Agent For Remediation Of Soil Research Articles

Bacillus subtilis Strain YJ-15, Isolated from the Rhizosphere of Wheat Grown under Saline Conditions, Increases Soil Fertility and Modifies Microbial Community Structure

Soil salinization during wheat cultivation considerably diminishes soil fertility and impedes wheat growth, primarily due to rhizosphere microbial community changes. Our study investigates the application of Bacillus subtilis YJ-15, a strain isolated from the rhizosphere of wheat cultivated in salinized soil, as a soil remediation agent. This strain has demonstrated significant salt tolerance, disease suppression capabilities, and growth-promoting attributes in previous studies. The wheat rhizosphere was examined to assess the impact of Bacillus subtilis YJ-15 on microbial community composition and soil fertility. Fertility of soil in saline soil was significantly increased by inoculating wheat with YJ-15. The microbial community structure within the wheat rhizosphere inoculated with Bacillus subtilis YJ-15 was analyzed through sequencing on the Illumina MiSeq platform. Phyla Proteobacteria and Acidobacteria were identified as the dominant bacteria. Basidiomycota, Mortierellomycota, and Ascomycota dominated the fungal phyla. Among the bacterial genera, Pseudomonas, Arthrobacter, and Bacillus were predominant. The predominant fungal genera included Alternaria, Cephalotrichum, Mortierella, and Chaetomium. A significant increase in Gaiella and Haliangium levels was observed in the YJ group compared to the control group. Additionally, the fungal genera Epicoccum, Sporidiobolus, and Lecythophora have significantly increased in YJ abundance. One of the potential benefits of Bacillus subtilis YJ-15 in the cultivation of wheat on salinized land is its ability to enhance the rhizosphere microbial community structure and improve soil fertility.

Selective lead capture using amide-containing COFs: A novel strategy for efficient soil remediation

A critical consideration in the application of phytoremediation to remediate sludge soil contaminated with heavy metals is the potential for leaching risks that prevail prior to the efficient uptake of these metals by plants. The most cost-effective method is to use heavy metal stabilizers with selective adsorption. A novel amide-based COF material (COF-TH) has been synthesized as a heavy metal stabilizer for Pb. COF-TH exhibits significant selectivity for Pb in five-metal-mixed solutions, with a distribution coefficient KD as high as 3279 mL·g–1, which was more than 7.3 times that of other heavy metals. The maximum adsorption capacity of COF-TH for Pb was 189 mg·g–1. The adsorption fitted Langmuir model and intra-particle diffusion model, and satisfied pseudo-second-order kinetic model. The excellent selectivity and adsorption performance originate from the complexation between abundant amide groups and Pb ions. Pot experiments and leaching assays confirm that COF-TH decreased Pb leachate concentrations by 77.8 % without significantly decreasing total phytoextracted amounts of other heavy metals, due to the high selectivity of COF-TH to Pb. Additionally, its positive impact on plant growth and microbial diversity makes it a promising soil remediation agent. This investigation offers a novel approach to mitigate the leaching risk of a specific heavy metal Pb during sludge land application by integrating soil phytoremediation with stabilization techniques.

UHPM dominance in driving the formation of petroleum-contaminated soil aggregate, the bacterial communities succession, and phytoremediation

This study focused on the effects of urea humate-based porous materials (UHPM) on soil aggregates, plant physiological characteristics, and microbial diversity to explore the effects of UHPM on the phytoremediation of petroleum-contaminated soil. The compositions of soil aggregates, ryegrass (Lolium perenne) biomass, plant petroleum enrichment capacity, and bacterial communities in soils with and without UHPM were investigated. The results showed that UHPM significantly increased soil aggregate content by 0.25 mm-5 mm, resulting in higher fertilizer holding capacity, erosion resistance capacity, and plant biomass and microbial number than the soil without UHPM mixed. In addition, UHPM decreased the absorption of petroleum by plants in the soil while increasing the abundance of degrading bacteria and petroleum-degrading-related genes in the soil, thereby promoting the removal of hard-to-degrade petroleum components. RDA showed that, compared with the unimproved soil, each soil indicator was positively correlated with a high abundance of degrading bacteria in the improved soil and was significant. UHPM can be regarded as a petroleum-contaminated soil remediation agent that combines slow nutrient release with soil improvement effects.

