Chemical Amendments Research Articles

Remediation of groundwater contaminated with arsenic through enhanced natural attenuation: Batch and column studies

Batch and column laboratory experiments were conducted on natural sediment and groundwater samples from a contaminated site in Maine, USA with the aim of lowering the dissolved arsenate [As(V)] concentrations through chemical enhancement of natural attenuation capacity. In batch factorial experiments, two levels of treatment for three parameters (pH, Ca, and Fe) were studied at different levels of phosphate to evaluate their impact on As(V) solubility. Results illustrated that lowering pH, adding Ca, and adding Fe significantly increased the sorption capacity of sediments. Overall, Fe amendment had the highest individual impact on As(V) levels. To provide further evidence for the positive impact of Ca on As(V) adsorption, isotherm experiments were conducted at three different levels of Ca concentrations. A consistent increase in adsorption capacity (26–37%) of sediments was observed with the addition of Ca. The observed favorable effect of Ca on As(V) adsorption is likely caused by an increase in the surface positive charges due to surface accumulation of Ca2+ ions. Column experiments were conducted by flowing contaminated groundwater with elevated pH, As(V), and phosphate through both uncontaminated and contaminated sediments. Potential in-situ remediation scenarios were simulated by adding a chemical amendment feed to the columns injecting Fe(II) or Ca as well as simultaneous pH adjustment. Results showed a temporary and limited decrease in As(V) concentrations under the Ca treatment (39–41%) and higher levels of attenuation in Fe(II) treated columns (50–91%) but only after a certain number of pore volumes (18–20). This study illustrates the importance of considering geochemical parameters including pH, redox potential, presence of competing ions, and sediment chemical and physical characteristics when considering enhancing the natural attenuation capacity of sediments to mitigate As contamination in natural systems.

Effects of Mix Vegetation and Root Shear Strength Grown on Carbonaceous Shale

Background: Carbonaceous shale is one of the common rock types in Malaysia. The most common types of landslides in Malaysia were happened on the cut slope before the construction of highway. Brachiaria ruziziensis and Colopogonium mucunoides were used as the mix vegetation to investigate the effect of chemical amendments on plant growth and root shear strength relationship. Objective: The objective of this study: (1) To investigate the effect of compound fertilizer nitrogen, phosphorus, potassium (NPK), NPK+Ground Magnesium Limestone (GML) (NGL), NPK+GML+foliar fertilizer (Vita-Grow™) (NGF) and control (Ctrl) and (2) To determine the soil shear strength, biomass and root growth. Materials and Methods: The soil samples were analyzed for pH, Total Nitrogen (TN), Soil Organic Carbon (SOC), available phosphorus, exchangeable Al, Ca, Mg and K and trace nutrients (Fe, Mn, Cu and Zn). Results: The carbonaceous shale was low in pH, total N, soil organic carbon, extractable P, basic cations (Ca, Mg and K) and micronutrients (Fe, Cu and Zn). Both P and Ca/Mg were low indicating inherent infertility and chemical constraints for root developments. The dry matter yield, root length and root weight of Brachiaria ruziziensis and Colopogonium mucunoides were increased significantly against NGF treatment. The increased of plant top and root dry weight treated with NGF were 26 and 38%, respectively, compared to the other treatments. The significant root shear strength relationship indicates that root enhanced shear strength by reducing the cohesion and increased the angle of internal friction component. The shear strength analysis from the direct shear test method is to determine the shear strength from the plotted graph. The shear strength analysis showed that NGF treatment was having high shear strength in 5.4, 10.9 and 16.3 and normal stress in 54, 109 and 163 kN m–2. Rapid vegetation growth observed within a 5 months period demonstrated that nutrient and lime application effectively ameliorated chemical constraints to plant growth. Conclusion: The plant mix species treated with NPK+GML+foliar fertilizer (NGF) indicated higher shear strength, dry matter yield and root densities in all layers.

Effect of chemical amendments on remediation of potentially toxic trace elements (PTEs) and soil quality improvement in paddy fields.

