Sequential extraction of nickel and zinc in sewage sludge- or biochar/sewage sludge-amended soil

Biochar and soil properties affect remediation of Zn contamination by biochar: A global meta-analysis

Zinc (Zn) is one of the most common heavy metals that pollute soils and can threaten both environmental and human health. Biochar is a potential solution for remediating soil Zn contamination. This meta-analysis investigates the effect of biochar application on the remediation of Zn-contaminated soils and the factors affecting the remediation efficiency. We found that biochar application in Zn-contaminated soils reduced Zn bioavailability by up to 77.2% in urban soils, 55.1% in acidic soils, and 50.8% in coarse textured soils. Moreover, the remediation efficiency depends on the biochar production condition, with crop straw and sewage sludge feedstocks, high pyrolysis temperature (450-550 °C), low heating rate (<10 °C min-1), and short residence time (<180 min) producing high performing biochars. Biochar affects soil Zn bioavailability by changing soil pH and organic carbon, as well as through its high surface area, ash content, and O-containing surface functional groups. Our findings highlight the role of biochar as a promising and environmentally friendly material for remediating Zn contamination in acidic and/or coarse textured soils. We conclude that soil properties must be considered when selecting biochars for remediating soil Zn contamination.

Influence of biochar produced from negative pressure-induced carbonization on transformation of potentially toxic metal(loid)s concerning plant physiological characteristics in industrially contaminated soil

Soil contamination and its subsequent impact on the food chain is a pressing challenge in the present day. The application of biochar has demonstrated a significant and positive effect on soil health, thereby enhancing plant growth and development. However, the application of biochar (BC) produced from negative pressure-induced carbonization to mitigate metal(loid) contamination is a new strategy that has been studied in current research. Results depicted that the application of biochar derived from the negative pressure carbonization (vacuum-assisted biochar (VBC) has a significant (p ≤ 0.05) positive impact on plant growth and physiological characteristics by influencing immobilization and speciation of metal(loid) in the soil system. Moreover, the interactive effect of VBC on physiological characteristics (photosynthesis, gas exchange, and chlorophyll contents) and antioxidant activities of maize (Zea mays L.) was significantly (p ≤ 0.05) positive by confining the translocation and movement of metal(loid)s to the aerial part of the maize plant. X-ray diffraction (XRD) provided information on the structural and chemical changes induced by the VBC-500 °C explaining metal(loid) adsorption onto mineral surfaces and complexation that can affect their mobility, availability, and toxicity in the contaminated soil. Fourier transform infrared spectroscopy (FTIR) further provided a more detailed understanding of the metal(loid)s and biochar complexation mechanisms influenced by VBC-based functional groups -OH, C-Hn, -COOH, CO, C-O-C, CC, C-O, C-H, OH, and C-C in the binding process. These results suggest that the application of biochar prepared at 500 °C under negative pressure-induced carbonization conditions to the soil is the most efficient way to reduce the uptake and transfer of metal(loid)s by influencing their mobility and availability in the soil-plant system.

Physicochemical characteristics and microbial communities of rhizosphere in complex amendment-assisted soilless revegetation of gold mine tailings

Amendment-assisted soilless revegetation is a promissing ecological restoration method of mine tailings because of its eco-friendliness and low-cost. However, it is difficult to establish the plant community during ecological restoration because of its nutrient deficiency and heavy metal toxicity. In this study, the complex amendment, consisting of 1% peat, 1% sludge and 4% bentonite, was used to assist tall fescue to revegetate gold mine tailings. The variation in physicochemical characteristics and microbial community diversity and composition of rhizosphere tailings were investigated. The complex amendments significantly promoted tall fescue growth with an increase of 35.33% in shoot length and 27.19% in fresh weight. The improved plant growth was attributed to the reduction in heavy metal accumulation and the variation in the characteristics of rhizosphere tailing microecology. The heavy metal concentrations in plant tissues were decreased by 27.71-53.44% in the amended groups. Compared with the control, the available nitrogen (N), phosphorus (P) and potassium (K) levels in TA (without plant cultivation) and TPA (with plant cultivation) were also enhanced by 36.67-49.09% and 42.21-71.47%, respectively. Besides, the amendments introduced more exclusive operational taxonomic units (OTU) and increased the relative abundance of ecologically beneficial microbes in the rhizosphere. Overall, this study provides insight into amendment-assisted soilless revegetation and its effects on microecology to expand ecological restoration of gold mine tailings.