Insights into remediation of cadmium and lead contaminated-soil by Fe-Mn modified biochar

Heavy metal contamination, particularly by lead and cadmium, poses a significant environmental challenge. Indiscriminate disposal of crop residues exacerbates environmental concerns. In this study, broad bean straw was utilized to produce biochar (BC), and further modifications were made using FeCl3-6 H2O and KMnO4 to obtain Iron-Manganese Modified Biochar (FMBC) for remediating cadmium and lead-contaminated soil. Results show that both BC and FMBC increased soil pH, available phosphorus, and potassium compared to the control groups. Adding 5 % BC led to a notable reduction of 60.98 % in available cadmium and 51.63 % in available lead. Simultaneously, FMBC decreased active cadmium and lead by 57.51–73.73 % and 52.25–69.87 %, respectively. Furthermore, FMBC decreased the content of cadmium and lead in the unstable state while increasing content in the residual state, demonstrating its ability to reduce accumulation in plant tissues. FMBC adsorption mechanisms primarily involve surface complexation and co-precipitation, where oxygen-containing functional groups form stable complexes with free cadmium and lead ions. In conclusion, FMBC proved to be an effective, environmentally friendly soil remediation agent with strong adsorption capabilities and a prolonged shelf-life. This provides a promising solution to alleviate the pollution of heavy metals such as cadmium and lead in soil.

Co-pyrolysis of saw dust and oily sludge with waste-heat utilization of steel slag on rotary kiln simulated engineering practice

Pyrolysis of oily sludge (OS) possesses actual problems of high viscosity and high energy consumption in industry. This paper introduced saw dust (SD) to achieve physical viscosity reduction of OS, and then completed OS pyrolysis via steel slag (SS) with sufficient waste heat to replace external heat sources. The rotation of rotary kilns reactor with fins inside were utilized for pyrolysis, which exhibited excellent heat transfer effect for SS heating as validated by discrete element analysis (DEM) simulation. Temperature program and fixed temperature pyrolysis were respectively investigated and the latter one obtained higher yield of oil and gas. Especially SD addition increased the yield and quality of calorific value products (pyrolysis oil and gas). SS not only provided heat source but a lot had catalytic effect on pyrolysis, in which the [O] compounds provided by metal oxides could destroy the stability of chemical bond and deepen the cracking reaction. The energy equilibrium was calculated by heat capacity and reaction energy barrier. Finally, the pyrolytic residue was utilized as soil remediation agent by evaluating Ryegrass growth. Trace FeOx promoted photosynthesis and cellular respiration in plants, while excessive FeOx led to difficulty in respiration and decay of roots. Therefore, this new approach provides an alternative direction for collaborative treatment of OS, SD, and SS with co-benefits from three feedstocks to save energy and produce high-quality products of gas and oil.

Rape Straw Biochar Application Enhances Cadmium Immobilization by Promoting Formation of Sulfide and Poorly Crystallized Fe Oxide in Paddy Soils

The mechanisms of rape straw biochar that affect the fixation of cadmium (Cd) in paddy soil by influencing redox of iron and sulfur are unclear. Several anaerobic incubation experiments were carried out using Cd-contaminated paddy soils (LY and ZZ). Rape straw biochar at pyrolysis temperatures of 450 °C (LRSB) and 800 °C (HRSB) was selected as the soil remediation agent. The electron exchange capacity and electrical conductivity were higher in HRSB than those in LRSB. The lower pe + pH in HRSB enhanced Fe oxide reduction, with a maximum increase in Fe2+ of 46.0% in ZZ. Compared to treatment without biochar (CK), the poorly crystallized Fe oxide (Feo) in HRSB increased by 16.8% in ZZ. This induced Cd bound to Fe, and Mn oxides fraction (Fe-Mn Cd) increased by 42.5%. The SO42−-S content in LRSB was 4.6 times that of HRSB. LRSB addition increased acid-volatile sulfide by 46.4% and 48.9% in LY and ZZ soils, respectively, compared to CK. This resulted in an increase in sulfide’s contribution to Cd fixation, with values rising from 24.2% to 37.8% in LY and 19.1% to 29.8% in ZZ. Overall, LRSB reduced Cd mobility by forming more sulfide, while HRSB increased Fe-Mn Cd by increasing Feo.

