accumulation. The proportionally large confidence interval shown for the pH parameter d, indicates greater error with respect to pH. This is consistent with the observation of high error with respect to pH in the response surface of batches one and two (Table 3). The error of parameter d subsequently increased error within parameter c due to the role of both parameters in the r term of the model. Analysis of the correlation coefficients revealed that parameters c and d have the highest correlation at 0.75. The large confidence interval for parameter c is also due to limited data; no observations were taken between 0 and 16 h. Since parameter c modulates the rate of increase, r, this leads to greater uncertainty in the exponential phase of the model.The corrected coefficient of determination (R2) was 0.85 indicating the model was in good agreement with the data gathered. Two trials (six samples; one at 16, 20, and 24 h for each trial), which were performed concurrently in batch 1, significantly under performed the model’s prediction. When these outlierห are excluded R2 improves to 0.91. The observed versus predicted plot demonstrated a good fit with the data, including a low bias of under or over predicting the outcome (see Supplementary material). This was further supported by the residual versus predicted plot that showed the residuals to be randomly distributed (see Supplementary mate-rials). Further investigation into the residuals showed they were balanced with respect to time confirming the model does not consistently overestimate at short times and underestimate at long times.The model contains multiple limitations. Comparison of this experiment to others has demonstrated that lactate production can peak at multiple pH values. Given the optimization at pH 5.5, this model is only relevant in scenarios controlling pH between 5 and 6. Further, differences in how inoculation was performed remain a barrier to adapting this model to experiments which do not co-digest with primary sludge due to the extended digestion time of these experiments [12]. Future experiments could broaden the applicable pH range to inform the incorporation of inoculation as an input to the r term (Eq. (4)) in the model. Until then, the model is effective at describing the co-digestion with primary sludge in the pH range of 5–6. Finally, the model is applicable for loading rates below 250 g VS L−1 food waste because if a denser food waste is utilized the maximum achievable concentration may become limited by the product rather than substrate.