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Industrial wastewater effluent containing dyes and hazardous waste, such as olive waste, pose serious threat to health and environment. This work investigated the removal of azo and non-azo dyes from a single and binary aqueous system using hydrochar produced from hazardous olive waste using hydrothermal carbonization (HTC). Optimisation suggested hydrochar obtained at 250°C (HC-9) exhibited best physiochemical, structural properties and around 300% increase in carboxylic and carbonyl groups indicated by nuclear magnetic resonance spectroscopy. HC-9 removed ∼100% of Methylene blue and Congo red in single (120 and 180 min) and binary system (60 min), respectively. Ex situ X-ray photon electron spectroscopy and surface area analysis after adsorption suggested chemisorption supported by pseudo-second order reaction, Langmuir, and Redlich-Peterson model. HC-9 exhibited around 80% reusability in three adsorption cycles. Thus, better working efficiency of our hydrochar in the complex wastewater make it a potential candidate to be employed in commercial plants.

Per- and polyfluoroalkyl substances (PFAS) are ubiquitous global environmental contaminants, environmentally persistent, mobile, can bioaccumulate and are toxic. Increasing emphasis is placed on the immobilisation and removal of PFAS from contaminated environmental matrices such as: potable water, surface water, groundwater, wastewater, sediments and soils (Dauchy et al., 2017; Cao et al., 2019; Hepburn et al., 2019). To achieve this, development of PFAS sorbents is increasingly undertaken (Du et al., 2014). Sorption studies are used to observe the interaction of sorbent and sorbate, but have two key limitations when undertaking sorption experiments for PFAS (1) the experimental protocol and (2) analytical techniques. The current batch sorption methods approached recommended by OECD Guideline 106 (OECD, 2000) are problematic, firstly, due to large sample numbers and PFAS specific laboratory difficulties, including near ubiquitous background PFAS contamination. Secondly, PFAS analytical techniques currently require solid-phase extraction (SPE) to be employed, which is slow and expensive, prior to instrumental analysis with liquid chromatography-mass spectrometry (LC-MS). A suitable alternative approach is needed to mitigate the drawbacks of current methodologies whilst catering for the high sample throughput required by benchtop trials characterising the sorption behaviour of PFAS - sorbent pairings. • A suitable method for PFAS measurement, overcoming shortcomings of current batch sorption methodologies is presented • The method can be applied to a wide range of sorbents and sorption environment conditions associated with PFAS immobilisation or removal in the environment • The presented method is novel through its high sample throughput, simple approach and minimisation of cross contamination sources