Table 1.
Properties of organic acids relevant to their separation from spent medium by electrodialysis
| Organic acid | Carbons | Valence | pK a | HPP mol−1 | BCE (%) |
|---|---|---|---|---|---|
| Butyrate | 4 | 1 | 4.81 | 10 | 13 |
| Lactate | 3 | 1 | 3.86 | 6 | 21.6 |
| Formate | 1 | 1 | 3.75 | 2 | N/A |
| Acetate | 2 | 1 | 4.76 | 7 | 32.5 |
| Succinate | 4 | 2 | 4.19, 5.57 | 7 | 27.1 |
The break‐even current efficiency (BCE: (energy expended/energy gained) × 100)) was calculated for individual organic acids. The lower the BCE, the less energy required to transport the organic acid. The electrical energy required for organic acid transport via electrodialysis relates to the number of charges and number of carbons; butyrate (4 carbons, 1 charge) is the most favourable and also has the highest proportion of charged butyrate (c.f. butyric acid) according to the pKa. HPP is hydrogen production potential of the dual system as defined by Eroğlu et al. (2004).