Remediation Of Arsenic-contaminated Soils Research Articles

Remediation of arsenic-contaminated soil using nanoscale schwertmannite synthesized by persulfate oxidation with carboxymethyl cellulose stabilization

Schwertmannite (SCH) is a promising material for adsorbing inorganic arsenic (As). We synthesized SCH nanoparticles (nano-SCH) via a modified chemical oxidation method and investigated the application of nano-SCH for the remediation of As-contaminated soils. The production of nano-SCH was successfully prepared using the persulfate oxidation method with carboxymethyl cellulose stabilization. The spherical structure of the nano-SCH particles had an average hydrodynamic diameter of 296 nm with high specific surface areas (108.9 m2/g). Compared with SCH synthesized via the H2O2 oxidation method, the percentage of Fe3+ precipitation in nano-SCH synthesis increased from 63.2% to 84.1%. The inorganic As adsorption capacity of nano-SCH improved by 2.27 times at solution pH = 6. After remediation of heavily As-contaminated soils by using 5% nano-SCH, the leachability of inorganic As rapidly decreased to 0.01% in 30 d. Correspondingly, the immobilization efficiencies of inorganic As in soil reached >99.9%. The inorganic As fractions in treated soil shifted from specifically and nonspecifically bound forms to amorphous and crystalline hydrous oxide-bound fractions. After treatment with 5% nano-SCH for 60 d, soil pH slightly decreased from 5.47 to 4.94; by contrast, soil organic matter content increased by 20.9%. Simultaneously, dehydrogenase concentration in soil decreased by 22.4%–34.7% during the remediation process. These changes in soil properties and As immobilization jointly decreased microbial activity and initiated the re-establishment of bacterial communities in the soil. In summary, this study presents a novel and high-productivity technology for nano-SCH synthesis and confirms the high As immobilization effectiveness of nano-SCH in the remediation of As-contaminated soils.

The technique of arsenic elimination from contaminated soil with enhanced conditions by electro-kinetic remediation.

Remediation of arsenic-contaminated soil by the technique of electro-kinetic using various enhanced conditions is the thrust of this study. Many tests were performed with different operating conditions, such as the electrodes solution (tap water) with a variable pH at (2, 5, and 8). Cyclodextrin (10% hydroxypropyl-beta-cyclodextrin, or HPCD) has been used as an activating agent that helps enhance this process of soil arsenic clean-up. Agricultural wastes (pomegranate peels) were used after treating them as an adsorbent to impede the return of pollutants to the soil as a result of reverse osmosis. The results obtained after the remediation's completion indicated that the best elimination capacity was 72% at a pH of 2. This indicates that the elimination capacity increases with the decreasing pH of the electrodes solution. Mixing the HPCD solution with soil as an enhanced solution increased the solubility and desorption of arsenic from the soil. Then, arsenic-containing HPCD micelles readily moved to the cathode electrode by electro-osmotic flow, and the elimination capacity increased (84%). It was concluded that pomegranate peels are a good adsorbent for arsenic returning to the soil during the treatment process as a result of reverse osmosis. Hence, the application of this material in this research gave a perfect impression of its use as an inexpensive, environmentally friendly adsorbent and an alternative to commercial absorbents.

Improved efficiency of Sedum lineare (Crassulaceae) in remediation of arsenic-contaminated soil by phosphate-dissolving strain P-1 in association with phosphate rock.

The selection of appropriate plants and growth strategies is a key factor in improving the efficiency and universal applicability of phytoremediation. Sedum lineare grows rapidly and tolerates multiple adversities. The effects of inoculation of Acinetobacter sp. phosphate solubilizing bacteria P-1 and application of phosphate rock (PR) as additives on the remediation efficiency of As-contaminated soil by S. lineare were investigated. Compared with the control, both the single treatment and the combination of inoculation with strain P-1 and application of PR improved the biomass by 30.7-395.5%, chlorophyll content by 48.1-134.8%, total protein content by 12.5-92.4% and total As accumulation by 45.1-177.5%, and reduced the As-induced oxidative damage. Inoculation with strain P-1 increased the activities of superoxide dismutases and catalases of S. lineare under As stress, decreased the accumulation of reactive oxygen species in plant tissues and promoted the accumulation of As in roots. In contrast, simultaneous application of PR decreased As concentration in S. lineare tissues, attenuated As-induced lipid peroxidation and improved As transport to shoots. In addition, the combined application showed the best performance in improving resistance and biomass, which significantly increased root length by 149.1%, shoot length by 33%, fresh weight by 395.5% and total arsenic accumulation by 159.2%, but decreased the malondialdehyde content by 89.1%. Our results indicate that the combined application of strain P-1 and PR with S. lineare is a promising bioremediation strategy to accelerate phytoremediation of As-contaminated soils.