Research on the Preparation of Biochar from Waste and Its Application in Environmental Remediation

Biochar is a carbon-rich material that can be composed of a variety of raw materials. From the perspective of resource reuse, it is quite feasible to use waste as a raw material for the preparation of biochar. This paper provides an overview of the types of waste that can be used to prepare biochar and their specific substances, and also summarises methods to enhance or improve the performance of biochar, including physical, chemical, biological and other methods. The feedstock for biochar includes four categories: agricultural and forestry waste, industrial by-products, municipal solid waste and other non-traditional materials. This paper also summarises and classifies the role played by biochar in environmental applications, which can be classified according to its role as an adsorbent, catalyst and soil conditioner, and other applications. In addition to being widely used as an adsorbent, catalyst and activator, biomass charcoal also has good application prospects as a soil remediation agent, amendment agent and supercapacitor, and in soil carbon sequestration. Finally, some ideas and suggestions are detailed for the present research and experiments, offering new perspectives for future development.

Porous adsorbent prepared from eco-friendly aqueous foam templates and carbonized for soil remediation

Porous adsorption materials have garnered extensive attention in environmental remediation in recent years, but green preparation and effective post-treatment remain the main challenges in practical applications. Here, a novel porous adsorbent was successfully fabricated from the aqueous foams templates stabilized by the natural plant Sapindus mukorossi (S. mukorossi) and nano-clay attapulgite (APT) via a thermally-initiated polymerization. The as-prepared porous adsorbents exhibited abundant interconnected pore structures and demonstrated excellent adsorption properties for chlortetracycline hydrochloride (CTC) and tetracycline hydrochloride (TC), with a maximum adsorption capacity of 620 mg/g and 538 mg/g, respectively. After adsorption, the waste porous adsorbent was converted into carbon/APT material through anaerobic calcination. At a carbonization temperature of 400 °C, carbon/APT with large amounts of negative charges and oxygen-containing functional groups exhibited a good adsorption capacity for Cd2+ and showed potential as a soil remediation agent. In summary, this study presents a feasible new idea for the green preparation and post-processing of waste adsorbents, offering a promising solution to the challenges faced in practical applications.

Characteristics prediction of hydrothermal biochar using data enhanced interpretable machine learning

Hydrothermal biochar is a promising sustainable soil remediation agent for plant growth. Demands for biochar properties differ due to the diversity of soil environment. In order to achieve accurate biochar properties prediction and overcome the interpretability bottleneck of machine learning models, this study established a series of data-enhanced machine learning models and conducted relevant sensitivity analysis. Compared with traditional support vector machine, artificial neural network, and random forest models, the accuracy after data enhancement increased in average from 5.8% to 15.8%, where the optimal random forest model showed the average of accuracy was 94.89%. According to sensitivity analysis results, the essential factors influencing the predicting results of the models were reaction temperature, reaction pressure, and specific element of biomass feedstock. As a result, data-enhanced interpretable machine learning proved promising for the characteristics prediction of hydrothermal biochar.

Remediation of di(2-ethylhexyl) phthalate (DEHP) contaminated black soil by freeze-thaw aging biochar

Di(2-ethylhexyl) phthalate (DEHP), a complex structure with high toxicity, is a common organic pollutant. This study investigated the effects of fresh biochar (FBC), and freeze-thaw cycled aged biochar (FTC-BC) on DEHP-contaminated soils using a pot experiment. The specific surface area of FBC increased from 145.20 to 303.50 m2/g, and oxygen-containing functional groups increased from 1.26 to 1.48 mol/g after freeze-thaw cycles, greatly enhancing the adsorption of DEHP by biochar in the soil. The comprehensive radar chart evaluation showed that FBC and FTC-BC reduced DEHP growth stress and improved the soil properties. Compared with FBC, FTC-BC performed better in protecting the normal growth of pakchoi and improving soil properties. In addition, the application of biochar increased the diversity and abundance of bacteria in the DEHP-contaminated soil and changed the composition of the soil bacterial community. The partial least squares path model (PLS-PM) showed that adding biochar as a soil remediation agent significantly positively impacted soil nutrients and indirectly reduced the DEHP levels in soil and plants by increasing soil microbial diversity. Compared with FBC, FTC-BC creates a more satisfactory living environment for microorganisms and has a better effect on the degradation of DEHP in the soil. This study provides a theoretical basis for future biochar remediation of DEHP-contaminated soils in cold high-latitude regions.

