Environmental management for dredging sediments - the requirement of developing nations

Evaluating ecological risks and metal bioavailability in post-dredging sediments of a wetland affected by artisanal gold mining

The evaluation of metal contamination, ecological risk, bioavailability, and the environmental dredging depth in sediments of two Colombian riverine systems impacted by artisanal gold mining and agricultural activities, was conducted following dredging processes. Results indicated significant contamination by Cd and Pb before dredging, based on the contamination factor (CF) and the geoaccumulation index (Igeo). Additionally, Cu and Hg were found to cause adverse biological effects according to sediment quality guidelines. Post-dredging, surface sediments exhibited a moderate ecological risk index (RI, 150-300), primarily due to increased contamination by Hg, Pb, and Cd. To mitigate this ecological risk (RI < 150), the environmental dredging depth needed to exceed 20 cm for all metals. On average, the bioavailable fraction increased 2.3 times within two months after dredging. However, the low environmental risk (%F1 = 1-10) calculated using risk assessment codes (RAC) indicates a potential risk due to metals entering the water column and bioaccumulating in organisms. These findings provide insights into the dynamics of metals and the impact of dredging activities on sediments in the Colombian Caribbean coast affected by various anthropogenic activities. The research underscores the importance of integrating sustainable practices in mining and agriculture to protect the ecological integrity of these riverine systems.

Fugacity model covering abiotic and biotic matrices to investigate the transfer and fate of perfluoroalkyl acids in a large shallow lake of eastern China

Solving the challenges faced during the measurement of the cross-interface transfer of perfluoroalkyl acids (PFAAs) in lakes is crucial for clarifying environmental behaviours of these chemicals and their efficient governance. This study developed a multimedia fugacity model based on the quantitative water-air-sediment interaction (QWASI) covering abiotic/biotic matrices to investigate the cross-interface transfer and fate of PFAAs in Luoma Lake, a typical PFAA-contaminated shallow lake in eastern China. The accuracy and reliability of the established model were confirmed using Percent bias and Monte Carlo simulation, respectively. Using the QWASI model, the multimedia transfer of the PFAAs and their accumulation and persistence in different sub-compartments were described and measured, and the differences among individual PFAAs were explored. The simulation results showed that the sedimentation and resuspension of PFAAs were the most intense cross-interfacial transfers, and the sediments served as a chemical sink in the long term. A significant negative correlation of NC-F (the number of CF bonds) with the relative outflow flux (TW·out-ct) but a positive correlation with the relative net transfer across the interface between water and aquatic plants (Tp-ct) was detected, indicating that the PFAA migration capacity decreased but the bioaccumulation potential increased with the CF bond number. The persistence in water (Pw) of individual PFAAs ranged from 19.65d (PFOA) to 32.22d (PFOS), with an average of 26.15d; their persistence in sediment (Ps) ranged from 432d (PFBA) to 3216d (PFOS), with an average of 1524d, increasing linearly with an increase in NC-F. The water advection flows into and out of the lake (QW·in and QW·out), the PFAA concentration of water inflow (CW·in), and bioconcentration factor of aquatic plants (BCFp) were the primary parameters sensitive to PFAAs in all sub-compartments, which are essential indexes for exploring promising remediation pathways for lacustrine PFAA contamination based on the fugacity model simulation.

Comprehensive assessment of enhancing dewaterability of dredged sediments by starch-based flocculant

Dredged sediment poses significant challenges for transportation and subsequent treatment due to its high water content and large volume. Coagulation, a common method of dewatering, can significantly enhance the dewatering performance of dredged sediment. This study synthesized a cationic starch-based flocculant [starch-3-chloro-2-hydroxypropyl trimethylammonium chloride (St-CTA)] through etherification for the flocculation dewatering of dredged sediment. The effectiveness and mechanism of St-CTA as a dewatering flocculant for dredged sediment were investigated. The results demonstrated that when the dosage of St-CTA was 12 mg g-1 TSS (total suspended solids), the dehydration property of dredged sediment substantially improved, with the specific resistance to filtration (SRF) decreasing by 93.3%, the capillary suction time (CST) by 93.5%, and the water content of the filter cake (WC) by 9.7%. The removal rate of turbidity of the supernatant from the conditioned dredged sediment reached 99.6%, accelerating the settling speed and effectively capturing and separating fine particles from the sediment. St-CTA significantly increased the median particle size (D50), altered the microstructure and extracellular polymeric substances (EPS) of the flocs, and increased the fractal dimension of the flocs, making them more compact and conducive to the formation of drainage channels. These findings confirm the feasibility of using potentially environmentally friendly St-CTA as a rapid dewatering conditioning agent for sediment.