Removal of arsenic from contaminated soils by combining tartaric acid with dithionite: An efficient composite washing agent

In the context of the increasing global problem of arsenic (As) contamination in soils, an efficient remediation method is urgently needed to alleviate it. In this study, a composite washing agent consisting of 0.2 mol L−1 dithionite and 0.05 mol L−1 tartaric acid (TA) in a 1:1 mixing volume ratio was prepared and used in the remediation of arsenic-contaminated soils. The results showed that the removal efficiency of arsenic was 62.47% in soil 1 at a concentration of 134 mg kg−1 and 70.08% in soil 2 at a concentration of 70 mg kg−1. Dithionite achieved greater release of the arsenic associated with amorphous hydrous oxides of iron and aluminium (F3) and arsenic associated with crystalline hydrous oxides of iron and aluminium (F4) forms of arsenic by the reductive dissolution of iron oxides, while also reducing Fe3+. TA released some arsenic in the specifically adsorbed (F2) and F3 forms through acidic effects. The mechanism of arsenic removal from the composite washing agent was found to be a synergistic effect between dithionite and TA. The TA complexation formed Fe-TA complexes with Fe2+ in solution, preventing the formation of new iron mineral phases and reducing the readsorption or precipitation of arsenic to the soil surface. Meanwhile, the formation of Fe-TA complexes kept the iron oxides dissolved, allowing more iron oxide-bound arsenic (F3 +F4) to be released. This study showed that combining TA with dithionite is a promising technology for remediating arsenic-contaminated soils because of its high efficiency.

Effects of Pretreatment and Polarization Shielding on EK-PRB of Fe/Mn/C-LDH for Remediation of Arsenic Contaminated Soils

In this study, coupling electrokinetic (EK) with the permeable reactive barriers (PRB) of Fe/Mn/C-LDH composite was applied for the remediation of arsenic-contaminated soils. By using self-made Fe/Mn/C-LDH materials as PRB filler, the effects of pretreatment and polarization shielding on EK-PRB of Fe/Mn/C-LDH for remediation of arsenic contaminated soils were investigated. For the pretreatment, phosphoric acid, phosphoric acid and water washing, and phosphate were adopted to reduce the influence of iron in soil. The addition of phosphate could effectively reduce the soil leaching toxicity concentration. The removal rate of the soil pretreated with phosphoric acid or phosphoric acid and water washing was better than with phosphate pretreatment. For the polarization shielding, circulating electrolyte, electrolyte type, anion and cation membranes, and the exchange of cathode and anode were investigated. The electrolyte circulates from the cathode chamber to the anode chamber through the peristaltic pump to control the pH value of the electrolyte, and the highest arsenic toxicity removal rate in the soil reaches 97.36%. The variation of total arsenic residue in soil using anion and cation membranes is the most regular. The total arsenic residue gradually decreases from cathode to anode. Electrode exchange can neutralize H+ and OH- produced by electrolyte, reduce the accumulation of soil cathode area, shield the reduction of repair efficiency caused by resistance polarization, enhance current, and improve the removal rate of arsenic in soil.

Microbial community composition in the rhizosphere of Pteris vittata and its effects on arsenic phytoremediation under a natural arsenic contamination gradient.

