based on which an orthogonal design Table L9 (34) was designed. Visual analysis and ANOVA were performed on the ciprofloxacin removal efficiency and Tween 80 retention efficiency during the orthogonal experiments in 9 groups, and the results showed that CI was usually degraded within 30 min, and 50% of TW 80 was still present at the end of the experiment, and there was no significant effect of all three factors. LC-MS demonstrated that CI was mainly degraded synergistically by ·OH and ACs, and ·OH effectively reduced the biotoxicity of the SWE, so the mixed electrolyte may be more suitable for the electrochemical recycling system of ACs. This paper conducted the washing remediation study of CI-contaminated soil for the first time, and applied the theory of selective oxidation by ACs on benzene ring to treat the SWE, which provides a new treatment idea for antibiotic-contaminated soil.

Remediation of soils contaminated with total petroleum hydrocarbons through soil washing with surfactant solutions

ABSTRACT Soil fulfils vital functions for life on Earth and so, just like water and air, its protection from all sources of contamination is a major concern. However, the extensive use of petroleum derived products, either as energy sources or as commodities, leads to important environmental liabilities. Ex situ soil washing is a technology to concentrate contaminants, allowing soil cleaning and the reuse of extracted petroleum derived products. This work focuses on the optimization of ex situ soil washing process using surfactants, introducing an evaluation of the washing solution recycling and its after use safe disposal, promoting the reduction of raw materials, energy and water resources costs. Two surfactants, sodium dodecyl sulphate (SDS) and polyoxyethylene sorbitan monooleate (Tween 80), were tested in the decontamination of an artificially contaminated soil with engine lubricant oil waste. The optimization of the washing conditions, such as stirring speed, liquid–solid ratio, number of washing stages, and surfactant concentration, was carried out using a design of experiments (DOE) software, so that the maximum extraction efficiency of total petroleum hydrocarbons (TPHs) was achieved. A TPH removal efficiency of (80.7 ± 3.2)% was obtained with Tween 80 after 5 h of washing and (90.7 ± 2.8)% with SDS after 2 h at 200 rpm on an orbital shaker with a liquid to solid ratio (L/S) of 15. The potential for reuse of the washing solutions was evaluated. Finally, the discharge of the washing solution was considered using activated carbon to remove the surfactants and ensure its safe disposal.

Remediation of lead-contaminated shooting range soil: Biodegradable chelator-assisted washing and subsequent post-treatment using FeCl[formula omitted] and CaO

Lead (Pb) contamination in shooting range soils is an increasing concern due to high Pb content, threatening the ecosystems and human health. Chelator-assisted washing and chemical immobilization are the most viable treatment options for Pb-contaminated soil remediation. Ethylenediaminetetraacetic acid (EDTA) has been the most widely used chelators in washing remediation. However, the prolonged environmental persistence and subsequent toxicity of EDTA have governed eco-concerns. Alternatively, biodegradable chelators have received substantial focus as a promising substitute for EDTA. Herein, the performance and efficiency of [S,S]-ethylenediaminedisuccinic acid (EDDS), N,N-dicarboxymethyl glutamic acid (GLDA), and 3-hydroxy-2,2′ -iminodisuccinic acid (HIDS) were evaluated as eco-compliant alternatives to EDTA for the remediation of Pb-contaminated shooting range soil. Additionally, a post-treatment preference for immobilizing residual Pb in treated soils using FeCl3 and CaO was highlighted. Among the tested biodegradable chelators, EDDS exhibited the highest Pb extraction and displayed comparable efficiency to EDTA. The Pb removal efficiency of chelators was positively correlated with soil washing parameters. In contrast, the post-treatment using FeCl3 and CaO significantly reduced the leachable Pb-content in chelator-washed soils. The proposed remediation strategy coupled with washing and fixation could be a practical treatment option for extracting bulk Pb from soil and suppressing the leaching potential of residual Pb.

