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A Review of Approaches and Techniques Used in Aquatic Contaminated Sediments: Metal Removal and Stabilization by Chemical and Biotechnological Processes
Abstract
The contamination of aquatic sediments with metals is a widespread environmental problem. Coastal aquatic ecosystems with low hydrodynamics need to be periodically dredged in order to maintain the navigation depth and facilitate sailing; consequently large volumes of contaminated sediments need to be managed. Conventional remediation strategies include in-place sediment remediation strategies (e.g. in situ-capping) and relocation actions; in particular, landfill disposal and dumping at sea are still widely applied. Both this options are becoming unsustainable, due to problems associated with contaminant transport pathways, the uncertainties about long-term stability under various environmental conditions, the limited space capacity, costs and environmental compatibility. Alternative approaches have received increased attention; treatment and reuse of contaminated sediments is politically encouraged, but its application is still very limited. Because of the potential human health and environmental impacts of contaminated sediment, different chemical treatments are conventionally applied for contaminated sediments before reuse in other environmental settings. Environmentally friendly techniques developed for soils and other environmental matrices have been investigated for applications with sediments. Biotechnological approaches are gaining increasing prominence in this field and they are often considered as a promising strategy for the eventual treatment of contaminated sediments. In this paper an overview of the main treatment strategies potentially available for sediment contaminated with metals is given, together with a brief overview of the issue associated with the problem of the sediment management.
... Sediment contamination is of the most concerning environmental issues worldwide that requires close attention not only towards its evaluation but also towards its remedial measures (Sparrevik et al. 2011;Akcil et al. 2015). Conventional techniques such as situ capping, landfill disposal, and sea dumping could be utilized keeping in consideration towards their effectiveness is not long term . ...
... Conventional techniques such as situ capping, landfill disposal, and sea dumping could be utilized keeping in consideration towards their effectiveness is not long term . Advanced biological treatment, thermal treatment, and in situ chemical treatment could be taken into consideration as these method are efficient and reliable for remediation of coastal sediments (Akcil et al. 2015). ...
The provenance, paleoweathering and paleoredox conditions of sandstones of the Vryheid Formation of the Ecca Group in the Highveld Coalfield, Mpumalanga, South Africa, were studied with the intention of identifying possible detrital source rocks. The investigation approach involved collecting sandstone samples from borehole cores, followed by laboratory studies of mineralogy and petrography and major and trace element analysis by X-ray fluorescence (XRF). Mineralogy and petrographic analyses indicate that these sandstones are arkosic to subarkosic arenites. The generalized mineralogical compositions, in order of abundance, consist of monocrystalline and polycrystalline quartz, plagioclase, igneous and volcanic rock fragments and minor to trace amounts of mudstone clasts. Quartz grains are predominantly monocrystalline, implying that they came from granitic and volcanic rocks as well as hydrothermal quartz veins. The presence of higher amounts of feldspars favors either a fast/high depositional rate or a relatively dry or cold climate in the source area and is also indicative of the dominance of felsic igneous or metamorphic rocks in the source area. The bulk rock geochemistry supports the petrographic results. The ratio of K2O/Na2O and the plots of Na2O-CaO-K2O and Th-Sc-Zr/10 attest to a passive margin tectonic setting. The observed patterns of REE values, ratios of K2O/Al2O3, Al2O3/TiO2, La/Sc, Th/Sc, Th/Co, and Th/Cr, plots of Th/Co vs La/Sc, Hf vs La/Th, Th vs Sc, V-Ni-Th and discriminant function further suggest felsic rock sources. The sediments were deposited by glacial material and underwent mechanical weathering and grinding; therefore, the sediments deviate from normal chemical weathering trends. The chemical index of alteration (CIA) suggests minimal chemically weathered source rocks typically deposited under a cool to temperate climate. U contents and authigenic U, V/Cr, Ni/Cu and Cu/Zn ratios attest to an oxidic depositional environment.
... Sediment contamination is of the most concerning environmental issues worldwide that requires close attention not only towards its evaluation but also towards its remedial measures (Sparrevik et al. 2011;Akcil et al. 2015). Conventional techniques such as situ capping, landfill disposal, and sea dumping could be utilized keeping in consideration towards their effectiveness is not long term . ...
... Conventional techniques such as situ capping, landfill disposal, and sea dumping could be utilized keeping in consideration towards their effectiveness is not long term . Advanced biological treatment, thermal treatment, and in situ chemical treatment could be taken into consideration as these method are efficient and reliable for remediation of coastal sediments (Akcil et al. 2015). ...
The hydrochemical characteristics and quality status was assessed in Luvuvhu catchment situated in Limpopo province, South Africa, with the help of 41 and 39 water samples spanning over 2 years (2015 and 2016). Groundwater was found safe for drinking purposes. Irrigational quality indices such as EC, RSC, %Na, SAR, SSP, KR, PI and USSL classifications indicated suitability of water agricultural usage, whereas MH indicated high probability of magnesium hazard in the study area. Ca-HCO3 facies was found to be dominating type followed by Ca-Mg-Cl mixed type. Dissolution of carbonates and silicates along the pathways was confirmed by Piper and Gibbs plots along with ion exchange, which is one of the major controlling mechanisms in the study area. Major ions (Na+, K+, Mg2+, Ca2+, Cl− and HCO3−) and metals (Zn, Pb, B and Cr) are found to be geogenic in nature where nutrients (NO3−, NH4+, F−) were found to be part of irrigational return flows and sewage from settlements. The leaching of metals is highest in the deforestation zones of the study area.KeywordsHydrochemical characteristicsGroundwater qualityGroundwater pollutionGroundwater resourcesTrace metals
... Sediment contamination is of the most concerning environmental issues worldwide that requires close attention not only towards its evaluation but also towards its remedial measures (Sparrevik et al. 2011;Akcil et al. 2015). Conventional techniques such as situ capping, landfill disposal, and sea dumping could be utilized keeping in consideration towards their effectiveness is not long term . ...
... Conventional techniques such as situ capping, landfill disposal, and sea dumping could be utilized keeping in consideration towards their effectiveness is not long term . Advanced biological treatment, thermal treatment, and in situ chemical treatment could be taken into consideration as these method are efficient and reliable for remediation of coastal sediments (Akcil et al. 2015). ...
The distribution of trace metals and microplastics (MPs) was evaluated along KwaZulu-Natal (KZN) coast considering 348 sediment samples from 9 zones (Sodwana bay, St. Lucia bay, Richards bay, Mtunzini coast, Tugela coast, Zinkwazi coast, Ballito coast, Durban north and Durban couth coast). Based on the results, Cr, Hg, Mo, Ni, Co, Cd and Cu are found to be enriched higher in the coastal sediments of KZN. The enrichment in the Northern coast of KZN was found to be of geogenic origin whereas the increased contamination in the Southern half mainly originated from anthropogenic sources. The major sources might include industrial and agricultural discharges mainly delivered through rivers. Among all the considered metals, Hg and Cr are the major contaminating factors and pose extreme ecological risk towards the existing biota. In case of humans, no adverse effects of Hg was confirmed by CDI and HI. Similar results were also acquired for MPs, where harbor activities at Richards Bay and Durban along with agricultural activities contributed majority of the MPs through river systems. Coastal currents such as Agulhas current and Durban Eddy (a cyclone) are playing major role in the retribution of microplastics.KeywordsSedimentsMetalsEnrichmentContaminationMicroplasticsSouth Africa
... Heavy metals-contaminated soil caused by anthropogenic activities have become one of the most critical environmental problems in the world [1,2]. These non-biodegradable, toxic, and persistent contaminants can enter the human food chain and damage human health [3,4]. Soil is a non-renewable natural resource, and the further utilization of soil after remediation is significant to social development [5]. ...
... Recently, cathodic electrochemical reduction (electrodeposition) technology has been widely used in combination with chelate soil washing technology. This technology can carry out recovery of metals and regeneration of chelating agents simultaneously, as illustrated in Eq. (4). ...
Contamination of soil with heavy metals has become a significant environmental issue worldwide. In previous studies, a technology that couped EDTA-washing and cathodic reduction technology was developed to further remove heavy metals from soil contaminated with electroplating waste compared with single soil washing technology. Although the method showed a synergistic effect in previous studies, the effect of soil suspension alkalization and the mechanism behind it remain unclear. High soil pH will have an impact on target metal removal, energy consumption and further utilization of soil. In this experimental research, we investigated the efficacy of pH control on coupling soil washing and cathodic reduction to remove multiple heavy metals from soil under various current densities. To alleviate the OH⁻ ions generated by the cathode and improve the reduction efficiency of metals, an automatic pH controller was used, resulting in a significant increase in the removal rate of target metals. The experimental results show that controlling the pH of soil suspension can increase the total removal rate of target metals by 3-6 times. Additionally, the removal efficiency of residual Pb in the soil is increased by about 30%. In terms of ecological risk, pH control could reduce the solubility and mobility of metals by 50%, and the ecological risk was greatly reduced, especially for Zn, from about 90 mg/kg to 50 mg/kg. Further research is needed to explore the mechanism of the synergistic effect and improve the efficiency of this technology for the subsequent development of coupling EDTA-washing and cathodic reduction.
... Once metals (such as Hg, Cd and Pb) enter into the atmosphere, they can be transported over long distances by air currents, leading to the dramatic increase of heavy metal content in remote areas [3][4][5][6]. In addition, through drainage, atmospheric bulk deposition, and soil erosion, heavy metals are prone to enter into water bodies and disturb the aquatic ecosystem [7]. Due to their persistence, metals are bioaccumulative and bioamplifying in predatory animals (e.g., fish) that can be used as food for humans. ...
... HNO 3 may have a higher capacity of destroying metal-organic complexes than HCl due to its strong oxidation [23]. Moreover, the additives of chelators (e.g., EDDS, EDTA, organic acid (AA and CA)) have been extensively studied and applied to increase the solubility of heavy metals [7]. Particularly, EDTA is the most efficient extractant because it can form very stable complexes with metals [24] but a significant part of metal-EDTA complexes remain in the soil/sediment due to adsorption on the mineral surface [25]. ...
Sediment is an important part of aquatic systems, which plays a vital role in transporting and storing metals. Due to its abundance, persistence, and environmental toxicity, heavy metal pollution has always been one of the hot spots in the world. In this article, the state-of-art ex situ remediation technology for metal-contaminated sediments is elaborated, including sediment washing, electrokinetic remediation (EKR), chemical extraction, biological treatment, as well as encapsulating pollutants by adding some stabilized/solidified materials. Furthermore, the progress of sustainable resource utilization methods, such as ecosystem restoration, construction materials (e.g., materials fill materials, partition blocks, and paving blocks), and agriculture use are reviewed in detail. Finally, the pros and cons of each technique are summarized. This information will provide the scientific basis for selecting the appropriate remediation technology in a particular scenario.
... On the other hand, once the physical and chemical conditions of the water body (e.g. pH, organic matter and redox potential) change, pollutants are likely to be released into the overlying water again, resulting in endogenous pollution of the water body, thereby affecting water quality and water environment safety, which results in toxic risks to aquatic organisms and human health [2,4]. When external pollution is controlled, pollutants in the sediments of rivers and lakes may cause the re-pollution of the overlying water [5]. ...
... Sediments are often the 'sink' of pollutants. Once physical and chemical conditions are changed, it may also become the 'source' of pollutants in overlying water [2,4]. Under the disturbed conditions of this experiment, CODCr in the overlying water of Guanzui section was significantly higher than that of the control group, and CODCr in the overlying water of the control group generally increases gradually (Figure 4b). ...
