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The detection of the highly toxic per- and polyfluoroalkyl substances, PFAS, constitutes a challenging task in terms of developing a generic method that could be rapid and applicable simultaneously to both long and short-chain PFAS at ppt concentration level. In the present study, the method introduced by the USA Environmental Protection Agency, EPA, to detect surfactants, using methylene blue, MB, which is identified an ideal candidate for PFAS-MB ion pairing, is extended at the lowest concentration range by a simple additional step that involves the dissociation of the ion pairs in water. In this work, Surface Enhanced Raman Scattering, SERS, is applied via Ag nanocolloidal suspensions to probe MB and indirectly either/or both short-chain (perfluorobutyric acid, PFBA) and long-chain (perfluoloctanoic acid, PFOA) PFAS downt to 5 ppt. This method, which can be further optimized to sub-ppt level via a custom-made SERS-PFAS dedicated Raman system, offers the possibility to be applied to either specific PFAS (both short and long-chain) in a targeted analysis or to total PFAS in a non-targeted analysis at very low detection limits, following any type of MB detection method in aqueous solutions and obviously with any type of SERS substrate. [Display omitted] • Generic PFAS detection method applicable to both short and long chain PFAS. • SERS method achieved LOD down to 5 ppt of PFAS. • Ion pairing between PFAS-MB triggered the process. • Dissociation of the ion pairs resulted the better LODs. [ABSTRACT FROM AUTHOR]

• SERS revealed reorientation and packing density of BG with respect to the AgNP surface as a function of its concentration. • The presence of the cationic surfactant CTAB improved the SERS enhancement of BG. • Micelles create the optimum distances for the generation of "hotspots". • The presence of CTAB at CMC created the optimum distances between AgNPs for appropriate SERS active "hotspots". • SERRS has been applied to detect BG below its maximum allowable discharge concentration from ClearBal in marine water. Surface-enhanced Raman scattering (SERS) has been applied utilizing colloidal suspensions of silver nanoparticles (AgNPs), for the detection of brilliant green (BG) at very low concentrations. Proper stimulated surface-enhanced resonance Raman scattering (SERRS) spectra collected from BG aqueous solutions at different low concentration ranges revealed a variation of the relative intensity ratio of certain BG bands attributed to a respective alteration of the molecular orientation of the analyte with respect to the AgNPs. This behavior is closely related to a different packing of the BG molecules on the nanoparticle surface when the concentration increases and the available space decreases. Additionally, the addition of suitable amounts of cetyl thrimethyl ammonium bromide (CTAB) to the BG aqueous solutions enhanced the detection limit of the analyte. This enlightens the role of the cationic surfactant in tuning the interparticle distances of AgNPs in the colloidal suspension; this presumably allows an optimization of the SERS enhancement factor. The concentration of CTAB that maximizes the SERS of BG is the same with the critical micelle concentration (CMC) of the surfactant. Most probably, CTAB at the CMC acts as a spacer keeping the AgNPs at a certain distance suitable for the generation of SE(R)RS hotspots. [ABSTRACT FROM AUTHOR]

• A pretreatment procedure for used disposable nappies was developed. • CaCl 2 and MgCl 2 were tested against their deswelling efficiency on SAP. • pH and solution volume did not affect SAP's deswelling. • Mixtures of CaCl 2 and MgCl 2 could reduce SAP's volume by 93% • Nappies hydrolysate can be used as substrate in co-digestion anaerobic processes. Typical used disposable nappies usually consist of nonwoven fabrics, Super Absorbent Polymer (SAP), and organic material, namely fluffy pulp, urine and/or excreta. Currently, this waste stream is being disposed to landfills causing many environmental issues. An alternative management method could be the valorisation of the biodegradable material through anaerobic digestion, and the recycling of plastics and SAP. Pretreatment of nappies is mandatory to separate SAP and plastics from the organic material. The aim of this work was the development of a process to minimize SAP's volume, as this component can swell up to 1500 times its own mass by water absorbance, thus hindering any further biological process. CaCl 2 , MgCl 2 , and a range of CaCl 2 /MgCl 2 combinations were tested against their deswelling efficiency on SAP, residual reagent concentration and reagent cost. The mixture of 20% CaCl 2 and 50% MgCl 2 (w/w) of SAP was concluded as the suitable combination of salts achieving a final SAP volume reduction of 92.7% with low residual cation concentrations and minimum cost. The physicochemical characterization of nappies' hydrolysate that took place to estimate its adequacy as substrate for anaerobic digestion resulted to a COD:N ratio within the acceptable range for a subsequent anaerobic digestion processing. [ABSTRACT FROM AUTHOR]