Remediation of potentially toxic trace elements (PTEs) in paddy fields is fundamental for crop safety. In situ application of chemical amendments has been widely adapted because of its cost-effectiveness and environmental safety. The main purpose of this research was to (1) evaluate the reduction in dissolved concentrations of cadmium (Cd) and arsenic (As) with the application of chemical amendments and (2) monitor microbial activity in the soil to determine the remediation efficiency. Three different chemical amendments, lime stone, steel slag, and acid mine drainage sludge, were applied to paddy fields, and rice (Oryza sativa L. Milyang 23) was cultivated. The application of chemical amendments immobilized both Cd and As in soil. Between the two PTEs, As reduction was significant (p<0.05) with the addition of chemical amendments, whereas no significant reduction was observed for Cd than that for the control. Among six soil-related variables, PTE concentration showed a negative correlation with soil pH (r=-0.70 for As and r=-0.54 for Cd) and soil respiration (SR) (r=-0.88 for As and r=-0.45 for Cd). This result indicated that immobilization of PTEs in soil is dependent on soil pH and reduces PTE toxicity. Overall, the application of chemical amendments could be utilized for decreasing PTE (As and Cd) bioavailability and increasing microbial activity in the soil.

Enriched cocoa pod composts and their fertilizing effects on hybrid cocoa seedlings

PurposeComposting has the potential to recycle wastes as a means of conserving natural resources. The study was aimed at examining feasibility of producing nutrient-enriched composts from pest infested cocoa pods with chemical amendments and using manure composts as a fertilizing material in cocoa seedling nursery.MethodsCocoa pod waste was composted in static vessels, aerobically, with chemical enrichments (triple super phosphate charged at 0.4% P or urea charged at 0.8% N or poultry manure charged at 22%) along with a control at the Cocoa and Coconut Institute, Papua New Guinea. The reaction (pH) of the composting mixtures (pH) and macro-nutrients dynamics was monitored at periodic intervals. Effect of soil incorporation of cocoa pod manure composts at 10 g kg−1 was assessed on the growth and foliar concentration of macro-nutrients in hybrid cocoa seedlings.ResultsIn the finished manure composts, dry matter loss ranged from 30.6 to 63.3%; greatest in composting mixtures charged with super phosphate and poultry manure. Besides, super phosphate enriched mixture lost small fraction of initial N (6.6%) compared to un-enriched cocoa pod waste (30.2%). Composting mixtures with greater pH values during composting process showed higher losses of N. Super phosphate charged manure compost outperformed the control, in terms of C/N ratio and concentration of macro-nutrients (P, K, Ca, Mg and S). Quality parameters for all the manure composts conformed to the Canadian Compost Guidelines indicating satisfactory standards. Waste cocoa pods enriched with superphosphate did not show any deleterious effects on cocoa seedlings’ growth, rather, improved plant height, dry matter production and foliar N concentration.ConclusionWaste cocoa pods, co-composted with triple super phosphate and poultry manure, produced composts of desirable quality and can be effectively used to fertilize the cocoa seedlings.

Can Organic Materials Reduce Excess Nutrient Leaching from Manure-Rich Paddock Soils?

Horse paddocks have been identified as a significant contributor of animal waste nutrients to natural waters; thus, modified paddock management is needed. Because chemical amendments pose a health risk to horses, an alternative for reducing nutrient translocation from manure is to add available organic residues to the soil. To examine the feasibility of outdoor use of organic materials to reduce nutrient losses from paddock soils, three commonly available organic materials (peat, wheat straw, and wood chips) were tested for their nutrient retention capacities in batch experiments followed by leaching experiments in an in-house lysimeter station using artificial rainfall. Results showed that the grounded peat and wood chips retained some phosphorus (P), whereas grounded wheat straw released P to the solution. In leaching experiments, peat reduced nitrogen (N) losses by 40% but increased P and carbon (C) losses severalfold. Wheat straw was ineffective in reducing P, N, or C losses and in some cases increased the losses. Wood chips effectively reduced P and C losses, by 70 and 40%, respectively, but not N losses. It was concluded that, among the three organic materials, only the wood chips can be used outdoors to reduce nutrient losses from paddock soils.