To explore the possible impact of river sediments on the endogenous pollution of water body under different dredging conditions, sediments in the Luling and Guanzui sections of Tuo River were selected as research object. On the basis of pollution assessment of typical heavy metals (i.e. Cd, Cr, Cu, Ni, Pb, Zn), the release characteristics of chemical oxygen demand (CODCr), total phosphorus (TP) and fluoride (F) in these two sediments were studied using an indoor disturbance test device. Results show that sediments of the Luling and Guanzui sections were unpolluted to moderately polluted by Cd and Cu. The comprehensive ecological risk of the selected heavy metals in the Luling and Guanzui sediments was low. However, the single potential ecological risk of Cd was at moderate risk level. Pollution level of heavy metals in Guanzui sediment is higher than that in Luling sediment. Owing to the influences of mineral composition, content of pollutants and chemical species of pollutants in sediments, CODCr, TP and F in the sediments of the two sections show different release characteristics. The Guanzui and Luling sediments showed release 'source' characteristics for CODCr and F, respectively, to overly-ing water. CODCr and F were the priority pollutants of endogenous pollution in the Guanzui and Luling sections, respectively, of Tuo River.
... Dredging of reservoirs generates a large amount of sediment that requires appropriate management or disposal (Akcil et al. 2015;Kazberuk et al. 2021;Ferrans et al. 2021). According to estimates by the European SedNet network, 200 million m 3 of sediment is excavated annually in Europe (SedNet 2004). ...
... Their availability in the form of fertilisers represents a key factor in the overall question of global food security. On the other hand, high contents of potentially toxic trace elements and organic pollutants can be a barrier in the use of bottom sediments (Akcil et al. 2015; Baran et al. 2019c;Ferrans et al. 2019). ...
Purpose
The use of bottom sediments in agriculture reduces the storage of excavated material and allows the nutrients it contains to be applied for soil fertilisation and improvement. However, the direct application of sediments to soil may cause numerous problems. Therefore, the addition of other waste materials may be a promising and useful method in the production of bottom-sediment-based growing media. The aim of the study was to evaluate the effect of growing media prepared on the basis of bottom sediments and various waste materials on the properties of soil as well as on the yield and chemical composition of courgette biomass.
Methods
The growing media were prepared with substrates in the form of mixtures with bottom sediments taken from the Rożnów reservoir. The effect of mixtures on plant growth was determined in a laboratory pot experiment. Air-dry mixtures (M1—bottom sediment with water treatment sludge (BS + SW); M2—bottom sediment with biomass ash (BS + BA); M3—bottom sediment with coffee hulls (BS + CH)) were mixed with soil (S) in the following proportions: combination I—25%, combination II—50%, combination III—75%, and combination IV—100% mixture.
Results
The media did not have harmful effects on the plant or the soil environment. They had deacidifying properties; high contents of calcium, magnesium, potassium, and phosphorus; low total trace element content; and posed little risk of metal mobility. Heterocypris incongruens was the organism most sensitive to the substances contained in the studied media. The use of bottom-sediment-based media reduced the biomass of the test plant and, at the same time, limited the accumulation of trace elements in its aboveground parts.
Conclusion
Most of the analysed media were low-toxic to the test organisms and can potentially be used in agriculture, horticulture, or the reclamation of degraded land.
... Therefore, considering the results of this LCA study, the recommendation is to employ the material in soil conditioning processes. Future studies could focus on the reduction of potential toxicity impacts, for example, by pre-treating the dredged sediments to reduce the metal content using technologies such as phytoremediation or chemical extraction [50]. The reduction of the availability of metals is also recommended, for example, by mixing the material with biochar [51] or with some forms of phosphates. ...
... Similar results were reported by Zhou, Zhang, Li, Zhang and Wang [27], where the initial concentration of the handling material was one of the most influential parameters in an LCA focused on treatment and disposal strategies for dredged sediments. [50]. The reduction of the availability of metals is also recommended, for example, by mixing the material with biochar [51] or with some forms of phosphates. ...
The management of dredged sediments is a challenging issue since it involves the interconnection of complex economic, social, technical and environmental aspects. The EU LIFE SURE project aimed to apply a more sustainable dredging technique to Malmfjärden Bay in Kalmar/Sweden (a shallow urban water body with a high content of nutrients) and, additionally, it involved beneficial uses for the dredged material, in line with the circular economy concept. To achieve this, a life cycle assessment (LCA) study was carried out to assess the potential environmental impacts associated with two scenarios: sediment landfilling (S1) and soil conditioning (S2). This LCA study also aimed to evaluate and compare the costs related to each scenario. S1 contemplated the construction and operation of the landfill for 100 years, including the collection and discharge of leachate and biogas. S2 included the use of sediments in soils and the avoidance of producing and using fertilisers. Results showed that (S2) soil conditioning (total impact: −6.4 PE) was the scenario with fewer environmental impacts and the best economic evaluation. The S2 scenario was mainly related to the positive environmental savings produced by reducing fertiliser consumption (which also avoided purchase costs). However, S2 was also linked to potential negative effects associated with eutrophication and toxicity categories of impacts due to the possible spread of nutrients and pollutants in terrestrial and aquatic environments. In order to mitigate this problem, the sediments could be pre-treated to reduce their risk of pollution. Moreover, the main impact of the landfilling scenario (S1, total impact: 1.6 PE) was the emission of global warming-contributing gases during the operation of the facility. Implementing the soil conditioning scenario was therefore recommended, in line with the aim of the LIFE SURE project. Finally, it was recommended that LCA studies should be applied more often in the future when selecting beneficial uses for dredged sediments. The decision-making process is facilitated when the positive and negative impacts produced by each handling option are considered.
... Most in-situ remediation methods are appropriate selections for slightly contaminated sediment (Smolders et al., 2003), and could offer more costeffective (Song et al., 2017;Xu et al., 2022;Zhang et al., 2021) and sustainable solutions (NAVFAC, 2015). To date, some in-situ remedial actions such as capping and monitored natural recovery have been commonly practiced (Jersak et al., 2018), and based on their function, they can be divided into physical, chemical, biological, or hybrid remediation techniques (Song et al., 2017); such as monitored natural recovery (MNR), enhanced monitored natural recovery (EMNR) (Jersak et al., 2016), active and passive capping (Cornelissen et al., 2011;Zhang et al., 2016), Nano-remediation (Xue et al., 2022), stabilization (Akcil et al., 2015;Liu et al., 2019), phytoremediation (Haghnazar et al., 2021), Phyto-microorganisms (Wood et al., 2016), Electrokinetic-acidification, and chemical leaching-ultrasonic (Zhang et al., 2019). In in-situ remediation methods, amendments usually are involved in the process to accelerate the remediation or stabilization process of contaminants (The Interstate Technology & Regulatory Council, 2014). ...
Musa Bay, the largest wetland in Iran and one of the most important Hg-polluted media, plays a significant role in the ecosystem of the area and supports many forms of life. Mercury pollution has detrimental effects on the human body and at high levels leads to the loss of microorganisms in marine ecosystems. Hence, a comprehensive assessment for selecting an effective and sustainable remediation method is crucial to restoring the ecosystem promptly. The determination of a proper and practical treatment method not only is a case-based approach, but could be challenging due to its multi-criteria decision-making nature. Considering preferred crucial factors involved in the effectiveness of remedial actions, in this study a questionnaire is designed to assess the opinion of environmental experts, stakeholders, and some occupants of the area on remedial actions based on the importance weights of criteria. Subsequently, practical remediation and management strategies ranked by hybrid FVIKOR as a multi-criteria decision making (MCDM) method. Ranking results show that dredging and stabilization could offer a promising solution for the remediation of the case study. The results of the study demonstrate that the development of MCDM methods along with effective criteria and considering the analysis of the questionnaires, could offer the best remediation strategy for a specific contaminated site.
... The increasing human activities and natural conditions are responsible for the contamination of water bodies, viz., harbors, ports, estuaries, rivers, lakes, etc. (Akcil et al., 2015). In the realm of the dredging industry (capital and maintenance), the dredged sediments (DS) act like a by-product that has the potential to be utilized to replace natural mineral aggregates (Achour et al., 2014;Loudini et al., 2020). ...
The constraints associated with the availability of huge amounts of natural resources for infrastructure and agricultural development calls for the reuse and recycling of anthropogenically created geomaterials, which is in line with the UN Sustainable Development Goals. In this context, valorization of dredged sediments (DS), obtained from water bodies such as rivers, lakes, oceans, etc., as a resource material is worth considering. Unfortunately, DS might be contaminated and exhibit a higher moisture-holding capacity due to higher organic matter and clay minerals/colloids. These attributes pose a serious question towards dumping of the DS in the deep sea (in the case of marine sediments), a practice which though prevails presently but endangers marine life. Hence, the way forward would be to characterize them holistically, followed by adequate treatment to make them ecologically synergetic before developing a strategy for their valorization. In this regard, many studies have been focused on the characterization and treatment of DS to make them environmentally safe manmade resource. With this in view, a critical synthesis of the published literature pertaining to the (i) characterization, (ii) treatment, remediation, and immobilization of contaminants, and (iii) utilization of DS has been conducted, and the salient findings are presented in this paper. Based on this study, it was observed that the DS acts as a sink for emerging contaminants for which no remediation strategies are available. Moreover, the study highlighted the lacuna in upscaling the existing treatment and stabilization techniques to field conditions while highlighting the concept of circular economy.
... Sediment contamination as a consequence of human activities is a widespread environmental problem (Akcil et al., 2015;Barth et al., 2009). Polluted sediment can be found in estuaries (Chapman et al., 2013), harbours (Birch et al., 2020), ports (Cecchi et al., 2021), and coastal marine zones (Qian et al., 2015), as well as in freshwater ecosystems like rivers, waterways (Taylor and Owens, 2009), lakes (Niu et al., 2021), wetlands and flood plains (Du Laing et al., 2009;Tockner and Stanford, 2002). ...
Dredging activities produce large amounts of polluted sediments that require adequate management strategies. Sediment reuse and relocation can involve several environmental issues, such as the release of CO2 and nitrogen compounds in the environment, the transfer of metals to plant tissues and the persistence of phytotoxic compounds. In this framework, the aim of the present work is to evaluate the use of biochar at different doses, in combination with plant growth, to reduce the environmental impacts polluted dredged sediments.
Irrespective to the plant treatment, the amendment of the sediment with the lowest dose of biochar (3%) reduced by 25% the CO2 emissions of the substrate, by 89% the substrate carbon loss and by 35% the amount of nitrogen released into the environment (average values of the three plant treatments). The negative priming effect of biochar on organic matter mineralization can be responsible for the beneficial reduction of carbon and nitrogen release in the environment. The lack of similar effects observed at the higher biochar doses can depend on the low albedo of the biochar particles, causing the substrate warming (+1 °C for highest biochar dose) and accelerating the organic matter mineralization. Finally, shrub growth in combination with 3% biochar was able to offset the CO2 emission of the sediment and to reduce the amount of nitrogen lost.
This work provides new insight on the potential benefit related to the biochar amendment of organic matter-rich dredged sediments, suggesting that the use of moderate dose of wood biochar in combination with shrub plantation can reduce the release of CO2 and nitrogen compounds in the environment.
... Bioremediation is considered one of the most environmentally friendly and sustainable ways to reduce several aquatic contaminations, which plays a significant role in improving the production of associated aquaculture systems [37,38]. Generally, the bioremediation process is very effective in reducing the toxicity of heavy metals by converting them into less harmful forms with the help of either microbe [39,40] or their enzymes to lessen the contamination [41]. This is considered an ecofriendly and cost-effective method to revitalize the contaminated environment [36,42]. ...
Heavy metals, the most potent contaminants of the environment, are discharged into the aquatic ecosystems through the effluents of several industries, resulting in serious aquatic pollution. This type of severe heavy metal contamination in aquaculture systems has attracted great attention throughout the world. These toxic heavy metals are transmitted into the food chain through their bioaccumulation in different tissues of aquatic species and have aroused serious public health concerns. Heavy metal toxicity negatively affects the growth, reproduction, and physiology of fish, which is threatening the sustainable development of the aquaculture sector. Recently, several techniques, such as adsorption, physio-biochemical, molecular, and phytoremediation mechanisms have been successfully applied to reduce the toxicants in the environment. Microorganisms, especially several bacterial species, play a key role in this bioremediation process. In this context, the present review summarizes the bioaccumulation of different heavy metals into fishes, their toxic effects, and possible bioremediation techniques to protect the fishes from heavy metal contamination. Additionally, this paper discusses existing strategies to bioremediate heavy metals from aquatic ecosystems and the scope of genetic and molecular approaches for the effective bioremediation of heavy metals.
