Comparative efficiency of wheat straw and sugarcane bagasse biochar reduces the cadmium bioavailability to spinach and enhances the microbial activity in contaminated soil

Synergistic effect by Sorghum bicolor L., citric acid, biochar, and vermiwash amendment for the remediation of a mine-contaminated soil

Phytoremediation is an in situ remediation and eco-friendly technique employing accumulator plant species to remove trace elements (TEs) from contaminated sites. Moreover, it has been demonstrated that both natural and synthetic amendments can enhance trace elements (TEs) phytoremediation from polluted soils through bioenergy crops. This work assessed the synergistic impact of two tested biochar (BC) from data palm (B1) and Prosopis (B2) (1.5%/ kg), citric acid (CA, 1.5 mmol/kg) and vermiwash (VW, 20 ml/kg) to enhance the remediation of tested TEs (Mn, Zn, Cd, Pb, Ni, Cu, and Fe) from Mahad AD'Dahab mine-contaminated soil by sorghum (Sorghum bicolor L.). The BC and CA amendments alone and combined with VW significantly augmented the proliferation and survival of sorghum grown in mine-contaminated soil. Considering the individual and combined applications of VW and BC, the influence on plant growth followed this order: K < VW < B2 < B1 < B1 + VW < B2 + VW < CA < CA + VW. Applying tested BC/CA and VW significantly increased chlorophyll compared to unamended soil. The outcomes revealed a substantial elevation in TE absorption in both shoot and root (p ≤ 0.05) with all tested treatments compared to the untreated soil (K). The combined application of CA and VW resulted in the most significant TE uptake of TEs at both the root and the shoot. Furthermore, adding CA or VW as a foliar spray enhanced the bioaccumulation factor (BCF) and translocation factor (TF) of studied metals. The combined addition of CA and foliar spraying of VW was more effective than the sole addition of CA or VW. Such increase reached 20.0%, 15.6%, 19.4%, 14.3%, 14.0%, and 25.6% of TF, and 13.7%, 11.9%, 8.3%, 20.9%, 20.5%,18.7%, and 19.8% of BCE for Cd, Cu, Fe, Mn, Ni, Pb, and Zn, respectively. This study highlights the efficiency of combining CA/BC with VW as a more viable option for remediating mine-contaminated soil than individual amendments. However, future research should prioritize long-term field trials to assess the efficiency of using citric acid and vermiwash for restoring contaminated mining soils.

Evaluation Health Risks and Sorption of Hexavalent Chromium (Cr(VI) by Biochar and Iron Doped Zinc Oxide Modified Biochar (Fe-ZnO@BC) Using Trifolium: A Green Synthesis Technique

Contamination of aquatic and terrestrial environment with hexavalent chromium Cr(VI) is one of the major hazards worldwide due its carcinogenicity, persistency and immobility. Different research techniques have been adopted for Cr(VI) remediation present in terrestrial and aquatic media, while adsorption being the most advance, low cost, environmentally friendly and common method. The present study discussed the mechanisms of Parthenium hysterophorus derived biochar, iron-doped zinc oxide nanoparticles (nFe-ZnO) and Fe-ZnO modified biochar (Fe-ZnO@BC) involved in Cr(VI) mobility and bioavailability. Pot experiments were conducted to study the effect of Parthenium hysterophorus derived biochar, nFe-ZnO and Fe-ZnO@BC application rates (2%, 2 mg/kg, 10 mg/kg, respectively). The results indicated that the addition of soil amendments reduced Cr(VI) mobility. The findings revealed that the reduction in chromium mobility was observed by P. hysterophorus BC, and Fe-ZnO@BC but nFe-ZnO application significantly (p = 0.05) reduced Cr(VI) and CrT uptake as compared to the control treatments. The results of SEM coupled with EDS showed a high micropores and channel, smooth surface which helped in adsorption, and may enhance soil conditions. The concentration index (CI) by different amendments in trifolium plant was followed the descending order as: nFe-ZnO > Fe-ZnO@BC > P. hysterophorus BC after 30, 60 and 90 days of harvesting, respectively. In addition, human health risk index was found less than one (H1 < 1.0) in amended soils as compared to control treatments.

