Abstract
Though suggested by international conventions for a long time, there are still several technical and legislative limitations to a complete reuse and recycling of dredged sediments. In particular, reuse of unpolluted sediments can be practiced, whereas sediment recycling is still affected by several downsides, and a significant proportion of the recycled fine sediments has no practical use and must be landfilled. However, the silty clayey fraction of the recycled sediments is rich in organic matter and macro- and micronutrients useful for plant growth. Nevertheless, sediment recycling in agriculture is not possible, even in non-food agricultural sectors, due to the lack of a permissive legislation and of consolidated supply chains. In addition to plant nutrients, the silty-clay sediment fraction may also accumulate organic and inorganic pollutants, and while the organic pollutants can be effectively biodegraded, metals and metalloids may concentrate at concentrations higher than the limits set by the environmental and agricultural legislations. In this paper, I briefly summarize the scientific evidence on the potential reuse and recycling of sediments in agriculture, and I discuss the main reasons for hindrance of sediment recycling in agriculture. I also present evidence from a real industrial biodegradation process that produces bioremediated fine sediment fractions with suitable properties as a mineral ingredient for plant-growing media. I propose that nutrient-rich recycled sediments could be reconsidered as a component material category in the new EU regulation on fertilizers.
Highlights
Sediment is a natural mineral matrix formed by the weathering and erosion of bedrocks under the action of water and climatic and biotic factors
For both solid phase and leaching, organic pollutant classes such as total and heavy (C > 12) hydrocarbons, polychlorinated hydrocarbons (PCB), benzene, toluene, ethylbenzene and xilene (BTEX), phenols, polycyclic aromatic hydrocarbons (PAH), and agrochemical such as DDD, DDE, DDT atrazine, endrin, and dieldrin were below the concentration limits for sediment reuse in urban and industrial areas according to the Italian environmental legislation
The main EU Directives dealing with sediment management concern water, waste, and landfills, and mainly focus on the impact of sediment reuse or dumping, whereas sediment recycling is seldom on the environmental public agenda
Summary
Sediment is a natural mineral matrix formed by the weathering and erosion of bedrocks under the action of water and climatic and biotic factors. Besides the dredging size and time frame, characteristics of the dredging site, dredging operations, and equipment depend on a number of factors on site such as water depth, type and cohesiveness of materials, presence of organic debris, chemical precipitates, levels of contamination, availability of disposal, and confined facilities [4,5] For these reasons, dredging activities must be carefully planned, and only start when all technical requirements are met. In relation to the contamination level, in situ sediment reuse or sea disposal is generally allowed when concentration of contaminants is below the legislative threshold limits, and is not much practiced in industrial sites where sediment accumulates high concentrations of organic contaminants and heavy metals transported to the recipient water bodies by soil erosion, sewage outfalls, urban and industrial runoff, and atmospheric precipitation [10].
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