Provenance analyses of silted sediments in Shenzhen Bay: Insights based on rare earth elements and stable isotopes

Shenzhen Bay (SZB) in southern China is a typical eutrophic area, with internal pollution from its sediments representing an important nutrient source. However, the transport paths and sources of sediments in SZB remain unclear, making it difficult to analyze the nutritional budget and propose effective sediment management strategies. To address this, we linked a sediment fingerprinting technique to a Bayesian mixing model (MixSIAR) and conducted provenance analyses. We collected particle samples from SZB sediment and surrounding areas, including the Shenzhen River (SZR), Pearl River Estuary (PRE), and the northern South China Sea (SCS). Two groups of natural tracers were measured to trace different phases of sediments: (1) C and N parameters for the fates of the organic phase of sediments, and (2) rare earth element (REE) patterns for the provenance of mineral fragments. The results showed that the concentrations of total organic C and total N were 0.89-1.44 % and 0.05-0.13 %, respectively. MixSIAR suggested that fluvial inputs from SZR and PRE contributed 46.6 % and 30.3 % of organic matter, respectively. The organic matter in the PRE mainly originated from sewage and the upper reaches of the Pearl River. The concentration range of REEs in SZB sediments was 153.12-480.09 mg/kg with clear enrichment for light REE. MixSIAR results showed that the mineral fragments mainly originated from the outer bay (SCS and PRE, which contributed 57.2 % and 32.7 %, respectively). These results indicate that organic pollution follows a different path from the inorganic base, which is mainly related to anthropogenic input from land. This study highlights that complex sediment transport processes and pollution intrusions from the Pearl River are the issues that must be considered for eutrophication restoration in SZB.

Beneficial use of dredged sediments as a resource for mine reclamation: A case study of Lake Dianchi's management in China

Dredging is one of the most effective methods for inhibiting the endogenous contamination of natural lakes. However, both the amount and the scope of dredging will be restricted if the disposal of the dredged sediment incurs considerable environmental and economic costs. The use of dredged sediments as a post-mining soil amendment for mine reclamation benefits both sustainable dredging and ecological restoration. This study incorporates a field planting experiment with a life cycle assessment to confirm the practical effectiveness of sediment disposal via mine reclamation, as well as its environmental and economic superiority over other alternative scenarios. The results show that the sediment offered plentiful organic matter and nitrogen for mine substrate, stimulating plant growth and increasing photosynthetic carbon fixation density, followed by enhanced plant root absorption and an improved soil immobilization effect on heavy metals. A 2:1 ratio of mine substrate to sediment is recommended to significantly promote the yield of ryegrass while reducing levels of groundwater pollution and soil contaminant accumulation. Due to the significant reduction in electricity and fuel, mine reclamation had minimal environmental impacts on global warming (2.63 × 10^-2 kg CO₂ eq./kg DS), fossil depletion (6.81 × 10^-3 kg oil eq./DS), human toxicity (2.29 × 10^-5 kg 1,4-DB eq/kg DS), photochemical oxidant formation (7.62 × 10^-5 kg NO_x eq./kg DS), and terrestrial acidification (6.69 × 10^-5 kg SO₂ eq./kg DS). Mine reclamation also had a lower cost (CNY 0.260/ kg DS) than cement production (CNY 0.965/kg DS) and unfired brick production (CNY 0.268/kg DS). The use of freshwater for irrigation and electricity for dehydration were the key factors in mine reclamation. Through this comprehensive evaluation, the disposal of dredged sediment for mine reclamation was verified to be both environmentally and economically feasible.

Evaluation of sediment dredging in remediating toxic metal contamination - a systematic review

Toxic metal pollution is a leading environmental concern for aquatic systems globally, and remedial dredging has been widely employed to mitigate its harmful impacts. In terms of the short-term impacts of remedial dredging, mixed results are reported in several studies. Despite its immediate negative impacts including saturation of water with toxic metals, increased turbidity, and sediment resuspension, positive impacts can be recorded over a stabilization period of 6-24 months after dredging. Nevertheless, the sustainability of these recorded positive effects cannot be ascertained as some studies have reported long-term regression in remediated sites' conditions. Evaluation of success determinants, site-measure compatibility, and determination of supplementary measures are keys to achieving and sustaining the projected benefits of remedial dredging and justifying its overall cost. This multicomponent study reviewed published literatures that documented the outcomes of short- and long-term dredging projects in toxic metal-polluted systems globally with a broad goal of examining how sediment removal impacts toxic metal dynamics in the aquatic system and understanding why the sustenance of positive impacts is controversial. In the meantime, this study also explored the preventative and remedial management strategies for attaining and sustaining positive dredging outcomes. The purpose of this study is to provide key recommendations for decision-making and policy development in aquatic toxic metal remediation.