Effect of biochars on the immobilization and form of Cadmium (Cd) in simulated Cd deposition of iron rich soils

Atmospheric deposition of Cd poses a serious threat to ecosystem security. Biochar is widely used for polluted soil remediation, however, whether biochar already applied to the soil can reduce the hazards of newly deposited Cd remains to be studied. Thus, an indoor cultural experiment and static adsorption method were conducted to study the isothermal and kinetic adsorption processes of three types of biochar (rice husk, rubber wood, and tobacco stem biochars) on Cd in iron rich soils and the effect of biochar on the morphological distribution of Cd in the soil and the soil pH. The results showed that the soil with biochar in our study could quickly fix "the new deposited Cd" in the soil in 3 h with the maximum adsorption capacity in rubber wood biochar-treated sample (3227.34 mg/kg）. The addition of all three biochar treatments significantly increased the soil pH and reduced the soil exchange state Cd content, with a 13.69-17.32% increase in the pH and a 13.22-54.39% reduction in the exchange state Cd content when contrasted with the control, which could promote those Cd converting into unavailable Cd (carbonate-bound form Cd, Fe-Mn oxide-bound form Cd, or residual form Cd) for crops. In summary, the addition of three kinds of biochar treatments could effectively reduce the ecological and environmental risk of soil that was contaminated by Cd and could provide a reliable theoretical basis for the effect of biochar on the improvement of the quality of soil that is contaminated by heavy metals.

Effects of biochar on soil microbial communities: A meta-analysis

Changes in soil microbial communities may impact soil fertility and stability because microbial communities are key to soil functioning by supporting soil ecological quality and agricultural production. The effects of soil amendment with biochar on soil microbial communities are widely documented but studies highlighted a high degree of variability in their responses following biochar application. The multiple conditions under which they were conducted (experimental designs, application rates, soil types, biochar properties) make it difficult to identify general trends. This supports the need to better determine the conditions of biochar production and application that promote soil microbial communities. In this context, we performed the first ever meta-analysis of the biochar effects on soil microbial biomass and diversity (prokaryotes and fungi) based on high-throughput sequencing data. The majority of the 181 selected publications were conducted in China and evaluated the short-term impact (<3 months) of biochar. We demonstrated that a large panel of variables corresponding to biochar properties, soil characteristics, farming practices or experimental conditions, can affect the effects of biochar on soil microbial characteristics. Using a variance partitioning approach, we showed that responses of soil microbial biomass and prokaryotic diversity were highly dependent on biochar properties. They were influenced by pyrolysis temperature, biochar pH, application rate and feedstock type, as wood-derived biochars have particular physico-chemical properties (high C:N ratio, low nutrient content, large pores size) compared to non-wood-derived biochars. Fungal community data was more heterogenous and scarcer than prokaryote data (30 publications). Fungal diversity indices were rather dependent on soil properties: they were higher in medium-textured soils, with low pH but high soil organic carbon. Altogether, this meta-analysis illustrates the need for long-term field studies in European agricultural context for documenting responses of soil microbial communities to biochar application under diverse conditions combining biochar types, soil properties and conditions of use.