Chemical speciation and release kinetics of Ni in a Ni-contaminated calcareous soil as affected by organic waste biochars and soil moisture regime

Biochars vary widely in properties and have been shown to have variable effects on potentially toxic element(s) stabilization in soil. This is the first study to examine the interaction effects of biochar and soil moisture regime on Ni stabilization in a Ni-contaminated calcareous soil. Three different organic waste (cow manure, municipal compost and licorice root pulp) biochars produced at two temperatures (300 and 600 °C) were applied (3% wt.) to a Ni-contaminated calcareous soil and incubated at field capacity and saturated conditions for 70 d. Sequential chemical fractionation and Ni release kinetics were then performed. All applied biochars, especially the high-temperature biochars, were significantly able to enhance Ni stabilization in the studied soil. In particular, the biochars significantly decreased Ni content in the water-soluble and exchangeable fractions (10-42% decrease), while increasing the immobile residual fraction (13-38% increase). The biochars also significantly decreased the rate and cumulative amount of EDTA-extractable Ni from the calcareous soil. Among the studied biochars, the cow manure and municipal compost biochars produced at 600 °C were the most effective at reducing Ni mobility factor (27-28% decrease) and initial release rate (42-49% decrease), likely due to their high ash content and pH, which promotes Ni sorption in soil. Soil moisture regime was not found to significantly affect the Ni mobility factor or rates of Ni release from the calcareous soil but did, however, affect certain soil Ni chemical fractions. Soil water saturation significantly decreased Ni in the Mn (4%) and non-crystalline Fe oxides (17%) fractions, while increased the crystalline Fe oxide fraction (3%), attributed to reductive dissolution of Mn and Fe oxide crystallinity enhancement. Saturation also significantly enhanced Ni in the residual fraction (4%), attributed to the associated pH increase and potential sulfide formation. The results of this study demonstrate that high temperature, ash-rich, and alkaline biochars are most effective at Ni immobilization, and that soil water saturation can further enhance Ni in the residual fraction.

Structural study and metal speciation assessments of waste PCBs and environmental implications: Outlooks for choosing efficient recycling routes

Environmental protection from risks and disposal management of discarded mobile phone printed circuit boards (MPhPCBs) is a global issue. Although recycling is proposed as a solution, it is challenging to choose a sustainable method due to the insufficient recognition from extreme structural heterogeneity of these wastes based on their types. To this end, a thorough study on the structural characterization of PCBs using different analyses and metal speciation by sequential extraction procedure were performed. Understanding these information is an essential step in order to choose efficient methods to maximize selective recycling of metals and minimize environmental implications. PCBs were found to be potent metallic reservoirs after all metal content of PCBs were precisely measured. The structural analysis results of the sample included identification of different phases, functional groups, 45.1 % of the crystalline and 54.9 % of amorphous, the mesoporous nature (pore diameter mean ∼ 7.24 nm), hydrophobic property (contact angle ∼93.4°), the positive ζ-potential of particles at pH < (isoelectric point ∼5.4) and vice versa, and the particle size that were not oversized. The metal speciation outcome indicated over 80 % of the total content of elements such as Si, Sn, Ag, Au, Sr, Al, Cr, Nd, Ca, Ba, and P was in a solid crystal structure/residual fraction, which were hard recycled. The assessment of contamination levels of waste indicated the considerable contamination for the environment at global contamination factor ∼27.7, the moderate ecological risk at potential ecological risk assessment ∼82.9, and threats to public health. In addition, the metals of Pr, Mn, and Zn pose high risks because of their risk assessment code values of 42.7 %, 36.7 %, and 33.1 %, respectively. Leaching tests proved Waste Extraction Test was an aggressive method. ANC4 proposed high level of H⁺ consumption are required for metal leaching in future works.

Toxic waste sludge derived hierarchical porous adsorbent for efficient phosphate removal

Global effective treatment of phosphorus crisis and toxic waste sludge in one way is urgently needed but still insufficient due to single function, environmental damage, and complicated fabrication process. Herein, we proposed a facile, low-cost, and sustainable strategy to fabricate NiAl layered double oxides/nickel-containing sludge (LDOs/NCS) adsorbent using toxic NCS as raw material via two-step method including hydrothermal process and calcination. The as-designed hierarchical porous adsorbent with large specific surface area and pore volume exhibited excellent adsorption properties towards phosphate. Langmuir adsorption model exhibited the best fit to the experimental data, which illustrated that the adsorption process was dominated by monolayer adsorption. Moreover, even in various double anions systems or in a wide pH range environment (2-12), the as-designed LDOs/NCS still maintained relatively stable adsorption capacity. A possible adsorption mechanism involving surface complexation and electrostatic interactions was investigated. Besides, the LDOs/NCS also displayed admirable durability and reusability. Therefore, this waste-control-waste strategy not only simultaneously addresses phosphorus crisis treatment and toxic NCS management, but also could be potentially extended towards rational design of other metals-containing sludge derived functional materials.

