Modeling of solubilization dynamics of manure organic matter and phosphorus as a function of pH control and enzyme supplementation

The potential use of commercial enzyme and pH control has been investigated for enhancing dairy manure fermentation and modeling dissolved organic matter and orthophosphate (PO₄-P) dynamics of fermenters. Anaerobic lab-scale batch fermenters (initial total solids concentration (TS_o) = 3.8 wt. %) were fed with separated dairy manure solids and operated under pH controls (5 and 9.5). The enzyme-supplemented alkaline fermenters clearly outperformed the acidic fermenters in terms of chemical oxygen demand (COD) solubilization: ca. 50% vs. 20%, respectively. Soluble PO₄-P in the acidic fermenters was comparably higher but constituted less than 20% of total phosphorus. Better soluble COD (>80%) and soluble PO₄-P (>70%) yields were noted for the dilute fermenters (TS_o = 0.6–0.8 wt. %). An existing model was retrofitted, calibrated and validated for simulating dynamics of soluble COD, volatile fatty acids, and soluble orthophosphate under various pH and enzyme conditions.