The modern society needs an urgent shift to new engineered biotechnologies to achieve the millennium development goals and accomplish the energy transition from traditional fossil resources to sustainable alternatives. These technologies are aimed for the production of renewable energy and recovery of new resources from solid wastes and wastewater streams. Hence, a linear economy system, based on the “take-make-dispose” model, i.e. resources are “taken”, products are “made”, used and then “disposed” as waste, is no longer sustainable and should be entirely replaced by a new system of circular economy. This is based on the “take(reduced)-make-reuse&recycle” model, i.e. “reduced” resources are “taken” as products are “made” with mainly “reused&recycled” material, while energy is extracted from wastes as well. Science plays a critical role in making this possible by addressing the wide range of challenges that need to be overcome before a circular economy model can be widely adopted.
In this direction, novel research outcomes have been achieved during the implementation of the ABWET program in terms of:
• optimization of the anaerobic digestion (AD) process. Valuable work has especially been done on mathematical modelling, as a powerful tool to control the yield of the process, and on the valorization and clean-up of the AD products, i.e. digestate and biogas, for the recovery of nutrients (N, P and others), metals and energy as biomethane (CH4);
• production of bio-hydrogen (H2) via dark fermentation maximizing the hydrogen yields and production rates under mesophilic, thermophilic and hyperthermophilic conditions;
• reuse of toxic gases (e.g. H2S) and AD waste by-products (i.e. biogenic elemental sulfur) as electron donors to stimulate the biological removal of nitrate from wastewaters;
• algal growth and biorefinery through cultivation of microalgal species in digestates or through the supplementation of simulated CO2-containing biogas or flue gases;
• enrichment of a solventogenic anaerobic sludge converting carbon monoxide and syngas into acids and alcohols;
• anaerobic utilization of gas-phase methanol coupled to thiosulphate reduction and resource recovery through volatile fatty acids production;
• H2S removal and microbial community composition analysis in an anoxic biotrickling filter operated under autotrophic and mixotrophic conditions;
• exploitation of biochar for an efficient removal and recovery of resources, such as metals.
The program has contributed to train specialists in environmental technologies and circular economy, able to understand the life-cycle of waste to energy processes, think and work in a multidisciplinary way, and cooperate with people having different educational backgrounds. During the secondments, the ESRs gained different research methodologies and approaches on how to look at the problems with different scientific viewpoints. During the summer schools and conferences, the ESRs have learnt focusing on transferrable skills such as entrepreneurship, presentation and communication. A close cooperation between different research organizations and industry provided the ESRs networking abilities and good chances of finding future employment.
