Life cycle analysis for the production of volatile fatty acids from wastewater treatment plant sludge

Society is shifting to an environmental basis due to threats caused by climate change, resource scarcity, and excessive generation of plastics. Biotechnology has sought alternatives to valorise waste streams, such as sludge generated in municipal wastewater treatment plants (WWTPs). Sludge bio-fermentation is suitable for sustainable volatile fatty acids (VFA) production by anaerobic digestion (AD). This biotechnological process is an excellent opportunity, as VFAs are in high demand by industry. This work aimed to study the environmental impacts generated by the bioproduction of VFA from primary sludge (PS) from the El Salitre WWTP in Bogotá using the life cycle analysis (LCA) methodology. VFA production was carried out in three semi-continuous reactors, using PS, an initial organic load of 14 gVS/L, a temperature of 25 °C, and a pH of 10 for 7 and 16 d, obtaining a higher VFA production and yield for the 16-day experiment with 6048 mgCOD/L; 432 gCOD/gVS, compared to 5472 mgCOD/L; 391 gCOD/gVS produced in 7 d. An LCA was carried out to select the best retention time considering eighteen environmental categories. The study of the impact categories and the modelling of the inventory data were carried out using the ReCiPe Midpoint method and Simapro software. The results showed that energy use in the process steps is the bottleneck point for sustainability and causes significant effects in almost all the impact categories evaluated. Additionally, it was found that producing VFA from municipal WWTP sludge can be considered a sustainable process due to the indicators obtained being lower than those found in the literature. Also, the concentrations achieved allow the use of these VFAs as carbon sources for making polyhydroxyalkanoates.