Effects of carbonaceous susceptors on microwave pretreatment of waste activated sludge and subsequent anaerobic digestion

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

“…MW prehydrolysis has been studied extensively in the literature (Figure ). ,, The literature analysis indicated that MW prehydrolysis is effective converting MWs into heat owing to their favorable dielectric properties and ability to directly interact with the incidental electric and magnetic radiation (more effective than conventional MW absorbers such as silicon carbide, SiC, and other iron oxide crystals such as hematite and maghemite). − In addition, approximately 75 articles were published in the past 15 years exploring the effect of MW hydrolysis on excess wastewater sludge. These studies report successful MW hydrolysis on secondary sludge (77% of all articles) as a function of specific energy input, as summarized in Figure .…”

“…In principle, sludge prehydrolysis aims at enhancing organic matter (bio)availability by breaking cell walls and disrupting sludge floc assemblies; however, chemical complexity of the sludge matrix and abundance of water limit the selectivity and energy efficiency of pretreatment processes. Therefore, microwave (MW) heating has gained increasingly interest as an alternative thermal pretreatment approach as it provides selective and rapid heating and has been recognized as a versatile and scalable heating alternative for decades. , Particularly, MWs promote solubilization (∼0.1%–2% soluble chemical oxygen demand, sCOD increase per kJ of MW energy) by (i) breaking down the microfloc assemblies to release extracellular polymeric substances, (ii) disintegrating cell walls to release intracellular organic matter, and (iii) degrading complex molecules into simpler monomers and oligomers. As a consequence, AD of sludge shows increased biogas quality (e.g., 20% improvement in fuel quality), decreased digestate production (e.g., 60%–65% solid reduction), improved dewaterability, improved pathogen removal (e.g., 4.2 log fecal coliforms inactivation), and enhanced kinetics (e.g., 40% increase in digestion rates) …”