... Though tannery water treatment, involving physiochemical methods like ion exchange, reverse osmosis and diffusion can be practiced, however biological wastewater treatment is favourable [8]. Bioremediation mediated by microorganisms and different microbial enzymes is also practiced to transform this toxic waste material into its comparatively lesser injurious state [9,10,11]. Being eco-friendly and cost competitive, it aids in revivality of the environment and maintains the ecological balance as well [12,13]. In our previous study, the role and efficacy of Brevibacillus brevis US575 in combatting Cr pollution has been well investigated. ...
Various leather factories in West Bengal have resulted in an enormous amount of leather that is processed annually. Regular discharges of tannery effluents into land and open water have led to significant soil and water pollution, with one of the most dangerous inorganic pollutants being chromium (Cr). This study aims to recover the most harmful components from industrial water using efficient biosorbents. Brevibacillus brevis US575 has been initially found in tannery effluents, where it has a high tolerance level to Cr6+ ions. The Cr(VI) adsorbed from the solution in aqueous phase during the course of the 60-minute contact period in this experiment was nearly 74%. Studies on the concentration of biomass, pH of the medium, and the starting concentration of metal ions have also been seen to affect the rate of biosorption. According to the desorption investigation, 1 M HCl outperformed all other concentrations of HCl, NaOH and pure water. Highest capacity of adsorption of the bio-adsorbent was calculated using the Langmuir model. The monolayer adsorption process was determined, and since the Freundlich model's 1/n value fell inside 1, favourable adsorption has been postulated. According to the results of this study, the bacterium isolated from tannery wastewater was found to be the best alternative and could be used to create plans for using biosorption to combat current environmental pollution.
... Internationally, the most common disposal methods are disposal at a land ll or in the sea (Akcil, et al., 2015, Bortone, et al., 2004. In the EU, changes in legislation decreased the possibility of land lling materials such as soil and sediment and as a consequence, land lling costs are increasing (European Environment Agency, 2009). ...
Purpose
Stabilization and solidification (S/S) is a technique that enhances the structural properties of the sediment and reduces contaminant mobility, enabling the utilization of dredged contaminated sediment. Further reduction of the contaminants before S/S is, however, desirable to minimize leaching. The metal and organotin content in sediment could be reduced by electrochemical treatment. This is the first study on how electrochemical pretreatment impacts the strength and leaching properties of stabilized sediments.
Methods
Sediment was sampled from a port and was treated by using electrolysis. The removal of metals and organotin was investigated. Both treated and non-treated sediment was stabilized to investigate how electrolysis and also how different salinity and concentrations of organic matter during the curing affected the S/S properties by doing compression tests and leching tests.
Results
The electrolysis resulted in a 22% reduction of tributyltin (TBT) and a 44% reduction of zinc in the sediment. The results showed that the electrolyzed stabilized samples passed the requirements for compression strength and had a reduced surface leaching of zinc. Curing in saline conditions was beneficial for strength development and reducing the leaching of TBT.
Conclusion
Electrolysis reduced the sediment’s TBT and metal content, and the results indicate that pretreatment before stabilization could be beneficial to reduce contaminant leaching and to recover metals from the sediment. This study highlights the importance of investigating if a specific stabilization recipe fulfills the strength and leaching criteria in water similar to the field condition to assure satisfying results once implemented in the field.
... Arsenic present in aquatic environments is readily adsorbed on particles, gets deposited and accumulated in sediments and sinking sediments, and ultimately becomes a source of contamination (Wang et al. 2019). Arsenic accumulation in sediments adversely affects the sediment quality and benthic ecology (Akcil et al. 2015;Wen and Zeng 2016). Changes in physical and chemical states of sediment-water systems pose risks of As release from contaminated sediments (LeMonte et al. 2017;Bettoschi et al. 2018;Ding et al. 2018). ...
Purpose
Aluminum- and iron-impregnated food waste biochar (Al-FWBC and Fe-FWBC) have been suggested for the remediation of dredged sediments contaminated with arsenic (As).
Materials and methods
Sediment was obtained from a reservoir surrounded by several abandoned gold mines. High As concentration (102.7 mg kg⁻¹) of the sediment corresponded to a severely contaminated level, but other heavy metals were in acceptable ranges without toxic concerns. Al-FWBC and Fe-FWBC, successfully synthesized in a previous study to remove As from aqueous solutions, were used as stabilization/solidification (S/S) agents in the current study. A sequential extraction procedure was applied to investigate the fractionation and stability of As in sediments.
Results and discussion
Amendment of Al-FWBC and Fe-FWBC for 6 months reduced the non-specifically and specifically sorbed fractions but increased the residual fraction. Fe-FWBC 1% was most efficient in stabilizing As in the sediment and it decreased 45.4% of non-specifically and specifically sorbed fractions. The effect of Al-FWBC and Fe-FWBC amendments was further confirmed by measuring potential ecological risk, and the contamination factor decreased from a considerably polluted to moderately polluted level. Arsenic and other heavy metals that leached from the S/S-treated sediments via toxicity characteristic leaching procedure did not exceed the values prescribed by the US Environmental Protection Agency.
Conclusions
Stabilization/solidification treatment using Al-FWBC and Fe-FWBC, converted from waste to value-added substances for environmental pollution control, can be applied to remediate sediments contaminated with As.
... Although several physical separation processes have been used for cleaning polluted sediments, mainly screening (Peng et al., 2009), flotation (Cauwenberg et al., 1998), ultrasonic-assisted extractions (Kyllönen et al., 2004;Meegoda and Perera, 2001) or hydrocyclones (Mulligan et al., 2001a(Mulligan et al., , 2001b, magnetic extraction has not been successfully applied so far (Akcil et al., 2015;Mulligan et al., 2001a). However, this approach has been effectively tested in soil remediation (Baragaño et al., 2021;Dermont et al., 2008;Sierra et al., 2014b). ...
Several metals and metalloids (e.g., As, Cd, Cu, Pb, Zn) are toxic at low concentrations, thus their presence in sediments can raise environmental concern. However, these elements can be of economic interest, and several techniques have been used for their recovery and some of them have been widely applied to mining or to industrial soils, but not to sediments. In this work, wet high-intensity magnetic separation (WHIMS) was applied for As, Cd, Cu, Pb and Zn recovery from polluted sediments. A composite sample of 50 kg was taken in the Avilés estuary (Asturias, North Spain) with element concentrations above the legislation limits. Element distribution was assessed using wet-sieving and ICP-MS analysis, revealing that the 125-500 μm grain-size fraction accounts for the 62 w% of the material and that element concentration in this fraction is lower than in the other grain size fractions. Subsequently, WHIMS was applied at three different voltage intensities for the 125-500 μm and <125 μm fractions, revealing excellent recovery ratios, especially for the coarser material. Furthermore, magnetic property measurements coupled to microscopy analysis revealed that the success of the technique derives from concentrating metal-enriched iron oxides particles (ferro-and para-magnetic material) in a mixture of quartz and other minerals (diamagnetic particles). These results indicate the feasibility of the magnetic separation for metal and metalloid recovery from polluted sediments, and thus offer a double benefit of coastal area restoration and valuable material recovery in the context of a circular economy.
... Plant-based removal or detoxification of toxic metals and dyes also uses microbe-based strategies for successful decontamination of polluted sites. The bioremediation technique utilizes the inherent biological mechanisms of microorganisms and plants for the removal of heavy metals and dyes from polluted environments (Akcil et al., 2015;Ojuederie and Babalola, 2017;Tripathi and Singh, 2022). ...
Toxic wastes like heavy metals and dyes are released into the environment as a direct result of industrialization and technological progress. The biosorption of contaminants utilizes a variety of biomaterials. Biosorbents can adsorb toxic pollutants on their surface through various mechanisms like complexation, precipitation, etc. The quantity of sorption sites that are accessible on the surface of the biosorbent affects its effectiveness. Biosorption’s low cost, high efficiency, lack of nutrient requirements, and ability to regenerate the biosorbent are its main advantages over other treatment methods. Optimization of environmental conditions like temperature, pH, nutrient availability, and other factors is a prerequisite to achieving optimal biosorbent performance. Recent strategies include nanomaterials, genetic engineering, and biofilm-based remediation for various types of pollutants. The removal of hazardous dyes and heavy metals from wastewater using biosorbents is a strategy that is both efficient and sustainable. This review provides a perspective on the existing literature and brings it up-todate by including the latest research and findings in the field.
... As a result, it is important to remove and reduce the heavy metals contamination in order to protect the environment from the toxic hazardous consequences (Ndeddy & Babalola, 2016;Sall et al., 2020). The increasing awareness about the toxic effects of heavy metals has led researchers to look for new techniques to clean the environment for cultivating the land and preventing the contamination of food (Akcil et al., 2015;Oladoye et al., 2022). In this study, we used different levels of citric acid and EDTA to accelerate Ni uptake and induced tolerance in the seedling of two cultivars of rapeseed plant (Oscar and Corn-II) under Ni stress. ...
Heavy metals like nickel, cadmium, and chromium found in industrial waste pose a seri- ous threat to living organisms. Nickel is extremely poisonous and causes numerous human ailments when it is exceeded from the permissible limit. The most efficient and cost-effective method of removing nickel from contaminated soil is phytoremedia- tion and chelating agents act as supporting material for phytoremediation. Consequently, the purpose of the current study was to enhance the phytoextraction potential of Brassica napus by using chelating agents such as citric acid and ethylene diamine tetra acetic acid (EDTA). For phytoremediation, experimental treatments were comprised of different levels of citric acid, i.e., 10 mM and 20 mM and EDTA, i.e., 1.5 mM and 2.0 mM and the combinations of both (citric acid + EDTA), i.e., 10 mM + 1.5 mM 20 mM+1.5 mM, 10 mM+2.0 mM, and 20 mM+2.0 mM respectively under Ni toxicity. A control without citric acid and EDTA was kept for comparison. Different growth, physiological, and biochemical attributes were measured and analyzed statistically. Results revealed that the concentration of citric acid (10 mM) and EDTA (1.5 mM) separately and in combination EDTA (1.5 mM)+citric acid (10 mM) performed better for the purpose of phy- toremediation and accelerate phytoextraction of Ni through hyper-accumulated Brassica napus. Highest Ni content (27.33 mg/kg) were observed in plants of Corn-II receiving EDTA followed by CA treatment (24.33 mg/pot) and combined EDTA + CA treatment (24.85 mg/pot). The ability of Rapeseed to bio-accu- mulate heavy metals can be used to reduce the level of contaminants in the soil making it suitable for the cultivation of other metals sensitive food crops. The current work demonstrates the effective application of chelating agents (CA and EDTA) to reduce Ni stress as well as to increase Ni accumulation, a requirement for phytoremediation. It is suggested that B. napus species can be utilized for phytoremediation as it is a good accumulator of Ni and other metals.
... Dredging reduces labile metal fractions in soil, which improves the metal-binding ability of available sediment solids and delays metal leaching from solids (Chen et al., 2019a, b). On the other hand, it has some drawbacks, including the inability to remove all contaminants, the fact that new pollutants can move downward and contribute to pollution again, the loss of native benthic communities present in the soil, and the technique is costly (Akcil et al., 2015). Given the disadvantages of dredging, utilizing less expensive biochar for in situ capping to encapsulate contaminants is a feasible and growing option. ...
... Dredging reduces labile metal fractions in soil, which improves the metal-binding ability of available sediment solids and delays metal leaching from solids (Chen et al., 2019a, b). On the other hand, it has some drawbacks, including the inability to remove all contaminants, the fact that new pollutants can move downward and contribute to pollution again, the loss of native benthic communities present in the soil, and the technique is costly (Akcil et al., 2015). Given the disadvantages of dredging, utilizing less expensive biochar for in situ capping to encapsulate contaminants is a feasible and growing option. ...
