Analysis of changes on substrates filling constructed wetland systems after landfill leachate treatment - FTIR study

Abstract

A rapid and inexpensive method, Fourier transform infrared spectroscopy (FTIR), can be used to identify impurities and determine the functional groups responsible for the sorption of specific ions. The FTIR method has already been used in research. However, there is a lack of research on constructed wetland (CW) infill materials used to treat landfill leachate (LL). Therefore, the aim of this study was to verify the changes occurring in selected substrates (zeolite, expanded clay and bark) constituting vertical flow CW infill (VFCW) supplied with municipal LL. The principal component analysis carried out mainly showed differences in the results between the variants of the experiment with an infill of expanded clay and the others (for the values obtained at wave numbers in the range 1600-400 cm−1, in which most changes occurred). All peaks of the FTIR spectra of the pine bark filling the CW differ in location and intensity between the samples. In most cases, the stripes were elongated at exposure to 25% and 100% LL (compared to tap water). In all CW variants infill made of zeolite, peaks occurred at wave numbers within 1049-1012 cm−1, which were most likely caused by the presence of inorganic substances corresponding to clay minerals, and to silica. The FTIR spectra for zeolites, do not show large differences between the different infill samples used for LL treatment (100% LL and 25% LL). In all CW variants with expanded clay infill, peaks in the 1250-900 cm−1 wave number region, possibly indicating the presence of polysaccharides and phosphodiesters. FTIR spectroscopy has proven to be a very useful tool for rapid grade assessment determination of changes occurring on selected substrates and the identification of contaminants that remained after treatment in VFCWs fed with LL.