High-efficiency control of pesticide and heavy metal combined pollution in paddy soil using biochar/g-C3N4 photoresponsive soil remediation agent

The control of pesticide and heavy metal combined pollution in the paddy field is of great significance in terms of controlling agriculture nonpoint source pollution. Herein, an alkali-modified biochar (BCNaOH)/graphitic carbon nitride (g-C3N4) photoresponsive soil remediation agent was synthesized to control the pesticide and heavy metal compound pollution in paddy fields. Compared with g-C3N4, the photocurrent density increased 2.72 times for BCNaOH/g-C3N4, exhibiting a strong photocatalytic activity. In the simulated compound pollutant solution, the simultaneous Atrazine (ATZ) degradation and Pb sorption efficiencies of BCNaOH/g-C3N4 reached 94.70 % and 47.75 % under visible light irradiation, respectively. In the paddy field, both ATZ and Pb concentrations were well controlled in the overburden water and paddy soil. ATZ and Pb in overburden water reached 0 mg/L and 0.24 μg/L, respectively, and in paddy soil decreased by 60.21 % and 65.49 %, respectively. Excellent ATZ degradation performance was due to the construction of an intact photogenerated electron transfer pathway via the π-π stacking structure. Meanwhile, excellent Pb removal performance was due to the strong sorption capability of BCNaOH. The results provided a cost-effective photoresponsive soil remediation agent with good pesticide and heavy metal combined pollution control performance for paddy fields.

The Potential of Centong Cactus (Opuntia cochenillifera) as a Remediation Agent for Sidoarjo Mud Polluted Soil with Indicators of Fe Content Reduction and Plant Growth

Iron (Fe) is one of the heavy metals with high levels in Sidoarjo mud and is toxic to cultivated plants. This study aims to measure the potential of Centong Cactus (Opuntia cochenillifera) as a candidate for soil remediation agent in Sidoarjo Mud contaminated land by using soil Fe uptake and plant growth as indicators. This research was carried out for 3 months from December to March 2022 in the yard of Gebang Village, Sidoarjo District. This study used the correlational regression method to determine the relationship between 0-30% content of Sidoarjo mud with Fe content and various plant growth parameters. The data were statistically processed using regression at the 95% confidence level to determine the significance of the effect and the correlation between the mud content and the decrease in soil Fe content and plant growth. The results showed that there was an increase in soil Fe uptake by plants and a decrease in plant growth with an increase in silt content in the soil of the growing media. O. Cochenillifera has the potential as a candidate for phytoremediation agents that can be applied to areas exposed to Sidoarjo mud, especially for its use to reduce Fe metal levels.

Preparation and characterization of eco-friendly polysaccharide-based liquid mulch with soil amendment function

Plastic pollution and soil degradation pose substantial threats to the ecosystem. The need for a cleaner environment and a protector of degraded soil is urgently calling for a green alternative to petroleum-based plastic mulch . Here, we prepared a polysaccharide-based liquid mulch with soil amendment function by an emulsification method, which was used as a sprayable and green alternative to the petroleum-based plastic mulch and a soil remediation agent for degraded soil. Tamarind polysaccharides from tamarind industrial waste was applied as the film-forming agent and the soil particle aggregator . Additionally, Camellia saponins — the natural surfactant, and regenerated oil from waste cooking oil were added to the mulch to improve its homogeneity , mechanical property and hydrophobicity . By just adding 1% of regenerated oil to the system, the elongation at break and contact angle notably increased from 43.97% to 74.46% and 47.00°–86.82°, respectively; the water-vapor permeability of the liquid mulch reduced from 5.63 g⋅mm⋅h −1 ⋅kPa −1 ⋅m −2 to 1.76 g⋅mm⋅h −1 ⋅kPa −1 ⋅m −2 . Application tests showed that the polysaccharide-based liquid mulch effectively achieved a high rate of soil resistance (90.36%) to wind erosion. Topsoil erosion caused by wind can be considerably reduced. Scanning electron microscopic characterization revealed the effect of xyloglucan on soil particle aggregation. The liquid mulch also increased the germination rate by 31.00%. Moreover, after liquid mulch degradation, the nitrogen and carbon contents of the soil increased significantly from 0.05% to 0.60% and 1.42%–13.54%, respectively, thereby substantially increasing the soil organic matter content. The developed low-cost, yield-improving liquid mulch shows promising prospects for mulches and soil amendment in agriculture. • The liquid mulch was predominantly made from industrial wastes. • The preparation method is green, clean, simple, and cost-effective. • The liquid mulch improved water retention and effectively promoted soil aggregation. • Soil C and N contents were notably increased after the liquid mulch degradation. • The liquid mulch is greatly degradable and eco-friendly.

