Fossil fuel continued overuse and carbon emissions issues have prompted increased research efforts on sustainable and renewable energy sources as alternative to fossil fuels. Biofuels include products derived from biomasses or their residues, such as: biogas, biodiesel, bioethanol, biomethanol, synthetic biofuels, biohydrogen and vegetable oil. Due to their properties, all of these may be used in conventional engines as produced, or blended with fossil fuels. First and second generation biofuels may be produced from a large variety of feedstocks, including food crops such as sugar beet, sugar cane, sorghum, energy-crops, such as lignocellulosic masses, and waste, like the organic fraction of municipal solid waste, or landfill leachate. In the last decade, a third generation of biofuels has emerged, i.e. those derived from microalgae. Even though their yield is higher, and their greenhouse gas footprint lower than previous generations’, they still need large amounts of water and nutrients for production. In this paper, the most common biofuels (biogas, syngas, biodiesel, bioethanol and biobutanol) are reviewed and analyzed with particular attention on their carbon and water footprints and economic sustainability perspective.

Nature (ecosystem) based processes for wastewater treatment include constructed wetlands (CWs), waste stabilization ponds, vegetated drainage ditches, buffer zones, instream or bankside river techniques, and mixotrophic systems, where light and CO₂ are utilized, in addition to organic carbon compounds, by algal cultures. Algae-based systems can simultaneously remove organic matter, N, and P and may offer substantial energetic advantages compared to traditional biological treatment systems, require small spatial footprint, and contribute to biofuels production and CO₂ emissions mitigation. Bioelectrochemical systems (BES) such as microbial fuel cells (MFCs) present characteristics compatible with the use in isolated realities for water and wastewater treatment with contextual energy recovery and may be combined with other nature-based process technologies to achieve good treatment and energy efficiencies. Despite that their application in real-scale plants has not been assessed yet, the most probable outcome will be the in situ/on site treatment (or pretreatment) of wastes for small “in house” plants not connected to the sewerage network. This paper focuses on the current practices and perspectives of hybrid nature-based systems, such as constructed wetlands and microalgae integrated phytoremediation plants, and their possible integration with microbial electrochemical technologies to increase recovery possibilities from wastes and positively contribute to a green economy approach.