Chemical factors governing growth of nutraceutical Chlorella sorokiniana on thermal hydrolysate of poultry processing waste

The growing poultry processing industry generates large quantities of meat byproducts and wastes. Many of these wastes are currently land applied because they contain high water content, leading to putrid odors that impact nearby communities. Herein, we developed a process to valorize this waste: thermal hydrolysis followed by cultivation of nutraceutical Chlorella on the resulting aqueous phase. We investigated the impact of two solids loading levels (7% and 25% w/v) into thermal hydrolysis and their respective impacts on downstream Chlorella growth and toxicity. It was found that solids loading was a powerful governing factor in the growth of Chlorella: lower solids loading (7%¦w/v) led to robust algae growth without hydrolysate dilution (>2.2 g/L in 4 days) while higher solids loading (25%¦w/v) led to complete growth inhibition that could not be undone with eightfold dilution. Because high solids loading is economically attractive, non-targeted LC/MS-MS and dose-response assays were used to identify molecules that likely contributed to toxicity. Aldehydes, such as phthalaldehyde, present at 1.9 mg/L in the 25% hydrolysate, were identified for the first time in aqueous phase and found to contribute to the observed toxicity. This work makes important progress in our understanding of chemical toxicity in hydrothermally treated aqueous phases and establishes solids loading as a major governing parameter.