Arsenic contamination causes numerous health problems for humans and wildlife via bioaccumulation in the food chain. Phytoremediation of arsenic-contaminated soils with the model arsenic hyperaccumulator Pteris vittata provides a promising way to reduce the risk, in which the growth and arsenic absorption ability of plants and the biotransformation of soil arsenic may be greatly affected by rhizosphere microorganisms. However, the microbial community composition in the rhizosphere of P. vittata and its functional role in arsenic phytoremediation are still poorly understood. To bridge this knowledge gap, we carried out a field investigation and pot experiment to explore the composition and functional implications of microbial communities in the rhizosphere of four P. vittata populations with a natural arsenic contamination gradient. Arsenic pollution significantly reduced bacterial and fungal diversity in the rhizosphere of P. vittata (p < 0.05) and played an important role in shaping the microbial community structure. The suitability of soil microbes for the growth of P. vittata gradually decreased following increased soil arsenic levels, as indicated by the increased abundance of pathogenic fungi and parasitic bacteria and the decrease in symbiotic fungi. The analysis of arsenic-related functional gene abundance with AsChip revealed the gradual enrichment of the microbial genes involved in As(III) oxidation, As(V) reduction, and arsenic methylation and demethylation in the rhizosphere of P. vittata following increased arsenic levels (p < 0.05). The regulation of indigenous soil microbes through the field application of fungicide, but not bactericide, significantly reduced the remediation efficiency of P. vittata grown under an arsenic contamination gradient, indicating the important role of indigenous fungal groups in the remediation of arsenic-contaminated soil. This study has important implications for the functional role and application prospects of soil microorganisms in the phytoremediation of arsenic-polluted soil.

Destabilization and exchange removal of arsenic in contaminated soils by washing: A new remediation strategy with high efficiency and low mineral loss

Mineral loss is considered a reason of the adverse effect induced by soil washing. In this research, we established a destabilization and exchange removal strategy, whose removal efficiency is higher but whose Fe mineral loss extent is lower than that of traditional soil washing method in the same dosage. In our research, three destabilizers, including oxalic acid (OA), citric acid (CA), tartaric acid (TA), and one exchanger KH2PO4 (KP), were used as single and composite agents for soil washing of As-contaminated soil. The influence of dosage, pH, washing time, and As fractions change along with time were carefully investigated. Our results showed a higher As removal efficiency and lower iron loss extent by composite washing agents than single agents. The removal efficiency was in the order of OA&KP>OA>CA&KP>CA>TA>KP at the concentration of 0.4 mol/L. The Fe loss extent was OA>OA&KP>CA&KP>CA>TA>KP. The mechanism was supposed to be the synergistic effect between destabilizer and exchanger, in which Fe minerals were destabilized by the former and benefitted by the latter to absorb on the mineral surface instead of As. In addition to a low iron loss extent, this strategy is a potential fertilizer, which benefits the reuse of washed soils and soil function recovery. Thus, destabilization and exchange removal strategy will be a more suitable method compared with traditional soil washing methods for contaminated soils.Capsule: The synergistic effect between organic acids and phosphate gives us novel insights into remediation of arsenic-contaminated soils more environment-friendly.

Indigenous Cyanobacteria Enhances Remediation of Arsenic-Contaminated Soils by Regulating Physicochemical Properties, Microbial Community Structure and Function in Soil Microenvironment

Indigenous Cyanobacteria Enhances Remediation of Arsenic-Contaminated Soils by Regulating Physicochemical Properties, Microbial Community Structure and Function in Soil Microenvironment

Advances in study on the effects of arbuscular mycorrhizal fungi on plants in remediation of arsenic-contaminated soil

ABSTRACT It is important to study the role and mechanism of arbuscular mycorrhizal fungi (AMF) on plants in arsenic-contaminated soil phytoremediation. In this paper, it was introduced that the ways of AMF acting on arsenic hyperaccumulator and non-hyperaccumulator were different; then the mechanism of AMF acting on plants was discussed from five aspects: (1) AMF improved the absorption of nutrients; (2) AMF would have participated in the reduction process of As (V) to As (III) and changed the form of As in plant; (3) AMF would have participated in the transformation process of inorganic arsenic to organic arsenic; (4) AMF absorbed and assimilates arsenic; and (5) AMF could improve the rhizosphere soil environment, thus affecting the arsenic absorption and accumulation of plants. Finally, the shortcomings and future of the research were prospected to promote the relevant research progress.

Remediation of arsenic-contaminated soil by nano-zirconia modified biochar.