The forgotten ones of ports: The filter feeders at the heart of siltation processes

Siltation is a major concern in dynamic and complex ecosystems, such as ports. The mud must be regularly dredged to avoid disturbing the navigation channels. Sediments are carried by the waters entering the port and are partially trapped by harbour structures. Numerous studies have been conducted on the physical factors influencing siltation in port areas, whereas, few have focused on the role of biotic factors in mud formation. However, research in other contexts has shown that organisms that are abundant in pontoons, such as bivalves and tunicates, play an important role in this siltation process. All of these organisms belong to the filter feeder group. The sediments sucked in by the filter feeders are excreted in the form of faeces or mucus-bound pseudo-faeces. These waste materials, called bioproducts, settle efficiently and are involved in the composition of the mud. This study aimed to highlight the role of filter feeders in the siltation process in port areas and to determine the factors that influence the production of bioproducts by filter feeders. To investigate the role of filter feeders in the siltation processes, an experimental analysis was conducted in the largest marina in Europe (La Rochelle, France). It is divided into four basins with distinct filter feeder communities and environmental conditions, allowing for a detailed study of the environmental factors that influence the production of bioproducts. This analysis consisted of recovering and studying the bioproducts generated by the filter feeders using sediment traps fixed under pontoons. To explore the evolution of this biological production, 16 campaigns were conducted from January to March 2020 and May to July 2020. The total amount of dry matter produced was constant between seasons at approximately 130 g/m²/d; marina-wide, this amount represents a total daily production of 3.2 tons. However, the production amount varies spatially and temporally in relation to marine hydrodynamics and the organisms involved. Bioproduction was taxon-dependent: areas abundant in oysters and mussels were the areas with the most pronounced bioproduction, whereas there was no significant relationship between bioproduction and the presence of tunicates or scallops. If we consider bioproduction on a seasonal scale, we can see that the campaigns with the greatest production correspond to the periods when the sediment supply was the highest, i.e. when the tidal range was the highest. The quality of the bioproducts (organic matter content) differed between seasons, which can be explained by both environmental and metabolic changes. Understanding the role of filter feeders in siltation processes appears to be essential in port environments that need to be regularly dredged to ensure safe navigation.

Biochar as additive for improved building performances and heavy metals solidification of sediment-based lightweight concrete

The sustainable disposal of large volumes of contaminated dredged river sediment has become a challenge for municipal management. In this study, a cutting-edge biochar application method was innovated, which converted the polluted dredged sediment into a low-carbon and environmentally friendly building material through an autoclave-free method. As the amount of biochar addition increased from 0 to 2% (w/w), the compressive strength of the dredged sediment-based lightweight concrete (DS-LC) increased from 3.92 to 4.61 MPa. Accordingly, the thermal conductivity decreased from 0.237 to 0.222 W/(m K), the water absorption decreased by 6%, and the water resistance coefficient increased by 33%. Results of X-ray diffraction (XRD) and thermogravimetric (TG) analysis showed that biochar promoted the hydration reaction and the carbonation process. Scanning electron microscopy (SEM) attached with energy-dispersive X-ray spectroscopy (EDX) showed that biochar addition changed the microstructure of the DS-LCs, which made the pore distribution more uniform and densified. Biochar addition also strengthened the immobilization of heavy metals (Cu, Zn, Cr, and As) by approximately 18-27% and combination of biochar and silica fume could increase the heavy metal immobilization by 28-44%. Compared with the traditional concrete material, the DS-LC with biochar addition could not only reduce the carbon emission but also has potential economic benefit for the treatment and utilization of dredged sediment.

The desorption mechanism of dissolved organic matter on pollutants and the change of biodiversity during sediment dredging

Sediment dredging is an effective means to control the endogenous pollution of lakes, which could significantly change the concentration and composition of organic matter, especially dissolved organic matter (DOM) in the lake. DOM is particularly important for the release of endogenous pollutants, which will inevitably bring an impact on aquatic biodiversity. Nevertheless, in recent research little attention has been paid to the desorption mechanism of DOM on pollutants and the change of biodiversity during dredging. This study investigated the physicochemical properties of DOM in the sediment by taking a sediment dredging project in Dianchi Lake in China for example. The correlations of DOM properties with the desorption behavior of nitrogen (N), phosphorus (P), cadmium (Cd), lead (Pb) and the biodiversity of aquatic organisms were analyzed. The results show that the aromaticity and humification of DOM were improved after dredging, and the high molecular weight DOM was degraded into low molecular weight substance. The desorption amount of N, P and heavy metals (Cd, Pb) were decreased as the pH values increased. Moreover, NH₄⁺-N promoted the release of Pb²⁺ from DOM, while the release of PO₄^3--P was inhibited. Correlation analysis shows that the physicochemical properties of DOM exactly affected the release of N, P, Cd and Pb. It was easier to desorb pollutants with low aromaticity and humification of DOM, leading to a decrease in the diversity of aquatic organisms. This study identified the desorption mechanism of endogenous pollutants in DOM and the ecological risk to aquatic organisms, providing a theoretical basis for the prevention and control of water pollution.

