## 2 Materials and Methods  
### General Characterisation of the Textile Effluent  
The samples of textile effluent were supplied by a Portuguese textile manufacturer. The samples were taken at two different points in the wastewater treatment plant, before (RE) and after (TE1 and TE2) the application of a sequential treatment. The treated effluent was collected at two different moments, separated by a few days. The treated effluent was subjected to physical, biological and chemical treatments carried out in the company's own wastewater treatment plant. The raw effluent (highly alkaline and coloured) first went through a physical process that removed the main solid residues present. Afterwards, the effluent passed to a homogenisation tank with a Venturi-type submerged aerator for a pre-oxidation of the organic matter. At this step, sulphuric acid was added to correct the pH (between 6 and 9) and make the effluent suitable for the biological treatment. The biological treatment was performed in aeration tanks where the organic matter resulting from the dyeing processes, both the cotton waste and the chemicals and dyes used, was decomposed by the action of bacteria through aerobic digestion. In this tank, flocculants were further added to allow the agglomeration of the suspended particles that were not biodegradable. Next, the effluent was sent to a decanter to separate the biological sludge from the treated effluent. The treated effluent was then discharged to a municipal collector, while part of the biological sludge was recirculated back to the biological tank, and the other part was sent to a tank where a flocculant was added so they could be removed through a filter press and sent to landfill. The samples of treated effluent (TE1 and TE2) were collected immediately before being discharged to the municipal collector at different times in a tank with a continuous mixture. Before testing, all the samples were filtered with a glass fiber Whatman filter (Sigma-Aldrich Quimica, S.L., Sintra, Portugal) with a porosity of 1.2 \(\upmu\)m. The colour of the samples was measured in a photometer C200 (Hanna Instruments, Povoa de Varzim, Portugal) using the Platinum Cobalt from Standard Method for the Examination of Water and Wastewater (American Public Health Association, 1998). The values of pH, conductivity and total dissolved solids (TDS) were measured with a portable multiparameter (HI 991300, Hanna Instruments, Povoa de Varzim, Portugal). Gas Chromatography Coupled to Mass Spectrometry (GC-MS) Methodology  
The samples of textile effluent (RE and TE1) were concentrated using solid-phase extraction (SPE). For the isolation and preconcentration of pollutants, two different sorbents were used: C18 (Sigma-Aldrich Quimica, S.L., Sintra, Portugal) (500 mg, 6 mL) and styrene divinylbenzene (Sigma-Aldrich Quimica, S.L., Sintra, Portugal) (200 mg, 6 mL). A loading volume of 50 mL of effluent sample was applied to the C18 cartridge and acidified to pH 3. After that, it was loaded on the styrene divinylbenzene cartridge at 15 mL/min and eluted with 10 mL of triethylamine (5 mM) and acetic acid/methanol (5 mM) (1:9, _v/v_) for the desorption of anionic substances. The elements used for desorption were the following: 2 \(\times\) 5 mL of hexane followed by 2 \(\times\) 5 mL of dichloromethane/hexane (4:1, _v/v_) and 2 \(\times\) 5 mL of methanol/dichloromethane (9:1, _v/v_). Finally, total evaporation of the extracts was carried out with a stream of nitrogen. The extracts were reconstituted to a final volume of 1 mL in methanol prior to analysis. The GC-MS analyses were performed on a Shimadzu apparatus (Shimadzu Limited, Milton Keynes, UK) equipped with a capillary column (DB-17-HT; 30 m \(\times\) 0.25 mm \(\times\) 0.1 \(\upmu\)M). The sample (0.2 mL) was injected at a pressure of 15 psi, where helium was used as a carrier gas at a rate of 35 mL/min. The temperature program started at 40 \({}^{\circ}\)C and then increased up to 350 \({}^{\circ}\)C at a rate of 8 \({}^{\circ}\)C/min.