... The sediment management depends on local normative and the types and the concentrations of pollutants limit sediment reuse for different purposes (Casper 2008). Usually, dredged sediment, managed as waste materials, are landfilled (Akcil et al. 2015), and pre-treatment techniques applied to recover polluted sediment includes the combination of different techniques, such as chemical and mechanical treatments (Hung et al. 2021), stabilizationsolidification method and electrolysis (Svensson et al. 2022) and sediment washing and bioactivators (Doni et al. 2018). However, costs and environmental impact change, based on the applied treatment (Svensson et al. 2022). ...
Purpose
There is a high quantity of dredged sediments produced every year. Both their landfill disposal and high pollutant concentrations lead to concerns regarding sustainability. The use of dredged sediment in growing media for horticulture is an opportunity to improve its recycling and to reduce the use of non-renewable materials, such as peat. For this purpose, marine sediments, phytoremediated in the framework of the AGRIPORT project (ECO/08/239065), were selected as a substrate component for pomegranate cultivation.
Material and methods
Phytoremediated sediments underwent 3-months landfarming, to improve their chemical and physical properties and to reduce hydrocarbon concentration. Afterwards, remediated sediment (RS) was mixed with peat (P) in a ratio of 50%. The tested substrates were (v:v) 100% RS (S100), 50% RS and 50% P (S50) and 100% P (S0) as control. Punica granatum L. var. “Mollar de Elche” and “Purple Queen” were selected as target plants. The sediment during the landfarming and the growing media during the plant growth were monitored through physical, chemical, and biological analysis. In addition, the plant performance was evaluated by dry biomass determination.
Results and discussion
Landfarming decreased electrical conductivity and bulk density as well as increased soluble C and N, reducing hydrocarbon concentration in RS, due to the increase in microbial metabolism. The RS respected the Italian legislation limits for growing media, except for bulk density and organic carbon. The RS + P substrate reached the required legal limits. During plant growth, substrates showed low mineralization, and the increased release of nutrients suggested beneficial changes in the rhizosphere. Higher availability of nutrients was detected in P and a decrease of metal concentrations occurred, as result of the plant uptake. The differences in the substrate properties influenced the pomegranate development with a variety-specific effect. “Purple Queen” increased the dry biomass, while no differences were observed for “Mollar de Elche.”
Conclusion
The use of sediment-based substrates (50% and 100%) for pomegranate cultivation, specifically for the “Mollar de Elche” variety, contributes to reducing peat application in horticulture.
... O processo de E/S dos resíduos em materiais cimentícios é considerado como uma das técnicas mais eficientes estudadas, devido principalmente ao pH alcalino. Substâncias alcalinas, como o Ca(OH)2, são am-plamente utilizadas para tecnologias de imobilização combinadas com o tratamento de resíduos perigosos [28], podendo realizar o encapsulamento físico e a fixação química de substâncias tóxicas. Estudos anteriores incorporando escória com cromo [8], cinza de bagaço de cana de açúcar [5], lodo de fosfatização [29], lodo galvânico [30,31] e aparas de couro [25] com cimento Portland mostraram-se eficientes na E/S destes resíduos que apresentavam cromo em sua composição. ...
The search for materials in eco-efficient civil construction can be carried out by adding or replacing raw materials with waste generated in other industrial sectors. Many of these residues are classified as hazardous, and the inertization of compounds that confer dangerousness can be performed through stabilization by solidification (S/S) that causes the encapsulation and chemical fixation of toxic substances. However, in Brazil there is no regulated standard or even a technical recommendation, which is specific for S/S products used as building components. In this context, the present study aimed to evaluate the leaching of chromium in Portland cement concrete matrix by immersion and irrigation methods, with a view to the use of these methods in the environmental assessment of materials and components of civil construction. For this, specimens of 25x200x400 mm were made with and without the addition of 2% Cr2O3 (chromium oxide) in relation to the Portland cement mass, which were subjected to immersion and irrigation leaching tests. The results obtained allowed to verify the encapsulation of chromium in the concrete and that the leaching tests proposed in concrete monoliths, during the use phase, proved to be applicable in 28 days.
Keywords
Environmental assessment; Stabilization by solidification; Leaching; Chromium; Concrete; Portland cement
... In recent years, the treatment of black and odorous water has been a difficult issue in the field of civil engineering and environmental protection. Sediment dredging, as a common method, generates a large amount of contaminated dredged sediment during the treatment process [1,2]. This type of sediment is mainly composed of fine-grained silty clay, which is difficult to dehydrate [3]. ...
The treatment of metal-contaminated sediment generated in environmental dredging projects often requires both reduction and remediation, and the electric field has good application prospects in the integration of reduction and remediation. In this study, based on the electro-osmosis, vacuum, and vacuum electro-osmosis methods, a detachable test system was made. Experiments of the three methods were carried out independently on the reduction and remediation of dredged sediment from Tai Lake under pollution-free and Cu-contaminated conditions. The results show that copper contamination weakens the effect of reduction, and the production of copper precipitates makes the soil more prone to cracking and blocking drainage channels, which has the greatest impact on the electro-osmosis method. In terms of copper concentration, vacuum electro-osmosis achieves the transport and discharge of contaminants, and has the best remediation effect. The removal rates at the anode and cathode are 45.1% and 50.0%, respectively. A correlation model based on electrical conductivity, moisture content, and contaminant concentration was established to facilitate the determination of contaminant concentrations in actual projects. Electro-migration plays a dominant role in the remediation process, and the reduction affects the electric field distribution and, thus, the migration efficiency.
... In recent years, the application of microorganisms which degrade or convert hazardous pollutants to less toxic compounds have become popular. Fungi proved to have high potential in the degradation of high molecular weight compounds and therefore are used widely to remediate environmental pollution (Akcil et al. 2015;Deshmukh et al. 2016;. Fungi are eukaryotic, chemoheterotrophic, parasitic or saprophytic, unicellular or multicellular filamentous organisms that include molds, yeasts, and mushrooms. ...
Microalgae cultures offers solutions for pollution control at water reuse. The ability to nutrient and heavy metal up-take along with disinfection is a considerable more sustainable solution than conventional wastewater treatment processes based on mechanical aeration. Since microalgae have evolved together with bacteria in natural aquatic environments a whole range of interactions take place between both organisms. Ecology descriptions and population characterizations of the phycosphere are key elements for the design of microalgae-based units addressed to pollution control and for the understanding of the biochemical transformations that take place during cultivation. Negative interactions occur as consequence of resources competence or parasitism. Mutualism have the basis on substrate exchange and release of promotors. These and other interactions take place during the environmental applications such as wastewater treatment, gas treatment, or water reuse affecting the final performance.
... In recent years, the application of microorganisms which degrade or convert hazardous pollutants to less toxic compounds have become popular. Fungi proved to have high potential in the degradation of high molecular weight compounds and therefore are used widely to remediate environmental pollution (Akcil et al. 2015;Deshmukh et al. 2016;. Fungi are eukaryotic, chemoheterotrophic, parasitic or saprophytic, unicellular or multicellular filamentous organisms that include molds, yeasts, and mushrooms. ...
For over 60 years, global apparent food fish consumption has increased considerably generating a large volume of preconsumer and postconsumer residues, which consists mainly of shells and bones. Usually, fish by-products are used directly as feed in aquaculture or fertilizers. However, other applications have been gathering attention recently, such as the production of biofuel and biogas, pharmaceuticals, cosmetics and many others. Nowadays, this biowaste represents a promising source of biomaterials from marine discarded materials and this approach is very attractive due to their abundant availability, accessibility and low-cost source. Direct Digital Manufacturing (DDM) is currently a main subject in the manufacturing industry placing many advantages, such as a high degree of geometric freedom for design and reduction of material waste, when compared to conventional manufacturing techniques. Therefore, DDM is seen as an energy-efficient technology. The use of biobased and biodegradable polymers in DDM technologies has been an emerging field in recent years, mainly in biomedical areas, due to the increasing interest in sustainable products and solutions, instead of using limited resources such as fuel-based polymers. Thus, the valorization of bioactive compounds from fish by-products is of great interest due to their high market value, also can satisfy the demand of low-cost biomaterials, reduce marine pollution and can be used as alternative materials for DDM technologies. The reuse of these waste resources to produce biomaterials through sustainable processes can be a way to create new companies and job opportunities.
... In recent years, the application of microorganisms which degrade or convert hazardous pollutants to less toxic compounds have become popular. Fungi proved to have high potential in the degradation of high molecular weight compounds and therefore are used widely to remediate environmental pollution (Akcil et al. 2015;Deshmukh et al. 2016;. Fungi are eukaryotic, chemoheterotrophic, parasitic or saprophytic, unicellular or multicellular filamentous organisms that include molds, yeasts, and mushrooms. ...
The current sustainable transition plans seek to pursuit energy supply security with low carbon emissions. Although electrification is presented as a key factor to decarbonize demanding sectors (transport, buildings, and industry), energy provided by fuel combustion will be essential to cope with future demands. In this sense, it is necessary to rely on circular economy models based on low carbon biofuels. During the last decade, the biofuels industry transitioned from being sustainable and socially accepted to a deeply questioned solution due to the food versus energy debate. Therefore, using alternative feedstocks, such as wastes or residual biomass, is convenient to obtain biofuels creating new value chains during the transformation. This chapter is focused on the technologies developed for biofuel production capable of minimizing the carbon footprint. Production methods for gaseous biofuels and liquid biofuels are described. The possible integration of each technology is evaluated considering the availability of feedstocks and the emission savings obtained by main biofuels (bioethanol, biobutanol, and biomethane). This analysis reveals the need for diversification in feedstocks utilization and transformation and the intensification of waste management technologies. In this sense, a case study is presented considering the most extensive wastes produced worldwide (agricultural by-products) and the potential production of regular biofuels (bioethanol, biomethane, and biobutanol). Net energy production as biofuel and emission savings are analyzed for each case. This analysis reveals that bioethanol presents the best performance in terms of carbon neutrality. Finally, a revision of the most recent regulations affecting biomass transformation in biofuels and their role in the circular economy in Europe is included in the last section. This section provides a framework for the application of the technologies and the case study presented.
... Molecules 2023, 28, 176 2 of 16 precipitation/co-precipitation, and photochemical processes, biological techniques include aerobic decomposition, bacterial destruction, and biosorption [16]. Even though these approaches are successful, they have several drawbacks, including increased chemical consumption and sludge formation, and they are expensive [17]. ...
In this study, a V@TiO2 nanocomposite is examined for its ability to eliminate carcinogenic Rhodamine (Rh-B) dye from an aqueous medium. A simple ultrasonic method was used to produce the nanosorbent. In addition, V@TiO2 was characterized using various techniques, including XRD, HRTEM, XPS, and FTIR. Batch mode studies were used to study the removal of Rh-B dye. In the presence of pH 9, the V@TiO2 nanocomposite was able to remove Rh-B dye to its maximum extent. A correlation regression of 0.95 indicated that the Langmuir model was a better fit for dye adsorption. Moreover, the maximum adsorption capacity of the V@TiO2 nanocomposite was determined to be 158.8 mg/g. According to the thermodynamic parameters, dye adsorption followed a pseudo-first-order model. Based on the results of the study, a V@TiO2 nanocomposite can be reused for dye removal using ethanol.
... While several researchers have examined the use of reactive capping materials for inorganic and organic-contaminated sediments, the heavy metals in sediments have received little attention. The knowledge about in-situ capping is inadequate for heavy metal contaminated sediments (Akcil, 2015). Clay, gravel, zeolites, and activated carbon are the main materials used in today's capping remediation techniques (Fadaei et al., 2015;Jacobs and Förstner, 1999). ...
