Characterization of how contaminants arise in a dredged marine sediment and analysis of the effect of natural weathering

A comprehensive review of dredged marine sediments -multiple roles of utilization in cement-based materials and construction products

Dredged marine sediments (DMS), produced during harbor maintenance and waterway development, pose significant environmental and disposal challenges. Increasingly, research has focused on their potential reuse in construction materials, offering a sustainable alternative to waste disposal and promoting resource conservation. This paper provides a comprehensive review of the potential application of DMS in cementitious systems, exploring their multiple roles as alternative binders or aggregates in sustainable practices. Key properties and treatment methods of DMS are summarized, and the mechanical and durability of DMS-incorporated materials are critically evaluated, highlighting their suitability and challenges. The carbon emissions of DMS blended cement are calculated and found to be 16.58 % lower than those of OPC. Further research is needed to standardize processing techniques, evaluate long-term performance, and facilitate large-scale adoption in sustainable construction.

Geochemical characterization data of harbors dredged sediments in the Occitanie region (southern France)

Over the last 15 years, numerous analyses of sediment from the Mediterranean harbors of Occitanie (Southern France) has been made before dredging operations in order to assess geochemical quality of dredged sediment and define the extend of dredging project and the potential fate of dredged sediment (sea dumping vs management on land). However, these data are today scattered, printed and stored as archives, and not directly accessible. With time, those data are expected to be lost for the community whereas they constitute an irreplaceable and mobilizable knowledge base to address the challenges of the circular economy. Characterization data aid in developing regulations for better land-based management of dredged sediments. Existing data are also needed to define pollutant limits in sediments for different uses of marine resources. The collection of these data can thus offer a unique opportunity to assess the geochemical quality of dredged marine sediments and their determining factors. The dataset collected is composed of geochemical characteristics of 146 marine sediments wastes collected before dredging operations between 2010 and 2021. The sampling was designed to capture the large diversity of sediment distribution in harbors of southern France. The dataset contains a wide range of variability in the composition characteristics of dredged sediment (dry matter, organic matter, total nitrogen and phosphorus, sulphate, chloride, trace metals and organics elements). Because the dataset provides information about the characteristics defining the geochemical quality of dredged sediments, it can be used further for research, waste management or dredged sediment valorization, and represent a great interest to other researchers, harbors managers and stakeholders in search of references on the geochemical quality of dredged sediments for their reuse.

Leaching Remediation of Dredged Marine Sediments Contaminated with Heavy Metals

There are more than 150 ports in China and a considerable proportion of dredged sediments in ports and waterways are contaminated with heavy metals as the typical contaminants. It is mandatory to remediate the contaminated dredged sediments prior to further resource utilization. The over-arching objective of this study was to use natural organic acids (oxalic acid, citric acid, tartaric acid, and malic acid) as leaching agents to remove heavy metals (Cu, Cd, and Pb) from contaminated dredged sediments. Batch experiments were conducted to investigate the factors governing the removal rate of heavy metals and leaching kinetics. Citric acid had the best leaching effect on heavy metals Cu, Cd, and Pb with an optimal leaching concentration of 20 mmol/L and a solid-to-liquid ratio of 1:20. The average removal rates of Cu, Cd, and Pb were 85%, 73%, 56%, and 35% for citric acid, malic acid, tartaric acid, and oxalic acid, respectively. The leaching kinetics showed that the removal of heavy metals increased rapidly with time and then gradually reached the maximum value which was best described by the Elovich equation model. The outcomes of this study suggest that citric acid is an effective and environmentally friendly leaching agent for removing heavy metals from marine dredged sediments.

Formulation of Compressed Earth Blocks Stabilized by Glass Waste Activated with NaOH Solution

Due to the increase in demand for building materials and their high prices in most developing countries, many researchers are trying to recycle waste for use as secondary raw materials. The aim of this study is the optimization of a mixture of compressed earth blocks based on two sediments. These sediments were tested through the Vicat test to determine the proportion of each one and the optimal water content. The mixtures were treated by adding 10% of blast furnace slag and different proportions of dissolved glass in a NaOH solution. The results indicated that the mixture of 70% Oran sediments with 30% Sidi Lakhdar sediments treated with 4% glass waste produced a CEB (compressed earth block) with high compressive strength with low porosity. In addition, formulated CEBs have a very good resistance to water immersion.

Landfarming as a sustainable management strategy for fresh and phytoremediated sediment

The aim of this study was to evaluate the effectiveness of a landfarming process (LP) in recovering sediments at different biodegradation phases: phytoremediated dredged sediments (PDS) and fresh dredged sediments (FDS). The PDS landfarming was applied to (1) reduce residual contamination and (2) improve the biological activities in order to obtain a decontaminated matrix rich in organic matter and enzymatic activity to be reused as agronomic substrate. In 3 months of LP, a microbial activity stimulation (from 7 to 48%) and a decrease in organic contamination (about 15%) were recorded. In addition, no phytotoxicity and the content in total organic carbon and nitrogen make the sediments suitable to be reused in agriculture. The FDS landfarming was carried out to (1) reduce water content, (2) transform the organic matter into a more stable form, and (3) decrease organic contaminant level. Five months of LP led to a considerable reduction in water content (40%) and to the activation of microbial biomass metabolism (from 4 to 50 times higher), which achieved proper mineralization of organic matter and contaminants (polycyclic aromatic hydrocarbons near to zero and a total petroleum hydrocarbon reduction of about 60%). The LP also enhanced the stoichiometric ratios of nutrients and enzymes. In conclusion, the LP was a promising and economical methodology to improve the physical, chemical, and biological properties of polluted sediments at different biodegradation phases, creating a substrate ready for several environmental applications. Notably, the PDS resulted appropriate for agricultural use and FDS for civil applications.