Co-Carbonized Waste Polythene/Sugarcane Bagasse Nanocomposite for Aqueous Environmental Remediation Applications

The conversion of worthless municipal solid wastes to valuables is a major step towards environmental conservation and sustainability. This work successfully proposed a technique to utilize the two most commonly available municipal solid wastes viz polythene (PE) and sugarcane bagasse (SB) for water decolorization application. An SBPE composite material was developed and co-pyrolyzed under an inert atmosphere to develop the activated SBPEAC composite. Both SBPE and SBPEAC composites were characterized to analyze their morphological characteristics, specific surface area, chemical functional groups, and elemental composition. The adsorption efficacies of the composites were comparatively tested in the removal of malachite green (MG) from water. The SBPEAC composite had a specific surface area of 284.5 m²/g and a pore size of ~1.33 nm. Batch-scale experiments revealed that the SBPEAC composite performed better toward MG adsorption compared to the SBPE composite. The maximum MG uptakes at 318 K on SBPEAC and SBPE were 926.6 and 375.6 mg/g, respectively. The adsorption of MG on both composites was endothermic. The isotherm and kinetic modeling data for MG adsorption on SBPEAC was fitted to pseudo-second-order kinetic and Langmuir isotherm models, while Elovich kinetic and D-R isotherm models were better fitted for MG adsorption on SBPE. Mechanistically, the MG adsorption on both SBPE and SBPEAC composites involved electrostatic interaction, H-bonding, and π-π/n-π interactions.

Recent advances in biochar amendments for immobilization of heavy metals in an agricultural ecosystem: A systematic review

Over the last several decades, extensive and inefficient use of contemporary technologies has resulted in substantial environmental pollution, predominantly caused by potentially hazardous elements (PTEs), like heavy metals that severely harm living species. To combat the presence of heavy metals (HMs) in the agrarian system, biochar becomes an attractive approach for stabilizing and limiting availability of HMs in soils due to its high surface area, porosity, pH, aromatic structure as well as several functional groups, which mostly rely on the feedstock and pyrolysis temperature. Additionally, agricultural waste-derived biochar is an effective management option to ensure carbon neutrality and circular economy while also addressing social and environmental concerns. Given these diverse parameters, the present systematic evaluation seeks to (i) ascertain the effectiveness of heavy metal immobilization by agro waste-derived biochar; (ii) examine the presence of biochar on soil physico-chemical, and thermal properties, along with microbial diversity; (iii) explore the underlying mechanisms responsible for the reduction in heavy metal concentration; and (iv) possibility of biochar implications to advance circular economy approach. The collection of more than 200 papers catalogues the immobilization efficiency of biochar in agricultural soil and its impacts on soil from multi-angle perspectives. The data gathered suggests that pristine biochar effectively reduced cationic heavy metals (Pb, Cd, Cu, Ni) and Cr mobilization and uptake by plants, whereas modified biochar effectively reduced As in soil and plant systems. However, the exact mechanism underlying is a complex biochar-soil interaction. In addition to successfully immobilizing heavy metals in the soil, the application of biochar improved soil fertility and increased agricultural productivity. However, the lack of knowledge on unfavorable impacts on the agricultural systems, along with discrepancies between the use of biochar and experimental conditions, impeded a thorough understanding on a deeper level.

Efficiency of Soil Amendments for Copper Removal and Brassica Juncea (L.) Growth in Wastewater Irrigated Agricultural Soil

Wastewater irrigation is becoming a massive challenge for sustainable agriculture. Particularly, copper (Cu) presence in wastewater poses a great threat to the food chain quality. Thus, scientists need to address this issue by using chemical and organic soil amendments to restore the soil ecosystem. Therefore, this study aims to examine the efficacy of sulphur, compost, acidified animal manure and sesame straw biochar for Cu immobilization, adsorption and Brassica growth in wastewater irrigated soil. The current findings presented that all the soil amendments prominently improved brassica yield and significantly minimized the Cu uptake by Brassica shoots and roots in sesame straw biochar (SB) (64.2% and 50.2%), compost (CP) (48% and 32.5%), acidified manure (AM) (37% and 23.2%) and Sulphur (SP) (16% and 3.1%) respectively relative to untreated soil. In addition, Cu bioavailability was reduced by 51%, 34%, 16.6%, and 7.4% when SB, CP, AM, and SP were incorporated in wastewater irrigated polluted soil. The Cu adsorption isotherm results also revealed that SB treated soil has great potential to increase Cu adsorption capacity by 223 mg g^- 1 over control 89 mg g^- 1. Among all the treatments, SB and CP were considered suitable candidates for the restoration of Cu polluted alkaline nature soil.