The public concern over sediment contamination brought on by mining operations, excessive use of chemical
fertilisers or pesticides, industrial, agricultural, and municipal effluent, is increasing. Dredging is a more expensive
treatment option than in situ capping of polluted sediment for immobilising pollutants in sediments on site. In
order to stop the release of Cr and Cu from chemically contaminated sediments, this study aimed to evaluate the
efficiency of utilising active capping materials such as bentonite (B), kaolin (K), and a 1:1 combination of bentonite and kaolin (BK) as capping materials. In a 90-day laboratory experiment carried out in glass tanks with a 1 cm
thickness cover of capped material plus sand spread over the polluted sediment, the efficacy of B, K, and BK in
inhibiting trace metal leachability was examined. The findings demonstrated that B and BK decreased the ability of
sediments to leach Cr and Cu. The results suggest that BK and B should be considered as a suitable active material
for capping treatment of polluted sediment sites because of their high Cu and Cr trapping. According to an analysis
of adsorption kinetics, chemisorption was the adsorption process. The outcomes of this study demonstrated the
potential for using kaolin, a bentonite-kaolin clay mixture covered with sand, and bentonite as capping materials
for the in-situ treatment of Cr and Cu polluted coastal sediments.
... The heavy metal components associated with iron or sulphur minerals in sediments are the primary targets of bioleaching. As a result, the most commonly used bioleaching microbes are members of the Proteobacteria (e.g., Acidithiobacillus, Acidiphilium, Acidiferrobacter, Ferrovum), Nitrospirae (e.g., Leptospirillum), Firmicutes (e.g., Alicyclobacillus, Sulfobacillus), Actinobacteria (e.g., they can oxidize iron or sulphide minerals, provide an acidic environment, and thereby solubilize immobilized heavy metals in water [141][142][143]. ...
Heavy metal contamination of the ecosystem remains one of the severe global threats. Even in trace quantities, heavy metals and metalloids such as chromium, lead, mercury, cadmium, nickel, and cobalt are toxic and carcinogenic, posing a serious threat to human life. Certain microbes and plants have evolved detoxifying pathways to fight the harmful effects of these inorganic metals, paving the door for bioremediation. Because of its environmentally benign nature, economic viability, and low labor and effort requirements, bioremediation outperforms other approaches in eliminating heavy metals. This review highlights the potential of microbes on remediation of heavy metals in the context of environmental protection and also focuses on the critical tolerance mechanisms used by these microbes in combating heavy metal contaminations. Furthermore, the bioremediation potential of bacteria, fungus, algae, plants, biosurfactants, biofilms and genetically altered microorganisms for the removal of these heavy metals was reviewed in this study. Applying these techniques as a sustainable environmental technology in the near future has shown synergistic benefits with a many-fold increase in the removal of heavy metals.
... As evident from the above studies, A. flavus and A. niger are the most Cr tolerant Aspergillus species, with Infrared Seragadam et al. (2021) Spectral Analysis of functional groups showing that hydroxyl, amine, and carbonyl conjugated with -NH were responsible for adsorption of Cr (VI) (Bennett et al., 2013). Metabolism-dependent Cr remediation by fungi involves enzyme production and various mechanisms involved include active metal uptake, intracellular and extracellular precipitation, and redox reactions (Akcil et al., 2015). Fungi also produce different metabolites including phosphates, nitrogen-containing ligands, and proteins. ...
Heavy metal (HM) pollution has become a serious global problem due to the non-biodegradable nature of the HMs and their persistence in the environment. Agricultural soil is a non-renewable resource that requires careful management so that it can fulfill the increasing demand for agricultural food production. However, different anthropogenic activities have resulted in a large-scale accumulation of HMs in soil which is detrimental to soil and plant health. Due to their ubiquity, increased bioavailability, toxicity, and non-biodegradable nature, HM contamination has formed a roadblock in the way of achieving food security, safety, and sustainability in the future. Chromium (Cr), specifically Cr(VI) is a highly bioavailable HM with no proven role in the physiology of plants. Chromium has been found to be highly toxic to plants, with its toxicity also influenced by chemical speciation, which is in turn controlled by different factors, such as soil pH, redox potential, organic matter, and microbial population. In this review, the different factors that influence Cr speciation were analyzed and the relationship between biogeochemical transformations of Cr and its bioavailability which may be beneficial for devising different Cr remediation strategies has been discussed. Also, the uptake and transport mechanism of Cr in plants, with particular reference to sulfate and phosphate transporters has been presented. The biological solutions for the remediation of Cr contaminated sites which offer safe and viable alternatives to old-style physical and chemical remediation strategies have been discussed in detail. This review provides theoretical guidance in developing suitable approaches for the better management of these remediation strategies.
... For heavy metals remediation from contaminated soil, several species of microbes and plants are being tested (Kcil et al. 2015;Chiang et al. 2006;Abhilash et al. 2012Abhilash et al. , 2013Glick 2010). Nonetheless, the efficiency of every phyto-remediation measures largely be influenced by the following aspects: (i) intrinsic nature of plants such as easy propagation, production of phytoproducts, degradation and tolerance potential, (ii) microflora present in soil with plant growth promotion potential and ability to thrive in dirt, and (iii) physicochemical belongings such as water solubility, long range transport potential, persistence to the environment and phyto-accumulation of heavy metals itself (Fig. 27.2). ...
Soil is a dynamic life-supporting component of this Planet Earth but its contamination with toxic heavy metalsHeavy metals (HMs) is omnipresent throughout the planet. Abundances of these HMs in soil have augmented considerably in last 2–3 decades due to rapid industrialization, agricultural practices (fertilizers and pesticides application), and other anthropogenic activities, which causing environmental, ecological and health risks. Consequently, their remediation approaches from the environmental components are critical. Among the several procedures for metals remediation, organic residues with the plant-microbes (phyto-remediation) can simultaneously increase the fertility of soil along with the bio-remediation, which in turn is thought as one of the lucrative and cost-effective approaches of HM’s remediation from soil. Efficacy of phyto-remediation can be improved by simultaneous participations of plant-growth-promoting bacteria which can convert HMs into soluble and bio-available forms by the activities of siderophores, redox processes, biosurfactants, organic acids, and biomethylation. This work highlights the recent applications and advancements made hitherto to understand the molecular and biochemical mechanisms of metal-microbe-plant interactions with organic residues along with their functions in major processes belong to the phyto-remediation, for instance heavy metalHeavy metals detoxification, transformation, mobilization, distribution, and immobilization.
The combination of UiO-66-NH2/chitosan (CTS) and microalgae was effective in precious metal recovery of electronic wastes (E-wastes) from discarded microchips. Herein, zirconium-based metal–organic frameworks were introduced to bind metal ions from the E-waste. Thus, UiO-66-NH2 was linked to CTS as examined by Fourier-transform infrared spectroscopy (FT-IR). Au(III) leachate solutions were prepared via acidic treatments from the microcomputer chips that were used to test metal binding using UV–Vis absorption spectroscopy. The prepared UiO-66-NH2/CTS was tested to recover Au(III) ions from the liquid phase waste, which exhibited higher adsorption capacity than UiO-66, UiO-66-CTS, and UiO-66-NH2. The inclusion of microalgae in UiO-66-NH2/CTS system enhanced gold adsorption efficiency and binding of Au(III) ions onto UiO-66-NH2/CTS and UiO-66-NH2/CTS/microalgae attained equilibrium within a few hours. UiO-66-NH2/CTS showed an adsorption capacity of ∼ 576 mg/g, which increased to ∼ 671 mg/g after the introduction of microalgae of Spirulina maxima. The pH effect on Au(III) binding revealed that electrostatic interactions between the negatively charged UiO-66 particles and gold anions decreased the adsorption capacities at higher pH values. The findings highlighted the potential use of UiO-66-NH2/CTS and microalgae for effective gold recovery from the E-waste.
Aquatic pollution negatively affects water bodies, marine ecosystems, public health, and economy. Restoration of contaminated habitats has attracted global interest since protecting the health of marine ecosystems is crucial. Bioremediation is a cost-effective and eco-friendly way of transforming hazardous, resistant contaminants into environmentally benign products using diverse biological treatments. Because of their robust morphology and broad metabolic capabilities, fungi play an important role in bioremediation. This review summarizes the features employed by aquatic fungi for detoxification and subsequent bioremediation of different toxic and recalcitrant compounds in aquatic ecosystems. It also details how mycoremediation may convert chemically-suspended matters, microbial, nutritional, and oxygen-depleting aquatic contaminants into ecologically less hazardous products using multiple modes of action. Mycoremediation can also be considered in future research studies on aquatic, including marine, ecosystems as a possible tool for sustainable management, providing a foundation for selecting and utilizing fungi either independently or in microbial consortia.
The management of sediment-water interfaces, especially bed stability, is essential for controlling accumulated contaminants in the sediment. In this study, the relationship between sediment erosion and phosphorus (P) release under the remediation strategy of contaminated sediment backfilling (CSBT) was explored through a flume experiment, i.e. the dredged sediment was calcined into ceramsite after dewatering and detoxification and then backfilled to the dredged area for sediment capping, thus avoiding the introduction of foreign materials via in-situ remediation and the large-scale land occupation associated with ex-situ remediation. Acoustic Doppler velocimeter (ADV) and optical backscatter sensor (OBS) were used to measure the vertical distributions of flow velocity and sediment concentration in the overlying water, respectively, and diffusive gradients in thin films (DGT) was used to measure the P distribution in the sediment. The results revealed that improving bed stability from CSBT can considerably improve the robustness of sediment-water interface and reduce sediment erosion by more than 70%. The corresponding P release from the contaminated sediment could be inhibited with an inhibition efficiency as high as 80%. CSBT is a potent strategy for managing contaminated sediment. This study provides a theoretical reference for controlling sediment pollution, further supporting river and lake ecological management and environmental restoration.
A novel mercury-resistant bacterium, designated strain DCL_24T, was isolated from the legacy waste at the Daddu Majra dumping site in Chandigarh, India. It showed resistance up to 300 µM of inorganic mercury (mercuric chloride). The isolate was found to be a Gram-negative, facultative anaerobic, motile, and rod-shaped bacterium that can grow at 4 - 30 °C (optimum 25 °C), pH 6.0 - 12.0 (optimum 7.0), and 0 - 4.0 % (w/v) NaCl (optimum 0.5 - 2.0 %). The 16 S rRNA gene-based phylogenetic analysis showed that DCL_ 24 T shared a 97.53 % similarity with itsºlosest type strain Rheinheimera muenzenbergensis E-49T. Insilico DNA-DNA hybridization and average nucleotide identity values were found to be 18.60 % and 73.77 %, respectively, between the genomes of DCL_24T and R. muenzenbergensis E-49T. The strain DCL_24T has 44.33 DNA G+C content (mol %). Based on the phenotypic, chemotaxonomic, and genotypic data, the strain DCL_24T represents a novel species within the genus Rheinheimera, for which the name Rheinheimera metallidurans sp. nov is proposed. The type strain is DCL_24T (MTCC13203T = NBRC115780T = JCM 35551 T). The isolate was found to volatilize and remove mercury efficiently, as demonstrated by X-ray film and dithizone-based colorimetric methods. Around 92 % of mercury removal was observed within 48 h. The mercury-resistant determinant mer operon consisting of merA, encoding the mercuric reductase enzyme, and transport and regulatory genes (merT, merP, merD, and merR) were found in the isolate. Relative expression analysis of merA at increasing concentrations of HgCl2 was confirmed by quantitative real-time PCR. These data indicate the merA-mediated reduction of toxic Hg2+ into a non-toxic volatile Hg0. The phytotoxicity assay performed using Arabidopsis thaliana seeds further demonstrated the mercury toxicity reduction potential of DCL_24T. The study shows that this novel isolate, DCL_24T, is an interesting candidate for mercury bioremediation. However, further studies are required to assess the bioremediation efficacy of the strain under the harsh environmental conditions prevailing in polluted sites.
