Dredged Sediments Research Articles

Effects of water replenishment on lake water quality and trophic status: An 11-year study in cold and arid regions

Water replenishment is an important measure for maintaining and improving the aquatic environmental quality of lakes. The problems of water quality deterioration and water shortage can be alleviated by introducing water of higher quality. However, the mechanism of water replenishment in the improvement of the water quality and trophic status of lakes remains unclear. This study investigated water replenishment in Wuliangsuhai Lake (WLSHL) from 2011 to 2021 by collecting seasonal water samples and conducting laboratory analyses. Water replenishment was found to be capable of significantly improving lake water quality and alleviating eutrophication. It is worth noting that single long-term water replenishment measures have limitations in improving the water quality and trophic status. The whole process was divided into three stages according to the water quality and trophic status, namely the buffer period, decline period, and stable period. During the buffer period, the water quality and trophic status showed only slight improvement because of the small amount of water replenishment and the low proportion of higher-quality water from the Yellow River. In the decline period, with increasing water replenishment, the proportion of higher-quality water from the Yellow River gradually increased, leading to the most significant and stable degree of improvement. In the stable period, increases in the amount of water replenishment had little effect on improving the water quality and trophic status, which is attributable to the balance between internal pollutants (lake water–sediment), and the balance between internal-external pollutants (lake water–irrigation return flow + Yellow River water). On the premise of stable water quality, with eutrophication control as the management goal, the optimal water replenishment would be approximately 10.58 ×108 m3. Further necessary measures for solving aquatic environmental problems include the combination of sediment dredging, optimization of the water replenishment route, and implementation of quality management in water replenishment.

Study of design parameters for staged-filled slurry treated by prefabricated horizontal drains under vacuum preloading

The method of using Prefabricated Horizontal Drains (PHDs) placed in layers under vacuum preloading can significantly speed up consolidation of staged-filled soil slurry. The PHDs can settle with the soil slurry and maintain their shape/pattern and dewatering capacity largely in comparison with Prefabricated Vertical Drains (PVDs). This study presents a field trial focused on treating dredged sediments using PHDs under vacuum preloading for land reclamation purposes. The staged filling involved in the field trial is analyzed using a finite strain consolidation model based on the piecewise-linear finite-difference method. Then, the effects of horizontal and vertical spacings of PHDs on settlement and vacuum consolidation rate are evaluated, considering various combinations of variables for staged-filled soil. It is found that for soils with low compressibility, the consolidation rate is primarily affected by the vertical spacing of PHD layers. For soils with higher compressibility, the consolidation rate is more significantly affected by the horizontal spacing of PHDs, and the final settlement after vacuum preloading is mainly influenced by the vertical spacing of PHD layers. This study provides practical recommendations for cost-effective design of horizontal and vertical spacings of PHDs in efficiently treating soil slurry with different compressibility and initial conditions.

Effect of precursor element composition on compressive strength of alkali-activated dredged sediment

The disposal of dredged sediment (DS) is a major challenge in urban construction projects, which is expected to be solved by alkali activation. For a long time, the lack of precise understanding regarding the precursor composition and reaction mechanisms has hindered the development of higher-strength alkali-activated dredged sediment (ADS) materials. This study investigates the impact of adjusting the element composition of the solid precursor (SP) on the uniaxial compressive strength (UCS) of ADS. Orthogonal analysis, as well as XRD, FTIR, Raman, and SEM methods, were utilized to examine the effects. The findings demonstrate that the molar ratio n(Ca)/n(Si) of the SP significantly influences the UCS of ADS, particularly during the mid-to-late stages of curing (≥7 days). Moreover, the polymerization degree of the product C(A)SH serves as a vital link between the macroscopic strength of the ADS samples and the microscopic elemental composition of the SP. The high content of Ca2+ and OH-, as well as the coordination of silicon-oxygen and aluminum-oxygen units, will promote the polymerization reaction in the system and form more CASH and CSH gels. Furthermore, as the polymerization degree of C(A)SH decreases, the pore composition and distribution in the sample become more complex, ultimately resulting in the deterioration of the macro-mechanical properties. These findings offer valuable insights for the solidification and comprehensive utilization of DS.