Remediation of Pb-diesel fuel co-contaminated soil using nano/bio process: subsequent use of nanoscale zero-valent iron and bioremediation approaches

The effectiveness of the nano/bio process was investigated as a remediation option for co-contaminated soils. Nano/bio process is a hybrid treatment method that may be defined as the use of nanoscale zero-valent iron (nZVI) and bioremediation approaches subsequently/concurrently. Different bioremediation approaches (bioattenuation, biostimulation, and/or bioaugmentation) were performed together with nZVI application to remediate Pb- and diesel fuel-spiked soils. Nutrient (N and P) and activated sludge amendment were made to realize biostimulation and bioaugmentation, respectively. The nZVI application decreased the total percentage of the most mobile and bioavailable soil Pb fractions (exchangeable and carbonate-bound) from 68.3 to 31.7%. The biodegradation levels of nZVI-applied co-contaminated soils were significantly higher than the soils without nZVI indicating the positive effect of the reduced mobility, bioavailability, and toxicity of Pb content. The use of nano/biostimulation or nano/bioaugmentation treatments resulted in higher than 60% total n-alkane degradation, whereas 89.5% degradation was obtained by using nano/biostimulation + bioaugmentation. Hydrocarbon-degrader strains belonging to phyla Actinobacteria, Proteobacteria, or Firmicutes were identified from samples subjected to nano/bio process and the strains from biostimulation and bioaugmentation treatments were different. These results indicate that the stress on the microbial population caused by the co-contamination might be subsided and the biodegradation of alkanes might be improved by using the nano/bio process.

The efficiency of potato peel biochar for the adsorption and immobilization of heavy metals in contaminated soil

We investigated the potential application of potato peel biochar (PPB) for the adsorption and immobilization of heavy metals (Cd, Pb, and Ni) in contaminated acidic soil. The addition of PPB to the soil, especially at the application rate of 8%, increased soil pH, cation exchange capacity (CEC), and organic carbon (OC). The maximum adsorption capacity of Cd, Pb, and Ni in the soil amended with PPB at the application rate of 8% was 3215.9, 4418.67, and 3508.51 mg kg^-1, respectively. Compared to the control, the addition of 8% PPB to the soil decreased the soluble and exchangeable fraction of Cd, Pb, and Ni to 84.3, 90.6, and 79.1 mg kg^-1, respectively. In contrast, the addition of 8% PPB to the soil increased the organically-bound and residual fractions of metals in the following order: Pb > Cd > Ni, and Cd > Pb > Ni, respectively. The results of this study showed that potato peel biochar has the potential to stabilize and reduce the bioavailability of heavy metals in contaminated acidic soil. Therefore, potato peel biochar can serve as an eco-friendly, low-cost, and efficient adsorbent to immobilization of heavy metals in contaminated acidic soils.NOVELTY STATEMENTEffect of biochar produced from potato peel on the adsorption of the heavy metals in contaminated acidic soil.Immobilization of heavy metals in contaminated acidic soil amended with potato peel biochar.Improving the chemical properties of soil amended with potato peel biochar.

Effects on metal availability of the application of tree biochar and municipal waste biosolid in a metalliferous mine tailings substrate

The phytostabilization of mine tailings requires a previous assessment of the effects of soil amendments on metal mobility. The goal of this work was to evaluate the response of metal availability (both labile and potentially available pools) to the addition of two organic amendments (a municipal waste biosolid and a tree biochar), separately and in combination, in a mine tailings substrate. For this purpose, a comprehensive comparison among several single extraction procedures and a sequential extraction procedure was performed. The effects on metals phytotoxicity were assessed through a germination test using seeds of Zygophyllum fabago. When evaluating the effect of the amendments in the labile metal pool, the biochar resulted effective in decreasing metal-extractable concentrations, especially for Cd, Mn and Zn. The treatment with biochar also showed better germination parameters (percentage of germinated seeds and sooner germination) than the rest of the unamended and amended treatments. The use of the municipal organic biosolid increased labile metal concentrations and potentially available metal pools assessed with EDTA and did not contribute to achieve better results of seed germination. Compared to the single biosolid treatment, the combination of biochar/biosolid modulated some labile metal concentrations and showed similar germination parameters to those obtained for the treatment amended only with biochar. This positive effect of biochar in modulating the soluble metal concentrations associated with certain urban/agricultural organic materials supported the suitability of using these combinations in field applications, although a higher rate of biochar application would be recommended to obtain a more beneficial effect.

Fractionation of Metal(loid)s in Three European Mine Wastes by Sequential Extraction

Mine waste can constitute an environmental hazard, especially when poorly managed. Environmental assessment is essential for estimating potential threats and optimizing mine waste management. This study evaluated the potential environmental risk of sulfidic mine waste samples originating from the Neves Corvo Mine, Portugal, and the closed Freiberg mining district, Germany. Metal(loid)s in the waste samples were partitioned into seven operationally defined fractions using the Zeien and Brummer sequential extraction scheme. The results showed similar partitioning patterns for the elements in the waste rock and tailing samples from Neves Corvo Mine; most metal(loid)s showed lower mobility, as they were mainly residual-bound. On the contrary, the Freiberg tailing sample had considerably elevated (24–37%) mobile fractions of Zn, Co, Cd, and Mn. The majority of Fe (83–96%) in all samples was retained in the residual fractions, while Ca was highly mobile. Overall, Pb was the most mobile toxic element in the three samples. A large portion of Pb (32–57%) was predominantly found in the most mobilizable fractions of the studied waste samples. This study revealed that the three mine wastes have contamination potential for Pb and Zn, which can be easily released into the environment from these waste sources.