Causal Approach to Determining the Environmental Risks of Seabed Mining

Mineral deposits containing commercially exploitable metals are of interest for seabed mineral extraction in both the deep sea and shallow sea areas. However, the development of seafloor mining is underpinned by high uncertainties on the implementation of the activities and their consequences for the environment. To avoid unbridled expansion of maritime activities, the environmental risks of new types of activities should be carefully evaluated prior to permitting them, yet observational data on the impacts is mostly missing. Here, we examine the environmental risks of seabed mining using a causal, probabilistic network approach. Drawing on a series of expert interviews, we outline the cause-effect pathways related to seabed mining activities to inform quantitative risk assessments. The approach consists of (1) iterative model building with experts to identify the causal connections between seabed mining activities and the affected ecosystem components and (2) quantitative probabilistic modeling. We demonstrate the approach in the Baltic Sea, where seabed mining been has tested and the ecosystem is well studied. The model is used to provide estimates of mortality of benthic fauna under alternative mining scenarios, offering a quantitative means to highlight the uncertainties around the impacts of mining. We further outline requirements for operationalizing quantitative risk assessments in data-poor cases, highlighting the importance of a predictive approach to risk identification. The model can be used to support permitting processes by providing a more comprehensive description of the potential environmental impacts of seabed resource use, allowing iterative updating of the model as new information becomes available.

Stability of metal-rich residues from laboratory multi-step treatment system for ferriferous acid mine drainage

Passive systems are often used for the treatment of acid mine drainage (AMD) on closed and abandoned mine sites. Metal-rich residues (solid precipitates) with variable chemical composition and physical properties can be generated. Their characterization is required to better anticipate the potential fate, including stability for disposal, potential recovery, or reuse. The present study evaluated the leaching potential of solids from a laboratory passive multi-step treatment for Fe-rich AMD (2350 ± 330 mg/L Fe_tot, 0.7 ± 0.4 mg/L Ni, 0.2 ± 3.0 mg/L Zn, and 5073 ± 407 mg/L SO₄^2-, at pH 3.04 ± 0.45). To do so, post-treatment solids from three units (Fe-pretreatment reactor (50% wood chips and 50% wood ash, WA50), passive biochemical reactor, PBR for SO₄^2- treatment (30% inorganic materials, 70% organic substrate), and polishing reactor (50% calcite and 50% wood chips, C50)) of a pilot laboratory treatment system were sampled. Physicochemical and mineralogical characterization, as well as static leaching tests were then performed. Results showed that all solids had high neutralizing potential, while high inorganic carbon was found in C50. Moreover, high metal concentrations were found in WA50. Metals and sulfates in all solids precipitated in the form of oxyhydroxides, oxy-hydroxy-sulfates, carbonates, sulfides, sulfate, and native sulfur. The Fe was not found as problematic contaminant in solids, but it was in AMD. However, a probable generation of contaminated neutral drainage by Ni and Zn could occur from WA50. The C50 had the highest acid neutralizing capacity and could better resist to acid aggression relative to solids from PBR and WA50. The PBR and C50 solids were considered as non-hazardous towards regulation's limits and a potential co-disposal with municipal wastes could be a storage option. Further studies should be undertaken by testing other leaching and kinetic tests to assess long-term metal stability.

Novel synergy of Si-rich minerals and reactive MgO for stabilisation/solidification of contaminated sediment

Disposal of significant amounts of dredged contaminated sediment poses an economic and environmental problem worldwide. Transforming contaminated sediment into value-added construction materials using low-carbon MgO cement is a sustainable option; however, the weak mechanical strength and unreliable water-solubility of MgO cement restrict its practical engineering applications. This study elucidates the potential role of industrial Si-rich minerals in the performance enhancement of MgO-based products via the promotion of magnesium silicate hydrate (M-S-H) gel formation. Quantitative X-ray diffraction and ²⁹Si nuclear magnetic resonance analyses indicated that compositions and crystallinities of the Si-rich minerals significantly influence the formation and polymerisation of the M-S-H gel. Pulverised fly ash was found to be a promising Si-rich mineral for generating polymeric M-S-H gel, whereas incinerated sewage sludge ash samples demonstrated a low degree of polymerisation, and the use of glass powder samples gave a low yield of M-S-H. The formation of M-S-H gel enhanced the compressive strength and water resistance (strength retention after water immersion). Further experiments demonstrated that Si-modified MgO cement can transform dredged sediment into fill materials with satisfactory mechanical properties and contaminant immobilisation. Therefore, the synergy between reactive MgO and Si-rich industrial waste is a novel option for sustainable remediation and environmental applications.