Cofermenting Algal Biomass with Municipal Primary Solids to Enhance Carboxylate Production

Abstract

As water resource recovery facilities (WRRFs) implement biological nutrient removal (BNR) processes to remove excess wastewater nutrients, carboxylic acid demands increase; resource recovery processes (e.g., struvite, polyhydroxyalkanoate production) also demand carboxylates. In this regard, interest in algae to achieve tertiary treatment creates a new intraWRRF fermentation substrate. Indeed, fermentation potential tests indicated that algal augmentation could prove beneficial; carboxylate concentrations increased 31 % over primary solids. However, unexpectedly, and disproving a key research hypothesis, algal augmentation in a fed‐batch fermenter decreased the production of carboxylic acids (26–34% at SRTs of 5–7 d); preliminary analyses suggest heterotrophic algae consumed carboxylates. Disproving a second research hypothesis, algal biomass did not significantly diversify carboxylate speciation. Finally, and unexpectedly, algal fermentation realized significant ammonia removal (39–96 % at SRTs of 5–7 d). Although decreased carboxylate yield is not desired, reduced ammonia load could potentially decrease WRRF energy demands and decrease carboxylic acid demands to achieve denitrification.