RII Track-4: Superparamagnetic Iron Oxide Nanoparticles as Recoverable Microwave Susceptors for Pre-hydrolysis of Waste Activated Sludge prior to Anaerobic Digestion

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Municipal sewage treatment plants generate 6.5 million metric tons of excess sludge every year in the United States. Transportation and disposal of this excess sludge comprise half of the total wastewater treatment cost, exceeding $2 billion per year with a steady 1% annual increase. A common practice to stabilize waste sludge is anaerobic digestion (AD) prior to disposal. This technology can be described as the microbial transformation of sludge into biogas in the absence of free oxygen. The biogas produced from AD is a valuable green fuel, and it has comparable calorific value to natural gas. Furthermore, the digested sludge becomes easier to transport and dispose of after AD. Despite these environmental and economic advantages, AD has long reaction times, and low process yields. Even under 20-30 days of retention, sludge decomposition is incomplete, leaving 35-45% of the sludge undigested. This project utilizes extremely reactive, recoverable magnetic iron oxide nanoparticles (or superparamagnetic iron oxide nanoparticles) to improve the efficiency of sludge digestion and improve the economic and environmental benefits of the process. This RII Track-4:NSF project aims to minimize the costs and environmental impacts associated with excess sewage sludge management. This fellowship will take place at Yale University within the Department of Chemical and Environmental Engineering and involves support for a graduate trainee.Superparamagnetic iron oxide nanoparticles (SPIONs) are ground-breaking nanomaterials with remarkable application potential in a multitude of industries. SPIONs can respond to magnetic domains rapidly and efficiently without significant remanence. In addition, they can heat rapidly under microwave (MW) irradiation. Their properties make them promising candidates for sludge pretreatment applications. First, they have the potential to bind to components of sludge floc assemblies and deliver immediate and intense MW heating strategically to cells or extracellular polymers. MW irradiation creates an oscillating electromagnetic field that causes SPIONs to have both their electrical dipole moments and their magnetic moments rotate, creating internal vibrations that dissipate energy in the form of heat locally. Second, due to their size (typically 50 nm) SPIONs have spin electrons packed within a minuscule physical domain that can respond to the magnetic field without remanence magnetism (i.e., showing properties of both paramagnetic and ferromagnetic materials). Therefore, SPIONs do not have the burden of magnetic hysteresis, which empowers their effective and rapid recovery from slurries even in complicated reactor installations. The key merit of this proposed study is that SPION properties can be strategically tuned for superior dielectric heating and magnetic reactivity while maintaining material integrity to accomplish repeated use for MW pretreatment. Through this RII Track-4:NSF fellowship, the PI aims to develop a practical technology that will tailor and employ SPIONS as dielectric and recoverable susceptors for MW-induced pre-hydrolysis of wastewater sludges. First, the PI and a graduate trainee will learn protocols for advanced SPION synthesis. Next, the team will focus on at least three SPIONs that show promise in terms of paramagnetic abilities, MW heating, and material integrity for repeated use. Finally, the process for wastewater treatment will be optimized, and experiments to identify hydrolysis pathways such as the role of temperature, water chemistry, slurry viscosity and formation of hydroxyl radicals and other basic controls will be conducted to ensure data quality. This fellowship will take place at Yale University within the Department of Chemical and Environmental Engineering.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.