Re-use of surplus foundry sand by composting

PROJECT DESCRIPTION

BACKGROUND

The capacity of landfill sites to receive waste is limited, and new ways must be found to re-use waste. While cleaned and recycled soil material can be valuable for agricultural and geo-engineering applications (e.g. green construction), its acceptance needs to be better established. In Europe, around 18 million tonnes of foundry waste sand is produced every year, and even large landfill sites often have insufficient capacity to accept it. In most countries, several smaller landfills are being closed and replaced by large ‘EU landfills’. However, the distances and transport costs to these sites are increasing for foundry companies and alternative means of treating these wastes in a more environmentally friendly way are being sought.

OBJECTIVES

The LIFE-FOUNDRYSAND project aimed to promote sustainable production, waste prevention and recycling by piloting new, innovative biological methods of cleaning different foundry waste sand types and eliminating hazardous, organic, trace contaminants. The objective was to study the quality of the piloted samples and ensure that they fulfil the product requirements for the re-use of cleaned sand as a substitute for ground construction materials or other soil-like materials for agricultural and geo-engineering applications.

Specifically, the project aimed to:

Develop a new method for cleaning and reusing foundry waste sand through composting;

Create a compost from foundry waste sand mixed with other biowaste (household waste, sludge, animal manure and the waste from the wood and paper industries) and demonstrate the microbiological degradation processes in open heaps;

Verify compost quality and applicability in different fields of application (gardening, green fields, ground construction, etc.);

Fulfil the national regulations and limit values set for the compost end-products, such as mixture soil material;

Produce guidelines for foundries and suppliers of cleaning service in Europe;

Implement the procedure in foundries to minimise their waste and reduce operational costs;

Reduce the amount of contaminated material entering landfill sites; and

Improve the use and acceptance of this valuable material (the cleaned foundry waste sand) for agricultural and geo-engineering applications.

RESULTS

Pilot trials of the LIFE-FOUNDRYSAND project’s innovative composting method resulted in the cleaning of 960 tonnes of surplus foundry sand composting material during the period 2015-2017. The method was shown to be at least 95% effective in treating hazardous organic compounds (such as phenols, BTEX, fluoride and PAHs). The compost end-product is within the national limits established in Finland by the Decree on Fertiliser Products, and in Spain by the Royal Decree on Fertilisers. The cleaned foundry sand end-product can therefore be used for geo-engineering and green construction purposes, thus providing foundries with a new revenue source, while reducing the financial and environment cost of landfilling.

The project sought first to establish the origins of the surplus sands from foundries, such as steel and iron foundries. Based on that, the quality of surplus foundry sand was found to differ greatly between foundries and within a foundry depending on the type of casting.

The trails demonstrated that composting is especially effective for cleaning surplus foundry sands that have a high concentration of harmful organic substances. However, the method is not suitable for all sand types. For example, waste sands and dusts including heavy metals cannot be cleaned by such composting. Therefore, surplus foundry sands and dust specimens must always be carefully analysed to determine the suitable treatment method (e.g. stabilization or incineration). However, due to the method’s efficiency and cost-effectiveness in recycling and re-using, the aim should be that around 70-80% of the surplus sands are cleaned by composting. Reliable knowledge of the composition of surplus foundry sands and their impact on the environment is vital. For foundry sand to be certified as a safe composting material a quality control system must be introduced. The re-use of surplus materials requires reliable analysis of waste and an efficient sampling procedure.

Foundries should be advised to separate different waste sand specimens carefully to ensure that only a minimum amount of foundry sands or dusts containing heavy metals is incinerated, stabilised or landfilled. Re-using waste as new end-products via an eco-friendly biological treatment process will foster public acceptance of foundries.

The project produced guidelines for the implementation of the composting method by foundries, composters and waste recycling companies. There are already some foundries in Finland using the composting method for cleaning the waste sand or dust.

During the project, the team provided input to the preparation of the new Finnish MARA decree on the re-use of waste in geo-construction work, that now includes surplus foundry.

Further information on the project can be found in the project's layman report and After-LIFE Communication Plan (see "Read more" section).