Volatile Fatty Acids (VFA) Production from Wastewaters with High Salinity—Influence of pH, Salinity and Reactor Configuration

Valorizing meat processing industry brines to produce added-value organic acids

During the production of certain meat processed products, such as cured ham and cold meat, large amounts of wastewater with high organic matter and salt content are generated. In contrast with the conventional management processes, which involves high energy consumption, this study proposes the valorisation of such meat brines through anaerobic fermentation to produce added-value organic acids. Several brines coming from different meat processing processes were tested to evaluate their acidification potential as well as to establish the main operation parameters in the fermenter: pH and the substrate-to-inoculum ratio. The brine with the best acidification results in both experiments was selected to be fed into a fed-batch fermenter at pH close to neutrality (6.5-7.3) and with an HRT of 6 d. With such conditions, a 27% of acidification in average was observed under an electrical conductivity up to 155 mS cm-1. Acetic and propionic acid were the most produced volatile fatty acids (VFAs) (39% and 22.0%, respectively), being the rest (up to 40%) ≥ C4 (including butyric, valeric and their isomeric forms). Finally, a selective separation between the salt and the VFAs were achieved working at low current density (<100 A m-2) in an electrodialysis system (80% of recovery in the diluate). The technological approach proposed in this study can be considered as a starting point to valorize high-salinity industrial wastewater, aligning with the circular economy model principles.

Polyhydroxyalkanoates Production by Mixed Microbial Culture under High Salinity

The fishing industry produces vast amounts of saline organic side streams that require adequate treatment and disposal. The bioconversion of saline resources into value-added products, such as biodegradable polyhydroxyalkanoates (PHAs), has not yet been fully explored. This study investigated PHA production by mixed microbial cultures under 30 gNaCl/L, the highest NaCl concentration reported for the acclimatization of a PHA-accumulating mixed microbial culture (MMC). The operational conditions used during the culture-selection stage resulted in an enriched PHA-accumulating culture dominated by the Rhodobacteraceae family (95.2%) and capable of storing PHAs up to 84.1% wt. (volatile suspended solids (VSS) basis) for the highest organic loading rate (OLR) applied (120 Cmmol/(L.d)). This culture presented a higher preference for the consumption of valeric acid (0.23 ± 0.03 CmolHVal/(CmolX.h)), and the 3HV monomer polymerization (0.33 ± 0.04 CmmolHV/(CmmolX.h) was higher as well. As result, a P(3HB-co-3HV)) with high HV content (63% wt.) was produced in the accumulation tests conducted at higher OLRs and with 30 gNaCl/L. A global volumetric PHA productivity of 0.77 gPHA/(L.h) and a specific PHA productivity of 0.21 gPHA/(gX.h) were achieved. These results suggested the significant potential of the bioconversion of saline resources into value-added products, such as PHAs.