Context. Cheese whey, an aqueous by-product of the dairying industry with high organic load, has 42% of its annual production (154 Mm3·y-1) underutilized as animal feed, fertilizer or discharged in surface water leading to eutrophication.
Gap. Volatile fatty acids (VFAs) production often arises from petroleum. In order to decrease fossil fuel dependency, sustainable alternatives are sought. Acidogenic fermentation of aqueous agri-food wastewater together with selective pressure mechanisms can be suitable processes for that, as they can dictate microbial metabolism towards the production of VFAs.
Aim. Our main goal was to investigate how microbial selective pressures (i.e., pH, inoculum pre-treatment, headspace pressure and F/M ratio) influenced the production of VFAs while suppressing methanogenesis.
Methods. In batch experiments, we applied alkaline (pH 8.0 controlled for 6 hours) and thermal (90°C for 5 minutes then decreased to 23°C in ice bath) pre-treatments of inoculum to perform acidogenic fermentations in presence/absence of headspace pressure and at different initial pH (7.0 and 9.0). We measured the fermentation product spectra by HPLC and GC.
Findings.Two independent experiment replicates, demonstrated methanogenesis inhibition in thermal pre-treatment, non-pressurized batches with pH 9.0. Microbial communities consisted of VFA-producing Sedimentibacter and Longilinea, lipid-accumulating and bulking Candidatus Microthrix, sulfur and nitrogen-cycling Magnetovibrio and Sulfurovum, and acetoclastic methanogen Methanosaeta. A posterior experiment evaluated F/M ratio (0.5, 1.0, 2.0, and 4.0 g COD g VSS-1) on thermal pre-treated inoculum at initial pH of 9.0 and non-pressurized headspace. F/M 0.5 produced the most VFAs (1,769.38 mg L-1).
Utilization.Selective pressures (i.e. thermal pre-treatment, non-pressurized headspace, pH 9.0 and low F/M ratio) help halt methanogenesis and enhance VFAs production, valorizing aqueous agri-food wastes via batch acidogenic fermentation. Understanding their impacts on long-term process ecology is pivotal for process implementation.
