Two-stage continuous cultivation of microalgae overexpressing cytochrome P450 improves nitrogen and antibiotics removal from livestock and poultry wastewater
Rui Xiao, Chang Tian, Haijun Wang, Hui Zhang, Huan Chen, Howard H. Chou
Abstract
• Implemented a continuous LPWW treatment process using a two-stage CSTR system. • Continuous feedback process reduced HRT to 4 days and NH 4 -N to ∼30 mg/L. • Application of synthetic biology improved NH 4 -N removal rate to 470 mg/L/d. • Clarified mechanisms for nitrogen and antibiotics removal from LPWW by microalgae. • C. vulgaris P450 A23292 plays essential role in nitrogen and antibiotics removal. Improper treatment of livestock and poultry wastewater (LPWW) rich in ammonium nitrogen (NH 4 -N) and antibiotics leads to eutrophication, and contributes to the risk of creating drug-resistant pathogens. The design-build-test-learn strategy was used to engineer a continuous process using Chlorella vulgaris to remove NH 4 -N and antibiotics. The optimized system removed NH 4 -N at a rate of 306 mg/L/d, degraded 99 % of lincomycin, and reduced the hydraulic retention time to 4 days. The physiological, metabolic, and genetic mechanisms used by microalgae to tolerate LPWW, remove NH 4 -N, and degrade antibiotics were elucidated. A new cytochrome P450 enzyme important for NH 4 -N and antibiotic removal was identified. Finally, application of synthetic biology improved the NH 4 -N removal rate to 470 mg/L/d, which is the highest removal rate using microalgae reported to date. This research contributes to the mechanistic understanding of wastewater detoxification by microalgae, and the goal of achieving a circular bioeconomy for nutrient and water recycling.