Effects of Chemical Amendments to Swine Manure on Runoff Quality

Effects of Chemical Amendments to Swine Manure on Runoff Quality

Effect of wet-and-dry ageing in seawater on the swelling properties and hydraulic conductivity of two amended bentonites

Amended bentonites have been proposed with the primary purpose of improving their chemical compatibility relative to conventional bentonite. As these materials are relatively new, their durability and long-term performance need to be evaluated. Wet-dry conditions may occur in many applications where bentonite liners are in use. In this study, two amended materials, the MultiSwellable bentonite and a DPH (Dense Prehydrated) GCL were subjected to simulated wet-dry ageing. Distilled water (DW) and natural seawater (NSW) were used as permeant liquids. After five wet-dry cycles, the hydraulic conductivity of both materials increased by two to three orders of magnitude. Unhealed desiccation cracks were identified as responsible for the increase in permeability. Conversely, wet-dry ageing in DW did not impact significantly the permeability of the DPH GCL. For both materials, post-test swell index and XRD diffraction indicated a loss of the chemical amendment, likely solubilised and/or eluted during the wet phases. The results point out that further investigation is necessary to fully address the permanence of swelling and permeability performances of these amended clays after long-term field service. Adequate measures are recommended to prevent or limit desiccation damage for use in applications where aggressive inorganic permeant liquids (e.g., NSW) are present.

Managing land application of coal seam water: A field study of land amendment irrigation using saline-sodic and alkaline water on a Red Vertisol

Coal seam (CS) gas operations coproduce water with gas from confined CS aquifers. This CS water represents a potential agricultural resource if the water is able to be chemically amended to comply with management guidelines. Stoichiometric quantities of sulphur and gypsum amendments can be used to neutralise the alkalinity and reduce the sodicity of CS water respectively. These amendments can either be mixed in-line at a water treatment plant or applied directly to land prior to the application of CS water (a practice termed land amendment irrigation - LAI). This study compared the efficacy of LAI with in-line chemical amendment of CS water and irrigation with non-saline, non-sodic and non-alkaline (good quality) water under field conditions in southern Queensland. Soil chemical properties, soluble Ca, Mg, K, Na, electrical conductivity (EC), pH, chloride and alkalinity, as well as saturated hydraulic conductivity were measured to determine the impact of the irrigation treatments on soil chemical and physical conditions. Irrigation of lucerne pasture using solid-set sprinklers applied a total of 6.7 ML/ha of each treatment irrigation water to the experimental plots over a 10-month period. Alkalinity was neutralised using LAI, with no increase in soil alkalinity observed. Soil sodicity did not exceed threshold electrolyte concentration values under either CS water irrigation treatment. Soil chemical and physical properties were comparable for both LAI and in-line chemical amendment of CS water. Soil saturated hydraulic conductivity was maintained under all irrigation treatments. Results showed that the constrained capacity of the irrigation system was unable to meet crop evapotranspiration demand. This resulted in accumulation of salt within the root-zone under the CS water treatments compared to the good quality water treatment. LAI successfully chemically amended Bowen Basin CS water facilitating its beneficial use for agricultural irrigation.

Solubility and Phytoavailability of Phosphorus and Lead in a Contaminated Soil Amended with Two Phosphorus Fertilizers

ABSTRACTApplication of some chemical amendments such as diammonium phosphate (DP) and triple superphosphate (TP) to contaminated soils is an effective technique to stabilize Pb and decrease its uptake by plants. A calcareous soil was spiked with the rates of 0, 250, 500, and 750 mg of lead (Pb) kg−1 soil as Pb acetate, treated with 760 mg of P kg−1 soil as DP and TP, and incubated for 120 days. The results showed that available phosphorus (P) increased immediately after addition of DP or TP to soil, but it declined sharply after only a few days of incubation time. Pot experiment was conducted on sorghum and spinach. The accumulation of Pb was significantly (P ≤ 0.05) lower in sorghum than in spinach, and also was lower in soil amended with DP than TP. The decreased Pb accumulation in the plants by application of both amendments was mainly attributed to the formation of chloropyromorphite.

