Environmental Engineering Processes and Systems

Acidogenic fermentation of process water from the hydrothermal carbonization of sewage sludge to obtain volatile fatty acids.

A laboratory-scale continuously stirred tank reactor (CSTR) with a working volume of 2 L will be used in the acidogenic fermentation of process water from the hydrothermal carbonization of sewage sludge. Experiments at mesophilic (35 ± 1 ºC) and thermophilic (55 ± 1 ºC) conditions will be carried out. The organic loading rate (OLR) will vary in the range of 1000 to 3000 mg COD L-1 d-1 to determine the operating conditions allowing the maximum VFA (volatile fatty acids)  concentration. The liquid sample will be centrifuged and then filtered (0.45 mm) before analyses. TS, VS, pH, COD, TKN, lipids, and carbohydrates will be determined (APHA, 2005) and individual VFA concentrations (C2-C7, including isoforms) will be quantified by GC-FID. In addition, biogas production will be determined. Biogas composition will be determined by GC-TCD with the aim of knowing biohydrogen production.

The parameters selected to evaluate the optimal conditions of the process will be the degree of acidification, defined as the sum of each individual VFA produced in the effluent, expressed as COD equivalents (mg COD L-1), divided by the initial COD added (mg COD L-1), and the quality of the effluent expressed as the ratio between the sum of each individual organic acid produced in the effluent as COD equivalents (mg COD L-1) and the COD of the effluent (mg COD L-1).

Microbial populations in the reactors will be characterized by Next-Generation Sequencing. 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.