iChip increases the success of cultivation of TBT-resistant and TBT-degrading bacteria from estuarine sediment

Standard methods of microbial cultivation only enable the isolation of a fraction of the total environmental bacteria. Numerous techniques have been developed to increase the success of isolation and cultivation in the laboratory, some of which derive from diffusion chambers. In a diffusion chamber, environmental bacteria in agar medium are put back in the environment to grow as close to their natural conditions as possible, only separated from the environment by semi-permeable membranes. In this study, the iChip, a device that possesses hundreds of mini diffusion chambers, was used to isolate tributyltin (TBT) resistant and degrading bacteria. IChip was shown to be efficient at increasing the number of cultivable bacteria compared to standard methods. TBT-resistant strains belonging to Oceanisphaera sp., Pseudomonas sp., Bacillus sp. and Shewanella sp. were identified from Liverpool Dock sediment. Among the isolates in the present study, only members of Pseudomonas sp. were able to use TBT as a sole carbon source. It is the first time that members of the genus Oceanisphaera have been shown to be TBT-resistant. Although iChip has been used in the search for molecules of biomedical interest here we demonstrate its promising application in bioremediation.

Higher dissolved oxygen levels promote downward migration of phosphorus in the sediment profile: Implications for lake restoration

Lake restoration (typically sediment dredging) commonly involves producing a new sediment-water interface (SWI). This study comprehensively investigated the migration and transformation of P during the formation of a new SWI under different dissolved oxygen (DO) levels in the overlying water, based on Fe/Al-rich sediment. The results suggest that DO had a profound effect on the 0-7 cm sediment layer properties and higher DO levels in the overlying water resulted in the diffusion of DO deeper into the sediments. Importantly, besides preventing Fe reductive dissolution and sulfides competition, higher DO levels inhibited the release of P from sediment by inducing the mitigation of P from the upper (0-3 cm) into the bottom (3-7 cm) sediments. The migration of P was found to be closely related to the interactions between organic matter and Al, Fe, and Ca in the sediment profile caused by higher DO levels in overlying water. Particularly, the decrease in organic matter in the upper sediments increased the mobility of Ca and promoted aging of Al and Fe, which increased the migration of the different forms of P. The increased organic matter in the bottom sediments retained the mobile Ca and increased amorphous Fe, which immobilized the P that had migrated from the upper sediments. These results demonstrate the relatively high mobility of P in the upper sediments and the importance of P immobilization capability of bottom sediments on regulating P release from SWI under higher DO levels in overlying water. Accordingly, measures for lake restoration with producing a new SWI were recommended to be applied in combination with P immobilization method to develop more feasible strategies.

Phosphorus mining from eutrophic marine environment towards a blue economy: The role of bio-based applications

Global phosphorus reserves are under pressure of depletion in the near future due to increased consumption of primary phosphorus reservoirs and improper management of phosphorus. At the same time, a considerable portion of global marine water bodies has been suffering from eutrophication due to excessive nutrient loading. The marine environment can be considered as a valuable phosphorus source due to nutrient rich eutrophic seawater and sediment which could potentially serve as phosphorus mines in the near future. Hence, sustainable phosphorus recovery strategies should be adapted for marine systems to provide phosphorus for the growing market demand and simultaneously control eutrophication. In this review, possible sustainable strategies for phosphorus removal and recovery from marine environments are discussed in detail. Bio-based strategies relying on natural phosphorus uptake/release metabolism of living organisms are suggested as promising options that can provide both phosphorus removal and recovery from marine waters for achieving a sustainable marine ecosystem. Among them, the utilization of microorganisms seems promising to develop novel strategies. However, the research gap for the technical applicability of these strategies is still considerably big. Therefore, future research should focus on the technical development of the strategies through laboratory and/or field studies. Coupling phosphorus mining with other valorisation pathways (i.e., metal recovery, energy production) is also suggested to improve overall sustainability and economic viability. Environmental, economic and societal challenges should altogether be well addressed prior to real scale applications.

