## 1 Introduction  
Effluents from the sawmill industry are generated by the sprinkling of logs and percolation through the piles of logs, bark, and wood stored [1; 2]. This leachate is then drained into surface water or groundwater. The main specific compounds in the leachate from _Pinus radiata_ and _Eucalyptus globulus_ are resin acids (up to 512 mg/L), terpen, fatty acids (up to 90 mg/L), phenols (1-30 mg/L), tannins, and lignins (900-3000 mg/L), among other compounds commonly found in wood processing wastewater [3; 4; 5]. Endocrine disruption effect can be produced by some of these specific compounds in sawmill industry leachate [4; 6]. Moreover, organic matter measured as biological oxygen demand (BOD\({}_{5}\); 500 to 5000 mg/L) could be infiltrated to the groundwater [7]. Such leachates have been treated in aerobic trickling filters reaching high removal rates of BOD\({}_{5}\), chemical oxygen demand (COD), tannins, and lignins [8]. The combination of biological treatment with ozonation has also shown good results for BOD5, COD, tannins and lignins with 99%, 80%, and 90% removals, respectively [2; 9]. However, these technologies are not easily applicable in small-scale industries, with production of 2000 to 20,000 m\({}^{3}\) sawn per year, given the high costs for both investment and maintenance-operation and their technical complexity. Thus, it is necessary to study alternative technologies with less operational costs and maintenance requirements [3; 4].  
Constructed wetlands (CW) are an established nature-based solution for wastewater treatment [2; 8; 10; 11; 12; 13; 14; 15], providing multiple economic and environmental benefits coupled with high treatment performance for various wastewater sources [5; 14; 15; 16; 17]. Moreover, CW have mechanisms to eliminate aromatic compounds via bacteria [13]. High removal rates have been reported for pollutants such as COD, BOD5, long-chain fatty acids, tannins, and lignins in wood leachate treated in CW [7; 10; 11]. Removal rates up to 91% are reported for various phenolic compounds such as gallic, syringic, and ellagic acids from corkwood processing wastewater [5]. A complete removal of phenols is also reported in pilot CW treating groundwater contaminated with fuel hydrocarbons and petroleum derivatives [16]. In general, international experiences dictate the strong potential of CW system to remediate contaminated effluents from various agro-industries [15; 18; 19].  
Due to the different feedstock, leachates from _P. radiata_ and _E. globulus_ sawmill have different concentrations of aromatic compounds (i.e., resin acids, terpenes, fatty acids, phenols, and tannins and lignins). At the same time, there is limited information in the published literature on the behavior of aromatic compounds in constructed wetland systems. In order to examine the behavior of these specific pollutant groups during aerobic treatment, the relation with UV-vis measurements was previously evaluated [12]. It has also been indicated that a kraft mill wastewater treatment plant can be monitored using UV/VIS spectroscopy [20]. Considering the above, the goal of this study was to investigate the behavior of aromatic compounds and organic matter contained in _Pinus radiata_ and _Eucaliptus globulus_ sawmill industry leachate treated in pilot constructed wetlands and evaluate their efficiency.