Phytoremediation of dredged marine sediment: monitoring of chemical and biochemical processes contributing to sediment reclamation

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.

Reed restoration decreased nutrients in wetlands with dredged sediments: Microbial community assembly and function in rhizosphere

Using dredged sediments as substrate for aquatic plants is a low-cost and ecological friendly way for in situ aquatic ecological restoration. However, the limited information available about how aquatic plant restoration affects the microbial ecology and nutrients in dredged sediments. In this study, nutrient contents, enzyme activities, and bacterial and archaeal communities in vertical sediment layers were determined in bulk and reed zones of wetlands constructed with dredged sediments in west Lake Taihu for three years. Reed restoration significantly decreased total nitrogen, total phosphorus, and organic carbon contents and increased alkaline phosphatase, urease, and sucrase activities compared to bulk area. Bacterial communities in vertical sediment layers had higher similarity in reed zone in comparison to bulk zone, and many bacterial and archaeal genera were only detected in reed rhizosphere zones. Compared with the bulk zone, the reed restoration area has a higher abundance of phylum Actinobacteriota, Hydrothermarchaeota, and class α-proteobacteria. The assembly process of the bacterial and archaeal communities was primarily shaped by dispersal limitation (67.03% and 32.97%, respectively), and stochastic processes were enhanced in the reed recovery area. Network analysis show that there were more complicated interactions among bacteria and archaea and low-abundance taxa were crucial in maintaining the microbial community stability in rhizosphere of reed zone. PICRUST2 analysis demonstrate that reed restoration promotes metabolic pathways related to C and N cycle in dredged sediments. These data highlight that using dredged sediments as substrates for aquatic plants can transform waste material into a valuable resource, enhancing the benefits to the environment.

Phytoremediation of chloride from marine dredged sediments: A new model based on a natural vegetation recolonization

Phytoremediation is a type of bioremediation process that involves the use of plants to remove or degrade contaminants from soil, water, or air. In most of the observed phytoremediation models, plants are introduced and planted on a polluted site to take up, absorb, or transform contaminants. This study aims to explore a new mixed phytoremediation approach that involves natural recolonization of a contaminated substrate, by identifying the species growing naturally, their bioaccumulation capacity, and by modeling annual mowing cycles of their aerial parts. This approach aims to evaluate the phytoremediation potential of such a model. Both natural and human interventions are involved in this approach, which is referred to as a mixed phytoremediation process. The study focuses on chloride phytoremediation from a chloride-rich and regulated substrate that is marine dredged sediments abandoned for 12 years and recolonized for 4 years. The sediments are colonized by a Suaeda vera dominated vegetation and possess heterogeneity in lixiviate chloride and conductivity. The study found that despite Suaeda vera is the well adapted species for this environment, it is not an effective species for phytoremediation as it has low bioaccumulation and translocation rates (9.3 and 2.6 respectively), and disturbs chloride leaching below in the substrate. Other identified species, such as Salicornia sp., Suaeda maritima, and Halimione portulacoides, have better phytoaccumulation (respectively 39.8, 40.1, 34.8) and translocation rates (respectively 7.0, 4.5, 5.6) and can successfully remediate the sediment in 2-9 years. The following species have been found to bioaccumulate chloride in aboveground biomass at the following rates: Salicornia sp. (181 g/kg DW), Suaeda maritima (160 g/kg DW), Sarcocornia perennis (150 g/kg DW), Halimione portulacoides (111 g/kg DW) and Suaeda vera (40 g/kg DW).

New methodology for assessing the environmental efficiency of transport: Application to the valorization of biomass from phytoremediation

It is known that any environmental remediation process must be approached as a system and that the transport of materials is key to determining its sustainability. The aim of this work is to establish how far it was possible to transport plant material from a phytoextraction process in such a way that the environmental gain of the remediation process is not compromised. In the absence of a general methodology to answer our question, a new methodology based on spatial analysis and the life cycle perspective is proposed to calculate, under different hypotheses and depending on the type of remediation, the maximum distance that a lorry can travel, taking as a limit the distance in which the environmental benefit would be equal to 0. The results obtained show that there are significant differences depending on the type of optimisation proposed for the transport route as well as the type of valorization of the plant material to be carried out. Thus, in the case of bioethanol, biomass could be transported up to 25 km. For biodiesel, it can be shipped over distances between 255 and 415 km and finally, if it is valorized by anaerobic co-digestion, biodigesters up to 267 km away could be sought for the most favourable case.