Life cycle assessment of cementitious materials based on calcined sediments from Chorfa II dam for low carbon binders as sustainable building materials

This research was carried out to reuse calcined dredged sediments as a sustainable building material to reduce greenhouse gas emissions, and save significant energy consumption and costs. Moreover, the Life Cycle Assessment (LCA) of cementitious materials (cements, pastes, and mortars) based on calcined sediments was studied in order to quantify its energy consumption and Global Warming Potential (GWP). This study demonstrated that this calcined sediment could be used as a partial cement replacement in the cement industry in Algeria. The potential indicators of climate change for cements based on 0%, 5%, 15%, and 25% of calcined sediments release only 935.10 kg CO₂ eq/T, 901.73 kg CO₂ eq/T, 835 kg CO₂ eq/T and 768.29 kg CO₂ eq/T respectively, which represents a significant reduction of 3.57%, 10.70%, and 17.84%, for cement based on 5%, 15%, and 25% of calcined sediment. The potential indicators of climate change for pastes based on calcined sediments at 0%, 5%, 15%, and 25% rates release only 476.95 kg CO₂ eq/T, 459.79 kg CO₂ eq/T, 425.45 kg CO₂ eq/T, and 391.12 kg CO₂/T respectively, which represents a reduction of 3.6%, 10.80%, and 18%. Indeed, the potential indicators of climate change for mortars based on calcined sediments with 0%, 5%, 15%, and 25% rates release only 436.89 kg CO₂ eq/T, 422.00 kg CO₂ eq/T, 393.07 kg CO₂ eq/T, and 364.40 kg CO₂/T respectively, which represents a reduction of 3.41%, 10.03%, and 16.59%. In conclusion, the LCA of cements, mortars, and pastes with a high substitution rate of calcined sediments offer the best reduction in environmental impacts. These results present prospects for industrializing calcined sediments as green building materials in the cement industry.

Development of alternative disposals for waste rice husk and dredged harbor sediment by sintering as lightweight aggregates

This study developed the alternative disposals for dredged harbor sediments by co-sintering with waste rice husk into lightweight aggregates (LWA) to benefit resource sustainability and waste valorization. The effects of rice husk addition and sintering temperature on LWA performances such as water absorption, particle density, crushing strength, weight loss, volume shrinkage, and open porosity were investigated. The key parameters (e.g. C/Fe ratio in raw materials) controlling the LWA performances and engineering applications were determined. Results showed that dredged harbor sediments could be made into suitable LWA for engineering applications from the controlled rice husk addition and sintering temperature. The addition of rice husk led to lower LWA particle density, but raised water absorption and reduced crushing strength. The increase of sintering temperature reduced water absorption and improved crushing strength. The aggregates with 10-15% rice husk, sintered at 1150 °C had appropriate particle density (1.60-1.73 g/cm³), water absorption (11.8-16.6%), and crushing strength (6.0-10.6 MPa), which could be suitable for lightweight concrete applications. Low water-soluble chloride and heavy metals leachabilities aligned with Taiwan's regulatory standards for concrete aggregates. Co-treating waste rice husk and dredged harbor sediment into LWA can benefit the waste reduction and circular economy, and reduce the environmental impacts associated with their disposals.

Combining sediment management and bioremediation in muddy ports and harbours: A review

This paper reviews two important sources of innovation linked to the maritime environment and more importantly to ports: the potential coupling of sediment management and (bio)remediation. The detrimental effects of dredging are briefly considered, but the focus here is on a sustainable alternative method of managing the problem of siltation. This technique consists of fluidizing the sediment in situ, lowering the shear strength to maintain a navigable under-keel draught. Preliminary investigations show that through this mixing, aeration occurs, which results in a positive remediation effect as well. An overview of port contamination, remediation, and the recent research on aerobic (bio)degradation of port contaminants is made in order to show the potential for such innovative sediment management to reduce dredging need and remediate contaminated mud in ports. This review also highlights the lack of full-scale field applications for such potential remediation techniques, that remain largely confined to the laboratory scale.

