Scaling up carboxylic acid production from cheese whey and brewery wastewater via methane-arrested anaerobic digestion

In a circular economy, organic waste streams are valuable resources for sustainably producing chemicals and fuels. This study investigates a new methane-arrested anaerobic digestion (MAAD) process that converts high-strength cheese whey and brewery wastewater into carboxylic acids. The process was developed and optimized under various bench-scale semi-continuous (fed-batch) operating conditions (e.g., retention time, organic loading rate, pH, and feed/harvest frequency). The MAAD responses to various control-failure scenarios were also systematically investigated. The highest total acid productivity was 26 g/(L-liq center dot d) with a substrate conversion of 0.79 g CODdigested/g CODfed at a hydraulic retention time (HRT) of approximately 2 d in a 14-L digester. The most stable conditions for digester operation (HRT 3 d at pH 6.0 and 40 degrees C) were selected for process scale-up to 100 gal (similar to 380 L). Semi-continuous, pilot-scale MAAD successfully produced a total acid concentration of 40.6 +/- 1.1 g/L with 8.1 % acetic acid, 45.1 % butyric acid, and 44.5 % lactic acid. The links between wastewater characteristics, operation mode, digester scale, and microbial community structure were statistically analyzed. The results show genera Sporolactobacillus and Clostridium positively correlate with butyric acid production (Pearson correlation coefficient >0.5). Moreover, four kinetic models were developed and fit to batch MAAD experimental datasets (R-2 > 95 %) and were successfully applied to predict the total acid production in both bench-and pilot-scale semi-continuous MAADs. This study shows MAAD has the potential for industrial-scale applications and is a robust platform to valorize low-or negative-value waste streams into high-value bioproducts.