Life Cycle Assessment (LCA) of Substrate Mixes Containing Port Sediments for Sustainable 'Verna' Lemon Production

The increase in maritime trade and its global economic importance have forced port management actors to carry out the periodic dredging of their sediments to maintain an adequate depth for the passage of large ships to maintain their operation and competitiveness. During the dredging process, large volumes of port sediment are generated. Dredged port sediment is currently considered a waste material and its disposal is regulated. Finding ways to safely reuse port sediments is necessary for sustainable development. In this study, a life cycle assessment (LCA) methodology was applied to identify the environmental impact of port sediments when used as a culture medium for lemon trees. A total of 90 lemon trees (Citrus limon L. Burm var ‘Verna’) were used in the trial. The trees were grown under controlled conditions using three substrates, with different portions of peat and port sediment (25%, 50%, and 75%) to identify the real impacts of the culture media on the growth process. The LCA was calculated and analyzed according to the ISO 14040:2006 standard, using the SimaPro v. 9.3 software (PRé Sustainability B.V, Amersfoort, The Netherlands). The functional unit defined for the three-culture media was 1 kg of lemons. The LCA results showed a significant increase in the environmental impact of lemon cultivation proportional to port sediment content (75%), due to the decrease in fruit production caused by the sediment. However, the least impact was identified for the culture medium at 50% peat and 50% port sediment. The greatest impacts were more related to crop management rather than the port sediment content. The results showed that the use of the port sediment, mixed with other substrates as an agricultural medium amendment, is a viable option for lemon growers.

Physico-Chemical Attributes of Lemon Fruits as Affected by Growing Substrate and Rootstock

Due to its high content of bioactive compounds, the lemon is considered one of the most relevant species around the world. Its great economic importance is motivated, in addition to its fresh consumption, by its applications in the medical, pharmaceutical, and food industries, etc. However, the chemical and nutritional composition of lemon is not constant and can be influenced by external factors such as variety, weather conditions, crop management, etc. Determining the compositional variations of the fruit, essential to defining its potential use, was the main objective of this study. The physicochemical characteristics of the ‘Verna’ lemon were studied as a function of two controlled variables, the growing substrate and the rootstock. For this, 90 lemon trees were cultivated in three rootstocks and three different culture media. Lemon trees cultivated with 50% sediment/peat mix substrate presented a higher total production (590 lemons and 90.53 kg) while this production was 80% lower on trees cultivated with 75% marine sediment. Citrus macrophylla and Citrus aurantium/Citrus sinensis rootstocks showed a significantly higher production than the Citrus aurantium. All the fruits presented a predominantly yellow color appropriate for the market (0 < CI < +5). Nutritional and chemical parameters were consistent with data reported for the ‘Verna’ clones. All the obtained lemons were suitable for marketing and consumption both in fresh and processed forms. The results indicated the limited influence that the studied variables have on the quality parameters of lemon fruits, but they also could confirm the potential of marine sediment as a culture substrate.

Chloride accumulation in aboveground biomass of three macrophytes (Phragmites australis, Juncus maritimus, and Typha latifolia) depending on their growth stages and salinity exposure: application for Cl- removal and phytodesalinization

Anthropogenic activities can be the source of saline solid wastes that need to be treated to reduce their salt load to meet the purposes of reuse, valorization or storage. In this context, chloride remediation can be achieved using high-salt accumulating plants. However, there is very limited information on the comparative potential of different species in the same environment, and only scarce data concerning their efficiency as a function of growth stage. In order to rationalize these selection criteria, three macrophytes i.e., common reed (Phragmites australis), sea rush (Juncus maritimus), and cattail (Typha latifolia), were cultivated at two growth stages (6-months old and 1-year old) for 65 days in Cl^- spiked substrates (from 0 up to 24 ‰ NaCl). The plants' survival and potential capacity for removal of Cl^- from substrates and accumulation in shoots were investigated. For the three studied species, mature and juvenile plants display a high tolerance to salinity. However, mature specimens with higher shoot biomass and Cl^- contents are capable of greater chloride removal than juvenile plants. The sole exception is P. australis which displays just the same phytoremediation potential for both mature and juvenile specimens. Moreover, P. australis has the lowest potential when compared with other species, being 1.5 and 3 times lower than for J. maritimus and T. latifolia. When considering the plant growth and the shoot biomass production, chloride removal rates from the substrate point that mature J. maritimus should preferentially be used to design an operational chloride remediation system. The results highlight the relevance of considering the growth stage of plants used for Cl^- removal. HIGHLIGHTS: 1) Mature and juvenile specimens of J. maritimus, P. australis, and T. latifolia have high salinity tolerance in solid media spiked up to 24 ‰ NaCl. 2) Mature plants have generally better Cl^- removal and phytoremediation performances than juvenile specimens. 3) J. maritimus is the most effective species for chloride phytoremediation with high survival and high Cl^- sequestration in shoots. 4) T. latifolia has high Cl^- removal in shoots and good remediation capacities but also shows sign of stress. 5) P. australis shows low Cl^- sequestration and is a poor candidate for chloride remediation from substrate.