Removal of potentially toxic elements from contaminated soil and water using bone char compared to plant- and bone-derived biochars: A review

Conversion of hazardous waste materials to value-added products is of great interest from both agro-environmental and economic points of view. Bone char (BC) has been used for the removal of potentially toxic elements (PTEs) from contaminated water, however, its potential BC for the immobilization of PTEs in contaminated water and soil compared to bone (BBC)- and plant (PBC)-derived biochars has not been reviewed yet. This review presents an elaboration for the potentials of BC for the remediation of PTEs-contaminated water and soil in comparison with PBC and BBC. This work critically reviews the preparation and characterization of BC, BBC, and PBC and their PTEs removal efficiency from water and soils. The mechanisms of PTE removal by BC, BBC, and PBC are also discussed in relation to their physicochemical characteristics. The review demonstrates the key opportunities for using bone waste as feedstock for producing BC and BBC as promising low-cost and effective materials for the remediation of PTEs-contaminated water and soils and also elucidates the possible combinations of BC and BBC aiming to effectively immobilize PTEs in water and soils.

Application of cotton straw biochar and compound Bacillus biofertilizer decrease the bioavailability of soil cd through impacting soil bacteria

Background

Cd seriously threatens soil environment, remedying Cd in farmland and clearing the response of soil environment to modifiers in Cd-contaminated soils is necessary. In this study, the effects of cotton straw biochar and compound Bacillus biofertilizer used as modifiers on the biochemical properties, enzyme activity, and microbial diversity in Cd-contaminated soils (1, 2, and 4 mg·kg⁻¹) were investigated.

Results

The results showed that both cotton straw biochar and compound Bacillus biofertilizer could improve the soil chemical characteristics, including the increase of soil C/N ratio, electrical conductance (EC) and pH, and the most important decrease of soil available Cd content by 60.24% and 74.34%, respectively (P < 0.05). On the other hand, adding cotton straw biochar and compound Bacillus biofertilizer in Cd stressed soil also improved soil biological characteristics. Among them, cotton straw biochar mainly through increasing soil alkaline phosphatase activity and improve bacteria abundance, compound Bacillus biofertilizer by increasing soil invertase, alkaline phosphatase, catalase, and urease activity increased bacterial community diversity. On the whole, the decrease of soil available Cd was mainly caused by the increase of soil pH, C/N, urease and alkaline phosphatase activities, and the relative abundance of Acidobacteria and Proteobacteria.

Conclusions

In summary, the applications of cotton straw biochar and compound Bacillus biofertilizer could decrease soil available Cd concentration, increase soil bacterial community diversity and functions metabolism, and reduce the damage of Cd stress, compared with cotton straw biochar, compound Bacillus biofertilizer was more effective in immobilizing Cd and improving soil environmental quality.

Effects of sheep bone biochar on soil quality, maize growth, and fractionation and phytoavailability of Cd and Zn in a mining-contaminated soil