Strategies for Soil Amelioration Using Sulphur in Salt Affected Soils

Abstract Effective use of salt affected soils needs the development of the most efficient and suitable reclamation technology to optimize farm management and better crop yields. Different chemical methods and amendments are used to reclaim the salt affected soils and after reclamation such soils may be used for sustainable agricultural production. Choice of a chemical amendment depends on its availability, cost, handling and time of application. Application of sulfur is very effective technique to suppress the uptake of undesired toxic elements and to improve the quantity and quality of produce in salt affected soils. So, a three-year field experiment was carried out to evaluate the comparative reclamation efficiency of two sulfur sources, i.e elemental sulfur and gypsum to improve the soil conditions by reducing the salinity/sodicity impact and yield characteristics of rice and wheat crop. A saline-sodic field {(ECe = 6.10 dS m−1, pHs = 9.21 and SAR = 41.67 (mmol L−1)1/2, SO4-S = 16.0 (mg kg−1) and soil gypsum requirement (SGR) of 9.10 t ha−1 for 0-15 cm soil depth} was selected. The treatments included were: control, gypsum application @ 100 SGR, S application @ 25, 50, 57, 100 and 125 % of SGR. Statistical analysis of three-year pooled data showed that varying levels of sulfur and gypsum significantly improved soil properties and rice-wheat yield than control, however, gypsum @ 100% of soil GR was at par with S @ 125 and 100% of SGR in term terms of improving yield component of both test crops and reducing soil pHs, ECe and SAR. Efficiency of treatment could be arranged as gypsum @ 100% SGR = S @ 125 % of SGR= S @ 100% of SGR&gt; S @ 75 % of SGR&gt; S @ 50 % of SGR&gt; S @ 25% of SGR&gt;control.

Editorial: Current Challenges and Future Perspectives on Emerging Bioelectrochemical Technologies.

Editorial: Current Challenges and Future Perspectives on Emerging Bioelectrochemical Technologies.

Effect of litter treatment on growth performance, intestinal development, and selected cecum microbiota in broiler chickens

The objective of this study was to determine whether the type of bedding materials (sand, wood shavings, and paper) and of two chemical amendments (lime and bentonite) could interfere with litter quality (moisture, pH, and total bacterial counts), thereby influencing also the growth performance and the development of intestinal traits and cecum microbiota of chickens. Two hundred and seventy male Ross 308 broiler chickens were randomly assigned into nine treatment groups with three replicates per treatment. Broiler productive parameters, relative weight of different intestinal segments, content of cecal total bacterial counts (total aerobic bacteria, Lactobacilli, and coliforms), as well as litter moisture, pH, and total aerobic bacteria and coliforms counts, were assessed. Litter material, per se, did not significantly affect the productivity parameters at the end of the experimental period (42 days) with the exception of protein efficiency. A significant trend was found among treatments with regard to weight gain and feed intake, with lower performance in birds on sand beddings. Litter pH was relatively homogenous between bedding types and amendments, but the moisture was significantly lower when sand was used. Litter type did not influence the relative weight of the different intestinal segments; however, the type of amendment affected the relative jejunum weight, which was increased in bentonite-treated litter. The use of lime and bentonite treatments may be helpful to decrease the differences in litter moisture associated with particular bedding materials. The tested amendments do not interfere with the productive performance of birds.