Research on the efficient water-absorbing ceramsite generated by dredged sediments in Dian Lake-China and coal fly ash

In order to transform the dredged sediment (DS) into an efficient water-absorbing ceramsite (EWAC), the coal fly ash (CFA) and expansion agent were used to blend, expand, and sinter with the DS in the Dian Lake-China. A new type of high EWAC was prepared with the absorption ratio of 66.71%, which was much higher than similar products. The heavy metals leaching (HML) of EWAC showed that the concentration of As was 0.90 mg/L and the Hg, Pb, Cd, and Cr were too low to be detected. The characterization analysis showed that the EWAC cross section contained a lot of hydroxyl, ether, and P-Cl hydrophilic group by Fourier transform infrared (FT-IR), scanning electron microscope (SEM), and Brunauer-Emmett-Teller (BET) specific surface area (SSA) test method. The above groups and structures could greatly improve the water absorption (WA) performance of the EWAC. What's more, the SSA of the EWAC could reach 4.468 m² /g. The results of Comsol Multiphysics indicated that the SSA and average pore size (APS) of the EWACs were 10 and 6 times higher than the commercial ceramsites, respectively. The research provided the utilization of the DS with technical and theoretical basis for the construction of sponge city. PRACTITIONER POINTS: The article was focus on the utilization of dredged sediment (DS) and coal fly ash (CFA) for the basic material preparation technology and its toxicity test as the sponge city. First, the raw materials were the DS in Dian Lake (Kunming, Yunnan, China) and CFA (thermal power plants), which were all belonged to the hazardous solid waste and was made to the efficient water-absorbing ceramsite (EWAC). Second, the water absorption (WA) performance of the EWAC was improved greatly whose absorption ratio was much higher than similar products reached 66.71%. The specific surface area (SSA) and average pore size (APS) of the EWACs were 10 and 6 times higher than the commercial ceramsites (CCs), respectively. Finally, the heavy metals leaching (HML) of As was 0.90 mg/L, and the HML of Hg, Pb, Cd, and Cr was all lower than 0.05 mg/L, which could not only not cause secondary pollution but provide the new ideas for the resource utilization of large amount of DS. So, we thought this article was suitable for the journal.

Port Sediments: Problem or Resource? A Review Concerning the Treatment and Decontamination of Port Sediments by Fungi and Bacteria

Contamination of marine sediments by organic and/or inorganic compounds represents one of the most critical problems in marine environments. This issue affects not only biodiversity but also ecosystems, with negative impacts on sea water quality. The scientific community and the European Commission have recently discussed marine environment and ecosystem protection and restoration by sustainable green technologies among the main objectives of their scientific programmes. One of the primary goals of sustainable restoration and remediation of contaminated marine sediments is research regarding new biotechnologies employable in the decontamination of marine sediments, to consider sediments as a resource in many fields such as industry. In this context, microorganisms—in particular, fungi and bacteria—play a central and crucial role as the best tools of sustainable and green remediation processes. This review, carried out in the framework of the Interreg IT-FR Maritime GEREMIA Project, collects and shows the bioremediation and mycoremediation studies carried out on marine sediments contaminated with ecotoxic metals and organic pollutants. This work evidences the potentialities and limiting factors of these biotechnologies and outlines the possible future scenarios of the bioremediation of marine sediments, and also highlights the opportunities of an integrated approach that involves fungi and bacteria together.

Development of a Dredging Sensitivity Index, applied to an industrialized coastal environment in Brazil

Ports link world commerce via maritime routes, and dredging services are essential to establish and maintain these connections. However, one question is critical when dredging is being considered: where are the best places to do it? To try to answer this question, a Dredging Sensitivity Index (DSI) was developed as a management tool to be used in project planning steps. In order to diminish environmental damages and quality-of-life losses, DSI provides alternatives by identifying sensitivity areas. This new methodology quantifies impacts caused by the sediment removal step and points out favorable areas to dredge, with a simple map. Parameters such as fine-grain content (% < 63 μm), Acid Volatile Sulfides (AVS), Shannon-Wiener Index and fisheries, among others, were used to calculate the DSI. Formulas were used to weight and aggregate both, the parameters and the DSI itself. Sepetiba Bay was chosen to apply this methodology because of its relevant economic and environmental aspects. The methodology was applied to dredging situations, but it can be used to indicate areas for dredged material disposal, with a few modifications in the DSI formulas. A DSI map was a final result of this methodology, and showed that the northern portion of the bay, close to the littoral is a more sensitive area, where dredging should be avoided, or carried out very carefully. DSI is a very useful tool for reducing damages from dredging services, it contributes with zonation and it provides alternatives to decision-makers who manage these areas.