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.

Tensile strength behavior of cement-stabilized dredged sediment reinforced by polypropylene fiber

Tensile strength behavior of cement-stabilized dredged sediment reinforced by polypropylene fiber

Toward a water-sensitive precinct with stormwater harvesting: a case study in South Africa

ABSTRACT The study assessed static management, i.e., without planned periodic maintenance of the storage (no sediment dredging) denoted as SC1, or with maintenance denoted as SC2. The second approach was dynamic management based on applying Real-Time Control (RTC) techniques to scenario SC1 and scenario SC2 denoted as RTC-1 and RTC-2, respectively. The dynamic management of the UCT dam with RTC-1 and RTC-2 approaches increase yield by 2.1 and 1.1 ml, respectively. Additionally, RTC-1 and RTC-2 approaches increase volumetric reliability by 5.3 and 2.5%, respectively, while maintaining the required level of service of a stormwater harvesting system. SC1 and SC2 results in water savings of up to 21.15 and 21.45 ZAR/kl, respectively, while RTC-1 and RTC-2 could save up to 19.35 and 19.45 ZAR/kl. Thus, static configurations results in water savings approximately 9% in comparison to RTC. In addition, static configurations harvested stormwater at a relatively lowest unit cost in comparison to RTC configurations. Notwithstanding this finding, the RTC system exhibits a great potential in reshaping the stormwater harvesting system to simultaneously deliver water conservation and stormwater management.

Environmental availability of some trace metals in dredged sediments disposed on-land before use in fired brick processing

Environmental availability of some trace metals in dredged sediments disposed on-land before use in fired brick processing

Microplastic in Dredged Sediments: From Databases to Strategic Responses.

Microplastics (MPs) accumulate in sediments, yet guidelines for evaluating MP risks in dredged sediments are lacking. The objective of this study was to review existing literature on MPs in sediments to improve fundamental knowledge of MP exposures and develop a publicly available database of MPs in sediments. Twelve percent of the reviewed papers (nine studies) included sediment core samples with MP concentrations generally decreasing with depth, peaking in the top 15cm. The remaining papers evaluated surficial grab samples (0 to 15cm depth) from various water bodies with MPs detected in almost every sample. Median MP concentrations (items/kg dry sediment) increased in this order: lakes and reservoirs (184), estuarine (263), Great Lakes nearshore areas and tributaries (290), riverine (410), nearshore marine areas (487), dredge activities (817), and harbors (948). Dredging of recurrent shoaling sediments could be expected to contain MPs at various depths with concentrations influenced by the time elapsed since the last dredging event. These results offer key insights into the presence and variability of MPs in dredged sediments, informing environmental monitoring and risk assessment strategies.

Occurrence of dissolved organic matter in storm-drain inlet sediments and its implication for urban stormwater infrastructure sustainability

In the context of climate change, the effective management of carbon in urban stormwater infrastructure (USI) become increasingly crucial. Research indicates that dissolved organic matter (DOM) plays a significant role in the carbon cycle within USI. However, there is a lack of comprehensive information regarding the occurrence of DOM in urban storm-drain inlet (SDI) sediments. This study was undertaken to examine the land use type-related distribution of DOM in SDI sediments, and then provide the suggestion for urban infrastructure sustainability. There are three findings: (1) The characteristics of DOM in SDI sediments, including content, hydrophilicity, molecular weight, and functional groups of aromatic rings, exhibited variation with land functional type; (2) Urban SDI DOM had low humification, and was primarily originated from autochthonous sources, with the proportion of humic-like components close to or exceeding 50%; and (3) SDI sediment DOM was likely to have different characteristics from road dust and stormwater due to microbial activities over dry season. Based on these findings, measures for urban stormwater infrastructure sustainability are proposed, including properly road sweeping, frequently SDI sediment dredging, decreasing in emission from industrial activities, promoting local educational practices, and limiting improper organic waste disposal. These results have implications for the management of stormwater-related carbon and provide valuable insights for the development of sustainable practices for urban ecosystems.