Biochar prepared from various feedstock materials has been utilized in recent years as a potential stabilizing agent for heavy metals in smelter-contaminated soils. However, the effectiveness of animal bone-derived biochar and its potential for the stabilization of contaminants remains unclear. In the present study, sheep bone-derived biochar (SB) was prepared at low (500 °C; SBL) and high temperatures (800 °C; SBH) and amended a smelter-contaminated soil at 2, 5, and 10% (w/w). The effects of SB on soil properties, bioavailable Zn and Cd and their geochemical fractions, bacterial community composition and activity, and the response of plant attributes (pigments and antioxidant activity) were assessed. Results showed that the SBH added at 10% (SBH₁₀) increased soil organic carbon, total nitrogen, and phosphorus, and also increased the oxidizable and residual Zn and Cd fractions at the expense of the bioavailable fractions. The SBH₁₀ lowered the Zn and Cd contents in maize roots (by 57 and 60%) and shoot (by 42 and 61%), respectively, compared to unamended control. Additionally, SBH₁₀ enhanced urease (98%) and phosphates (107%) activities, but reduced dehydrogenase (58%) and β-glucosidase (30%) activities. Regarding the effect of the pyrolysis temperature, SBH enhanced the activity of Acidobacteria, Bacteroidetes, Firmicutes, Nitrospirae, Verrucomicrobia, Chlorobi, and Microgenomates, but reduced Actinobacteria and Parcubacteria in comparison to SBL. However, only the SBL₁₀ reduced the Proteobacteria community (by 9%). In conclusion, SB immobilized Zn and Cd in smelter-affected soils, enhanced the bacterial abundance and microbial function (urease, phosphates), and improved plant growth. However, validation of the results, obtained from the pot experiment, under field conditions is suggested.

Copper uptake, physiological response, and phytoremediation potential of Brassica juncea under biochar application

Biochar can enhance the phytoremediation of copper-contaminated soils by improving soil quality and increasing plant growth. However, the impact of biochar varies with the biomass feedstock and soil condition. Our study investigated the effect of biochar from orange bagasse-OBB and coconut husk-CHB and two copper concentrations (0.17 mg kg^-1-CLS soil; 100 mg kg^-1- CTS soil) on plant growth, copper uptake, and physiological response of Brassica juncea. The low- and high-Cu soils were also tested without biochar. We evaluated plant biomass, plant Cu, N and P, chlorophyll content, and chlorophyll's transient fluorescence. Plant growth was meager without biochar, indicating that the high Cu concentration was not the only limiting factor. Biochar (OBB and CHB) increased shoot mass by 300-574% and root mass by 50-2900%, and improved chlorophyll content and photosynthetic activity by 6-16%. Both biochars were efficient in the low-Cu soil as they increased plant biomass, shoot copper concentration, and translocation factor. In the high-Cu soil, both biochars increased plant biomass and copper uptake and reduced shoot copper concentration and translocation factor. The CHB and OBB removed 342% and 783% more Cu from the contaminated soil than the Control; therefore, the OBB was proven to be the best choice for phytoremediation.Novelty statement Our study showed that the orange bagasse biochar can be successfully applied for the phytoremediation of copper-contaminated soils using Brassica juncea. The orange bagasse biochar was effective regardless of the copper level in the soil, removing twice as much copper as the coconut biochar; therefore, it can speed up the process and reduce the time needed to clean up the site. HighlightsBiochar significantly improved the plant's physiological responseBiochar increased plant growth and copper uptake in the contaminated soilTranslocation factor was increased in the clean soil and reduced in the contaminated soilBiochar from orange bagasse is more effective than coconut husk for phytoremediation.

Salinity-induced changes in cadmium availability affect soil microbial and biochemical functions: Mitigating role of biochar

Biochar may improve soil microbial and biochemical functions under abiotic stresses. In this research, we studied changes in soil microbial properties and processes after sugarcane bagasse biochar (SCB) application (1% w/w) to a soil contaminated with Cd under saline conditions during an incubation experiment. SCB produced at 400 °C (B400) and 600 °C (B600) increased soil organic carbon (SOC) content by 89-127% and dissolved organic carbon content by 21-70%. NaCl salinity mobilized Cd by 16-19%, while biochar immobilized Cd by 14-18%, indicating the use of biochar would offset the increase in Cd availability induced by salinity. SCB application improved microbial and biochemical functions (up to 280%) in the soils contaminated with Cd under salinity stress. B400 biochar was often more effective in improving the soil microbial properties and functioning than B600 biochar. SCB application reduced the detrimental effects of salinity-induced Cd toxicity on soil microbial community and enzyme activity mainly through retaining Cd and supplying C substrate for microbial uptake and activity. The factor analysis and redundancy analysis results also confirmed that SOC and Cd availability was the most important factors and accounted for a large portion of the variation in soil microbial properties and enzyme activities in saline Cd-contaminated soils amended with SCB. This study indicated that B400 applied at 1% could be used in saline Cd-contaminated soils to protect the soil microbial communities from Cd toxicity, and to mitigate the potential stresses associated with the co-occurrence of Cd contamination and salinity on critical soil microbial and biochemical functions.