The application of machine learning methods for prediction of metal immobilization remediation by biochar amendment in soil

Biochar has been used widely in heavy metal contaminated sites as a soil remediation agent. However, due to the diversity of soils, biochars, and heavy metal contamination status, the remediation efficiency is difficult to measure, owing to a variety of parameters such as soil, biochar properties, and remediation procedure. Thus, an appropriate method to predict the remediation results and to select the appropriate biochar for the remediation is required. We initially created a database on soil remediation by biochars, which has 930 datasets with 74 biochars and 43 soils in it, based on collecting and organizing data from published literatures. Then, using data from the database, we modeled the remediation of five heavy metals and metalloids (lead, cadmium, arsenic, copper, and zinc) by biochars using machine learning (ML) methods such as artificial neural network (ANN) and random forest (RF) to predict remediation efficiency based on biochar characteristics, soil physiochemical properties, incubation conditions (e.g., water holding capacity and remediation time), and the initial state of heavy metal. The ANN and RF models outperform the lineal model in terms of accuracy and predictive performance (R2 > 0.84). Meanwhile, model tolerance of the missing data and reliability of the interpolation were studied by the predicted outputs of the models. The results showed that both ANN and RF have excellent performances, with the RF model having a higher tolerance for missing data. Finally, through the interpretability of ML models, the contribution of factors used in the model were analyzed and the findings revealed that the most influential elements of remediation were the type of heavy metals, the pH value of biochar, and the dosage and remediation time. The relative importance of variables could provide the right direction for better remediation of heavy metals in soil.

The release of arsenic from biologically formed arsenic-containing FeS under aerobic environment: Implications for the stability and species variation of nano-sized iron sulfide in remediation

Biologically formed nano-FeS is a potential and low-cost adsorbent and soil remediation agent. Remediation of arsenic from contaminated groundwater and soil by biological FeS is promising, however, the fate and transport of arsenic associated with nano-FeS in the natural environment are poorly understood. To investigate the fate of adsorbed arsenic on nano-FeS under aerobic conditions, static and dynamic experiments were carried out at different pH values and different oxidants. Batch and column sets showed that arsenic(V)-loaded FeS could release arsenic into solutions at pH 3.0 and 9.0. Especially noteworthy is the release of arsenic sustained at pH 9.0. Introducing Fe3+ and H2O2 at pH 3.0 showed that Fe3+ and a high concentration of H2O2 could reduce the release of arsenic, which might be ascribed to the oxidants promoting secondary Fe mineral phases to form on the arsenic(V)-FeS solid surface. X-ray diffraction patterns indicated that elemental S(0) and arsenic(V)-bearing Fe(II)/Fe(III) minerals formed as the main products. The generated secondary parasymplesite and FeAsO4 were mainly responsible for dissolved arsenic retention. The performance of hydraulic conductivity followed the sequence pH 7.0 > 50 mg/L Fe3+ > 1 mg/L Fe3+ > pH 9.0 > pH 3.0. In addition, H2O2 always kept good hydraulic conductivity. XPS analysis demonstrated that arsenic(III) and arsenic(V) were the main arsenic speciation on the surfaces of the solids, implying that lower valence arsenic was oxidized to arsenic(III/V) during the oxidation processes. The present study facilitates a better understanding of the stability of arsenic-loaded FeS in aerobic environment.

Comprehensive Study on the Feasibility of Pyrolysis Biomass Char Applied to Blast Furnace Injection and Tuyere Simulation Combustion.

