Proano, Camila AAnaerobic digestion (AD) is a sustainable waste-to-energy method for converting organic waste to methane. Various pre-treatment of food waste (FW) with free nitrous acid (FNA; pKa=3.25) were used to stabilize FW and mitigate obstacles (odor in FW storage and pathogenic bacteria) in AD. FNA concentrations ranging from 0-5 mg-N/L were tested in this study at pH ranging from 3-5.5, and volatile solids (VS) content of 16.8-135 g/L. Solubilization of organic material, inhibition of N-related biological processes, and control of problematic microorganisms, including sulfate-reducing bacteria (SRB) and pathogenic bacteria, were compared with the groups without FNA addition. At the tested pH (3, 4, and 5) and concentrations of FNA (0.3-5.0 mg-N/L), FNA addition showed inhibition to N-related biological processes contributing to a consistent FNA concentration over the 72 hours pre-treatment. However, it did not enhance the solubilization of organic materials compared with control group without FNA addition. The FNA concentration affected the bacterial inhibition of SRB. As the concentration of FNA increased from 0.3-5.0 mg-N/L, so did SRB inhibition. Similarly, increasing FNA concentration resulted in a faster reduction (2.5 logs within 4 hours) in pathogenic bacteria compared with the group without FNA addition. Overall, a shorter pre-treatment time (<24 hours) is recommended for using low FNA concentration (1.5 mg N/L) and high solids content (> 80.57 g /L), as the effective FNA concentration cannot be maintained for longer due to NO2- and bioavailable organic carbon consumption by N-related or other microorganisms that remain active or recoverable under the added FNA concentration.enThesisEnvironmental engineeringAnaerobic digestionFood wasteFree nitrous acidPathogensSulfate reducing bacteria