Pretreatment Removes Organic Molecules in Anaerobic Digestates That Inhibit Algal Productivity

Abstract

Algal growth on anaerobic digestates enables simultaneous wastewater treatment and biomass production, but dilution water is often used to overcome algal growth inhibition in digestates. It was previously shown that aerobic bacterial pretreatment alleviates algal growth inhibition in full strength digestates, but the mechanism was not elucidated. The objectives of the present study were to elucidate how aerobic bacterial and biochar pretreatments alleviate algal growth inhibition in anaerobic digestates using a combination of culture studies and LCMS/MS analysis. The results showed that aerobic bacterial and biochar pretreatments significantly (p < 0.05) enhanced algal productivity in the manure digestates by >7.1 fold and >3.1 fold, respectively. Aerobic bacterial pretreatment also enhanced nitrogen removal by algae (p < 0.002). Pretreatment removed many phenolic, antibiotic, and animal hormone metabolites. Six of the 12 “high-priority” molecules that underwent dose–response testing were inhibitory to Chlorella sorokiniana at <1 mg L^–1 levels. Four of these were confirmed to have MS/MS and retention time matches in a subsequent spiking test, including butylparaben, salicylic acid, androsterone, and tiamulin. Although prior studies have focused on ammonia and turbidity as algal growth inhibitors in digestates, this study shows specific organic compounds in digestates that also inhibit algal growth and wastewater treatment.