Enhancing Carboxylic Acid Yields from Duckweed By Acidogenic Digestion

Duckweeds are efficient aquatic plants for wastewater treatment due to their high nutrient uptake capabilities, growth rates, and resilience to severe environmental conditions. Their high starch, high cellulose, and low lignin content makes them an attractive alternative to agricultural residue and energy crops for conversion into bioethanol, as they do not require intensive pretreatment prior to saccharification. In this study, we investigate an alternative strategy, acidogenic digestion with undefined microbial cultures, to convert duckweed into carboxylates (i.e., volatile fatty acids, VFAs), precursors of higher-value chemicals and biofuels. Previous literature suggests that higher VFA concentrations can be achieved under alkaline conditions of pH 9 to 10, which should simultaneously suppress methanogenic activity to avoid VFA loss. However, the behavior of acidogenic microbial consortia at high pH is not well understood.

This study aims to evaluate the effects of operating conditions such as temperature (35^oC or 55^oC) and pH (5.3 or 9.2) on the acidogenic digestion of duckweed, to quantify conversion rates, and to identify shifts in dominant microbial taxa.

The highest duckweed-to-carboxylic acid conversion of 388 mg acetic acid/g total solids was observed under basic mesophilic conditions with 25 g/L solid loading, resulting in an average production rate of 0.59 g acetic acid equivalent/L·d. These values are comparable to those reported for other highly digestible organics such as food waste. The superior performance under these conditions was attributed to both chemical treatment and microbial bioconversion. Biochemical mechanisms behind these observations will be explored through microbial community analysis (in progress).