Treatment of Motor Oil-Contaminated Soil with Green Surfactant Using a Mobile Remediation System

Leak of fuels and lubricants occurring during exploration, distribution, refining and storage operations is the major cause of environmental pollution due to petroderivatives dispersion. The quick use of a series of physicochemical and biological techniques is needed to drastically reduce the magnitude of damage provoked by these pollutants. Among them, soil washing proved to be an effective alternative to the remediation of hydrocarbon-polluted sites, mainly if combined with surfactant utilization. However, the direct use of surfactants can lead to problems related to the toxicity and dispersion of the resulting by-products, as the majority of marketed surfactants are produced from oil derivatives. In this context, green surfactants appear as a promising alternative to their synthetic counterpart. In the present study, two green surfactants, i.e., a chemically synthesized biobased surfactant and a Starmerella bombicola biosurfactant, were applied in soil decontamination tests using a concrete mixer-type Mobile Soil Remediation System (MSRS). The system was designed and developed with 3D printing based on bench-scale results. A commercial biosurfactant was formulated based on the microbial surfactant, which was compared with the biobased surfactant in various experimental conditions. A set of factorial designs combined with Response Surface Methodology was used to select the optimal conditions for pollutant removal using the prototype. The following variables were tested: Surfactant type, Surfactant volume, Surfactant dilution, Contaminant concentration, Soil type, Soil mass, Washing duration, Tank tilt angle, Mixing speed, and Type of basket. Under the optimized experimental condition, the commercial biosurfactant allowed to remove 92.4% of the motor oil adsorbed in the sand. These results demonstrate the possibility of using natural surfactants and the development of novel mechanical technologies to degrade hydrocarbons with economic earnings for oil industry.

Extraction of Cobalt and Cadmium in Municipal Dump Sites around Zaria, Kaduna State Using EDTA and Citrate as Complexing Agents

Heavy metals contamination of the soil is detrimental to the environment with implications for human health. This result from several anthropological activities, urbanization and industrialization. Cobalt and cadmium are among the heavy metals of interest in Nigeria.The labile fractions of cobalt and cadmium in the soil from two dumpsites using EDTA and Citrate as complexing agents was evaluated. The Physiochemical parameters and the total metal concentrations of the soil was determined, extraction with EDTA and Citrate were used to study the potential metal extraction capacity at different time intervals and the extraction rates of metal was released as a function of time . The relatively low levels of silt, clay, organic matter and CEC indicates high permeability, hence leachability of heavy metals in the soil and suggest that it might be amenable to remediation by soil washing. Thus result shows that EDTA yielded much more than citrate for both metals under consideration. Therefore extraction time plays a very important role in soil washing process and determines the optimum contact time for contaminants removal. Hence the removal of metals from the soil is a function of time and concentration. Cadmium was extracted more than cobalt, which suggests cadmium has been more labile in solution than cobalt and EDTA as a stronger complexing agent than citrate. Keywords: Extraction, Complexing agent, Mobility, Soil, Cobalt, Cadmium, Heavy metals. DOI: 10.7176/CMR/15-1-01 Publication date: May 31 st 2023

K-nearest neighbor based computational intelligence and RSM predictive models for extraction of Cadmium from contaminated soil

• CI predictive models’ application on soil washing are scare in literature. • Predictive models faced dwindling accuracy when few sample data are available. • Performance of Cd ions soil extraction prediction using KNN were investigated. • KNN performance was better over traditional RSM for Cd soil extraction. • KNN are suitable for soil washing predictions under RSM few samples data. Computational intelligence (CI) predictive models based on k -Nearest Neighbor (KNN) algorithms were developed for Cd ions removal from contaminated soil using environmentally friendly chelating-agent polyaspartate. Based on extracted Cd ions into the chelating-agent, residual Cd ions in treated soil and Cd removal efficiency, the performances of the KNN models were compared with response surface methodology (RSM) models using whole data set (KNN1) and split data (KNN2) scenarios using correlation coefficient (R 2 ) and root mean square error (RMSE). Optimal performances of the developed KNN based models were found to be significantly influenced by the nearest neighbor’s k -parameter attributed to the disparity in the two approaches. The KNN1 demonstrated better performances characterized by higher R 2 = 0.984–0.999 and lower RSME of 0.399–6 against the RSM models’ R 2 = 0.7882–0.990 and RSME 2.08–20.36, respectively. For the KNN2 models, even though lower performances were obtained, yet the soil remediation efficiency models, demonstrated enhanced performance over the RSM models.

Effect of Soil Washing with an Amino-Acid-Derived Ionic Liquid on the Properties of Cd-Contaminated Paddy Soil.

