The lipid fraction of the effluents generated in several food-processing activities can be transformed into polyhydroxyalkanoates (PHAs) and triacylglycerides (TAGs), through open culture biotechnologies. Although competition between storing and non-storing populations in mixed microbial cultures (MMCs) has been widely studied, the right selective environment allowing for the robust enrichment of a community when different types of accumulators coexist is still not clear. In this research, comprehensive metabolic analyses of PHA and TAG synthesis and degradation, and concomitant respiration of external carbon, were used to understand and explain the changes observed in a laboratory-scale bioreactor fed with the lipid-rich fraction (mainly oleic acid) of a wastewater stream produced in the fish-canning industry. It was concluded that the mode of oxygen, carbon, and nitrogen supply determines the enrichment of the culture in specific populations, and hence the type of intracellular compounds preferentially accumulated. Coupled carbon and nitrogen feeding regime mainly selects for TAG producers whereas uncoupled feeding leads to PHA or TAG production function of the rate of carbon supply under specific aeration rates and feast and famine phases lengths.

Industrial waste fish oil streams contain high concentrations of medium and long-chain fatty acids suitable to produce value-added compounds. However, to process them dilution is required, and the water produced in the fish-canning industry commonly contains high salinity, which might limit its reuse as a dilution stream. Although NaCl is well-known to negatively affect biological activity, its effect on triacylglycerides (TAG) and polyhydroxyalkanoates (PHA) storage has not been well studied yet. Here, it was explored if intracellular TAG and PHA production can be efficient under saline conditions (10 g NaCl/L). For that purpose, waste fish oil was valorised using a mixed microbial culture (MMC) in a two-stage process (culture selection plus accumulation). Results showed that salinity influenced not only the activity but the structure of the microbial communities developed in the bioreactors. The bacterial genera Acinetobacter and Rhizobium and the mold Candida glaebosa clade were observed as the storing microorganisms which abundance increased under saline conditions whereas Dipodascus and Mortierella notably decreased. Nonetheless, despite the osmotic stress, promising results were obtained and maximum intracellular accumulations of 54.2 wt% (TAG:PHA = 28:72, 0.131 Cmmol_TAG/Cmmol_S, 0.303 Cmmol_PHA/Cmmol_S) and 50.9 wt% (TAG:PHA = 63:37, 0.291 Cmmol_TAG/Cmmol_S, 0.114 Cmmol_PHA/Cmmol_S) were observed when PHA and TAG were preferentially stored, respectively.