Nowadays, the soil arsenic pollution is considered as a serious environmental issue, and the high toxicity of arsenic can seriously affect the quality and safety of agricultural products and human health. Biochar, as a solidifying/passivating agent, has been widely used in the treatment of soil heavy metal pollution. Pine biochar (BC) was used as a carrier in this study, and biochar-loaded nano-zirconia (N-ZrO2-BC) was synthesized to investigate its adsorption and fixation characteristics on As (V) in soil and water. The adsorption experiment showed that the second-order kinetic equation had a good fitting effect on the adsorption curve of As (V) on the N-ZrO2-BC surface, which indicated that chemical adsorption was the main factor controlling the reaction rate. FTIR and SEM results showed that ion exchange and surface complexation were the main mechanisms of As (V) adsorption by N-ZrO2-BC. Soil culture experiments showed that the stabilization efficiency of arsenic in soil with 2% N-ZrO2-BC reached 99.30% after 60 days, and the extractable arsenic content was reduced to 3.07 μg·L-1, which reached the quality standard of class III groundwater (<0.01 mg·L-1, GB/T 14848-2017). Comparing with the control, the content of acid extractable arsenic in soil decreased by 90.57%, and the residual arsenic increased by 51.46%, indicating that the addition of N-ZrO2-BC could effectively promote the transformation of active arsenic to stable arsenic in soil.

Remediation of arsenic-contaminated soil by chelating agents in shallot plantation land in Bima, West Nusa Tenggara

Arsenic (As) contaminated agricultural land in Bima is due to the use of synthetic fertilizers and excessive pesticides in the shallot cultivation system. One of the efforts to remediate the contaminated soil by using the chelating agent. The research aims to study the ability of various chelating agents to remediate As contaminated soil and also examined the effect of chelating agents on arsenic concentration in shallot bulbs and production. The study was conducted at the shallot production center of Kalampa Village, Woha Subdistrict, Bima Regency, West Nusa Tenggara, which indicated As contamination. The experiment used a randomized block design with three replication and five chelating agents i.e. biochar-compost, chitosan, EDTA, ammonium thiosulfate, zeolite, and control. All treatment of chelating agents can reduce As in the soil up to 70% and significantly different with control. Arsenic content in shallot bulbs with chelating agents treatment is within the safe limit (<1 mg kg−1). Biochar-compost significantly increased the shallot yield. Meanwhile, EDTA treatment did not support shallot production. Biochar-compost and zeolite are recommended for application due to their ability to remediate arsenic in the soil, the lowest concentration of arsenic in shallot bulbs, and the ability to support optimal shallot production.

Remediation of arsenic-contaminated paddy soil by intercropping aquatic vegetables and rice

Soil contamination by arsenic (As) is an important environmental issue globally. Intercropping of hyperaccumulators with main crop is typically applied for remediation of As-contaminated soil. Most hyperaccumulators are wild plants with small biomass and slow growth rates. Thus, remediation is slow. Here, we propose an effective intercropping system for remediation of As-contaminated paddy soil. Four treatments—intercropping with water spinach (Ipomoea aquatica Forsk) (T1), water celery (Oenanthe javanica (Blume) DC.) (T2), or Guangdong white arrowhead (Sagittaria sagittifolia L. var) (T3), with rice (Oryza sativa L.) monoculture (control, CK)—were used. Compared with the CK, grain yield per plant of rice under T1 and T2 increased by 58.13% and 10.48%, respectively, but decreased by 46.90% in T3. As concentration, bioaccumulation factor, and translocation factor in brown rice were significantly lower in the intercropping treatments than in CK. As removal by water spinach was 7.04 and 1.47 times that by water celery and arrowhead, respectively. The pH of paddy soil was significantly higher in all treatments than in CK, and iron plaque on rice roots under T1 and T2 decreased significantly but increased significantly under T3 compared with that of CK. Rice intercropped with water spinach had the best remediation effect. Novelty Statement: We believe that the following highlights of this manuscript will make it interesting to general readers of this journal. First, in recent years, many articles about intercropping system for the remediation of soil heavy metal pollution focus on dry land, and few studies have focused on paddy soil. The present study was on arsenic-contaminated paddy soil remediation. Second, water spinach, water celery, and arrowhead have great potential for phytoremediation. Studies have shown that these three aquatic vegetables play a role in the removal of certain pollutants, such as heavy metals. Moreover, when intercropped with rice, they can effectively increase rice yield and reduce rice diseases and insect pests. However, studies on remediation of arsenic-contaminated soil by intercropping aquatic vegetables and rice have not been reported. We propose here a rice-aquatic vegetables (water spinach, water celery and arrowhead) intercropping pattern for remediation of arsenic in soil. Third, according to the arsenic concentration and removal rate, we used a bioaccumulation factor, translocation factor, and arsenic removal per unit area of plants for the quantitative evaluation of the remediation effects of the intercropping systems. We found that the intercropping of rice and water spinach could be used to remediate arsenic-contaminated soil. Moreover, the extraction contents of arsenic using intercropping with water spinach was higher than that achieved in a previous study that applied intercropping with the arsenic hyperaccumulator Pteris vittata over the same growth time. This study provides a reference for realizing both remediation and increased production in arsenic-contaminated soil and for promoting sustainable development of agriculture.

