397 Land Contamination & Reclamation, 11 (4), 2003 © 2003 EPP Publications Ltd DOI 10.2462/09670513.628 Optimisation and assessment of different railway ballast cleaning systems P. Anderson, C.J. Cunningham, R.A. Hearnden, D.A. Barry and J.C. Philp Abstract Spent railway ballast is a source of recycled aggregate. Recycling of aggregates con- tributes to sustainable development by reducing the volume of construction waste going to landfill, reducing transportation and reducing the impact of primary mineral extraction supplying primary aggregates. Railway ballast is renewed when it loses its geotechnical properties and is no longer able to support the track adequately and provide drainage. Alternatively, ballast is removed from locations where contamination, primarily by die- sel, is unsightly and adds to the characteristic smell of a UK railway station. In this case ballast must first be cleaned before reuse as aggregate. Track-mounted systems exist to remove the ballast by vacuum and return it to the track after processing. Off-site sys- tems are similar to traditional soil- and gravel-washing plants. An optimised cleaning system can represent savings in both time and money, producing less waste for processing and disposal and returning more materials to the marketplace. Such an approach is in keeping with the overall thrust of sustainable engineering. In this study, the primary factors of contact time, cleaner concentration and abrasive action were investigated for a surfactant-based cleaning agent (Biosolve  ), applied to contaminated railway ballast using a laboratory-scale cleaning system. It was found that a 15-minute wash cycle incorporating a 1% surfactant solution concentration with abrasive action gave the optimum cleaning efficiency, reducing contamination by 86% from 17510 ±445 to 2525 ±345 mg kg –1 . Several batches of contaminated ballast could be cleaned before significant reduction in cleaning efficiency was observed. Potential environmen- tal impacts of surfactant and hydrocarbon residues were considered. The metal content and the biodegradability, with respect to the biochemical oxygen demand (BOD), of wastewaters generated were also measured. Key words: cleaning, contamination, environmental impact, optimisation, railway ballast INTRODUCTION Spent railway ballast is a source of recycled aggregate. Recycling of aggregates contributes to sustainable development by reducing the volume of construction waste going to landfill, reducing transportation and reducing the impact of primary mineral extraction sup- plying primary aggregates. Railway ballast is renewed when it loses its geotechnical properties and is no longer able to support the track adequately and provide drainage (Awoleye 1998). Alternatively, ballast is removed from locations where contamination, prima- rily by diesel, is unsightly and adds to the characteristic smell of a UK railway station. In this case ballast must first be cleaned before reuse as aggregate. One track- mounted system developed in the UK lifts contami- nated ballast from the track by vacuum. Ballast then passes through two consecutive rotating drums contain- ing a cleaning agent (terpene solvent) and then a water rinse. The system is capable of cleaning a 300 m length of track to a sleeper depth of 150 mm in 12 hours, returning the ballast to the track. Oil-containing waste solvent can be processed as a low-grade fuel, or dis- posed of (Monbiot 1999). Off-site systems are similar to traditional soil- and gravel-washing plants. These Received May 2003; accepted September 2003 Authors P. Anderson,* C.J. Cunningham, R.A. Hearnden and D.A. Barry, Contaminated Land Assessment and Remediation Research Centre (CLARRC), School of Engineering and Elec- tronics, The University of Edinburgh, Edinburgh EH9 3JN, Scotland. J.C. Philp, CLARRC, School of Life Sciences, Napier Univer- sity, Edinburgh EH10 5DT, Scotland. *Author for correspondence. Tel. +44 (0)131 650 7326; Fax +44 (0)131 650 7276; e-mail: peter.anderson@ed.ac.uk