Three sediment cores recovered from the Alvarado Lagoon System (ALS) in the Gulf of Mexico were used to reconstruct the history of metals and metalloids and their environmental importance. The sedimentary profiles were dated with 210Pb and verified with 137Cs. Maximum ages of 77 and 86 years were estimated. Sediment provenance was described by sedimentological and geochemical proxies. The chemical alteration index (CIA) and weathering index (CIW) revealed moderate to high intensity of weathering in the source area that is controlled tropical climatic conditions, runoff, and precipitation in the basin that feeds sediments to this coastal lagoon. The Al2O3/TiO2 ratios indicated that the sediments were derived from intermediate igneous rocks. The enrichment factor values revealed the lithogenic and anthropic contribution of metals and metalloids. Cd is classified under the category extremely severe enrichment; agricultural activities, fertilizers, herbicides, and pesticides containing Cd are expected to supply this metal to the ecosystem. Factor Analysis and Principal Components provided two main factors, terrigenous and biological origins; ANOVA indicated that there are significant differences between the cores for the parameters analyzed and revealed that there are differences in depositional environments between the recovery zones of the cores. The ALS presented natural variations associated with the climatic conditions, terrigenous input, and its relationship with the hydrological variations of the main rivers. The contribution of this work was to identify the magnitude of the natural component versus the human contribution, mainly of risk metals such as Cd, to support better management of the hydrological basin that affects the ALS.
Soil contamination by heavy metals has become a serious environmental issue considering its effects on health and the environment. Several techniques are being used for the treatment of contaminated soil, but these methods have limitations on account of cost, chemical/energy efficiency, and application in the field. On the other hand, phytoremediation is a cost-effective, solar energy-driven, and eco-friendly method for heavy metal removal. The present study discusses hyperaccumulating ornamental plants that can remove metal contaminants from the soil without any visible phytotoxic symptoms. Besides the uptake and translocation, the specific metal accumulation potential of ornamental plants, the mechanism involved in the removal, and the growth response of hyperaccumulators towards metal exposure have also been discussed. The essential indices- bioconcentration factor and translocation factor to determine the suitability of plants towards phytoextraction, the role of different plant parts in translocation and biochemical mechanisms for detoxification of metals have been presented as a highlight of this study. For optimum removal and efficient management of a phytoremediation design, the role of controlling factors such as soil characteristics, type of metal, plant species, organic amendments, phytochelators, bio-inoculants, etc. is very important. Considering the advent of biotechnology, the use of genetically modified plants is also recommended for significantly improved efficiency. It is expected that the present study will provide a guiding path for future researchers in exploring the scope of phytoremediation using ornamental plants.
Heavy metal pollution has resulted in serious environmental damage and raised significant public health concerns. One potential solution in terminal waste treatment is to structurally incorporate and immobilize heavy metals in some robust frameworks. Yet extant research offers a limited perspective on how metal incorporation behavior and stabilization mechanisms can effectively manage heavy metal-laden waste. This review sets forth detailed research on the feasibility of treatment strategies to incorporate heavy metals into structural frameworks; this paper also compares common methods and advanced characterization techniques for identifying metal stabilization mechanisms. Furthermore, this review analyses the typical hosting structures for heavy metal contaminants and metal incorporation behavior, highlighting the importance of structural features on metal speciation and immobilization efficiency. Lastly, this paper systematically summarizes key factors (i.e., intrinsic properties and external conditions) affecting metal incorporation behavior. Drawing on these impactful findings, the paper discusses future directions in the design of waste forms that efficiently, effectively treat heavy metal contaminants. By examining tailored composition-structure-property relationships in metal immobilization strategies, this review reveals possible solutions for crucial challenges in waste treatment and enhances the development of structural incorporation strategies for heavy metal immobilization in environmental applications.
Urban stormwater sediments are associated with non-point source pollution. In Bogotá, Colombia, two urban rivers (Molinos - Arzobispo) and a constructed wetland with contributions from stormwater runoff located in different...
An eddy deep leaching technology was developed in this paper to address the challenge of treating heavy metal contaminants in industrial mining areas. The desorption effect of As, Cd, Sb and Pb was investigated utilizing chemical leaching and physical eddy techniques. It was found that the heavy metals concentration increased with decreasing particle size. The highest proportion of Cd in the form distribution of soil was in the bound to iron and manganese oxides, while the maximum proportion of As, Sb and Pb were in the residual. The optimal solid-liquid ratio of the hydrocyclone was 1:20, and the corresponding separation efficiency and flow rate were 84.7% and 1.76 m³/hr, respectively. The grade efficiency of soil particle separation increases with particle size and exceeds 99% for particles above 1,000 µm. Leaching experiments have revealed that oxalic acid (OA) and a combination of oxalic acid and EDTA (OAPE) were more efficient than citric acid (CA) and a combination of citric acid and EDTA (CAPE) for the desorption of heavy metals, respectively. The comparison of OAPE and eddy leaching found that the latter improved the desorption efficiency by 9.4%, 7.5%, 7.2% and 7.8% for As, Cd, Sb and Pb compared to the former, respectively. The results demonstrated that the eddy leaching technique could further enhance the desorption efficiency of heavy metals. It is expected to provide technical support for soil remediation with reduced usage of leaching agents.
The environment and human health are now seriously threatened by pollution. Organic contaminants have a long half-life in the environment and possess hydrophobic, mutagenic, and cytotoxic properties. Hence, they are a big challenge to the health of environment. Due to their hydrophobic and persistent character, non-biodegradable and recalcitrant chemicals have an adverse effect on terrestrial and aquatic ecosystems. According to current pollution management methods, biodegradation and bioremediation using various microorganisms is an efficient, reliable, and eco-friendly approach to combat the pollutants. Marine-derived fungi play a significant role in the remediation of organic pollutants because their unique morphological and physiological properties including survival in the extreme conditions and a diverse metabolic capability. This chapter highlights the role and mechanisms of marine-derived fungi in removal of various pollutants as polyaromatic hydrocarbons (PAHs), heavy metals, dyes, and the biomass valorization. Fungi can oxidize PAHs, alkanes, and other complex hydrocarbons using various intracellular and extracellular enzymatic machineries including monooxygenases and lignin-modifying enzymes. Marine-derived fungi act as biosorbents to remove heavy metal contaminants through active and passive mechanisms. Both living and non-living fungal biomass can be used to detoxify and degrade dyes from the contaminated environment. Furthermore, fungal biomass valorization facilitates the sustainable development of value-added products such as biofuels, enzymes, amino acids, organic acids, alcohol, pigments etc. Thus, the chapter emphasizes to understand the mechanisms of marine-derived fungi in degradation of organic pollutant, metabolic pathways, and enzymes responsible for degradation of organic compounds which would help to develop the future mycoremediation policies and production of value-added products for sustainable future development.
To mitigate the serious environmental problems caused by aquaculture wastewater discharge, the development of improved aquaculture systems with more self-purification capacity and less environmental impact has become essential. A novel recirculating aquaculture system (RAS) with ecological ponds was introduced. However, the mechanism of how the ecological ponds decompose the nutrients from the residual feed and excrement of fish is still unclear. Therefore, we designed a seven-week field experiment to explore the dynamic of water quality and the shift of bacterial communities during the initial stage of the RAS ecosystem to maintain the stability of the system. According to the result, the dissolved oxygen concentration maintained at 5.63 to 10.22 mg·L−1 in aquaculture water, and electrical conductivity increased by 100% to over 800 μs·cm−1. High-throughput sequencing showed that the abundance and diversity of the bacterial communities in sediment samples were significantly higher than in water samples, and the Proteobacteria, Bacteroidetes, Cyanobacteria, and Actinobacteria were dominant phyla in all samples. The relative abundance of ammonia-oxidizing archaea, ammonia-oxidizing bacteria, and nitrite-oxidizing bacteria was lower than 0.10, but rising. Redundancy analysis suggested that TOC, EC, NO3−, and NO2− were the most important factors shaping the bacterial communities in aquaculture water. Our studies assessed the RAS with ecological ponds for the first time based on water quality parameters and bacterial communities, which indicates that decomposition capacity is insufficient but improved at the initial stage of the operation, and potential risks like eutrophication require attention.
Bioleaching is a promising technology to remediate sediments contaminated by heavy metals. However, the complex heterogeneities of the sediments can reduce the acidification efficiency and the heavy metal removal rate, thus hindering the practical application of sediment bioleaching. This experiment conducted comparative bioleaching experiments between the inoculated group (average leaching percentages: Cu 67.64%; Zn 54.44%; Ni 29.59%) and the non-inoculated control group (Cu 37.10%; Zn 41.04%; Ni 19.89%) on 28 sediments characterized by different physicochemical properties to explore the key factors influencing bioleaching. The results indicated that the bioleaching process was predominated by the indigenous bioleaching bacteria and the bioleaching inoculum, respectively. The ACCpH=4 (acid-consuming capacity), TOC (total organic carbon), and TN (total nitrogen) of the sediments played an essential role in influencing the microbial community structure and bioleaching performance: the ACCpH=4, as the inhibitive factor, could influence the succession growth of the indigenous bioleaching bacteria and the inoculum during the bioleaching process, while the TOC and TN, as the contributing factor, could influence the metabolism of the indigenous bioleaching bacteria. Based on these results, the bioleaching process was improved with the classification and pretreatments of sediment to realize successful bioleaching of all types of the sediments examined in this research.
PurposeThis research attempts to describe the partitioning pattern of metals with particle size distribution and to reveal its underlying mechanisms in natural sediments, in order to explain the variability of metal spatial patterns and its potential environmental implications at a large spatial scale.Materials and methodsA set of individual sediment samples from two shallow lakes was separated into size-grouped particles ranging from 1 to 50 μm and was analyzed to determine the concentrations of iron (Fe) oxides, aluminum (Al) oxides, arsenic (As), chromium (Cr), copper (Cu), zinc (Zn), lead (Pb), and cadmium (Cd). The adsorption isotherms of the metals on sediments, with Cu and Pb as representatives, were used to explain the underlying mechanisms of this proposed exponential partitioning pattern.Results and discussionThe ranges of trace metals in sediment samples are 18.0–40.3 mg kg−1 for As, 81.3–141.4 mg kg−1 for Cr, 18.2–33.7 mg kg−1 for Cu, 74.7–249.1 mg kg−1 for Zn, 23.2–47.4 mg kg−1 for Ni, 22.0–51.4 mg kg−1 for Pb, and 0.20–0.70 mg kg−1 for Cd. We propose the equation cx = c0 + cmexp(− kdx), in which the metal concentration (cx) of sediment particles decreases exponentially with increase in particle size (x). The c0 is a constant based on the background concentration, cm represents the maximum metal concentration of the finest particles reflecting metal pollution degree, and kd is a constant describing the decrease rate with particle size (x). The partitioning amount is proportional to the sorption affinity of particles, which is a comprehensive parameter dependent on the amount of metal adsorbents including organic matter, Fe, and Al (hydr)oxides contained in particles.Conclusion
The exponential equation separated the affecting factors of metal concentration into metal pollution level and particle size with environmental implications. This partition pattern can be well explained by adsorption isotherms conducted on size-fractionated particles.
Preliminary experimental results on the solification/stabilzation of dredged marine sediments (MS) and the non-metallic fraction of automotive shredder residues (NMASR) with coal fly ashes (CFA) are reported. Lab scale experiments of wet granulation at room temperature of these wastes are presented and discussed: cement was used as a binder, while water addition was dosed to optimize granules amount and size.
The obtained granules were then subjected to standard leaching tests according to Italian regulation. The results of the leaching tests showed, for all the experimented wastes, a good level of stabilization: heavy metals and ions content was within the limits provided by Italian regulation for landfill disposal as not dangerous waste, while a COD content exceeding the above mentioned limit was detected. This was attributed to plastics and an organic contamination by vehicles fluids in the case of NMASR, and to sulphides and iron content in the case of marine sediments.
Heavy metals are stable and persistence environmental contaminant of marine sediments. The vast increase in population growth, urbanisation and industrialisation leads to increase in of marine discharges, which results in total loads of pollutants being delivered to the sea. Heavy metal pollution in aquatic environment and subsequent uptake in food chain by aquatic organisms and humans put public health at risks. However, even at lower concentrations heavy metals like Cd, Hg, Cr and Pb may exhibit extreme toxicity under certain condition. Thus, this makes regular monitoring of aquatic environment to be more imperative and necessary. This paper therefore, review the occurrence of heavy metals and various speciation methods used for heavy speciation in soil and sediments.