Effect of humus on the remediation of arsenic-contaminated soil by electrokinetic technology

The effect of humus on the remediation of arsenic (As)-contaminated soil by electrokinetic technology was investigated in this study. The results showed electromigration regulated the spread of As in soil and the addition of humus significantly promoted the release of As from the soil during electrokinetic remediation (EKR). The remediation efficiency was obviously enhanced by 20% when the added amount of humus was 4g. The removal efficiency was also improved with the increase of running time. The results of functional group analysis of humus indicated the presence of several oxygen-containing functional groups, which desorbed As from the soil particles under both acidic and base conditions. When the pH was 10, approximately 11.63% of bonded As was desorbed as free As, which was in favor of EKR. The main result of this work suggests that humus can be used as a green agent to improve the EKR technology.

Adsorption and Mechanism of Arsenic by Natural Iron-containing Minerals

Natural iron-containing minerals present in the geosphere in the form of crystalline minerals can be used as adsorption material for removal of arsenic from wastewater and remediation of arsenic-contaminated soils. In this paper, the adsorption and desorption of arsenic onto different iron-containing materials including hematite, limonite, siderite, ilmenite, magnetite, Fe2O3, Fe3O4, and Fe-Mn binary oxide (FMBO) were studied in laboratory experiments. The mechanism of arsenic adsorption was analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD), and fourier transform infrared spectroscopy (FTIR). The results showed that arsenic adsorption is fitted by pseudo-second-order kinetics and the Langmuir isotherm model for almost all adsorbents, suggesting monolayer adsorption of arsenic onto the minerals. The sorption efficiency and capacity of arsenic by FMBO are much higher than those of other materials. Furthermore, limonite has high sorption efficiencies for both As(Ⅲ) and As(Ⅴ) among the natural iron-containing minerals, and their adsorption capacities are 3.96 mg·g-1 and 2.99 mg·g-1, respectively. The XRD results showed that natural limonite contains a large number of weak crystalline mineral components such as goethite, which can provide relatively abundant arsenic adsorption sites. Thus, limonite appears to be the most suitable natural mineral for arsenic adsorption.

Remediation of arsenic-contaminated soils via waste-reclaimed treatment agents: Batch and field studies

The potential of three different waste-reclaimed treatment agents (WRTAs) for removing arsenic was evaluated via laboratory-scale batches, column experiments, and field tests. WRTA1 was synthesized using acid mine drainage sludge (AMDS), cement, and sand. WRTA2 and WRTA3 were synthesized by adding fly ash or Ca(OH)2, respectively, to WRTA1. The maximum adsorption capacities of WRTA1, WRTA2, and WRTA3 for As(III) using the Langmuir model were 16.6 mg g−1, 14.5 mg g−1, and 20.6 mg g−1, respectively, and for As(V) were 29.6 mg g−1, 27.3 mg g−1, and 31.3 mg g−1, respectively. The pseudo-second-order equation for the adsorption of As(III) and As(V) fit the kinetics data well. The column study showed that the WRTAs are very effective adsorbents and exhibit > 80% removal of As from the contaminated soil. The inhibition of As accumulation in plants (i.e., rice, chili, and sesame) by the WRTAs was evaluated and showed a 96% inhibition in As accumulation in chili roots for WRTA2. The suggested WRTAs are promising agents for the removal of As and heavy metals from heavily contaminated agricultural soil.

