The proposed research project will aimed at implementing innovative processes for the treatment and exploitation of biodegradable organic residues from both municipal and industrial sources. These will be engineered to allow sequential generation of bio-hydrogen and biopolymers, thus allowing for energy or materials recovery from the mentioned wastes. The proposed biological processes are based on the so-called biorefinery concept, which involves the integration of different processes to produce value-added solid, liquid and gaseous products from biomass materials. The main objective of the research is the production of bio-hydrogen from dark fermentation of various kinds of organic residues (including the organic fraction of municipal solid waste and agroindustrial residues), with the concomitant generation of a pool of organic acids that can be further processed for materials recovery. Specifically, the dark fermentation stage will be combined with two additional biological stages that will aim at aerobically degrading the organic acids from the first stage under stress conditions for the active biomass. Stress pressure will be engineered in the system through a feast/famine operation regime in order to force the biomass to store intracellular organic polymers during high-load operation as an energy reserve for cell growth and maintenance, to be used during the starvation periods. The intracellular biopolymers will then be concentrated in a final stage operated under nutrient starvation conditions and then separated and recovered from the biomass.
A dedicated experimental campaign will be conducted on the proposal topic using fully automated reaction systems that can be operated under different conditions and monitored through a proprietary remote control software.
Achieving the results outlined above will allow the knowledge in the field of bio-hydrogen and biopolymers to make a step forward, filling in some of the existing gaps and strengthening the knowledge required to upscale the process to an industrial level.
The proposed research has a high degree of scientific innovation, since ¿ to the knowledge of the project proponents ¿ no pilot-scale nor full-scale example of combined production of bio-hydrogen and biopolymer from organic waste is currently in place. On the other hand, this alternative has the potential for a synergistic integration of the two individual processes, since the hydrolytic reactions that produce hydrogen during fermentation of biodegradable organic waste also give rise to the production of organic acids, which are considered to be the preferred substrate for the generation of biopolymers such as polyhydroxyalkanoates (PHAs). On the other hand, the first fermentation stage may also be combined with an electrochemical process for H2 generation from the generated organic acids, enhancing the overall H2 production of the full process scheme. Other potential alternatives include a two-stage fermentation for the sequential production of biohydrogen and biomethane, followed by a final aerobic stage for the production of a composted soil amending material. All such schemes are only at their initial development stage and have therefore a scientifically innovative character. They also have the potential, if adequately exploited, to contribute to move a large step forward towards the full definition and understanding of the best available technologies for biowaste management, which is a highly debated issue within the European Union. Specifically, the implementation of the organic waste biorefinery concept outlined in section 1 of the present proposal is regarded as being rather promising in terms of related direct and indirect environmental benefits, so that the scientific research on such a topic has rapidly grown over the last five years.
The results of the proposed research are expected to clarify the mechanisms and processes of combined bio-hydrogen and biopolymer production when complex matrices, such as real biodegradable organic residues, are used as the substrate. To date, a considerable share of the results currently available in the scientific literature refers to ¿synthetic¿ matrices, intended to mimic the (simplified) composition of real substrates including organic wastes of different origin, and pure microbial cultures, which would hardly be the case for full-scale industrial applications. The results attained on simple selected substrates and pure microbial cultures may yet provide some pivotal knowledge and understanding of the biochemical mechanisms involved. However, full knowledge of the real conditions requires accounting for the complexity of the biological systems when complex substrates and mixed microbial cultures are involved. Another important issue that is believed to deserve further investigation is the influence of the relevant process variables on the underlying metabolic pathways and the related process yield in terms of bio-hydrogen and biopolymers production. Important structural variables include the carbon/nitrogen ratio, the presence of competitive microorganisms, the presence of inhibitory elements and/or compounds, which are closely related to the substrate and inoculum properties. Thus, their effect can be clarified only upon a deep investigation of complex substrates and mixed cultures which can better adapt to the variability and inhomogeneity of the substrate.
Moreover, investigating the individual and joint effects of the operating conditions, such as the organic loading rate, the cell residence time, the optimal sequence of feast/famine conditions will provide the knowledge basis to identify the most appropriate conditions to be applied at the full scale. The research may also contribute to provide a preliminary systematic clarification of the technical and environmental properties of the produced biopolymers, paving the way to a better understanding of the whole process performance.
The research group has a valuable long-lasting expertise in the field and, thanks to its numerous collaboration both at the national and international level, is potentially able to provide useful scientific results from the proposed research program.