Recycling Cigarette Filters as Plant Growing Substrate in Soilless System

Two massive wastes are cigarette butts (CB) and stone wool (SW), both representing a threat to the environment. Although the cellulose acetate filters (CAF) in CB are long-term degradable, SW soilless substrates are not. Here, a soilless substrate for growing ornamental plants was manufactured with CAF and compared to commercial SW substrate. CB treatment consisted of a washing in boiling water with a dramatic reduction of pollutants in CAF. Then, cleaned filters were separated, dried, carded to fibers, and subsequently compacted into plugs. The trace pollutants in recycled CAF substrate did not negatively affect the germination of Spartium junceum L. and Lavandula angustifolia Miller seeds as well as the root development of Salvia officinalis L. and Salvia rosmarinus Schleid. stem cuttings. Plants grown in recycled CAF showed a differential species-dependent change of pigments in comparison with those in SW, without compromising their photosynthesis performance. Overall, the results demonstrated that these plants can be well established and grow in recycled CAF, as comparable to SW substrate. This study highlights a novel and promising solution in CAF recycling by turning this litter into an efficient soilless substrate for growing ornamental plants, thus limiting the use of SW and indirectly decreasing its industrial waste flow.

Agronomic performance and food safety of strawberry cultivated on a remediated sediment

A marine sediment phytoremediated and homogenized by landfarming was tested for its potential recycle as growing media in horticulture. Two strawberry cultivars, Camarosa and Monterey, were grown on remediated sediment alone (TS100), commercial peat/pumice based growing medium (TS0) and a mixture 1:1 in volume of sediment and peat (TS50). Chemical fertility and strawberry production and safety of produced food were monitored for three consecutive productive seasons on the same growing media. During the first year of cultivation, plants grown on sediment-based media showed a significantly lower biomass production and fruit yield compared with peat, mainly due to the sediment low fertility. In the subsequent two years, the plant re-cultivation improved the sediment structure and N mineralization, and on the third cultivation year both strawberry cultivars showed higher fruit productivity and no accumulation of potentially toxic trace metals. The produced fruits did non accumulate high concentrations of trace metals, and risk assessment showed no risks for human health related to the consumption of strawberry produced on sediment-based growing media. We concluded that a phytoremediated sediment could be recycled as an ingredient of soilless growing media for reducing the environmental impact of plant nursery production and posing no risks for human health. These results show that reclaimed sediments could be reconsidered as a component material category in the new EU regulation on fertilizers.

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.

Remediated marine sediment as growing medium for lettuce production: assessment of agronomic performance and food safety in a pilot experiment

BACKGROUND

The use of reclaimed dredged sediments as growing media may offer a profitable alternative to their disposal as a waste and at the same time meets the need of peat-substitute substrates in horticulture. When sediments are reused to cultivate food crops, issues related to human health rise due to potential accumulation of contaminants in the product. This pilot study aimed at verifying the suitability of a reclaimed dredged port sediment, used pure or mixed with peat, as a growing medium for lettuce cultivation.

RESULTS

The pure sediment caused a reduction in crop yield, probably due to its unsuitable physical properties, whereas the mixture sediment-peat and pure peat resulted in the same yield. Although the sediment contained potentially phytotoxic heavy metals and some organic pollutants, no symptoms of plant toxicity were noted. Besides, no organic contaminants were detected in lettuce heads, and heavy metals amounts were not hazardous for consumers. Conversely, plants grown in the sediment were particularly rich in minerals like Ca, Mg and Fe, and showed higher concentrations of organic acids and antioxidants.

CONCLUSION

The use of the sediment as a growing medium for lettuce was shown to be safe for both inorganic and organic contaminants. Nevertheless, considering crop yield results, the mixture of the sediment with other materials is recommended in order to produce a substrate with more suitable physicochemical properties for vegetable cultivation. © 2019 Society of Chemical Industry.