Zinc in soil-plant-human system: A data-analysis review

Zinc (Zn) plays an important role in the physiology and biochemistry of plants due to its established essentiality and toxicity for living beings at certain Zn concentration i.e., deficient or toxic over the optimum range. Being a vital cofactor of important enzymes, Zn participates in plant metabolic processes therefore, alters the biophysicochemical processes mediated by Zn-related enzymes/proteins. Excess Zn can provoke oxidative damage by enhancing the levels of reactive radicals. Hence, it is imperative to monitor Zn levels and associated biophysicochemical roles, essential or toxic, in the soil-plant interactions. This data-analysis review has critically summarized the recent literature of (i) Zn mobility/phytoavailability in soil (ii) molecular understanding of Zn phytouptake, (iii) uptake and distribution in the plants, (iv) essential roles in plants, (v) phyto-deficiency and phytotoxicity, (vi) detoxification processes to scavenge Zn phytotoxicity inside plants, and (vii) associated health hazards. The review especially compares the essential, deficient and toxic roles of Zn in biophysicochemical and detoxification processes inside the plants. To conclude, this review recommends some Zn-related research perspectives. Overall, this review reveals a thorough representation of Zn bio-geo-physicochemical interactions in soil-plant system using recent data.

An overview and assessment of the existing technological options for management and resource recovery from beach wrack and dredged sediments: An environmental and economic perspective

The present work discusses the problems and management options of beach wrack and dredged sediments. Beach wrack and dredged sediments near the shores have affected the coastal ecosystem, badly. The piles of beach wrack residues might be a significant emitter of greenhouse gases (GHGs) and dredged sediment is a substantial source of heavy metals and other pollutants. The recovery of valuable resources such as metals and nutrients from these so-called "wastes" is a sustainable strategy to enhance the resilience of the coastal ecosystem and management. The beach wrack meadows can be a potential source for green energy production. Even the demand for biodegradable polymers can be supplied by utilizing the waste beach wracks. The residues of beach wrack species like Posidonia oceanica, Zostera marina, Ulva spc. and Enhalus acorodies can be very beneficial species in terms of economic growth. Red algae have been the most favored and efficient candidate for methane yield. In case of dredged sediment, dewatering of sediment is an essential step for successful resource extraction. Although, extraction methods are almost similar to that applied for soil treatment, which includes pretreatment, physical partitioning, washing, thermal treatment, biological extraction, and immobilization. The fractionation study can be a beneficial tool for determining the metal species present in the sediment. Immobilization techniques are successful but continuous monitoring is required. The vitrification technique is highly effective but very expensive. Thermal treatment is useful for volatile metals such as mercury (Hg), but costs are high. Biological extractions are comparatively cheap but time-consuming. Henceforth, very few extraction methods are available for sediment and required further advancement in this field.

Nickel in soil and water: Sources, biogeochemistry, and remediation using biochar

Nickel (Ni) is a potentially toxic element that contaminates soil and water, threatens food and water security, and hinders sustainable development globally. Biochar has emerged as a promising novel material for remediating Ni-contaminated environments. However, the potential for pristine and functionalized biochars to immobilize/adsorb Ni in soil and water, and the mechanisms involved have not been systematically reviewed. Here, we critically review the different dimensions of Ni contamination and remediation in soil and water, including its occurrence and biogeochemical behavior under different environmental conditions and ecotoxicological hazards, and its remediation using biochar. Biochar is effective in immobilizing Ni in soil and water via ion exchange, electrostatic attraction, surface complexation, (co)precipitation, physical adsorption, and reduction due to the biogeochemistry of Ni and the interaction of Ni with surface functional groups and organic/inorganic compounds contained in biochar. The efficiency for Ni removal is consistently greater with functionalized than pristine biochars. Physical (e.g., ball milling) and chemical (e.g., alkali/acidic treatment) activation achieve higher surface area, porosity, and active surface groups on biochar that enhance Ni immobilization. This review highlights possible risks and challenges of biochar application in Ni remediation, suggests future research directions, and discusses implications for environmental agencies and decision-makers.

