8Anaerobic digestion of autoclaved (160 °C, 6.2 bar) and untreated source segregated 9 food waste (FW) was compared over 473 days in semi-continuously fed mesophilic 10 reactors with trace elements supplementation, at organic loading rates (

Volatile fatty acids (VFAs) are intermediates in the methane formation pathway of anaerobic digestion and can be produced through the fermentation of organic wastes. VFAs have become an anticipated resource- and cost-effective way to replace fossil resources with higher added value and more versatile fuels and chemicals. However, there are still challenges in the production of targeted compounds from diverse and complex biomasses, such as urban biowastes. In this study, the aim was to modulate the microbial communities through inoculum treatment to enhance the production of green chemicals. Thermal and freeze-thaw treatments were applied to the anaerobic digester inoculum to inhibit the growth of methanogens and to enhance the performance of acidogenic and acetogenic bacteria. VFA fermentation after different inoculum treatments was studied in batch scale using urban biowaste as the substrate and the process performance was assessed with chemical and microbial analyses. Inoculum treatments, especially thermal treatment, were shown to increase VFA yields, which were also correlating with the dynamics of the microbial communities and retention times of the test. There was a strong correlation between VFA production and the relative abundances of the microbial orders Clostridiales (families Ruminococcaceae, Lachnospiraceae and Clostridiaceae), and Lactobacillales. A syntrophic relationship of these taxa with members of the Methanobacteriales order was also presumed.

8Digestate characteristics such as organic and nutrient content, hygienic quality and 9 stability are valuable measures when evaluating the use of food waste (FW) digestate as 10 organic fertiliser. This study compared the characteristics of FW and autoclaved (160 11 °C, 6.2 bar) FW and their digestates from laboratory-scale reactors. Decreased 12 ammonification and low ammonium nitrogen content were observed in the digestate 13 from an autoclaved FW reactor due to autoclave treatment of FW, which affected the 14 nitrogen-containing molecules by formation of Maillard compounds. The methane 15 potential of autoclaved FW and its digestate was decreased by 40% due to reduced 16 microbial activity as microbes were not able to adapt to the conditions within a reactor 17 fed with autoclaved FW. Both studied materials were suitable for agricultural use in 18 terms of their nutrient content, hygienic quality and stability, and thus the decrease in 19 ammonium nitrogen in digestate from an autoclaved FW reactor supported the use of 20 digestate as soil amendment rather than fertiliser. 21