Paolo Pavan

Waste-based sustainable solutions proposed by scientific and industrial communities for energy production are an approach that can respond to the growing concerns regarding climate change and fossil resources depletion. This study investigates a two-phase bioprocess combining dark fermentation (DF) and photo-fermentation (PF) to enhance hydrogen yield while anaerobically treating urban organic food waste and sewage sludge. A key objective was to assess the effect of waste composition and temperature on hydrogen accumulation, with particular attention to the fermentation product and the role of zeolite in improving process efficiency. In the DF stage, the addition of zeolite significantly enhanced hydrogen production by increasing microbial activity and improving substrate bioavailability. As a result, hydrogen production increased up to 27.3 mmol H₂/(L d) under thermophilic conditions. After the suspended solids were removed from the dark fermentation broth, a photo-fermentation step driven by a pure strain of Rhodopseudomonas palustris was performed under permanent IR light and different substrate-to-inoculum [S/I] ratios. The maximum hydrogen production rate was 9.33 mmol H₂/(L d), when R. palustris was inoculated at the lowest [S/I] ratio (<20 COD/COD) and with 0.5 g VSS/L as the initial concentration. This condition in the photo-fermentation process led to an increase in the hydrogen yield up to 35% compared to values obtained from dark fermentation alone.

Tannery sludge is disposed of in landfills as it is considered a special residue by the Italian legislation, creating pollution and waste. This paper aims at evaluating the performance of the anaerobic fermentation process to obtain short-chain fatty acids (SCFAs) from this waste. The assessment of the most appropriate conditions, in terms of pH, temperature, initial total solids (TSs) content, and application of oxidizing-thermal pretreatment has been developed. The batch test trials revealed that the combined microwave and hydrogen peroxide (MW-H₂O₂) pretreatment followed by thermophilic conditions gave the best results, in terms of the acidification yield (0.31 gCOD_SCFA/gVS₀) and maximal SCFA concentration (above 26 g COD_SCFA/L). In the tests conducted without pretreatment, the mesophilic temperature should be preferred since the acidification performances were comparable to or even better than their thermophilic counterparts. The SCFA composition analysis showed that in mesophilic fermentation, tannery sludge can generate up to 50% acetic acid (COD_Ac/COD_SCFA), if previously pretreated (MW-H₂O₂). This research acts as a forerunner for the appropriate handling of this resource, to employ it for the development of a new tannery industry focused on a circular approach, rather than to simply dispose of it in landfills.