Basic property analysis is the most comprehensive evaluation of metallurgical characteristics of blast furnace injection fuel. In this study, the basic properties of 16 types of pyrolysis biomass char samples were comprehensively investigated; the results showed that components harmful to a blast furnace, such as the ash content and alkali metal content of Jiangsu Suzhou woodblock char (B3), Jiangsu Changzhou branch char (B8), Jiangsu Zhangjiagang bamboo char (B10), and Jiangsu Zhangjiagang coconut shell char (B12) in all of the biomass char samples, are lower and close to the level of blast furnace injection bituminous coal. The grindability, particle size distribution, and safety all met the requirements of the blast furnace. Among them, the ash melting characteristic temperature of B3, B8, Jiangsu Zhangjiagang rice husk char (B11), and Shanghai soil remediation agent (B16) was greater than 1250 °C, indicating that they are not easy to block the blast furnace raceway and spray guns. Most of the biomass char samples had good combustibility, and the burnout temperature was less than 700 °C. A self-developed blast furnace injection combustion simulation experimental device was used to simulate the combustion behavior of biomass char in the blast furnace raceway tuyere, and the burnout rates of 16 biomass chars were measured. The results showed that that the burnout rate is related to both the volatiles and fixed carbon and the influence of volatiles on the burnout rate is greater than that of fixed carbon. The burnout rates of B3 and B8 were 77.12 and 67.03%, respectively. Above all, B3 and B8 showed good properties, but the burnout rate of B3 was higher, so B3 had the feasibility of applying to blast furnace injection, which indicates that woodblock char has the potential to be used as blast furnace injection fuel.

Evaluation of three common alkaline agents for immobilization of multi-metals in a field-contaminated acidic soil.

We investigated three common alkaline agents (NaOH, CaO, and Mg(OH)2) for immobilization of four heavy metals (Pb, Zn, Cu, and Cd) in a field-contaminated soil and elucidated the underpinning principles. NaOH caused the highest pH spike in the soil, while CaO and Mg(OH)2 served as a longer-lasting source of OH-. Amending the soil with CaO or Mg(OH)2 at ≥0.1 mol as OH- (kg·soil)-1 for 24 h was able to immobilize all four metals, while NaOH failed. NaOH leached up to 3 times more organic carbon than CaO and Mg(OH)2, resulting in elevated leachability of the metals. Column elution tests showed that amendments by CaO and Mg(OH)2 lowered the leachable Pb2+, Zn2+, Cu2+, and Cd2+ by 52-54%, 71-75%, 69-73%, and 68%, respectively, after 1440 pore volumes of elution. Sequential extraction revealed that the soil amendments converted the exchangeable fraction of the metals to the much less available forms. XRD and FTIR analyses indicated that formation of metal oxide precipitates and complexation with soil organic matter were responsible for the metals immobilization. Taken together the chemical cost, technical effectiveness, and environmental impact, CaO is the most suitable alkaline agent for remediation of soil contaminated with heavy metals.

Lignocellulosic-Based Sorbents: A Review

The combustion of fossil fuels is intensifying global warming and destructing the ecosystem with negative human health impacts as well. Even so, other anthropogenic activities have unfortunately constituted pollution also to our environment, say, in the form of waste waters. Beside these, the existing technologies for waste water treatment have problems such as high costs, sludge disposal challenges, etc. Thus, it is now important to find economically viable and safe alternatives to decontaminate waste waters. Hence, low cost, renewable, easily accessible, and readily prepared biosorbents have become favourable alternatives to traditional counterpart for the elimination of pollutants from aqueous systems. Fortunately, these biosorbents also have requisite and comparable properties necessary for adsorption of pollutants. Many studies have been reported on the application of biosorbents for pollutants removal. However, this paper provides an overview of biosorbents preparation, properties, their applications in pollutants removal and related use. Biosorbents are usually used in raw or processed forms such as activated carbon (AC), biobar (BC), and charcoal (CC) for removal of pharmaceuticals, pesticides, organics, inorganics, mycotoxins, etc. from aqueous systems. Besides classical sorption of the pollutants, biosorbents have prospect of applications as electrodes in the microbial fuel cells, green packaging materials, energy storage devices, catalysts, soil remediation agent, carbon sequestration, etc. Hence, further concerted investigations should be exercised to develop feasibly best conditions for the preparations and modifications of biosorbents. In addition, mean pore size, pore size distribution, porosity, surface functionality, and zeta potential studies are necessary to be had about biosorbents, especially novel types. There is need for development of biosorbents for specific tasks. Another essential thing is to determine desorption studies of these novel biosorbents. Focus should also be directed on more economically viable and sustainable biosorbents to enhance their use. Again, it is suggested that more suitable biomasses be identified to enable successful preparation of efficient biosorbents. More so, biosorbents can be recycled after use to avoid littering and possible pollution.