Agricultural Soils Amended With Thermally-Dried Anaerobically-Digested Sewage Sludge Showed Increased Risk of Antibiotic Resistance Dissemination

The application of sewage sludge (SS) to agricultural soil can help meet crop nutrient requirements and enhance soil properties, while reusing an organic by-product. However, SS can be a source of antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs), resulting in an increased risk of antibiotic resistance dissemination. We studied the effect of the application of thermally-dried anaerobically-digested SS on (i) soil physicochemical and microbial properties, and (ii) the relative abundance of 85 ARGs and 10 MGE-genes in soil. Soil samples were taken from a variety of SS-amended agricultural fields differing in three factors: dose of application, dosage of application, and elapsed time after the last application. The relative abundance of both ARGs and MGE-genes was higher in SS-amended soils, compared to non-amended soils, particularly in those with a more recent SS application. Some physicochemical parameters (i.e., cation exchange capacity, copper concentration, phosphorus content) were positively correlated with the relative abundance of ARGs and MGE-genes. Sewage sludge application was the key factor to explain the distribution pattern of ARGs and MGE-genes. The 30 most abundant families within the soil prokaryotic community accounted for 66% of the total variation of ARG and MGE-gene relative abundances. Soil prokaryotic α-diversity was negatively correlated with the relative abundance of ARGs and MGE-genes. We concluded that agricultural soils amended with thermally-dried anaerobically-digested sewage sludge showed increased risk of antibiotic resistance dissemination.

Ecotoxicological assessment of sewage sludge-derived biochars-amended soil

The study aimed to evaluate the ecotoxicity of soil (S) amended with biochars (BCKN) produced by the thermal conversion of sewage sludge (SSL) at temperatures of 500 °C, 600 °C, or 700 °C and SSL itself. The ecotoxicological tests were carried out on organisms representing various trophic levels (Lepidium sativum in plant, Folsomia candida in invertebrates, and Aliivibrio fischeri in bacteria). Moreover, the study evaluated the effects of three plants (Lolium perenne, Trifolium repens, and Arabidopsis thaliana) growing on BCKN700-amended soil on its ecotoxicological properties. The experiment was carried out for six months. In most tests, the conversion of sewage sludge into biochar caused a significant decrease in toxicity by adding it to the soil. The pyrolysis temperature directly determined this effect. The soil amended with the biochars produced at higher temperatures (600 °C and 700 °C) generally exhibited lower toxicity to the test organisms than the SSL. Because of aging, all the biochars lost their inhibition properties against the tested organisms in the solid-phase tests and had a stimulating influence on the reproductive ability of F. candida. With time, the fertilizing effect of the BCKN700 amended soil also increased. The aged biochars also did not have an inhibitory effect on A. fischeri luminescence in the leachate tests. The study has also demonstrated that the cultivation of an appropriate plant species may additionally reduce the toxicity of soil fertilized with biochar. The obtained results show that the conversion of sewage sludge to biochar carried out at an appropriate temperature can become a useful method in reducing the toxicity of the waste and while being safe for agricultural purposes.

Heavy Metals Behavior in Soil/Plant System after Sewage Sludge Application

One of the possibilities of removing heavy metals (HMs) from soil is the use of phytoremediation techniques supported with biosolids, which also allow for their disposal. Therefore, the objective of the research was the determination of the sewage sludge suitability after its application to urban soil in order to increase the phytoremediation efficiency of contaminated soil. A field experiment was established on lawns in Białystok (Poland) in two locations with different traffic. The research plots were fertilized with sludge in doses of 14.5 t DM/ha and 29 t DM/ha. A mixture of lawn grasses was sown on the prepared plots. During two years of experiment soil/plant samples were collected, and pH, organic matter, dehydrogenase and catalase activity (soil), the total content of Cd, Cr, Cu, Mo, Ni, Pb, Zn, and Hg (soil/plant), and their fractions (soil) were determined. The HMs in soil were present mainly in residual and reducible fractions. Zn had the highest share in acid-soluble fractions (17–45%). The efficiency of urban soil phytoremediation was determined by the calculation of bioconcentration (BCF) and translocation (TF) factors. The highest values for BCF and TF were obtained for Mo (1.97 and 1.99, respectively). In the presented study, sludge amendment caused an immobilization of heavy metals.

Induced changes of pyrolysis temperature on the physicochemical traits of sewage sludge and on the potential ecological risks

Biochar from sewage sludge is a low-cost sorbent that may be used for several environmental functions. This study evaluates the induced effects of pyrolysis temperature on the physicochemical characteristics of sewage sludge (SS) biochar produced at 350 (SSB₃₅₀), 450 (SSB₄₅₀) and 600 (SSB₆₀₀), based on the metal enrichment index, metal mobility index (MMI), and potential ecological risk index (PERI) of Cd, Cu, Pb, and Zn. Increased pyrolysis temperature reduced the biochar concentration of elements that are lost as volatile compounds (C, N, H, O, and S), while the concentration of stable aromatic carbon, ash, alkalinity, some macro (Ca, Mg, P₂O₅, and K₂O) and micronutrients (Cu and Zn), and toxic elements such as Pb and Cd increased. Increasing the pyrolysis temperature is also important in the transformation of metals from toxic and available forms into more stable potentially available and non-available forms. Based on the individual potential ecological risk index, Cd in the SS and SSB₄₅₀ were in the moderate and considerable contamination ranges, respectively. For all pyrolysis temperature biochar Cd was the highest metal contributor to the PERI. Despite this, the potential ecological risk index of the SS and SSBs was graded as low.