This review presents developments and applications in bioleaching and mineral biooxidation since publication of a previous mini review in 2003 (Olson et al. Appl Microbiol Biotechnol 63:249-257, 2003). There have been discoveries of newly identified acidophilic microorganisms that have unique characteristics for effective bioleaching of sulfidic ores and concentrates. Progress has been made in understanding and developing bioleaching of copper from primary copper sulfide minerals, chalcopyrite, covellite, and enargite. These developments point to low oxidation-reduction potential in concert with thermophilic bacteria and archaea as a potential key to the leaching of these minerals. On the commercial front, heap bioleaching of nickel has been commissioned, and the mineral biooxidation pretreatment of sulfidic-refractory gold concentrates is increasingly used on a global scale to enhance precious metal recovery. New and larger stirred-tank reactors have been constructed since the 2003 review article. One biooxidation-heap process for pretreatment of sulfidic-refractory gold ores was also commercialized. A novel reductive approach to bioleaching nickel laterite minerals has been proposed.
Nonlinear dynamic rolling forces in the vertical and horizontal directions are, respectively, established, considering the impact of vertical and horizontal directions vibration of rolls. Then a vertical-horizontal coupling nonlinear vibration dynamic model of rolling mill rolls is proposed, based on the interactions between this dynamic rolling force and mill structure. The amplitude-frequency equations of the main resonance and inner resonance are carried out by using multiple-scale method. The characteristics of amplitude frequency under nonlinear stiffness, damping, and amplitude of the disturbance are obtained by adopting the actual parameters of 1780 rolling mills. Finally, the bifurcation behavior of the system is studied, and it is found that many dynamic behaviors such as period, period-3 motion, and chaos exist in rolling mill, and this behavior could be restrained effectively by choosing proper system parameters.
Biosorption is a physico-chemical and metabolically-independent process based on a variety of mechanisms including absorption, adsorption, ion exchange, surface complexation and precipitation. Biosorption processes are highly important in the environment and conventional biotreatment processes. As a branch of biotechnology, biosorption has been aimed at the removal or recovery of organic and inorganic substances from solution by biological material which can include living or dead microorganisms and their components, seaweeds, plant materials, industrial and agricultural wastes and natural residues. For decades biosorption has been heralded as a promising cost-effective clean-up biotechnology. Despite significant progress in our understanding of this complex phenomenon and a dramatic increase in publications in this research area, commercialization of biosorption technologies has been limited so far. This article summarizes existing knowledge on various aspects of the fundamentals and applications of biosorption and critically reviews the obstacles to commercial success and future perspectives.
The ability of heavy metals bioaccumulation to cause toxicity in biological systems—human, animals, microorganisms and plants—is an important issue for environmental health and safety. Recent biotechnological approaches for bioremediation include biomineralization (mineral synthesis by living organisms or biomaterials), biosorption (dead microbial and renewable agricultural biomass), phytostabilization (immobilization in plant roots), hyperaccumulation (exceptional metal concentration in plant shoots), dendroremediation (growing trees in polluted soils), biostimulation (stimulating living microbial population), rhizoremediation (plant and microbe), mycoremediation (stimulating living fungi/mycelial ultrafiltration), cyanoremediation (stimulating algal mass for remediation) and genoremediation (stimulating gene for remediation process). The adequate restoration of the environment requires cooperation, integration and assimilation of such biotechnological advances along with traditional and ethical wisdom to unravel the mystery of nature in the emerging field of bioremediation. This review highlights better understanding of the problems associated with the toxicity of heavy metals to the contaminated ecosystems and their viable, sustainable and eco-friendly bioremediation technologies, especially the mechanisms of phytoremediation of heavy metals along with some case studies in India and abroad. However, the challenges (biosafety assessment and genetic pollution) involved in adopting the new initiatives for cleaning-up the heavy metals-contaminated ecosystems from both ecological and greener point of view must not be ignored.
The efficiency and mechanism of nano-hydroxyapatite (nHA) in immobilizing Pb and Cd in contaminated soil were assessed in this work. The X-ray diffraction analysis indicated that the key mechanisms for Pb/Cd immobilization in the soil involve both surface complexation on the surface of nHA and dissolution of the nHA amendments and precipitation of Pb/Cd-containing phosphates. We tested the effects of different nHA dose (the molar ratio of P/(Pb+Cd)) on the water extraction of heavy metals, and phytoavailability of soil metals. The nHA application could significantly reduce water soluble Pb with 72% and Cd with 90%, bioaccessible Pb with a reduction of 12.5-27.5% and Cd with a reduction of 17.66-34.64%, respectively. The nHA reduced phytoavailability of Pb and Cd with 65.3% and 64.6% in contaminated soil, respectively. In addition, the treatment efficiency increased along with the nHA dose (based on the molar ratio of P/(Pb+Cd)) increased, and most effective ratio was molar ratio of P/(Pb+Cd) at 5:1. The results in this study showed that nHA can immobililize Pb and Cd in contaminated soil effectively.
Bioleaching of metal sulfides is performed by a diverse group of microorganisms. The dissolution chemistry of metal sulfides follows two pathways, which are determined by the mineralogy and the acid solubility of the metal sulfides: the thiosulfate and the polysulfide pathways. Bacterial cells can effect this metal sulfide dissolution via iron(II) ion and sulfur compound oxidation. Thereby, iron(III) ions and protons, the metal sulfide-attacking agents, are available. Cells can be active either in planktonic state or in forming biofilms on the mineral surface; however, the latter is much more efficient in terms of bioleaching kinetics. In the case of Acidithiobacillus ferrooxidans, bacterial exopolymers contain iron(III) ions, each complexed by two uronic acid residues. The resulting positive charge allows an electrostatic attachment to the negatively charged pyrite. Thus, the first function of complexed iron(III) ions is the mediation of cell attachment, while their second function is oxidative dissolution of the metal sulfide, similar to the role of free iron(III) ions in non-contact leaching. In both cases, the electrons extracted from the metal sulfide reduce molecular oxygen via a redox chain forming a supercomplex spanning the periplasmic space and connecting both outer and inner membranes. In this review, we summarize some recent discoveries relevant to leaching bacteria which contribute to a better understanding of these fascinating microorganisms. These include surface science, biochemistry of iron and sulfur metabolism, anaerobic metabolism, and biofilm formation. The study of microbial interactions among multispecies leaching consortia, including cell-to-cell communication mechanisms, must be considered in order to reveal more insights into the biology of bioleaching microorganisms and their potential biotechnological use.
Bottom sediments in coastal regions have been considered the ultimate sink for a number of contaminants, e.g., toxic metals. In this current study, speciation of metals in contaminated sediments of Oskarshamn harbor in the southeast of Sweden was performed in order to evaluate metal contents and their potential mobility and bioavailability. Sediment speciation was carried out by the sequential extraction BCR procedure for As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn and the exchangeable (F1), reducible (F2), oxidizable (F3), and residual (R) fractions were determined. The results have shown that Zn and Cd were highly associated with the exchangeable fraction (F1) with 42-58 % and 43-46 %, respectively, of their total concentrations in the mobile phase. The assessment of sediment contamination on the basis of quality guidelines established by the Swedish Environmental Protection Agency (SEPA) and the Italian Ministry of Environment (Venice protocol for dredged sediments) has shown that sediments from Oskarshamn harbor are highly contaminated with toxic metals, especially Cu, Cd, Pb, Hg, As, and Zn posing potential ecological risks. Therefore, it is of crucial importance the implementation of adequate strategies to tackle contaminated sediments in coastal regions all over the world.
An account is presented of a series of investigations and collaborative studies, initiated by BCR, on current methods of metal speciation by extraction of soils and sediments with chemical reagents. It was established by extensive consultation with European experts that the diverse procedures used could be harmonized into agreed methods. These methods, including both single extractant and sequential extraction procedures were subjected to collaborative, interlaboratory trials and the results, presented briefly here, showed that it was both possible and desirable that reference soils and sediments, characterised by certified values for extractable contents, be prepared. As a consequence of these studies two soils have been prepared and will shortly be the subject of interlaboratory analysis with a view to certification of their EDTA and acetic acid extractable contents of some heavy metals. Following this workshop a feasibility study of the agreed sequential extraction procedure will, it is believed, shortly lead to certification of sediments for contents extractable by a defined sequential extraction procedure.
Most sediment dredged in Italian harbours is discharged into coastal areas. Italian legislation provides physical and chemical characterisations of dredged material. However, to determine whether materials are discharged to a dumping site, used for coastal nourishment or other beneficial use, toxicological assessment should be required. In 1995, 12 sediment cores were taken from dredged areas of Viareggio harbour (Tyrrhenian coast). Nine superficial sediments were collected in two coastal areas: a disposal site and a potential nourishment site. Particle size, total organic matter, heavy metals, polycyclic aromatic hydrocarbons and polychlorinated biphenyls were analysed. In order to assess sediment toxicity and evaluate the best destination, three bioassays were performed on two harbour and one offshore superficial samples using Vibrio fisheri, Corophium volutator and larvae of Crassostrea gigas.
The different harbour areas showed an increase of contaminant levels from the entrance to the inner zones. A comparison of sediment quality of the harbour and coastal areas (physical, chemical and ecotoxicological characteristics) suggested that materials dredged from different areas should be handled in different ways depending on contaminant types and loads. Dredged sediments could be dumped off-shore without decontamination or further use, used to build up eroded areas or be subjected to on-site decontamination treatment.
This study deals with laboratory-scale investigations to evaluate the efficiency of different chemical leaching agents (i.e. sulfuric, oxalic and citric acids) and bioleaching processes (based on different acidophilic bacterial strains) on the mobilisation of metals/semi-metals in contaminated harbour sediments. A simplified life-cycle assessment was also performed in order to compare the investigated strategies in terms of their main environmental impacts. The different chemical leaching agents provided different extraction efficiencies of toxic metals. Among the investigated chemical leaching agents, citric acid 0.5 M and sulfuric acid pH 2 were the most effective, with average mobilisation efficiencies of 30% for Zn and Cr, 40% for Ni, and 35 and 58% for As, under citric and sulfuric acid, respectively. Similar higher extraction efficiencies of metals were also observed in bioleaching experiments with the presence of ferrous iron. The life-cycle assessment revealed that treatments based on diluted sulfuric acid are a better option considering both resource requirements and emissions, leading to lower environmental impacts compared with the other treatment strategies. Overall results from this study provide new insights for the definition of the most efficient and environmentally friendly strategies to be used for dredged sediments contaminated with metals.
The Microbial hydrometallurgy and microbial mineral processing of metal sulphides is currently a well established
technology. Over past years there has been a huge amount of developments with regards to the understanding of its both
engineering perspective as well as fundamental approach with regards to the microorganisms. The huge diversity of the
microorganisms, which has come into picture over the years of research and development have made the engineers to go
beyond several limitations of working temperature to salt tolerance of the microorganisms in harsh conditions to deliver
better technologies for the future operative plants. Today scientists have been able to deliver the various mechanisms
involved in bioleaching but still there are facets to be really understood and more importantly on the front how lab scale
research can be turned out into full scale operation by scaling up the research and optimizing the engineering aspects of the
research. Most of the bioleaching operation has shown their productivity in commercial application of refractory gold
concentrates using mesophilic microorganisms followed by the cyanide leaching to recover optimum amount of gold with an
environment friendly method compared to the conventional method of roasting. Research in the area of chalcopyrite
bioleaching is still continuing o solve the mysteries of jarosite precipitation and formation of passivation layer, which
inhibits the copper recovery in a heap leaching of chalcopyrite by biological methods. Use of extreme thermophiles in
chalcopyrite bioleaching is making a revolutionary movement to solve the mystery behind the scaling up the process, which
could be possible to be solved in future. Bioleaching with other sulphide minerals together with Acid Mine Drainage (AMD)
mitigation, which is a serious concern today, is taking is taking shape today in order to cater the needs of the mankind.
However the biohydrometallurgy research seems to contribute to a greater extent in framing environmental friendly process
with regards to hydrometallurgical operations in future and establish a developed technology to benefit human beings needs
by its upcoming research and development.