Recycling dredged harbor sediment to construction materials by sintering with steel slag and waste glass: Characteristics, alkali-silica reactivity and metals stability

This work recovered the dredged sediment around Kaohsiung Harbor, Taiwan, for preparing lightweight aggregates (LWA), of which physicochemical properties as affected by the addition of basic-oxygen-furnace (BOF) slag and waste glass were investigated. LWA properties included water absorption, particle density, compressive strength, shrinkage, and microstructure of sintered pellets were evaluated to ensure feasibility of dredged harbor sediment reutilization technique. Results showed that adding appropriate amount of glass powders (~7%) to the mixtures of sediment and slag significantly reduced the water absorption (as low as 2.2%) of the sintered pellets and increase the compressive strength (as high as 23.1 MPa) of LWA, which were found to be controlled by open porosity and shrinkage. Excessive addition of glass (>10%) led to increase in internal pore sizes of the sintered pellets, and thus reduced the compressive strength. The alkali-silica reactivity (ASR) of the LWA was innocuous according to the ASTM C289 test. Sintering and glass addition improved the stability of heavy metal and environmental compatibility of the LWA. The recycling of waste sediment, slag, and glass for LWA production can provide an alternative for the disposal of dredge harbor sediment and has positive impact on waste reduction, which not only can reduce secondary contamination to the environment, but also can contribute to circular economy.

Microbial community shift under exposure of dredged sediments from a eutrophic bay

Microbial communities occur in almost every habitat. To evaluate the homeostasis disruption of in situ microbiomes, dredged sediments from Guanabara Bay-Brazil (GB) were mixed with sediments from outside of the bay (D) in three different proportions (25%, 50%, and 75%) which we called GBD25, GBD50, and GBD75. Grain size, TOC, and metals-as indicators of complex contamination-dehydrogenase (DHA) and esterase enzymes (EST)-as indicators of microbial community availability-were determined. Microbial community composition was addressed by amplifying the 16S rRNA gene for DGGE analysis and sequencing using MiSeq platform (Illumina).We applied the quality ratio index (QR) to the GB, D, and every GBD mixture to integrate geochemical parameters with our microbiome data. QR indicated high environmental risk for GB and every GBD mixture, and low risk for D. The community shifted from aerobic to anaerobic profile, consistent with the characteristics of GB. Sample D was dominated by JTB255 marine benthic group, related to low impacted areas. Milano-WF1B-44 was the most representative of GB, often found in anaerobic and sulfur enriched environments. In GBD, the denitrifying sulfur-oxidizing bacteria, Sulfurovum, was the most representative, typically found in suboxic or anoxic niches. The canonical correspondence analysis was able to explain 60% of the community composition variation and exhibit the decrease of environmental quality as the contamination increases. Physiological and taxonomic shifts of the microbial assemblage in sediments were inferred by QR, which was suitable to determine sediment risk. The study produced sufficient information to improve the dredging plan and management.

Sediment management in coastal infrastructures: Techno-economic and environmental impact assessment of alternative technologies to dredging

The presence of anthropic activity in the coastal or riverine environment modifies the wave as well as the water and sediment current regime. In particular, the body of water around ports is an area where intense currents and sediment transport rates are usually present and can be affected by low water velocities that take place close to the entrance and inside the port basin. Consequently, sediment can be entrained and accumulated in such areas, creating problems to navigation. Ports and moorings are filled with fine sediments due to deposition resulting from solid transport. In particular, silt particles settle because of the weak vertical and lateral shearing of the velocity field. The result is that harbours frequently require ordinary maintenance dredging. The dredging process involves the removal of sediment in its natural deposited condition by using either mechanical or hydraulic equipment. Dredging is a consolidated and proven technology, but involves considerable drawbacks. In particular, dredging has a notable environmental impact on marine flora and fauna, contributes to the mobility and diffusion of contaminants and pollutants already present in the silted sediments, obstructs navigation and is characterized by relatively high and low predictable costs. This paper aims to provide an original structured overview of technologies alternative to dredging that have been tested in the past 50 years. More than 150 articles have been analysed to compare standard dredging technologies with market-ready competitors from techno-economic and environmental perspectives. In particular, the paper focuses on anti-sedimentation infrastructures and on innovative plant solutions characterized by low maintenance costs and by a very limited environmental impact. The final aim of the paper is to describe the currently available technologies that prevent port inlet and channel siltation and to classify them through a techno-economic and environmental impact assessment. The comparison shows that dredging has both the higher costs and environmental impact, while fixed sand by-passing plants are characterized by the lowest environmental impact and operation costs that are competitive with dredging.