Clays, Limestone and Biochar Affect the Bioavailability and Geochemical Fractions of Cadmium and Zinc from Zn-Smelter Polluted Soils

Ca-bentonite (CB) alone and in a mixture with limestone (L), tobacco biochar (TB) and zeolite (Z) on the fixation, geochemical fractions and absorption of Cd and Zn by Chinese cabbage in smelter heavily polluted (S-HP) and smelter low polluted (S-LP) soils were investigated. The results showed that the CB + TB and CB + L + TB treatments significantly immobilized Cd up to 22.0% and 29.7%, respectively, and reduced uptake by Chinese cabbage shoot to 36.0% with CB + Z + L and 61.3% with CB + L in S-HP and S-LP soils compared with the control. The CB + Z + L + TB treatment mobilized Cd up to 4.4% and increased absorption in the shoot by 9.9% in S-HP soil. The greatest immobilization of Zn was 53.2% and 58.2% with the CB + Z + L + TB treatment, which reduced Zn uptake in the plant shoot by 10.0% with CB + L and 58.0% with CB + Z + L + TB in S-HP and S-LP soils. The CB + Z + TB and CB + TB treatments mobilized Zn up to 35.4% and 4.9%, respectively, in both soils. Furthermore, the uptake of Zn in plant shoot was observed by 59.0% and 7.9% with application of CB + Z and CB + TB treatments, respectively, in S-HP and S-LP soils. Overall, our results suggest that Ca-bentonite alone and in mixtures with different amendments can be used to reduce the phyto-extraction of Cd and Zn in Zn-smelter polluted soils.

Effects of hematite on the stabilization of copper, cadmium and phosphorus in a contaminated red soil amended with hydroxyapatite

Iron (Fe) oxides are intimately coupled with phosphorus and closely associated with the bioavailability of potential toxic elements (PTEs) in soil. Thus, Fe oxides may influence the stabilization of PTEs in contaminated soils amended by phosphorus. To evaluate the effects of hematite (HMT) on the stabilization of PTEs, 1-5% (by weight) of HMT was added into a contaminated red soil amended with hydroxyapatite (HAP) to simulate naturally occurring Fe oxides. The stabilization efficiencies of soil copper (Cu) and cadmium (Cd) amended with HAP in soils with low, moderate, and high content of HMT were assessed after a 60-day incubation. HAP treated the soil with high rate HMT decreased the CaCl₂-extractable and acid-soluble fractions of Cu and Cd than that of HAP alone. In particular, CaCl₂-extactable Cu and Cd in the soil with 5% HMT amended by HAP were 91-95% and 41-68% lower than those amended with only HAP. High content of HMT in soil could decrease the concentration of labile phosphorus in the presence of HAP, but it did not increase the concentration of NaOH-extractable inorganic phosphorus (the fraction bound to Fe oxides). The concentrations of free and crystalline Fe oxides were significantly increased by adding high dosages of HMT with or without HAP. High content of HMT in soil amended by HAP reduced metal phytotoxicity and uptake by wheat shoots than the soil containing HAP without HMT. The results indicate that HMT can promote Cu and Cd stabilization while decrease labile phosphorus in red soil amended with HAP, suggesting that phosphorus-based amendments combined with Fe oxides can be used to stabilize PTEs in contaminated red soils.

Wheat Straw Biochar as a Specific Sorbent of Cobalt in Soil

There is an urgent need to search for new sorbents of pollutants presently delivered to the environment. Recently biochar has received much attention as a low-cost, highly effective heavy metal adsorbent. Biochar has been identified as an efficient material for cobalt (Co) immobilization from waters; however, little is known about the role of Co immobilization in soil. Hence, in this study, a batch experiment and a long-term incubation experiment with biochar application to multi-contaminated soil with distinct properties (sand, loam) were conducted to provide a brief explanation of the potential mechanisms of Co (II) sorption on wheat straw biochar and to describe additional processes that modify material efficiency for metal sorption in soil. The soil treatments with 5% (v/w) wheat straw biochar proved to be efficient in reducing Co mobility and bioavailability. The mechanism of these processes could be related to direct and indirect effects of biochar incorporation into soil. The FT-IR analysis confirmed that hydroxyl and carboxyl groups present on the biochar surface played a dominant role in Co (II) surface complexation. The combined effect of pH, metal complexation capacity, and the presence of Fe and Mn oxides added to wheat straw biochar resulted in an effective reduction of soluble Co (II), showing high efficiency of this material for cobalt sorption in contaminated soils.

