• Energy Research
• 7. Clean energy close

It is urgent that we increase global food production to support population growth. Food production requires significant resources, amongst them water and energy. Therefore, any losses of food or other agricultural products also means a waste of water and energy resources. A significant amount of these losses occurs during the postharvest stage, primarily during processing and storage. This is considered avoidable food waste. The water-energy-waste nexus (WEW), and its relationship to food production, needs to be investigated from a circular bioeconomy lens. Furthermore, alternative uses of the wastes should be investigated. This review focuses on agro-wastes and their management as sources for bioactive compounds, biofertilizers, biomaterials, nanomaterials, pharmaceuticals and medicinal agents, and growth media, e.g., for plant tissue culture. We also investigated the potential contribution of agro-wastes to bioenergy production (bioethanol, biogas, and biofuel). Proper management of agro-wastes may support the mitigation of climate change, produce innovative bio-ingredients and biodegradable materials, and enhance green growth and a circular bioeconomy. We argue that the management of agro-wastes cannot be discussed without referring to the role of water and energy within the food system. Thus, this review focuses on agricultural wastes and their handling, applications, environmental impacts, and potential benefits in the agricultural and medical industries in light of the WEW nexus.

In recent years, giant reed (Arundo donax L) has received considerable attention as a promising plant for energy production. Giant reed is able to grow in a range of environments, including wetlands and marginal soils, and has shown promise in phytoremediation efforts. A pot experiment was carried out to investigate the ability of giant reed to restore ecosystems of different soils, including bauxite-derived red mud-amended soil and pure red mud (red mud—a waste generated by the Bayer process in the aluminum industry—is strongly alkaline and has a high salt content and electrical conductivity (EC) dominated by sodium). Samples were exposed to high temperatures, which simulate the effects of bushfires. Selected soil properties that were measured included soil dehydrogenase, alkaline phosphatase, urease and catalase activities, soil organic carbon, soil pH, EC, available soil macronutrients NPK, and above- and below-ground plant biomass yield. The results showed that giant reed reduced EC in all autoclaved soils and red mud-contaminated soils by 24–82 %. Significantly, available N was increased, and a slight increase was recorded for available K. The presence of giant reed enhanced the soils’ enzyme activities to recover in all tested autoclaved soils and red mud-contaminated soils; specifically, dehydrogenase activity increased by 262 and 705 % in non-autoclaved and autoclaved soils, respectively, and urease and catalase activities increased by 591 and 385 % in autoclaved soils, respectively. Total bacterial and fungal counts were higher in autoclaved soils than non-autoclaved soils after cultivating giant reed for 12 weeks. Autoclaved soils enabled higher biomass production for giant reed than non-autoclaved soils. These results demonstrate that giant reed is not only able to survive on soil that has lost its microbial community as a result of heat, but can also yield significant amounts of biomass while assisting recovering soil ecosystems after bushfires.

To evaluate copper uptake and its toxicity on bioenergy grass giant reed (Arundo donax L.), experiments were carried out using two epigenetic clonal lines - American (BL) and Hungarian (20SZ) ecotypes - grown on elevated Cu concentrations up to 26.8 mg L(-1). Neither ecotype showed any noticeable foliar symptoms of Cu toxicity at concentrations tested up to 10 mg L(-1). Dry mass of plants of both ecotypes significantly increased at the highest Cu treatment compared to control. Although the BL ecotype had greater capacity to uptake Cu than 20SZ, the dry mass and shoot length of BL was higher than that of 20SZ. Values of bioconcentration and transportation factors were higher in the BL than in the 20SZ ecotype. Almost 45 % of total Cu content within the whole plant was found in the plant root of both ecotypes. This demonstrated both ecotypes can be utilized for Cu phytoremediation alongside with significant biomass production.