Bio-indicators in cadmium toxicity: Role of HSP27 and HSP70

Heat shock proteins (HSPs) are a family of proteins that are expressed by cells in reply to stressors. The changes in concentration of HSPs could be utilized as a bio-indicator of oxidative stress caused by heavy metal. Exposure to the different heavy metals may induce or reduce the expression of different HSPs. The exposure to cadmium ion (Cd²⁺) could increase HSP70 and HSP27 over 2- to 10-fold or even more. The in vitro and in vivo models indicate that the HSP70 family is more sensitive to Cd intoxication than other HSPs. The analyses of other HSPs along with HSP70, especially HSP27, could also be useful to obtain more accurate results. In this regard, this review focuses on examining the literature to bold the futuristic uses of HSPs as bio-indicators in the initial assessment of Cd exposure risks in defined environments.

Comparative role of animal manure and vegetable waste induced compost for polluted soil restoration and maize growth

Soil amendment with two types of composts: animal manure (AC) and vegetable waste (VC) induced composts have potential to alleviate Cd toxicity to maize in contaminated soil. Therefore, Cd mobility in waste water irrigated soil can be addressed through eco-friendly and cost effective organic soil amendments AC and VC that eventually reduces its translocation from polluted soil to maize plant tissues. The comparative effectiveness of AC and VC at 3% rate were evaluated on Cd solubility, its accumulation in maize tissues, translocation from root to shoot, chlorophyll contents, plant biomass, yield and soil properties (pH, NPK, OM). Results revealed that the addition of organic soil amendments significantly minimized Cd mobility and leachability in soil by 58.6% and 47%, respectively in VC-amended soil over control. While, the reduction was observed by 61.7% and 57%, respectively when AC was added at 3% over control. Comparing the control soil, Cd uptake effectively reduced via plants shoots and roots by 50%, 46% respectively when VC was added in polluted soil. However, Cd uptake was decreased in maize shoot and roots by 58% and 52.4% in AC amended soil at 3% rate, respectively. Additionally, NPK contents were significantly improved in polluted soil as well as in plant tissues in both composts amended soil Comparative to control, the addition of composts significantly improved the maize dry biomass and chlorophyll contents at 3% rate. Thus, present study confirmed that the addition of animal manure derived compost (AC) at 3% rate performed well and might be consider the suitable approach relative to vegetable compost for maize growth in polluted soil.

Efficiency of different types of biochars to mitigate Cd stress and growth of sunflower (Helianthus; L.) in wastewater irrigated agricultural soil

