Critical raw materials (CRMs) are essential in the development of novel high-tech applications. They are essential in sustainable materials and green technologies, including renewable energy, emissionfree electric vehicles and energy-efficient lighting. However, the sustainable supply of CRMs is a major concern. Recycling end-of-life devices is an integral element of the CRMs supply policy of many countries. Waste electrical and electronic equipment (WEEE) is an important secondary source of CRMs. Currently, pyrometallurgical processes are used to recycle metals from WEEE. These processes are deemed imperfect, energy-intensive and non-selective towards CRMs. Biotechnologies are a promising alternative to the current industrial best available technologies (BAT). In this review, we present the current frontiers in CRMs recovery from WEEE using biotechnology, the biochemical fundamentals of these bio-based technologies and discuss recent research and development (R&D) activities. These technologies encompass biologically induced leaching (bioleaching) from various matrices,biomass-induced sorption (biosorption), and bioelectrochemical systems (BES).

In the last decades the increasing energy requirements along with the need to face the consequences of climate change have driven the search for renewable energy sources, in order to replace as much as possible the use of fossil fuels. In this context biomass has generated great interest as it can be converted into energy via several routes, including fermentation and anaerobic digestion. The former is the most common option to produce ethanol, which has been recognized as one of the leading candidates to substitute a large fraction of the liquid fuels produced from oil. As the economic competitiveness of bioethanol fermentation processes has to be enhanced in order to promote its wider implementation, the most recent trends are directed towards the use of fermentation by-products within anaerobic digestion. The integration of both fermentation and anaerobic digestion, in a biorefinery concept, would allow the production of ethanol along with that of biogas, which can be used to produce heat and electricity, thus improving the overall energy balance. This work aims at reviewing the main studies on the combination of both bioethanol and biogas production processes, in order to highlight the strength and weakness of the integrated treatment for industrial application.

This paper examines the effectiveness of sonolysis in improving the anaerobic biodegradability of the organic fraction of municipal solid waste coming from mechanical selection, thus enhancing biogas production and energy recovery as well. Methane yield of solid organic material anaerobic digestion is significantly affected by substrate availability that was evaluated, in this investigation, through organic matter solubilisation tests carried out at different conditions of ultrasound treatment. Results show that sonolysis can significantly improve the solubilisation of organic solid waste, thus allowing higher biogas production from anaerobic treatment of sonicated substrates. After 45 days, the biogas produced during anaerobic codigestion tests for the sonicated mixture was 24% higher than untreated one. Therefore, these results can lay the basis for the development of technologies useful to produce high biogas quantities, in order to improve clean energy generation from biowaste.