Keywords: Biomining, refractory gold, copper, chalcopyrite, bioleaching, nickel sulphide, biooxidation, acid mine drainage
Filamentous fungi and lithotrophic bacteria were used to leach heavy metals from dredged sediments in semi-pilot scale air-lift bioreactors. A preliminary physico-chemical characterization of the sediments comprising a sequential extraction study revealed their high metallic contamination and a predominant association of the metals with sulphides and organic matter. The mobility of heavy metals from sediments was ranked by decreasing order as follows: Mn > Zn > Cd > Cu > Pb. The conditions that favoured the solubilization of heavy metals by filamentous fungi turned out to be also favourable for the activity of the sediment organotrophic bacteria. The latter produced organic acids under temporary hypoxic conditions and resulted in the solubilization of 77% of manganese, 44% of zinc, 12% of copper, and less than 2% of cadmium or lead. In general, the fungal organotrophic treatments were limited to the relatively mobile metals due to the weak nature of the organic acids produced and to their microbial consumption under limited saccharose conditions. The lithotrophic treatments yielded higher solubilization results than the organotrophic experiments. Sulphur resulted in a faster, and for some metals such as copper and cadmium, in better bioleaching results compared with reduced iron or with a combination of reduced iron and sulphur. The bioleaching percentages varied between 72 and 93% for cadmium, copper, manganese and zinc, except for lead because of the poor solubility of lead sulphate. The sediment's lithotrophic bacteria acidified the matrix through sulphur oxidation, and leached both loosely and tightly bound metals.
The present study was aimed at assessing the per-formance of different nonliving macrophytes sampled in the Adriatic coast in arsenic(V) sorption. Full factorial experiments were carried out where the main factors were the macrophyte species (brown algae: Cystoseira, Dictyopteris, and Eisenia; green algae: Caulerpa and Ulva; red algae: Ceramium, Gracilaria, and Porphyra; and seagrass: Zostera), biosorbent washing pre-treatment (deionized water, acid pH 2 and basic pH 10), equilibrium pH (in the range 1 to 8), under relatively high (10 mg L −1) and relatively low (100 μg L −1) arsenic concentration. All species exhibited significant adsorption. Indeed, they showed a good performance, with the highest observed value of about 1.3±0.1 mg g −1 for the red alga Ceramium and the seagrass Zostera, comparable with those of activated carbon and other low-cost adsorbents reported in the literature under similar experimental conditions. Moreover, red algae known in the literature to be bad cationic metal sorbents showed very good arsenic sorption performance. This work shows that the performance of arsenic biosorption depends on many factors: the different composition and struc-ture of outer layer of the macrophytes, arsenic speciation and functional group availability under different pH, and eventual counter-ion interactions with arseniate.
The removal of heavy metals from contaminated river sediments was studied using suspension leaching under laboratory conditions and percolation leaching in a pilot plant. The leaching potential of indigenous sulfur-oxidizing bacteria was compared with acid treatment. Bioleaching with elemental sulfur as substrate was found to be better than treatment with sulfuric acid for the solubilization of all metals tested. The physical and chemical properties of the sediments used in this study did not affect leaching capacity under optimum conditions in the laboratory.
Under the practical conditions in the pilot plant, the redox state of sludge had a considerable influence on leaching efficiency. In a deposited oxic sediment with good permeability, about 62% of the metals tested were removed by percolation leaching after 120 days. Zn, Cd, Ni, Co and Mn were sufficiently leached to enable treated sediments to be reused as soil. In a freshly dredged anoxic sediment, only a total of 9 % of metals were removed. The results indicate that freshly dredged sediments need to undergo pretreatment before percolation leaching to improve mass transfer and to activate the leaching active bacteria.
The effects of sulfur concentration on the bioleaching of heavy metals from the sediment by indigenous sulfuroxidizing bacteria were investigated in an air-lift reactor. Increasing the sulfur concentration from 0.5 to 5 g/l enhanced the rates of pH reduction, sulfate production and metal solubilization. A Michaelis-Menten type equation was used to explain the relationships between sulfur concentration, sulfate production and metal solubilization in the bioleaching process. After 8 days of bioleaching, 97-99% of Cu, 96-98% of Zn, 62-68% of Mn, 73-87% of Ni and 31-50% of Pb were solubilized from the sediment, respectively. The efficiency of metal solubilization was found to be related to the speciation of metal in the sediment. From economical consideration, the recommended sulfur dosage for the bioleaching of metals from the sediment is 3 g/l.
Management of contaminated sediments, i.e. linking risk assessment and problem solutions, needs both quality criteria respecting recent findings on the bioavailability of pollutants and in-depth knowledge on processes controlling their particular hydrological and biogeochemical dynamics.
To understand bioavailability is the key issue for managing contaminated sediments. Therefore, scrutiny of the geochemical situation, toxicity, and biodegradability is needed. The first part of this review refers to the new insights into ‘diagenetic’ mechanisms on particles including ageing and their effects on biological interactions.
Chemical and physical methods are described to quantify the retarded desorption behaviour of hydrophobic organic substances and toxic metals. Results of analyses on the extractability of particle-bound pollutants (e.g. solid phase micro-extraction) can be correlated with the bioavailability. Some techniques recently developed to mimic bioavailabilty are briefly summarised. As can be derived from this review, there is a clear need to refine bioavailability models including equilibrium partitioning.
A set of bioassays is a powerful supplement to assess sediment quality. Consequently, a paradigm shift should be initiated for the evaluation of biological data. All information of a survey have to be implemented in an assessment scheme. Multivariate statistics and fuzzy mathematics provide promising means to interpret multiple data pattern.
The leaching characteristics of zinc and lead in two contaminated sediments were studied, and the effect of low molecular weight organic acids (LMWOAs) and pH value on the leaching of zinc and lead from two contaminated sediments were examined. The results showed that zinc and lead in the sediments were partly dissolved by three LMWOA solutions under different concentrations in batch experiment. The leaching of heavy metals from two sediments followed the descending order: citric acid > malic acid > tartrate acid (for zinc); citric acid > tartrate acid > malic acid (for lead). The leaching concentrations of heavy metals in solution were enhanced with the increasing of LMWOA concentration and the decreasing of pH value. In addition, all LMWOAs leached more heavy metals than inorganic salt did. The leaching capability under the condition of LMWOAs followed the order: zinc > lead.
Three laboratory experiments investigating the feasibility of extracting lead from saturated Norwegian marine clay by electrokinetic remediation is presented. Cylindrical specimens of 10 cm in diameter and 5 cm in length were treated under constant direct current with electrodes placed at each side of the specimens in a liquid. Electrokinetic remediation enhancement techniques were also investigated by using acetic acid depolarization of the cathode reaction and an ion-selective membrane that veils hydroxyl ion back-transport at the cathode. The results were compared with electrokinetic remediation without enhancement after 52 days of treatment.
This article outlines the important biogeochemical roles that fungi play in the degradation, utilization, and transformation of organic and inorganic substrates. Fungal populations are intimately involved in biogeochemical transformations at local and global scales and such processes have major implications for other aspects of living organisms, notably plant productivity and human health. While most prior attention has focused on carbon and nitrogen cycling, the involvement of fungi in almost all other elemental cycles is emphasized. Of special significance are the mutualistic relationships with phototrophic organisms, lichens (algae, cyanobacteria) and mycorrhizas (plants). Some of these fungal transformations have beneficial applications in environmental biotechnology, for example, in metal leaching, recovery and detoxification, and xenobiotic and organic pollutant degradation. Adverse effects may also result when these processes are associated with the degradation of foodstuff, natural products, and building materials.
Most sediment dredged in Italian harbours is discharged into coastal areas. Italian legislation provides physical and chemical characterisations of dredged material. However, to determine whether materials are discharged to a dumping site, used for coastal nourishment or other beneficial use, toxicological assessment should be required. In 1995, 12 sediment cores were taken from dredged areas of Viareggio harbour (Tyrrhenian coast). Nine superficial sediments were collected in two coastal areas: a disposal site and a potential nourishment site. Particle size, total organic matter, heavy metals, polycyclic aromatic hydrocarbons and polychlorinated biphenyls were analysed. In order to assess sediment toxicity and evaluate the best destination, three bioassays were performed on two harbour and one offshore superficial samples using Vibrio fisheri, Corophium volutator and larvae of Crassostrea gigas.
The search for cheap and environmentally friendly materials is essential for remediation of heavy-metal-contaminated agricultural soils. A pot experiment was undertaken to evaluate the application of rice straw and filamentous fungus Penicillium chrysogenum (P. chrysogenum) on the fractionation of copper (Cu) and cadmium (Cd), soil microbial properties, and Cu and Cd uptake by romaine lettuce (Lactuca sativa) in a contaminated agricultural soil. Rice straw was applied at three rates (0, 7.8, and 11.7 g kg−1 soil), and in combinations with P. chrysogenum (1.0 × 106 spores g−1 soil). It was found that the combined treatment of rice straw and P. chrysogenum significantly decreased the acid-extractable Cu and Cd by 15.4–25.1% and 20.2–27.3%, and increased the oxidizable Cu and Cd by 16.1–18.0% and 72.1–98.4%, respectively. Soil microbial biomass and fresh weight of lettuce were also remarkably enhanced after rice straw plus P. chrysogenum addition. Rice straw combined with P. chrysogenum was more effective in reducing Cu and Cd uptake by lettuce than rice straw alone. The joint application of rice straw and P. chrysogenum remarkably reduced Cu and Cd concentrations in lettuce shoots by 13.6–21.9% and 32.9–41.7%, respectively. These results indicate that the combined application of P. chrysogenum and rice straw is a promising method to alleviate the bioavailability of metals, and to improve soil microbial properties and plant yield in heavy-metal-polluted agricultural soils.
Economic and environmental assessments of products are commonly performed at product level in a comparative way to identify possible improvement solutions. The problem with this approach is that introduction of new technologies leads to increased functionality that alters the economic and environmental impacts. In addition, a growing market leads to the demand for higher volume of products. When these factors are combined, overall increase in economic and environmental impacts occurs in the society even though improvements were made at product level. Therefore, this research article proposes a new approach to product assessment to cater for technology changes and increasing volume. Using Axiomatic Design Theory, the drivers of economic and environmental impacts are identified by characterising these impacts as a function of product features. The assessment method is applied for a range of functionality and increasing volume to determine the total economic and environmental impact caused in society. Furthermore, ratio analysis is used to determine the economic and environmental impact changes over product generations to identify additional environmental improvements needed to reach target score. The methodology is validated using a comparative case study of different battery technologies for a range of functionality and assumed volume increase in the next generation of batteries to be produced.
The aim of the current work is to develop an environmentally friendly process for the removal of heavy metals (Cu, Zn, Ni, Cd, Al, Cr, Pb) from recycling industry electronic waste with a consortium of Sulfobacillus thermosulfidooxidans and Thermoplasma acidophilum. The performances of commercial S0 powder and biogenic S0 sludge as substrates for the bio-removal of heavy metals were compared. Empirical models for the bioleaching process based on a statistical analysis were developed to evaluate the individual and combined effects of critical variables including S0 dosage, particle size, pulp density and bacterial feed formulation (inoculum size and inoculation style) in shaken flasks while specifying the effective variable ranges. Upscale feasibility experiments in a stirred tank reactor demonstrated a maximum metal bio-removal efficiency (92%) at a 1% dosage of biogenic S0 sludge and 2% dosage of commercial S0 powder (82%), given a 15% pulp density and 150 μm particle size with an intermittent low-concentration addition of inoculum (1ｘ106 cells/mL). Biogenic S0 sludge showed a higher degree of S0 oxidation (95%) in a shorter time period (12 days) compared to commercial S0 powder (82% in 24 days), thereby reducing the process cost. Risk assessments of discarded electronic wastes before and after bioremediation by the toxicity characteristic leaching procedure (TCLP), waste extraction test (WET), synthetic precipitation test (SPLP) and total threshold limit concentration (TTLC) indicated that the leaching/toxicity of bio-remediated residue was well within the regulatory limits.
