Enhancing biodegradation of quaternary ammonium compounds (QAC)

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PI Name: Bruce E. RittmannProposal Number: 1702445 Quaternary ammonium compounds (QACs) are widely used as surfactants and disinfectants in human and animal healthcare, agriculture, and industry. Discharge of QACs can be harmful to biological wastewater treatment and aquatic habitats. Most QACs are biodegradable in the presence of oxygen, and delivery of oxygen is a key to good biodegradation; however, the common practice of bubbling air does not work because the QACs, being surfactants, cause serious foaming. The PIs will study and develop a novel biotechnology to efficiently biodegrade QACs: the oxygen-based membrane biofilm reactor (O2-MBfR). Oxygen is delivered without bubbling to bacteria that grow on the outer surface of hollow-fiber membranes. Thus, an O2-MBfR can sustain QAC biodegradation without foaming and with excellent retention of the QAC-biodegrading bacteria. The PIs will develop the science and engineering foundations for a new environmental-biotechnology system able to bring about QAC biodegradation. The educational component will involve community-college students through a summer internship. The PIs will initiate a program to disseminate sustainability and green-chemistry principles in high school science laboratories, and they will stimulate public interest by participating in the NSF-sponsored website "Ask a Biologist". In the O2-MBfR, oxygen is delivered by diffusion to a biofilm accumulating on the outer surface of hollow-fiber membranes, thereby eliminating the foaming problem and providing excellent resistance to toxicity. Thus, an O2-MBfR should sustain QAC degradation even at the high QAC concentrations found in QAC-bearing wastewater from industrial facilities. The project's over-arching goal is to achieve high-efficiency biodegradation of QACs without incurring foaming and toxicity problems. This goal will be attained by (a) understanding the mechanistic principles of QAC biodegradation in the O2-based MBfR; (b) identifying the conditions leading to optimized performance of a two-stage O2-based MBfR to optimize QAC biodegradation; and (c) developing a mathematical model that integrates the kinetics of QACs biodegradation, mass-transfer kinetics, and biofilm accumulation and detachment. On the practical side, results of the work will demonstrate QAC biodegradation by using efficient O2 delivery by bubbleless diffusion. At the same time, the PIs will develop mechanistic and quantitative understanding of QAC biodegradation, including the microbial ecology and physiology of membrane-bound biofilms.