Catalyzed hydrogen peroxide combined with CO2 sparging for the treatment of contaminated groundwater

In this work we propose and investigate an innovative groundwater remediation option based on the combination of catalyzed hydrogen peroxide (H2O2) with CO2 sparging. The effectiveness of this new process was evaluated by carrying out lab-scale tests on a soil–water system spiked with Methyl Tertiary Butyl Ether (MtBE). The results achieved with the combined process, evaluated in terms of H2O2 lifetime and MtBE residual concentration in the liquid phase, were then compared with those obtained using H2O2 only or amended with KH2PO4 as stabilizing agent. The experimental results showed that the combined H2O2–CO2 process has basically two beneficial effects. On the one hand, fluxing CO2 into the oxidizing solution can lead to a pH decrease to acidic values that enhance the H2O2 stability. Indeed, from the results obtained in the stability tests carried out, it was observed that the hydrogen peroxide lifetime in the combined H2O2–CO2 process proved to be longer than the one achieved in the tests carried out with H2O2 only, although slightly lower than the one achieved using KH2PO4 as stabilizing agent. On the other hand, it was observed that with respect to a traditional chemical oxidation application, the CO2 sparging can further enhance the overall effectiveness of the process as a result of contaminant stripping by CO2. Indeed, the residual MtBE concentration observed after application of the combined H2O2–CO2 process was slightly lower than the ones obtained using H2O2 only or comparable to the one achieved using H2O2 amended with KH2PO4. Overall, these results showed that the combined H2O2–CO2 process could represent a promising alternative to traditional formulations, avoiding the use of chemical amendments, while leading to comparable residual contaminant’s concentration.

Efficiency of Chemical Amendments for Reducing Ecotoxicity in Heavy Metal Polluted Agricultural Fields

This study was conducted to evaluate effect of chemical amendments on reducing bioavailable fraction of heavy metals in soil along with ecotoxicological effect on earthworms, Eisenia fetida. Three different chemical amendments, lime (L), steel slag (SS), and acid mine drainage sludge (AMDS), were applied with varied application ratio (1, 3, 5%). Heavy metal contaminated soil was mixed with chemical amedments and earthworms, Eisenia fetida, were cultivated for 28 days. Bioavailable fraction of heavy metals (Cd, Cu, Pb, and Zn) extracted with 0.1N HCl was monitored and also, mortality, growth, and metal concentration in earthworm were assessed. Result showed that all three amendments had high efficiency to reduce bioavailable fraction of heavy metals in soil. In particular, lime showed the highest reduction rate of Cu (63.9-87.7%), Pb (7.90-24.65%), and Zn (40.83-77.60%) among three amendments. No mortality of earthworm was observed during experimental period except 3% and 5% AMDS treatment indicating that application of chemical amendments is safe in terms of ecotoxicological aspect. However, no positive correlation was observed between reduction of bioavaialble fraction of heavy metals in soil and earthworms. Overall, application of chemical amendments in agricultural field can be adapted for reducing bioavailable fraction of heavy metals and detoxification in soil.

Dynamics of iron under long-term application of chemical fertilizers and amendments on maize-wheat cropping sequence

ABSTRACTIron (Fe) is one of the essential micronutrient plays a crucial role in redox systems in cells and in various enzyme. The Fe-deficient plants have lower redox reaction and enzymatic activity. Intensive chemical fertilizer resulted in depletions of micronutrients especially Fe from the soil. To understand the dynamics of Fe under long-term fertilizer experiment the present study was initiated during 1972 at experimental farm of College of Agriculture CSK HPKV, Palampur in randomized block design with eleven treatments replicated thrice. The soil of the experimental area was silty loam, acidic in reaction and taxonomically classified as “Typic Hapludalfs.” Surface (0–20 cm) and subsurface (20–40 cm) soil samples collected after the harvest of maize (Kharif, 2008). The continuous use of chemical fertilizers and amendments for the last 36 years in maize-wheat system in an acid Alfisol brought out marked depletion in the pools of Fe as compared to buffer plots. All the pools of Fe were noticeably higher in farmyard manure (FYM) amended plots compared to zero-fertilized plots. Although, residual fraction was found to be the most dominant fraction but organically bound and exchangeable forms were found to play major role in the nutrient supply and crop productivity and nutrients’ uptake. Highest productivity of maize (2008) and wheat (2008–2009) was recorded under 100% nitrogen, phosphorus and potassium (NPK) + FYM treatment. FYM and lime treatments resulted in significantly higher uptake of all the nutrients by both the crops compared to other treatments. Organically bound fraction was found to have highest significant and positive correlation with yield and nutrient uptake of maize and wheat crops. Further, regression analysis studies too revealed that organic form was the most important pool contributing towards the variation in the above parameters. While, exchangeable and organically bound forms contributed significantly towards diethylene triamine pentaacetic acid (DTPA)-extractable Fe.

