pH-Regulated Acidogenic Fermentation of Chicken Manure Promotes Lactic Acid and Acetic Acid Production While Limiting Nitrogen Release

Acidogenic fermentation offers a promising approach to convert chicken manure into carbon-rich liquid products for various practical applications. However, the high nitrogen content in chicken manure hinders acidogenesis and limits product utilization due to ammonium accumulation. To address this, a 320-day fermentation experiment was conducted in a two-stage operation (Stage I: uncontrolled pH; Stage II: pH controlled at 5.0). pH adjustment was conducted by adding HCl. The continuously stirred tank fermentation reactor was operated at 37 °C and manually fed daily. Results showed that pH adjustment shifted the metabolic pathway from volatile fatty acid (VFA)-dominated production to lactic acid-enriched production: lactic acid increased from 12.6 to 35.7 g-COD/L, total VFAs decreased by 58%, while acetic acid remained at a relatively high level of chemical oxygen demand (COD) of 17.6 gCOD/L. Total ammonia nitrogen (TAN) decreased from 7.0 to 3.1 g/L, increasing the ratio of soluble COD (SCOD) to TAN from 19:1 to 38:1. The ammonium reduction was primarily due to selective inhibition of uric acid degradation under low pH, while protein hydrolysis remained largely unaffected. These findings demonstrate the potential of pH-regulated chicken manure fermentation liquor as a high-value product.