waste that did not co-digest and achieved optical purities of greater than 80% l(+)-lactate [12]. Many species of lactic acid bacteria (LAB)produce l(+)-lactate exclusively, however lactate is converted from the l to d form or vice versa by the lactate racemase enzyme [22].Production of lactate racemase is induced by l-lactate presence in L. plant arum, a dominant species previously identified in food waste fermentations [10,12,23]. Therefore, it is speculated that continuous separation of lactate during fermentation has the potential to improve control of optical purity.3.5. Optimal pH and temperature Both pH and temperature influence the selection of the microbial community, and mediate the biochemical reactions that the community performs. It follows that both factors were significant and the interaction of pH and temperature was near significant(p = 0.08) as shown in Table 3. Additional experimentation could prove the interaction to be statistically significant. These results are supported by the fermentation of food waste only, which also demonstrated both f
actors and their interaction to be significant[12].A narrow pH range of 5–6 was used in order to minimize demand for buffer and identify an optimum that could inform practical process scale up. The screening experiments in batches 1 and 2 identified an optimum within these bounds but did not preclude the possibility of additional optimums outside this pH range. The optimal pH of 5.5 identified is distinct from the pH of 7–8 identified to maximize lactate production in the digestion of food waste only [12]. Additional experimentation is needed to clarify whether this difference is an artifact of co-digestion with primary sludge,smaller pH intervals tested, or whether there are multiple pH value sat which this system can be optimized for total lactate concentration. Nevertheless, the difference constitutes a sizable reduction in chemical demand for pH buffering which bolsters the feasibility of scaling up the process.