Remediation of Arsenic-Contaminated Soil Using Alkaline Extractable Organic Carbon Solution Prepared from Wine-Processing Waste Sludge

ABSTRACTPast studies have shown that dissolved organic carbon (DOC) washing can effectively remove heavy metals from contaminated soil. In this study, we used alkaline DOC solutions for remediation of arsenic (As)-contaminated soil (with an initial As concentration in the topsoil of 390 mg kg−1). The removal of As and the change in soil nutrients during DOC washing were studied for 60 min at pH 10 with a 60:1 liquid/soil ratio (v/m). Approximately 88% of As was removed by washing the soil twice using a 3000 mg L−1 DOC solution at 25°C. Following this treatment, the pH of the soil had increased from 5.6 to 9.2; organic carbon content had increased from 3.5% to 4.1%; cation exchange capacity, ammonium-N, and available phosphorus had increased to 2.3, 1.4, and 6.6 times their original levels, respectively; and exchangeable K, Na, Ca, and Mg had increased to 91, 6.1, 4.2, and 2.2 times their original levels, respectively. A sequential extraction investigation revealed that residual As and easily exchangeable As in the fraction were initially 10.2% and 9.2%, respectively, but that the former became the maximum remainder (64%) after the ultimate DOC washing.

Pilot Scale Ex-Situ Electrokinetic Remediation of Arsenic-Contaminated Soil

In this study, the effectiveness of ex situ electrokinetic remediation (EKR) in treating actual As-contaminated soil was evaluated at a pilot scale (1 m [W] × 1 m [L] × 1.5 m [H]). Ethylenediamine tetraacetic acid (EDTA) and sodium hydroxide as the catholyte and anolyte, respectively, were circulated to enhance the desorption of As. Two types of soil were collected from a real contaminated agricultural area: silty loam from a rice paddy and sandy clay loam from dry land. An average of 78% of the As was removed from the two types of soil after 8 weeks, and the residual As concentration met the level set by Korean legal regulations. The average removal rates were 1.06 and 1.55 mg/kg/day, respectively, for the paddy and dry field soil samples. In addition, fractionation analysis showed that most other fractions and even a large portion of the residual fraction were removed after EKR. The ex situ application provided electrolyte more uniformly to the entire soil sample; therefore, there was no significant variation in As removal depending on the depth of the soil. These results indicated that ex situ EKR is an effective technique for the remediation of As-contaminated sites.

Remediation of Arsenic-Contaminated Soils by Iron Amendments: A Review

Arsenic (As) in soil is a serious environmental issue, and although As occurs naturally in soil, anthropogenic activities have greatly increased As soil contamination. Several technologies can be used to reduce arsenic contamination in soils, among them in situ chemical immobilization by application of inorganic amendments, which are incorporated and mixed with the contaminated soil. The binding of As to the additive reduces its mobility and bioavailability in the soil, with the long-term stability of the new compounds formed being an important issue. The objective of this study was to review the literature concerning remediation of As-contaminated soils with different iron sources and to evaluate their effectiveness.

Remediation of arsenic-contaminated soils and washing effluents

Laboratory experiments were conducted to determine the distribution of various arsenic species in tailings and soils. Other specific goal of the tests were to evaluate the extraction efficiency of arsenic using alkaline or acid washing, to determine optimum operational parameters of alkaline washing, and to evaluate the arsenic precipitation of washing effluents by pH adjustment or ferric chloride addition. Alkaline washing using sodium hydroxide was found to be favorable in removing arsenic from tailings or soils having a higher portion of arsenic in the operationally defined crystalline mineral fraction of crystalline oxide and amorphous aluminosilicates. This is due to the ligand displacement reaction of hydroxyl ions with arsenic species and high pH conditions that can prevent readsorption of arsenic because predominant negatively charged crystalline oxides do not attract the negatively charged oxyanions. For tailings, sodium hydroxide had 10–20 times higher extraction efficiencies than hydrochloric- or citric acid. The optimum concentration of sodium hydroxide for soil washing was determined to be 200 mM for all samples, while the optimum ratios were 10:1 and 5:1 for tailings and field/river sedimentary soils, respectively. The washing effluent of river soil was effectively treated by adjusting pH to 5–6 with hydrochloric acid, resulting in arsenic concentrations of <50 μg l −1. In the case of field soil effluent, an addition of ferric chloride with a minimum mass ratio of 11 (Fe/As) was needed to reduce the arsenic below 50 μg l −1.