Water Budget for Lake Trafford, a Natural Subtropical Lake in South Florida: An Example of Enhanced Groundwater Influx in a Subtropical Lake Subsequent to Organic Sediment Dredging

A very detailed water budget analysis was conducted on Lake Trafford in South Florida. The inflow was dominated by surface water influx via five canals (61%), with groundwater influx constituting 12% and direct rainfall constituting 27%. Lake discharge was dominated by sheet flow (69%) and evapotranspiration (30.5%), with groundwater recharge of the hydraulically connected unconfined aquifer accounting for only 0.5%. The removal of 30 M tons (4.4 × 106 m3) of organic sediment impacted the groundwater influx, causing enhanced groundwater flow into the deeper parts of the lake and mixed flow along the banks, creating a rather unusual pattern. The large number of groundwater seepage meters used during this investigation led to a very reliable set of measurements with occasional failure of only a few meters. A distinctive relationship was found between the wet-season lake stage, heavy rainfall events, and pulses of exiting sheet flow from the lake. Estimation of the evapotranspiration loss using data collected from a weather station on the lake allowed the use of three different models, which, when averaged, produced results comparable to Lake Okeechobee (South Florida). A limitation of this investigation was the inability to directly measure sheet-flow discharges, which had to be estimated as a residual within the calculated water budget.

Management of dredged marine sediments in Southern France: main keys to large-scale beneficial re-use.

Fifty million cubic meters of marine sediments are dredged each year in France in order to maintain harbor activities and sustain the economy of littoral territories. Because of anthropogenic activities in and around harbors, sediments can contain significant amounts of chemical and organic pollutants whose behavior during dredging must be addressed in order to avoid releasing risks for humans and the environment. French regulations come to govern the management of dredged sediments, considering them "safe" and possible to be dumped at sea or "contaminated" and needed to be treated on land as waste. In recent years, new constraints have been pushed toward the management of land. This management is, however, challenging as few channels are proposed to reuse marine sediments, and elimination appears to be economically and environmentally unsustainable. This study provides an overview of the technical and regulatory aspects related to dredged marine sediment management in France and aims to identify and discuss the limits of their valorization. Dredged sediments are mainly composed of particles with heterogeneous grain size, some being known for many applications such as building materials and growing media. However, several reasons have been put forward to explain why these particles are not reused when extracted from dredged sediments. Several technical, socio-economic, and regulatory obstacles explain the low demand for dredged sediments. This demand can be stimulated by government incentives and a good regulatory framework. National regulations could help streamline their reuse by removing their "waste" status and creating a regulated market for dredged sediment.

Effect of incorporation of calcined sediments and perlite as partial cement replacement on mortars behavior

The accumulation of sediments in varied dams built in Algeria denotes a vital problem that requires immediate attention and action from the authorities and managers of the National Agency for Dams and Transfers (ANBT). More than that, various research studies on sediments have revealed that subjecting them to heat treatment can exploit these sediments as a viable substitute for some of the cement used to produce cementitious materials. Combining the different types and quantities of natural Perlite pozzolan can achieve many benefits, including reduced consumption, minimized heat generation, improved workability, reduced permeability, and increased strength. This study aims to explore the potential of using dredged sediments from Chorfa II dams and perlite from Hammam Boughrara (located in western Algeria) as substitutes for cement in mortar analysis. A thorough examination of calcined sediments and perlite revealed the feasibility of partial cement replacement. Research has mainly focused on evaluating the properties of mortars in fresh and hardened states.

