Valorizing waste biomass via hydrodynamic cavitation and anaerobic digestion

It is essential to valorize waste biomass and promote a circular economy for realizing sustainability and decarbonization goals. In this review, we specifically focus on anaerobic digestion (AD) intensified via hydrodynamic cavitation (HC) and modeling as an effective biomass valorization strategy. AD is known to generate renewable energy (biogas) and fertilizer (digestate) and is therefore aligned with the circular economy framework and has the potential to decarbonize the transportation, energy, and heat sectors, which contribute a major share to the current global carbon emissions. The AD-based pathway, though robust, has key challenges such as poor carbon conversion and subpar biogas yields coupled with long residence times. This is mainly due to the recalcitrance offered by the feedstock. HC-based biomass pretreatment is critically reviewed here as a promising AD intensification strategy to overcome this recalcitrance. HC devices and their key aspects of design and scale-up are discussed. Vortex-based HC devices were found to be superior to conventional linear flow HC devices in terms of pretreatment performance and ease of scale up. The use of reaction engineering models of AD for overall optimization of biomass valorization is also discussed. The need for developing an intermediate modeling approach between empirical models and complex biochemical pathway-based models is highlighted. Such an intermediate approach requires simple biomethane potential (BMP) measurements for obtaining essential model parameters. With such parameters obtained from BMP data, the model was found to be useful for simulating and optimizing performance of AD. A prospective AD-based biorefinery is briefly discussed with multiple allied valorization pathways. This review will be useful to researchers and practicing engineers for realizing effective valorization of waste biomass.