Simultaneous remediation and fertility improvement of heavy metals contaminated soil by a novel composite hydrogel synthesized from food waste

Soil contamination by heavy metals constitutes a serious global environmental problem, and numerous remediation technologies have been developed. In this study, a novel soil remediation agent, namely composite hydrogel (leftover rice-g-poly(acrylic acid)/montmorillonite/Urea, LR-g-PAA/MMT/urea), was prepared based on free radical polymerization cross-linking technology. Experimental results indicated that the LR-g-PAA/MMT/urea dosage increased from 0% to 10%, the oxidizable state proportions of Cd, Cu, Pb and Zn in contaminated soil increased from 8.3%, 23.7%, 54.0% and 11.4%–71.3%, 61.0%, 76.5%, and 27.9%, respectively. Compared with control experiment, the residue state growth rate were 56.6%, 23.4% and 39.8% for Cu, Pb and Zn respectively with 10% dosage of composite hydrogel. Simultaneously, the LR-g-PAA/MMT/urea was also seen to enhance soil fertility, including organic matter content, cation exchange capacity, and N and P contents. Pot experiments for biological toxicity suggested that the addition of hydrogel weakened the toxic effect of heavy metals on cotton seeds, and the action effect was increasingly visible with the increase of hydrogel dosage. The analysis of the mechanism involved suggested that the organic matter and its possessed characteristic functional groups could weaken the biological toxicity via complexation, adsorption, and ion exchange. Overall, the synthesized composite hydrogel exhibits great potential for the simultaneous remediation and fertility improvement of heavy metal contaminated soil.

Effects of different types of microbial inoculants on available nitrogen and phosphorus, soil microbial community, and wheat growth in high-P soil.

Irrational application of chemical fertilizers causes soil nutrient imbalance, reduced microbial diversity, soil diseases, and other soil quality problems and is one of the main sources of non-point pollution. The application of microbial inoculant (MI) can improve the soil environment and crop growth to reduce problems caused by irrational application of chemical fertilizers. Field experiments were carried out in high-phosphorus soils to study the effects of the addition of various MIs combined with chemical fertilizers on soil properties, wheat growth, and soil microbial composition and structure. The MIs consisted of one fungal agent: Trichoderma compound agent (TC) and five bacterial agents, namely soil remediation agent (SR), anti-repeat microbial agent (AM), microbial agent (MA), plant growth-promoting rhizobacteria (PG), and biological fertilizer agent (BF). The wheat yield increased by 15.2-33.4% with the addition of MIs, and PG with Bacillus subtilis as the core microorganism had the most obvious effect on increasing the production (p < 0.05). For the entire growth period of wheat, all MIs applied significantly increased the available nitrogen (AN) (p < 0.05) but did not significantly affect the available phosphorus (AP). BF has the best effect on increasing AN in the soil. The 16S rRNA sequencing results indicated that the dominant phyla of soil bacteria were Proteobacteria, Acidobacteria, Bacteroidetes, Actinobacteria, and Verrucomicrobia. The addition of MIs increased the relative abundance of Acidobacteria, Actinobacteria, Chloroflexi and decreased Proteobacteria and Bacteroidetes. The diversity of soil bacterial community (Chao1) was significantly higher in the soil added with TC than that added with BF (p < 0.05). All bacterial agents significantly enriched various genera (p < 0.05), while the fungal agent (TC) did not enrich the genera significantly. pH and AN, but not TP, were closely related to the dominant bacteria phylum in high-P soil. The application of MIs improved AN in soil, increased the wheat yield, and changed the relative abundance of the soil dominant phylum, and these changes were closely related to the type of MIs. The results provide a scientific basis for rational use of different types of MIs in high-P soil.