The flow of a foam in a two‐dimensional porous medium

AbstractFoams have been used for decades as displacing fluids for enhanced oil recovery and aquifer remediation, and more recently, for remediation of the vadose zone, in which case foams carry chemical amendments. Foams are better injection fluids than aqueous solutions due to their low sensitivity to gravity and because they are less sensitive to permeability heterogeneities, thus allowing a more uniform sweep. The latter aspect results from their peculiar rheology, whose understanding motivates the present study. We investigate foam flow through a two‐dimensional porous medium consisting of circular obstacles positioned randomly in a horizontal transparent Hele‐Shaw cell. The local foam structure is recorded in situ, which provides a measure of the spatial distribution of bubble velocities and sizes at regular time intervals. The flow exhibits a rich phenomenology including preferential flow paths and local flow nonstationarity (intermittency) despite the imposed permanent global flow rate. Moreover, the medium selects the bubble size distribution through lamella division‐triggered bubble fragmentation. Varying the mean bubble size of the injected foam, its water content, and mean velocity, we characterize those processes systematically. In particular, we measure the spatial evolution of the distribution of bubble areas, and infer the efficiency of bubble fragmentation depending on the various control parameters. We furthermore show that the distributions of bubble sizes and velocities are correlated. This study sheds new light on the local rheology of foams in porous media and opens the way toward quantitative characterization of the relationship between medium geometry and foam flow properties. It also suggests that large‐scale models of foam flows in the subsurface should account for the correlation between bubble sizes and velocities.

Graphene oxide and H2 production from bioelectrochemical graphite oxidation.

Graphene oxide (GO) is an emerging material for energy and environmental applications, but it has been primarily produced using chemical processes involving high energy consumption and hazardous chemicals. In this study, we reported a new bioelectrochemical method to produce GO from graphite under ambient conditions without chemical amendments, value-added organic compounds and high rate H2 were also produced. Compared with abiotic electrochemical electrolysis control, the microbial assisted graphite oxidation produced high rate of graphite oxide and graphene oxide (BEGO) sheets, CO2, and current at lower applied voltage. The resultant electrons are transferred to a biocathode, where H2 and organic compounds are produced by microbial reduction of protons and CO2, respectively, a process known as microbial electrosynthesis (MES). Pseudomonas is the dominant population on the anode, while abundant anaerobic solvent-producing bacteria Clostridium carboxidivorans is likely responsible for electrosynthesis on the cathode. Oxygen production through water electrolysis was not detected on the anode due to the presence of facultative and aerobic bacteria as O2 sinkers. This new method provides a sustainable route for producing graphene materials and renewable H2 at low cost, and it may stimulate a new area of research in MES.

Reliability and stability of immobilization remediation of Cd polluted soils using sepiolite under pot and field trials

Long-term effectiveness and persistence are two important criterias to evaluate alternative remediation technology of heavy metal polluted soils. Pot and field studies showed addition of sepiolite was effective in immobilizing Cd in polluted soils, with significant reduction in TCLP extracts (0.6%–49.6% and 4.0%–32.5% reduction in pot and field experiments, respectively) and plant uptake (14.4%–84.1% and 22.8%–61.4% declines in pot and field studies, correspondingly). However, the applications of sepiolite offered a limited guarantee for the safety of edible vegetables in Cd-polluted soils, depending on the soil type, the Cd pollution type and level, and the dose and application frequency of chemical amendments. Bioassays, such as plant growth, soil enzymatic activities and microbial community diversity, indicated a certain degree of recovery of soil metabolic function. Therefore, sepiolite-assisted in situ remediation is cost-effective, environmentally friendly, and technically applicable, and can be successfully used to reduce Cd enter into the food chain on field scale.

