Superparamagnetic Iron Oxide Nanoparticles as Additives for Microwave-Based Sludge Prehydrolysis: A Perspective

A perspective on utilization of superparamagneticiron oxidenanoparticles in microwave-enabled prehydrolysis to reduce the costand environmental footprint of sludge management in wastewater treatmentfacilities. Wastewater treatment plants are critical for environmentalpollutioncontrol. The role that they play in protecting the environment andpublic health is unquestionable; however, they produce massive quantitiesof excess sludge as a byproduct. One pragmatic approach to utilizingexcess sludge is generating methane via anaerobic digestion. For this,a prehydrolysis step can significantly improve digestion by increasingbiogas quality and quantity while decreasing final sludge volumes.One of the many prehydrolysis approaches is to deliver heat into sludgevia microwave irradiation. Microwave-absorbing additives can be usedto further enhance thermal degradation processes. However, the implicationsof such an approach include potential release of said additive materialsinto the environment via digested sludge. In this perspective, wepresent and discuss the potential of superparamagnetic iron oxidenanoparticles (SPIONs) as recoverable, hyperreactive microwave absorbersfor sludge prehydrolysis. Due to their size and characteristics, SPIONspack spin electrons within a single domain that can respond to themagnetic field without remanence magnetism. SPIONs have propertiesof both paramagnetic and ferromagnetic materials with little to nomagnetic hysteresis, which can enable their rapid recovery from slurries,even in complicated reactor installations. Further, SPIONs are excellentmicrowave absorbers, which result in high local heat gradients. Thisperspective introduces the vision that SPION properties can be tunedfor desirable dielectric heating and magnetic responses while maintainingmaterial integrity to accomplish repeated use for microwave-enhancedpretreatment.

Automated summary

This article discusses the utilization of superparamagnetic iron oxide nanoparticles as recoverable microwave absorbers in the prehydrolysis of sludge to reduce costs and environmental impact. The use of microwave irradiation and microwave-absorbing additives can significantly improve the digestion of sludge, and the superparamagnetic iron oxide nanoparticles show great potential in this process.