To reduce contamination levels in Cd-contaminated paddy soil while retaining soil characteristics, we have studied the Cd-removing ability of 15 different amino acid-based ionic liquids, which are considered to be green solvents, as soil washing agents and their impact on soil. The results indicated that the glycine hydrochloride ([Gly][Cl]) removed the most Cd, and under optimized conditions could remove 82.2% of the total Cd. Encouragingly, the morphology of the soil had not been significantly changed by the washing process. After the soil was rinsed twice with water and the pH was adjusted to 6.2 by adding Ca(OH)2, the germination index of the rice increased by 7.5%. The growth of the rice was also stimulated, with lengths and weights of the rice plants increasing by 56% and 32%, respectively, after two weeks. These experiments demonstrate that amino-acid-derived ionic liquids can be promising soil-washing agents of Cd-contaminated paddy soil.

A review on natural based deep eutectic solvents (NADESs): fundamentals and potential applications in removing heavy metals from soil.

Natural based deep eutectic solvent (NADES) is a promising green solvent to replace the conventional soil washing solvent due to the environmental benign properties such as low toxicity, high biodegradability, high polarity or hydrophilicity, and low cost of fabrication process. The application of NADES is intensively studied in the extraction of organic compounds or natural products from vegetations or organic matters. Conversely, the use of the solvent in removing heavy metals from soil is severely lacking. This review focuses on the potential application of NADES as a soil washing agent to remove heavy metal contaminants. Hydrophilicity is an important feature of a NADES to be used as a soil washing solvent. In this context, choline chloride is often used as hydrogen bond acceptor (HBA) whereby choline chloride based NADESs showed excellent performance in the extraction of various solutes in the past studies. The nature of NADES along with its chemistry, preparation and designing methods as well as potential applications were comprehensively reviewed. Subsequently, related studies on choline chloride-based NADES in heavy metal polluted soil remediation were also reviewed. Potential applications in removing other soil contaminants as well as the limitations of NADES were discussed based on the current advancements of soil washing and future research directions were also proposed.

Influence of grain size, organic carbon and organic matter residue content on the sorption of per- and polyfluoroalkyl substances in aqueous film forming foam contaminated soils - Implications for remediation using soil washing

A soil that was historically contaminated with Aqueous Film Forming Foam (AFFF) was dry sieved into size fractions representative of those produced during soil washing. Batch sorption tests were then conducted to investigate the effect of soil parameters on in situ per- and polyfluoroalkyl substances (PFAS) sorption of these different size fractions: < 0.063 mm, 0.063 to 0.5 mm, 0.5 to 2 mm, 2 to 4 mm, 4 to 8 mm, and soil organic matter residues (SOMR). PFOS (513 ng/g), 6:2 FTS (132 ng/g) and PFHxS (58 ng/g) were the most dominant PFAS in the AFFF contaminated soil. Non-spiked, in situ Kd values for 19 PFAS ranged from 0.2 to 138 L/Kg (log Kd −0.8 to 2.14) for the bulk soil and were dependant on the head group and perfluorinated chain length (spanning C4 to C13). The Kd values increased with decreasing grain size and increasing organic carbon content (OC), which were correlated to each other. For example, the PFOS Kd value for silt and clay (< 0.063 mm, 17.1 L/Kg, log Kd 1.23) were approximately 30 times higher compared to the gravel fraction (4 to 8 mm, 0.6 L/Kg, log Kd −0.25). The highest PFOS Kd value (116.6 L/Kg, log Kd 2.07) was found for the SOMR fraction, which had the highest OC content. Koc values for PFOS ranged from 6.9 L/Kg (log Koc 0.84) for the gravel fraction to 1906 L/Kg (log Koc 3.28) for the silt and clay, indicating that the mineral composition of the different size fractions also influenced sorption. The results here emphasize the need to separate coarse-grained fractions and fine-grained fractions, and in particular the SOMR, to optimize the soil washing process. Higher Kd values for the smaller size fractions indicate that coarser soils are better suited for soil washing.

