1718 * For correspondence. Journal of Environmental Protection and Ecology 15, No 4, 1718–1726 (2014) Clean technologies DETERMINATION OF COLOUR REMOVAL EFFICIENCY OF Lemna minor L. FROM INDUSTRIAL EFFLUENTS Y. UYSAL*, D. AKTAS, Y. CAGLAR Department of Environmental Engineering, Faculty of Engineering and Architecture, Kahramanmaras Sutcu Imam University, 46 100 Kahramanmaras, Turkey E-mail: yuysal@ksu.edu.tr; yagmur_uysal@hotmail.com Abstract. Industrial and domestic wastewater treatment by using loating aquatic plants such as duckweed (Lemna minor L.) is a promising technology and, also an alternative method to traditional treatment methods in recent years. Some characteristics of this natural treatment technology such as its low capital and operation costs, easy to operate and low energy requirement make duckweed-based systems very attractive for wastewater treatment. Coloured industrial efluents that are very important for environment because of containing more pollutants are mostly resulted from dyeing processes. The most important parameter of these wastewaters is colour, and there are a lot of physical and chemical methods to remove it from wastewater. In this study, the potential of duckweed, L. minor grown in a laboratory scale pond system to remove colour from industrial efluent was investigated. According to the results, the percentage colour removal of system continuously decreased with time. The maximum removal eficiencies of the system having HRT (hydraulic retention time) of 3 days were found to be 85.9% for COD (chemical oxygen demand), 79.4% for MLSS (mixed liquor suspended solids), 66.1% for Pt–Co (platinum–cobalt colour unit), and 68.2% for DFZ (European norm for colour at three wavelengths)-436 nm, 68.4% for DFZ-525 nm, and 83.8% for DFZ-620 nm. Keywords: Lemna minor, duckweed, colour, wastewater treatment, phytoremediation. AIMS AND BACKGROUND Phytoremediation is an alternative method to traditional expensive treatment meth- ods in order to remove different pollutants such as heavy metals and xenobiotics from wastewater. In this study, it was aimed to ind the eficiency of Lemna minor to remove colour from coloured industrial efluents as an alternative phytoreme- diation technology. One of the negative consequences of industrialised societies is the spread of several xenobiotic compounds contaminating our environment. These compounds are causing a lot of public and ecological health problems. These potential health risks are mostly associated with increasing of wastewater discharges spreading the entire of aquatic environment containing toxic chemicals such as heavy metals, phenolic compounds and dyes. Such extensive use of dyes and pigments in the