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The presence of pharmaceutical products in the water cycle may cause harmful effects such as morphological, metabolic and sex alterations in aquatic organisms and the selection/development of organisms resistant to antimicrobial agents. The compounds’ stability and persistent character hinder their elimination by conventional physico-chemical and biological treatments and thus, the development of new water purification technologies has drawn great attention from academic and industrial researchers. Recently, the electro-Fenton process has been demonstrated to be a viable alternative for the removal of these hazardous, recalcitrant compounds. This process occurs under the action of a suitable catalyst, with the majority of current scientific research focused on heterogeneous systems. A significant area of research centres working on the development of an appropriate catalyst able to overcome the operating limitations associated with the homogeneous process is concerned with the short service life and difficulty in the separation/recovery of the catalyst from polluted water. This review highlights a present trend in the use of different materials as electro-Fenton catalysts for pharmaceutical compound removal from aquatic environments. The main challenges facing these technologies revolve around the enhancement of performance, stability for long-term use, life-cycle analysis considerations and cost-effectiveness. Although treatment efficiency has improved significantly, ongoing research efforts need to deliver economic viability at a larger scale due to the high operating costs, primarily related to energy consumption.

The objective of this study was to find a suitable and versatile agroforestry waste as alternative low-cost biosorbents for the removal of inorganic and organic compounds present in the wastewater of tannery industry [leather dyes and Cr(VI)]. Grapefruit peelings, fern, eucalyptus barks, oak leaves and cane pruning of grapevines were evaluated as biosorbents. Among them, grapefruit peelings showed the best results reaching 45 and 55% for the mixture of dyes and Cr(VI), respectively. A significant improvement in the performance of this biosorbent was obtained when it was pretreated with H 2 O 2 (1 M) attaining the highest removal capacity of 80% and 100%, respectively. This biosorbent was characterised showing an adsorption capacity of 1.1003 meq/g and pH ZPC 3.48. The adsorption working parameters, kinetics and isotherms were deeply studied in order to scale up the process to a continuous treatment system. Adsorption isotherms data fitted well to the Langmuir model with a maximum uptake of 37.427 mg/g for dyes mixture and 39.0628 mg/g for Cr(VI). Finally, the dynamic behaviour of the system, operating at different flow rates, was evaluated using a Homogeneous Surface Diffusion Model. Pretreated grapefruit peelings demonstrated to be a suitable low-cost biosorbent in the treatment of wastewater of tannery industry.

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