Coupling soil washing with chelator and cathodic reduction treatment for a multi-metal contaminated soil: Effect of pH controlling

Contamination of soil with heavy metals has become a significant environmental issue worldwide. In previous studies, a technology that couped EDTA-washing and cathodic reduction technology was developed to further remove heavy metals from soil contaminated with electroplating waste compared with single soil washing technology. Although the method showed a synergistic effect in previous studies, the effect of soil suspension alkalization and the mechanism behind it remain unclear. High soil pH will have an impact on target metal removal, energy consumption and further utilization of soil. In this experimental research, we investigated the efficacy of pH control on coupling soil washing and cathodic reduction to remove multiple heavy metals from soil under various current densities. To alleviate the OH− ions generated by the cathode and improve the reduction efficiency of metals, an automatic pH controller was used, resulting in a significant increase in the removal rate of target metals. The experimental results show that controlling the pH of soil suspension can increase the total removal rate of target metals by 3-6 times. Additionally, the removal efficiency of residual Pb in the soil is increased by about 30%. In terms of ecological risk, pH control could reduce the solubility and mobility of metals by 50%, and the ecological risk was greatly reduced, especially for Zn, from about 90 mg/kg to 50 mg/kg. Further research is needed to explore the mechanism of the synergistic effect and improve the efficiency of this technology for the subsequent development of coupling EDTA-washing and cathodic reduction.

Heavy Metal Removal from Contaminated Soil Using Soil Washing Techniques

Heavy metals are discharged into the soil around us from various anthropogenic sources and also by the use of fertilizers, pesticides, pharmaceuticals, etc. In most cases, industrialization can be pointed to as the reason behind soil pollution. Contamination of soil leads to large-scale environmental degradation and health impacts. Many investigators have studied techniques for removing heavy metals from soil. Soil washing is an emerging area that can be implemented for this purpose. Studies were carried out in the controlled conditions of a laboratory environment to determine the suitability of soil-washing techniques for removing lead from polluted land. The results showing the influence of various parameters in soil washing, such as duration of washing, molar strength of the solution used, the weight ratio of soil to wash solution, etc., are presented in this paper. Batch studies were conducted to investigate the performance of chelating agents such as Na2EDTA, HCl, HNO3 and CaCl2 with regard to the removal of lead from artificially contaminated locally available soil. Based on the batch studies, it is observed that the strength of the washing solution, the proportion of soil and solution, the period of agitation, etc. influence the removal of contaminants. Based on the studies, it is concluded that, while recommending soil washing using chelating agents for remediating lead-contaminated soils, it is essential to identify the influencing parameters and determine the optimum conditions so that higher removal can be achieved without any adverse effect.

The efficacy of soil washing for the remediation of per- and poly-fluoroalkyl substances (PFASs) in the field.

This paper aims to describe the performance of a soil washing plant (SWP) for remediating a per- and poly-fluoroalkyl substances (PFASs)-contaminated soil with a high clay content (61%). The SWP used both physical and chemical processes; fractionation of the soil particles by size and partitioning of PFASs into the aqueous phase to remove PFASs from the soil. Contaminated water was treated in series with granulated activated carbon (GAC) and ion-exchange resin and reused within the SWP. Approximately 2200t (dry weight) of PFAS-contaminated soil was treated in 25 batches of 90t each, with a throughput of approximately 11t soil/hr. Efficiency of the SWP was measured by observed decreases in total and leachable concentrations of PFASs in the soil. Average removal efficiencies (RE) were up to 97.1% for perfluorocarboxylic acids and 94.9% for perfluorosulfonic acids. REs varied among different PFASs depending on their chemistry (functional head group, carbon chain length) and were independent of the total PFAS concentrations in each soil batch. Mass balance analysis found approximately 90% of the PFAS mass in the soil was transferred to the wash solution and >99.9% of the PFAS mass in the wash solution was transferred onto the GAC without any breakthrough.

Evaluation of Soil Health by Soil Washing of As and Heavy Metal Contaminated Soils

Evaluation of Soil Health by Soil Washing of As and Heavy Metal Contaminated Soils

Cost and health benefit analysis of remediation alternatives for the heavy-metal-contaminated agricultural land in a Pb–Zn mining town in China

Remediation is necessary for severely polluted soils due to metal mining activities in China. For decision making of future soil remediation, field-scale information on the cost effectiveness of remediation is substantially required. This study presents a field-scale assessment of the health benefit of soil remediation technologies, which were seldom considered in the previous cost–benefit analyses (CBAs) in China. Four frequently applied technologies, namely, soil replacement, soil washing, stabilization/solidification, and phytoremediation, are analyzed for the agricultural land in a typical lead/zinc town in China. “Disability-adjusted life years” (DALY) is applied to quantify health impact, and cost–benefit analysis is utilized to identify the most economically feasible technology. For the target mining area in China, all four remediation technologies are found to be effective, reducing over 70% of the personal lifetime DALY for the residents. Cost–benefit analysis shows that the health benefit of soil remediation exceeds the cost, indicating economically feasible remediation. Considering the health and economic benefit estimated in this research, phytoremediation is identified as potentially the best technology, with 672.59% benefit rate and 96.90% reduction in health impact. Compared with the other types of benefits reported in previous studies, health benefit is at an unneglectable level. Including health benefits in future CBAs for agriculture soil remediation projects is significant.

