Waste to Value

Temperature-phased anaerobic digestion for biowaste valorization
This activity will focus on the start-up and operation of temperature-phased anaerobic digestion (TPAD) experiments at thermophilic-mesophilic temperature. Specifically in the optimization of the thermophilic stage.
A mesophilic anaerobic sludge from a WWTP will be initially adapted to thermophilic (55 ± 1 ºC) conditions. To eliminate hydrogen-consuming microorganisms and promote the development of a hydrogen-producing microbial consortium, the sludge will be subjected to a heat treatment: 100 ºC, 30 min under atmospheric pressure.
Acidogenic fermentation discontinuous runs will be carried out to determine the capacity of the obtained inoculum (thermophilic and heat pretreated) to produce hydrogen and VFA. In addition, runs with thermophilic untreated inoculum will be also performed as controls. The experiments will be run at several residence times (24-240 h) to determine the operating conditions allowing the maximum hydrogen and VFA concentration. 
A laboratory-scale CSTR (2 L) will be used in the hydrolytic-acidogenic fermentation of the slurry. Experiments at thermophilic conditions will be carried out at the pH selected, regulated through the addition of a NaOH solution (2 M). The reactor will be operated using progressively lower hydraulic retention times (HRT, 10 d – 1 d), while the organic loading rate (OLR) will vary in the range of 1000 to 3000 mg COD/Ld (Iglesias-Iglesias et al., 2021). The gas generated will be analyzed through specific online gas sensors (Bluesens®). Three times a week TS, VS, pH, COD, ammoniacal nitrogen, lipids, carbohydrates (APHA, 2005) and individual VFA concentrations (C2-C7, including isoforms) by GC-FID, will be determined. Microbial populations in the reactors will be characterized by Next-Generation Sequencing after reaching stationary state. Total genomic DNA in the biomass will be determined and paired-end sequencing of extracted DNA will be accomplished, by using an Illumina MiSeq platform. This analysis will let to know the relative abundance of microorganisms from taxonomical classification of the microbial community at phylum level.