Influence of enhancing electrolytes on the removal efficiency of heavy metals from Gabes marine sediments (Tunisia)

This study focused on the feasibility of the treatment of heavy metals-contaminated sediments from Gabes harbor (Tunisia) using enhanced electrokinetic process. It presented a laboratory short-time electrokinetic experiment. The enhancing agents, as citric, acetic acids and sodium dodecyl sulfate (SDS) were used regarding their low environmental hazard. The electrokinetic cell was specially designed in order to elaborate two experiments at the same time. This paper is composed of three parts. The first part introduces the characterization of Gabes sediments. The second part describes the design of laboratory electrokinetic cell and the followed methods. The third part is dedicated to the results analysis. Treatment efficiency revealed that more than 80% of lead was removed from Gabes marine sediments. The reduction of cooper concentration, in sediments after treatment, ranged from 74 to 87%. Despite, the high removal of cadmium that ranged from 58 to 79%, treated sediments presented Cd concentration above the threshold limit.

Reclamation of river dredged sediments polluted by PAHs by co-composting with green waste

Polluted dredged sediments are classified as waste and cannot be re-used in civil and environmental engineering nor in agriculture, posing serious logistical, economic and environmental problems for their management. We tested co-composting of sediments (S) slightly polluted by PAHs with urban green waste (GW), as a sustainable technique to both degrade the organic pollutants and lend to sediments suitable properties to be reused as technosol. Four treatments were tested: sediments only (S), GW only (GW), 1:1 w:w S:GW (SGW1:1), and 3:1 w:w S:GW (SGW3:1) for a co-composting period of one year. The co-composting materials underwent to an initial short and moderate thermophilic phase. However, at the end of the co-composting process, SGW3:1 and SGW1:1 achieved suitable physical and chemical properties as plant substrate in terms of organic C, N and humic substances contents, electrical conductivity and bulk density. In the first six months of treatment, the PAHs concentration in SGW3:1 and SGW1:1 was reduced by 26% and 57%, respectively, reaching values below under 1mgg(-1), whereas such a reduction in S alone was observed only after nine months. We concluded that co-composting with green waste can be a suitable approach for reclamation of dredged sediments opening opportunities for their use as technosol or as plant growing substrate.

Investigation of heavy metal (Cu, Pb, Cd, and Cr) stabilization in river sediment by nano-zero-valent iron/activated carbon composite

Nano-zero-valent iron/activated carbon (nZVI/AC) composite was evaluated for its effectiveness in the stabilization of Cu, Pb, Cd, and Cr in dredged river sediment. Synthetic precipitation leaching procedure (SPLP) and toxicity characteristic leaching procedure (TCLP) were adopted to compare the effects of nZVI/AC dosage, particle size, time duration, and temperature on heavy metal leachability. The results show that leachability dropped considerably with the addition of nZVI/AC and powdered particles in the size of 0.075-0.18 mm was more effective in stabilization than granular ones. Stabilization effect was stable in long-term and robust against changes in temperature. Tessier sequential extraction revealed that heavy metals were associated with solid particle, inorganic or organic matters in sediment. The addition of nZVI/AC was able to convert relatively weakly bound heavy metals into more strongly bound species and thus reduce the bioavailability and toxicity. Also, the standard potential of heavy metals may decide the mechanism of stabilization process.

Is phytoremediation without biomass valorization sustainable? - comparative LCA of landfilling vs. anaerobic co-digestion

This study examines the sustainability of phytoremediation for soils contaminated with heavy metals, especially the influence of management of the produced metal-enriched biomass on the environmental performance of the complete system. We examine a case study in Asturias (north of Spain), where the land was polluted with Pb by diffuse emissions from an adjacent steelmaking factory. A Phytoremediation scenario based on this case was assessed by performing a comparative life cycle assessment and by applying the multi-impact assessment method ReCiPe. Our Baseline scenario used the produced biomass as feedstock for an anaerobic digester that produces biogas, which is later upgraded cryogenically. The Baseline scenario was compared with two alternative scenarios: one considers depositing the produced biomass into landfill, and the other considers excavating the contaminated soil, disposing it in a landfill, and refilling the site with pristine soil. A sensitivity analysis was performed using different yields of biomass and biogas, and using different distances between site and biomass valorization/disposal center. Our results show that the impacts caused during agricultural activities and biomass valorization were compensated by the production of synthetic natural gas and the avoided impact of natural gas production. In addition, it was found that if the produced biomass was not valorized, the sustainability of phytoremediation is questionable. The distance between the site and the biomass processing center is not a major factor for determining the technology's sustainability, providing distances are less than 200-300 km. However, distance to landfill or to the source of pristine soil is a key factor when deciding to use phytoremediation or other ex-situ conventional remediation techniques.