Combination of Lagrangian Discrete Phase Model and sediment physico-chemical characteristics for the prediction of the distribution of trace metal contamination in a stormwater detention basin.

Elevated trace metal concentrations in sediments pose a major problem for the management of stormwater detention basins. These basins provide a nature-based solution to remove particulate pollutants through settling, but the resuspension of these contaminated deposits may impact the quality of both surface and groundwater. A better understanding of trace metal distribution will help to improve basin design and sediment management. This study aims to predict the distribution of trace metal contamination in a stormwater detention basin through (i) investigation of the correlation between metal content in sediments and their settling velocity, and (ii) the coupling of such correlation with a Lagrangian Discrete Phase Model (LDPM). The correlation between Fe, Cr, Cu, Ni, Pb contents and the settling velocity is firstly investigated, based on the sediments collected from 6 sites (inlet and 5 traps at the bottom of a detention basin situated in Chassieu, France) during 5 campaigns in 2017. Results show that Fe is strongly correlated to settling velocity and can be considered as a good indicator of trace metal contents. The derived correlation is then combined with a LDPM for the prediction of trace metal distribution, producing results consistent with in situ measurements. The proposed methodology can be applied for other stormwater basins (dry or wet). As described in this article, the interactions between hydrodynamics and sediment physico-chemical characteristics is crucial for the design and management of stormwater detention basins, allowing managers to target the highest contaminated sediments.

Legal situation and current practice of waste incineration bottom ash utilisation in Europe.

Almost 500 municipal solid waste incineration plants in the EU, Norway and Switzerland generate about 17.6 Mt/a of incinerator bottom ash (IBA). IBA contains minerals and metals. Metals are mostly separated and sold to the scrap market and minerals are either disposed of in landfills or utilised in the construction sector. Since there is no uniform regulation for IBA utilisation at EU level, countries developed own rules with varying requirements for utilisation. As a result from a cooperation network between European experts an up-to-date overview of documents regulating IBA utilisation is presented. Furthermore, this work highlights the different requirements that have to be considered. Overall, 51 different parameters for the total content and 36 different parameters for the emission by leaching are defined. An analysis of the defined parameter reveals that leaching parameters are significantly more to be considered compared to total content parameters. In order to assess the leaching behaviour nine different leaching tests, including batch tests, up-flow percolation tests and one diffusion test (monolithic materials) are in place. A further discussion of leaching parameters showed that certain countries took over limit values initially defined for landfills for inert waste and adopted them for IBA utilisation. The overall utilisation rate of IBA in construction works is approximately 54 wt%. It is revealed that the rate of utilisation does not necessarily depend on how well regulated IBA utilisation is, but rather seems to be a result of political commitment for IBA recycling and economically interesting circumstances.