Biomass and chemical amendments for enhanced phytoremediation of mixed contaminated soils

Pot experiments were conducted to investigate the impact of biomass amendments (biochar, compost and nutrient solution) and chemical amendments (Ethylenediaminetetraacetic acid (EDTA) and Igepal CA-720) on the phytoremediation of soil co-contaminated with organic and metal contaminants by Helianthus annuus (sunflower) and Avena sativa (oat plant). Mixed contaminated soil was prepared by mixing clean soil with naphthalene, phenanthrene, lead (Pb), cadmium (Cd), and chromium (Cr). To study the biomass amendments, soil was amended with biochar, compost, or a nutrient solution. To study chemical amendments, plants raised in contaminated soils were amended with a solution of EDTA, Igepal CA-720 or both. The combination of biomass and chemical amendments were studied by treating composted soil with either EDTA or Igepal CA-720. The results showed that the biochar and compost amendments improved the growth characteristics and biomass of the plants. Growth improvement was best observed for sunflower plants in composted soil. Average maximum plant height of sunflower in contaminated soil was increased by 115% with the addition of compost. Cd and Pb removal was best in the presence of biochar and compost amendments, but Cr removal was unaffected by the use of amendments. The best removal rate was observed for Pb by oat plant in compost amended soil, with average final Pb concentration decreased by 57.8% with the addition of compost to soil. Nutrient solution amendment did not improve the removal of the metal contamination from the soil. The overall growth and biomass were less for plants grown in soil that was treated with chemical amendments. A combination of compost and chemical amendments also did not provide positive results on the plant growth or contaminant dissipation. Polycyclic aromatic hydrocarbon (PAH) degradation improved in the presence of all of the amendments studied. The results suggest that biochar and compost amendments can improve the plant growth characteristics and enhance phytoremediation of mixed contaminated soils.

The effect of chemical and organic amendments on sodium exchange equilibria in a calcareous sodic soil.

In this study, the reclamation of a calcareous sodic soil with the exchangeable sodium percentage (ESP) value of 26.6% was investigated using the cheap and readily available chemical and organic materials including natural bentonite and zeolite saturated with calcium (Ca2+), waste calcite, three metal oxide nanoparticles functionalized with an acidic extract of potato residues, and potato residues. Chemical amendments were added to the soil at a rate of 2%, while potato residues were applied at the rates of 2 and 4% by weight. The ESP in the amended soils was reduced in the range of 0.9-4.9% compared to the control soil, and the smallest and the largest decline was respectively observed in treatments containing waste calcite and 4% of potato residues. Despite the reduction in ESP, the values of this parameter were not below 15% at the end of a 40-day incubation period. So, the effect of solutions of varying sodium adsorption ratio (SAR) values of 0, 5, 10, 20, 30, 40, and 50 on sodium (Na+) exchange equilibria was evaluated in batch systems. The empirical models (simple linear, Temkin, and Dubinin-Radushkevich) fitted well to experimental data. The relations of quantity to intensity (Q/I) revealed that the potential buffering capacity for Na+ (PBCNa) varied from 0.275 to 0.337 ((cmolc kg(-1)) (mmol L(-1))(-1/2)) in the control soil and amended soils. The relationship between exchangeable sodium ratio (ESR) and SAR was individually determined for the control soil and amended soils. The values of Gapon selectivity coefficient (KG) of Na+ differed from the value suggested by U.S. Salinity Laboratory (USSL). The PHREEQC, a geochemical computer program, was applied to simulate Na+ exchange isotherms by using the mechanistic cation exchange model (CEM) along with Gaines-Thomas selectivity coefficients. The simulation results indicated that Na+ exchange isotherms and Q/I and ESR-SAR relations were influenced by the type of counter anions. The values of K G increased in the presence of bicarbonate, sulfate, and phosphate in comparison with the presence of chloride, and the largest value was obtained in the presence of phosphate. So, it can be concluded that the presence of chloride anion is more favorable to reduce ESP compared to other anions, while the presence of phosphate anion makes the reclamation process more difficult. Furthermore, it is possible to reclaim sodic soils using inexpensive and readily available compounds such as potato residues and water management.