Microbial community activity in response to multiple contaminant exposure: a feasible tool for sediment quality assessment

Sediments represent complex mixtures and the impacts of their physical and chemical processes on biota are important for assessing potential health risks. We aimed to rank sediment samples from Guanabara Bay by developing an algorithm (quality ratio-QR), focusing on key sediment parameters (fine grain size, total organic carbon (TOC), metal concentrations) and enzymatic activities (dehydrogenase (DHA-energy production into cell) and esterases (EST-hydrolase organic matter outside the cell membrane)) of in situ microbial communities. Our QR is supported by quantitative information and significant correlations between geochemical and microbial processes. The QR is a function of the dependent term DHA/EST and the geochemical term (TOC×∑CF)/fine-grained sediment, where ∑CF is the sum of contamination factors (ratio between actual and background metal concentrations). We could rank our sampling sites into three risk classes based on QR: low, medium, and high. Our findings suggest altered homeostasis due to the development of contamination resistance. We applied a sensitivity analysis, using Brazilian law for sediment quality assessment, to calibrate our risk index. Our QR is suitable for measuring the potential health risk of any sediment, especially in developing countries with serious technical limitations, since its evaluated parameters are cheap, fast, and easy to obtain.

Framework for determining optimal strategy for sustainable remediation of contaminated sediment: A case study in Northern Taiwan

Contaminated sediment may pose a serious threat to human health and ecosystems. However, sediment remediation is typically an expensive and time-consuming process. Therefore, an effective decision-making process for the remediation of contaminated sediment is essential for identifying the optimal approach. Since a single assessment for sediment remediation may be insufficient, combining different analytical approaches is highly recommended. The objective of this study was to develop a comprehensive assessment framework based on the concept of green and sustainable remediation that considers various environmental, economic, and social aspects for the management of contaminated sediment. We propose a framework based on human health risk assessment (HHRA) and cost-benefit analysis (CBA) and apply the multicriteria decision analysis (MCDA) technique to implement integrated and sustainable strategies for sediment management. We used the framework to determine the best alternative for managing heavy-metal-contaminated sediment in a river in Northern Taiwan. The results of the pre-remediation HHRA indicated an unacceptably high cancer risk to children, while the CBA revealed that a remediation project was economically feasible. Moreover, the results of the MCDA revealed that a strategy involving in-situ capping with anthracite-based activated carbon would be relatively inexpensive and result in low risk to human health. In addition, this strategy would have a higher environmental impact and greater public acceptance as compared to a method involving the dredging and washing of soil. Thus, in this case study, in-situ capping using anthracite-based activated carbon was identified as the preferable remediation alternative from multiple perspectives. The proposed framework should allow decision-makers to choose the optimal integrated management strategy for similar river sites with contaminated sediment.

Screening-level risk assessment applied to dredging of polluted sediments from Guanabara Bay, Rio de Janeiro, Brazil

Guanabara Bay is characterized by predominant eutrophication and anoxic sediments with a mixture of pollutants. The risk prognosis associated with the dumping of its dredged sediments into the open ocean was addressed by our algorithm. Our algorithm could prioritize areas, characterize major processes related to dredging, measure the potential risk of sediments, and predict the effects of sediment mixing. The estimated risk of dredged sediment was >10-fold than that of ocean sediments. Among metals, mercury represented 50-90% of the total risk. The transfer of dredged material into the ocean or internal dumping in the bay requires a 1:10 dilution to mitigate the risk and bring the risk levels close to that in the EPA criteria, below which there is less likelihood of adverse effects to the biota, and a 1:100 dilution to maintain the original characteristics of the ocean disposal control area. Our algorithm indicator can be used in the design of both aquatic and continental disposal of dredged materials and their management.

Selection of an appropriate management strategy for contaminated sediment: A case study at a shallow contaminated harbour in Quebec, Canada

Harbours, as strategic places in tourism and transportation, are exposed to many sources of contamination. Assessing the quality of harbours sediment by guidelines and regulations does not reflect the actual level of contamination and the risk posed to aquatic ecosystems. Selection of an appropriate management technique for contaminated sediments in those strategic locations is crucial for the aquatic environment. The purpose of this study is to show that insufficient information, provided by sediment quality guidelines (SQGs) to identify the actual contaminants, could lead to a destructive or potentially ineffective decision for risk reduction in contaminated harbours. A comprehensive evaluation on physicochemical characteristics of sediment and water samples of a shallow harbour in St. Lawrence River was performed. Results of trace metal fractionation and risk assessment indicated that Cd and Pb were the contaminants that could pose a threat to aquatic ecosystem, although the SQG outcomes implied that Cu and Zn may cause an adverse effect on the benthic organisms. The results of multivariate statistical analysis demonstrated that the locations in the vicinity of the maintenance area contained the most contaminated sediment samples and require appropriate management. Antifouling paint particles and probably the runoff entering the harbour were the main sources of pollution. Among the diverse range of management strategies, the resuspension technique is suggested as a viable alternative in this specific case for shallow locations with contaminated sediments. A suitable management strategy could reduce the cost of remediation process by identifying the actual contaminated spots and also reduce the risk of remobilization of trace metals.