Other literature on this subject, that is the sewage and wastewater treatment, are , propose an "efficient phosphorus recovery from waste activated sludge", by means of a "pretreatment with natural deep eutectic solvent and recovery as vivianite". Lu et al., 2024, study the "anaerobic recovery of vivianite from waste-activated sludge through combined sludge pre-fermentation and agroforestry biomass-based biochar". "If enough iron is present in the sludge after anaerobic digestion, 70-90% of total phosphorus (P) can be bound in vivianite. Based on its paramagnetism and inspired by technologies used in the mining industry, a magnetic separation procedure has been developed" .