Remediation of PAH-contaminated soil using a combined process of soil washing and adsorption by nano iron oxide/granular activated carbon composite

This study investigated the application of magnetic granular activated carbon (MGAC) in soil washing process for the removal of polycyclic aromatic hydrocarbons (PAHs) from real contaminated soil. The magnetic composite was prepared using a facile-modified co-precipitation method. The presence of the synthesized magnetite (Fe3O4) nanoparticles on the composite surface was confirmed by the SEM and XRD characterization tests. The surface area and total pore volume of MGAC were determined to be 837.9 m2/g and 0.5 cm3/g, respectively, which were approximately 10% smaller than those for the bare GAC. The Langmuir model fitted the adsorption isotherm data the best; therefore, monolayer adsorption was predominant in the treatment process with MGAC. The maximum PAH adsorption capacity of MGAC was obtained at 153.5 µg/mg for the total PAHs, which was nearly 20% lower than that of bare GAC (190.3 µg/mg). The soil washing parameters were optimized, and the results demonstrated that the total PAH removal reached a maximum of 47.4% at an MGAC dose of 2% (w/w), washing time of 24 h, a liquid-to-soil ratio of 15:1, stirring speed of 100 rpm, pH of 8.3, and a temperature of 25 °C. For low molecular weight (LMW) PAHs, the removal from soil ranged from 34.6% to 57.7%, whereas the removal percentage of high molecular weight (HMW) PAHs was determined to be between 27.9 and 67.1 %. This indicated that the optimized soil washing with MGAC had a better efficiency for some HMW PAHs than the LMW PAHs. According to the thermodynamic studies, the adsorption of PAHs onto MGAC in the soil washing process was non-spontaneous (ΔG° > 0) and endothermic (ΔH° > 0) with increased randomness at the solid/solution interface of MGAC as temperature increases. The obtained results confirmed the efficiency of the magnetized activated carbon as adsorbent in soil washing to remove the hazardous PAH compounds from soil.

Surfactant recovery and efficient separation of PAHs from surfactant solutions by low-cost waste activated sludge and two-stage design optimization.

The treatment and surfactant recovery of soil washing/flushing effluent containing high levels of surfactants and organic pollutants are critical for the surfactant-assisted remediation of soils and waste management due to their complexity and high-potential risks. Combination of waste activated sludge material (WASM) and a kinetic-based two-stage system design was introduced in this study as a novel strategy for the separation of phenanthrene and pyrene from Tween 80 solutions. The results showed that WASM can effectively sorb phenanthrene and pyrene with high affinities (Kd) of 2325.5 L·kg-1 and 9911.2 L·kg-1, respectively. This allowed a high-level recovery of Tween 80 of 90.47 ± 1.86%, with selectivity of up to 69.7. In addition, a two-stage design was constructed, and the results showed an improved reaction time (approximately 5% of equilibrium time in conventional single-stage process) and increased the separation levels of phenanthrene or pyrene from Tween 80 solutions. For instance, the minimal total operating time for the sorption of 99% pyrene from 1.0g·L-1 Tween 80 was only 23.0min in the two-stage process compared to that of 480min with a 71.9% removal level in the single-stage system. Results indicated that the combination of low-cost waste WASH and two-stage design was a high-efficiency and time-saving way to recover surfactants from soil washing effluents.