Time-dependent evolution of Zn(II) fractions in soils remediated by wheat straw biochar

Biochar is a cost-effective and multifunctional carbon material, which can be used to immobilize heavy metal (HM) in soil. To date, the immobilization of different HM by various biochars are well-studied, however, little is known about the release condition of the immobilized HM. As the released HM may bring a threat to the soil environment, it is critical to understand the release pattern of biochar-sorbed HM in soil. Herein, six wheat straw-derived biochars (WBs) pyrolyzed under different temperature and duration time were loaded with zinc(Zn (II)), and the evolution of Zn(II) fractions in soils remediated by WBs over time was investigated by Community Bureau of Reference (BCR) three-step sequential extraction method. The main Zn(II) species sorbed on WBs were the Zn(II) sorbed on the acidic functional groups of WB and that sorbed on WB surface via electrostatic interaction. Generally, Zn(II) sorbed on high-temperature WB was more mobile than that sorbed on low-temperature WB. In the red soil, the soluble and exchangeable Zn(II) (i.e., Zn(II) in Fraction 1) in WB was inclined to transform to organic matter associated-Zn(II) (i.e., Zn(II) in Fraction 3) and residual Zn(II) (i.e., Zn(II) in Fraction 4). In the yellow-brown soil, the soluble and exchangeable Zn(II) in WB was prone to convert into amorphous Fe/Mn oxide associated-Zn(II) (i.e., Zn(II) in Fraction 2) and residual Zn(II). These results imply that Zn(II) sorbed by WB has the risk to be released into the soil environment, and WB produced at low temperature are more suitable to remediate soils with low/neutral pH.

Evolution of heavy metals during thermal treatment of manure: A critical review and outlooks

Manure treatment has become a focal issue in relation to current national policies on environmental and renewable energy matters. Heavy metals can be excreted with the animal manure, contributing to pollution of soil and water. Therefore, animal manure needs proper treatment before application to agricultural soils. Here, we review the species transformation of HMs and fate during incineration, pyrolysis, gasification and hydrothermal processing of animal manures. During thermal processes, 75%-90% of thermally stable HMs such as Cr, Ni, and Mn were concentrated in the solid-phase. HMs with less thermal stability such as Cd, As, Hg, and Pb are inclined to concentrate in the aqueous phase and gas phase, accounting for less than 5% of their total concentrations. In general, thermal processes transform HMs in the exchangeable fraction with high biotoxicity to oxidizable fraction or residual fraction with less bioavailability. In addition, the operating conditions and co-processing with other materials may influence the species transformation of HMs. Finally, recommendations for future research on the proper disposal and utilization of animal manure are proposed. More large-scale experiments are required to elucidate the precise mechanism behind the immobilization of HMs. The influence of additives (catalysts and HM stabilizers) and the influence of the type of solvent on HM transformation needs further study.

Effect of biochar addition to sewage sludge on cadmium, copper and lead speciation in sewage sludge-amended soil

The goal of the present work was to evaluate the speciation of cadmium (Cd), copper (Cu) and lead (Pb) in sewage sludge (SL) amended soil and SL-biochar (BC) amended soil in a long-term field experiment. SL or SL with biochar (at the dose of 2.5%, 5.0% or 10%) were applied to the soil. The dose of SL in the soil was 11 t_dw/ha. At the beginning of the study, after 12 and 18 months the distribution of Cd, Cu and Pb was determined between the following fractions: (1) water soluble, exchangeable and bound to carbonates (F1), (2) bound to Fe-Mn oxides (F2), (3) bound to organic matter (F3) and (4) bound to quartz, feldspars, etc. (F4). The soil, SL and biochar were characterized by different distribution of Pb, Cu and Cd. The highest mobility of Cd and Cu was observed in the control soil, while Pb in SL. Addition of SL to the soil caused the increased of the mobility index of Cu and Pb, increasing the risk associated with the presence of these metals in the mobile soil fraction (F1). However, the addition of biochar to SL before application to the soil modified the distribution of studied elements. The most mobile and bioavailable fractions (F1) were transferred to less bioavailable (F2, F3) and potentially immobile fractions (F4).

Biosolids and sludge management

The advancements in the field of sludge and biosolids have been made over the past year. This review outlines the major contributions of researchers that have been published in peer-reviewed journals and conference proceedings throughout 2018. The review is organized in sections including regulatory developments and market analysis; analysis and quantification of characteristics including microconstituents and metals; treatment advances for the conversion of sludge to biosolids including pretreatment and sludge minimization, conditioning and dewatering, digestion, composting, and innovative technologies; product development and reuse including adsorbents and thermal products, agricultural and other uses, and innovative uses; odor and air emissions; and energy factors. PRACTITIONER POINTS: Summary of advances in the field of residuals and biosolids research in 2018. This review outlines the major contributions of researchers that have been published in peer-reviewed journals and conference proceedings. Topics covered range from regulation to innovation.

