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Activated carbon (AC) and activated biochar (ABC) are widely used as sorbents for micropollutant removal during water and wastewater treatment. Spent adsorbents can be treated in several ways, e.g., by incineration, disposal in landfills, or reactivation. Regeneration is an attractive and potentially more economically viable alternative to modern post-treatment practices. Current strategies for assessing the performance of regeneration techniques often involve only repeated adsorption and regeneration cycles, and rarely involve direct measurements of micropollutants remaining on the adsorbent after regeneration. However, the use of regenerated adsorbents containing such residual micropollutants could present an environmental risk. In this study, the extraction of eight active pharmaceutical ingredients (APIs) commonly found in treated effluents was evaluated using 10 solvents and sorption onto three different carbon materials. An optimized extraction method was developed involving ultrasonication in 1:1 methanol:dichloromethane with 5% formic acid. This method achieved recoveries of 60 to 99% per API for an API concentration of 2 μg/g char and 27 to 129% per API for an API concentration of 1 mg/g char. Experiments using a mixture of 82 common APIs revealed that the optimized protocol achieved extraction recoveries above 70% for 29 of these APIs. These results show that the new extraction method could be a useful tool for assessing the regenerative properties of different carbon sorbents.

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<p>The emergence of micropollutants, such as pharmaceuticals in wastewater, presents a potential risk for human health as well as the aquatic environment. Current wastewater treatment plants are generally not capable of removing these pollutants without additional treatment steps. Adsorption on activated carbon is an effective way to remove these contaminants, however, the use of non-renewable feedstocks as well as low regeneration efficiencies increase the environmental costs of this method<sup>1</sup>. Biochar as a renewable carbon platform material can be specifically designed to overcome these drawbacks<sup>2</sup>.</p><p>This study is aimed at designing activated mineral biochar composites with enhanced adsorption capacity for pharmaceuticals while simultaneously optimising their regeneration performance. Two standard biochars from the UK Biochar Research Centre produced at 550°C from softwood and wheat straw were activated in CO<sub>2</sub> at 800°C. Additionally, activated mineral biochar composites were produced by the addition of ochre – a Fe-rich mining waste – prior to pyrolysis and activation.</p><p>The activated biochars and activated mineral biochar composites were analysed for their maximum adsorption capacity for two micropollutants - caffeine and fluconazole - and compared to a commercial activated carbon as a reference material. While the activated carbon outperformed all biochar samples, the addition of ochre increased the performance of the activated biochar samples. The regeneration performance was tested in a subsequent experiment. The materials were first loaded with a mix of 10 pharmaceuticals covering antibiotics, fungicides and antidepressants. The loaded biochars were then subjected to a novel regeneration method directly utilising wet adsorbents in contrast to common methods requiring prior drying. Similar to a powerful pressure cooker, solvolytic conversion conditions of water at temperatures ranging from 160 to 320°C and elevated pressures of 15 to 120 bar were used to regenerate the biochars. Hydrothermal treatment at 320°C was found to successfully degrade the adsorbed micropollutants across all biochars. The mineral biochar composites showed increased pollutant degradation most likely due to the catalytic effects of Fe in hydrothermal conditions, lowering the necessary treatment temperature to 280°C.</p><p>The results show that while designing biochar for certain applications, a simultaneous focus on both the application as well as the regeneration of the material can give a more comprehensive picture of the overall requirements for further optimisation of biochar adsorbents.</p><p> </p><ol><li>Thompson, K. A. et al. Environmental Comparison of Biochar and Activated Carbon for Tertiary Wastewater Treatment. Environ. Sci. Technol. (2016). doi:10.1021/acs.est.6b03239</li> <li>Liu, W. J., Jiang, H. & Yu, H. Q. Development of Biochar-Based Functional Materials: Toward a Sustainable Platform Carbon Material. Chem. Rev. <strong>115,</strong> 12251–12285 (2015).</li> </ol>