An experimental study on dredged Qinhuai river sediment-based flowable fill treated by flocculation-cementation method

The traditional Portland cement solidification method has low efficiency in treating dredged sediments with high water content. In this study, flowable fill was prepared using dredged sediments by the flocculation-cementation method. By utilizing dredged sediments with high water content, the need for additional water during the flowable fill preparation process is eliminated. The influences of flocculant types and dosages on dehydration efficiency, flowability, and strength were investigated through a series of laboratory tests, including settling column tests, rapid dehydration tests, flowability tests, and unconfined compressive strength (UCS) tests. The results indicate that the use of flocculants improves the dehydration efficiency. The dehydration efficiency of guar gum is the highest, with a settlement rate reaching 78 mL/min during the settling stage. The inclusion of flocculants clearly impacts the flowability and UCS of flowable fill, and the addition of amphoteric polyacrylamide and guar gum decreases the flowability. Furthermore, the Portland cement dosage also has a significant influence on both the flowability and the UCS. As the cement dosage increases, the flowability decreases while the UCS increases. To study the effectiveness of flocculation-cementation method in treating dredged sediment, four sets of recommended schemes are provided based on the actual transportation and re-excavation methods employed in the project to cater for different requirements. This research holds significant reference value for both the resource utilization of dredged sediments with high water content and the engineering application of flowable fill.

EDTA biodegradability and assisted phytoextraction efficiency in a large-scale field simulation: Is EDTA phasing out justified?

Enhanced phytoextraction of metal-polluted soils using EDTA is phasing out in favor of biodegradable chelants. However, these are too short-lived to be effective in the acclimated biodegrading soil environment established in long-term phytoextraction operations. We hypothesize that full-scale EDTA-enhanced phytoextraction can be both effective and environmentally safe, provided that soil leaching is prevented while EDTA persists in the soil profile. This was tested for 4 years in two sealed, well-monitored constructed lagoons (70-m3 each) packed with Cd-contaminated dredged sediment. Fast-growing, high-biomass, salinity-resistant eucalypts were planted in June 2010. Under controlled deficit irrigation, the 3-year average EC was 14.2 dS m−1. Summer leakage accounted for ∼1.2 % of the overall irrigation water and was prescribed for monitoring the composition of the soil solution. Altogether, 486 leachate and 261 suction-cap solutions were collected at average intervals of 5.5 days. EDTA was intermittently applied with summer irrigation, in multiple low doses at average seasonal concentrations of 1.1–9.2 mM. The soil solution EDTA biodegraded quickly after those applications were stopped. This cessation was timed well before the start of the rainy season. Spontaneous EDTA leaching during the three winters accounted for <0.02 % of the total 423 mol/basin applied. Prescribed summer leaching constituted ∼1 % of this total. Peak heavy metal (HM) concentrations in the leachate and suction-cap solutions (e.g., Cd, up to 18.5 and 14 mg L−1, respectively) were observed soon after EDTA application. Winter HM concentrations were not significantly different from the background. As the amounts of EDTA diminished, HM also disappeared from the soil solution, probably by adsorption. Eucalyptus occidentalis was by far the most efficient Cd sink of the five species tested,. The results of this study strongly support our hypothesis that EDTA-enhanced phytoextraction can be both effective and environmentally safe.

Manufacturing non-sintered ceramsite from dredged sediment, steel slag, and fly ash for lightweight aggregate: production and characterization.

Green and low-carbon materialization for dredged sediment (DS) is limited due to its low pozzolanic activity. In this study, a novel DS-based non-sintered lightweight aggregate (LWA) is developed by steel slag (SS) and fly ash (FA) activation. Process optimization is performed by the response surfaces, and the basic properties and characterization of the optimal product are investigated. Results indicated that the optimized design ceramic aggregate (ODCA) was prepared as follows: raw pellets comprising of 59.2% DS, 5% SS, 35.8% FA, 5% MK, 5% H2O2, and 2‰ foam stabilizer were activated by alkali activator (1.5 weight ratio of 14 M NaOH to water glass) and then cured at 80 °C and 95% humidity for 24 h. The basic and environmental performances of ODCA were in accordance with standards, whose bulk density was as low as 665.8 kg/m3, the high cylinder compressive strength was 6.143 MPa, and leaching concentrations of heavy metals were controllable. The regulation mechanism of LWA performances could be summarized as follows. SS and FA additives played the role for the mechanical strength enhancement and passivation of heavy metals, which promoted the formation of sillimanite, chabazite, and C-S-H / C-S-A-H gels in ODCA. The bulk density of ODCA was greatly reduced by H2O2 addition, where ODCA had an open-pore structure with a median pore size of 4969.75 nm. Note that C-S-H/C-S-A-H were the key hydration products to give ODCA light density and high mechanical strength, simultaneously.