Immobilization of Pb, Cu and Zn in contaminated soil using ball milling technique

Soil contamination caused by heavy metals has gained widespread attention from both government and public. In the present research, ball milling was utilized to remediate soil contaminated by Pb, Cu, and Zn and the influence of milling time on immobilization effectiveness was also investigated. The effectiveness of immobilization was evaluated by analyzing the leachable fraction of heavy metals from the ball-milled soil. When the milling time was 2 h, Pb, Cu, and Zn leaching concentrations decreased from 13.92 mg·L^-1, 2.83 mg·L^-1, and 114.42 mg·L^-1 to 0.027 mg·L^-1, 0.59 mg·L^-1, and 0.16 mg·L^-1, respectively; these values were all lower than the surface water Class III standard regulatory thresholds proposed by the Chinese Ministry of Ecology and Environment. Furthermore, the leaching characteristics of Pb, Cu, and Zn were investigated through pH-dependent tests and those results indicated that mechanical treatment improved the anti-acid ability of soil. In addition, the BCR sequential extraction procedure revealed that speciation shiftsof heavy metals are the root cause for the reduction of leaching concentrations; after ball milling of 4 h, the primary components of Pb, Cu and Zn in the soil were relatively stable (F₂ + F₃) and residual fraction (F₄), which accounted for 76.75%, 67.06% and 48.05% of total Pb, Cu and Zn, respectively.

Combining biochar and sewage sludge for immobilization of heavy metals in mining soils

Excess heavy metal concentrations in mining areas is a worldwide problem due to their toxicity and persistence. Applying amendments to those areas is a cost-effective remediation technique that would aid revegetation efforts. The aim of this work was to study the ability of sewage sludge-derived biochar (SSB), wood charcoal powder (hereafter named wood biochar - WB), raw sewage sludge (SS), and their blending (WB/SS) to improve soil properties and to immobilize Cd, Pb, and Zn after their addition to heavy-metal contaminated soils from a Zn-mining area. Biochar was prepared from dried sewage sludge and a greenhouse experiment was set using different amendment doses (WB = 30 and 60 g kg^-1, SS = 10 and 20 g kg^-1). Addition of wood biochar and sewage sludge-derived biochar to soils led to increased leachate and soil pH. Biochar materials were responsible for the greatest reduction of Cd, Pb, and Zn bioavailability. The use of sewage sludge-derived biochar or the combination of sewage sludge with wood biochar in mining areas are potential alternatives for reusing and aggregating value to these locally available wastes, offering an opportunity to solve both soil remediation and waste disposal problems at once.

Classification and Disposal Strategy of Excess Sludge in the Petrochemical Industry

The excess sludge in the petrochemical industry is large in quantity, complex in composition, and highly harmful, and its rational disposal is of great significance for environmental protection and sustainable development. In the present study, a classification and disposal strategy for the excess sludge in the petrochemical industry is proposed. The strategy first analyzes the dioxin, flammability, corrosivity, reactivity, and leaching properties of the sludge, from which the waste type of the sludge (general waste or hazardous waste) can be determined. Then, methods of disposal can be selected depending on the type of waste and the corresponding risk analysis, enabling rationalized disposal of the sludge. To verify the effectiveness and practicability of the proposed sludge classification and disposal strategy, research on petrochemical excess sludge samples (i.e., Ah, Bl, and Cq) originated from three different regions in China is carried out as a case study. The component analysis of the above three sludge samples revealed that they are all general wastes. In addition, the possibility of employing Cq sludge for landfill, soil modification, and greening mud, as well as the risk of landfill and incineration disposal in solid waste landfills are investigated. Furthermore, natural radioactive elements uranium and thorium in Cq sludge sample are studied. The results show that Cq sludge cannot be used for landfill, soil modification, and greening mud due to excessive arsenic content. The proposed strategy provides a basis for the selection of reasonable petrochemical excess sludge disposal methods.

The suitability of growing mulberry (Morus alba L.) on soils consisting of urban sludge composted with garden waste: a new method for urban sludge disposal

Efficient disposal of urban sewage sludge, material that typically contains high concentrations of heavy metals, has become a significant concern worldwide. The empirical purpose of the current study is to investigate physical and chemical parameters of composted sludge and garden waste at different ratios. Results reveal that nutrient content has significantly increased after the application of composts as compared to the controlled sample. Composting garden waste with sewage sludge at a 1:1 ratio promoted plant growth and gradually showed superiority in the later period. The maximum plant height, total biomass, and crown width of mulberry trees increased by 12.1, 33.5, and 45.7%, respectively, compared with the control treatment. The bound to organic matter of Hg, Cr, and Pb in the sewage sludge increased after composting with garden waste, and the mulberry exhibited a high ability to accumulate Ni and Cd from the soil. Conclusively, compared to using the two soil mediums separately, composting garden waste and sewage sludge together is beneficial for soil improvement and vegetation growth.