Evaluation of frameworks for ecotoxicological hazard classification of waste.

A new harmonized EU regulation for the classification of waste came into effect on 1st June 2015, in which the criteria and assessment methods for the classification of hazardous waste are harmonized with other internationally agreed-upon systems for hazard classification of chemicals (CLP). However, criteria and guidance for the assessment of ecotoxicological hazard (Hazard Property 14, HP14) are still lacking for waste classification. This paper have evaluated and compared two HP14 classification frameworks: (i) a calculation method (summation) for mixtures, and (ii) leaching tests. The two frameworks were evaluated by surveying and evaluating ecotoxicological data for Cu, Zn, K and Ca species in bottom ash from incinerated waste, together with geochemical speciation modelling. Classification based on the summation method proved to be highly sensitive to the choice of speciation and ecotoxicological classification. This results in a wide range of critical concentrations triggering hazardous classification (in particular for Cu and Zn). Important parameters governing the availability of toxic elements, such as transformation from one species to another and complexation on organic or inorganic sorbents, are not accounted for. Geochemical modelling revealed that a testing strategy built on CLP based leaching tests (liquid/solid ratio (L/S)⩾10,000, pH range 5.5-8.5) avoids bias and is superior to the summation method with respect to both precision and accuracy. A testing strategy built on leaching tests, designed for risk assessment purposes, (L/S ratio of 10, natural pH of the ash) severely underestimate the hazard associated with the presence of toxic compounds (Cu and Zn), while simultaneously falsely indicate a hazardousness due to the presence of non-toxic compounds (Ca and K). However, the testing methods adopted by CLP are problematic from a practical and functional point of view. To conclude, the L/S ratio and pH were found to be critical for hazard classification based on leaching test methods. Further studies are needed to develop a relevant, practical and functional testing strategy for HP14 hazardous waste classification.

Metal leaching from MSWI bottom ash as affected by salt or dissolved organic matter.

In order to manage municipal solid waste incineration (MSWI) bottom ash safely, risk assessments, including the prediction of leaching under different field conditions, are necessary. In this study, the influence of salt or dissolved organic matter (DOM) in the influent on metal leaching from MSWI bottom ash was investigated in a column experiment. The presence of salt (0.1M NaCl) resulted in a small increase of As leaching, whereas no impact on leachate concentration was found when lakewater DOM (35.1mg/l dissolved organic carbon) was added. Most of the added DOM was retained within the material. Further, X-ray spectroscopy revealed that Cu(II) was the dominating form of Cu and that it probably occurred as a CuO-type mineral. The Cu(2+) activity in the MSWI bottom ash leachate was most likely determined by the dissolution of CuO together with the formation of Cu-DOM complexes and possibly also by adsorption to (hydr)oxide minerals. The addition of lake DOM in the influent resulted in lower saturation indices for CuO in the leachates, which may be due to slow CuO dissolution kinetics in combination with strong Cu-DOM complexation.

Leaching of different elements from subbase layers of alternative aggregates in pavement constructions.

The objective of this study was to analyze the accumulated effects of leaching in two test roads were municipal solid waste incineration (MSWI) bottom ash and aggregate from a railway embankment, respectively, were used as subbase aggregates. Solid samples from the subbase and the subgrade were collected in trenches, which were excavated perpendicular to the road extension. The samples were analyzed with respect to pH, water content, electrical conductivity and extractable fractions of macro and trace constituents. To conclude, spatial distribution patterns of different constituents in subbase and subgrade layers confirms the existence of two major transport processes in a road with permeable shoulders: diffusion underneath surface asphalt layers driven by a concentration gradient directed horizontally towards the shoulder of the road where the dissolved elements are carried away by advection.