Waste materials are increasingly reused in road foundations, noise barriers and other construction applications. In addition to pollutants, these materials do often contain natural organic matter that originates from the decomposition of dead plant and animal matter. In particular, humic and fulvic acids can be formed that dissolve in ground- and surface water and are able to bind insoluble heavy metals and organic pollutants. This process may enhance the mobility of these contaminants in the environment, caused by the phenomenon of 'leaching'; the release of contaminants from the solid waste materials through dissolution in contact with rainwater. Until recently it was difficult to estimate the environmental risks of this enhanced leaching process, since there was insufficient knowledge of the relevant natural organic matter characteristics.
André van Zomeren, a researcher at ECN Biomass, Coal & Environmental Research, has obtained his doctorate at Wageningen University on October 10th with a dissertation entitled ‘Characterisation of natural organic matter in relation to the mobility of contaminants in the environment’. In his dissertation he has demonstrated that natural humic and fulvic acids do also occur in waste materials, and greatly enhance the leaching of heavy metals such as copper.
Van Zomeren: “It is very important to determine the concentration and binding properties of humic and fulvic acids in waste materials that are reused. Only with this information a better assessment can be made of the long-term risks associated with reuse. Important materials that are reused in construction include, for example, ashes from municipal solid waste incineration, asphalt and construction and demolition waste.”
New analysis method
At present, conventional analytical methods exist to measure the different organic substances, but these methods are very time-consuming and costly. Therefore, van Zomeren has developed an apparatus for automatic isolation of these organic fractions, together with a method to measure the concentrations of humic and fulvic acids more easily. In view of the environmental relevance of these organic fractions, the latter method has now been submitted for standardisation by the International Standardisation Organisation (ISO).
“A nice example of the use of this new knowledge is that we can now assist the municipal solid waste incinerators to improve the environmental quality of their ashes. The leaching of copper from these materials is a point of attention. We have discovered that this process is caused by a small amount of natural organic matter and we can help the incinerators to determine this amount and to reduce it. We have already shown at a pilot scale that the leaching of copper can then be significantly reduced.”
Results
“The potential risks associated with reuse of waste materials depend on the extent to which the contaminants are mobile in the environment through leaching. To make a realistic assessment one has to determine what substances and amounts may be leached from the waste materials. Since we want to know upfront what will happen in100 years, we use computer models to calculate the potential risks. The quantities of humic and fulvic acid are very important in these models, but have until now been extremely difficult to measure.”
Van Zomeren explains: “The measurement data are entered in a computer model that predicts the leaching and mobility of contaminants into the soil and groundwater. Based on this approach, new environmental criteria have recently been established for construction materials in the Dutch Soil Protection Act (Besluit Bodemkwaliteit).”
Furthermore, the finding that organic substances such as humic and fulvic acids increase the leaching of contaminants from waste materials, has led to a new technology to reduce this effect and thus improve the quality of the waste materials. “With this technology, waste materials can be reused in a more environmentally-friendly manner. But I cannot say much more about this process because ECN has applied for a patent on this technology and the procedure is still ongoing.”
Contact
André van Zomeren
ECN Biomass, Coal & Environmental Research
Phone: +31 (0)224 - 564768
vanzomeren@remove-this-part-removethis.ecn.nl