Exploring nonlinear responses of lake nutrients and algal blooms to restoration measures: A three-dimensional flux network modelling approach

Excessive anthropogenic nitrogen (N) and phosphorus (P) inputs accelerate harmful algal blooms (HABs) and pose a significant global threat to lake ecosystems. Despite the adoption of extensive restoration measures to improve water quality, their effects on nutrient cycles and the underlying pathways remain unclear. In this study, a three-dimensional nutrient flux modelling approach was developed based on a validated Environmental Fluid Dynamics Code (EFDC) model and the Spatiotemporal Integral for Nutrient Networks (SINN) to compute nutrient storages and fluxes in lakes. We then conducted a scenario analysis, composed of 10 schemes, to assess the eight restoration measures in Lake Dianchi, China. The results showed that our model exhibited a high level of agreement with observed data and fluxes reported in previous studies. Of all the measures implemented, pollution interception by lakeshore wastewater treatment plants (WWTPs) accounted for the largest historical improvements in water quality, with reductions of total nitrogen (TN) by 9.3%, total phosphorus (TP) by 36.4%, and chlorophyll a (Chla) by 18.2%. Furthermore, combined implementation of transboundary water transfer and wastewater diversion contributed to a reduction of 13.3% in TN, 11.5% in TP, and 6.2% in Chla. To achieve greater improvements in water quality, efforts must be made to improve the emission standard of WWTPs and ensure compliance with water quality standard of inflow rivers. The cyanobacteria biomass catch can only be used as a supplementary approach to restrict the HAB peaks. The nonlinear responses of lakes were characterized by large loading abatement but slight changes in water quality. Through the SINN approach, we revealed that weakened internal cycling was the primary driver of water quality improvements in all restoration measures. Further analysis demonstrated that measures targeting reducing external loadings significantly weakened internal cycling processes. In contrast, measures targeting the internal loadings, such as sediment dredging, exhibited limited effectiveness in reducing the intensity of internal cycling and Chla in the lake. For eutrophic lakes with substantial legacy nutrients, the abatement of external loadings remains the principal strategy. The approach presented in this study can be used to assess and optimize lake restoration measures.

Study on preparation and activation enhancement effect of cold bonded multi-solid waste wrap-shell lightweight aggregates (SWSLAs) with low cement content

Cement production consumes large amounts of depleted resources and energy, and causes environmental pollution. In order to reduce cement consumption and realize the closed-loop recycling of solid waste, cold bonded solid waste wrap-shell lightweight aggregates (SWSLAs) with a sextuplet blended system composed of dredged sediments, mineral powder, steel slag, phosphogypsum, fly ash, and a minimal amount of cement were prepared. Through the single-factor experiment, the influences of the types and dosages of solid wastes in the nuclear phase of SWSLAs (SWSLAs-NP) and shell phase of SWSLAs (SWSLAs-SP) on the strength and water resistance were explored, and the optimum ratio was obtained. On this basis, the influence of the types and amounts of activators incorporated in SWSLAs on the physical properties of aggregates was studied, and the primary microstructure of the aggregate was characterized. Our results showed that the optimal ratio of solid waste in the SWSLAs-NP was: 40 wt% of dredged sediments, 24 wt% of mineral powder, 18 wt% of steel slag, and 18 wt% of phosphogypsum. The optimal weight ratio of cement and solid waste in the SWSLAs-SP was 5:95. The resulting aggregate had a bearing capacity of single grain of 73.83 N and a water-resistance coefficient of 0.67. After the above aggregates were treated with Na2SO4 (activator) at 2%, the bearing capacity and water-resistance coefficient of the aggregates increased by 47.00% and 11.94%, respectively. The performances were even better than that of the aggregate composed of100w cement in the shell phase. Microstructural observations demonstrated that the structure of the raw material was reconstructed under the action of Na2SO4, and the raw materials reacted with each other, and thus the densification of the aggregate and its core-shell interface structure was enhanced, which improved the comprehensive performance of the aggregate. This study represents a step toward efficient utilization of industrial solid wastes.