Burnt-Bricks Production Using Extracted Finer Particles from Soil with Fly Ash Addition

Earthen building materials, including mud, adobe, rammed earth, and bricks, have a long history of use in civil engineering construction all throughout the world. Burnt bricks are one of these materials thatis important. However, the availabilityof raw materials for making bricks is limited. As a result, numerous alternatives have been investigated as raw materials for making bricks. These substitutes include fly ash, rice husk and ash, industrial, and agricultural waste. The current study suggests a novel method for producing burnt bricks using extracted finer and fly ash.Finer particle extraction was done through soil washing. Since the extracted finer is having high plasticity index and high linear shrinkage, extracted finer was mixed with 20%, 25%, 30%, 40% and 50% fly ash. Fly ash is an industrial waste; hence the use of fly ash for this kind of production would give a sustainable solution for waste management. Every finer-fly ash combination underwent an Atterburg test to evaluate its qualities, particularly its plasticity index and linear shrinkage. Standard-type mold (220 x 115 x 75 mm) was used to producethe handmade bricks. Compressive strength, flexural strength, water absorption, density, and dimension variations of burned bricks were all examined. Results were compared with SLS 39: Specification for burnt clay bricks. Further, these properties were compared with the same properties of bricks made with soil taken from the brick-making industry mixed with fly ash and industrial available burnt-bricks.Additionally, wire-cut bricks were produced using extractedfiner and 25% fly ash. The dimensional variationof finer-fly ash mixed burnt bricks is decreasing when the fly ash % is increased relative to the mold size. Compressive strength of the Grade 2 category was demonstrated using bricks manufactured with a 25% fly addition, according to SLS 39. According to the aforementioned findings, burnt bricks composed of extractedfiner and fly ash have higher desirable qualities when 25% more fly ash is added. Additionally, it shows that using fly ash results in lightweight bricks.The wire-cut bricks made with this selected mixture give 10.64 N/mm2 of compressive strength and it satisfies the SLS 39 requirements for wire-cut bricks. Also, its water absorption was nearly 16% which is below the SLS required value (18%).

Environmental remediation of Pb–Cd contaminated soil with organic phosphonic acids-saponin: Conditions, effectiveness, ecological risk and recovery

Soil washing is a rapid and efficient method for heavy metals removal. In this study, a kind of novel environmentally friendly eluent is proposed, consisting of ethylenediamine tetra methylene phosphonic acid and saponin (E-S). In a response surface optimization design (RSOD), the operating parameters were optimized and ecological effects were investigated. Additionally, soil microbial diversity and composition were discussed. Finally, an optimal method for chelator recovery was presented. The single-factor and RSOD results showed that E-S had higher remediation efficiency for Pb–Cd contaminated soil with the best parameters of duration 240 min, temperature 40 °C, E/S ratio 1:1. Under these operating conditions, the removal rates of Pb and Cd were (72.2 ± 0.5)% and (61.2 ± 0.4)% for the artificially contaminated soil and (69.2 ± 0.1)% and (65.2 ± 0.2)% for in situ contaminated soil, respectively. The contents of Pb and Cd decreased from 562.36 mg/kg to 180.41 mg/kg and 80.96 mg/kg to 27.2 mg/kg respectively, and the soil ecological risk indexes reduced from 32% to 24% for Pb and 36%–27% for Cd. Owing to the efficient enrichment of Stenotrophomonas in soil, E-S has a potential of simultaneous removal effect on organic pollutants as well. Furthermore, the results revealed that E-S can be effectively recovered (>95%) by sodium sulfide precipitation.

Effect of deep softeners on irrigation, salt washing and cotton yield on soils whose mechanical composition is heavy and meliorative status is difficult

In the article, studies were conducted on the economy of quality saline washing and irrigation water of saline soils by deepening medium coarse soils with a mechanical content of melioration, plaster, salinity in the conditions of Bukhara region. In experiments, basically, there were three ways to soften the field: plowing in the first experiments at a depth of 35 cm, plowing in the second experiment at 60 cm, and plowing in the third experiments at a depth of 80 cm. During the experiments, in the first variant of the studies, the norm of salt washing was set to 6480 cbm/ha, in the second variant to 5210 cbm/ha and in the third variant to 5010 cbm/ha. First studies in irrigation of Bukhara included 102 varieties, that is, in the control variant to 5821 cbm/ha, in the second variant to 5284 cbm/ha and in the third variant to 5100 cbm/ha. They were watered 5 times during the season. At the same time, high quality cotton was harvested due to the increase in the cotton yield to 0.39 t/ha in variant 2 and 0.129 t/ha in variant 3 compared to the control. And the land reclamation situation improved. The amount of chlorine ion in the active layer is 0.003 in variant 2 compared to the control. The amount of dry residue decreased by 0.058% in variant 2 and the amount of dry residue by 0.063% in variant 3.