Biofertilizer recovery from organic solid wastes via hydrothermal liquefaction

Hydrothermal liquefaction (HTL) has emerged as a viable pathway for processing wet organic solid wastes (OSW) to yield biocrude oil which could be upgraded to transportation fuels and specialty chemicals. The HTL process results in two byproducts laden with high levels of carbon, nitrogen, and phosphorous. Recovery of phosphates in the byproducts as struvite and ammoniacal-nitrogen (NH₄-N) as ammonium sulfate is proposed here as a promising pathway to utilize the HTL byproducts. A case study of this pathway using algal biomass as a model OSW yielded 8.2 g struvite/100 g OSW and 10.7 g ammonium sulfate/100 g OSW. Heavy metal levels in both struvite and ammonium sulfate crystals were below EPA regulations for land application. This biofertilizer recovery pathway could render OSW processing by HTL a greener alternative to anaerobic digestion, offering feedstock versatility, substantially smaller footprint, and a higher degree of OSW valorization.