Cadmium contamination in croplands is recognized one of the major threat, seriously affecting soil health and sustainable agriculture around the globe. Cd mobility in wastewater irrigated soils can be curtailed through eco-friendly and cost effective organic soil amendments (biochars) that eventually minimizes its translocation from soil to plant. This study explored the possible effects of various types of plants straw biochar as soil amendments on cadmium (Cd) phytoavailability in wastewater degraded soil and its subsequent accumulation in sunflower tissues. The studied biochars including rice straw (RS), wheat straw (WS), acacia (AC) and sugarcane bagasse (SB) to wastewater irrigated soil containing Cd. Sunflower plant was grown as a test plant and Cd accumulation was recorded in its tissues, antioxidant enzymatic activity chlorophyll contents, plant biomass, yield and soil properties (pH, NPK, OM and Soluble Cd) were also examined. Results revealed that addition of biochar significantly minimized Cd mobility in soil by 53.4%, 44%, 41% and 36% when RS, WS, AC and SB were added at 2% over control. Comparing the control soil, biochar amended soil effectively reduced Cd uptake via plants shoots by 71.7%, 60.6%, 59% and 36.6%, when RS, WS, AC and SB. Among all the biochar, rice husk induced biochar significantly reduced oxidative stress and reduced SOD, POD and CAT activity by 49%, 40.5% and 46.5% respectively over control. In addition, NPK were significantly increased among all the added biochars in soil–plant system as well as improved chlorophyll contents relative to non-bioachar amended soil. Thus, among all the amendments, rice husk and wheat straw biochar performed well and might be considered the suitable approach for sunflower growth in polluted soil.

Biochar for cadmium pollution mitigation and stress resistance in tobacco growth

Pot experiments were conducted to investigate the influence of biochar addition and the mechanisms that alleviate Cd stress in the growth of tobacco plant. Cadmium showed an inhibitory effect on tobacco growth at different post-transplantation times, and this increased with the increase in soil Cd concentration. The growth index decreased by more than 10%, and the photosynthetic pigment and photosynthetic characteristics of the tobacco leaf were significantly reduced, and the antioxidant enzyme activity was enhanced. Application of biochar effectively alleviated the inhibitory effect of Cd on tobacco growth, and the alleviation effect of treatments is more significant to the plants with a higher Cd concentration. The contents of chlorophyll a, chlorophyll b, and carotenoids in the leaves of tobacco plants treated with biochar increased by 9.99%, 12.58%, and 10.32%, respectively, after 60 days of transplantation. The photosynthetic characteristics index of the net photosynthetic rate increased by 11.48%, stomatal conductance increased by 11.44%, and intercellular carbon dioxide concentration decreased to 0.92. Based on the treatments, during the growth period, the antioxidant enzyme activities of tobacco leaves comprising catalase, peroxidase, superoxide dismutase, and malondialdehyde increased by 7.62%, 10.41%, 10.58%, and 12.57%, respectively, after the application of biochar. Our results show that biochar containing functional groups can effectively reduce the effect of Cd stress by intensifying the adsorption or passivation of Cd in the soil, thereby, significantly reducing the Cd content in plant leaves, and providing a theoretical basis and method to alleviate soil Cd pollution and effect soil remediation.

Biochar assisted phytoremediation and biomass disposal in heavy metal contaminated mine soils: a review

Mining activities causes heavy metal pollution and adversely affect the ecological safety and human well-being. Phytoremediation-biochar synergy can effectively remediate mine spoils contaminated with heavy metals (HM). A review which focuses exclusively on the application of biochar assisted phytoremediation in HM contaminated mine spoil is lacking. Mechanisms of metal immobilization by biochar, potential plants and contaminated biomass disposal methods has also been reviewed. Availability of biochar feedstock and production conditions, optimization of application rate, application techniques, selection of suitable hyperaccumulators and cost optimization of bulk biochar production are the key to a successful biochar-based HM remediation of mine tailings and coalmine spoil. Presently, herbs and shrubs are mostly used as phytoremediators, use of woody trees would encourage a long-term metal sequestration which would reduce the cost of biomass disposal. Also, use of non-edible plants would prevent the plants from entering the food chain. For a holistic biochar-phytoremediation technique, incineration and pyrolysis can effectively dispose contaminated biomass. From the economical viewpoint, the environment cost-benefit analysis should be considered before considering the feasibility of a technology.HighlightsMass scale in-situ biochar production and economics are keys issues.Biochar assisted phytoremediation for HM contaminated mine spoils.Long term studies using woody biomass needs attention.Disposal of contaminated biomass by pyrolysis method.