The results of the PHAs production process using acidified OMW under conditions of nitrogen and dual nitrogen–oxygen limitation are shown in Table 4. The use of OMW instead of a mixture of synthetic VFAs as carbon source generally led to smaller PHAs accumulation yields, rates and capacities [25].
Based on the results shown in Table 4, the enriched culture exhibited the higher PHAs accumulation efficiency,reaching 8.8% g PHAs/g CDM, the higher yield coefficient YPHAs/S= 0.07 g PHAs/g VFAs and the higher production rate qPHAs= 1.8 mg L−1h−1 compared to the other cultures. Those results are in agreement with the ones that had been obtained in our previous study [8]. PHAs production efficiency of the enriched culture in batch mode is the same with the one obtained in continuous mode using an SBR reactor. This proves that the particular enriched culture can store, in maximum, approximately 9% g PHAs/g CDM using olive mill wastewater as carbon source under conditions of nitrogen limitation.
However, these values were considerably smaller when OMW was used for PHAs production compared to the synthetic medium. PHAs production ranged from 0.9 to 6.2% g PHAs/g CDM in the isolates using OMW under nitrogen limited conditions. When OMW was used the enriched culture seemed to accumulate non-PHA intracellular products, as can be concluded from the difference between the YX/Sand YPHAs/Syield coefficients. Because of the oilynature of the waste, accumulation of lipids seems possible.