On the use of seashells as green solution to mechanically stabilise dredged sediments

The article reports the results of an experimental activity conducted on dredged fine-grained marine sediments and aimed to find out novel eco-friendly solutions for their mechanical stabilisation. The main idea of this research is to use seashells, i.e., another waste material, to partially replace cement binders in the mechanical stabilisation of sediments for the production of a new stable material that can potentially be used in construction. To this aim, an original procedure has been developed to obtain a powder of mussel shells without their calcination. Physical properties, one-dimensional compression behaviour and permeability of the novel mixtures including sediments, mussel shell powder and cements are presented for different curing times. The efficacy of the solutions is assessed also by comparison with the performance of control mixtures prepared by mixing the same sediments with cement only. The effects of the different treatments on the soil properties were analysed, demonstrating multiple beneficial effects of using the mussel shell powder. Evidence is provided that seashells represent a viable alternative to cement, as they were found to be as effective as traditional hydraulic binders, when replacing them up to 1/4, in enhance geomechanical and geochemical performance of the stabilized material.

Life cycle analysis of sediment valorization by means of geopolymerization from laboratory to industrial scale

Geopolymerization has become a potential competitor to cement over the last 10 years due to its lower carbon impact. However, the development of geopolymerized applications on an industrial scale still faces numerous limits. As an answer, the valorisation of local sources of materials such as dredged sediment as precursors has been identified in the literature of high interest as it could solves sediment management problems as well as reducing geopolymerization environmental and economic cost. Therefore, this study evaluates, through a Life Cycle Analysis (LCA), the impact of mortars developed from untreated dredged sediments mixed with cement or alkalis. The solutions developed in the laboratory were transposed to a hypothetical industrial scale around the Port of Bordeaux area. Four mortars were compared with equivalent mechanical resistance: a classic Ordinary Portland Cement (OPC) mortar and three geopolymer mortars with NaOH and Na2SiO3 alkalis. Results showed that, compared to the use of cement, in this specific case, geopolymerization effectively reduces the impact on climate change by 66% when sediment beneficial recovery was taken into account. This article is a first step in the industrial development adoption of waste geopolymer based mortar for public works as several conclusions were found to justify their implementation on a larger scale. Among them the use of alternative local precursors is effective in order to reduce the environmental cost of geopolymer. However, the market potential of geopolymer mortars will also highly depend on alternatives to silicate as an alkaline reagent.

VALORIZATION OF DREDGED SEDIMENTS FROM DAMS IN PAVEMENT DESIGN

Introduction: This study is part of research aimed at valorizing dredged sediments through the development of formulations for use in road engineering. The purpose of the study was to determine if the materials selected for pavement layers comply with road design standards, in particular, with specific requirements for density, grain size, plastic properties, organic matter, and mechanical performance. Methods: To determine the physical-chemical and mechanical characteristics of the dredged sediments obtained from samples taken from the Bakhadda dam located in western Algeria’s semi-arid climate, the sediments were treated with binders in small amounts (3% lime (L), 6% cement (C)) for reuse in road construction. The study focused on the evolution of physical and mechanical characteristics of the treated sediments, including LL, PI, VBS, immediate bearing index (IBI%), UCS, tensile strength Ϭt, as well as small strain modulus ESS and large strain modulus E50. The results showed that adding lime and cement to the dredged sediments improved their strength, as evidenced by the increased compressive strength (UCS) over time for the samples containing different amounts of binders (3%L, 6%C, and 3%L + 6%C). Additionally, the effect of the water content on the mechanical properties of the formulations was demonstrated. The study showed that the strength increased when the water content decreased.